PATENT DOCUMENT

Publication Number: US-10955978-B2
Application Number: US-201916588845-A
Country: US
Kind Code: B2

Title: Touch sensor panel with top and/or bottom shielding

Abstract:
A touch sensor panel is disclosed. The touch sensor panel can include a first substrate layer; a first electrode layer comprising one or more of a touch electrode and a trace configured to couple the touch electrode to sense circuitry, the first electrode layer located on a first side of the first substrate layer; a second electrode layer located on the first side of the first substrate layer; a passivation layer disposed in between the first electrode layer and the second electrode layer; and a third electrode layer located on a second side of the first substrate layer, different from the first side of the first substrate layer. The first electrode layer can be comprised of a first conductive material, the second electrode layer can be comprised of a second conductive material, and the third electrode layer can be comprised of a third conductive material. The touch sensor panel may not include a second substrate layer between the first substrate layer and the second electrode layer.

Claims:
The invention claimed is: 
     
       1. A touch sensor panel stackup comprising:
 a substrate; 
 a first electrode layer formed from a first conductive material and including one or more touch electrodes and one or more traces configured to couple the one or more touch electrodes to sense circuitry, the first electrode layer located on a first side of the substrate; 
 a second electrode layer formed from a second conductive material and located on a second side of the substrate, different from the first side; 
 a polarizer formed on the first side of the substrate; and 
 a third electrode layer formed from a third conductive material and located on the first side of the substrate; 
 wherein the second electrode layer is configured to shield the first electrode layer from first noise, and the third electrode layer is configured to shield the first electrode layer from second noise. 
 
     
     
       2. The touch sensor panel stackup of  claim 1 , wherein the third electrode layer is formed on the polarizer. 
     
     
       3. The touch sensor panel stackup of  claim 1 , wherein a location of the second electrode layer is limited to keep the one or more touch electrodes substantially unshielded from one or more objects proximate to the second side of the substrate. 
     
     
       4. The touch sensor panel stackup of  claim 1 , wherein the second electrode layer is configured to receive a guard signal. 
     
     
       5. The touch sensor panel stackup of  claim 1 , further comprising a passivation layer disposed between the first electrode layer and the polarizer. 
     
     
       6. The touch sensor panel stackup of  claim 5 , wherein the substrate, first and second electrode layers, and the passivation layer are laminated to the polarizer and the third electrode layer. 
     
     
       7. The touch sensor panel stackup of  claim 1 , further comprising a passivation layer disposed over the second electrode layer. 
     
     
       8. The touch sensor panel stackup of  claim 1 , wherein the third electrode layer comprises nanowire materials. 
     
     
       9. The touch sensor panel stackup of  claim 1 , wherein the third electrode layer is configured to receive a guard signal. 
     
     
       10. The touch sensor panel stackup of  claim 1 , wherein the polarizer is disposed between the first electrode layer and the third electrode layer. 
     
     
       11. The touch sensor panel stackup of  claim 1 , wherein the third electrode layer is disposed between the first electrode layer and the polarizer. 
     
     
       12. The touch sensor panel stackup of  claim 11 , further comprising at least one conductive line electrically coupled to the third electrode layer and configured to lower an effective sheet resistance of the third electrode layer. 
     
     
       13. The touch sensor panel stackup of  claim 12 , wherein the at least one conductive line is disposed on a surface of the third electrode layer. 
     
     
       14. The touch sensor panel stackup of  claim 12 , wherein the at least one conductive line is embedded in the third electrode layer. 
     
     
       15. The touch sensor panel stackup of  claim 11 , wherein the polarizer is incorporated into a display. 
     
     
       16. A method for reducing an effect of noise on a touch sensor panel stackup, comprising:
 supporting first shielding on a front side of a substrate for shielding one or more traces formed on a back side of the substrate from first noise, the one or more traces configured to couple one or more touch electrodes to sense circuitry; and 
 supporting second shielding on a polarizer located on the back side of the substrate for shielding the one or more traces from second noise. 
 
     
     
       17. The method of  claim 16 , further comprising locating the first shielding to keep the one or more touch electrodes substantially unshielded from one or more objects proximate to the front side of the substrate. 
     
     
       18. The method of  claim 16 , further comprising driving the first shielding with a guard signal. 
     
     
       19. The method of  claim 16 , further comprising disposing the polarizer between the one or more touch electrodes and the second shielding. 
     
