US20130279769A1 - Biometric Sensing - Google Patents

Abstract

An novel sensor is provided having a plurality of substantially parallel drive lines configured to transmit a signal into a surface of a proximally located object, and also a plurality of substantially parallel pickup lines oriented proximate the drive lines and electrically separated from the pickup lines to form intrinsic electrode pairs that are impedance sensitive at each of the drive and pickup proximal locations.

Description

RELATED APPLICATIONS
• This application claims the benefit of U.S. Provisional Application No. 61/622,474, filed Apr. 10, 2012, which is hereby incorporated herein in its entirety.
BACKGROUND
• The embodiments are generally related to electronic sensing devices, and, more particularly, to sensors for sensing objects located near or about the sensors for use in media navigation, fingerprint sensing and other operations of electronic devices and other products.
• In the electronic sensing market, there are a wide variety of sensors for sensing objects at a given location. Such sensors are configured to sense electronic characteristics of an object in order to sense presence of an object near or about the sensor, physical characteristics of the object, shapes, textures on surfaces of an object, material composition, biological information, and other features and characteristics of an object being sensed.
• Sensors may be configured to passively detect characteristics of an object, by measuring such as temperature, weight, or various emissions such as photonic, magnetic or atomic, of an object in close proximity or contact with the sensor, or other characteristic. An example of this is a non-contact infrared thermometer that detects the black body radiation spectra emitted from an object, from which its temperature can be computed.
• Other sensors work by directly exciting an object with a stimulus such as voltage or current, then using the resultant signal to determine the physical or electrical characteristics of an object. An example of this is a fluid detector consisting of two terminals, one that excites the medium with a voltage source, while the second measures the current flow to determine the presence of a conductive fluid such as water.
• Since a single point measurement of an object often does not provide enough information about an object for practical applications, it is often advantageous to collect a two-dimensional array of measurements. A two dimensional array of impedance may be created by moving a line sensing array over the surface of an object and then doing a line by line reconstruction of a two dimensional image like a fax machine does. An example of this is a swiped capacitive fingerprint sensor that measures differences in capacitance between fingerprint ridges and valleys as a finger is dragged across it. The swiping motion of the fingerprint by a user allows the one-dimensional line of sensor points to capture a large number of data points from the user's fingerprint surface. Such sensors reconstruct a two dimensional fingerprint image after the fact using individual lines of the captured data points. This reconstruction process requires a great deal of processing by a device, and is subject to failure if the swipe movement and conditions are not optimum.
• A more user friendly way to obtain a two dimensional image is to create a two dimensional sensing array that can capture a user's fingerprint data while the user holds the fingerprint surface still on the sensor surface, rather than swipe across a sensor. Such sensors however can be prohibitive in cost due to the large number of sensing points needed in the array. An example of this is a two dimensional capacitive fingerprint sensor. A number of these are currently manufactured. These sensors, however, are based use 150 mm²or more of silicon area and are therefore cost prohibitive for many applications. They are also delicate and fragile. They are sensitive to impact and even temperature changes, and thus are simply not durable enough for most applications, such as smart phones and other mobile electronic devices that are handled and sometimes dropped by users.
• These different types of electronic sensors have been used in various applications, such as biometric sensors for measuring biological features and characteristics of people such as fingerprints, medical applications such as medical monitoring devices, fluid measuring monitors, and many other sensor applications. Typically, the sensing elements of the various devices are connected to a processor configured to process object information and to enable interpretations for object features and characteristics. Examples include ridges and valleys of a fingerprint, temperature, bulk readings of presence or absence, and other features and characteristics.
• There are many applications for two dimensional image sensors as a particular example, and innovators have struggled with state of the art technology that has come short of desired features and functions. Fingerprint sensors, for example, have been in existence for many years and used in many environments to verify identification, to provide access to restricted areas and information, and many other uses. In this patent application, different types of fingerprint sensors will be highlighted as examples of sensor applications where the embodiment is applicable for simplicity of explanations, but other types of applications are also relevant to this background discussion and will also be addressed by the detailed description of the embodiment. These placement sensors may be configured to sense objects placed near or about the sensor, such as a fingerprint placement sensor that is configured to capture a full image of a fingerprint from a user's finger and compare the captured image with a stored image for authentication. Alternatively, sensors may be configured to sense the dynamic movement of an object about the sensor, such as a fingerprint swipe sensor that captures partial images of a fingerprint, reconstructs the fingerprint image, and compares the captured image to a stored image for authentication.
• In such applications, cost, though always a factor in commercial products, has not been so critical—accuracy and reliability have been and still remain paramount factors. Typically, the placement sensor, a two-dimensional grid of sensors that senses a fingerprint image from a user's fingerprint surface all at once, was the obvious choice, and its many designs have become standard in most applications. Once the fingerprint image is sensed and reproduced in a digital form in a device, it is compared against a prerecorded and stored image, and authentication is complete when there is a match between the captured fingerprint image and the stored image. In recent years, fingerprint sensors have been finding their way into portable devices such as laptop computers, hand held devices, cellular telephones, and other devices. Though accuracy and reliability are still important, cost of the system components is very important. The conventional placement sensors were and still are very expensive for one primary reason: they all used silicon sensor surfaces (this is excluding optical sensors for this example, because they are simply too large and require more power than a portable device can afford to allocate, among other reasons, and thus they are generally not available in most commercially available devices). These silicon surfaces are very expensive, as the silicon material is as expensive as the material to make a computer chip. Computer chips, of course, have become smaller over the years to reduce their cost and improve their performance. The reason the fingerprint silicon could not be made smaller: they need to remain the size of the average fingerprint, and the requirement for full scanning of the users' fingerprints simply cannot be compromised. Substantially the full print is required for adequate security in authentication.
• Enter the fingerprint swipe sensor into the market. Swipe sensors are fundamentally designed with a line sensor configured to sense fingerprint features as a user swipes their finger in a perpendicular direction with respect to the sensor line. The cost saver: swipe sensors need much less silicon, only enough to configure a line sensor with an array of pixel sensors. The width is still fixed based on the average fingerprint width, but the depth is substantially smaller compared to the placement sensor. Some swipe sensors are capacitive sensors, where capacitance of the fingerprint surface is measured and recorded line by line. Others send a small signal pulse burst into the surface of the fingerprint surface and measure a response in a pickup line, again recording fingerprint features line by line. In either case, unlike the placement sensors, the full fingerprint image needs to be reconstructed after the user completes the swipe, and the individual lines are reassembled and rendered to produce a full fingerprint image. This image is compared with a fingerprint image stored in the laptop or other device, and a user will then be authenticated if there is an adequate match.
• For the capacitive swipe sensors, the first generation sensors were constructed with direct current (DC) switched capacitor technology (for example U.S. Pat. No. 6,011,859). This approach required using two plates per pixel forming a capacitor between them, allowing the local presence of a finger ridge to change the value of that capacitor relative to air. These DC capacitive configurations took images from the fingerprint surface, and did not penetrate below the finger surface. Thus, they were easy to spoof, or fake a fingerprint with different deceptive techniques, and they also had poor performance when a user had dry fingers. RF (Radio Frequency) sensors were later introduced, because some were able to read past the surface and into inner layers of a user's finger to sense a fingerprint. Different radio frequencies have been utilized by various devices along with different forms of detection including amplitude modulation (AM) and, phase modulation (PM). There are also differing configurations of transmitters and receivers, one type (for example U.S. Pat. No. 5,963,679) uses a single transmitter ring and an array of multiple low quality receivers that are optimized for on chip sensing. In contrast another type (for example U.S. Pat. No. 7,099,496) uses a large array of RF transmitters with only one very high quality receiver in a comb like plate structure optimized for off chip sensing.
• One key impediment to the development of low cost placement sensors has been the issue of pixel density, and the resultant requirement for a large number of interconnections between layers of the sensor device. A typical sensor for a fingerprint application will be on the order of 10 mm×10 mm, with a resolution of 500 dpi. Such a sensor array would be approximately 200 rows by 200 columns, meaning there would need to be 200 via connections between layers in the device. While semiconductor vias can be quite small, the cost for implementing a sensor in silicon has proven to be prohibitive, as mentioned above.
• In order to produce a placement sensor at a low enough cost for mass market adoption, lower cost processes such as circuit board etching must be employed. The current state of the art in circuit board via pitch is on the order of 200 um, vs. the 50 um pitch of the sensor array itself. Additionally, the added process steps required to form vias between layers of a circuit board significantly increase the tolerances for the minimum pitch of traces on each of the layers. Single-sided circuits may be readily fabricated with high yield with line pitch as low as 35 um, whereas double sided circuits require a minimum line pitch on the order of 60 um or more, which is too coarse to implement a full 500 dpi sensor array. One further consideration is that at similar line densities, double-sided circuits with vias are several times more expensive per unit area than single sided, making high-density double sided circuits too expensive for low cost sensor applications.
• For laptop devices, adoption of the swipe sensor was driven by cost. The swipe sensor was substantially less expensive compared to the placement sensors, and most manufacturers of laptops adopted them based solely on price. The cost savings is a result of using less silicon area. More recently a substitute for the silicon sensor arose, using plastic Kapton™ tape with etched sensing plates on it, connected to a separate processor chip (for example U.S. Pat. No. 7,099,496). This allowed the silicon portion of the sensor to be separated from the sensing elements and the silicon to follow Moore's law, shrinking to an optimal size, in length, width and depth in proportion to advances in process technology. Although this advance in the art enabled cheap durable Swipe Sensors, it did not overcome the basic image reconstruction and ergonomics issues resulting from changing from a simple two dimensional placement format. In addition to Swipe Sensors being cheaper, they take up less real estate in a host device, whether it is a laptop or a smaller device, such as a cellular phone or personal data device.
• In most swipe class sensors, the fingerprint reconstruction process turned out to be a greater ergonomic challenge to users and more of a burden to quality control engineers than initially expected. Users needed to be trained to swipe their finger in a substantially straight and linear direction perpendicular to the sensor line as well as controlling contact pressure. Software training programs were written to help the user become more proficient, but different environmental factors and the inability of some to repeat the motion reliably gave Swipe Sensors a reputation for being difficult to use. Initial data from the field indicated that a large number of people were not regularly using the Swipe Sensors in the devices that they had purchased and opted back to using passwords. Quality control engineers who tried to achieve the optimum accuracy and performance in the matching process between the captured and reconstructed image found that the number of False Rejects (FRR), and False Acceptances (FAR), were much higher in Swipe Sensors than in placement sensors. Attempts to improve these reconstruction algorithms failed to produce equivalent statistical performance to placement sensors.
• Development of sensors that take up less space on devices have been tried without much success. Various ramps, wells and finger guides had to be incorporated into the surfaces of the host devices to assist the user with finger placement and swiping. These structures ended up consuming significant space in addition to the actual sensor area. In the end, swipe sensors ended up taking up almost as much space as the placement sensors. This was not a big problem for full size laptops, but is currently a substantial problem for smaller laptops and netbooks, mobile phones, PDAs, and other small devices like key fobs.
• Real estate issues have become even more of an issue with mobile device manufacturers who now require that the fingerprint sensor act also as a navigation device, like a mouse or touch-pad does in a laptop. The swipe sensor has proved to be a poor substitute for a mouse or touch pad due to the fact that they are constructed with an asymmetric array of pixels. Swipe sensors do a good job of detecting motion in the normal axis of the finger swipe but have difficulty accurately tracking sideways motion. Off axis angular movements are even more difficult to sense, and require significant processor resources to interpolate that movement with respect to the sensor line, and often have trouble resolving large angles. The byproduct of all this is a motion that is not fluid and difficult to use.
• It is clear that low cost two dimensional fingerprint sensor arrays would serve a market need, but present art has not been able to fill that need. Conventional capacitive fingerprint sensors typically use distinct electrode structures to form the sensing pixels array. These electrode structures are typically square or circular and can be configured in a parallel plate configuration (for example U.S. Pat. Nos. 5,325,442 and 5,963,679) or a coplanar configuration (for example U.S. Pat. No. 6,011,859 and U.S. Pat. No. 7,099,496).
• These prior art approaches cannot be configured into a low cost two dimensional array of sensing elements. Many capacitive fingerprint sensors (for example U.S. Pat. Nos. 5,963,679 and 6,011,859) have plate structures that must be connected to the drive and sense electronics with an interconnect density that is not practical for implementation other than using the fine line multilayer routing capabilities of silicon chips and therefore require lots of expensive silicon die are as stated before. Other sensors (for example U.S. Pat. No. 7,099,496) use off chip sensing elements on a cheap polymer film, but the sensor cell architecture is inherently one dimensional and cannot be expanded into a two dimensional matrix.
• Another application for capacitive sensing arrays has been in the area of touch pads and touch screens. Because touchpad and touch screen devices consist of arrays of drive and sense traces and distinct sense electrodes, they are incapable of resolutions below a few hundred microns, making this technology unsuitable for detailed imaging applications. These devices are capable of detecting finger contact or proximity, but they provide neither the spatial resolution nor the gray-scale resolution within the body of the object being sensed necessary to detect fine features such as ridges or valleys.
• Conventional art in the touchpad field utilizes a series of electrodes, either conductively (for example U.S. Pat. No. 5,495,077) or capacitively (forexample US publication 2006/0097991). This series of electrodes are typically coupled to the drive and sense traces. In operation these devices produce a pixel that is significantly larger in scale than the interconnect traces themselves. The purpose is to generally sense presence and motion of an object to enable a user to navigate a cursor, to select an object on a screen, or to move a page illustrated on a screen. Thus, these devices operate at a low resolution when sensing adjacent objects.
• Thus, there exists a need in the art for improved devices that can provide high quality and accurate placement sensors for use in different applications, such as fingerprint sensing and authentication for example, and that may also operate as a navigation device such as a mouse or touch pad in various applications. As will be seen, the embodiment provides such a device that addresses these and other needs in an elegant manner. Given the small size and functional demands of mobile devices, space savings are important. Thus, it would also be useful to be able to combine the functions of a sensor with that of other components, such as power switches, selector switches, and other components, so that multiple functions are available to a user without the need for more components that take up space.
• Still further, it would be also useful for different embodiments of a touch sensor to provide various alternatives for providing biometric sensors that are easy to use and feasible in different applications.
• Even further, it would be useful for sensors to not only act as image capturing components, but to also provide navigation operations for viewing and exploring various media, such as with touch-screens used in many smart phones, such as the iPad™, iPod™, iPhone™ and other touch-sensitive devices produced by Apple Corporation™, the Galaxy™ and its progeny by Samsung Corporation™, and other similar devices.
