US20050248548A1 - Acoustic touch sensor - Google Patents

Abstract

A touch sensor comprises a substrate capable of propagating acoustic waves. The substrate includes a first surface having a touch sensitive region. A transducer is formed on the substrate. The transducer comprises a piezoelectric element which is thermally cured after being formed on the substrate. The transducer is configured for at least one of generating acoustic waves and detecting acoustic waves. Alternatively, the transducer may include a strip comprising the piezoelectric element.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is related to U.S. Provisional Patent Application Ser. No. 60/562,461, attorney docket number ELG064-US1, entitled “Acoustic Touch Sensor,” filed Apr. 14, 2004, and U.S. Provisional Patent Application Ser. No. 60/562,455, attorney docket number ELG065-US1, entitled “Acoustic Touch Sensor,” filed Apr. 14, 2004, and to U.S. patent application Ser. No. ______, attorney docket number ELG065-US2, entitled “Acoustic Touch Sensor”, filed contemporaneously with this application, the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention relates to touch sensors, in particular to acoustic touch sensors and acoustic touchscreens having narrow functional borders and increased touch-sensitive areas.
• 2. Introduction to the Invention
• An acoustic touch sensor has a touch sensitive area on which the presence and location of a touch is sensed by the touch's effect on the transmission of acoustic waves across a touch sensor substrate. Acoustic touch sensors may employ Rayleigh waves (including quasi-Rayleigh waves), Lamb or shear waves, or a combination of different types of the acoustic waves.
• FIG. 1 illustrates the operation of a conventional acoustic touch sensor, anacoustic touchscreen1. Thetouchscreen1 has a touch-sensitive area2 inside of which two-dimensional coordinates of touches are determined. For example, the touch-sensitive area2 may include the region bounded by thedashed line16 which represents the inner boundary of abezel10. Afirst transmitting transducer3ais positioned outside of touch-sensitive area2 and is acoustically coupled to the surface oftouchscreen1. Thetransducer3asends an acoustic signal in the form of anacoustic wave11atraveling parallel to the top edge oftouchscreen1 and generally in the plane oftouchscreen1. Aligned in the transmission path ofacoustic wave11ais a firstlinear array13aof partially acousticallyreflective elements4, each of which partially transmits the acoustic signals and partially reflects them (by an angle of approximately 90°), creating a plurality of acoustic waves (e.g.,5a,5band5c) traveling vertically across touch-sensitive area2. The spacing ofreflective elements4 is variable to compensate for the attenuation of the acoustic signals with increasing distance fromfirst transmitter3a. It is also well known even ifreflective elements4 are uniformly spaced, signal equalization may be achieved by varying the reflective strength ofreflective elements4.Acoustic waves5a,5b, and5care again reflected by an angle of approximately 90° (seearrow11b) by a secondlinear array13bof partially acousticallyreflective elements4 towards a first receivingtransducer6aupon reaching the lower edge oftouchscreen1. At thereceiving transducer6a, the waves are detected and converted to electrical signals for data processing. Similar arrangements of reflective elements are located along the left and right edges oftouchscreen1. A second transmittingtransducer3bgenerates anacoustic wave12aalong the left edge, and a third linear array13cof partially acousticallyreflective elements4 creates a plurality of acoustic waves (e.g.,7a,7b, and7c) traveling horizontally across touch-sensitive area2.Acoustic waves7a,7b, and7care redirected along12bby a fourthlinear array13dof partially acousticallyreflective elements4 towards receivingtransducer6b, where they are detected and converted to electrical signals for data processing.
• If touch-sensitive area2 is touched atposition8 by an object such as a finger or stylus, a portion of the energy of theacoustic waves5band7ais absorbed by the touching object. The resulting attenuation is detected by receivingtransducers6aand6bas a perturbation in the acoustic signal. A time delay analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates oftouch position8. The device ofFIG. 1 can also function as a touchscreen with only two transducers using a transmit/receive transducer scheme.
• A housing9, indicated by dashed lines inFIG. 1, may be associated withtouchscreen1. The housing can be made of any suitable material, for example molded polymer or sheet metal. The housing9 includes abezel10, indicated bydashed line16 representing an inner boundary ofbezel10 and dashedline17 indicating an outer boundary ofbezel10 inFIG. 1. The innerdashed line16 shows that the housing9 overlays a periphery oftouchscreen1, concealing the transmitting and receiving transducers, the reflective elements, and other components, but exposing touch-sensitive area2. This arrangement can protect the concealed components from contamination and/or damage, provide an aesthetic appearance, and define the touch-sensitive area for the user.
• A touchscreen may comprise a separate faceplate overlaid on a display panel. The faceplate is typically made of glass, but any other suitable substrate may be used. The display panel may be a cathode ray tube (CRT), a liquid crystal display (LCD), plasma, electroluminescent, organic light-emitting-diode (OLED) display, or any other type of display.
• As shown inFIG. 1, the touchsensitive area2 is surrounded byborder regions15 where thereflective elements4 and the transmitting and receivingtransducers3a,3b,6aand6bare located. Reducing the width ofborder regions15 increases the touchsensitive area2. For touch sensor applications using transparent touch sensors such as touchscreens, the width of the border can be especially important. A touch sensor with narrowedborder regions15 can be integrated into display monitors that themselves have a narrow border around the displayed image. This feature is desirable as the general market trend for devices such as monitors is towards sleeker and more mechanically compact designs. A touch sensor with narrowedborder regions15 also is more easily sealed as well as being lighter and can have increased sensor area. Amongst competing touchscreen technologies, (e.g., acoustic, capacitive, resistive and infrared) acoustic touchscreens tend to have wider borders.
• It is known to mount transducers used for transmitting and receiving acoustic waves substantially on the top touch sensitive surface of a substrate of an acoustic touch sensor. Transmitter-to-detector pathways may be used for the acoustic waves instead of incorporating reflective arrays for directing acoustic waves across a touch sensitive region of the touch sensor, but a large number of transducers may be required to be used. The transducers are wedge transducers mounted on the touch surface, thereby taking up valuable border space. Interdigital transducers may be used to design touchscreens that do not use reflective arrays, as disclosed in U.S. Pat. No. 6,756,973, the disclosure of which is incorporated herein by reference. The interdigital transducers disclosed therein are placed on the touch surface of the touchscreen thereby taking up valuable border space. To date, touch sensors using few transducers and incorporating reflective arrays to direct acoustic energy across the touch sensor have located the arrays on the borders of the same surface of the substrate as the touch sensitive region, thereby occupying border space.
• It is known to mount transducers used for transmitting and receiving acoustic waves on the sidewalls of a substrate of an acoustic touch sensor. However, in both cases, the reflective arrays must be placed on the touch surface thereby taking up valuable border space.
• It is possible to reduce the size of the border region on the touch surface of a touchscreen by using a waveguide to concentrate an acoustic wave in the border region, as disclosed in U.S. Pat. No. 6,636,201, the disclosure of which is incorporated herein by reference. However, alternate solutions may be desired which do not require providing a waveguide on the surface of the touch sensor substrate.
• In addition to reducing the border region of a touch sensor, it is desired to make a touch sensor as flat as possible. This is especially advantageous for integrating a touch sensor with an LCD panel to make a touchscreen. If the touch sensor is very flat and parallel to the LCD panel, the two are easily combined into a compact system that can be easily sealed. If the touch sensor has bulky bezels and border regions, sealing of the touch sensor to the LCD panel may be complicated.
• For the reasons outlined above, it is desirable to have new acoustic touch sensor designs capable of accommodating a very narrow border region. In addition, it is desirable to have new acoustic touch sensor designs in which the sensor is flat, allowing it to be easily integrated and sealed with planar devices, such as an LCD monitor.
BRIEF SUMMARY OF THE INVENTION
• In a first embodiment, a touch sensor comprises a substrate capable of propagating acoustic waves. The substrate includes a first surface having a touch sensitive region. A transducer is formed on the substrate. The transducer comprises a piezoelectric element which is thermally cured after being formed on the substrate. The transducer is configured for at least one of generating acoustic waves and detecting acoustic waves.
• In another embodiment, a touch sensor comprises a substrate capable of propagating acoustic waves. The substrate includes a first surface having a touch sensitive region. A transducer is configured for at least one of generating acoustic waves and receiving acoustic waves. The transducer includes a strip comprising a piezoelectric material. The strip is attached to the substrate.
• In another embodiment, a method for forming a transducer on a touch sensor substrate is provided. The substrate includes a first surface having a touch sensitive region. A conductive layer is applied to the substrate. A piezoelectric layer is applied to the substrate, and the piezoelectric layer covers at least a portion of the first conductive layer. The piezoelectric layer is thermally cured after being applied to the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
