The present application claims priority from U.S. provisional application entitled "Capacitive Sensor Packaging" filed on day 5, month 18, 2012, U.S. provisional application entitled "Capacitive Sensor Packaging" filed on day 6, month 29, 2012, U.S. provisional application entitled "Capacitive Sensor Packaging" filed on day 61, month 666,607, and U.S. non-provisional application entitled "Capacitive Sensor Packaging" filed on day 3, month 15, 2013, U.S. 13/842,920 filed on day 3, month 15, 2013, all of which are incorporated herein by reference.
Detailed Description
Embodiments described herein generally disclose various structures and methods for packaging sensors, such as capacitive sensors. Embodiments may disclose various layouts of sensors, structures surrounding sensors, connection structures (electrical, physical, or both) of sensors, methods and structures for enhancing sensor imaging, methods and structures for securing sensors, methods and structures for guiding a finger into place over a sensor when the sensor itself is not visible to a user, and so forth.
Embodiments described herein generally discuss the placement of sensors within recesses in a frame, such as a cover glass, sapphire elements, or lenses. In other embodiments, the sensor may be embedded in a structure or housing (such as a plastic structure) of the electronic device or other suitable device. As another option, the frame may include an opening in which the sensor is placed, and over-molded (over-mold) plastic or another material over the sensor. In such embodiments, the overmolded or extruded material may replace any of the lenses mentioned herein.
Fig. 1 shows a schematic diagram of a fingerprint recognition sensor 102 included in a portion of a device 100.
An exploded view of a portion of the device 100 shows the assembled components positioned to form the fingerprint recognition sensor 102 circuitry and to position the sensor 102 circuitry under the button. Although the present application describes specific components with specific buttons and specific sensor 102 circuitry, there is no particular requirement for any such limitation in the context of the present invention. For example, the button may be positioned slightly off center of the fingerprint sensor 102 circuitry, with the effect of: the button is still active for its purpose, while the sensor 102 circuitry still operates with the user's finger positioned nearby. Upon reading this application, those skilled in the art will recognize that many other and further example components will be within the scope and spirit of the invention, will be feasible, and will not require further invention or undue experimentation.
A Cover Glass (CG) frame 106 is disposed to couple to a cover glass 107 of a smartphone, touchpad, portion of a mobile computing device, input mechanism, key of a keyboard, portion of an input or output device housing, panel or body of a vehicle, appliance, etc., a touch screen or other device 100, and is disposed to couple to a frame of the device 100. (in many embodiments, device 100 is some form of mobile computing device). When the assembly is built, the cover glass frame 106 includes button holes 108 positioned to locate the buttons, and one or more screw clamps 110 positioned to match the external screw locations and positioned to receive horizontal screws for securing the cover glass frame 106 to the substrate (as described further below).
A button hole 108 in the cover glass frame 106 is positioned to hold the button 104 (which may constitute a top member of the button, as described below), as shown. The button 104 is positioned to fit into the button aperture 108. The button 104 includes a lens 112, at least a portion of the lens 112 helping to form a concave shape with the effect of directing a user's finger onto the button 104. The concave shape may likewise be formed at least in part by a chamfer in the base ring. In one embodiment, the button 104 may be made of one or more of the following materials or equivalents thereof: alumina, glass or chemically treated glass, sapphire, chemically treated compounds having at least some of its characteristics, or another compound having similar properties. The lens 112 is positioned within the base ring 114. In one embodiment, the ground ring 114 may be used to shield electromagnetic effects, with the effect of providing capacitive isolation or other electromagnetic isolation. The base ring 114 is shown in the figure as having a cylindrical edge that holds the lens 112 and a substrate that can be aligned or oriented within the apparatus 100 when the assembly is built.
The button 104 is positioned above and coupled to the fingerprint sensor 102 circuitry. In one embodiment, the fingerprint recognition sensor 102 circuit is relatively rectangular with the effect of being able to sense a two-dimensional (2D) image of the user's fingerprint. However, in alternative embodiments, the fingerprint recognition sensor 102 circuitry may be placed in another shape, such as a circular or hexagonal shape, which may also be adapted to receive 2D fingerprint image information.