BRIEF DESCRIPTION OF DRAWINGS
• FIG. 1 shows a diagrammatic view of one embodiment showing the drive and pickup plate structures with an insulating dielectric layer separating the drive and pickup lines.
• FIG. 2 shows a basic diagrammatic view of one embodiment showing the basic electrical field operation without an object in close proximity to the drive and pickup plate structures with one drive plate excited by a voltage source.
• FIG. 3 shows a basic diagrammatic view of one embodiment showing the basic electrical field operation with an object in close proximity to the drive and pickup plate structures with one drive plate excited by a voltage source.
• FIG. 4 shows a basic diagrammatic view of one embodiment of the sensor showing the differences in field intensity with and without an object in close proximity to the drive and pickup plate structures with one drive plate excited by a voltage source.
• FIG. 5 shows a basic diagrammatic view of one embodiment showing the basic electrical field operation with an object in close proximity of the drive and pickup plate structures with the selected pickup plate amplified and all inactive drive and pickup plates grounded.
• FIG. 6ashows a basic diagrammatic view of one embodiment showing the basic electrical field operation with a finger or object containing a ridge surface feature in close proximity to the active electrode pair.
• FIG. 6bshows a basic diagrammatic view of one embodiment showing the basic electrical field operation with a finger or object containing a valley surface feature in close proximity to the active electrode pair.
• FIG. 7 shows a diagrammatic view of an x-y grid of plate rows and columns depicted by lumped circuit components that represent the electric field couplings of the sensor at each drive/pickup crossover.
• FIG. 8 shows an example of an embodiment of the placement embodiment using a differential amplifier to take the signal from the selected pickup plate and subtract it from a reference signal plate for noise reduction purposes.
• FIG. 9ashows the drive and sense multiplexing circuitry of an embodiment that incorporates a tank circuit to compensate for input loading effects.
• FIG. 9bshows the drive and sense multiplexing circuitry of an embodiment that incorporates cascaded buffers to minimize input loading effects.
• FIG. 9cshows the drive and sense multiplexing circuitry of an embodiment that incorporates dedicated buffers for each sense to minimize loading effects.
• FIG. 10 shows an embodiment that incorporates an analog receiver to process the sensed signal, and processing circuitry to perform the drive and sense line scanning function.
• FIG. 11 shows an embodiment that incorporates a direct digital conversion receiver to process the sensed signal, and processing circuitry to perform the drive and sense line scanning function.
• FIG. 12A shows one example of a layout of the drive and sense traces for an embodiment that incorporates the folded aspect of the embodiment laid out flat prior to folding.
• FIG. 12B shows one example of a layout of the drive and sense traces for an embodiment that incorporates the folded aspect of the embodiment laid out flat prior to folding.
• FIG. 13ashows the layer stack-up of an embodiment that incorporates the folding aspect subsequent to folding.
• FIG. 13bshows an embodiment that incorporates the folding aspect subsequent to folding and assembly into a rigid module.
• FIG. 14 shows a sensor system configured according to the embodiment for the purpose of sensing features of an object.
• FIG. 15 shows an example of the sensing of a fingerprint features.
• FIG. 16 shows the process flow steps required to collect a 2-dimensional image with a sensor system configured according to one embodiment.
• FIG. 17ashows the process flow steps required to authenticate a user with a fingerprint sensor system configured according one embodiment.
• FIG. 17bshows the process of template extraction from a fingerprint image typically utilized in user authentication applications.
• FIGS. 18A-18D show an example of a fingerprint sensor system having an integrated switch to allow a user to contact a fingerprint sensor and to actuate a switch simultaneously.
• FIGS. 19A-J show another example of a fingerprint sensor system having an integrated switch, a dome switch in this example, to allow a user to contact a fingerprint sensor and to actuate a switch simultaneously.
• FIG. 20 shows a top view of an embodiment of a switch formed on the same substrate as the fingerprint sensor.
• FIGS. 21A and B are detailed views which show the operation of the embedded switch depicted inFIG. 20.
• FIGS. 22A-26C illustrate other embodiments of the invention.
• FIGS. 27-29 illustrate a method for integrating a folded flex fingerprint sensor directly onto a touch-screen device.
• FIGS. 30-32 illustrate a fingerprint sensor integrated onto the same substrate layers as a conventional touch-screen.
• FIGS. 33 and 34 illustrate a novel “Dual Grid” touch-screen.
• FIGS. 35-37 illustrate a fully integrated Dual Grid touch-screen and fingerprint sensor, which advantageously share a common drive and sense circuit.
• FIGS. 38-40 illustrated a fully integrated display with integral touch-screen and fingerprint sensing over the entire display area.
• FIGS. 41-50 illustrate how the dual grid finger motion tracking process operates.
• FIG. 51 illustrates a flexible fingerprint sensor integrated with a touchscreen.
• FIG. 52 illustrates an embodiment of a fingerprint sensor sharing a substrate layer with a touchscreen.
• FIG. 53 illustrates a sensor and a touchscreen implemented on common substrate layers utilizing a common controller chip.
DETAILED DESCRIPTION
• As discussed in the background, there are many applications for a two dimensional impedance sensor, and the embodiments described herein provide broad solutions to shortcomings in the prior art for many applications. The underlying technology finds application in many different sensor features for use in many types of products, including mobile phones, smart phones, flip phones, tablet computers such as Apple™ iPads™ and Samsung™ Galaxy™ devices, point of entry devices such as door knobs, fence, drug cabinets, automobiles, and most any device, venue or thing that may be locked and require authentication to access.
• Generally, one embodiment is directed to a two-dimensional sensor, and may also be referred to as a placement sensor, touch sensor, area sensor, or 2D sensor, where a substantial area of an object such as a user's fingerprint is sensed rather than a point or line like portion of space that may or may not yield a characteristic sample that is adequate for identification. The sensor may have sensor lines located on one or more substrates, such as for example a flexible substrate that can be folded over on itself to form a grid array with separate sensor lines orthogonal to each other. The sensor lines may alternatively be formed on separate substrates. In either or any configuration, the crossover locations of different sensor lines create sensing locations for gathering information of the features and/or characteristics of an object, such as the patterns of ridges and valleys of a fingerprint for example.
• Other embodiments provide a touch sensor having common electrical connections with a touch screen. For example, touch screen circuitry that resides under protective glass, such as Gorilla Glass™ used in many touch screen devices, may share common electrical connections with a two dimensional sensor used for navigation, and/or fingerprint sensing, or other operations. This provides benefits for manufacturing a device with both a touch screen and a fingerprint sensor, and may simplify the electrical layout of such a device. Exemplary configurations are described below and illustrated herein.
• Other embodiments provide novel approaches to two-dimensional sensors integrated with a touch screen to provide the ability to capture a fingerprint image in one mode, and to operate as a conventional touch-screen when in another mode. In one example, a sensor grid may act as a touch screen by sensing presence of a user's finger or fingers and also movement of the fingers from one location to another together with speed to determine a swipe direction and speed. In another mode, the same sensor lines may act as drive lines and pickup lines, where a signal is transmitted from the screen to the user's finger or fingers, and the resulting signal is received by a pickup line and measured to determine the impedance of the fingerprint surface. Impedance values of fingerprint ridges are different than the impedance measurement of fingerprint valleys, and thus the fingerprint image may be mapped once the impedance values are captured of a two dimensional surface of a fingerprint surface. The resulting fingerprint image may then be compared to a stored fingerprint image to authenticate the user, much in the same way a simple password is compared to a stored password when users authenticate themselves with electronic devices using numerical and alphanumeric passwords with devices. The difference is that the use of a fingerprint in place of a password is much more secure.
• A two dimensional sensor may be configured in different ways, such as for example a component that may be integrated on a portable device, a sensor integrated with a touch-screen used to provide touch sensitive surfaces for navigation of electronic content and operations in a portable device, or as a stand-alone component that may be electrically connected to a system or device to transmit and receive information for authentication, activation, navigation and other operations.
• In one embodiment, the drive lines and pickup lines are not electrically intersecting or connected in a manner in which they would conduct with each other, they form an impedance sensing electrode pair with a separation that allows the drive lines to project an electrical field and the pickup lines to receive an electrical field, eliminating the need for distinct electrode structures. The two lines crossing with interspersed dielectric intrinsically creates an impedance sensing electrode pair. Thus, the sensor is configured to activate two one-dimensional sensor lines to obtain one pixel of information that indentifies features and/or characteristics of an object. Unlike conventional sensors, a sensor configured according to certain embodiments may provide a two dimensional grid that is capable of capturing multiple pixels of information from an object by activating individual pairs of drive and pickup lines and capturing the resultant signal. This signal can be processed with logic or processor circuitry to define presence and absence of an object, features and/or characteristics of an object.
• In yet another embodiment, a touch screen may operate as a sensor configured in one mode to capture information on a nearby object, such as information for forming an image of a fingerprint, and may operate in another mode to perform navigation or other operations when another mode. In one example, an OLED touch screen is configured to operate in at least two modes, one as a touch screen, and another as a fingerprint sensor, where a fingerprint may be captured in any part of the OLED touch screen desired, and even multiple fingerprints from two or more user fingers may be captured.
• In examples described herein, these sensors may be configured to capture information of a nearby object, and the information may be used to produce renderings of an object, such as a fingerprint, and compare the renderings to secured information for authentication.
• According to one embodiment, and in contrast to conventional approaches, a device can utilize the intrinsic impedance sensing electrode pair formed at the crossings between the drive and pickup lines. In operation, the electric fields may be further focused by grounding drive and pickup lines near or about the area being sensed by the particular crossover location at one time. This prevents interference that may occur if other drive and pickup lines were sensing electric fields simultaneously. More than one electrode pair may be sensed simultaneously. However, where resolution is an important factor, it may be preferred to avoid sensing electrode pairs that are too close to each other to avoid interference and maintain accuracy in sensing object features at a particular resolution. For purposes of this description, “intrinsic electrode pair” refers to the use of the impedance sensing electrode pairs that are formed at each of the drive and pickup line crossover locations. Due to the fact that the embodiments use each intrinsic electrode pair at each crossover as a sensing element, no differentiating geometric features exist at individual sensing nodes to distinguish them from the interconnect lines. As a result, the alignment between the drive layers and sense layers is non-critical, which significantly simplifies the manufacturing process.
• Grounding the adjacent inactive drive and pickup lines restricts the pixel formed at each intrinsic electrode pair without requiring complex measures such as the dedicated guard rings employed in prior art (for example U.S. Pat. No. 5,963,679). Instead, guard grounds around the pixel are formed dynamically by switching adjacent inactive drive and pickup lines into ground potential. This allows the formation of high density pixel fields with relatively low resolution manufacturing processes, as the minimum pixel pitch for a given process is identical to the minimum feature spacing. This, in turn, enables the use of low cost manufacturing process and materials, which is the key to creating a low cost placement sensor.
• In one example, the sensor lines may consist of drive lines on one layer and pickup lines on another layer, where the layers are located over each other in a manner that allows the separate sensor lines, the drive and pickup lines, to cross over each other to form impedance sensing electrode pairs at each crossover location. These crossover locations provide individually focused electrical pickup locations or pixels, or electrode pairs where a number of individual data points of features and/or characteristics of an object can be captured. The high degree of field focus is due to the small size of the intrinsic electrode pairs, as well as the high density of the neighboring ground provided by the inactive plates. The flexible substrate may have a second substrate configured with logic or processor circuitry for sending and receiving signals with the sensor lines to electronically capture information related to the object. Alternatively, there may be two separate substrates carrying the separate sensor lines and layered on each other, and yet connected to a third substrate for connection to logic or processor circuitry.
• The utilization of the crossover locations between perpendicular lines on adjacent layers for the pickup cell greatly reduces the alignment requirements between the layers. Since there are no unique features at a sensor pixel location to align, the only real alignment requirement between the layers is maintaining perpendicularity. If the sense cell locations had specific features, such as the parallel plate features typical of prior art fingerprint sensors, the alignment requirements would include X and Y position tolerance of less than one quarter a pixel size, which would translate to less than +/−12 um in each axis for a 500 DPI resolution fingerprint application.
• In operation, a drive line is activated, with a current source for example, and a pickup line is connected to a receiving circuit, such as an amplifier/buffer circuit, so that the resulting electric field can be captured. An electric field extends from the drive line to the pickup line through the intermediate dielectric insulating layer. If an object is present, some or all of the electric field may be absorbed by the object, changing the manner in which the electric field is received by the pickup line. This changes the resulting signal that is captured and processed by the pickup line and receiving circuit, and thus is indicative of the presence of an object, and the features and characteristics of the object may be sensed and identified by processing the signal. This processing may be done by some form of logic or processing circuitry.
• In other embodiments, the signal driving the drive line may be a complex signal, may be a varying frequency and/or amplitude, or other signal. This would enable a sensor to analyze the features and/or characteristics of an object from different perspectives utilizing a varying or complex signal. The signal may include simultaneous signals of different frequencies and/or amplitudes that would produce resultant signals that vary in different manners after being partially or fully absorbed by the object, indicating different features and characteristics of the object. The signal may include different tones, signals configured as chirp ramps, and other signals. Processing or logic circuitry may then be used to disseminate various information and data points from the resultant signal.
• In operation, the varying or complex signal may be applied to the drive line, and the pickup line would receive the resulting electric field to be processed. Logic or processing circuitry may be configured to process the resulting signal, such as separating out different frequencies if simultaneous signals are used, so that features and/or characteristics of the object may be obtained from different perspectives.
• Given the grid of pixels that can be activated at individual pairs, each pixel may be captured in a number of ways. In one embodiment, a drive line may be activated, and pickup lines may be turned on and off in a sequence to capture a line of pixels. This sequencing may operate as a scanning sequence. Here a first drive line is activated by connecting it to a signal source, and then one pickup line is connected to amplifier/buffer circuitry at a time, the information from the pixel formed at the crossing of the two lines is captured, and then disconnected. Then, a next pixel is processed in sequence, then another, then another, until the entire array of pickup lines is processed. The drive line is then deactivated, and another drive line is activated, and the pickup lines are again scanned with this active drive line. These may be done one at a time in sequence, several non-adjacent pixels may be processed simultaneously, or other variations are possible for a given application. After the grid of pixels is processed, then a rendering of object information will be possible.
• Referring toFIG. 1, a diagrammatic view of one embodiment of asensor100 configured according to one embodiment is illustrated. In this configuration, pickup lines or top plates102a[m],102b[m+1] are located on a insulating dielectric substrate layer104 and configured to transmit a signal into a surface of an object located in close proximity to the sensor lines. Drive lines or bottom plates106a[n],106b[n+1] are juxtaposed and substantially perpendicular to the drive lines or plates and are located on an opposite side of the a insulating dielectric substrate to form a type of a grid. The pickup lines are configured to receive the transmitted electromagnetic fields modified by the impedance characteristics on an object placed within the range of those electric fields.