• The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. It should be understood that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.
• FIG. 1 illustrates the operation of a conventional acoustic touch sensor, an acoustic touchscreen.
• FIG. 2 illustrates a touch sensor substrate having a touch surface, edges, and sidewalls in accordance with an embodiment of the present invention.
• FIG. 3 illustrates a touch sensor having mechanisms for generating or detecting acoustic waves formed on the sidewalls in accordance with an embodiment of the present invention.
• FIG. 4 illustrates a mechanism for generating or receiving an acoustic wave formed on a sidewall in accordance with an embodiment of the present invention.
• FIG. 5 illustrates cross sections of the layers on the substrate ofFIG. 4 in accordance with an embodiment of the present invention.
• FIG. 6 illustrates touch areas on the touch surface of the substrate in accordance with an embodiment of the present invention.
• FIG. 7 illustrates a geometry of a touch sensor in which transmitting mechanisms are located on two of the sidewalls of the substrate, and receiving mechanisms are located on the other two sidewalls of the substrate, in accordance with an embodiment of the present invention.
• FIG. 8 illustrates the transmitting or receiving mechanism having interdigital electrodes in accordance with an embodiment of the present invention.
• FIG. 9 illustrates a polymer-film pressure-mode piezo strip for generating and receiving diagonal acoustic path “U” or “V” coordinates in accordance with an embodiment of the present invention.
• FIG. 10 illustrates a side-view of the substrate having the piezo strip attached to the second surface in accordance with an embodiment of the present invention.
• FIG. 11 illustrates the gratings formed on the touch surface in accordance with an embodiment of the present invention.
• FIG. 12 illustrates an alternative polymer-film piezo strip for generating and receiving acoustic waves in accordance with an embodiment of the present invention.
• FIG. 13 illustrates an alternative polymer-film piezo strip for generating and receiving acoustic waves in accordance with an embodiment of the present invention.
• FIG. 14 illustrates a polymer-film piezo transducer for generating and receiving acoustic waves in accordance with an embodiment of the present invention.
• FIG. 15 illustrates an alternative polymer-film piezo strip for generating and receiving acoustic waves from the sidewall in accordance with an embodiment of the present invention.
• FIG. 16 illustrates a geometry of a touch sensor in accordance with an embodiment of the present invention.
• FIG. 17 illustrates a side view of a transmitting or receiving mechanism ofFIG. 3 in accordance with an embodiment of the present invention.
• FIG. 18 illustrates spacing or distance between the electrode fingers (FIG. 4) for the U1 direction (FIG. 6) in accordance with an embodiment of the present invention.
• FIG. 19 illustrates a coupling mechanism in the U1 region between an acoustic wave and electric field-induced expansion and contraction of a piezoelectric film (e.g., a PVDF film or fired-on piezoceramic layer), such as piezoelectric material, in accordance with an embodiment of the present invention.
• FIG. 20 illustrates an acoustic power density of zeroth order horizontally polarized shear waves (ZOHPS or sometimes referred to commercially as “GAW”) within the substrate in accordance with an embodiment of the present invention.
• FIG. 21 illustrates transmission of higher order plate waves in accordance with an embodiment of the present invention.
• FIG. 22 illustrates transmission of Rayleigh waves in accordance with an embodiment of the present invention.
• FIG. 23 illustrates the piezoelectric material of the mechanism coupling to Rayleigh waves primarily via “33” coupling in accordance with an embodiment of the present invention.
• FIG. 24 illustrates a transducer structure having a periodic modulation layer in accordance with an embodiment of the present invention.
• FIGS. 25 and 26 illustrate an example of the first case wherein a piezoelectric mechanism comprises the piezoelectric layer having a thickness that is much less than a half-wavelength in accordance with an embodiment of the present invention.
• FIGS. 27 and 28 illustrate an example of the second case wherein a piezoelectric mechanism comprises the piezoelectric layer having the thickness that is only somewhat thinner than a half-wavelength and phase-shifting is used to accomplish modulation in accordance with an embodiment of the present invention.
• FIG. 29 illustrates the dependence of phase and amplitude for coupling through a resonance at □o in accordance with an embodiment of the present invention.
• FIG. 30 illustrates a piezoelectric mechanism designed to generate Rayleigh waves in accordance with an embodiment of the present invention.
• FIG. 31 illustrates an example wherein the substrate can be periodically altered to result in modulation in accordance with an embodiment of the present invention.
• FIG. 32 illustrates a grating transducer being formed on the substrate in accordance with an embodiment of the present invention.
• FIG. 33 illustrates a comb transducer being formed on the substrate in accordance with an embodiment of the present invention.
• FIG. 34 illustrates an interdigital transducer being formed on the substrate in accordance with an embodiment of the present invention.
• FIG. 35 illustrates a touch sensor having transducers formed along a perimeter of the touch surface in accordance with an embodiment of the present invention.
• FIG. 36 illustrates an alternative interdigital transducer being formed on the substrate in accordance with an embodiment of the present invention.
• FIG. 37 illustrates a touch sensor having transducers formed along a perimeter of the touch surface in accordance with an embodiment of the present invention.
• FIG. 38 illustrates an alternative touch sensor formed in accordance with an embodiment of the present invention.
• FIG. 39 illustrates a waveguide positioned to accomplish signal equalization in accordance with an embodiment of the present invention.
• FIG. 40 illustrates the waveguide being formed to accomplish signal equalization in accordance with an embodiment of the present invention.
• FIG. 41 illustrates another embodiment of a touch sensor in accordance with an embodiment of the present invention.
• FIG. 42 illustrates a touch sensor incorporating the strips in accordance with an embodiment of the present invention.
• FIG. 43 illustrates a touch sensor having transducers formed on the sidewalls of the substrate in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• Conventional reflective arrays as shown inFIG. 1 range in width between about 5 mm and 15 mm, which corresponds to a range of about 9-26 acoustic wavelengths (assuming a conventional frequency of about 5 MHz, corresponding to a wavelength of about 0.57 mm). The reflective arrays having narrower widths are typically used on smaller screens.
• FIG. 2 illustrates atouch sensor substrate20 having atouch surface24, edges22, and sidewalls32 in accordance with an embodiment of the present invention. Opposingedges26 are formed on thesubstrate20 at an intersection between a plane corresponding to asecond surface28 of thesubstrate20 and the planes corresponding to each of thesidewalls32. Any suitable material can be used for thesubstrate20, including glass, ceramic, and metals (e.g., aluminum or steel). For some applications, low acoustic loss glass may be desired. For example, borosilicate glasses have low loss, and can provide increased received signal amplitudes that may in turn enable larger touch sensor areas.
• Angles42 and44 formed where thesidewalls32 abut thetouch surface24 are 90°, or within 20° of 90°, makingsidewalls32 vertical or substantially vertical with respect to thetouch surface24. Thesidewalls32 are formed to be substantially free of defects, such that any deviations on thesidewalls32 such as chips, striations, dents, uneven regions, and the like have dimensions less than the acoustic wavelength, e.g., a Rayleigh wavelength, preferably less than 20% of a Rayleigh wavelength.
• Theclean sidewalls32 may be formed by any method suitable for the material from which thesubstrate20 is manufactured. For example, glass may be cut and machined to provideclean sidewalls32. Optionally, the glass may be scribed and broken which, if carefully done, can produce aclean edge22 opposite the scribed surface. Alternatively, aclean sidewall32 may be formed by propagating a controlled fracture using thermal stress, for example by utilizing localized laser heating and gas jet cooling processes. In addition, theedges22 may also be formed to be substantially free of defects in a manner similar to theclean sidewalls32.
• FIG. 3 illustrates atouch sensor50 having mechanisms52-58 for generating or detecting acoustic waves formed on thesidewalls32 in accordance with an embodiment of the present invention. Thesidewalls32 have been indicated as sidewalls34-40 for clarity. Thetouch sensor50 comprises thesubstrate20 having the touchsensitive surface24. Each of the mechanisms52-58, disposed on the sidewalls34-40, respectively, generates and/or detects acoustic waves. Therefore, it is not necessary to form any mechanism, such as a reflective array, on thetouch surface24 of thesubstrate20. Optionally, each mechanism52-58 has a tab60-66 extending beyond thesubstrate20 for making electrical connection thereto.
• By way of example only, two of themechanisms52 and56 may generate acoustic waves and two of themechanisms54 and58 may detect acoustic waves. Themechanisms52 and56 launch the acoustic waves, such as bulk shear waves, in directions that are generally parallel to one of the diagonals of therectangular substrate20 as indicated by thearrows71.
• FIG. 4 illustrates amechanism52 for generating or receiving an acoustic wave formed on asidewall32 in accordance with an embodiment of the present invention. A first conducting layer, orfirst electrode84, is disposed onsidewall32. Thefirst electrode84 may be formed to cover all, or nearly all, of the surface of thesidewall32. On top of thefirst electrode84 is applied a layer of piezoelectric material83 (e.g., a piezoelectric polymer film or a fired-on piezoceramic material). Aportion85 of thefirst electrode84 may extend beyond thepiezoelectric layer83 to allow electrical connection to be made, such as at thetab60. Asecond electrode80 having abase portion81 and periodic structures, such asfingers82, extending therefrom is disposed along thesidewall32 on top of thepiezoelectric layer83. Thesecond electrode80 may be formed of a material such as copper. Thefingers82 act as a phased array of transmitters or receivers coherently generating or receiving acoustic waves in desired directions. Alternatively, themechanism52 inFIG. 4 may be formed as a piezo strip separate from thesubstrate20 similar to the piezo strips discussed below forFIGS. 9 and 12-14.