As described below, the fingerprint sensor 102 includes a silicon wafer 308 on which fingerprint recognition circuitry is mounted, the fingerprint recognition circuitry being electrically coupled to other elements of the device 100. The fingerprint recognition circuit is arranged in a position relatively close to the finger of the user, and has the following effects: the fingerprint identification circuit may collect fingerprint image information in response to measurements of capacitance at each point on the user's finger in response to ridges and valleys of the user's finger. The electrical coupling between the fingerprint recognition circuit and the other elements of the device 100 will be described further below.
As described above, although the present application primarily describes components in which the fingerprint sensor 102 circuitry is disposed so as to be capacitively coupled to the epidermis of a user's finger, there is no particular requirement for any such limitation in the context of the present invention. For example, the fingerprint recognition sensor 102 circuitry may be capacitively coupled, or otherwise electromagnetically coupled, to the subcutaneous portion of the user's finger. Further, the fingerprint recognition sensor 102 circuitry may work in conjunction or combination with elements that perform optical, infrared, or other sensing of the user's fingerprint, which may themselves be coupled to the epidermis of the user's finger, the subcutaneous portion of the user's finger, or some other feature representative of the user's fingerprint.
In one embodiment, the fingerprint recognition sensor 102 comprises an integrated circuit including one or more capacitive plates arranged in a two-dimensional (2D) array, each such capacitive plate being positioned to collect at least some fingerprint image information in response to ridges and valleys of a user's finger at one or more pixels in its array. This has the effect of: the sets of capacitive plates collectively receive the fingerprint image information for the 2D array as each capacitive plate collects one or more pixels of fingerprint image information in its array. For example, the 2D array of fingerprint image information may be used to determine substantive features of the user's fingerprint, which may be used to register the user's fingerprint in a database for later use, or may be compared later to registered fingerprint image information to identify the user's fingerprint and possibly authenticate the user in response to the fingerprint image information.
The fingerprint recognition circuit is positioned over and coupled to the flexible member 116, the flexible member 116 being positioned to receive any force exerted by the user's finger on the button 104 and transmit that force to the tactile dome 118 (as described further below). The flexible element 116 is also arranged to receive electrical signals (such as representing fingerprint image information) from the fingerprint sensor 102 and to transmit these electrical signals from the fingerprint sensor 102 to the processor.
The flexible element 116 is disposed over and coupled to the tactile dome 118, and the tactile dome 118 receives any force exerted by the user's finger on the button 104, transmits an electrical signal to the button circuit indicative of the user's finger depressing the button 104, and optionally provides tactile feedback to the user's finger to indicate that the button 104 is depressed.
As further described herein, placing the tactile dome 118 in a column with the fingerprint sensor 102 circuitry has the effect of: when a user positions their finger on the button 104, the user's fingerprint may be identified. For example, a user may position their finger on the button 104 as part of a power-on or start-up sequence of the device 100, at which point the device 100 may concurrently (a) operate in the power-on or start-up sequence, and (B) receive fingerprint image recognition about the user's finger, such as for enrollment or authentication of the user.
The tactile dome 118 is positioned over and coupled to a switch pad 120, the switch pad 120 gripping the tactile dome 118 and being held in place by a button support plate 122. The button support plate 122 is coupled to the base plate and is held in place by one or more vertical screws. As described above, the base plate is held in place with the cover glass frame 106 by one or more horizontal screws. In one embodiment, the substrate also has other elements, such as holes for connecting other device elements, such as a microphone jack or other elements.
After reading this application, those skilled in the art will recognize that this particular arrangement of components as described above is not absolutely required, that many variations thereof will be feasible, will be within the scope and spirit of the invention, and that further invention or undue experimentation will not be required.
In one particular embodiment, positioning the fingerprint recognition sensor 102 circuitry in relative vertical alignment with the tactile dome 118 may combine the functions of the device 100 to receive fingerprint image information and button-press information in parallel.
Figure 2 shows a schematic view of a button assembly 200 showing a laminate layer as partially described with reference to figure 1.
The button assembly 200 as described with reference to fig. 1 includes the lens 112 with a concave shape formed at least partially through a portion of the lens 112 to direct a user's finger toward the button 104, as described above. As described above, the lens 112 is disposed within the base ring 114, the base ring 114 optionally including a button flange 115 that surrounds the sides of the button 104. In one embodiment, the button flange 115 may also result in a portion of the concave shape being formed at least partially by the button flange 115, again in order to direct a user's finger toward the button 104.