• Referring toFIG. 2, a diagrammatic view of asensor200 is shown having pickup lines ortop plates202a,202band insulatinglayer204, and drive lines orbottom plates206a,206b. The Figure further illustrates howelectromagnetic fields208a,208bextend between the drive lines and pickup plates through the substrate. Without an object within proximity, the electric field lines are uniform within the sensor structure and between the different lines. When an object is present, a portion of the electric field lines are absorbed by the object and do not return to the pickup plates through the insulating layer.
• Referring toFIG. 3, anobject310 is illustrated proximate thesensor300. Thesensor300 has pickup lines ortop plates302a,302b, an insulatingdielectric layer304, and drive lines orbottom plates306a,306b. In operation, the drive lines and pickup lines of this device example may be individually activated, where a drive line/pickup line pair is activated to produce an active circuit. The result is a circuit that transmits electric field fromactive drive plate316 into the combined dielectric of the insulatinglayer304 and object310 via electric field lines,306a,306b, and received by the active pickup plate. As the illustration shows, some of the field lines are captured by the object when it is placed about the active electrode pair. The variations in an object, such as peaks and valleys and other features of an object surface, can be detected and captured electronically by capturing and recording the resulting electric field variations occurring at different crossover locations of the drive and pickup lines. Similar to common capacitance based placement sensors, the sensor can capture a type of image of the object surface electronically, and generate a representation of the features and characteristics of an object, such as the features and characteristics of a fingerprint in the fingerprint sensor example described below.
• In this configuration ofFIG. 3, only one active electrode pair is illustrated. However, the embodiment is not limited to this particular configuration, where one single electrode pair, several electrode pairs, or even all electrode pairs may be active at one time for different operations. In practice, it may be desirable for less than all of the electrode pairs to be active at a given time, so that any interference that may occur between close-by pixels would be minimized. In one embodiment, a drive line may be activated, and the pickup lines may be scanned one or more at a time so that a line of pixels can be captured along the drive line and pickup lines as they are paired along a line at the crossover locations. This is discussed in more detail below in connection withFIG. 5.
• In general, in operation, each area over which a particular drive line overlaps a pickup line with a separation of the a insulating dielectric substrate is an area that can capture and establish a sensing location that defines characteristics or features of a nearby object about that area. Since there exist multiple sensing locations over the area of the sensor grid, multiple data points defining features or characteristics of a nearby object can be captured by the sensor configuration. Thus, the sensor can operate as a planar two-dimensional sensor, where objects located on or about the sensor can be detected and their features and characteristics determined.
• As described in the embodiments and examples below, the embodiment is not limited to any particular configuration or orientation described, but is only limited to the appended claims, their equivalents, and also future claims submitted in this and related applications and their equivalents. Also, many configurations, dimensions, geometries, and other features and physical and operational characteristics of any particular embodiment or example may vary in different applications without departing from the spirit and scope of the embodiment, which, again, are defined by the appended claims, their equivalents, and also future claims submitted in this and related applications and their equivalents.
• In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiment. However, it will be apparent to one skilled in the art that the embodiment can be practiced without these specific details. In other instances, well known circuits, components, algorithms, and processes have not been shown in detail or have been illustrated in schematic or block diagram form in order not to obscure the embodiment in unnecessary detail. Additionally, for the most part, details concerning materials, tooling, process timing, circuit layout, and die design have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the embodiment and are considered to be within the understanding of persons of ordinary skill in the relevant art. Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, components may be referred to by different names. This document does not intend to distinguish between components that differ in name, but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”
• Embodiments of the embodiment are described herein. Those of ordinary skill in the art will realize that the following detailed description of the embodiment is illustrative only and is not intended to be in any way limiting. Other embodiments of the embodiment will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will be made in detail to implementations of the embodiment as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts.
• In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
• In one embodiment, a sensor device includes drive lines located on or about an insulating dielectric substrate and configured to transmit a signal onto a surface of an object being sensed. Pickup lines are located near or about the drive lines and configured to receive the transmitted signal from the surface of an object. In order to keep a separation between the drive lines and pickup lines, the substrate may act as an insulating dielectric or spacing layer. The substrate may be for example a flexible polymer based substrate. One example is Kapton™ tape, which is widely used in flexible circuits such as those used in printer cartridges and other devices. The package may include such a flexible substrate, where the drive lines may be located on one side of the substrate, and the pickup lines may be located on an opposite side of the substrate.
• The drive lines may be orthogonal in direction with respect to the pickup lines, and may be substantially perpendicular to the pickup lines. According to one embodiment, a device may be configured with drive lines and pickup lines located on or about opposite sides of an insulating dielectric substrate, where the combination of these three components provides capacitive properties. The drive lines may be activated to drive an electric field onto, into or about an object. The pickup lines can receive electronic fields that originated from the drive lines, and these electronic fields can be interpreted by processing or logic circuitry to interpret features or characteristics of the object being sensed.
• Thus, in one embodiment the layer separating the drive lines from the pickup lines can provide a capacitive property to the assembly. If some or all of the drive lines are substantially perpendicular to the pickup lines, either entirely or in portions, then a grid may be formed. In such a configuration, from a three dimensional view, the drive lines are located and oriented substantially in parallel with respect to each other about a first plane. One surface of the substrate is located about the drive lines in a second plane that is substantially parallel relative to the drive lines. The pickup lines are located and oriented substantially in parallel with respect to each other about a third plane that is substantially parallel to the first and second planes and also located about another substrate surface that is opposite that of the drive lines, such that the substrate is located substantially between the drive lines and the pickup lines.
• In this description, including descriptions of embodiments and examples, there will be references to the terms parallel, perpendicular, orthogonal and related terms and description. It is not intended, nor would it be understood by those skilled in the art that these descriptions are at all limiting. To the contrary, the embodiment extends to orientations and configurations of the drive lines, the pickup lines, the substrate or related structure, and also various combinations and permutations of components, their placement, distance from each other, and order in different assemblies of a sensor. Though the embodiment is directed to a sensor configured with plurality of drive and pickup lines that generally cross over each other at a pixel location and are configured to detect presence and other features and characteristics of a nearby object, the embodiment is not limited to any particular configuration or orientation, but is only limited to the appended claims, their equivalents, and also future claims submitted in this and related applications and their equivalents.
• Also, reference will be made to different orientations of the geometric planes on which various components will lie, such as the drive and pickup lines and the substrate that may be placed in between the sets of drive and pickup lines. If flexible substrates are used for example, the use of such a structure will allow for planes to change as a flexible structure is flexed or otherwise formed or configured. In such embodiment will be understood that certain aspects of the embodiment are directed to the drive lines and pickup lines being configured on opposite sides of a substrate and in a manner that enables the sensing of particular features and/or characteristics of a nearby object at each crossover location of a drive line and a pickup line. Thus, the orientation of the planes (which may be deformable, and thus may be sheets separated by a substantially uniform distance) of groups of components (such as drive lines or pickup lines for example) or substrates may vary in different applications without departing from the spirit and scope of the embodiment.
• Also, reference will be made to pickup lines, pickup plates, drive lines, drive plate, and the like, but it will be understood that the various references to lines or plates may be used interchangeably and do not limit the embodiment to any particular form, geometry, cross-sectional shape, varying diameter or cross-sectional dimensions, length, width, height, depth, or other physical dimension of such components. Also, more sophisticated components may be implemented to improve the performance of a device configured according to the embodiment, such as for example small 65, 45, 32 or 22 nanometer conduction lines or carbon nano-tubes that may make an assembly more easily adapted to applications where small size and shape as well as low power are desired characteristics and features. Those skilled in the art will understand that such dimensions can vary in different applications, and even possibly improve the performance or lower power consumption in some applications, without departing from the spirit and scope of the embodiment.
• Reference will also be made to various components that are juxtaposed, layered, or otherwise placed on each other. In one example of an embodiment, a plurality of drive lines are juxtaposed on one surface of a generally planar substrate, and a plurality of pickup lines are juxtaposed on an opposite surface of the planar substrate. The drive lines are substantially orthogonal to the pickup lines, and may be described as substantially perpendicular to the pickup lines. The distance between the drive lines and pickup lines may be filled with a substrate or insulating material that will provide for a capacitive configuration. Here the drive lines on one side of the substrate forms one capacitive plate, and the pickup lines on an opposite side for the corresponding capacitive plate. In operation, when the drive plate is activated, an electrical field is generated between the drive lines and pickup lines and through the substrate to form a plurality of capacitive elements. These capacitive elements are located at an area at each cross-section of a drive line and a pickup line with a portion of the substrate located between the areas. This is a location where the respective drive lines and pickup lines overlap each other. In any particular application, these areas in which the three components interact during operation define a data location at which a sensor reading can be made.
• Reference will also be made to sensor lines, such as sensor drive lines and sensor pickup lines, and their orientation amongst themselves and each other. For example, there will be described substantially parallel drive lines. These drive lines are intended to be described as parallel conductive lines made up of a conductive material formed, etched, deposited or printed onto the surface such as copper, tin, silver and gold. Those skilled in the art will understand that, with the inherent imperfections in most any manufacturing process, such conductive lines are seldom “perfect” in nature, and are thus not exactly parallel in practice. Therefore, they are described as “substantially parallel”. Different applications may configure some of the drive lines even non-parallel, such that the lines may occur parallel for a portion of the line, and the line may necessarily deviate from parallel in order to connect with other components for the device to operate, or in order to be routed on or about the substrate on which it is formed or traced. Similarly, the separate array of lines may be described as orthogonal or perpendicular, where the drive lines are substantially orthogonal or perpendicular to the pickup lines. Those skilled in the art will understand that the various lines may not be perfectly perpendicular to each other, and they may be configured to be off-perpendicular or otherwise crossed-over in different angles in particular applications. They also may be partially perpendicular, where portions of drive lines may be substantially perpendicular to corresponding portions of pickup lines, and other portions of the different lines may deviate from perpendicular in order to be routed on or about the substrate or to be connected to other components for the device to operate.
• These and other benefits provided by the embodiment will be described in connection with particular examples of embodiments of the embodiment and also descriptions of intended operational features and characteristics of devices and systems configured according to the embodiment.
• In operation, generally, the drive lines can transmit an electromagnetic field toward an object that is proximal to the device. The pickup lines may receive a signal originating from the drive lines and then transmitted through the object and through the substrate and onto the pickup lines. The pickup lines may alternatively receive a signal originating from the drive lines that were then transmitted through the substrate and onto the pickup lines without passing through the object. This electric field can vary at different locations on the grid, giving a resultant signal that can be interpreted by some type of logic or processor circuitry to define features and/or characteristics of an object that is proximate the assembly.
• The drive lines and pickup lines may be controlled by one or more processors to enable the transmission of the signal to an object via the drive lines, to receive a resultant signal from an object via the pickup lines, and to process the resultant signal to define an object image. One or more processors may be connected in one monolithic component, where the drive lines and pickup lines are incorporated in a package that includes the processor. In another embodiment, the drive lines, pickup lines and substrate may be assembled in a package by itself, where the package can be connected to a system processor that controls general system functions. This way, the package can be made part of the system by connecting with a system's input/output connections in order to communicate with the system. This would be similar in nature for example to a microphone connected to a laptop, where the audio signals are received by the system processor for use by the laptop in receiving sounds from a user. According to this embodiment, the sensor can be connected as a stand-alone component that communicates with the system processor to perform sensor operations in concert with the system processor.
• In another embodiment, a sensor may be configured to drive signals at different frequencies since the impedance of most objects, especially human tissue and organs, will greatly vary with frequency. In order to measure complex impedance at one or more frequencies of a sensed object, the receiver must be able also to measure phase as well as amplitude. In one embodiment, the resulting signal generated from a given impedance sensing electrode pair may result from varying frequencies, known in the art as frequency hoping, where the receiver is designed to track a random, pseudo-random or non-random sequence of frequencies. A variation of this embodiment could be a linear or non-linear frequency sweep known as a chirp. In such an embodiment one could measure the impedance of a continuous range frequencies very efficiently.
• In yet another embodiment, a grid sensor as described above may be configured to also operate as a pointing device. Such a device could perform such functions as well known touch pads, track balls or mice used in desktops and laptop computers.
• In one example of this embodiment, a two dimensional impedance sensor that can measure the ridges and valleys of a finger tip may be configured to track the motion of the fingerprint patterns. Prior art swiped fingerprint sensors can perform this function, but due to the physical asymmetry of the array and the need to speed correct, or “reconstruct” the image in real time make these implementations awkward at best. The sensor could also double as both a fingerprint sensor and a high quality pointing device.
• One device configured according to the embodiment includes a first array of sensor lines on a flexible substrate, and a second array of sensor lines on a flexible substrate, and also a processor configured to process fingerprint data from the first and second arrays of sensor lines. When folded upon itself in the case of a single flexible substrate or when juxtaposed in the case of separate substrates, the separate sensor lines cross each other without electrically shorting to form a grid with cross-over locations that act as pixels from which fingerprint features can be sensed. In one embodiment, an array of substantially parallel sensor drive lines is located on a surface of the flexible substrate. These drive lines are configured to sequentially transmit signal into a surface of a user's finger activating a line at a time. A second array of sensor lines is similar to the first, consisting of substantially parallel sensor pickup lines that are substantially perpendicular to the drive lines. These pickup lines are configured to pick up the signal transmitted from the first.
• In the configuration where the first and second set of sensor lines, the drive and the pickup lines for example, are located on different sections of an extended surface of the flexible substrate, the flexible substrate is further configured to be folded onto itself to form a dual layer configuration. Here, the first array of sensor drive lines becomes substantially perpendicular to the second array of pickup sensor lines when the flexible substrate is folded onto itself. This folding process creates crossover locations between these separate arrays of sensor lines—though they must not make direct electrical contact so that they operate independently. These crossover locations represent impedance sensing electrode pairs configured to sense pixels of an object and its sub-features juxtaposed relative to a surface of the flexible substrate. The scanning of these pixels is accomplished by activating individual rows and columns sequentially. Once a drive column is activated with drive signal the perpendicular pickup rows are scanned one at a time over the entire length of the selected driver. Only one row is electrically active (high impedance) at a time, the non active rows are either shorted to ground or multiplexed to a state where they do not cross couple signal. When a finger ridge is placed above an array crossover location that is active, it interrupts a portion of the electric field that otherwise would be radiated through the surface film from the active drive column to the selected row pickup. The placement of an object's subfeature, such as a ridge or valley in the case of a fingerprint sensor, over an impedance sensing electrode pair results in a net signal decrease since some of the electric field is conducted to ground through the human body. In a case of a fingerprint sensor the placement of a fingerprint ridge/valley over an impedance sensing electrode pair, the valley affects the radiation of electric field from the selected drive line to the selected pickup line much less than a ridge would. By comparing the relative intensity of signals between the pixels ridges and valleys, a two dimensional image of a finger surface can be created.