• Themechanism52 may be used to generate and receive shear waves, Lamb waves, or Rayleigh waves. An oscillating voltage (not shown) may be applied to thesecond electrode80 while thefirst electrode84 is connected to ground. The application for shear waves will be discussed in more detail below. If being used for shear waves, themechanism52 is optimized if thebase portion81 is made to be small such that a length70 of thefingers82 extends along nearly the entire height of thesidewalls32, or adepth68 of thesubstrate20. However, as Rayleigh waves are concentrated near thetouch surface24 of thesubstrate20, if being used with Rayleigh waves, themechanism52 can be optimized by making the length70 of thefingers82 less than twice the wavelength λ, or less than the wavelength λ, of the acoustic waves. Thefingers82 may be spaced apart by a distance72, measured center to center or end to end (as illustrated), wherein the distance72 is larger than the wavelength λ of the generated or received acoustic wave. The ratio λ/distance72 equals the sine of the angle of emission or reception with respect to the normal to thesubstrate sidewall32.
• FIG. 5 illustratescross sections74 and76 of the layers on thesubstrate20 ofFIG. 4 in accordance with an embodiment of the present invention. Thecross section74 illustrates a portion including thefinger82 of thesecond electrode80. Thecross section76 illustrates a portion between thefingers82, wherein thesecond electrode80 occupies thebase portion81.
• FIG. 6 illustrates touch areas102-108 on thetouch surface24 of thesubstrate20 in accordance with an embodiment of the present invention. The sidewalls34-40 have been indicated as inFIG. 3 for clarity. Each of the touch areas102-108 is associated with a diagonal acoustic path “U” or “V” rather than conventional Cartesian “X” and “Y” coordinates. The arrows122-128 indicate the directions of representative acoustic paths from one side to an adjacent side of thesubstrate20. By way of example only, signals generated by a mechanism alongsidewall38 would generate U1 (touch area102) and V1 (touch area106) in the directions ofarrows122 and126, to be received by mechanisms along sidewalls36 and40, respectively. Two-dimensional touch coordinates can be reconstructed from the four diagonal signals U1, U2, V1, and V2.
• FIG. 7 illustrates a geometry of atouch sensor100 in which transmittingmechanisms52 and56 are located on thesidewalls34 and38 of thesubstrate20, respectively, and receivingmechanisms54 and58 are located on thesidewalls36 and40 of thesubstrate20, respectively, in accordance with an embodiment of the present invention. By way of example only, if thesubstrate20 has a rectangular shape with aheight116 andwidth118, such that the ratio is 3:4 (height:width), spacing136 for theelectrode fingers82 on the transmittingmechanisms52 and56 is 5λ/4, and spacing138 for theelectrode fingers82 on the receivingmechanisms54 and58 is 5λ/3. By spacing theelectrode fingers82 of the transmittingmechanisms52 and56 apart by a distance greater than 1 wavelength, coherent coupling in desired directions is achieved.
• FIG. 8 illustrates the transmitting or receivingmechanism52 having interdigital electrodes in accordance with an embodiment of the present invention.Piezoelectric material83 may be applied over a ground electrode (not shown) Afirst electrode88 and asecond electrode90 each form a series of periodic structures, such as interdigital electrodes havingelectrode fingers92 and94, respectively, formed over thepiezoelectric material83. Thefingers92 are regularly spaced with respect to each other, and thefingers94 are regularly spaced with respect to each other, and the spacing is determined as previously described inFIG. 4. For example, thefingers92 are spaced apart by the distance72 (FIG. 4), wherein the distance between onefinger92 and a neighboringfinger94 is one-half the distance72.
• It is possible to have the transmitting and receiving mechanisms52-58 assembled before disposing on thesidewall32. For example, strips of polymer-film sensors can be used. A specific subset of polymers (a material having long chains with a carbon backbone) is piezoelectric, having the characteristic of expanding and contracting when subjected to an electric field. The piezo polymer is a continuous film which is insulating. These strips comprise a piezoelectric polymeric layer (e.g., polyvinylidene fluoride (PVDF) or a copolymer of vinylidene fluoride, for example a copolymer of vinylidene fluoride and trifluoroethylene, p(VDF-TrFE)). Thepiezoelectric material83 is sandwiched between the ground electrode and the array ofinterdigital electrodes88 and90, which may be formed of copper trace or metalized aluminum. Thepiezoelectric material83, or the polymer, is typically a thin dimension (e.g. 30 microns) compared to the width of thefingers92 and94. The strips can be disposed on thesidewalls32 by any suitable method, preferably by using a layer that efficiently couples shear strains between the polymeric piezoelectric component and the substrate20 (e.g., glass), for example by using a thin rigid adhesive layer. Electric connection from a controller (not shown) to the strips can be made via a flexible cable, and optionally by continuation of the same polymer-film substrate that also serves as the piezoelectric material of the transducer or mechanisms52-58.
• The ground electrode (not shown) is connected to ground and thefingers92 and94 are excited with opposite polarities. Themechanism52 may transmit and/or receive acoustic waves, and thefingers92 and94 transmit 180° out of phase. When the first andsecond electrodes88 and90 are excited with the opposite phases, the polymer piezo, or thepiezoelectric material83, will tend to expand and contract in the plane indicated by arrows98. For example, when a negative voltage is applied to thefingers94, thepiezoelectric material83 shrinks. Thefingers92 and94 also experience a small measure of expansion and contraction, but more importantly, corresponding stresses are applied to sidewalls32 ofsubstrate20.
• FIG. 9 illustrates a polymer-film pressure-mode piezo strip250 for generating and receiving diagonal acoustic path “U” or “V” coordinates in accordance with an embodiment of the present invention. Thepiezo strip250 is formed of afirst electrode252 applied to afirst side258 of a polymerpiezo film254. Asecond electrode256 is applied to asecond side260 of the polymerpiezo film254. Thepiezo strip250 may be flexible, allowing easier assembly and interconnection compared to rigid and/or brittle materials. Afirst portion262 of thepiezo strip250 may be glued or otherwise adhered to thesecond surface28 of thesubstrate20 proximate theedges22. Asecond portion264 of thepiezo strip250 may extend beyond thesubstrate20 to allow electrical connections (not shown) to be easily attached to the first andsecond electrodes252 and256.
• Thepiezo strip250 is formed separate from thesubstrate20, allowing flexibility in manufacturing and assembly. Therefore, it is not necessary to consider warping and/or other destructive results which may occur within thesubstrate20 due to the high temperatures used when curing materials comprising thepiezo strip250. This may allow additional materials to be considered for use as thesubstrate20, opening possibilities in design of products, use environments, and the like.
• FIG. 10 illustrates a side-view of thesubstrate20 having thepiezo strip250 attached to thesecond surface28 in accordance with an embodiment of the present invention. A grating266 is formed on thetouch surface24 proximate theedge22, and opposite thepiezo strip250. Optionally, asolid material268 may be formed on or attached to thepiezo strip250, providing an inertial mass for thepiezo strip250 to push against to improve coupling efficiency.
• FIG. 11 illustrates thegratings266 formed on thetouch surface24 in accordance with an embodiment of the present invention. The piezo strip250 (not shown) has an active area corresponding to thefirst portion262 of thepiezo strip250 and the area covered by thegrating transducers266. When the first andsecond electrodes252 and256 are excited, acoustic waves are generated in the directions ofarrows244.
• FIG. 12 illustrates an alternative polymer-filmpiezo strip270 for generating and receiving acoustic waves in accordance with an embodiment of the present invention. Thepiezo strip270 is formed of afirst electrode272 applied to afirst side278 of a polymerpiezo film274. Asecond electrode276 is applied to asecond side280 of the polymerpiezo film274. Thesecond electrode276 hasfingers282. Afirst portion284 of thepiezo strip270 is fastened to thetouch surface24 of thesubstrate20 proximate theedges22. Asecond portion286 of thepiezo strip270 may extend beyond thesubstrate20 to allow electrical connections to be attached to the first andsecond electrodes272 and276.
• FIG. 13 illustrates an alternative polymer-filmpiezo strip290 for generating and receiving acoustic waves in accordance with an embodiment of the present invention. Thepiezo strip290 is formed of aground electrode292 applied to afirst side300 of a polymerpiezo film294. First and second electrodes296 and298 haveinterdigital fingers308 and310 and are applied to asecond side302 of the polymerpiezo film294. Afirst portion304 of thepiezo strip290 is fastened to thetouch surface24 of thesubstrate20. Asecond portion306 of thepiezo strip290 may extend beyond thesubstrate20 to allow electrical connections to be attached to theground electrode292 and first and second electrodes296 and298.