     
       20. The method of  claim 16 , further comprising disposing the second shielding between the one or more touch electrodes and the polarizer.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 15/713,361, filed Sep. 22, 2017 and published on Mar. 29, 2018 as U.S. Publication No. 2018-0088717, which claims the benefit under 35 USC 119(e) of U.S. patent application Ser. No. 62/399,182, filed Sep. 23, 2016, the contents of which are incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to touch sensor panels, and more particularly to touch sensor panels that are shielded from external noise. 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a clear panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD) that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus or other object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the computing system can then interpret the touch in accordance with the display appearing at the time of the touch, and thereafter can perform one or more actions based on the touch. In the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface. 
     Some capacitive touch sensor panels can be formed by a matrix of plates (e.g., touch electrodes) made of conductive materials (e.g., Indium Tin Oxide (ITO)) and coupled to routing traces made of a conductive material (e.g., copper). In some examples, plates and routing traces may be formed of the same conductive material. In some examples, a routing trace may comprise a first portion made of a first conductive material (e.g., ITO), and a second portion made of a second conductive material (e.g., copper), which in some examples may be overlaid onto the first conductive material. For instance, a first portion of a routing trace overlapping a viewable area of a display may be made of a transparent conductive material (e.g., ITO), such that the viewable area is visible through the first portion, while a second portion of the routing trace extending outside the viewable area may be made of an opaque conductive material (e.g., copper). 
     Some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). However, touch electrodes and routing traces can be susceptible to noise from above and/or below the touch sensor panel. For example, environmental noise, including capacitive coupling between objects above a touch sensor panel, such as human fingers, and routing traces, may interfere with proper operation of the touch sensor panel. Similarly, the display circuitry in a touch screen, which in some examples can be positioned below a touch sensor panel, may present noise that interferes with the ability of the touch sensor panel to detect changes in capacitance. It is desirable to shield touch electrodes and routing traces from noise from above and/or below the touch sensor panel. Some touch sensor panels accomplish this with a laminate including two layers of a substrate material (e.g., cyclo olefin polymer), with conductive materials applied to each of the two substrate layers. Fabricating a touch sensor panel using such a two-substrate structure can be costly and complex. Additionally, each substrate contributes to the thickness of the touch sensor panel. It is desirable to reduce the cost and complexity of fabricating touch sensor panels, and also to reduce the thickness of touch sensor panels, by eliminating the use of a substrate layer, or by substituting a substrate layer integrated in a display for a standalone substrate layer. 
     SUMMARY OF THE DISCLOSURE 
     Some examples of the disclosure are directed to reducing the cost and thickness of a touch sensor panel by eliminating a substrate layer, while retaining the ability to shield the touch sensor panel from noise sources. Some examples of the disclosure are directed to reducing the cost and thickness of a touch sensor panel by using a polarizer, such as may be integrated in a display, instead of a standalone substrate layer, while retaining the ability to shield the touch sensor panel from noise sources. It should be understood that, while the disclosure makes reference to touch screens by way of example, the disclosure is not limited to touch screens, but instead is also applicable to touch sensor panels that may or may not be integrated with a display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1E  illustrate an example mobile telephone, an example media player, an example personal computer, an example tablet computer, and an example wearable device that can each include an exemplary touch screen according to examples of the disclosure. 
         FIG. 2  is a block diagram of an example computing system that illustrates one implementation of an example self-capacitance touch screen according to examples of the disclosure. 
         FIG. 3A  illustrates an exemplary touch sensor circuit corresponding to a self-capacitance touch node electrode and sensing circuit according to examples of the disclosure. 
         FIG. 3B  illustrates an exemplary touch sensor circuit corresponding to a mutual-capacitance drive and sense line and sensing circuit according to examples of the disclosure. 
         FIG. 4A  illustrates an exemplary touch sensor panel with touch electrodes arranged in rows and columns according to examples of the disclosure. 
         FIG. 4B  illustrates an exemplary touch sensor panel with touch node electrodes arranged in a pixelated touch node electrode configuration according to examples of the disclosure. 
         FIG. 5A  illustrates a top view of an exemplary touch sensor panel according to examples of the disclosure. 
         FIG. 5B  illustrates a detail of a top view of an exemplary touch sensor panel according to examples of the disclosure. 
         FIG. 6  illustrates example layers of an exemplary touch sensor panel with two substrate layers, a touch electrode layer disposed between the two substrate layers, a top shield electrode layer, and a bottom shield electrode layer, according to examples of the disclosure. 
         FIGS. 7A-7C, 7D-1, 7D-2 and 7D-3  illustrate exemplary structures and an exemplary process for forming a touch sensor panel with a single substrate layer, a touch electrode layer disposed above the substrate layer, a top shield electrode layer, and a bottom shield electrode layer, according to examples of the disclosure. 
         FIGS. 8A-8C, 8D-1, 8D-2, 8D-3, 8E, and 8F  illustrate exemplary structures and an exemplary process for forming a touch sensor panel with a single substrate layer, a touch electrode layer disposed below the substrate layer, a top shield electrode layer, and a bottom shield electrode layer, according to examples of the disclosure. 
         FIGS. 9A-9D, 9E-1, 9E-2 and 9E-3  illustrate exemplary structures and an exemplary process for forming a touch sensor panel with a single standalone substrate layer, a touch electrode layer disposed below the substrate layer, a top shield electrode layer, a bottom shield electrode layer, and a polarizer, according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples. 
     Some capacitive touch sensor panels can be formed by a matrix of plates (e.g., touch electrodes) made of conductive materials (e.g., Indium Tin Oxide (ITO)) and coupled to routing traces made of a conductive material (e.g., copper). In some examples, plates and routing traces may be formed of the same conductive material. In some examples, a routing trace may comprise a first portion made of a first conductive material (e.g., ITO), and a second portion made of a second conductive material (e.g., copper), which in some examples may be overlaid onto the first conductive material. For instance, a first portion of a routing trace overlapping a viewable area may be made of a transparent conductive material (e.g., ITO) such that the viewable area is visible through the first portion, while a second portion of the routing trace extending outside the viewable area may be made of an opaque conductive material (e.g., copper). 
     Some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., the stacked material layers forming the display pixels). However, touch electrodes and routing traces can be susceptible to noise from above and/or below the touch sensor panel. For example, environmental noise, including capacitive coupling between objects above a touch sensor panel, such as human fingers, and routing traces, may interfere with proper operation of the touch sensor panel. Similarly, the display circuitry in a touch screen, which in some examples can be positioned below a touch sensor panel, may present noise that interferes with the ability of the touch sensor panel to detect changes in capacitance. It is desirable to shield touch electrodes and routing traces from noise from above and/or below the touch sensor panel. Some touch sensor panels accomplish this by employing a stackup structure comprising three electrode layers: for example, such stackup structures may comprise a first substrate layer (e.g., a layer of cyclo olefin polymer) between a first and second electrode layer, and a second substrate layer between the second electrode layer and a third electrode layer. Fabricating a touch sensor panel using such a two-substrate structure can be costly and complex. Additionally, each substrate layer contributes to the thickness of the touch sensor panel. It is desirable to reduce the cost and complexity of fabricating touch sensor panels, such as three-electrode-layer touch sensor panels, and also to reduce the thickness of such panels, by eliminating the use of a substrate layer, or by substituting a substrate layer integrated in a display for a standalone substrate layer. 
     As described herein, the examples of the disclosure relate to touch sensor panels featuring three-electrode-layer stackups, for example in which each electrode layer comprises one or more electrodes in a display region of the touch panel. Some examples of the disclosure are directed to reducing the cost and thickness of such touch sensor panels by eliminating a substrate layer from conventional panels, while retaining the ability to shield the touch sensor panel from noise sources. For instance, as described in greater detail below, some examples of the disclosure are directed to reducing the cost and thickness of a touch sensor panel by replacing a conventional standalone substrate layer (e.g., between a first and second electrode layer) with a polarizer, such as may be integrated in a display, while retaining the ability to shield the touch sensor panel from noise sources. It should be understood that, while the disclosure makes reference to touch screens by way of example, the disclosure is not limited to touch screens, but instead is also applicable to touch sensor panels that may or may not be integrated with a display. 
     In the examples described herein, components of a touch sensor panel can be made from various materials. For instance, some examples of the disclosure make use of nanowire materials. Nanowire materials can be composed of networks of randomly distributed metal nanowires (e.g., silver or copper) suspended in a suitable carrier or solution. Compared to some conductive materials, such as ITO, nanowire materials can exhibit better mechanical flexibility and lower sheet resistance. In some examples, the fabrication process for creating nanowire materials can be relatively cost-effective in comparison to other materials. It should be understood that, where the disclosure makes reference to nanowire materials, the disclosure is not limited to nanowire materials comprised of any particular metal (e.g., silver or copper) or combination of metals. 
     Similarly, some examples of the disclosure make use of metal mesh materials. Metal mesh materials can be composed of micro- or nano-grids with periodic or non-periodic metal lines (e.g., Cu, Ni, Al, Au, etc.). Metal meshes can exhibit good mechanical flexibility, and low sheet resistance. Specifically, because the thicknesses of these metal lines can be much greater than that of some metal films (e.g., ITO films), the conductivity of metal mesh materials can be close to that of their bulk material counterparts, which can be significantly higher than that of metal films (e.g., ITO films). 
       FIGS. 1A-1E  illustrate example systems in which a touch screen according to examples of the disclosure may be implemented.  FIG. 1A  illustrates an example mobile telephone  136  that includes a touch screen  124 .  FIG. 1B  illustrates an example digital media player  140  that includes a touch screen  126 .  FIG. 1C  illustrates an example personal computer  144  that includes a touch screen  128 .  FIG. 1D  illustrates an example tablet computer  148  that includes a touch screen  130 .  FIG. 1E  illustrates an example wearable device  152  that includes a touch screen  132 . It is understood that the above touch screens can be implemented in other devices as well, including in wearable devices. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130 , and  132  can be based on self-capacitance. A self-capacitance-based touch system can include a matrix of small, individual plates of conductive material that can be referred to as touch node electrodes (as described below with reference to touch screen  220  in  FIG. 2 ). For example, a touch screen can include a plurality of individual touch node electrodes, each touch node electrode identifying or representing a unique location on the touch screen at which touch or proximity (i.e., a touch or proximity event) is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch screen/panel. Such a touch screen can be referred to as a pixelated self-capacitance touch screen, though it is understood that in some examples, the touch node electrodes on the touch screen can be used to perform scans other than self-capacitance scans on the touch screen (e.g., mutual capacitance scans). During operation, a touch node electrode can be stimulated with an AC waveform, and the self-capacitance to ground of the touch node electrode can be measured. As an object approaches the touch node electrode, the self-capacitance to ground of the touch node electrode can change. This change in the self-capacitance of the touch node electrode can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. In some examples, the touch node electrodes of a self-capacitance-based touch system can be formed from rows and columns of conductive material, and changes in the self-capacitance to ground of the rows and columns can be detected, similar to above. In some examples, a touch screen can be multi-touch, single touch, projection scan, full-imaging multi-touch, capacitive touch, etc. 