In one embodiment, an ink assembly, comprising 2-5 layers of ink 202, is disposed beneath the lens 112. In one embodiment, the ink assembly may be printed on the lens 112, vapor deposited thereon, or applied thereto by another technique. This has the effect of: the otherwise translucent button 104 may be made opaque so that the elements of the fingerprint sensor are not immediately visible to the user. The lens 112 is coupled at its edges to the ground ring 114 using a heat activated membrane and perimeter seal 204.
As described above, the fingerprint recognition sensor circuit is disposed below the lens 112. The liquid laminate layer 206 is positioned under the lens 112 to which the fingerprint sensor circuit is coupled. The fingerprint recognition sensor circuit includes a silicon package 208 including a silicon circuit layer, solder (as shown in further detail below), and underfill 210 (as shown in further detail below).
As further described herein, the fingerprint recognition sensor circuit exhibits capacitive coupling with the ridges and valleys of the user's finger, such as at the epidermis of the user's finger, with the effect of: the fingerprint recognition sensor receives 2D fingerprint image information from which the device can determine whether the fingerprint is that of a user or that of some other person. As noted above, the fingerprint recognition sensor circuit may also or instead exhibit capacitive coupling with another portion of the user's finger, such as its subcutaneous layer, or with another feature of the user's finger.
As described above, the fingerprint identification circuit is disposed over and coupled to the flexible element 116. The flexible element 116 is coupled to the stiffener element 212. The edge of the base ring 114 that holds the lens 112 is coupled to the stiffener element 212 using a liquid adhesive 214. The stiffener element is positioned over and coupled to a high strength bonding strip, such as VHB strip 216, which in turn is positioned over and coupled to flexible element 117 and tactile switch (push button switch) 218.
After reading this application, those skilled in the art will recognize that the assembly as described above provides a fingerprint recognition sensor with a relatively small distance from the user's finger, as well as a relatively small stack height, while at the same time allowing the user to access buttons or other elements of a device using the fingerprint recognition sensor without further invention or undue experimentation.
In a first particular embodiment, the assembly as described above comprises a concave shape, with the effect that: the user's finger is directed to a location where the fingerprint recognition sensor may have excellent results. The concave shape is formed at least in part by a portion of the shape of the button 104, including the lens 112, and (optionally) by a portion of the shape of the base ring 114. As described above, the fingerprint recognition sensor is disposed under the button 104 with the effect that when the user's finger is guided to the concave shape, the user's finger is well positioned for fingerprint recognition.
In a second particular embodiment, the assembly as described above comprises tactile buttons at the bottom of the stack of elements, with the effect of: the fingerprint recognition sensor may have excellent effects in response to being positioned relatively closer to the epidermis of the user's finger, while the user may use the button with tactile feedback effects from pressing or releasing the button. As described herein, positioning the button in substantially perpendicular superimposition with the fingerprint recognition sensor circuit can (a) allow the device to accept a push button operation from a user and simultaneously perform fingerprint recognition on the user's finger pressing the button 104, and (B) allow the device to exhibit relatively excellent capacitive coupling between the fingerprint recognition sensor circuit and the user's finger without positioning the button or fingerprint recognition sensor circuit too far from the user's finger.
Fig. 3 shows another schematic view of a button assembly 200 showing a fingerprint recognition sensor as partially described with reference to fig. 1.
A set of ridges and valleys 302 of the user's fingerprint are shown disposed above the button assembly 200, the ridges and valleys 302 having the property that the ridges of the user's fingerprint are relatively closer to the outer surface of the button 104, while the valleys of the user's fingerprint are relatively further from the outer surface of the button 104. As described above, the fingerprint recognition sensor circuit exhibits capacitive coupling with the ridges and valleys 302 of the user's finger, such as at the epidermis of the user's finger 304, the fingerprint recognition sensor circuit being positioned relatively close to the epidermis of the user's finger 304.
Fig. 3 similarly illustrates the button assembly 200 as described with reference to fig. 1, including a concave shape 306 formed at least in part by a portion of the lens 112 to direct a user's finger 304 toward the button 104, and including the structure of the base ring 114, and optionally, a portion of the concave shape 306 to again direct the user's finger 304 toward the button 104. FIG. 3 similarly illustrates an ink assembly disposed below and coupled to lens 112, with the effect of: the otherwise translucent button 104 is made opaque so that the elements of the fingerprint sensor are not immediately visible to the user. Figure 3 similarly shows a fingerprint recognition sensor positioned below the lens 112 and coupled to the lens 112.