• FIG. 14 illustrates a polymer-film piezo transducer320 for generating and receiving acoustic waves in accordance with an embodiment of the present invention. Thepiezo transducer320 is formed of a ground electrode322 applied to afirst side330 of a polymerpiezo film324. First andsecond electrodes326 and328 haveinterdigital fingers372 and374, and are applied to asecond side332 of the polymerpiezo film324. Afirst portion334 of thepiezo transducer320 is fastened to thetouch surface34 of thesubstrate20 proximate two or more of the corners of thesubstrate20. Asecond portion336 of thepiezo transducer330 may extend beyond thesubstrate20 to allow electrical connections to be attached to the ground electrode322 and first andsecond electrodes326 and328. To form a touch screen, thepiezo transducer320 may be combined with reflective arrays formed along thetouch surface24 proximate theedges22, such as the linear arrays13a-13dofFIG. 1 previously discussed.
• FIG. 15 illustrates an alternative polymer-filmpiezo strip350 for generating and receiving acoustic waves fromsidewall32 in accordance with an embodiment of the present invention. Thepiezo strip350 is formed of aground electrode352 applied to afirst side360 of a polymerpiezo film354. First andsecond electrodes356 and358 haveinterdigital fingers368 and370 and are applied to asecond side362 of the polymerpiezo film354. Afirst portion364 of thepiezo strip350 is fastened to thesidewall32 of thesubstrate20. Asecond portion366 of thepiezo strip350 may extend beyond thesubstrate20 to allow electrical connections to be attached to theground electrode352 and first andsecond electrodes356 and358. Thepiezo strip350 bonded to thesidewall32 is an option for themechanism52 ofFIG. 3.
• FIG. 16 illustrates a geometry of atouch sensor340 in accordance with an embodiment of the present invention. Thetouch sensor340 comprises thesubstrate20 having thetouch surface24. Piezo strips342-348 have been attached, such as with an adhesive, to aperimeter338 of thetouch surface24. By way of example only, the piezo strips342-348 may be formed as one of the piezo strips illustrated inFIGS. 12 and 13. The strips342-348 may generate and receive acoustic waves in the directions as indicated byarrows376. It should be understood that the piezo strips342-348 are drawn for clarity and are not shown to scale with respect to thetouch sensor340.
• FIG. 17 illustrates a side view of a transmitting or receivingmechanism52 ofFIG. 3 in accordance with an embodiment of the present invention. Themechanism52 is formed having thefirst electrode84, thepiezoelectric layer83 and anouter electrode86, such as the interdigital first andsecond electrodes88 and90 as inFIG. 8 or thesecond electrode80 as inFIG. 4. Thefirst electrode84 of themechanism52 is bonded to thesidewall32 with anadhesive layer85, such as an epoxy. Optionally, themechanism52 can extend beyond one or both of the plane of thetouch surface24 and the plane of theopposite side28 of thesubstrate20 to allow electrical connections to be attached to theelectrodes84 and86.
• FIG. 18 illustrates spacing or distance between the electrode fingers82 (FIG. 4) for the U1 direction (FIG. 6) in accordance with an embodiment of the present invention. The spacing between theelectrode fingers82 as discussed previously inFIG. 4 (distance72) can be tuned to transmit and receive zeroth order horizontally polarized shear (ZOHPS) waves, also known as GAW, at the desired angles to provide U and V acoustic paths as shown inFIG. 6. Thesubstrate20 has theheight116 andwidth118. Solid lines110 and dashedlines111 represent maxima and minima (most negative amplitude with magnitude same as the maxima), respectively, in the acoustic waves generated from a horizontal side113. The spacing between maxima as projected along a horizontal axis along the horizontal side113 is shown as S_W. The acoustic waves launched from the horizontal side113 then travel towardvertical side114 as indicated byarrow112. The spacing between maxima (and minima) as projected along thevertical side114 is shown as S_H. The quantities S_Wand S_Hare given by the following equations:
  S_W=λ(H²+W²)^1/2/W
  S_H=λ(H²+W²)^1/2/H
  The wavelength λ will be determined by the phase velocity V of the acoustic mode used in the touch sensor to sense touches and the operating frequency f by the relation λ=V/f. Setting the spacing of theelectrode fingers82 using the S_Wand S_Has set out above will lead to coherent coupling to acoustic waves parallel to the diagonals of therectangular touch surface20 and will support the U1, U2, V1 and V1 signal paths which complete a two-dimensional coordinate measurement in the touch area.
• FIG. 19 illustrates a coupling mechanism in the U1 region between an acoustic wave and electric field-induced expansion and contraction of a piezoelectric film (e.g., a PVDF film or fired-on piezoceramic layer), such aspiezoelectric material83, in accordance with an embodiment of the present invention. Filled arrows120 represent the motion of the shear acoustic wave. Hollow arrows121 represent forces due to thetransmitting mechanism52 shown inFIG. 8, such as theinterdigital electrodes88 and90 and thepiezoelectric material83, along the horizontal side113. Asimilar receiving mechanism52 is present along thevertical side114. Regions ofexpansion140 are indicated by plus symbols and regions ofcontraction142 are indicated by minus symbols.
• If thepiezoelectric material83 is a fired-on piezoelectric coating or a polymer layer such as PVDF, it is poled using an electric field to induce a dipole moment, in order to demonstrate piezoelectric behavior. Referring toFIG. 17, thepiezoelectric material83 is most easily poled using the available electrode structures, that is, in adirection144 perpendicular to thesidewall32. With thepiezoelectric material83 poled in thedirection144, applying voltage to thefirst electrode84 and theouter electrode86 will generally induce expansion or contraction both in thedirection144 parallel to the applied electric field (referred to herein as “33” coupling) as well as expansion or contraction in adirection146 perpendicular to the electric field and parallel to the plane of sidewall32 (referred to herein as “31” coupling). Depending on the nature of thepiezoelectric material83, thedirection146 of contraction or expansion due to the “31” coupling may be parallel or perpendicular (or both) to thetouch surface24 ofsubstrate20. All of these three types of piezoelectric coupling, namely “33” coupling and the two types of “31” coupling, are available to provide coupling to generate and receive the desired acoustic waves.
• Returning toFIG. 19, a coupling mechanism between horizontally polarized shear waves, such as the zeroth order horizontally polarized shear (ZOHPS) wave, is illustrated. The filled arrows120 represent the motion of the shear acoustic wave while the hollow arrows121 represent forces due to “31” coupling of thepiezo material83 where thedirection146 is in the plane of thetouch surface24. While not shown, the “33” coupling in thepiezoelectric material83 can be used to generate acoustic waves by exciting the component of shear wave motion (indicated by the filled arrows120) that is perpendicular to thesidewall32. As diagonally propagating Rayleigh waves are associated with material motion at thesidewalls32 along all three axes, the “33” coupling and both polarizations of the “31” coupling may be used to excite Rayleigh waves as well as Lamb waves.
• By way of example only, the design of thetouch sensor50 or100 is desired which makes use of the coupling that provides the most efficient generation and reception of the desired acoustic mode with minimal coupling to undesired parasitic acoustic modes. In addition, the design of a transducer, such as themechanism52 and others previously discussed, depends in part on the depth profile of the desired mode. For example, shear waves may move through all or a large portion of the depth of thesubstrate20, while Rayleigh waves couple only near thetouch surface24 of thesubstrate20.
• FIG. 20 illustrates an acoustic power density of a zeroth order horizontally polarized shear waves (ZOHPS or sometimes referred to commercially as “GAW”) within thesubstrate20 in accordance with an embodiment of the present invention. The ZOHPS or GAW has a uniform acoustic power density throughout the bulk of thesubstrate20, as illustrated by arrows152-156. To excite and detect this acoustic wave, it is preferable for the active transmitting or receiving mechanism52 (which can comprise a layer of piezoelectric material83) to couple uniformly indepth158 along thesidewall32.
• FIG. 21 illustrates transmission of higher order plate waves in accordance with an embodiment of the present invention. Themechanism52 has first and secondpiezoelectric elements164 and166 having opposite polarity. The first and secondpiezoelectric elements164 and166 are formed on thesidewall32 proximate the top (the touch surface24) and bottom (the second surface28) of thesubstrate20 to transmit higher order horizontally polarized shear waves (or another higher order plate wave) as illustrated byarrows168 and170 proximate thetouch surface24 andarrows172 and174 proximate thesecond surface28.
• FIG. 22 illustrates transmission of Rayleigh waves in accordance with an embodiment of the present invention. The acoustic power in Rayleigh waves is concentrated near thetouch surface24, as illustrated byarrows192 and194. For “31” coupling where thedirection146 is perpendicular to thetouch surface24, it is desirable to limit the active area ofpiezoelectric material83 of themechanism52 to within approximately oneRayleigh wavelength λ176 of thetouch surface24 ofsubstrate20. It should be understood that although themechanism52 is illustrated as being only oneRayleigh wavelength λ176 indepth158, themechanism52 may have a larger dimension along thedepth158 while still limiting the active area of thepiezoelectric material83 to within the area of approximately oneRayleigh wavelength λ176 of thetouch surface24.
• FIG. 23 illustrates thepiezoelectric material83 of themechanism52 coupling to Rayleigh waves primarily via “33” coupling in accordance with an embodiment of the present invention. The phase of Rayleigh wave longitudinal motion, as indicated byarrows196 and198, flips polarity sign withdepth158. Therefore, the layer of activepiezoelectric material83 of themechanism52 is excited with different polarities at different depths. In general, a combination of simulation studies and experimental studies may be used to determine the structure of the layer of the activepiezoelectric material83 of themechanism52 as a function of the desired acoustic mode and the piezoelectric properties of the poled piezoelectric layer.