     In some examples, touch screens  124 ,  126 ,  128 ,  130 , and  132  can be based on mutual capacitance. A mutual-capacitance-based touch system can include drive and sense lines that may cross over each other on different layers, or that may be adjacent to each other on the same layer. The crossing or adjacent locations can be referred to as touch nodes. During operation, the drive line can be stimulated with an AC waveform and the mutual capacitance of the touch node can be measured. As an object approaches the touch node, the mutual capacitance of the touch node can change. This change in the mutual capacitance of the touch node can be detected and measured by the touch sensing system to determine the positions of multiple objects when they touch, or come in proximity to, the touch screen. 
       FIG. 2  is a block diagram of an example computing system  200  that illustrates one implementation of an example self-capacitance touch screen  220  according to examples of the disclosure. It is understood that computing system  200  can instead include a mutual capacitance touch screen, as described above, though the examples of the disclosure will be described assuming a self-capacitance touch screen is provided. Computing system  200  can be included in, for example, mobile telephone  136 , digital media player  140 , personal computer  144 , tablet computer  148 , or any mobile or non-mobile computing device that includes a touch screen, including a wearable device. Computing system  200  can include a touch sensing system including one or more touch processors  202 , peripherals  204 , a touch controller  206 , and touch sensing circuitry (described in more detail below). Peripherals  204  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  206  can include, but is not limited to, one or more sense channels  208  and channel scan logic  210 . Channel scan logic  210  can access RAM  212 , autonomously read data from sense channels  208  and provide control for the sense channels. In addition, channel scan logic  210  can control sense channels  208  to generate stimulation signals at various frequencies and phases that can be selectively applied to the touch nodes of touch screen  220 , as described in more detail below. In some examples, touch controller  206 , touch processor  202  and peripherals  204  can be integrated into a single application specific integrated circuit (ASIC), and in some examples can be integrated with touch screen  220  itself. 
     Touch screen  220  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of electrically isolated touch node electrodes  222  (e.g., a pixelated self-capacitance touch screen). Touch node electrodes  222  can be coupled to sense channels  208  in touch controller  206 , can be driven by stimulation signals from the sense channels through drive/sense interface  225 , and can be sensed by the sense channels through the drive/sense interface as well, as described above. Labeling the conductive plates used to detect touch (i.e., touch node electrodes  222 ) as “touch node” electrodes can be particularly useful when touch screen  220  is viewed as capturing an “image” of touch (e.g., a “touch image”). In other words, after touch controller  206  has determined an amount of touch detected at each touch node electrode  222  in touch screen  220 , the pattern of touch node electrodes in the touch screen at which a touch occurred can be thought of as a touch image (e.g., a pattern of fingers touching the touch screen). 
     Computing system  200  can also include a host processor  228  for receiving outputs from touch processor  202  and performing actions based on the outputs. For example, host processor  228  can be connected to program storage  232  and a display controller, such as an LCD driver  234 . The LCD driver  234  can provide voltages on select (e.g., gate) lines to each pixel transistor and can provide data signals along data lines to these same transistors to control the pixel display image as described in more detail below. Host processor  228  can use LCD driver  234  to generate a display image on touch screen  220 , such as a display image of a user interface (UI), and can use touch processor  202  and touch controller  206  to detect a touch on or near touch screen  220 . The touch input can be used by computer programs stored in program storage  232  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  228  can also perform additional functions that may not be related to touch processing. 
     Note that one or more of the functions described herein, including the configuration of switches, can be performed by firmware stored in memory (e.g., one of the peripherals  204  in  FIG. 2 ) and executed by touch processor  202 , or stored in program storage  232  and executed by host processor  228 . The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding signals) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks, and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation medium. 
       FIG. 3A  illustrates an exemplary touch sensor circuit  300  corresponding to a self-capacitance touch node electrode  302  and sensing circuit  314  according to examples of the disclosure. Touch node electrode  302  can correspond to touch node electrode  222 . Touch node electrode  302  can have an inherent self-capacitance to ground associated with it, and also an additional self-capacitance to ground that is formed when an object, such as finger  305 , is in proximity to or touching the electrode. The total self-capacitance to ground of touch node electrode  302  can be illustrated as capacitance  304 . Touch node electrode  302  can be coupled to sensing circuit  314 . Sensing circuit  314  can include an operational amplifier  308 , feedback resistor  312  and feedback capacitor  310 , although other configurations can be employed. For example, feedback resistor  312  can be replaced by a switched capacitor resistor in order to minimize a parasitic capacitance effect that can be caused by a variable feedback resistor. Touch node electrode  302  can be coupled to the inverting input (−) of operational amplifier  308 . An AC voltage source  306  (Vac) can be coupled to the non-inverting input (+) of operational amplifier  308 . Touch sensor circuit  300  can be configured to sense changes in the total self-capacitance  304  of the touch node electrode  302  induced by a finger or object either touching or in proximity to the touch sensor panel. Output  320  can be used by a processor to determine the presence of a proximity or touch event, or the output can be inputted into a discrete logic network to determine the presence of a proximity or touch event. 
       FIG. 3B  illustrates an exemplary touch sensor circuit  350  corresponding to a mutual-capacitance drive  322  and sense  326  line and sensing circuit  314  according to examples of the disclosure. Drive line  322  can be stimulated by stimulation signal  306  (e.g., an AC voltage signal). Stimulation signal  306  can be capacitively coupled to sense line  326  through mutual capacitance  324  between drive line  322  and the sense line. When a finger or object  305  approaches the touch node created by the intersection of drive line  322  and sense line  326 , mutual capacitance  324  can be altered. This change in mutual capacitance  324  can be detected to indicate a touch or proximity event at the touch node, as described previously and below. The sense signal coupled onto sense line  326  can be received by sensing circuit  314 . Sensing circuit  314  can include operational amplifier  308  and at least one of a feedback resistor  312  and a feedback capacitor  310 .  FIG. 3B  illustrates a general case in which both resistive and capacitive feedback elements are utilized. The sense signal (referred to as Vin) can be inputted into the inverting input of operational amplifier  308 , and the non-inverting input of the operational amplifier can be coupled to a reference voltage Vref. Operational amplifier  308  can drive its output to voltage Vo to keep Vin substantially equal to Vref, and can therefore maintain Vin constant or virtually grounded. A person of skill in the art would understand that in this context, equal can include deviations of up to 15%. Therefore, the gain of sensing circuit  314  can be mostly a function of the ratio of mutual capacitance  324  and the feedback impedance, comprised of resistor  312  and/or capacitor  310 . The output of sensing circuit  314  Vo can be filtered and heterodyned or homodyned by being fed into multiplier  328 , where Vo can be multiplied with local oscillator  330  to produce Vdetect. Vdetect can be inputted into filter  332 . One skilled in the art will recognize that the placement of filter  332  can be varied; thus, the filter can be placed after multiplier  328 , as illustrated, or two filters can be employed: one before the multiplier and one after the multiplier. In some examples, there can be no filter at all. The direct current (DC) portion of Vdetect can be used to determine if a touch or proximity event has occurred. 
     Referring back to  FIG. 2 , in some examples, touch screen  220  can be an integrated touch screen in which touch sensing circuit elements of the touch sensing system can be integrated into the display pixel stackups of a display. The circuit elements in touch screen  220  can include, for example, elements that can exist in LCD or other displays, such as one or more pixel transistors (e.g., thin film transistors (TFTs)), gate lines, data lines, pixel electrodes and common electrodes. In a given display pixel, a voltage between a pixel electrode and a common electrode can control a luminance of the display pixel. The voltage on the pixel electrode can be supplied by a data line through a pixel transistor, which can be controlled by a gate line. It is noted that circuit elements are not limited to whole circuit components, such as a whole capacitor, a whole transistor, etc., but can include portions of circuitry, such as only one of the two plates of a parallel plate capacitor. 
       FIG. 4A  illustrates touch sensor panel  400  with touch electrodes  404  and  406  arranged in rows and columns according to examples of the disclosure. Specifically, touch sensor panel  400  can include a plurality of touch electrodes  404  disposed as rows, and a plurality of touch electrodes  406  disposed as columns. Touch electrodes  404  and/or touch electrodes  406  may be comprised of a conductive material (e.g., ITO). Touch electrodes  404  and touch electrodes  406  can be on the same or different material layers on touch sensor panel  400 , and can intersect with each other, as illustrated in  FIG. 4A . In some examples, touch sensor panel  400  can sense the self-capacitance of touch electrodes  404  and  406  to detect touch and/or proximity activity on touch sensor panel  400 , and in some examples, touch sensor panel  400  can sense the mutual capacitance between touch electrodes  404  and  406  to detect touch and/or proximity activity on touch sensor panel  400 . 
       FIG. 4B  illustrates touch sensor panel  402  with touch node electrodes  408  arranged in a pixelated touch node electrode configuration according to examples of the disclosure. Specifically, touch sensor panel  402  can include a plurality of individual touch node electrodes  408 , each touch node electrode identifying or representing a unique location on the touch sensor panel at which touch or proximity (i.e., a touch or proximity event) is to be sensed, and each touch node electrode being electrically isolated from the other touch node electrodes in the touch sensor panel, as previously described. Touch electrodes  404  and/or touch electrodes  406  may be comprised of a conductive material (e.g., ITO). Touch node electrodes  408  can be on the same or different material layers on touch sensor panel  402 . In some examples, touch sensor panel  402  can sense the self-capacitance of touch node electrodes  408  to detect touch and/or proximity activity on touch sensor panel  402 , and in some examples, touch sensor panel  402  can sense the mutual capacitance between touch node electrodes  408  to detect touch and/or proximity activity on touch sensor panel  402 . 
     Touch electrodes, such as touch electrodes  404  and  406  in  FIG. 4A  and touch node electrodes  408  in  FIG. 4B , can be susceptible to external noise that can compromise the ability of a touch sensor panel to detect touch and/or proximity activity. Additionally, touch electrodes may be coupled to routing traces that are susceptible to external noise. Such external noise can originate from below the touch sensor panel (for example, from a display in a touch screen), and/or from above the touch sensor panel (for example, from capacitive coupling between a routing trace and the environment external to the touch sensor). Routing traces, in particular, are susceptible to capacitive coupling caused by contact between a user&#39;s fingers and the routing traces, which can manifest as a false touch reading (e.g., noise) detected at touch electrode(s) corresponding to one or more of the routing traces. It is desirable to provide shielding from such noise sources above the touch sensor panel (“top shielding”) and/or below the touch sensor panel (“bottom shielding”). 
       FIGS. 5A and 5B  illustrate a pixelated touch sensor panel  500  according to examples of the disclosure.  FIG. 5A  shows a top view of touch sensor panel  500 . Referring to  FIG. 5A , pixelated touch sensor panel  500  can include touch node electrodes  501 ,  503 ,  505 , and  507  (e.g., as described with reference to  FIG. 4B ) and routing traces  502 ,  504 ,  506 , and  508 . In some examples, each routing trace may be coupled to one touch node electrode. That is, touch node electrode  501  can be coupled to sense circuitry (e.g., sense channels  208  in  FIG. 2 ) via trace  502 ; touch node electrode  503  can be coupled to sense circuitry via trace  504 ; touch node electrode  505  can be coupled to sense circuitry via trace  506 ; and touch node electrode  507  can be coupled to sense circuitry via trace  508 . (To simplify explanation, other touch node electrodes of touch sensor panel  500  are not shown coupled to routing traces in the figure, though it is understood that they may be.) In  FIG. 5A , cross-section A-A′ corresponds to an exemplary cross-section of touch sensor panel  500  intersecting touch node electrode  501  and traces  502  and  504 .  FIGS. 7A through 7C, 7D-1 through 7D-3, 8A through 8C, 8D-1 through 8D-3, 9A through 9D, and 9E-1 through 9E-3  illustrate example touch sensor panel stackups that will be described with respect to cross-section A-A′ in  FIG. 5A . In examples in which touch sensor panel  500  is part of a touch screen, a display (not shown) could be attached to a bottom surface of touch sensor panel  500 . The examples of the disclosure should be understood to include examples in which a touch sensor panel is part of a touch screen, as well as examples in which a touch sensor panel is not part of a touch screen and is not associated with a display. 