• Referring again toFIG. 1, this general example of the grid sensor will be now used to illustrate how such a sensor configured according to the embodiment can be implemented as a fingerprint sensor, where the object would simply be the surface of the fingerprint on the user's finger. This example will be carried through the following Figures for illustration of the benefits and novel features of the impedance sensor configured according to the embodiment. However, it will be appreciated by those skilled in the art, however, that any object may be sensed by a device configured according to the embodiment. Again, the example and description are intended only for illustration purposes.
• In operation, the sensor can be configured to detect the presence of a finger surface located proximate to the sensor surface, where the drive lines can drive an active electromagnetic field onto the finger surface, and the pickup lines can receive a resulting electromagnetic field signal from the pickup lines. In operation, the drive lines can generate an electric field that is passed onto the surface of the finger, and the different features of the fingerprint, such as ridges and valleys of the fingerprint surface and possibly human skin characteristics, would cause the resulting signal to change, providing a basis to interpret the signals to produce information related to the fingerprint features.
• In one embodiment of a fingerprint sensor, referring again toFIG. 1 in the context of a fingerprint sensor, a flexible substrate is used as the insulating dielectric layer104, to allow for beneficial properties of durability, low cost, and flexibility. The drive lines or plates106a,106b, are located on the flexible substrate and configured to transmit a signal into a surface of a user's fingerprint features and structures, such as ridges and valleys, placed on or about the sensor lines. The pickup lines102a,102bare configured to receive the transmitted signal from the user's finger surface. A processor (not shown) can be configured to collect and store a fingerprint image based on the received signal from the pickup lines.
• Referring toFIG. 4, an example asensor400 configured as an object sensor, where the top plates orpickup lines402a,402b, . . . ,402nare located on one side of insulating dielectric layer or substrate404. Bottom plates orpickup lines406a,406b, . . . ,406nare located on an opposite side of the substrate404. Electric fields408a,408bextend from bottom plates or drivelines406a,406bthrough the insulating layer or substrate404 and onto activetop plate402a. According to the embodiment, these drive lines may be activated one at a time to reduce any interference effects, but the electric field results illustrated here are intended to illustrate a contrast between electric fields that are partially or fully absorbed by the object with electric fields that are not absorbed the object at all. This information may be collected from drive and pickup plate electrode pairs at each crossover location to sense features and characteristics of the object that is proximate the sensor lines. Partially covered top plate or pickup line402bis connected tovoltmeter417, and uncoveredtop plate402ais connected tovoltmeter418. Active drive line or bottom plate406bis connected is connected to AC signal source416, causing an electric field to radiate from active plate406b. According to a particular application, the number of drive lines and pickup lines can vary depending on the application, and it may depend on the cost and resolution desired. As can be seen, the electric field lines408ais partially captured by thepickup lines402aand402b, and part is captured by the object, in thiscase finger410. Also, in order to illustrate that the pickup lines will exhibit different reading when an object or object feature is present or not present or proximate to a given crossover location,volt meter417 illustrates the response to the top plate or drive line402b, andvoltmeter418 illustrates the response of top plate or driveline402a. The difference in the deflections ofvoltmeter417 incomparison418 show the delta in electric field intensity between the two electrode pair locations, one with a finger present the other without.
• Referring toFIG. 5, another example of a sensor configured according to the embodiment is illustrated the Drive and pickup configuration when detecting the presence of an object. The sensor500 is illustrated, where the top plates orpickup lines502a,502b, . . . ,502nare located on one side of insulating layer orsubstrate504, and bottom plates or drivelines506a,506b, . . . ,506nare located on an opposite side of thesubstrate504. Again, the pickup lines are shown on the layer closest to the object being sensed for maximum sensitivity, and the drive lines shown on the opposite side of the substrate.Electric fields508a,508bextend from bottom plates or drivelines506a,506bthrough the insulating layer orsubstrate504 and onto activetop plate502b. Other configurations are possible, perhaps having drive plates on the top, and pickup plates on the bottom. The embodiment, however, is not limited to any particular configuration that is insubstantially different than the examples and embodiments disclosed and claimed herein.
• FIG. 5, further shows a snapshot of one selected individual electrode pair located at the crossover ofpickup line502band driveline506b, where the remaining pickup and drive lines are not active, shown grounded inFIG. 5.Drive line506bis connected to AC voltage source516, andpickup line502bis connected to amplifier/buffer514. Once activated as shown here,electric field lines508a,508bare generated, and they radiate fromdrive line506band are sensed bypickup line502b, sending the resultant signal into amplifier/buffer514, and are later processed by analog and digital circuit functions. Grounding the inactive adjacent drive and pickup lines focuses theelectric fields508aand508bat the crossover location between the active the drive and pickup plates, limiting crosstalk from adjacent areas on the object being sensed. As the sensing operation proceeds in this embodiment, different drive line/pickup line crossover pairings may be activated to capture different pixels of information from the object. In the case of an object sensor, it can capture information on the shape of the object, and, if the electrical characteristics are non-uniform across its surface, it's composition. Again, the embodiment is not limited to this particular configuration, where one single electrode pair, several electrode pairs, or even all electrode pairs may be active at one time for different operations. In practice, it may be preferable for less than all of the impedance sensing electrode pairs to be active at a given time, so that any interference that may occur between close-by pixels would be minimized. In one embodiment, a drive line may be activated, and the pickup lines may be scanned one or more at a time so that a line of pixels can be captured along the drive line and pickup lines as they are paired along a line at the crossover locations. Thus, and still referring toFIG. 5, the AC voltage source516 may remain connected to driveline506b, and the connection of the amplifier/buffer516 may cycle or scan over to sequential pickup lines, so that another pixel of information can be captured from another pickup line crossover paired withdrive line506b. Once substantially all the pickup lines506a-nhave been scanneddrive line506bcan be deactivated, than another drive line in sequence can be activated with the AC voltage source, and a new scanning can commence through the pickup lines. Once substantially all drive line/pickup line pairings have been scanned to capture the full two-dimensional array of pixels, then a two dimensional image or rendering of the object features and characteristics can be made, such as a rendering of the shape of the object, and potentially a composition map.
• As another example of a sensor that can benefit from the embodiment, a reduced cost fingerprint swipe sensor could be configured using the same innovation provided by the embodiment. In this embodiment, a reduced number of pickup lines could be configured with a full number of orthogonal drive lines. Such a configuration would create a multi-line swipe sensor that would take the form of pseudo two-dimensional sensor, and when a finger was swiped over it would create a mosaic of partial images or slices. The benefit of this would be to reduce the complexity of image reconstruction task, which is problematic for current non-contact silicon sensors that rely on one full image line and a second partial one to do speed detection.
• The tradeoff would be that this pseudo two dimensional array would have to be scanned at a much faster rate in order to keep up with the varying swipe speeds of fingers that have to be swiped across it.
• FIGS. 6aand6billustrate the operation of the sensor when detecting surface features of an object such as fingerprint ridges and valleys. The sensor is configured identically to the previous example inFIG. 5, but in this case is interacting with a textured surface such as a fingerprint.
• Referring toFIGS. 6aandb, another example of a sensor configured according to the embodiment is illustrated. Thesensor600 is illustrated, where the top plates or pickup lines602a-nare located on one side of insulating layer orsubstrate604, and bottom plates or drive lines606a-nare located on an opposite side of thesubstrate604. For maximum sensitivity pickup lines are shown on the layer closest to the object being sensed, and the drive lines shown on the opposite side of the substrate.FIG. 6ashowselectric field lines620 as they interact with a proximally located object's valley andFIG. 6bshowselectric field lines621 as the interact with a proximally located object's peaks, extending from bottomplate drive line606bthrough the insulating layer orsubstrate604 and ontoactive drive line606b. In the case of sensing a fingerprint, the corresponding ridges and valleys over the fingerprint surface can be captured by the grid of drive line/pickup line crossover points, and the resulting data can be used to render an image of the fingerprint. A stored fingerprint can then be compared to the captured fingerprint, and they can be compared for authentication. This is accomplished using any one of many fingerprint matching algorithms which are available from vendors as stand alone products. Such vendors include Digital Persona, BioKey, and Cogent Systems, to name just a few.
• Also illustrated inFIGS. 6aandb, is the individual sensor line pairing ofpickup line602band driveline606b. Their crossover forms the active electrode pair, and the remaining pickup and drive lines are not active, and will nominally be grounded by electronic switches.Drive line606bis connected toAC voltage source616, andpickup line602bis connected to amplifier/buffer605. Once activated as shown here,electric field lines620 and621 are created as shown inFIGS. 6aand6brespectively, and they emanate between thedrive line606bandpickup line602b, sending a resultant signal that is radiated ontopickup line602band connected to amplifier/buffer605, and later processed by analog and digital processing circuitry. As the sensing operation proceeds in this embodiment, different drive line/pickup line crossover pairs may be activated to capture different pixels of information from the object. In the case of a fingerprint, it can capture information on different features and characteristics of the fingerprint and even the body of the finger itself. Again, the embodiment is not limited to this particular configuration, where one electrode pair, several electrode pairs, or even all electrode pairs may be active at one time for different operations. In practice, it may be preferable for less than all of the electrode pairs to be active at a given time, so that any interference that may occur between close-by pixels would be minimized. In one embodiment, a drive line may be activated, and the pickup lines may be scanned one or more at a time so that a line of pixels can be captured along the drive line and pickup lines as they are paired along a line at the crossover points. Thus, and still referring toFIG. 6a, thevoltage source616 may remain connected to driveline606b, and the connection to buffer/amplifier605 may cycle or scan over to another pickup line, so that another pixel of information can be captured from another electrodepair using driveline606b.
• In the snapshot shown inFIGS. 6aand6bdrive plate606bremains excited byAC signal source616 until an entire column of pixels is scanned, while unused drive plates (606a,c-netc.), are switched to ground for isolation purposes. Likewise, in one embodiment only one pickup plate is active at a time and some or substantially all other pickup plates are switched to ground to minimize crosstalk.
• The scanning process continues beyond the snapshot shown inFIGS. 6aand6b, with the next column in sequence being activated,606c, (although the sequence could be arbitrary), Once the entire sequence of Pickup Plates602a-nis scanned, the next driver line606dwould activated, until all, or substantially all of the drive lines606a-nhave been sequenced. Once all the drive columns have been activated and the pickup plates scanned for each column, one will have collected a complete two dimensional array of pixels equal to the number of driver rows times the number of pickup columns. For a 500 DPI sensor that would create a 10×10 mm array or 100 mm², consisting of 40,000 individual pixels. Depending on the application, all of the drive lines may be sequenced, or possibly some or most of them may be sequenced.
• Referring again toFIGS. 6aand6b, the two conductive layers Drive layer606 and Pickup layer602, are separated by an electrically insulatinglayer604. This insulatinglayer604 has high DC resistance and has a dielectric constant greater than one to allow the transmission of high frequency electric fields through it. In one embodiment this layer602 is created by folding a single sided flexible printed circuit board back onto itself. In another embodiment it is created by placing a dielectric layer between two electrically active layers to form a double sided circuit board.
• FIG. 7 shows an example of an x-y grid of plate rows and columns depicted by lumped circuit components that represent the electric field couplings of the sensor at each drive/pickup crossover.
• The bottom plates701a,b,cetc. are driven one at a time byAC signal source716 via switch matrix740a-n.FIG. 7 shows a scan snapshot where onedrive switch740bin the on condition connecting the corresponding plate to the signal source. This activates oneentire row740bwith AC signal over the entire length of the plate that is equal to the sensor width in one dimension. Correspondingly each column plate703a,b,cetc. will pickup up AC signal through insulatinglayer704 andcoupling capacitors761a,b,c. . . n. Only one pickup plate at a time is active being switched into thebuffer amplifier716. Top Plate702bis shown as the active plate inFIG. 7, while all or substantially all other pickups are shorted to ground via switch matrix730a-n, thus the information from one x-y pixel is captured.
• A single row remains active only as long as it takes the entire number of pickup plates/columns to be scanned. Scan time per pixel will depend on the frequency of operation and the settling time of the detection electronics, but there is no need to scan unduly fast as is typical with prior art swipe sensors. On the other hand prior art swipe sensors must scan at a very high pixel rate in order not to lose information due to undersampling relative to the finger speed that can be greater than 20 cm/sec. This reduction in capture speed relative to a swipe sensor relaxes the requirements of the analog electronics and greatly reduces the data rate that a host processor must capture in real time. This not only reduces system cost but allows operation by a host device with much less CPU power and memory. This is critical especially for mobile devices.
• Once anentire row706bhas been scanned by all or substantially all of its corresponding pickup plates702a-n, then the next row in the sequence is activated through switch matrix740. This process continues until all or substantially all of the rows and columns are scanned.
• The amount of signal that is coupled into thebuffer amplifier716 is a function of how much capacitance is formed by the insulating layer and the finger ridge or valley in close proximity. The detailed operation of how these electric fields radiate is shown inFIGS. 6aandb. The total coupling capacitance is a series combination of the insulatinglayer capacitance704 that is fixed for a given thickness, and the variable topological capacitance of the object being sensed. The variable portion of this is shown inFIG. 7 as a series of variable capacitors numbered760a-n,761a-n,762a-netc., forming a two dimensional array.
• FIG. 8 shows an example of an embodiment of the placement sensor using adifferential amplifier880 to take the signal from the selected pickup plate (802a-n), and subtract it from the reference signal ofplate805. The electrical subtraction of these signals performs several functions: first wide band common mode is subtracted out; second, subtracting againstreference plate805 provides a relative reference signal equivalent to an ideal ridge valley; third, common mode carrier signal that couples into both plates other than through a finger is also subtracted out. First order carrier cancellation of etch variation in the pickup plates also occurs when we subtract out carrier that is coupled in by other means than through fingers placed on the sensor. This is critical for high volume manufacturing at a low cost.
• Reference plate805 is intentionally located outside of the finger contact area of the sensor, separated from pickup plates802a-nbyGap885,Gap885 is much larger that the nominal gap between the pickup plates that is typically 50 um. In a realworld embodiment plate805 would be positioned under the plastic of a bezel to prevent finger contact, placing it at least 500 um apart from the other pickup plates.