• FIG. 24 illustrates a transducer structure having aperiodic modulation layer134 in accordance with an embodiment of the present invention. Asubstrate20 as shown inFIG. 2 can be used. As described above, thesubstrate20 can be any suitable material, including glass, ceramic, and metals such as aluminum or steel. For some applications, low acoustic loss glass may be desired. As described above, thesidewalls32 of the substrate are clean.
• A firstconductive layer130 is provided (or applied) to each of thesidewalls32 of thesubstrate20 and will function as a first electrode for piezoelectric transducers. Any suitable conductive material can be used, such as silver fret, copper traces or screen-printable conductive printable inks. By way of example only, the firstconductive layer130 may be screen printable ink which is baked at a high temperature, such as 450° C. after application to thesidewalls32.
• Apiezoelectric material layer131 is then applied on thesidewalls32 over the firstconductive layer130. Examples of materials that can be used forpiezoelectric layer131 include, but are not limited to, polymer piezoelectric materials as well as fired-on piezoceramic materials. Optionally,regions132 may be left exposed near the corners to allow an electrical connection to the firstconductive layer130 to be made.
• Next, a secondconductive layer133 is provided that will function as a second electrode for the piezoelectric transducers. Typically, the firstconductive layer130 will function as a ground electrode to minimize susceptibility to electromagnetic interference, and the secondconductive layer133 will function as an excitation electrode or received signal electrode. The secondconductive layer133 can be made of similar or identical materials as the firstconductive layer130. In contrast toelectrode80 shown inFIG. 4, the secondconductive layer133 is a continuous covering over thepiezoelectric layer131, and thus does not have an electrode structure of interdigital fingers. Instead, aperiodic modulation layer134 is added on top of the secondconductive layer133.
• Theperiodic modulation layer134 is formed of periodic structures, and comprises material applied as “stripes” periodically along the length of thesidewall32, extending essentially from the top (or touch surface24) of thesubstrate20 to the bottom (or second surface28). Therefore, the stack disposed on thesidewall32 is formed of the firstconductive layer130, thepiezoelectric layer131, the secondconductive layer133, and theperiodic modulation layer134 to form atransducer141 for generating or detecting acoustic waves traversing thetouch region24 of atouch sensor50.
• Theperiodic modulation layer134 of thetransducer141 serves to spatially modulate the acoustic waves either transmitted or detected by thetransducer141. Where theperiodic modulation layer134 is present, the transmission characteristics of thepiezoelectric layer131 are modulated. Applying an oscillating voltage between the first andsecond electrodes130 and133, respectively, will result in mechanical excitation of thepiezoelectric layer131. Piezoelectric “33” coupling leads to expansion and contraction of thepiezoelectric layer131 perpendicular to thesidewall32 and hence results in pressure being applied to the vertical surface of thesidewall32. The two orientations of piezoelectric “31” coupling result in expansion and contraction parallel to the plane ofsidewall32 and result in shear forces in the two orientations being applied to the vertical surface ofsidewall32. One or more of these types of piezoelectric couplings may be useful for generating and receiving a desired acoustic wave mode. For example, in order to coherently couple to acoustic waves to form acoustic paths U1, U2, V1, V2, the piezoelectric transducer must be modulated by adjusting the spacing between maxima and minima of the acoustic waves, as previously discussed inFIG. 18. If noperiodic modulation layer134 is used, coherent generation of acoustic waves only occurs in a direction perpendicular tosidewall32. However, if aperiodic modulation layer134 is used to coherently couple to diagonally propagating acoustic waves, even the piezoelectric “33” coupling may be used to excite and detect horizontally polarized shear waves (e.g., ZOHPS).Touch sensors50 and100 utilizing horizontally polarized shear waves are desired in some applications as the shear waves are not sensitive to water contamination.
• Theperiodic modulation layer134 can modulate either the amplitude or phase of the coupling between the piezoelectric transducers on thesidewalls32 and thesubstrate20. Theperiodic modulation layer134 may comprise resonators, phase shifters or absorbers. Three cases will be considered: (1) the thickness of thepiezoelectric layer131 is much less than λ/2 (here λ is the wavelength of a pressure wave in thepiezoelectric layer131, not substrate20) as is preferred if theperiodic modulation layer134 is intended to modulate amplitude by resonating; (2) the thickness of thepiezoelectric layer131 is somewhat less than λ/2 as is preferred if theperiodic modulation layer134 is intended to modulate phase by shifting the resonant frequency; and (3) thepiezoelectric layer131 is approximately equal to λ/2 as is preferred if theperiodic modulation layer134 is intended to modulate amplitude via damping effects.
• FIGS. 25 and 26 illustrate an example of the first case wherein apiezoelectric mechanism206 comprises thepiezoelectric layer131 having athickness200 that is much less than a half-wavelength in accordance with an embodiment of the present invention. Once thepiezoelectric layer131 is fabricated on (fired on) thesubstrate20, it is very rigid compared to the polymer-piezo strips discussed previously. The portion of thepiezoelectric mechanism206 illustrated inFIG. 25 does not have theperiodic modulation layer134 applied, and will have a resonance frequency much higher than the operating frequency of thetouch sensor50. The expansion and contraction of thepiezoelectric layer131 will not be effectively coupled into thesubstrate20 for either acoustic wave generation or detection. The portion of thepiezoelectric mechanism206 having theperiodic modulation layer134 present is illustrated inFIG. 26. For better efficiency, theperiodic modulation layer134 can be chosen so that thepiezoelectric mechanism206 with theperiodic modulation layer134 resonates at the operating frequency of the touch sensor50 (FIG. 3), such as 5 MHz. A material with low acoustic damping, such as glass frits, may be used to form and tune the resonance of thepiezoelectric mechanism206. Alternatively, when thethickness200 is set of a half-wavelength, theperiodic modulation layer134 may be used to detune themechanism206.
• FIGS. 27 and 28 illustrate an example of the second case wherein apiezoelectric mechanism208 comprises thepiezoelectric layer131 having thethickness200 that is only somewhat thinner than a half-wavelength and phase-shifting is used to accomplish modulation in accordance with an embodiment of the present invention. Thepiezoelectric mechanism208 illustrated inFIG. 27 does not have themodulation layer134 and is designed to have a resonant frequency slightly higher than the operating frequency of thetouch sensor50. Thepiezoelectric mechanism208 inFIG. 28 comprises themodulation layer134, and can be designed to have a resonant frequency slightly lower than the operating frequency of thetouch sensor50.
• FIG. 29 illustrates the dependence of phase and amplitude for coupling through a resonance at ω_oin accordance with an embodiment of the present invention. Asolid line150 represents the normalized resonance amplitude A (axis on left side of graph). A dashedline151 represents the phase in degrees (axis on right side of graph). FromFIG. 29, it is seen that a reasonably large amplitude (greater than about ⅔ of the maximum amplitude) remains when the phase relative to that at resonance is shifted relative to ω_o, for example, by ±45° or ±60°, and hence a total phase modulation of in the range from 90° to 120° can be achieved while still retaining much of the resonant amplitude. A material with low acoustic damping may be used to form the phase-shiftingmodulation layer134.
• For the third case (not shown in the figures), themodulation layer134 functions as an absorber. Thetransducer141 without themodulation layer134 is designed to resonate at the operating frequency for strong coupling to thesubstrate20. At locations where the absorbingmodulation layer134 is applied, the acoustic resonance is highly damped. Examples of materials that can be used as absorbing modulation layers are metal (e.g., tungsten) loaded epoxies and other ultrasonic wave absorbing materials.
• FIG. 30 illustrates apiezoelectric mechanism210 designed to generate Rayleigh waves in accordance with an embodiment of the present invention. Edge transducers for Rayleigh waves, such as themechanism52 inFIGS. 4 and 8, are more efficient and generate fewer acoustic parasitic signals if themechanism52 is limited in depth to match the Rayleigh-wave depth profile, such as themechanism52 ofFIGS. 13 and 14. Therefore, inFIG. 30 the active region of thepiezoelectric layer131 is limited todepth212 to match the Rayleigh wave depth profile. This can be done by limiting thepiezoelectric layer131, thesecond electrode133, themodulation layer134, theconductive layer130, or various combinations thereof, to thedepth212. In some cases, it may be desirable to provide a layer (not shown) on the bottom (or second surface28) of thesubstrate20 that can damp all acoustic modes except Rayleigh waves. An example of such a damping layer is a rigid optical bond comprising an epoxy layer between thesubstrate20 and a device (e.g., a display).
• Although theperiodic modulation layer134 can be provided on theconductive layer133 for example by deposition, periodic modulation can also be achieved by other methods. For example, thepiezoelectric layer131 itself can be modulated by annealing selected regions in a periodic fashion to render those regions inactive (e.g., by locally heating the piezoelectric material above a phase transition, for example the Curie point for a ceramic material).
• FIG. 31 illustrates an example wherein thesubstrate20 can be periodically altered to result in modulation in accordance with an embodiment of the present invention. For example, thesubstrate20 can be periodically marked135 using a localized energy source, such as a laser beam, to form periodic structures. If thesubstrate20 is glass, a tripled Nd:YAG operating at 355 nm can be used to finely shatter glass in internal regions of thesubstrate20. The finely shattered glass can have modified acoustic properties (e.g., increased damping or scattering) and can be used to provide periodic modulation for coherent coupling to acoustic waves. In other words, an optical diffraction grating may be formed having multiple, regularly spacedmarkings135 inside thesubstrate20. In general, the need for theperiodic modulation layer134 may be eliminated by any other means that modulates the acoustic behavior of thetransducer141 on thesidewalls32. By way of example only, thepiezoelectric layer131 may be a pressure mode piezo.