     Some examples of the disclosure can include a conductive line  520  coupled to an electrode layer in touch sensor panel  500 . The placement of conductive line  520  in a material stackup corresponding to touch sensor panel  500  will be discussed in more detail below. Conductive line  520  can be of a lower resistance than the electrode layer to which it is coupled, and the inclusion of conductive line  520  can thus lower the effective sheet resistance of that electrode layer. For example, conductive line  520  can be coupled to a shield electrode layer in touch sensor panel  500  to lower the effective sheet resistance of the shield electrode layer. Lowering this effective sheet resistance can allow touch sensor panel  500  to achieve better sensing performance, and potentially allow touch sensor panel  500  to scale to larger panel sizes more easily than would be possible without conductive line  520 . 
     Conductive line  520  may include one or more traces or lines that traverse one or more portions of the perimeter of the touch sensor panel  500  (e.g., in a trace region that is neither above nor below a touch node electrode). In the example shown in  FIG. 5A , conductive line  520  is shown as one contiguous region traversing the entire perimeter of touch sensor panel  500 . In other examples, conductive line  520  can include multiple regions, such as two “C”-shaped regions separated by a gap. In some examples, conductive line  520  may not traverse the entire perimeter of touch sensor panel  500 , but instead may only traverse a portion of the perimeter. Further, in some examples, an electrode layer may comprise two or more individually addressable electrodes (e.g., in touch sensor panels configured such that two or more regions, each corresponding to one or more individually addressable electrodes, perform different operations). In some such examples, each individually addressable electrode may correspond to an independent conductive line, such that the individually addressable electrodes are not electrically coupled. 
     In some examples, conductive line  520  may be made of copper, although other materials may be used. The examples of the disclosure are not limited to the use of any particular material for conductive line  520 . Further, while some examples of the disclosure depict conductive line  520  as embedded in a stackup layer, the examples of the disclosure are not limited to a conductive line of any specific size, shape (e.g., linear segments), dimension, or geometric arrangement with respect to surrounding stackup layers. Nor are the examples of the disclosure limited to any particular method of forming a conductive line. 
     Compared to routing traces (e.g., routing traces  502 ,  504 ,  506 , and  508  described below) for connecting a touch node electrode to sense circuitry, conductive line  520  does not provide a connective path between a touch node electrode and any circuitry external to touch sensor panel  500 . Accordingly, in some examples, conductive line  520  may be disposed entirely within an electrode layer (e.g., a shield electrode layer) of touch sensor panel  500 , such that some or all of conductive line  520  overlaps touch sensor panel  500 . Such configurations can simplify the fabrication of touch sensor panels, for example by limiting the need to interface conductive line  520  to external circuitry (e.g., via interface circuitry, such as bonding pads). Similarly, the physical robustness of touch sensor panel  500  need not be comprised by a need to accommodate such interface circuitry, which may serve as a potential point of mechanical failure (e.g., by exposure to environmental hazards), or to otherwise interface conductive line  520  to external circuitry. 
       FIG. 5B  shows a detail of example touch sensor panel  500  according to examples of the disclosure. In the example shown in  FIG. 5B , touch node electrodes  501 ,  503 ,  505 , and  507  are touch node electrodes belonging to a single column of touch sensor panel  500 , and can be coupled to sense circuitry via traces  502 ,  504 ,  506 , and  508 , respectively, with each trace coupled to one touch node electrode, as described above. (Conductive line  520 , shown in  FIG. 5A , is not shown in  FIG. 5B .) The touch node electrodes and traces in  FIG. 5B  are susceptible to noise, from above the touch sensor panel, that can interfere with the touch sensor panel&#39;s ability to detect touch input. It may be desirable to provide top shielding for such traces. However, top shielding may not be desired for the touch node electrodes, because top shielding may reduce the ability of an object (such as a user&#39;s finger) to interact with the touch node electrode, thereby decreasing the touch sensitivity of the touch sensor panel. In the example shown in  FIG. 5B , shielding regions  510  and  512  together are disposed above traces  502 ,  504 ,  506 , and  508 , but not above touch node electrodes  501 ,  503 ,  505 , and  507 . This can top-shield the traces from noise (such as from coupling with a finger), while leaving the top surfaces of the touch node electrodes unshielded, to avoid decreasing touch sensitivity of the touch sensor panel. (Though not shown in  FIG. 5B , additional shielding regions can analogously be provided above traces throughout touch sensor panel  500  to top-shield those traces.) In some examples, not shown in  FIG. 5B , a selective shielding region (e.g., an “interrogated” electrode) may be disposed above touch node electrodes  501 ,  503 ,  505 , and  507 . In some such examples, the selective shielding region may be configured to selectively top-shield touch node electrodes  501 ,  503 ,  505 , and  507  based on a touch sensing mode. For example, top-shielding such electrodes may be beneficial when operating in a self-capacitance touch sensing mode, but unnecessary or undesirable when operating in a mutual capacitance touch sensing mode. 
       FIG. 6  shows selected layers from an example material stackup  690 , corresponding to an example touch sensor panel  600 , according to examples of the disclosure. (It should be noted that other components of the example stackup, such as bonding pads and/or passivation layers, are not shown in  FIG. 6 , to simplify the following explanation. However, it is understood that such components may be present.) In some touch sensor panels, such as example touch sensor panel  600 , top and bottom shielding is provided using a material stackup that incorporates three electrode layers. The example shown in  FIG. 6  includes a first substrate layer  630 . As used herein, a substrate layer is a layer of a touch sensor panel that comprises one or more surfaces on which conductive or other material can be formed, and that has sufficient structural integrity to fully support itself as a freestanding structure (e.g., a structure that can substantially maintain its shape without needing structural support from the touch sensor panel or other material). Accordingly, the substrate layer can be relatively thick and rigid in comparison to the conductive or other material; and, in a touch sensor panel (e.g., touch sensor panel  600 ) example, the substrate layer provides structural support for layers of the panel (e.g., passivation layers, electrode layers) that lack the structural integrity to fully support themselves. In some examples, substrate layer  630  can include a flexible plastic material, such as cyclo olefin polymer (COP), although other materials are possible. Conductive material can be formed on a substrate layer using known patterning techniques, such as photolithography or etching. 
     In the example shown in  FIG. 6 , electrode layers  610  and  620  are formed on opposite sides of substrate layer  630 . That is, first substrate layer  630  is disposed between two electrode layers: electrode layer  610  and electrode layer  620 . In the example shown in  FIG. 6 , electrode layer  610  includes a touch node electrode  601  and one or more routing traces  602  to which the touch node electrode  601  is coupled. Electrode layer  610  can be formed on a surface (e.g., the bottom surface) of first substrate layer  630 , and can comprise a conductive material, such as ITO. In the example shown in  FIG. 6 , a second electrode layer  620  is formed on the opposite surface (e.g., the top surface) of substrate layer  630 . Like electrode layer  610 , electrode layer  620  can comprise a conductive material. In the example shown in  FIG. 6 , in which electrode layer  620  is disposed above electrode layer  610 , electrode layer  620  can provide top shielding for routing traces  602  in electrode layer  610 . However, top shielding of all, or a significant portion of, touch node electrode  601  could be undesirable, as it could reduce the touch sensitivity of the touch sensor panel, as described in more detail below. In the example shown in  FIG. 6 , electrode layer  620  does not include material (such as conductive material) disposed above all of touch node electrode  601 , and accordingly does not provide top shielding for all of touch node electrode  601 . (In some examples (not shown in  FIG. 6 ), electrode layer  620  may overlap a portion of touch node electrode  601 .) The layers including electrode layers  610  and  620  and first substrate layer  630 , with  610  and  620  disposed on opposite sides of  630 , can be thought of as a dual-layer structure (shown as  660  in  FIG. 6 ). 
     In the example shown in  FIG. 6 , the example stackup  690  includes a second substrate layer  640 . Like substrate layer  630 , substrate layer  640  is a base layer on which conductive material may be formed, and may comprise a flexible plastic material such as COP. In the example shown in  FIG. 6 , electrode layer  650  is formed on a single side (e.g., the bottom side) of substrate layer  640 . Electrode layer  650 , like electrode layers  610  and  620 , can comprise a conductive material (e.g., ITO). If electrode layer  650  is disposed underneath electrode layer  610 ,  650  can provide bottom shielding for touch node electrode  601  and routing traces  602  in electrode layer  610 . In the example shown in  FIG. 6 , substrate layer  640  has an electrode layer ( 650  in the figure) on only one side. The layers including electrode layer  650  and second substrate layer  640 , with  650  disposed on a single side of  640  and no electrode layer on formed on the other side of  640 , can be thought of as a single-layer structure (shown as  670  in  FIG. 6 ). 
     In the example shown in  FIG. 6 , the double-layer structure  660  can be attached to the single-layer structure  670  via a lamination process  680 . In the example shown in  FIG. 6 , the result of lamination process  680  can be material stackup  690 , which includes two substrate layers ( 630  and  640 ) and three electrode layers ( 610 ,  620 , and  650 ). In the example shown in  FIG. 6 , electrode layer  610  is disposed below electrode layer  620  (which can provide top shielding for routing traces  602  in electrode layer  610 ), and above electrode layer  650  (which can provide bottom shielding for touch node electrode  601  and routing traces  602  in electrode layer  610 ). In some examples in which touch sensor panel  600  is part of a touch screen, the touch sensor panel can be attached to the surface of a display (not shown). Touch node electrode  601  and routing traces  602  can be bottom-shielded from noise generated by the display by electrode layer  650 . 
     As shown in  FIG. 6 , example stackup  690  includes two substrate layers,  630  and  640 . Each substrate layer contributes to the overall thickness of the touch sensor panel. It may be desirable to reduce the thickness of a touch sensor panel, particularly when the touch sensor panel is part of a touch screen. For example, reducing the touch sensor panel thickness can improve the usability of a touch device by decreasing the distance between the panel surface and a display with which a user interacts via touch input. Reducing the touch sensor panel thickness can also enable touch-sensitive devices, such as those shown in  FIG. 1 , with thinner and/or more desirable form factors. Additionally, the use of two substrate layers in example stackup  690  can require a lamination process to join the substrate layers; this is shown in  FIG. 6  by lamination process  680 , which attaches dual-layer structure  660  to single-layer structure  670 . This lamination process is potentially costly, may require the use of adhesives and other materials, and can add time and complexity to the process of fabricating touch sensor panel  600 . Such a lamination process may not be necessary in touch sensor panels that utilize only a single substrate layer. It may thus be desirable to simplify this process by eliminating one of the two substrate layers in example stackup  690 . At the same time, it may be desirable to retain the top and bottom shielding of example stackup  690 . Additionally, in some examples, it may be desirable to make use of existing designs and fabrication processes, such as those that utilize a dual-layer structure, such as  660  in  FIG. 6 . This may be particularly true when substantial investment, such as by the touch sensor panel manufacturer or third parties, may have been made in those designs and fabrication processes. Some examples of the disclosure are directed to touch sensor panels that utilize a single substrate layer—and thus do not require laminating a dual-layer structure to a single-layer structure—while benefiting from top shielding and/or bottom shielding. Some examples of the disclosure are directed to touch sensor panels that utilize a polarizer in place of a standalone substrate layer, while benefiting from top shielding and/or bottom shielding. 