The fingerprint recognition sensor comprises a silicon wafer 308 on which is printed a circuit 310 for measuring the capacitance between one or more capacitive plates on the one hand and a user's fingerprint (such as ridges and valleys 302 on the skin of a user's finger 304) on the other hand, with the effect of providing fingerprint image information about the ridges and valleys 302 of the user's finger 304. The base ring 114 provides electrical isolation with the effect of: the measured capacitance is between the user's finger 304 and the fingerprint sensor, and not between any other object and the fingerprint sensor. The base ring 114 may be formed adjacent to the lens 112 of the button 104. As one example, the base ring 114 can be included on, or formed on, one side of a structure 312 (such as a button flange 115) for supporting or integrating the base ring 114.
In one embodiment, silicon wafer 308 includes one or more through-silicon vias (TSVs) positioned to provide electrical connections between, on the one hand, circuitry 310 positioned on the top of silicon wafer 308 and, on the other hand, circuitry positioned below or to the sides of silicon wafer 308. This has the effect of: bond wires 314 do not have to be bowed from the surface of silicon wafer 308 to connect circuit 310 from silicon wafer 308 elsewhere.
The use of bond wires 314 that arch upward from the surface of silicon wafer 308 would otherwise occupy the vertical space between silicon wafer 308 and the object immediately above silicon wafer 308. Using through-silicon vias to connect the circuitry 310 disposed on the top of the silicon wafer 308 to another location (such as circuitry on the bottom of the silicon wafer 308, or circuitry on the side of the silicon wafer 308) has the effect of: the fingerprint sensor requires a small amount of vertical space, with the effect of: the fingerprint recognition sensor may be placed closer to the user's finger 304 and may have relatively better resolution and effectiveness.
In one embodiment (which may be used in parallel with embodiments having through-silicon vias), the silicon wafer 308 includes one or more edge trenches 316, i.e., trenches etched through or excavated through the silicon wafer 308 from, on the one hand, the circuitry 310 disposed on the top of the silicon wafer 308, to, on the other hand, the circuitry disposed on the sides of the silicon wafer 308. This also has the effect of: bond wires 314 do not have to be bowed from the surface of silicon wafer 308 to connect circuit 310 from silicon wafer 308 elsewhere. As described above, reducing the necessity of arching bond wires 314 from the surface of silicon wafer 308 reduces the amount of vertical space required between user's finger 304 and the fingerprint recognition sensor.
In one embodiment (again, possibly used in parallel with other embodiments described above), the silicon wafer 308 is constructed by: encapsulated in a plastic resin (or alternatively in a ceramic), followed by removal of the top portion of the plastic resin to the extent that: the circuitry of the circuit 310, which is disposed on top of the silicon wafer 308, is almost exposed, or alternatively, has just been exposed. This has the effect of: the silicon wafer 308 is fabricated with as little vertical space as reasonably possible because the amount of additional vertical space used for wafer packaging of the finger recognition sensor is relatively limited.
In one embodiment, silicon wafer 308 is constructed to include a set of solder balls 318, the set of solder balls 318 being randomly (or pseudo-randomly) positioned to couple to wafer 308. Optionally, the solder balls 318 need not include actual solder, but may include other conductive materials, such as gold, other deformable metals, or other conductive or semiconductor materials that can deform in response to physical processes such as pressure. The solder balls 318 may be encapsulated in a plastic resin, followed by compression of the layers of the solder balls 318 and plastic resin to the extent that the solder balls 318 and plastic resin are compressed. This has the effect of: the plastic resin is substantially pressed away from the solder balls 318 and the solder balls 318 are positioned to conduct electrical signals between the silicon wafer 308 and other components such as the buttons 104. This also has the effect that, since the solder balls 318, or other material, are dispersed horizontally in their layers: their layers operate to conduct from a layer above to a layer below without conducting electricity across or at any level within their layers.
In case the silicon wafer 308 is coupled to the button 104, this has the effect of: the conductivity between the capacitive plates of the silicon wafer 308 and the surface of the button 104 is enhanced. This in turn has the effect of: as the distance between the skin of the user's finger 304 and the silicon wafer 308 is shortened, the capacitance between the user's finger 304 and the silicon wafer 308 increases. This in turn may enable the fingerprint identification sensor to achieve excellent capacitive sensing of the fingerprint image information of the user.