• Returning toFIG. 24, thetransducer141 may be fabricating in a process in which the sequential layers (firstconductive layer130,piezoelectric layer131, second conductive layer133), are “fired-on”. That is, thelayers130,131 and133 are applied in the form of uncured materials and then thermally cured. Themodulation layer134 can be fired on as well. Silver-loaded ceramics with relatively low sintering temperatures (“silver frit”) are well known for fabricating conductive traces on glass substrates and are available in screen printable form. By way of example only, silver frit may be used for the fabrication ofconductive layers130 and133. For themodulation layer134 as shown inFIGS. 16B and 17B, any rigid material with low acoustic loss may be used, including the same material used forlayers130 and133 for manufacturing convenience. Alternatively, themodulation layer134 can be made of a thermally cured tungsten polymer ifmodulation layer134 serves as a damping layer.
• For embodiments of structures such as shown inFIG. 24 in which the layers are fired on, a suitable example of a piezoelectric material forlayer131 is a sol-gel based piezoceramic material, such as PZT and LiTaO₃particles dispersed, respectively, in Al₂O₃and PZT sol-gel solutions. Films having thickness of 50-100 μm can result from the firing of such sol-gel solutions. Other piezoceramic materials may be used, such as Sr-doped potassium sodium niobate, or lead-free piezoceramics, such as bismuth-containing piezoceramics. Such piezoelectric material may be applied by any suitable method, including screen printing or spray coating. After being applied in an uncured state, such materials forlayer134 may be cured with the application of heat. Note that the materials oflayers130,131,133, and134 may each be sequentially applied and cured, applied and cured together in the same heating cycle, or combinations in between.
• If thepiezoelectric layer131 is a fired-on piezoceramic material, it needs to be poled in order to function as a piezoelectric. Poling can be accomplished by application of a large voltage between theconductive layers130 and133, thus generating a high electric field in the material ofpiezoelectric layer131. Such poling must be done after any processing steps that will occur at temperatures exceeding the ferroelectric Curie temperature of the piezoelectric material.
• If thepiezoelectric material131 is a fired-on piezoceramic material, the substrate material must be chosen to be able to withstand the firing temperature of the fired-on piezoceramic material and any subsequent annealing temperatures. For example, Corning 1737 may be used as its annealing point is 721° C. and its softening point is 975° C., both of which exceed the firing temperature (450° C.) and annealing temperature (650° C.) of the sol-gel formulation described above comprising PZT and LiTaO₃particles dispersed in Al₂O₃and PZT sol-gel solutions, respectively.
• Thepiezoelectric transducer141 can also be fabricated independently of thesubstrate20 and applied as an assembly. The assembly can be, for example, a strip (as previously discussed) that is bonded to thesubstrate20 using an adhesive or other suitable bonding technique. The adhesive or bonding layer is preferably thin and sufficiently free of acoustic damping to minimize perturbation to the acoustic operation of thetouch sensor50. A layered assembly comprising firstconductive layer130,piezoelectric layer131, secondconductive layer133, and optionally, themodulation layer134, could for example be fabricated on a strip material comprising a glass microsheet, having thickness of 100-200 μm. The layered assembly could then be subdivided (e.g., by dicing) intomultiple transducers141 which could be bonded tomultiple substrates20.
• FIG. 32 illustrates agrating transducer400 being formed on thesubstrate20 in accordance with an embodiment of the present invention. Afirst trace406 is formed on thesecond surface28. Thefirst trace406 comprises a conductive material such as silver frit. Thefirst trace406 may be applied using screen printing, pad printing, or other deposition techniques. Afirst side410 of a pressure-mode piezoelectric element408 is applied over and interconnected with a portion of thefirst trace406. Asecond trace414 is formed on thesecond surface28 and is applied over and interconnected with aside surface418 and asecond side412 of thepiezoelectric element408. As will be discussed further below, electrical connections for exciting thepiezoelectric element408 are interconnected with each of the first andsecond traces406 and414.
• Grating elements402 are formed on thetouch surface24. Thegrating elements402 may be formed adistance404 of a wavelength of the Rayleigh wave apart by deposit or removal of material, such as by screen printing or etching, as previously discussed. Areflective array416 is also formed on thetouch surface24, and may be formed of added or removed material.
• FIG. 33 illustrates acomb transducer420 being formed on thesubstrate20 in accordance with an embodiment of the present invention. As inFIG. 32,grating elements432 are formed on thetouch surface24. Afirst trace422 is formed on thetouch surface24 and over thegrating elements432. Afirst side424 of a thicknessmode piezoelectric element426 is applied over and interconnected with a portion of thefirst trace422. Asecond trace430 is formed on thetouch surface24 and is applied over and interconnected with a side surface434 and a second side428 of thepiezoelectric element426.
• FIG. 34 illustrates aninterdigital transducer440 being formed on thesubstrate20 in accordance with an embodiment of the present invention. Afirst trace442 and asecond trace444 are formed on thetouch surface24 of thesubstrate20. The first andsecond traces442 and444 have fingers (not shown) which are interdigital with respect to each other, such as the first andsecond electrodes88 and90 ofFIG. 8. Apiezoelectric element448 is applied over and interconnected with the first andsecond traces442 and444.
• FIG. 35 illustrates atouch sensor450 having transducers452-458 formed along aperimeter486 of thetouch surface24 in accordance with an embodiment of the present invention.Reflective elements460 are formed at 45° with respect to edges462-468 and form reflective arrays within theperimeter486.
• The transducers452-458 may comprise one of thetransducers400,420 or440 ofFIGS. 32-34. First and second traces470-484 are printed on thetouch surface24 proximate theedges466 and468, and are interconnected with the appropriate transducer452-458 as illustrated. The interconnection is determined by the type of transducer being utilized. The first and second traces470-484 are interconnected with acable488 such as by soldering.
• FIG. 36 illustrates analternative transducer490 being formed on thesubstrate20 in accordance with an embodiment of the present invention. First andsecond traces492 and494 are applied on thetouch surface24. A single trace is indicated in the view ofFIG. 36. The first andsecond traces492 and494 may for interdigital electrodes as discussed inFIG. 34. Afirst side550 of apiezoelectric element498 is applied over the first andsecond traces492 and494. Aground electrode548 is applied onto thetouch surface24 and to asecond side552 and aside surface554 of thepiezoelectric element498.
• FIG. 37 illustrates atouch sensor500 having transducers502-508 formed along aperimeter544 of thetouch surface24 in accordance with an embodiment of the present invention.Reflective elements510 are formed at450 with respect to edges512-518 and form reflective arrays within theperimeter544.
• The transducers502-508 may comprise thetransducer490 ofFIG. 36. Ground, first, and second traces520-542 are printed on thetouch surface24 and interconnected with the appropriate transducer502-508. The ground, first, and second traces520-542 may be interconnected with acable546 by soldering.
• Referring to bothFIGS. 35 and 37, a controller (not shown) provides electrical signals to the transducers via the first and second electrodes and a ground via the ground electrode, if necessary. Only one transducer is active at a time. In the configurations illustrated, four transducers are used, and therefore two transducers may operate as transmit transducers and two transducers may operate as receive transducers. It should be understood that other configurations may be formed to receive signals from the touch sensor having two or three transducers which may operate as either transmit or receive, both transmit and receive, or to cover different portions or areas of thetouch surface24.
• FIG. 38 illustrates analternative touch sensor214 formed in accordance with an embodiment of the present invention. Thesidewalls32 andedges22 are clean, as previously discussed. Thesubstrate20 hastransducers160,waveguides161, andreflective arrays162 disposed on thesidewalls32. Thereflective arrays162 may be formed proximate theedges22 or intersecting theedges22. On eachsidewall32, thetransducer160,waveguide161 andreflective array162 may be referred to as amechanism171. Optionally, additional waveguides and associated arrays may be formed on thetouch surface24 of thesubstrate20. As illustrated inFIG. 38, it is possible to position thewaveguides161 andreflective arrays162 on thesidewalls32 to further reduceborder area216 needed bytouch sensor mechanisms171 for generating, directing and detecting acoustic waves. Thereflective arrays162 andwaveguides161 may be formed of grooves insubstrate20 or of protrusions of material deposited on thesidewalls32 of thesubstrate20. Thetransducer160 generates an acoustic wave that is coupled into thewaveguide161, thereby focusing the acoustic energy in the core of thewaveguide161. The acoustic energy can then be coupled into thesubstrate20 as surface acoustic waves by means of thearray162. Themechanism171 comprisingtransducer160,waveguide161, andarray162 can operate to generate acoustic waves and direct them across thetouch region24 of thetouch sensor214, or to detect acoustic waves that have traversed thetouch region24 of thetouch sensor214.