       FIG. 7A  illustrates an exemplary material stackup  700  of a touch sensor panel with a single substrate layer, a touch electrode layer disposed above the substrate layer, a top shield electrode layer, and a bottom shield electrode layer, depicted along cross-section A-A′ in  FIG. 5A , according to examples of the disclosure.  FIG. 7A  shows an electrode layer  710 , an electrode layer  720 , and a substrate layer  730  in a dual-layer configuration, such as described above with respect to dual-layer structure  660  in  FIG. 6 . In the example shown in  FIG. 7A , electrode layer  710  is disposed above substrate layer  730 , and electrode layer  720  is disposed below substrate layer  730  (e.g., electrode layer  710  and/or electrode layer  720  may be in contact with substrate layer  730  on opposite surfaces of substrate layer  730 ). Electrode layer  710  includes touch node electrode  501 , and traces  502  and  504 , as shown in  FIGS. 5A-5B . Electrode layer  710  may also include bonding pad region  509  for connecting electrode layer  710  to circuitry. In the example shown in  FIG. 7A , touch node electrode  501 , traces  502  and  504 , and bonding pad region  509  can be comprised of a conductive material (e.g., ITO), and may be formed by patterning a single layer of that material (e.g., using photolithography and etching techniques). It should be understood that, throughout the disclosure, a conductive material may be ITO, or another conductive material, such as nanowire materials or metal mesh materials. Further, it should be understood that conductive materials may be transparent. The examples of the disclosure are not limited to any particular conductive material. 
     Bonding pads, comprised of conductive material, can be used to connect electrode layers to circuitry (e.g., sense circuitry). In the example shown in  FIG. 7A , trace  502  may include a bonding pad region electrically coupled to a first bonding pad  702  disposed above substrate  730  and trace  502  (e.g., bonding pad  702  may be in contact with trace  502 ), to connect trace  502  to first sense circuitry, such as shown in  FIGS. 2, 3A , and/or  3 B. (Trace  504  may be electrically coupled to second sense circuitry, which may be different from the first sense circuitry, via a bonding pad not shown in  FIG. 7A .) It should be understood that, throughout the disclosure, bonding pads may be comprised of copper, or another conductive material. The examples of the disclosure are not limited to any particular bonding pad material. 
     In the example shown in  FIG. 7A , electrode layer  720  can function as a bottom shield that provides noise shielding for touch node electrode  501  and traces  502  and  504  from noise sources located below electrode layer  720 . This shielding may be beneficial, for example, to prevent interference from noise generated by circuitry, such as a display screen, located below the touch sensor panel. In the example shown, electrode layer  720  can be comprised of a conductive material (e.g., ITO), and may be formed by patterning a single layer of that material (e.g., using photolithography and etching techniques). Electrode layer  720  may include a bonding pad region electrically coupled to a second bonding pad  704 , which can be disposed below substrate layer  730  and electrode layer  720  (e.g., bonding pad  704  may be in contact with electrode layer  720 ), to connect electrode layer  720  to first drive circuitry. The first drive circuitry may apply a guard signal, which may be an AC or DC voltage signal, to electrode layer  720 . While  FIG. 7A  depicts bonding pad  702  and bonding pad  704  on opposite sides of substrate  730 , the disclosure is not limited to such examples. For instance, bonding pad  702  and  704  could be electrically coupled (e.g., by one or more conductive vias) to a common surface disposed on a single side of substrate  730 . Further, while  FIG. 7A  depicts electrode layer  710  and electrode layer  720  as coupled to bonding pad  702  and bonding pad  704 , respectively, the disclosure is not limited to any particular relationship between electrode layers and bonding pads. For instance, a single electrode layer (e.g., electrode layer  710  or electrode layer  720 ) may comprise two or more electrodes, each such electrode connected to a different bond pad. 
     In the example shown in  FIG. 7A , substrate layer  730 , electrode layer  710  (which may be formed on one side of substrate layer  730 ), and electrode layer  720  (which may be formed on the opposite side of substrate layer  730 ) can be viewed as a dual-layer structure  735 , analogous to the dual-layer structure  660  in  FIG. 6 . In some examples, passivation layers can be added above and below dual-layer structure  735 , for example to protect dual-layer structure  735  from environmental hazards (e.g., scratching, moisture). In the example shown in  FIG. 7A , a first passivation layer  740  may be disposed above dual-layer structure  735 . That is, passivation layer  740  may be disposed above substrate layer  730 , touch node electrode  501 , and traces  502  and  504 , such that touch node electrode  501  and traces  502  and  504  may be disposed between substrate layer  730  and passivation layer  740  (e.g., passivation layer  740  may be in contact with substrate layer  730 , touch node electrode  501 , and/or traces  502  and  504 ). Similarly, a second passivation layer  750  may be disposed below dual-layer structure  735 . That is, passivation layer  750  may be disposed below electrode layer  720  (e.g., passivation layer  750  may be in contact with electrode layer  720 , and electrode layer  720  may be disposed between substrate layer  730  and passivation layer  750 ). 
     In the example shown in  FIG. 7A , the example stackup  700  includes a third electrode layer, shown in the figure as electrode layer  760 . Unlike electrode layers  620  and  650  shown in  FIG. 6 , however, electrode layer  760  in example stackup  700  need not be formed on a surface of a substrate layer. Instead, electrode layer  760  can be formed above and on passivation layer  740 , which in example stackup  700  is disposed above electrode layer  710  and substrate layer  730  (e.g., electrode layer  760  may be in contact with passivation layer  740 , and electrode layers  760  and  710  are both disposed above substrate layer  730 ). In the example shown in  FIG. 7A , electrode layer  760  includes shielding regions  762  and  764 . Electrode layer  760  can function as a top shield that provides noise shielding for traces  502  and  504 , which may be disposed directly below shielding regions  764  and  762 , respectively, from noise sources (such as finger coupling) that may be located above electrode layer  760 . Shielding regions  762  and  764  may be formed by patterning a single layer of conductive material (e.g., using photolithography and etching techniques). Electrode layer  760  may be comprised of nanowire materials, such as silver nanowire, although other conductive materials may be used. In the example shown, electrode layer  760  does not include material disposed directly above the touch node electrode  501  and thus may not provide top shielding for touch node electrode  501 . This is because top shielding of touch node electrode  501  could dampen the touch sensor panel&#39;s ability to detect changes in capacitance, as by limiting the extent and/or flux of fringing electric fields extending above touch node electrode  501 , with which an object, such as a user&#39;s finger, may capacitively interact. 
     In the examples of the disclosure, top and bottom shield electrode layers (e.g., electrode layers  760  and  720  in  FIG. 7A ) can be positioned completely or partially between one or more touch node electrodes (e.g., touch node electrode  501 ) in a touch electrode layer (e.g., touch electrode layer  710 ) and one or more noise sources, such as a display. This configuration (location of the shield layers between the touch electrodes and noise source) can provide a shielding effect by receiving capacitively coupled noise and shunting the charge away from the touch electrodes. The examples of the disclosure encompass various configurations in which such top and bottom shield electrode layers can shield a touch node electrode from noise. In some examples, one or both of the top and bottom shield electrode layers can be driven by a “guard” signal referenced to the stimulation signal of the touch electrodes. In such configurations, with the shield layers and the touch electrodes driven with signals referenced to each other (e.g., at the same frequency, phase and/or amplitude), parasitic capacitive coupling between the shield layers and the touch electrodes can be minimized, which further shields the touch electrodes from capacitively coupled noise. Similarly, while an “interrogated” touch electrode is being sensed to determine the occurrence of a touch, other “non-interrogated” touch electrodes can be driven with the same guard signal as the guard layer(s). In this configuration, the interrogated electrode can be surrounded by other touch electrodes that are also acting as a shield. As each electrode is interrogated in turn, the guard signal can be selectively applied to other non-interrogated electrodes. In other examples, one or both of the top and bottom shield electrodes can be held at earth ground. In some examples, depending on the touch sensing mode (e.g., self-capacitance sensing, mutual capacitance sensing), a guard signal may be of limited benefit, and accordingly may not be applied to one or more electrode layers. It should be understood throughout the examples of the disclosure that, where shielding behavior of an electrode layer is described, the examples are not limited to any particular mechanism (e.g., passive shielding, active shielding using a guard signal) by which the electrode layer exhibits such shielding behavior. 
     In the example shown in  FIG. 7A , the example stackup  700  includes passivation regions  772  and  774  disposed above shielding regions  762  and  764 , respectively (e.g., passivation region  772  may be in contact with shielding region  762 , and/or passivation region  774  may be in contact with shielding region  764 ; shielding region  762  may be disposed between passivation layer  740  and passivation region  772 ; and shielding region  764  may be disposed between passivation layer  740  and passivation region  774 ). Passivation regions  772  and  774  provide environmental protection for shielding regions  764  and  762  and the underlying circuitry. In examples in which electrode layer  760  includes nanowire materials, such as silver nanowire, only thin passivation regions  772  and  774  may be required. In some examples, electrode layer  760  may include a material combining nanowire materials with a passivation material, simplifying the process of forming passivation regions  772  and  774  above electrode layer  760 . In some examples, passivation regions  772  and  774  can be omitted from stackup  700 . 
     In the example shown in  FIG. 7A , electrode layer  710  includes bonding pad region  509 , which may be electrically coupled to a third bonding pad  706 , which may be disposed above substrate layer  730  and electrode layer  710  (e.g., bonding pad  706  may be in contact with electrode layer  710  via bonding pad region  509 ). Shielding regions  762  and  764  may be electrically coupled to bonding pad  706  to connect to second drive circuitry. The second drive circuitry may apply a guard signal, which may be an AC or DC voltage signal, to shielding regions  762  and  764 . (The second drive circuitry may be, but need not be, the same as the first drive circuitry.) In the example shown in  FIG. 7A , bonding pad  706  may be formed from the same layer, and in the same step of a fabrication process, as bonding pad  702 . While  FIG. 7A  depicts bonding pad  702  and bonding pad  706  as positioned on opposing sides of touch node electrode  501  (e.g., on opposing sides of a touch sensor panel), in some examples, bonding pad  702  and bonding pad  706  may be positioned on a common side (e.g., the leftmost edge of touch sensor panel  500  shown in  FIG. 5 ). 
       FIGS. 7B and 7C  show further examples of stackup  700  that include a conductive line  755  to reduce the effective sheet resistance of electrode layer  720 , such as described above with respect to conductive line  520  shown in  FIG. 5A . In some examples of stackup  700  that include a conductive line  755 , such as shown in  FIG. 7B , conductive line  755  may be disposed below substrate layer  730  (e.g., conductive line  755  may be in contact with substrate layer  730 ). Electrode layer  720  may be formed on the bottom surfaces of substrate layer  730  and conductive line  755  (e.g., electrode layer  720  may be in contact with substrate layer  730  and/or conductive line  755 , and conductive line  755  may be embedded in electrode layer  720 ). In some examples, such as shown in  FIG. 7C , conductive line  755  may be disposed below electrode layer  720  (e.g., conductive line  755  may be in contact with electrode layer  720 , and need not be in direct contact with substrate layer  730 ). Passivation layer  750  may be formed on the bottom surfaces of electrode layer  720  and conductive line  755  (e.g., passivation layer  750  may be in contact with electrode layer  720  and/or conductive line  755 , and conductive line  755  may be embedded in passivation layer  750 ). In the examples of both  FIGS. 7B and 7C , the inclusion and electrical coupling of conductive line  755  to electrode layer  720  can lower the overall sheet resistance of electrode layer  720 , allowing for better shielding performance when electrode layer  720  is acting as a noise shield, and potentially allowing stackup  700  to scale to larger panel sizes more easily than stackups that do not include the conductive line. 