Fig. 4A and 4B illustrate another schematic view of a button assembly 200 showing a fingerprint recognition sensor as partially described with reference to fig. 1.
Fig. 4A and 4B show a side cut-away view of the button 104 and fingerprint sensor (fig. 4A), and a top view of the fingerprint sensor silicon wafer 308 (fig. 4B).
As described above, the button 104 includes a lens 112 (which may be constructed from various materials such as glass, alumina, plastic, resin, etc.) having a concave shape 306 to direct a user's finger onto the button 104. As described above, the lens 112 is disposed within a base ring 114 (e.g., constructed of anodized aluminum such as SOS aluminum). As described above, the base ring 114 provides electrical insulation with the effect of: the measured capacitance is between the user's finger and the fingerprint sensor and not between any other object and the fingerprint sensor.
The base ring 114 is shown in the figure as having a cylindrical edge that holds the lens 112, and a base plate that can be aligned or oriented within the apparatus when the assembly is built. In an alternative embodiment, instead of the ground ring 114, one or more capacitive plates may be placed on one side of the user's finger, with the effect of providing capacitive isolation so that any capacitive coupling that occurs is only between the user's finger and the fingerprint recognition sensor. For example, the capacitive plates may be positioned around the area where the fingerprint sensor is located, with the effect of surrounding the fingerprint sensor with capacitive isolation. Similarly, the capacitive plates may be positioned near or within the housing of the device (such as the housing of a smartphone or other device), also with the effect of surrounding the fingerprint recognition sensor with capacitive isolation.
Disposed below and coupled to the lens 112 is an ink layer 202, as described above.
In one embodiment, the fingerprint recognition sensor includes a set of capacitive plates arranged in a 2D array, including pixels having a density of approximately 300 dots per inch (dpi) or more or less (or optionally, a greater or lesser density), with the effect of providing 2D fingerprint image information about a user's finger. In one embodiment, the 2D fingerprint image includes a set of gray scale values, each pixel having one or more of such values, with the effect of providing a set of 2D gray scale values for transmission to the processor for fingerprinting.
As described above, in one embodiment, the silicon wafer 308 assembly is constructed to include a set of solder balls 318, the set of solder balls 318 being randomly (or pseudo-randomly) positioned to couple to the wafer 308 and encapsulated in a layer of compressed plastic resin. Even with random or pseudo-random placement, the set of solder balls 318 provides a substantially uniform measure of electrical connectivity between the silicon wafer 308 and other circuitry, such as the flex elements 116 or 117, or both, described below.
As shown, solder balls 318, or other materials, may be placed at one or more of: (A) layers above the silicon wafer 308, with the effect of: the silicon wafer 308 is at least partially electrically coupled to the above layer, (B) the layer below the silicon wafer 308, with the effect of: the silicon wafer 308 is at least partially electrically coupled to the underlying layer.
As described above, the flexible element 116 or 177 is coupled to the silicon wafer 308 with the effect of: when the button 104 is pressed, the silicon wafer 308 can be pressed without substantial risk to the structure of the wafer 308. The figure shows a set of connectors between the flexible element 116 or 117 and the silicon wafer 308, with the effect of: when the button 104 is depressed, the flexible element 116 or 117 flexes, causing the wafer 308 to be depressed without structural strain.
As described above, the support plate 122 is positioned below and coupled with the wafer 308. The dome is positioned below and coupled to the support plate 122 to provide a tactile response to the user when the button 104 is pressed.
Fig. 5 shows a schematic view of the relationship between the button assembly 200 and the fingerprint recognition sensor 102.
In one embodiment, the button 104 comprises an element comprising a material as described above, such as treated glass or sapphire, at least partially forming a notch in the shape of a depression to direct the user's finger to a central location where the fingerprint recognition sensor circuit can be optimally used. For example, as shown, the portion of the device 100 that is relatively closer to the user may include a relatively larger button element (shown as a horizontally oriented rectangle) that covers a relatively concave shaped indentation (shown as a circle of dashed lines) that covers the fingerprint recognition sensor circuit (shown as a square approximately the same size as the circle of dashed lines). This has the effect of: a user can easily locate the fingerprint recognition sensor circuit by feel or touch and can easily orient their finger relative to the fingerprint recognition sensor circuit. This also has the effect of: if desired, the fingerprint sensor circuit can be made much larger than it should be to fit within the circular base ring surrounding the button because the user's finger is relatively well positioned with respect to the fingerprint sensor.