• Each one of the pickup plates802a-nis scanned sequentially being switched through pickup switches830a-nconnecting them toDifferential Amplifier880. During the scanning process of an entire pickup row, the positive leg of the differential amplifier remains connected toreference plate805 to provide the same signal reference for all of the pickup plates.
• FIG. 9ashows a circuit diagram of an example of a front end for the placement sensor in a topology that uses a bank of Single Pole Double Throw Switches or SPDTs to scan the pickup plate rows and a bank of Single Pole Single Throw switches to multiplex the pickup plate columns.
• InFIG. 9awe see a snapshot of the analog switches as the scanning process begins. Only the first SPDT switch1044ais shown in the “on” position, which allowspickup plate902ato conduct its plate signal intoDifferential Amplifier980. The remaining pickup plates are shorted to ground via switches944a-944n, preventing any pickup signal received by them from entering intodifferential amplifier980.
• Each SPDT has aParasitic Capacitance945, due to the fact that real world switches to not give perfect isolation. In fact the amount of isolation decreases with frequency, typically modeled by a parallel capacitor across the switch poles. By using a SPDT switch we can shunt this capacitance to ground when an individual plate is not active. Since there is a large array of switches equal to the number of pickup plates, typically 200 for a 500 dpi sensor, the effective shunt capacitance to ground is multiplied by that number. So if a given switch has 0.5 picofarads of parasitic capacitance and there where 200 pickups, that would add up to 100 picofarads of total shunt capacitance.
• In order to prevent this large capacitance from diverting most of the received signal from the active pickup to ground, it is desirable in this example to use a compensating circuit. This is accomplished by using resonatinginductor939, forming a classic bandpass filter circuit in conjunction with parasitic capacitors945 (one per switch) andtuning capacitors934 and937. A two step null & peak tuning calibration procedure is used wheretuning capacitor934 and937 are individually tuned withinductor939 using the same drive signal on both the plus and minus inputs todifferential amplifier980. The two bandpass filters formed with inductor1039 and resonatingcapacitors934, and937 respectively, will be tuned to the same center frequency when there is zero signal out ofdifferential amplifier980.Next capacitors934 and937 andinductor939 are tuned together using a differential input signal with opposite 180 degrees phases on the plus and minus inputs to thedifferential amplifier980. They are incremented in lock step until the exact drive carrier frequency is reached, this occurs when the output ofdifferential amplifier980 is at its peak, making the center frequency equal to the exact frequency of thecarrier drive signal916.
• In a systems implementation, a calibration routine would be performed before each fingerprint scan to minimize drift of this filter with time and temperature. The resonatinginductor939 needs to have a Q or Quality Factor of at least 10 to give the filter the proper bandwidth characteristics necessary to optimize the signal to noise ratio.
• Alternately,carrier source916 may be a variable frequency source, and capicitors (937 and934) may be fixed values. In this embodiment, tuning is accomplished by varying the frequency of source916) until peak output is obtained fromdifferential amplifier980
• FIG. 9bshows an alternate example of a device employing multiple banks of plates grouped together, each with their own differential amplifiers.
• Dividing up the large number of parallel pickup plates into groups each containing a smaller number of plates is an alternate architecture that would not require the use of a tuned bandpass filter in the front end because the parasitic switch capacitances would be greatly reduced. This would have two possible advantages, first lower cost, and second the ability to have a frequency agile front end. In this Figure we have a snapshot of the front end where thefirst switch944aof bank907ais active. All other switch banks907a-907nare shown inactive, shorting their respective plates to ground. Therefore, only voltage or currentdifferential amplifier980ahas any plate signal conducted into it, voltage or currentdifferential amplifiers980b-980nhave both their positive and negative inputs shorted to ground through theirrespective switches945a-nand945r, preventing any signal from those banks making a contribution to the overall output.
• Each of thedifferential amplifiers980a-980nis summed through resistors987a-987ninto summingamplifier985. Only thedifferential amplifier980ain this snapshot has plate signal routed into it, so it independently produces signal to the input of summingamplifier985. This process is repeated sequentially until all or substantially all of the switch banks907a-n, and switch plates944a-n,945a-n, etc, of the entire array are fully scanned. In different embodiments, all or substantially all of the array may be scanned, or less than the entire array may be scanned in different applications. In some applications, a lower resolution may be desired, so all of the array may not need to be scanned. In other applications, a full image may not be necessary, such as a navigation application, where limited images may be used to detect movement of speed, distance and/or direction to use as input for a pointing device, such as directing a cursor on a display similar to a computer touch-pad or a mouse.
• By splitting the pickup array up, the capacitive input load on each plate is reduced from that of the full array of switches to the number of switches within a given plate group. If we were to divide for example 196 potential pickup plates into 14 banks of 14 plates, resulting in a capacitance load equal to the parasitic capacitance of 14 switches (944), plus the capacitive load of the differential amplifier. If analog switches944 are constructed with very low parasitic capacitance then the overall input load would be small enough not to need a bandpass circuit in the front end in order to resonate out the load capacitance. As integrated circuit fabrication techniques improve we would be able design smaller switches with less parasitic capacitance, making this approach become more attractive.
• FIG. 9cillustrates another example of a front end circuit using individual plate buffers that are multiplexed into a second stage differential amplifier.
• Buffers982athrough982nas illustrated are special buffers that are designed to have very low input capacitance. In one embodiment, these buffers could be configured as single stage cascoded amplifiers in order to minimize drain-to-gate Miller capacitance and die area. To better maximize plate to plate isolation, two sets of switches could be used for each input. Analog switches930a-930nare included in this example to multiplex each selected buffer intodifferential amplifier980. Switches932 are included to shut down the power simultaneously to all the other input buffers that are not selected. This effectively puts them at ground potential. An alternate embodiment would be to put input analog switches in front of each amplifier to allow a short of the unused plates directly to ground. One effect of this approach may be an increase in input load capacitance for each plate.
• FIG. 9cshows a snapshot of the scanning process wheretop plate902ais being sensed thoughbuffer982athat has power supplied to it throughswitch932a. Analog switch930ais closed, routing it todifferential amplifier980. All other buffer outputs are disconnected from thedifferential amplifier980 via analog switches930b-nand power switches982b-n
• The positive input todifferential amplifier980 is always connected to thereference plate902r, providing an “air” signal reference to the amp. Thedifferential amplifier980 serves to subtract out noise and common mode carrier signal in addition to providing a “air” reference carrier value.
• FIG. 10 shows a particular embodiment of a placement sensor implemented with traditional analog receiver technology. The analog front end begins withDifferential Amplifier1080 where selected Pickup Plate1002a-nis subtracted fromReference Plate1005, which is located outside the finger contact area providing a reference signal equivalent to an ideal finger valley. A programmable gain stage orPGA1090 follows theDifferential Amplifier1090, but could be integrated into the same block providing both gain an subtraction in a single stage.PGA1090 is designed to have a gain range wide enough to compensate for production variations in plate etching and solder mask thickness between the layers.
• Control processor1030 orchestrates the scanning of the two dimensional sensor plate array. Drive plates/columns1002a-1002nare scanned sequentially by the DrivePlate Scanning Logic1040 in theControl Processor1030. When a selected drive plate is activated it is connected tocarrier signal source1016. All inactive drive plates are connected to ground. Before activating the next drive plate in the sequence the active drive plate remains on long enough for the entire row of Pickup Plates1002a-nto be scanned by Pickup Plate Logic1045.
• Analog mixer1074 multiplies the gained up plate signal against thereference carrier1013. The result is a classic spectrum of base band plus harmonic products at multiples of the carrier frequency. An analoglow pass filter1025 is employed to filter out the unwanted harmonics and must have a sharp enough roll of to attenuate the information associated with of the second harmonic without losing base band information.
• Following the low pass filter is an A/D Converter1074 that must sample at a least twice the pixel rate to satisfy the Nyquist criteria.Memory buffer1032 stores the A/D samples locally with sufficient size to keep up with the worst case latency of the host controller. The A/DSample Control Line1078 provides a sample clock for the converter to acquire the sequential pixel information that is created by the sequencing of the plate rows and columns.
• FIG. 11 shows an example of one embodiment of a placement sensor implemented with direct digital conversion receiver technology. In this example, the analog front end begins withDifferential Amplifier1180 where selected Pickup Plate1102a-nis subtracted fromReference Plate1105, which is located outside the finger contact area providing a reference signal equivalent to an ideal finger valley. The electrical subtraction of these signals performs several functions: first wide band common mode is subtracted out; second, subtracting againstreference plate1105 provides a relative reference signal equivalent to an ideal ridge valley; third, common mode carrier signal that couples into both plates other than through a finger is also subtracted out. Elimination of common mode is particularly important in high RF noise environments. First order carrier cancellation of etch variation in the pickup plates also occurs when we subtract out carrier that is coupled in by other means than through fingers placed on the sensor. This is critical for high volume manufacturing at a low cost.
• A programmable gain stage orPGA1190 follows the Differential Amplifier, which could easily be combined into a single differential amplifier including programmable gain as is commonly done in modern integratedcircuit design PGA1190 is designed to have a gain range wide enough to compensate for production variations in plate etching and solder mask thickness between the layers.
• Control processor1130 orchestrates the scanning of the two dimensional sensor plate array. Drive plates/columns1102a-1102nare scanned sequentially by the DrivePlate Scanning Logic1140 in theControl Processor1130. When a selected drive plate is activated it is connected tocarrier signal source1116. All inactive drive plates are connected to ground. Before activating the next drive plate in the sequence the active drive plate remains on long enough for the entire row of Pickup Plates1102a-nto be scanned byPickup Plate Logic1145 and captured by the A/D converter1125.
• The A/D Converter1125 is sampled at a rate of at least twice the carrier frequency to satisfy the Nyquist criteria. The A/DSample Control Line1107 provides a sample clock for the converter to acquire the sequential pixel information that is created by the sequencing of the plate rows and columns.
• Following the A/D converter is aDigital Mixer1118 that digitally multiplies the A/D output that is at the carrier frequency against the reference carrier generated by the Digitally ControlledOscillator1110. The result is that the signal is down converted to the base band with the carrier removed. There are other unwanted spectral components created by this process, namely a double time carrier side band, but these can easily be filtered out.
• A combination decimator anddigital filter1120 follows theDigital Mixer1118. This block performs sampling down conversion, reducing the sample rate from at least twice the carrier frequency to at least twice the pixel rate that is much lower. The digital filter would typically include a Cascaded Integrator Comb, or CIC filter, which removes the unwanted spectral byproducts of mixing as well as improving the receiver signal to noise. A CIC filter provides a highly efficient way to create a narrow passband filter after mixing the signal down to baseband with the digital mixer. The CIC filter may be followed by a FIR filter running at the slower decimated rate to correct passband droop.
• With a reduction of sample rate in the order of 100:1 a relatively small Control Processor Buffer (1132) could be used to capture and entire fingerprint. For example a 200×200 array producing 40 k pixels could be stored in a 40 kb buffer. This is in contrast to a swipe sensor that must scan the partial image frames at a rate fast enough to keep up with the fastest allowable swipe speed, usually around 200 ms. At the same time, a slow swipe of two seconds must also be accommodated, requiring ten times the amount of memory as the fastest one. Various techniques have been developed to throw away redundant sample lines before storage, but even with that the real time storage requirements are much greater for swipe sensors. This is a critical factor in Match on Chip applications where memory capacity is limited. In addition, a placement sensor has no real-time data acquisition or processing requirements on the host processor beyond the patience of the user for holding their finger in place.
• Referring toFIG. 12A, and example of asensor layout1200 configured according to one embodiment is illustrated in a configuration that is known in the semiconductor industry as a Chip on Flex (CoF). Chip on Flex is a configuration where a processor chip is attached to a flexible substrate, such as Kapton™ tape, and that is electrically connected to conductive lines and possibly other components located on the flexible substrate. In this example, thesensor layout1200 is shown within the borders of Kapton tape havingpitch rails1202,1204 withslots1206 located along both rails. These slots are used in the manufacturing process to feed the tape through the process while lines and possibly components are formed on the tape. The pitch of a device refers to the length of Kapton tape required to form a device on the CoF. The distance “d”1208, measured here betweenslots1207 and1209, is substantially constant throughout each rail, and the pitch is a shorthand method of determining the length of flex that a device covers. For the device shown in this example, the pitch1212 shows a span betweenslot1207 and1214 of eight slots, and thus would be characterized as an 8-pitch device. The example sensor device shown, which may be a fingerprint sensor or other type of placement, 2D or area sensor, illustrates anintegrated circuit1210, which may be a logic circuit formed on a silicon substrate, a microprocessor, or other circuit for processing pixel information captured from a sensor circuit. The example may also be formed or otherwise manufactured on a substrate other than flexible substrate or Kapton tape, in fact it may be formed on a silicon substrate, rigid board, or other substrate configured for various applications.
• If configured as a fingerprint sensor or other placement sensor, integratedcircuit1210 may be a mixed signal chip that enables all or some of the functions described inFIG. 16 below. In one embodiment, it has enough inputs and outputs to drive a 200 by 200 line array of drive and pickup lines, and may have more or less of either lines. Thetop layer1220 is formed by an array of pickup lines connected directly to integratedcircuit1210. This may be a flip chip mounted directly to the flex substrate without bond wires. In this example, the bottom layer is formed by folding the single layer back onto itself along the folding axis1230 to create double layer active sensor area1255. The drive lines fold to create the bottom layer1225. The drive lines in this example are split into left andright groups1240 and1242 respectively for the sake of layout balance, but could be all on the left or right side of the sensing area. The left drive plate bundles1240, and right drive plate bundles1242 are inter-digitated with alternating left and right feeds to form a continuous line array on bottom layer1225.
• Flexible substrate based connector1235 routes power, ground and interface signals out to an external host or onto another substrate that contains system level components, such as those illustrated inFIG. 16 and described below. These components may include but are not limited to a processor with memory, logic enabling imbedded matching algorithm(s) and encrypting/decrypting functions. In an alternative example, connector1235 may be attached to the host substrate using conductive adhesive otherwise known as anisotropic conductive film (ACF attach), which may be labeled as “high density” in some products.