     Example stackup  700  may provide several advantages over example stackup  690  shown in  FIG. 6 . In example stackup  690 , electrode layer  610  (which includes traces  602 ) can be top-shielded from noise by electrode layer  620 , where electrode layer  610  and electrode layer  620  are on opposite sides of a substrate layer (substrate layer  630 ) in a dual-layer structure. However, in stackup  700 , top shielding of electrode layer  710  (which includes traces  502  and  504 ) can instead be provided by electrode layer  760 . Unlike in example stackup  690 , electrode layer  710  and electrode layer  760  are not separated by a substrate layer in a dual-layer structure. Instead, electrode layer  710  and electrode layer  760  are both disposed on the same side of substrate layer  730 , with electrode layer  760  formed on passivation layer  740  instead of on a second substrate layer. That is, example stackup  700  does not include a second substrate layer between substrate layer  730  and electrode layer  760 . Compared to example stackup  690 , the configuration of example stackup  700  eliminates one substrate layer (e.g., substrate layer  630  in  FIG. 6 ), potentially eliminating the touch sensor panel thickness associated with that substrate layer. Additionally, no lamination process is required to laminate a dual-layer structure (such as  660  in  FIG. 6 ) to a single-layer structure (such as  670  in  FIG. 6 ); removing this lamination process can potentially reduce the cost and complexity of fabrication, and the costs and stackup thickness associated with materials (such as adhesive materials) that might otherwise be required for lamination. Additionally, in example stackup  700 , one or more bonding pads (e.g., bonding pads  702  and  706 ) can be formed from a single layer of conductive material on the same side of substrate layer  730 . This can simplify the cost and complexity of fabrication compared to examples, such as the example shown in  FIG. 6 , in which bonding pads may be formed from multiple layers of conductive material on opposite sides of a substrate layer. (For instance, in the example shown in  FIG. 6 , electrode layers  610 ,  620 , and  650  may connect to bonding pads formed from three separate layers, each layer separated from the other layers by substrate layers  630  and/or  640 .) Meanwhile, shielding of touch node electrode  501  and traces  502  and  504  need not be compromised by the elimination of a substrate layer, as electrode layer  710  (e.g., touch node electrode  501  and traces  502  and  504 ) can be shielded in the example from both the top and the bottom, similarly to electrode layer  610  in  FIG. 6 . 
     In some examples, such as shown in  FIGS. 7A-7C , electrode layer  760  can be comprised of nanowire materials, such as silver nanowire. An advantage that can be conveyed by nanowire materials is that they can exhibit improved mechanical flexibility over some other conductive materials (e.g., ITO), potentially allowing example  700  to be more structurally robust than stackups such as example  690  in  FIG. 6 . Further, nanowire materials may exhibit lower sheet resistance than some other conductive materials. Similarly, in examples that include a conductive line coupled to an electrode layer, such as described above with respect to  FIGS. 7B and 7C , that conductive line may contribute to lower sheet resistance. This lower sheet resistance can allow for more effective shielding and better touch sensor performance, and may allow example  700  to scale to larger panel sizes more easily than example  690 . 
       FIGS. 7D-1 through 7D-3  illustrate an example process for forming exemplary material stackup  700 , as shown in  FIG. 7B . Electrode layers  710 ,  720 , and  760 , substrate layer  730 , passivation layers  740  and  750 , bonding pads  702 ,  704 , and  706 , electrode layer  760  (e.g., shielding regions  762  and  764 ), passivation regions  772  and  774 , and conductive line  755  are as shown in  FIG. 7B .  FIG. 7D-1  shows stackup  700  after a standard annealing process, the result of which may include a dual-layer structure  735  such as shown in  FIG. 7B —electrode layers  710  and  720  formed on opposite sides of substrate layer  730 —with passivation layers  740  and  750  on the top and bottom sides, respectively, of dual-layer structure  735 . In  FIG. 7D-1 , shielding regions  762  and  764  and passivation regions  772  and  774  (shown in  FIG. 7B ) have not yet been formed. 
       FIG. 7D-2  shows electrode layer  760  formed above passivation layer  740  of stackup  700  via a lamination process (e.g., passivation layer  740  may be in contact with electrode layer  760 ), and passivation layer  770  formed above electrode layer  760  (e.g., passivation layer  770  may be in contact with electrode layer  760 ). In examples in which electrode layer  760  includes nanowire materials, such as silver nanowire, only a thin passivation layer  770  may be required. In some examples, electrode layer  760  may include a material combining nanowire materials with a passivation material, simplifying the process of forming passivation layer  770  above electrode layer  760 . Example stackup  700  can then be subjected to an exposure and development process, which can remove portions of electrode layer  760  and passivation layer  770  disposed above touch node electrode  501  and bonding pad  702 , while leaving portions of electrode layer  760  and passivation layer  770  disposed above traces  502  and  504 . As described above, this may provide top shielding of traces  502  and  504 , which may be desirable, while avoiding top shielding of touch node electrode  501 , which may not be desirable. Moreover, this can prevent electrode layer  760  from being electrically coupled to bonding pad  702  (which may be coupled to trace  502 ). This exposure and development process can result in shielding regions  762  and  764  and passivation regions  772  and  774 . A result of this exposure and development process is the example stackup  700  as shown in  FIG. 7B  (reproduced as  FIG. 7D-3  for clarity). Other processes can additionally or alternatively be used to form example stackup  700 . 
       FIG. 8A  illustrates an exemplary material stackup  800  of a touch sensor panel with a single substrate layer, a touch electrode layer disposed below the substrate layer, a top shield electrode layer, and a bottom shield electrode layer, depicted along cross-section A-A′ in  FIG. 5A , according to examples of the disclosure.  FIG. 8A  shows an electrode layer  810 , an electrode layer  820 , and a substrate layer  830  in a dual-layer configuration, such as described above with respect to dual-layer structure  660  in  FIG. 6 . In the example shown in  FIG. 8A , electrode layer  810  is disposed below substrate layer  830 , and electrode layer  820  is disposed above substrate layer  830  (e.g., electrode layer  810  and/or electrode layer  820  may be in contact with substrate layer  830  on opposite surfaces of substrate layer  830 ). Electrode layer  810  includes touch node electrode  501 , and traces  502  and  504 , as shown in  FIGS. 5A-5B . Electrode layer  810  may also include bonding pad region  509  for connecting to circuitry. In the example shown in  FIG. 8A , touch node electrode  501 , traces  502  and  504 , and bonding pad region  509  can be comprised of a conductive material, and may be formed by patterning a single layer of that material (e.g., using photolithography and etching techniques). Trace  502  may include a bonding pad region electrically coupled to a first bonding pad  842  disposed below substrate  830  and trace  502  (e.g., bonding pad  842  may be in contact with trace  502 ), to connect trace  502  to first sense circuitry, such as shown in  FIGS. 2, 3A , and/or  3 B. (Trace  504  may be electrically coupled to second sense circuitry, which may be different from the first sense circuitry, via a bonding pad not shown in  FIG. 8A .) 
     In the example shown in  FIG. 8A , electrode layer  820  can function as a top shield that provides noise shielding for traces  502  and  504  from noise sources located above electrode layer  820 . This shielding may be beneficial, for example, to protect the traces from interference from noise generated from above the touch sensor panel, such as from the contact environment. In the example shown, electrode layer  820  includes shielding regions  822  and  824 , which may be comprised of a conductive material (e.g., ITO), and may be formed by patterning a single layer of that material (e.g., using photolithography and etching techniques). In  FIG. 8A , shielding regions  822  and  824  may be disposed directly above traces  504  and  502 , respectively, and provide top shielding for those respective traces. Shielding regions  822  and  824  may correspond to shielding regions  510  and  512  in  FIG. 5B , which can similarly provide top shielding for traces  504  and  502 . In the example shown, electrode layer  820  does not include material disposed directly above the touch node electrode  501  and thus may not provide top shielding for touch node electrode  501 . This is because top shielding of touch node electrode  501  could dampen the touch sensor panel&#39;s ability to detect changes in capacitance, as by limiting the extent and/or flux of fringing electric fields, extending above touch node electrode  501 , with which an object, such as a user&#39;s finger, may capacitively interact. 
     In some examples, shielding region  824  may include a bonding pad region electrically coupled to a second bonding pad  844 , which may be disposed above substrate layer  830  and shielding region  824  (e.g., bonding pad  844  may be in contact with shielding region  824 ), to connect electrode layer  820  (e.g., shielding regions  822  and/or  824 ) to first drive circuitry. The first drive circuitry may apply a guard signal, which may be an AC or DC voltage signal, to shielding region  824  (and, via conductive material not shown in  FIG. 8A , to shielding region  822 ). 
     In the example shown in  FIG. 8A , substrate layer  830 , electrode layer  810  (which may be formed on one side of substrate layer  830 ), and electrode layer  820  (which may be formed on the opposite side of substrate layer  830 ) can be viewed as a dual-layer structure  835 , analogous to the dual-layer structure  660  in  FIG. 6 . In some examples, passivation layers can be added above and below dual-layer structure  835 , for example to protect dual-layer structure  835  from environmental hazards (e.g., scratching, moisture). In the example shown in  FIG. 8A , a first passivation layer  847  may be disposed above dual-layer structure  835 . That is, passivation layer  847  may be disposed above substrate layer  830  and electrode layer  820  (e.g., passivation layer  847  may be in contact with substrate layer  830  and/or shielding regions  822  and  824 ). Similarly, a second passivation layer  848  may be disposed below dual-layer structure  835 . That is, passivation layer  848  may be disposed below substrate layer  830 , touch node electrode  501 , and traces  502  and  504 , such that touch node electrode  501  and traces  502  and  504  may be disposed between substrate layer  830  and passivation layer  848  (e.g., passivation layer  848  may be in contact with substrate layer  830 , touch node electrode  501 , and/or traces  502  and  504 ). 
     In the example shown in  FIG. 8A , the example stackup  800  includes a third electrode layer, shown in the figure as electrode layer  850 . Unlike electrode layers  620  and  650  shown in  FIG. 6 , however, electrode layer  850  in example stackup  800  need not be formed on a surface of a substrate layer. Instead, electrode layer  850  can be formed below and on passivation layer  848 , which in example stackup  800  is disposed below electrode layer  810  and substrate layer  830  (e.g., electrode layer  850  may be in contact with passivation layer  848 , and electrode layers  850  and  810  are both disposed below substrate layer  830 ). In the example shown in  FIG. 8A , electrode layer  850  can function as a bottom shield that provides noise shielding for touch node electrode  501  and traces  502  and  504 , which may be disposed directly above electrode layer  850 , from noise sources (such as a display) that may be located below electrode layer  850 . Electrode layer  850  may be formed by patterning a single layer of conductive material. Electrode layer  850  may be comprised of nanowire materials, such as silver nanowire, although other conductive materials may be used. 
     In the example shown in  FIG. 8A , the example stackup  800  includes a passivation layer  860  disposed below electrode layer  850  (e.g., passivation layer  860  may be in contact with electrode layer  850 ). Passivation layer  860  can provide environmental protection for electrode layer  850  and the underlying circuitry. In the example shown in  FIG. 8A , electrode layer  810  includes bonding pad region  509 , which may be electrically coupled to a third bonding pad  846 , which may be disposed below substrate layer  830  and electrode layer  810  (e.g., bonding pad  846  may be in contact with region  509  of electrode layer  810 ). Electrode layer  850  may be electrically coupled to bonding pad  846  to connect to second drive circuitry. The second drive circuitry may apply a guard signal, which may be an AC or DC voltage signal, to electrode layer  850 . (The second drive circuitry may be, but need not be, the same as the first drive circuitry.) In the example shown in  FIG. 8A , bonding pad  846  may be formed from the same layer, and in the same step of a fabrication process, as bonding pad  842 . 
       FIGS. 8B and 8C  show further examples of stackup  800  that include a conductive line  855  to reduce the effective sheet resistance of electrode layer  850 , such as described above with respect to  FIG. 5A  (and below with reference to  FIGS. 8E and 8F ). In some examples of stackup  800  that include a conductive line  855 , such as shown in  FIG. 8B , conductive line  855  may be disposed below substrate layer  830  and electrode layer  810  (e.g., conductive line  855  may be in contact with substrate layer  830  and/or electrode layer  810 ). Conductive line  855  can be formed in the same layer as a bonding pad (e.g., bonding pad  842 ), from the same material as the bonding pad, and may be coupled to a region  853  in electrode layer  810 . Region  853  may not be electrically connected to other regions of electrode layer  810  (e.g., touch node electrode  501 , traces  502  and  504 , and bonding pad region  509 ). Electrode layer  850  may be formed on the bottom surfaces of passivation layer  848  and conductive line  855  (e.g., electrode layer  850  may be in contact with passivation layer  848  and/or conductive line  855 ). In some examples, such as shown in  FIG. 8C , conductive line  855  may be disposed below electrode layer  850  (e.g., conductive line  855  may be in contact with electrode layer  850 ). Passivation layer  860  may be formed on the bottom surfaces of electrode layer  850  and conductive line  855  (e.g., passivation layer  860  may be in contact with electrode layer  850  and/or conductive line  855 , and conductive line  855  may be embedded in passivation layer  850 ). In the examples of both  FIGS. 8B and 8C , the inclusion and electrical coupling of conductive line  855  to electrode layer  850  can lower the overall sheet resistance of electrode layer  850 , allowing for better touch sensor performance, and potentially allowing example  800  to scale to larger panel sizes more easily than examples that do not include the conductive line. 