In one embodiment, there is no particular requirement for a particular base ring. The device 100 may include capacitive plates or ground elements positioned to the sides of the fingerprint recognition sensor circuit with the effect of: the fingerprint recognition sensor circuit exhibits capacitive isolation with the effect that: the fingerprint recognition sensor circuit has a capacitive coupling to the epidermis of the user's finger, rather than to some external source of electromagnetic interference. For example, the apparatus 100 may include capacitive plates or grounding elements at one or more of: (A) directly to the side of the fingerprint recognition sensor circuit, positioned within the device 100 and proximate to the button, (B) to the side of the device housing or sub-housing that includes the button, or (C) otherwise positioned on or in the device housing or sub-housing that includes the button.
In one embodiment, there is no particular requirement for a physical tactile sensor of the button, such as a spring or other tactile element. For example, the device 100 may include one or more sensors capable of determining whether a user is pressing on the cover glass 107 (such as whether the user is pressing on the cover glass 107 with a depression indicating where to press). As described above, the depression indicating where to press also helps to position the user's finger over the fingerprint recognition sensor circuit.
In a first example, the device 100 may include one or more sensors capable of determining whether a user is pressing on the cover glass 107 by measuring the area ratio of the fingerprint area where the user touches the glass. Such a sensor may be sensitive to an area of the cover glass 107 obscured by a user's fingerprint, with the effect of: when the user presses harder onto the cover glass 107, the area covered by the user's finger will change from a relatively small point (when pressed hard to touch) to a relatively large area (when pressed harder) to a relatively largest area (when the user's finger is pressed substantially completely against the cover glass 107).
In a second example, the device 100 may include one or more sensors capable of determining whether a user is pressing on the cover glass 107 by measuring a ratio of ridges of a fingerprint area where the user touches the glass (or is otherwise positioned relatively close to the glass). Such a sensor would be sensitive to several ridges of the user's fingerprint, with the effect that: when the user presses harder onto the cover glass 107, the number of ridges of the user's fingerprint will change from a relatively small number (when pressed hard) to a relatively large number (when pressed harder) to a relatively maximum number (when the user's finger is pressing substantially completely against the cover glass 107).
In a third example, the device 100 may include one or more sensors that can use strain gauges to determine whether a user is pressing on the cover glass 107, with optional temperature compensation. Such a sensor can measure the relative amount of strain on the cover glass 107 from the pressure of the user's finger, with the effect of: when the user presses harder onto the cover glass 107, the amount of strain will vary from a relatively minimum value (when pressed hard to the touch) to a relatively large value (when pressed harder) to a relatively maximum value (when the user's finger is pressing substantially completely against the cover glass 107).
In certain embodiments, a rigid substrate may be used in addition to the flexible element 116, or in place of the flexible element 116. In such an embodiment, the sensor may be attached to a rigid substrate and placed under the lens. A tactile switch or other pressure sensitive feedback device may be attached to the underside of the rigid substrate. Alternatively, a pressure sensitive feedback device or switch may be mounted with its underside facing another circuit element, such as another rigid substrate, with the first rigid substrate acting as a bottom support plate.
In one embodiment, the fingerprint sensor circuit may utilize one or more electrical properties of the button 104, such as anisotropy of the button material (such as alumina, sapphire, or another anisotropic material), to better sense the epidermis of the user's finger (or optionally, the subcutaneous portion of the user's finger). This has the effect of: the fingerprint sensor circuit will exhibit a relatively excellent capacitive coupling with the user's finger by virtue of the anisotropy of the button material, and will obtain a relatively excellent set of fingerprint image information. Similarly, where applicable, the fingerprint recognition sensor circuit may utilize the electromagnetic properties of other button materials to, with the help of these other electromagnetic properties of the button materials, exhibit relatively excellent capacitive coupling with the user's finger,
it should be understood that an anisotropic dielectric material may be used to form one or more layers over the capacitive sensor, such as the cover glass 107 or the button surface layer. The anisotropic dielectric may reduce blurring that would otherwise be introduced by the distance between the capacitive fingerprint sensor array and the surface (or subcutaneous) of the finger. For example, orienting a sapphire layer that covers or extends between the finger and the capacitive sensor array may enhance imaging. The sapphire layer may be oriented such that one of its axes perpendicular to its C-plane (such as the M-plane and a-plane) extends between the sensor imaging array and the surface contacted by the finger to be imaged or the surface near the finger. In general, the sapphire axis perpendicular to the C-plane may have a higher dielectric constant than the direction parallel to the C-plane, thus enhancing capacitive sensing and/or imaging. Although single crystal or polycrystalline sapphire may be used in various embodiments, certain embodiments may use single crystal sapphire exclusively. Fig. 7 generally illustrates an example lattice structure 700 of sapphire with critical plane 702 (in this case, the C-plane) oriented as the top surface.