• Referring toFIG. 12B, another example of asensor1250 is shown having a different orientation and configuration on a substrate. Similar to the above example, thesensor1250 is a placement sensor, and is configured to be folded onto itself along thefolding axis1251 to create two layers, thebottom layer1252 withdrive lines1256, andtop layer1254, withpickup lines1257, integratedcircuit1258, flexexternal connections1262, andprocessor connections1260 that may be used to connect the integrated circuit to external devices, such as for manufacturing testing for example. This configuration, however, has a much smaller pitch, again where the distance “d” is the distance between each pair ofslots1206, and the pitch in this example is betweenslots1270 and1272, making this device a 5-pitch device. This example device takes up 5 pitches of Kapton tape compared to the other example device1200 (FIG. 12A) taking up 8 pitches of Kapton tape. This device performs substantially the same function as that of example1200,FIG. 12A, yet takes up less Kapton tape, saving in material costs. The device may take up even less pitches of tape if the size of the resulting sensor surface were reduced, allowing the space needed to accommodate the pickup lines, drive lines, and other components to be reduced. In this example, the effective sensor surface may be ten square millimeters, and could be reduced to nine or even eight millimeters, and the structures could be reduced accordingly to reduce the overall area of the device, likewise reducing the area of substrate required to accommodate the overall device.
• As will be appreciated by those skilled in the art, given these examples, different designs may be accomplished to optimize different aspects of the invention, including size is the substrate used for a device, and both the size and pixel density of the sensing area. The invention, however, is not limited to a particular optimization done by others, and indeed the invention should inspire others to improve upon the design using well known and alternative processes, materials, and know-how available to them. The scope of the invention is only limited by claims that are either appended or submitted for examination in the future, and not by information that is extemporaneous to this specification.
• Referring toFIG. 13a, an illustration of aflex layout structure1300 is illustrated. As shown, theflex layer structure1300 includes animaging area1350, in which drive lines form crossover locations with pickup lines, where the crossover locations are formed by folding thetop layer1370 overbottom layer1372, folding the flexible substrate upon itself aboutflex bend radius1374. From a side view, thetop flex1364 is layered overtop soldermask1362, which is layered upon top copper or pickup lines1360. Bottomlayer solder mask1370 is folded under top copper1360, andbottom copper1372 is formed undersolder mask1370 and overbottom flex1375.
• Referring toFIG. 13b, an example of amodule structure1301 is shown for mounting theflex layer structure1300 ofFIG. 13a. Those skilled in the art will understand that the structure of a particular module may vary according to the embodiment, and that this example, though it shows a substantially complete example of a module that can be used to base a practical implementation, is but one example and is not intended and should not be considered as limiting the embodiment in any way. Theexample structure1301 includesrigid substrate1330 that receives theflex top layer1370 on its top layer with flex locating pins orplastic frame1337 configured to ensure alignment of the drive plates with the pickup plates. Because the sensing electrode pairs are formed by crossovers of the drive and pickup lines on the two layers, the x-y alignment tolerance requirements may be on the order of several pixels, rather than the sub-pixel alignment tolerances that would be required if there were features to be matched between the two layers. The four mounting holes (1337) on each layer are sufficient to ensure angular and x-y alignment. Also illustrated isdriver chip1310 andimaging area1350.
• Referring toFIG. 14, an illustration is provided of anexample system1400 incorporating asensor system1402 generally configured according to the embodiment. A sensor device may be incorporated into a system, or may be configured as a stand-alone product. As a stand-alone product, the sensor components may be encased in a housing (not shown), and electrical connections exposed for connection to a device or system that would utilize such a device. Those skilled in the art will immediately see how a sensor configured according to the embodiment as described herein can be incorporated into a housing such as those that widely used in different industry sectors. Thus, for example, in a system, the mechanical connections, designs and structures may necessarily vary according to a particular application. For example, if incorporated into a laptop for use as a fingerprint sensor, a surface mounting module would need to be employed to expose the sensor grid lines to a user. If incorporated into a mobile phone, personal data assistant (PDA) or the like, another type of mounting module would be needed to conform to the particular device design while providing the operational capability of the sensor. Again,FIG. 14 illustrates a diagrammatic representation of asystem1400 that incorporates asensor1402 configured according to the embodiment with the folded flexible orrigid substrate1404 having a top layer1406 and abottom layer1408, and each having either pickup lines or plates and drive lines or plates respectively depending on the application, though not shown here. The two-dimensional sensing area1411 is shown with anobject1410 on top, which may be a finger in the case of a fingerprint sensor, or another object in another application. The top layer's pickup plates or lines (not shown) communicate with topplate processing circuitry1410 viacommunication link1412 to send resultant signals received. Drive lines or plates are located but not shown here onbottom layer1408, and receive drive signals from bottomplate processing circuitry1414 viacommunication line1416. The topplate processing circuitry1410 includes front end buffers andamplifiers1416 configured to receive, amplify and/or buffer or store a resultant signal received from the pickup plates or lines. Aswitch array1418 such as that illustrated inFIG. 9 is configured to receive the signal from thefront end1416 and send the switched signal to analog to digital (A/D)converter1420 for conversion to a digital signal. Digital signal processor (DSP)1422 is configured to receive the digital signal from A/D converter1420 and process the signal for transmission.
• Bottomplate processing circuitry1414 is configured to produce a drive signal for use by drive plates or lines located on thebottom layer1408 of thesensor substrate1404, and includes drivers and scanning logic1424 for producing the signal, and programmable frequency generate1426 for programmable setting the frequency in which the drive signal is set. The bottomplate processing circuitry1414 includescommunication link1428, likewise, top plate circuitry hascommunication link1420 for communicating with system buss1432 for sending and receiving communications among the system, such as to processors, memory modules, and other components. System buss1432 communicates withpersistent memory1434 viacommunication link1436 for storingalgorithms1428,application software1440,templates1442, and other code for persistent and frequent use byprocessor1444.Processor1444 includes processor logic having logic and other circuitry for processing signals received from the system buss and originating from thesensor1402, and also includes arithmetic logic unit1450 configured with logical circuits for performing basic and complex arithmetic operations in conjunction with the processor. Processor memory1452 is configured for local storage for theprocessor1444, for example for storing results of calculations and retrieval for further calculations.
• In operation, drive signals are controlled byprocessor1444, and parameters for the drive signals originating from bottomplate processing circuitry1414 are set in the bottomplate processing circuitry1414 by theprocessor1444. Drive signals are generated by logic1424 within the parameters set in generator1426 and sent tobottom plate1408 viacommunication link1416. These signals generate electromagnetic fields that extend to pickup lines on top layer1406 about thesensing area1411. These signals are cycled through different pixel electrode pairs on the sensor grid (not shown here, but described above), and some of these electromagnetic fields are absorbed by the object1410 (such as a fingerprint for example). The resultant signal is picked up by the pickup plates or lines located on top layer1406 about the sensing area (not shown here, but described above). The resultant signal is then transmitted to topplate processing circuitry1410 viacommunication line1412, and the signal is processed and transmitted to storage orprocessor1444 for further processing. Once the drivers and scanning logic have cycled through the pixels on the grid sensor, data related to features and characteristics of the object can be defined and utilized by the system. For example, in a fingerprint sensor system, the image may be a fingerprint image that can be compared to a stored fingerprint image, and, if there is a match, it can be used to validate a user.
• FIG. 15 Illustrates how a device configured according to the embodiment may be applied to a fingerprint sensing application. A user places a finger with fingerprint (1510) over the sensor grid, which is formed by the crossover locations of the drive plates (1506a-1506n) and the pickup plates (1502a-1502m).Image pixel1561asenses the fingerprint area above the electrode pair ofdrive plate1506aand pickup plate1502a,pixel1561asenses the crossover ofdrive1506nand pickup1502a, andpixel1562nsenses the area above the crossover ofdrive1506nand pickup1502m
• FIG. 16 illustrates the steps required to collect the fingerprint image as shown inFIG. 15, using the embodiment shown inFIGS. 11 and 14. Image capture begins atstep1601. As part of the initialization a row counter is initialized to 1 atstep1602.Step1603 is the beginning of a row scan sequence. At the beginning of each row, a column counter is set to 1 atstep1603. Instep1604, the topplate scanning logic1145 activates the appropriate analog switch (one of1103athrough1103n) for the selected row. InStep1605 the sense of an individual pixel begins when the bottomplate scanning logic1140 activates the appropriate drive plate (one of1106athrough1106n) with thecarrier signal1116. Atstep1606 the signal fromdifferential amplifier1180 is sampled repeatedly by A/D converter1125 after processing throughprogrammable gain amplifier1190.Digital mixer1118 mixes the samples down to the baseband frequency set bydigital oscillator1110. The baseband signal is then filtered by digital decimatingfilter1120 to produce a signal level value for the current pixel. The functions performed for this step in the embodiment ofFIG. 11 could alternatively be performed by the corresponding analog receiver shown inFIG. 10, or other functionally similar arrangements. Instep1607 the signal level value derived instep1606 is stored in the appropriate position inmemory buffer1132 that corresponds to the currently selected row and column. Instep1608 the column number is incremented, and instep1609 the column number is tested to determine whether the current row collection has been completed. If the row has not been completed, we return to step1605 to collect the next pixel in the row. If the row is complete, we proceed to step1610 and increment the row number. Instep1611, we test the row number to determine if all the rows have been scanned. If not, flow returns to1603 to start the next row back at the first column. Once all the rows have been scanned, image capture is complete, and we proceed to step1612, at which point the image is ready for further processing or transfer to long term storage.
• Those skilled in the art will recognize that row and column scanning order may not correspond directly to physical position in the array, as some implementations may more optimally be sampled in interleaved fashions.
• InFIG. 17, an example of the example as shown inFIG. 14 in a user authentication application. In step1701asystem level application1440 onprocessor1444 requires user authentication. At step1702 the user is prompted to provide a finger for verification. The system waits for finger presence to be detected instep1703. This can be performed by collecting a reduced size image as described inFIG. 16 and testing for finger image, or via other dedicated hardware. Once finger presence is detected, a complete image is collected instep1704, using the method described inFIG. 16 or other substantially similar method. This image is then stored and instep1705 converted into a template1712 as shown inFIG. 17B, typically consisting of a map of minutia point locations and types (such as bifurcations1710, and terminations1711), or possibly of ridge frequency and orientation, or some combination of both. Instep1707 the template is then compared against one or more enrollment templates that were retrieved frompersistent template storage1142 instep1706. If a match is found, the user is authenticated instep1708 and granted access to the application. If no match is found, the user is rejected instep1709, and access is denied.
• In an authentication system such as described by FIGS.16 and17A-B, there can be a tradeoff between security and operational speed. A device such as a smartphone may have differing security and convenience (speed) requirements for differing operating modes, as well. These tradeoffs may be governed by the value of security for different types of information. As an example, users may place a low value on security for simply powering up their smartphone or other device. But, they may place a much higher value on performing a financial transaction or other sensitive transfer. They may want to lock out the ability to access personal contact information or customer lists, or may also want to lock out the ability for others to make local calls, long distance calls, access personal photos, access social networking websites, sent and receive text messages or emails, and they may want to have different security protocols for the access to different information. Users having conventional systems without the benefit of biometrics will typically lock their telephone handset with a four-digit PIN, which is a fairly low level of security. Securing a financial transaction over the same device, a new development that is desired in the industry, would cause a user to desire a much higher level of security. Conversely, the amount of time a user would find acceptable to unlock the phone for a simple call would be much shorter than the time they would wait to secure a high value transaction, where a user may be more tolerant of a higher time demand for authenticating the user for a financial transaction.
• Embodiments described herein facilitate supporting both of these requirements by providing variable captured image resolution and matching algorithm security level. In one example, when operating in high security mode (such as when enrolling a user or validating a high-value transaction) the image capture procedure described inFIG. 16 and the match procedure described inFIG. 17A-B may operate in full resolution mode. When operating in ‘convenience’ mode (such as unlocking the phone, looking at photos, surfing the internet or switching users), the fingerprint image may be acquired in a half-resolution mode by skipping every other column and every other row—for example wheresteps1608 and1610 would increment the Column and Row counters, respectively, by two instead of one. This may result in an image with half the resolution in each axis compared to the high security mode, and one-fourth the size. This could cut by a factor of four both the time required to acquire the image (FIG. 16) and the time required to extract the template from the image (step1705). Due to the reduced resolution of the image, and the relaxed security requirements for this convenience mode, the matching threshold applied instep1707 may be accordingly reduced.
• Referring toFIGS. 18A-D, another embodiment of a sensor module or assembly is illustrated as asensor1800, first shown in an expanded view inFIG. 18A, made up of a foldedflex sensor1802, amodule folding base1804 and mountingboard1806. In this embodiment, a switch having aplunger1812 andbase1813 is incorporated into a sensor assembly that allows the integration of the sensor operations, such as fingerprint sensor operations, together with other operations of a device. Still further, this assembly allows for the configuration of a personalization switch for use on a device, such as a mobile telephone or smart phone for example, that has extended functions including biometric operations. If used together with a power or selector switch, such as for example a modular replacement for the main selection switch on an iPhone™ manufactured by Apple Computer Corporation or a navigation selection switch used on a BlackBerry™ smartphone manufactured by Research in Motion (RIM™) next to the display screen of these devices, a fingerprint sensor can be used for authentication while using these personal devices. The authentication can be used to access the device entirely, access different levels of information such as different information that a user wishes to protect, or could be used for authentication of the user for financial transactions that require a higher level of security. These settings may be preset by the manufacturer, may be reset by the user, may be set by a financial institution associated with the user or the device, or may be configurable by anyone with an interest in protecting the information.
• Still referring toFIG. 18A, the foldedflex sensor1802 may be folded at1805 and1807 respectively to fit about themodule folding base1804 at mounting locations loop brace1805-A and folding edge1807-A respectively, along withplacement holes1808 to aid in placing the flex about the module and holding it in place. If the embodiments of the flex sensor circuit formed or otherwise configure on a substrate according to the examples ofFIG. 12A or12B, different mounting operations may be required to accommodate these or other designs that requires a different folding or forming of the substrate. Thesensor1802 may includeprocessor1810 as described in similar embodiments above. Mountingboard1806 includes aswitch1813 mounted aboutswitch opening1811 to accommodateplunger1812, and may also have aprocessor opening1814 configured to accommodateprocessor1810.
• Referring toFIG. 18B, another expanded view of the sensor ofFIG. 18A is shown from another angle, where one side of theflex sensor1802 shows more clearly theopenings1808 andprocessor1810, where theopenings1808 are configured to receive placement or mountingpegs1816 for holding thesensor1802 substrate in place and then received by mountingopenings1818. The placement or mountingpegs1820 are received by mountingopenings1822.Switch base opening1824 is configured to receiveswitch base1813. In another embodiment, the opening for theplunger1812 and thebase1813 may be a single sized opening that will accept the entire switch, or the switch may have base with the same diameter as the plunger so that a single cylindrical or rectangular or other shaped opening may be sufficient to accommodate the switch.
• FIG. 18C shows a side cut away view of the assembled sensor assembly with thesensor substrate1802 mounted onmodule folding base1804 and mounted onbase1806, and with theopenings1811 and1824 accommodating theswitch plunger1812 and switch base1813 respectively.FIG. 18D shows a close-up view of the side view ofFIG. 18C.