     Example stackup  800  may provide several advantages over example stackup  690  shown in  FIG. 6 . In example stackup  690 , electrode layer  610  (which includes touch node electrode  601  and traces  602 ) can be bottom-shielded from noise by electrode layer  650 , where electrode layer  610  and electrode layer  650  are on opposite sides of a substrate layer (substrate layer  640 ) in a dual-layer structure. However, in stackup  800 , bottom shielding of electrode layer  810  (which includes touch node electrode  501  and traces  502  and  504 ) can instead be provided by electrode layer  850 . Unlike in example stackup  690 , electrode layer  810  and electrode layer  850  are not separated by a substrate layer in a dual-layer structure. Instead, electrode layer  810  and electrode layer  850  are both disposed on the same side of substrate layer  830 , with electrode layer  850  formed on passivation layer  848  instead of on a second substrate layer. That is, example stackup  800  does not include a second substrate layer between substrate layer  830  and electrode layer  850 . Compared to example stackup  690 , the configuration of example stackup  800  eliminates one substrate layer (e.g., substrate layer  640  in  FIG. 6 ), potentially eliminating the touch sensor panel thickness associated with that substrate layer. Additionally, no lamination process is required to laminate a dual-layer structure (such as  660  in  FIG. 6 ) to a single-layer structure (such as  670  in  FIG. 6 ); removing this lamination process can potentially reduce the cost and complexity of fabrication, and the costs and stackup thickness associated with materials (such as adhesive materials) that might otherwise be required. Additionally, in example stackup  800 , one or more bonding pads (e.g., bonding pads  842  and  846 ) can be formed from a single layer of conductive material on the same side of substrate layer  830 . This can simplify the cost and complexity of fabrication compared to examples, such as the example shown in  FIG. 6 , in which bonding pads may be formed from multiple layers of conductive material on opposite sides of a substrate layer. (For instance, in the example shown in  FIG. 6 , electrode layers  610 ,  620 , and  650  may connect to bonding pads formed from three separate layers, each layer separated from the other layers by substrate layers  630  and/or  640 .) Meanwhile, shielding of touch node electrode  501  and traces  502  and  504  need not be compromised by the elimination of a substrate layer, as electrode layer  810  (which includes touch node electrode  501  and traces  502  and  504 ) is shielded in the example from both the top and the bottom, similar to electrode layer  610  in  FIG. 6 . 
     In some examples, such as shown in  FIGS. 8A-8C , electrode layer  850  can be comprised of nanowire materials, such as silver nanowire. An advantage that can be conveyed by nanowire materials is that they can exhibit improved mechanical flexibility over some other conductive materials (e.g., ITO), potentially allowing example  800  to be more structurally robust than example  690  in  FIG. 6 . Further, nanowire materials may exhibit lower sheet resistance than some other conductive materials. Similarly, in examples that include a conductive line coupled to an electrode layer, such as described above and shown in  FIGS. 8B and 8C , that conductive line may contribute to lower sheet resistance of the electrode layer. This lower sheet resistance can allow for more effective shielding and better touch sensor performance, and may allow example  800  to scale to larger panel sizes more easily than example  690 . 
       FIGS. 8D-1 through 8D-3  illustrate an example process for forming exemplary material stackup  800 , as shown in  FIG. 8C . Electrode layers  810 ,  820  (e.g., shielding regions  822  and  824 ), and  850 , substrate layer  830 , passivation layers  847 ,  848 , and  860 , bonding pads  842 ,  844 , and  846 , and conductive line  855  are as shown in  FIG. 8C .  FIG. 8D-1  shows stackup  800  after a standard annealing process, the result of which may include a dual-layer structure  835  as shown in  FIG. 8C —electrode layers  810  and  820  formed on opposite sides of substrate layer  830 —with passivation layers  847  and  848  on the top and bottom sides, respectively, of dual-layer structure  835 . In  FIG. 8D-1 , electrode layer  850  and passivation layer  860  (shown in  FIG. 8C ) have not yet been formed. 
       FIG. 8D-2  shows electrode layer  850  formed below passivation layer  848  of stackup  800  via a lamination process (e.g., passivation layer  848  may be in contact with electrode layer  850 ), and passivation layer  860  formed below electrode layer  850  (e.g., passivation layer  860  may be in contact with electrode layer  850 ). In some examples that include a conductive line  855 , such as shown in  FIG. 8C , conductive line  855  may be disposed under electrode layer  850  and embedded in passivation layer  860 . In examples in which electrode layer  850  includes nanowire materials, such as silver nanowire, only a thin passivation layer  860  may be required. In some examples, electrode layer  850  may include a material combining nanowire materials with a passivation material, simplifying the process of forming passivation layer  860  below electrode layer  850 . Example stackup  800  can then be subjected to an exposure and development process, which can remove unwanted or unnecessary portions of electrode layer  850  and passivation layer  860 . For example, this can prevent electrode layer  850  from being electrically coupled to bonding pad  842  (which may be coupled to trace  502 ). The remaining portions of electrode layer  850 , as shown in  FIG. 8D-3 , can provide bottom shielding for electrode layer  810 . A result of this exposure and development process is the example stackup  800  as shown in  FIG. 8C  (reproduced as  FIG. 8D-3  for clarity). Other processes can additionally or alternatively be used to form example stackup  800 . 
       FIGS. 8E and 8F  show an expanded view of an example stackup  800 , as shown in  FIG. 8B , according to examples of the disclosure.  FIG. 8E  shows a horizontal cross section A-A′ of a touch sensor panel shown in  FIG. 8F , the cross section extending from the left edge of the touch sensor panel to the right edge of the touch sensor panel and intersecting a row of touch node electrodes  501 A through  501 D.  FIG. 8F  shows a partial top view of the touch sensor panel. In the example shown in  FIGS. 8E and 8F , as in  FIG. 8B , electrode layer  810  is formed on the bottom surface of substrate layer  830 . Electrode layer  810  can include touch node electrodes  501 A through  501 D, routing traces  502 A through  502 D, bonding pad regions  509 A and  509 B, and electrode layer regions  853 . In the example shown in  FIGS. 8E and 8F , touch node electrodes  501 A through  501 D can be coupled to external sense circuitry  898  via traces  502 A through  502 D and bonding pads  849 A- 849 D. In the example shown in  FIGS. 8E and 8F , as in  FIG. 8B , electrode layer  850  is disposed below electrode layer  810  and can provide bottom shielding for electrode layer  810 . As visible in  FIG. 8F , electrode layer  850  may not extend to the edges of the touch sensor panel; a touch sensor panel region  851  may extend beyond electrode layer  850  and allow for connections to electrode layer  810  (e.g., connections of lines from sense circuitry  898  to traces  502 A- 502 D at bonding pads  849 A- 849 D). In the example shown in  FIGS. 8E and 8F , electrode layer  850  can be connected to external shield circuitry  899  via trace  897  at bonding pads  846 A and  846 B, which can be coupled to bonding pad regions  509 A and  509 B, respectively, in electrode layer  810 . 
     In the example shown in  FIGS. 8E and 8F , electrode layer  850  can be coupled to a conductive line  855 , which may have lower resistance than electrode layer  850 , and which may correspond to conductive line  520  shown in  FIG. 5A . Conductive line  855  can be coupled to one or more electrode layer regions  853 , which in some examples can be electrically unconnected to touch node electrodes  501 A through  501 D, traces  502 A through  502   d , or bonding regions  509 A and  509 B in layer  810 . Conductive line  855  and one or more of bonding pads  846 A and  846 B can be made of the same conductive material (e.g., copper), and can be deposited as a single layer  840  between electrode layers  810  and electrode layer  850  (e.g., conductive line  855  and/or bonding pads  846 A and  846 B may be in contact with electrode layer  810  and/or electrode layer  850 ). However, conductive line  855  can be electrically unconnected to bonding pads  846 A and  846 B. Gaps  848 A,  848 B, and  848 C between substrate layer  830  and electrode layer  850  can be filled with a passivation material for providing electrical isolation and structural support. A purpose of conductive line  855  is to lower the effective sheet resistance of electrode layer  850  by coupling electrode layer  850  to a conductive material of lower resistance, thereby potentially improving the shielding performance of electrode layer  850  and the scalability of the touch sensor panel. 
       FIG. 9A  illustrates an exemplary material stackup  900  of a touch sensor panel with a single standalone substrate layer, a touch electrode layer disposed below the substrate layer, a top shield electrode layer, a bottom shield electrode layer, and a polarizer, depicted along cross-section A-A′ in  FIG. 5A , according to examples of the disclosure.  FIG. 9A  shows an electrode layer  910 , an electrode layer  920 , and a substrate layer  930  in a dual-layer configuration, as described above with respect to  FIG. 6  and dual-layer structure  660 . In the example shown in  FIG. 9A , electrode layer  910  is disposed below substrate layer  930 , and electrode layer  920  is disposed above substrate layer  930  (e.g., electrode layer  910  and/or electrode layer  920  may be in contact with substrate layer  930  on opposite surfaces of substrate layer  930 ). Electrode layer  910  includes touch node electrode  501 , and traces  502  and  504 , as shown in  FIGS. 5A-5B . In the example shown in  FIG. 9A , touch node electrode  501  and traces  502  and  504  can be comprised of a conductive material, and may be formed by patterning a single layer of that material (e.g., using photolithography and etching techniques). Trace  502  may include a bonding pad region electrically coupled to a first bonding pad  942  disposed below substrate  930  and trace  502  (e.g., bonding pad  942  may be in contact with trace layer  502 ), to connect trace  502  to first sense circuitry, such as shown in  FIGS. 2, 3A , and/or  3 B. (Trace  504  may be electrically coupled to second sense circuitry, which may be different from the first sense circuitry, via a bonding pad not shown in  FIG. 9A .) 
     In the example shown in  FIG. 9A , electrode layer  920  can function as a top shield that provides noise shielding for traces  502  and  504  from noise sources located above electrode layer  920 . This shielding may be beneficial, for example, to protect the traces from interference from noise generated from above the touch sensor panel, such as from the contact environment. In the example shown, electrode layer  920  includes shielding regions  922  and  924 , which may be comprised of a conductive material (e.g., ITO), and may be formed by patterning a single layer of that material (e.g., using photolithography and etching techniques). However, other conductive materials may be used. In  FIG. 9A , shielding regions  922  and  924  may be disposed directly above traces  504  and  502 , respectively, and provide top shielding for those respective traces. Shielding regions  922  and  924  may correspond to shielding regions  512  and  510  in  FIG. 5B , which can similarly provide top shielding for traces  504  and  502 . In the example shown, electrode layer  920  does not include material disposed directly above the touch node electrode  501  and thus may not provide top shielding for touch node electrode  501 . This is because top shielding of touch node electrode  501  could dampen the touch sensor panel&#39;s ability to detect changes in capacitance, as by limiting the extent and/or flux of fringing electric fields extending above touch node electrode  501 , with which an object, such as a user&#39;s finger, may capacitively interact. 
     In some examples, shielding region  924  may include a bonding pad region electrically coupled to a second bonding pad  944 , which may be disposed above substrate layer  930  and shielding region  924  (e.g., bonding pad  944  may be in contact with shielding region  924 ), to connect electrode layer  920  to first drive circuitry. The first drive circuitry may apply a guard signal, which may be an AC or DC voltage signal, to shielding region  924  (and, via conductive material not shown in  FIG. 9A , to shielding region  922 ). 
     In the example shown in  FIG. 9A , substrate layer  930 , electrode layer  910  (which may be formed on one side of substrate layer  930 ), and electrode layer  920  (which may be formed on the opposite side of substrate layer  930 ) can be viewed as a dual-layer structure  935 , analogous to the dual-layer structure  660  in  FIG. 6 . In some examples, passivation layers can be added above and below dual-layer structure  935 , for example to protect dual-layer structure  935  from environmental hazards (e.g., scratching, moisture). In the example shown in  FIG. 9A , a first passivation layer  946  may be disposed above dual-layer structure  935 . That is, passivation layer  946  may be disposed above substrate layer  930  and electrode layer  920  (e.g., passivation layer  946  may be in contact with substrate layer  930  and/or shielding regions  922  and  924 ). Similarly, a second passivation layer  948  may be disposed below dual-layer structure  935 . That is, passivation layer  948  may be disposed below substrate layer  930 , touch node electrode  501 , and traces  502  and  504 , such that touch node electrode  501  and traces  502  and  504  may be disposed between substrate layer  930  and passivation layer  948  (e.g., passivation layer  948  may be in contact with substrate layer  930 , touch node electrode  501 , and/or traces  502  and  504 ). 