In one embodiment, the fingerprint sensor circuit may include an element coupled to the button 104 with the effect that the fingerprint sensor circuit may take advantage of additional physical and electrical characteristics of the button 104.
For a first example, the fingerprint recognition sensor circuit may include circuit elements printed on a surface of the button 104 (such as a bottom surface that is remote from the user's finger, and thus relatively less susceptible to damage).
For a second example, the fingerprint sensor circuit may include circuit elements deposited on the surface of the button 104. In such examples, these circuit elements may be deposited using etching, sputtering, or other techniques for integrating semiconductor circuitry to a surface of a relatively non-conductive surface.
In one embodiment, the fingerprint recognition sensor circuit may be assisted by an optical element such as an optical element that uses a transparent feature of the button 104. For example, the optical element may obtain an optical view of the epidermis of the user's finger (whether determined as a still image, as a sequence of still images, or as a video sequence). In one example, the optical view may be processed relative to optical differences detected between ridges and valleys of the user's finger (such as any shading differences that may be present). The shadow difference may be present due to ambient light, or due to an optical (or optionally infrared or another suitable electromagnetic frequency) source from within the device 100.
In one embodiment, the fingerprint recognition sensor circuit may be aided by an infrared sensing element, such as an infrared sensing element using transparent or translucent properties of the button 104. For example, the infrared sensing element may obtain an infrared view of the epidermis of the user's finger or the subcutaneous portion of the user's finger (whether determined as a still image, as a sequence of still images, or as a video sequence). In one example, the infrared view may be processed relative to the detected infrared differences (such as any temperature differences or infrared frequency differences that may be present) between the ridges and valleys of the user's finger. The temperature difference or infrared frequency difference may exist due to the temperature inside the user's finger, or due to optical, infrared, or other suitable electromagnetic frequencies from inside the device 100.
In such an example, the capacitive coupling between the fingerprint recognition sensor circuit and the epidermis of the user's finger, as well as any optical or infrared information, may be combined to form a unified set of fingerprint image information. Alternatively, in such an example, the capacitive coupling between the fingerprint identification sensor circuit and the epidermis of the user's finger, as well as any optical or infrared information, may be processed separately to identify the user's fingerprint, one or more of which may be needed, or optionally weighted, to derive an identification of the user's fingerprint.
Certain aspects of the embodiments described in this disclosure may be provided as a computer program product or software, which may include, for example, a computer-readable storage medium or a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to this disclosure. A non-transitory machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The non-transitory machine-readable medium may take the form of, but is not limited to: magnetic storage media (e.g., floppy disks, video tapes, etc.); optical storage media (e.g., CD-ROM); a magneto-optical storage medium; read Only Memory (ROM); random Access Memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flashing; and so on.
Fig. 6 shows another schematic view of a button assembly 200 showing a fingerprint recognition sensor as partially described with reference to fig. 1.
Fig. 6 similarly illustrates a button assembly 200 with a substantially flat or planar lens 112, which lens 112 may be slightly recessed relative to a cover glass 107 of an electronic device, such as device 100, as described with reference to fig. 1. In this design, the lens 112 has a planar shape 307 formed at least in part by a portion of the shape of the lens 112 to receive a user's finger onto the button 104, including the structure of the base ring 114, and optionally also a portion of the planar shape 307, in a flush, slightly recessed, or slightly raised arrangement relative to the lens 112. Figure 3 similarly shows a fingerprint recognition sensor disposed below the lens 112 and coupled to the lens 112.
While the present disclosure has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure are described in the context of particular embodiments. The functions may be separated or combined in different ways or described using different terminology in the processes in the embodiments of the present disclosure. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.