• As an acoustic wave travels along the length of thewaveguide161, energy will be lost. Inmany touch sensor214 applications, it is desired that acoustic energy received by detectors, such as themechanism171, not depend strongly on the length of the path traveled. Therefore, various acoustic signal equalization schemes may be incorporated, such as various reflective arrays designed to equalize the signal amplitude as a function of path length. These designs include variations in height or depth of the reflective elements making up reflective arrays, or variations in densities of the reflective elements.
• FIG. 39 illustrates awaveguide161 positioned to accomplish signal equalization in accordance with an embodiment of the present invention. Thetransducer160,waveguide161, andreflective array162 are shown to be disposed on thesidewall32 of thetouch sensor substrate20. Thewaveguide161 is formed having a curve along alength218 of thesidewall32, such that thewaveguide161 is positioned further from thearray162 at afirst end220 near thetransducer160 when the acoustic energy in thewaveguide161 will be the highest. Thewaveguide161 is positioned closer to, intersecting and/or on top of thearray162 at asecond end222 away from thetransducer160 when the acoustic energy in thewaveguide161 will be the lowest. By curving thewaveguide161 in such a manner, signal equalization can be achieved.
• FIG. 40 illustrates thewaveguide161 being formed to accomplish signal equalization in accordance with an embodiment of the present invention. The core of thewaveguide161 is narrowed, effectively weakening the core, as the distance from thetransducer160 is increased, or as thewaveguide161 moves from thefirst end220 to thesecond end222. As the core width is reduced, the acoustic wave becomes less confined to thewaveguide161 and spreads out, and the acoustic wave increases its overlap with thereflective array162. In this case, the spacing betweenelements163 of thereflective array162 may also be varied to account for any effect that the tapered waveguide core has on the wave velocity in the core. It should be understood that the signal equalization provided through thewaveguide161 being formed and/or positioned as illustrated inFIGS. 39 and 40 may be applied equally well to the case in which thewaveguide161 is disposed on thetouch surface24.
• FIG. 41 illustrates another embodiment of atouch sensor224 in accordance with an embodiment of the present invention. Asubstrate20 havingclean sidewalls32 is provided (seeFIG. 2). Astrip180 capable of propagating acoustic waves along its axis is provided. Thestrip180 is a waveguide, having a function similar to thewaveguide161 ofFIGS. 38-40. The acoustic wave propagating along thestrip180 may be an extensional wave, a flexural wave, or any other type of acoustic wave. Thestrip180 is disposed on asidewall32 of theglass substrate20. Thestrip180 is bonded to thesidewall32 with abonding layer186 comprisingbonding elements187. On one end181 of thestrip180 is mounted a pressure modepiezoelectric element183, and on theopposite end182 of thestrip180, anenergy dump region184 can optionally be provided. Theenergy dump region184 can be applied to one end of thestrip180 to suppress reflections. Theenergy dump region184 can comprise any suitable material, for example, tungsten-loaded epoxies, which can be tuned to match the acoustic impedance of thesubstrate20. Acoustic waves generated in thestrip180 are coupled to acoustic waves in thesubstrate20 which are sensitive to touches on thesubstrate surface24.
• Thestrip180 can comprise any material that can propagate acoustic waves, e.g., metal or glass. Preferably, the coefficient of thermal expansion (CTE) of the strip material is close to that of thesubstrate20. In some applications, it may be advantageous for the height (measured along the height of the sidewall32) of thestrip180 to be approximately equal to the glass substrate thickness. The thickness of the strip180 (measured perpendicular to its height) is preferably small so that it does not extend a large distance from thesubstrate20, thereby keeping the outer edge size of thetouch sensor224 minimized. Examples of strip materials that can be used include a glass rod and a metal strip having CTE close to that of glass (e.g., a nickel alloy such as Invar™ or related materials). Examples of suitable cross-sections of the strip materials are a 3 mm×1 mm rectangle and a ½ mm×½ mm square.
• Electrical excitation of thepiezoelectric element183 may result, for example, in a longitudinal wave propagating along the length of thestrip180. Because of boundary conditions imposed by the cross-section of thestrip180, the wave in thestrip180 is not a pure pressure wave, but might be better described as an extensional wave, dialational wave or lowest-order symmetric Lamb wave. As a wave with a longitudinal component propagates, material in thestrip180 has a component of motion parallel to the direction of the wave propagation (i.e., along the length of the strip180).
• Thebonding layer186 provides a mechanical bond and the spacing of the periodically spacedbonding elements187 determines the scattering angle from the wave generated in thestrip180 to the acoustic wave launched into thesubstrate20. Thebonding elements187 are formed as periodic structures similar to a reflective array. For example if thetouch sensor224 is rectangular, and it is desired to scatter at 90° to thesidewall32, then the spacing of thebonding elements187 should be equal to the wavelength of the acoustic wave in thestrip180. Scattering at 90° is indicated inFIG. 41 by thearrow188. As one example of a coupling mechanism,bonding elements187 may transfer shear forces thus coupling longitudinal motion of the wave in thestrip180 to transverse motion of a shear wave in thesubstrate20 as is indicated by thearrows189 inFIG. 41. The compressive stiffness ofbonding elements187 can also couple transverse motion of a strip wave to the longitudinal component of motion of a touch sensing wave (e.g. Rayleigh wave) in substrate20 (this coupling mode is not shown in the figure). Thestrip180 can also function to receive acoustic waves from thesubstrate20.
• FIG. 42 illustrates atouch sensor226 incorporating thestrips180 in accordance with an embodiment of the present invention. Thestrips180 are indicated asstrips228 and230 for clarity. Afirst strip228 havingpiezoelectric element232 is disposed along afirst sidewall234 of thesubstrate20, and asecond strip230 havingpiezoelectric element236 is disposed along a secondadjacent sidewall238 of thesubstrate20. As indicated byarrow190, the shear waves generated bypiezoelectric element232 and directed intosubstrate20 by thestrip228 can reflect offsidewall240 and be directed bystrip228 to be detected bypiezoelectric element232. As indicated byarrow191, shear waves generated bypiezoelectric element236 and directed bystrip230 intosubstrate20 can reflect offsidewall242 and be directed bystrip230 to be detected byelement236. Electronics (not shown) connected topiezoelectric elements232 and236 can be used to time-multiplex signals in order to coordinate between transmitting and receiving modes.
• Alternately, a touch sensor may include strips mounted on all sidewalls32 (not shown). For example, for arectangular substrate20, fourstrips180 can used, wherein two of thestrips180 operate in transmission mode and two of thestrips180 operate in receiving mode.
• Ifstrips180 mounted to thesidewalls32 of thesubstrate20 are designed to excite Rayleigh waves in thesubstrate20, thebonding elements187 should be bonded on thesidewall32 within about one Rayleigh wavelength of thetouch surface20 in order to effectively couple to Rayleigh waves as shown inFIGS. 22 and 23. The depth dimension ofstrip180 may or may not match the depth dimension of thebonding elements187.
• The strength of coupling between thestrip180 andsubstrate20 can be affected by one or more of the stiffness, thickness or bonding area of thebonding elements187. Preferably the amplitude of the acoustic wave coupled into thesubstrate20 is independent of the point along asidewall32 at which it is coupled in. Any parameter affecting the coupling between thestrip180 and thesubstrate20 can be used to equalize acoustic signal amplitude as a function of distance along a length of thesubstrate20.
• FIG. 41 illustrates the case wherebonding layer186 alternates between the presence of bonding material (bonding elements187) and the absence of bonding material. This provides a spatial modulation of the coupling strength between thestrip180 andsubstrate20. Alternate means exist to provide the desired spatial modulation of coupling, for example a bonding layer with no air gaps, but for which the mechanical properties (such as stiffness) of the bonding material are modulated. It should be understood that the strip181 andbonding elements187 may be formed separate from thesubstrate20 and then attached as an assembly.
• FIG. 43 illustrates atouch sensor560 havingtransducers562 formed on thesidewalls32 of thesubstrate20 in accordance with an embodiment of the present invention. When excited, thetransducers562 generates an edge wave which propagates along theedge22 and is reflected across thetouch surface24 by thereflective array564. Such touch sensors are described in U.S. Provisional Patent Application Ser. No. 60/562,461, attorney docket number ELG064-US1, which is incorporated herein by reference. Thetransducers562 may include piezoelectric material printed on thesidewalls32 using the screen printing and other techniques described previously. Alternatively, thetransducers562 may include piezoelectric material formed separately and bonded to thesidewalls32.
• For any of the embodiments for touch sensors described herein, the touch sensor may be connected to a controller by means of an electrical interconnect. Any suitable interconnect may be used, for example, a cable harness. Alternatively, the touch sensor may be integrated directly into a touch sensor system, for example, the touch sensor may be integrated with a display to make a touchscreen. Optionally, screen printing may be accomplished on the surface of a substrate used in a vacuum fluorescent display, such as an instrument panel. By way of example, the substrate may form an external layer of a display device, such as a vacuum fluorescent display.
• It will be understood that the above-described arrangements of apparatus are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the claims.