• FIGS. 19A-J show an alternative sensor/switch assembly where a dome switch is used for the underlying switch that is integrated in the assembly. Referring toFIG. 19A, theassembly1900 includes adome switch1912 integrated withmodule folding base1904 mounted on mountingboard1906. In this embodiment, a switch having a domed shapedplunger1912 and base1913 (FIG. 19C) is incorporated into a sensor assembly that allows the integration of the sensor operations, such as fingerprint sensor operations, together with other operations of a device.
• Referring toFIGS. 19A, B and C, the foldedflex sensor1902 may be folded at1905 and1907 respectively to fit about themodule folding base1904 at mounting locations loop brace1905-A and folding edge1907-A respectively, along with placement holes1908 (FIG. 19D) to aid in placing the flex about the module and holding it in place. If the embodiments of the flex sensor circuit formed or otherwise configure on a substrate according to the examples ofFIG. 12A or12B, different mounting operations may be required to accommodate these or other designs that requires a different folding or forming of the substrate. Thesensor1902 may includeprocessor1910 as described in similar embodiments above. Mountingboard1906 includes aswitch1913 mounted belowplunger1912, and may also have aprocessor opening1914 configured to accommodate processor1910 (FIG. 19D).
• Referring toFIGS. 19G, H and I, side views of the sensor is shown, showing theflex sensor1902 and theopenings1908 andprocessor1910, where theopenings1908 are configured to receive placement or mountingpegs1916 for holding thesensor1902 substrate in place and then received by mountingopenings1918. The placement or mountingpegs1920 are received by mountingopenings1922. Switch base opening1924 is configured to receiveswitch base1913. In another embodiment, the opening for theplunger1912 and thebase1913 may be a single sized opening that will accept the entire switch, or the switch may have base with the same diameter as the plunger so that a single cylindrical or rectangular or other shaped opening may be sufficient to accommodate the switch.
• FIGS.19E,F, and J show a normal, cutaway, and expanded cut away views of the sensor assembly mounted in a device such as a smartphone, with thesensor substrate1902 mounted onmodule folding base1904 and mounted onbase1906, and with theopenings1911 and1924 accommodating theswitch dome plunger1912 and switch base1913 respectively. Thesensor area1901 is accessed by abezel opening1909 which is incorporated into the finished case1925 of the device. When the user places a finger onsensor surface1901 they will simultaneously depressswitch plunger1912.
• FIG. 20 illustrates a perspective view of one embodiment of an embeddedswitch2000 that can provide a means to electronically connect a topconductive layer2002 through insulatinglayer2004 toconductive layer2006 upon the touch of a user on the surface of the sensor, not shown here, but it may be a layer aboveconductor2002. The three layers may be embedded within a fingerprint sensor as described above, allowing for a switch located within the double-layered fingerprint sensor, so that a user can activate a function upon touch, such as power, select, initiate, enter, or other switch functions in a device. The three layers may be placed on asurface2006 ofmodule2008, where the module is located on thesurface2010 of asubstrate2012.
• FIGS. 21A and 21BFIG. 21A shows an embodiment where a switch is formed on the same substrate as the sensor. The figures show the folded flex stack-up consisting offlex substrates2102 and2103, typically but not limited to Kapton©,metalized layers2104 and2105 are typically etched or formed copper traces and insulatinglayers2106 and2107 are typically solder mask. Insulatinglayers2106 and2107 have acutout section2110 out exposing theconductive layers2104 and2105. When no vertical pressure is applied over thegap2110conductive layers2104 and2105 are not electrically in contact with each other and are in the off position.
• FIG. 21B shows theflex top layer2103 and conductive layer2112 mechanically depressed by a contacting object such as a finger. Topconductive layer2107 can be pushed physically into electrical contact withconductive layer2106 at pressure focal point2112. This forms an embedded flex switch, which is shown in the on position.
• FIGS. 22A-26C illustrate alternative embodiments and further examples. These examples may be configured using different materials and structures, and they may further be oriented or integrated in different structures such as power buttons in mobile devices, stationary devices, computers, laptops, access devices (doorknobs, entryways, or the like). Note that in these figures and the number of plates is greatly reduced to simplify the drawings, and the size of individual drive and pickup plates are increased for simplicity as well. In practice, both drive and pickup plates may be formed at fixed or variable pitch, and unlike the drawings, the spacing between plates may be greater or less than the individual plate size.
• FIG. 22 depicts an embodiment where the drive and detection electronics are implemented on separate silicon components. This configuration minimizes interconnect between layers by directly mounting the drive die on the substrate layer for the drive lines, and directly mounting the pickup die on the substrate for the pickup plates. The rigid substrate for the drive plates also serves as a common base layer which provides interconnect for synchronizing signals between the two subsystems, as well as power and communications to the host device.
• In this particular example, the common substrate (2201) is a two layer rigid circuit board, which also provides a mechanical base for the sensor. The drive circuitry is implemented in integrated circuit die (2204) which is mounted on rigid drive substrate (2201). The die is connected to the circuit on the rigid substrate by a number of bonding pads (2206) using standard flip-chip mounting processes. A large number of drive lines (typically more than 100) are connected to the drive plates (2209), which are formed on the top side of the rigid substrate.
• A dielectric layer (2208) separates drive plates (2209) from pickup plates (2210). In this instance dielectric layer (2208) is provided by a solder mask layer applied to the drive plates (2209) and rigid substrate (2201).
• Pickup substrate assembly (2202) with pre-attached pickup circuit die (2205) is mounted on top of drive substrate (2201). The die is connected to the circuit on the flexible substrate by a number of bonding pads (2216) using standard flip-chip mounting processes. Because substrate (2202) is flexible, attach pads (2211) can mate with their corresponding pads (2212) on base substrate (2201). A cutout (2203) is provided in base substrate (2201) to accommodate pickup chip (2205) so the assembly lies flat. Attach pads (2211) provide interconnect to the mating pads (2212) on the substrate layer (2201).
• Interconnect traces (2214) formed on the top layer of base substrate (2201) provide synchronizing signals between the integrated circuits (2204) and (2205).
• Interconnect traces (2215) in the base substrate (2201) route signals to interconnect pads (2213) for power, ground, and communications interconnect to the host system.
• FIGS. 23a-fillustrates an example of an assembly stackup of the two-chip.FIG. 23ashows the rigid base (2201) with the drive plates (2209), host interconnect traces (2215) and contact pads (2213), pickup communications traces (2214) and contact pads (2212). Cutout (2203) is mad in base (2201) to accommodate the pickup IC which will be attached in a subsequent step.
• Rigid base (2201) could be fabricated from standard circuit board materials, such as FR4, in which case plates (2209), interconnect (2213 and2214) and pads (2213 and2212) would typically be formed from copper by use of circuit board etching techniques. Rigid base (2201) could also be formed from glass, in which case plates (2209), interconnect traces (2213 and2214), and pads (2212 and2213) would typically be formed from a transparent conductive material such as Indium-Tin Oxide (ITO).
• FIG. 23bshows drive electronics die (2204) attached to the traces on the assembly fromFIG. 23a. The die is shown attached to the traces via standard flip-chip mounting processes.
• FIG. 23cshows the exemplary assembly after the addition ofdielectric layer2208. This dielectric layer may be formed by a standard soldermask process, such as LPI, or by applying a piece of dielectric such as Kapton film.
• FIG. 23dshows a cutaway view of the exemplary flexible substrate (2202) with pickup plates (2210) and pickup communications pads (2211) formed on it. Flexible substrate (2202) may be formed from a Kapton film, in which case the plates (2210), traces, and pads (2211) would likely be formed of copper by standard etching techniques. Flexible substrate (2202) could also be made of a transparent material, such as polyester, with plates, traces, and pads formed from by depositing a film of a transparent conductive material such as ITO.
• FIG. 23eshows the cutaway view of the exemplary flexible substrate with the addition of pickup electronics die (2205). Electrical connections between the die and elements on the flex are made by bonding interconnect bumps (2216) on the die to contacts (2217) on the flex assembly, as shown inFIG. 22e. Interconnect bumps (2216) are typically made of gold, while contacts (2217) are features formed of the same material as the plates and traces.
• FIG. 23fshows a cutaway view of the exemplary completed assembly, as the flex assembly is mounted onto the rigid assembly. Electrical connection between the two sub-assemblies is made by mating flex assembly pads (2211) to rigid assembly pads (2212).
• FIG. 24 shows an example of steps required to assemble the exemplary embodiment shown inFIGS. 22 and 23. InStep2401 traces2214 and2215,host contact pads2213,layer interconnect pads2212, and driveplates2209 are all formed by an etching process onsubstrate2201. A number of instances of the substrate assemblies may be formed at the same time by repeating the pattern across a large panel of base material. InStep2402cutout2203 is formed insubstrate2203 by a standard circuit board routing process. This may take place at the same time that the multiple instances ofsubstrate2201 are separated by cutting out the substrate outline from the common panel. InStep2403dielectric layer2208 is created by applying a layer of material such as LPI solder mask tosubstrate2201 and driveplates2209. InStep2404pickup plates2210,interconnect pads2211, andbonding pads2217 are formed onsubstrate2202 by an etching process. InStep2405, drive electronics die2204 is mounted onto thesubstrate assembly2201 using a standard chip-on-board flip-chip bonding process. InStep2406, pickup electronics die2205 is mounted ontosubstrate assembly2202 using standard flip-clip chip-on-flex bonding process. InStep2407,flex substrate assembly2202 is mounted ontobase substrate assembly2201. InStep2408pads2211 and2212 are electrically connected using an anisotropic conducting film (ACF) attach process.
• FIG. 25 shows an embodiment where the drive and detection electronics are implemented on separate structures, such as separate silicon components for example. This configuration minimizes interconnect between layers by directly mounting the drive die on the substrate layer for the drive lines, and directly mounting the pickup die on the substrate for the pickup plates. The drive and pickup layers may be both connected to a common base layer which provides interconnect for synchronizing signals between the two subsystems, as well as power and communications to the host device. In this particular example, the common substrate (2500) may be a two layer rigid circuit board, which may also provide a mechanical base for the sensor. The drive circuitry may be implemented in integrated circuit die (2504) that is mounted on flexible drive substrate (2501). The die may be connected to the circuit on the flexible substrate by a number of bonding pads (2506) using standard flip-chip mounting processes or other mounting processes known in the art. A large number of drive lines (possibly 100 or more) may be connected to the drive plates (2509), which may or may not be formed on the same flexible substrate. Attach pads (2511) can provide interconnect to the mating pads (2512) on the substrate layer (2500). Substrate (2500) may incorporate a cutout (2513). In one example, the cutout may be configured so that when the drive substrate (2501) is attached drive electronics chip (2504) will not contact substrate (2501), and the assembly lies flat or planar. In another embodiment, a surface may not be entirely planar or even molded over an object such as a power button, the different layers my have a cutout to accommodate different structures such as the drive electronics. Pickup substrate assembly (2502) with pre-attached pickup circuit die (2505) may be mounted on top of both drive substrate (2501) and base substrate (2500). In this embodiment, drive substrate (2501) provides the dielectric layer between the drive and pickup plates, without the need for a separate dielectric layer as in previously discussed embodiments. If substrate (2502) is flexible, attach pads (2507a) may be able to mate with their corresponding pads (2507b) on base substrate (2500). A cutout (2503) may be provided in base substrate (2500) to accommodate pickup chip (2505) so the assembly lies flat. Interconnect traces (2514) formed on the top layer of base substrate (2500) may be included to provide synchronizing signals between the integrated circuits (2504) and (2505). Vias (2507c) or other openings in the base substrate (2500) may be used to route signals to the bottom layer, where lower layer traces (2509) may connect the signals to interconnect pads (2508) for possibly power, ground, communications interconnect to the host system, and other connections.
• FIG. 26 shows an exemplary embodiment where the drive and detection electronics are both provided by a single integrated circuit. In one example, substrate (2601) may be composed of a dielectric material which separates the drive (2602) and pickup (2603) plates. Substrate (2601) may be a flexible material, such as Kapton, or a thin rigid material, such as an aramid laminate layer in a FlipChip package, or it may be another material. Integrated circuit die (2604) incorporates contact pads (2611) which are mounted onto bonding pads (2605) the bottom layer of the substrate. The bonding pads provide connections from die (2604) to interconnect traces (2606), drive plates (2602), and pickup interconnect traces (2607), A number of vias (2609) electrically connect pickup interconnect (2607) on the bottom layer to pickup plates (2602), which may be located on the top layer. Interconnect traces (2606) may connect die (2604) to host connector pads (2608). A dielectric layer (2610) may be formed atop pickup plated (2603) to prevent direct contact of the finger with the pickup plates. The dielectric layer (2610) may be formed from a number of materials, including but not limited to an LPI soldermask material, an ink, or a top kapton coversheet. In another embodiment, a surface may not be entirely planar or even molded over an object such as a power button,
• FIGS. 27-29 illustrate a method for integrating a folded flex fingerprint sensor directly onto a touch-screen device. An unfolded Chip on Flex (COF) substrate is shown inFIG. 28 and is folded back onto itself as is shown inFIG. 27 callouts (2701-2705). Host interface tab (2705) connects the sensor to the host using a connector that accepts the etched flex tab directly or is attached to the host circuit board using an industry standard conductive adhesive referred to as ACF.FIG. 28 shows a COF layout where the substrate is folder end-over-end but could also be reconfigured to fold on another axis such as side-by-side.
• FIGS. 30-32 illustrate a fingerprint sensor integrated onto the same substrate layers as a conventional touch-screen.
• FIG. 51 illustrates a method for integrating a folded flex fingerprint sensor with a touchscreen device that utilizes a protective cover layer. Display substrate (5106) is a conventional display assembly, which may optionally incorporate a touchscreen. Flexible substrate (5120) has driver receiver chip (5104) mounted on it, and provides a substrate for both the drive and pickup lines of the fingerprint sensor. Substrate (5120) is then folded and mounted on top of display substrate (5106). Host interface connector (5205) provides data and control interconnect between the fingerprint sensor assembly and the host device. An optically transparent dielectric spacer (5130) is placed on top of the display substrate. This dielectric spacer is the same thickness as the stacked fingerprint sensor substrate (5112). A cutout (5108) in the dielectric spacer allows the fingerprint sensor sensing area (5112) to sit flush with the top of dielectric spacer. Top layer (5107) may be made of a protective material such as Corning Gorilla Glass or a protective polymer film. This top layer has a cutout (5109) which allows direct finger contact with finger sensing area (5112).