Claims (20)

1. A touch sensor comprising:

a substrate capable of propagating acoustic waves, the substrate including a first surface having a touch sensitive region; and

a transducer formed on the substrate, the transducer comprising a piezoelectric element being thermally cured after being formed on the substrate, the transducer being configured for at least one of generating acoustic waves and detecting acoustic waves.

2. The touch sensor ofclaim 1, wherein the piezoelectric element is formed on the substrate by one of screen printing and pad printing.

3. The touch sensor ofclaim 1, the substrate further comprising a second surface parallel to the first surface, the transducer further comprising grating elements formed on the first surface, the piezoelectric element being formed on the second surface opposite the grating elements.

4. The touch sensor ofclaim 1, the transducer further comprising grating elements formed on the first surface, the piezoelectric element being formed over the grating elements.

5. The touch sensor ofclaim 1, the transducer further comprising:

a first conductive layer formed on the substrate;

a second layer formed over the first conductive layer, the second layer comprising the piezoelectric element; and

a third conductive layer being formed over the second layer, the first and third conductive layers being interconnected with first and second electrical connections, respectively.

6. The touch sensor ofclaim 1, the transducer further comprising:

a first layer formed on the substrate, the first layer being interconnected with a ground connection;

a second layer formed over the first layer, the second layer comprising the piezoelectric element; and

a third conductive layer formed over the second layer, the third conductive layer comprising first and second electrodes, the first and second electrodes being interconnected with first and second electrical connections.

7. The touch sensor ofclaim 1, wherein the substrate being an external layer of a display device.

8. The touch sensor ofclaim 1, the transducer further comprising:

a first conductive layer formed on the substrate;

a second layer formed over the first conductive layer, the second layer comprising the piezoelectric element;

a third conductive layer formed over the second layer, the first and third conductive layers being interconnected with electrical connections; and

a fourth modulation layer comprising periodically applied material being formed over the third conductive layer.

9. A touch sensor comprising:

a substrate capable of propagating acoustic waves, the substrate including a first surface having a touch sensitive region; and

a transducer configured for at least one of generating acoustic waves and receiving acoustic waves, the transducer including a strip comprising a piezoelectric material, the strip being attached to the substrate.

10. The touch sensor ofclaim 9, the piezoelectric material comprising a polymer piezo material.

11. The touch sensor ofclaim 9, the strip further comprising at least two layers of conductive material, the piezoelectric material being formed between two layers of the at least two layers of conductive material.

12. The touch sensor ofclaim 9, the first surface further comprising a touch area having a perimeter, the substrate further comprising a second surface being parallel to the first surface, the touch sensor further comprising a grating transducer formed on the first surface within the perimeter, the strip being attached to the second surface opposite the grating transducer.

13. A method for forming a transducer on a touch sensor substrate, the substrate including a first surface having a touch sensitive region, the method comprising:

applying a conductive layer to the substrate;

applying a piezoelectric layer to the substrate, the piezoelectric layer covering at least a portion of the first conductive layer; and

thermally curing the piezoelectric layer.

14. The method ofclaim 13, further comprising applying a second conductive layer to the substrate, the second conductive layer covering at least a portion of the piezoelectric layer.

15. The method ofclaim 13, further comprising:

applying a second conductive layer to the substrate; and

applying first and second voltages to the conductive layer and the second conductive layer, respectively, to pole the piezoelectric layer.

16. The method ofclaim 13, wherein the applying a piezoelectric layer step further comprising screen printing the piezoelectric material.

17. The method ofclaim 13, further comprising forming grating elements on the substrate by removing material from the substrate, the applying steps further comprising applying the conductive layer and the piezoelectric layer over the grating elements.

18. The method ofclaim 13, further comprising:

forming conductive traces on the substrate; and

interconnecting the conductive traces with the conductive layer to provide electrical signals to the conductive layer.

19. The method ofclaim 13, wherein the piezoelectric material comprising a sol-gel material.

20. The method ofclaim 13, wherein the substrate further comprising a sidewall intersecting the first surface at an edge, the sidewall being substantially perpendicular to the first surface.

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