• FIG. 52 illustrates a method for integrating a fingerprint sensor on the same substrate layers as a touchscreen. Display substrate (5206) contains a standard LDC module. The lower layer plates (5211) of the fingerprint sensor are formed or etched on top of the display substrate, from a conductive material such as Indium Tin Oxide (ITO). Flexible substrate (5520) has driver receiver chip (5204) mounted on it. Connections from the driver receiver chip (5502) are made to the lower layer plates (5211) through a lower layer edge connector (5210). This connector may be attached through anisotropic conductive film (ACF) or other means. An optically transparent dielectric spacer (5230) is placed on top of the display substrate. The spacer has a cutout (5209) to accommodate lower edge connector (5510) and upper edge connector (5221). Top layer (5210) is fabricated from a thin glass or transparent polymer film. This layer (5510) has upper layer sensor plates (5212) formed or etched on its lower surface made of a conductive material such as Indium Tin Oxide (ITO).Flexible substrate5520 connects signals from driver receiver chip (5204) through upper edge connector (5221), again through ACF or other means.
• FIG. 53 illustrates a configuration where the fingerprint sensor and a touchscreen are implemented on common substrate layers utilizing a common controller chip. Driver receiver chip (5304) is mounted to flexible substrate (5320) which provides interconnect between the chip and the host through a host interface connector (5305). Display substrate (5306) is the upper surface of a display module. Both the lower touchscreen plates (5330) and the lower layer fingerprint sensor plates (5311) are formed or etched on top of display substrate (5306). These plates mat be etched or formed from a transparent material such as Indium Tin Oxide (ITO) or other suitable conductive material. Upper fingerprint sensor plates (5312) and upper touchscreen plates (5331) are both etched or formed on the lower side of top layer (5307). A dielectric layer (5330) separates the lower sets of plates for the two sensors from the upper sets of plates. Flexible substrate provides signal interconnect between driver/receiver chip (5304) to the lower sets of plates through lower edge connector (5310) and interconnect to the upper plate sets throughupper edge connector5321. These edge connectors may be electrically connected through an Anisotropic Conductive Film (ACF) bond or other suitable means.
• FIGS. 33 and 34 illustrate a novel “Dual Grid” touch-screen.
• User motion tracking is required in touchscreen devices for a number of functions, including icon selection and movement, control selection, gesture recognition, text selection, and so on. Many motion tracking functions only require coarse position determination, but may be done at high speed. This is especially true of gesture recognition. Other functions may require much finer position determination, but these generally are performed at low speeds of motion to allow the user more precise control. Such functions include text selection and drawing tasks.
• While it may be difficult to precisely track motion at high speeds due to the high number of positions that need to be sampled at high speed, in practice high speed and high precision are not needed simultaneously.
• Given the relative large size of fingers compared to the size of pixels on a typical touchscreen, it is difficult to accurately determine the precise position of a finger. In practice, users actually do not rely on exact finger placement determination to perform precise tasks. Instead, they place their finger on the touchscreen at the approximate location of interest, and then rely on visual feedback from the screen to complete fine positioning tasks.
• The important characteristics for a touchscreen display input, then, are good high speed coarse absolute position determination, and highly responsive high resolution low-speed relative motion determination.
• This invention addresses the need for high speed coarse absolute positioning and responsive high resolution slow speed motion tracking by providing a dual resolution sensing system. A primary grid is formed at a spacing equal to that used by commercially available touch screens with a spacing of 5-10 per inch while a secondary grid is formed about the primary lines with a much finer resolution equal to that of a commercial fingerprint sensor at 500 lines per inch. The result is a sensor that is capable of detecting macro finger movements using the primary grid as well as small incremental movements using the secondary grid which tracks the movements of fingerprint ridge and valley features.
• FIG. 33 shows one embodiment of this dual grid concept in a touchscreen application where the cover layer has been omitted. The touchscreen consists of a matrix of passive capacitance sensing junctions formed at the crossover points of each row an column arranged in a pattern to facilitate both coarse absolute position detection and high resolution relative motion tracking. The illustration shows a simplified embodiment where the sense and drive lines are configured to provide a regularly space series of 3×3 pixel high resolution patches, where the high resolution pixels are spaced in a manner to detected localized features of a fingerprint. These pixels within the cluster would typically be spaced approximately 50 to 100 microns apart. The clusters of pixels are spaced in a manner to provide several contact points within a finger, leading to a typical cluster spacing of 1 to 3 millimeters apart. Active circuitry is located on the periphery of the array outside the sensing area and is used to make the individual crossovers impedance sensitive to a proximally located object as well as scan the entire array
• FIG. 34 is an exploded view of the embodiment shown inFIG. 33, showing the stack up of the substrate, with the drive lines atop that, and the chip with the processing electronics mounted to routing lines which feed the drive plates, as well as feed lines with connect to the sense lines on the upper layers and host interconnect. A dielectric layer separated the drive and pickup lines. The dielectric has cutouts to allow the interconnect pads to feed the pickup signals back to the processing electronics. A thin protective layer, typically of a polymer film or very thin glass is mounted on top of the sense plates.
• FIGS. 35-37 illustrate a fully integrated Dual Grid touch-screen and fingerprint sensor, which advantageously share a common drive and sense circuit. In this embodiment, a dedicated area of high density pixels if provided to create a fingerprint sense area for user authentication or other similar purposes, adjacent to a dual-grid touchscreen array configured as inFIG. 33.FIGS. 36 and 37 are exploded views of the embodiment shown inFIG. 35.
• FIGS. 38-40 illustrated a fully integrated display with integral touch-screen and fingerprint sensing over the entire display area. In this embodiment, the drive plates are formed below the OLED emissive pixels, while the pickup plates are formed of transparent conductors, such as ITO, in a layer above the OLED emissive layer.
• FIGS. 41-46 illustrate how the dual grid finger motion tracking process operates.
• FIGS. 41 and 42 show the location of a finger on the dual grid sensor before and after a coarse position change. Coarse position finding and fast motion tracking is performed by activating all the pixels in a cluster simultaneously and taking a single measurement to determine if the cluster is covered by a finger.FIG. 43 is a flowchart for this coarse scan process.FIG. 44 illustrates the computation of the centroid locations for the finger in the two samples collected before and after the move. If the coarse coverage changes between two scans, then the finger is moving quickly, and fine position tracking is not needed. In this case the device will report a new absolute position for each sensed finger to the host system.
• If the coarse finger position has not changed, then it is possible that the user is performing a fine positioning task.FIG. 45 illustrates a sequence of images taken at a single high resolution cluster as a finger moves over it. It can be seen that a coarse centroid measurement would not detect the motion of the finger, but examination of the ridge pattern at a fine pixel resolution can detect this relative motion.FIG. 46 shows the local images collected at three different high resolution clusters before and after a very fine motion. For this example, we examine a 4×4 cluster of high resolution pixels at each location on the coarse grid. The advantage provided by taking samples at multiple locations is demonstrated by examining the results from each cell individually. Assuming sufficient sample rate to capture any motion of one pixel or less, there are nine possible relative locations that must be examined when comparing two sequential samples to determine the motion of the finger between the samples. For each possible adjacent move, we compute a match score by shifting the image to the adjacent location, and then counting pixels which match in the overlap region. The number of pixels matched is divided by the total number of pixels that in the overlap region between the shifted and unshifted images to produce a relative match score. A score of 1 indicates a perfect match. When we apply this method tocell #1 in the example (FIG. 47) and cell #2 (FIG. 48) a single location receives a strong score relative to the other possibilities. When we apply the method to cell #3 (FIG. 49) however, there are three equally high scoring possible final positions. This outcome for a localized area can be quite common when tracking regular patterns such as fingerprints. The example inFIG. 49 demonstrates that a ridge tracking system can be locally insensitive to movement that is parallel to the local ridge orientation. In order to reliably track motion of fingerprints, therefore, it is strongly advantageous to sample the finger at several different locations. The dual grid configuration enables this by dispersing the pixel clusters widely about the finger, so that it samples the finger at locations with a variety of local orientations, without requiring the resources to cover the entire finger area at a high resolution.FIG. 50 shows the combination of results from the three measurement cells to produce a single robust score to determine if the pattern has remained stationary or moved. If motion is detected, the previously computed position (initially from the coarse position) is adjusted by the detected motion, and the updated position is transmitted to the host.
• It should be noted that many operating modes of a device may only require coarse location information from the touch sensor. In these cases the system can advantageously omit the fine motion tracking operations of the position sensor in order to save power.
• While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad embodiment, and that this embodiment is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Hence, alternative arrangements and/or quantities of, connections of various sorts, arrangements and quantities of transistors to form circuits, and other features and functions can occur without departing from the spirit and scope of the embodiment. Similarly, components not explicitly mentioned in this specification can be included in various embodiments of this embodiment without departing from the spirit and scope of the embodiment. Also, different process steps and integrated circuit manufacture operations described as being performed to make certain components in various embodiments of this embodiment can, as would be apparent to one skilled in the art, be readily performed in whole or in part to make different components or in different configurations of components not explicitly mentioned in this specification without departing from the spirit and scope of the embodiment. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
• While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad embodiment, and that this embodiment is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
• Again, the embodiment has application in many areas, particularly in biometric sensors. Fingerprint sensors, for example, and other biometric sensors are gaining increasing acceptance for use in a wide variety of applications for security and convenience reasons. Devices, systems and methods configured according to the embodiment will have improved security of the biometric verification process without increasing the cost of the system. Furthermore, the embodiment may extend to devices, systems and methods that would benefit from validation of components. As discussed above, the embodiment includes the ability for the host and sensor to include any combination or subset of the above components, which may be arranged and configured in the manner most appropriate for the system's intended application. Those skilled in the art will understand that different combinations and permutations of the components described herein are possible within the spirit and scope of the embodiment, which is defined by the appended Claims, their equivalents, and also Claims presented in related applications in the future and their equivalents.
• The embodiment may also involve a number of functions to be performed by a computer processor, such as a microprocessor. The microprocessor may be a specialized or dedicated microprocessor that is configured to perform particular tasks according to the embodiment, by executing machine-readable software code that defines the particular tasks embodied by the embodiment. The microprocessor may also be configured to operate and communicate with other devices such as direct memory access modules, memory storage devices, Internet related hardware, and other devices that relate to the transmission of data in accordance with the embodiment. The software code may be configured using software formats such as Java, C++, XML (Extensible Mark-up Language) and other languages that may be used to define functions that relate to operations of devices required to carry out the functional operations related to the embodiment. The code may be written in different forms and styles, many of which are known to those skilled in the art. Different code formats, code configurations, styles and forms of software programs and other means of configuring code to define the operations of a microprocessor in accordance with the embodiment will not depart from the spirit and scope of the embodiment.
• Within the different types of devices, such as laptop or desktop computers, hand held devices with processors or processing logic, and also possibly computer servers or other devices that utilize the embodiment, there exist different types of memory devices for storing and retrieving information while performing functions according to the embodiment. Cache memory devices are often included in such computers for use by the central processing unit as a convenient storage location for information that is frequently stored and retrieved. Similarly, a persistent memory is also frequently used with such computers for maintaining information that is frequently retrieved by the central processing unit, but that is not often altered within the persistent memory, unlike the cache memory. Main memory is also usually included for storing and retrieving larger amounts of information such as data and software applications configured to perform functions according to the embodiment when executed by the central processing unit. These memory devices may be configured as random access memory (RAM), static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, and other memory storage devices that may be accessed by a central processing unit to store and retrieve information. During data storage and retrieval operations, these memory devices are transformed to have different states, such as different electrical charges, different magnetic polarity, and the like. Thus, systems and methods configured according to the embodiment as described herein enable the physical transformation of these memory devices. Accordingly, the embodiment as described herein is directed to novel and useful systems and methods that, in one or more embodiments, are able to transform the memory device into a different state. The embodiment is not limited to any particular type of memory device, or any commonly used protocol for storing and retrieving information to and from these memory devices, respectively.
• The term “machine-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that causes the machine to perform any one or more of the methodologies of the present embodiment. The machine-readable medium includes any mechanism that provides (i.e., stores and/or transmits) information in a form readable by a machine (e.g., a computer, PDA, cellular telephone, etc.). For example, a machine-readable medium includes memory (such as described above); magnetic disk storage media; optical storage media; flash memory devices; biological electrical, mechanical systems; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.). The device or machine-readable medium may include a micro-electromechanical system (MEMS), nanotechnology devices, organic, holographic, solid-state memory device and/or a rotating magnetic or optical disk. The device or machine-readable medium may be distributed when partitions of instructions have been separated into different machines, such as across an interconnection of computers or as different virtual machines.
• While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad embodiment, and that this embodiment not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
• Reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments. The various appearances “an embodiment,” “one embodiment,” or “some embodiments” are not necessarily all referring to the same embodiments. If the specification states a component, feature, structure, or characteristic “may”, “might”, or “could” be included, that particular component, feature, structure, or characteristic is not required to be included. If the specification or Claim refers to “a” or “an” element, that does not mean there is only one of the element. If the specification or Claims refer to “an additional” element, that does not preclude there being more than one of the additional element.
• The methods, systems and devices include improved security operations and configurations with a novel approach to biometric systems. Such systems would greatly benefit from increased security features, particularly in financial transactions. Although this embodiment is described and illustrated in the context of devices, systems and related methods of validating biometric devices such as fingerprint sensors, the scope of the embodiment extends to other applications where such functions are useful. Furthermore, while the foregoing description has been with reference to particular embodiments of the embodiment, it will be appreciated that these are only illustrative of the embodiment and that changes may be made to those embodiments without departing from the principles of the embodiment, the scope of which is defined by the appended Claims and their equivalents.

Claims (1)

1. An impedance sensor, comprising: a plurality of substantially parallel drive lines configured to transmit a signal to a proximally located object; and

a plurality of substantially parallel pickup lines configured to receive a resultant signal and oriented substantially perpendicular to the drive lines and physically separated from the pickup lines on a different layer by a substantially incompressible dielectric located between the drive lines and pickup lines to form a two dimensional array of intrinsic electrode pairs that are impedance sensitive to detect ridge and valley features of a proximally located finger when driven by circuitry located outside the sensing area which is connected to each drive and pickup line of the array in order to activate one or more junctions formed at individual dive and pickup line crossovers where the circuitry compromises a driver or drive multiplexor connected to each drive line, and buffer, switch or input multiplexor attached to each pickup line, and at least one differencing amplifier configured to receive it's inputs from the input buffers or input multiplexor where a signal proportional to impedance about each drive line and pickup crossover location can be differenced with a signal proportional to impedance about another drive line and pickup crossover location to differentiate impedance values in order to determine relative object proximity.

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