     In the example shown in  FIG. 9A , the example stackup  900  includes a third electrode layer, shown in the figure as electrode layer  950 . Unlike in the example shown in  FIG. 6 , however, electrode layer  950  in example stackup  900  need not be formed on a surface of a standalone substrate layer. Instead, electrode layer  950  can be formed on a surface of a polarizer  960 , which may be a circular polarizer on the surface of (or otherwise part of) a display (e.g., electrode layer  950  may be in contact with polarizer  960 ). In the example shown in  FIG. 9A , dual-layer structure  935 , along with passivation layers  946  and  948 , may be laminated to polarizer  960 , with adhesive layer  970  disposed between dual-layer structure  935  and polarizer  960 . That is, adhesive layer  970  may be disposed below passivation layer  948  and above polarizer  960  (e.g., adhesive layer  970  may be in contact with passivation layer  948  and polarizer  960 ). In the example shown in  FIG. 9A , electrode layer  950  can function as a bottom shield that provides noise shielding for touch node electrode  501  and traces  502  and  504 , which may be disposed directly above electrode layer  950 , from noise sources (such as a display) that may be located below electrode layer  950 . Electrode layer  950  may be formed by coating polarizer  960  with a single layer of conductive material. Electrode layer  950  may be comprised of nanowire materials or ITO, for example, although other conductive materials may be used. 
     Electrode layer  950  may be electrically coupled to one or more bonding pads, to connect to second drive circuitry. In some examples, such as shown in  FIG. 9A , the one or more bonding pads may include bonding pad  962 , which can be disposed below polarizer layer  960  (e.g., bonding pad  962  may be in contact with polarizer layer  960 ). The second drive circuitry may apply a guard signal, which may be an AC or DC voltage signal, to electrode layer  950 . (The second drive circuitry may be, but need not be, the same as the first drive circuitry.) 
       FIG. 9B  illustrates an exemplary material stackup  900  of a touch sensor panel with a single standalone substrate layer, a touch electrode layer disposed below the substrate layer, a top shield electrode layer, a bottom shield electrode layer, and a polarizer, depicted along cross-section A-A′ in  FIG. 5A , according to examples of the disclosure. Unlike the example stackup shown in  FIG. 9A , in which electrode layer  950  is disposed below polarizer  960 , the example stackup shown in  FIG. 9B  shows electrode layer  950  disposed above polarizer  960 . In examples such as shown in  FIG. 9B , electrode layer  950  can be formed on the top surface of polarizer  960  (e.g., electrode layer  950  may be in contact with polarizer  960 ), which in some examples may be integrated into a display (not shown). Electrode layer  950  may be coupled to drive circuitry via a bonding pad, such as bonding pad  962 , disposed above polarizer  960  (e.g., bonding pad  962  may be in contact with polarizer  960 ). In the example shown in  FIG. 9B , example stackup  900  includes a conductive line  955  to reduce the effective sheet resistance of electrode layer  950 , such as described above with respect to  FIG. 5A . In the example shown, conductive line  955  is shown disposed between polarizer  960  and electrode layer  950  (e.g., conductive line  955  may be in contact with polarizer  960  and/or electrode layer  950 , and conductive line  955  may be embedded in electrode layer  950 ). Other examples may not include conductive line  955 . 
       FIGS. 9C and 9D  show further examples of stackup  900  that include a conductive line  955  to reduce the effective sheet resistance of electrode layer  950 , such as described above with respect to  FIG. 5A  and  FIG. 9B . In some examples of stackup  900  that include a conductive line  955 , such as shown in  FIG. 9C , conductive line  955  may be disposed below polarizer  960  (e.g., conductive line  955  may be in contact with polarizer  960 ). Electrode layer  950  may be formed on the bottom surfaces of polarizer  960  and conductive line  955  (e.g., electrode layer  950  may be in contact with polarizer  960  and/or conductive line  955 , and conductive line  955  may be embedded in electrode layer  950 ). In some examples, such as shown in  FIG. 9D , conductive line  955  may be disposed below electrode layer  950  (e.g., conductive line  955  may be in contact with electrode layer  950 ). A passivation layer  980  may be formed on the bottom surfaces of electrode layer  950  and conductive line  955  (e.g., passivation layer  980  may be in contact with electrode layer  950  and/or conductive line  955 , and conductive line  955  may be embedded in passivation layer  980 ). In the examples of both  FIGS. 9C and 9D , the inclusion and electrical coupling of conductive line  955  to electrode layer  950  can lower the overall sheet resistance of electrode layer  950 , allowing for better touch sensor performance, and potentially allowing example  900  to scale to larger panel sizes more easily than examples that do not include the conductive line. 
     Example stackup  900  may provide several advantages over example stackup  690  shown in  FIG. 6 . In example stackup  690 , electrode layer  610  (which includes touch node electrode  601  and traces  602 ) can be bottom-shielded from noise by electrode layer  650 , where electrode layer  610  and electrode layer  650  are on opposite sides of a standalone substrate layer (substrate layer  640 ) in a dual-layer structure. However, in stackup  900 , bottom shielding of electrode layer  910  (which includes touch node electrode  501  and traces  502  and  504 ) can instead be provided by electrode layer  950 . Unlike in example stackup  690 , electrode layer  910  and electrode layer  950  are not separated by a standalone substrate layer in a dual-layer structure. Instead, electrode layer  910  and electrode layer  950  are both disposed on the same side of substrate layer  930 , with electrode layer  950  formed on polarizer  960  (which may be incorporated into a display) instead of on a standalone substrate layer. Compared to example stackup  690 , the configuration of example stackup  900  eliminates one standalone substrate layer (e.g., substrate layer  640  in  FIG. 6 ), potentially eliminating the touch sensor panel thickness associated with that substrate layer. Moreover, in some examples in which the touch sensor panel is part of a touch screen, example stackup  900  may integrate the touch sensor panel into a display, which can reduce the thickness of the resulting touch screen stackup. Further, in some examples in which a touch sensor panel is integrated into a display, a polarizer component of the display (e.g., polarizer  960  in  FIG. 9A ) can be used as a substrate on which an electrode layer (e.g., electrode layer  950 ) can be formed. Economic efficiencies can be gained, and fabrication of some touch screen examples may be simplified, by this shared use of components. Meanwhile, shielding of touch node electrode  501  and traces  502  and  504  need not be compromised by the elimination of a standalone substrate layer, as electrode layer  910  (which includes touch node electrode  501  and traces  502  and  504 ) is shielded in the example from both the top and the bottom, similar to electrode layer  610  in  FIG. 6 . 
     In some examples, such as shown in  FIGS. 9A-9D , electrode layer  950  can be comprised of nanowire materials, such as silver nanowire. An advantage that can be conveyed by nanowire materials is that they can exhibit improved mechanical flexibility over some other conductive materials (e.g., ITO), potentially allowing example  900  to be more structurally robust than example  690  in  FIG. 6 . Further, nanowire materials may exhibit lower sheet resistance than some other conductive materials. Similarly, in examples that include a conductive line coupled to an electrode layer, such as described above and shown in  FIGS. 9B, 9C, and 9D , that conductive line may contribute to lower sheet resistance. This lower sheet resistance can allow for more effective shielding and better touch sensor performance, and may allow example  900  to scale to larger panel sizes more easily than example  690 . 
       FIGS. 9E-1 through 9E-3  illustrate an example process for forming exemplary material stackup  900 , as shown in  FIG. 9C . Electrode layers  910 ,  920  (e.g., shielding regions  922  and  924 ), and  950 , substrate layer  930 , passivation layers  946  and  948 , bonding pads  942 ,  944 , and  962 , polarizer  960 , and conductive line  955  are as shown in  FIG. 9C .  FIG. 9E-1  shows stackup  900  after a standard annealing process, the result of which may include a dual-layer structure  935  as shown in  FIG. 9C —electrode layers  910  and  920  formed on opposite sides of substrate layer  930 —with passivation layers  946  and  948  on the top and bottom sides, respectively, of dual-layer structure  935 . In  FIG. 9E-1 , electrode layer  950  and polarizer  960  (shown in  FIG. 9C ) are not shown. 
       FIG. 9E-2  shows electrode layer  950  formed below polarizer  960  of example stackup  900 , for example via a lamination process (e.g., electrode layer  950  may be in contact with polarizer  960 ), with electrode layer  950  coupled to bonding pad  962 , disposed below polarizer  960  (e.g., bonding pad  962  may be in contact with polarizer  960 ). (In some examples, such as shown in  FIG. 9B , electrode layer  950  and bonding pad  962  may be formed above polarizer  960 .) In some examples in which the touch sensor panel is part of a touch screen, polarizer  960  and electrode layer  950  may be integrated into a display (not shown). The dual-layer structure  935 , with the addition of passivation layers  946  and  948 , can be laminated (via lamination process  975 ) to polarizer  960 . Lamination process  975  may add adhesive layer  970  between polarizer  960  and the passivation layer  948  below dual-layer stackup  935 . (In some examples, such as shown in  FIG. 9B , in which electrode layer  950  may be disposed above polarizer  960 , adhesive layer  970  may be disposed between electrode layer  950  and passivation layer  948 .) A result of this lamination process is the example stackup  900  as shown in  FIG. 9A  (reproduced as  FIG. 9E-3  for clarity). Other processes can additionally or alternatively be used to form example stackup  900 . 
     According to the above, some examples of the disclosure are directed to a touch sensor panel stackup comprising: a first substrate layer; a first electrode layer comprising one or more of a touch electrode and a trace configured to couple the touch electrode to sense circuitry, the first electrode layer located on a first side of the first substrate layer; a second electrode layer located on the first side of the first substrate layer; a passivation layer disposed in between the first electrode layer and the second electrode layer; and a third electrode layer located on a second side of the first substrate layer, different from the first side of the first substrate layer, wherein: the first electrode layer is comprised of a first conductive material, the second electrode layer is comprised of a second conductive material, the third electrode layer is comprised of a third conductive material, and the touch sensor panel stackup does not include a second substrate layer between the first substrate layer and the second electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the second electrode layer is configured to shield the first electrode layer from first noise, and the third electrode layer is configured to shield the first electrode layer from second noise. Additionally or alternatively to one or more of the examples disclosed above, in some examples the first electrode layer is in contact with the passivation layer and the second electrode layer is in contact with the passivation layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the first electrode layer is in contact with a surface of the first substrate layer on the first side of the first substrate layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the third electrode layer is in contact with a surface of the first substrate layer on the second side of the first substrate layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the first electrode layer comprises a touch electrode and a trace, the second electrode layer is configured to shield the trace, the second electrode layer is configured to not shield a region of the touch electrode, and the third electrode layer is configured to shield the trace and the touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples the touch sensor panel stackup further comprises a conductive line electrically coupled to the third electrode layer and configured to lower an effective sheet resistance of the third electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is disposed on a surface of the third electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is embedded in the third electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is in contact with the first substrate layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the first electrode layer comprises a touch electrode and a trace, the second electrode layer is configured to shield the trace and the touch electrode, the third electrode layer is configured to shield the trace, and the third electrode layer is configured to not shield a region of the touch electrode. Additionally or alternatively to one or more of the examples disclosed above, in some examples the touch sensor panel stackup further comprises a conductive line electrically coupled to the second electrode layer and configured to lower an effective sheet resistance of the second electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is disposed on a surface of the second electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is coupled to a region of the first electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the touch sensor panel stackup further comprises one or more bonding pads, wherein the conductive line and the one or more bonding pads comprise a layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the second electrode layer is in contact with a component of a display. Additionally or alternatively to one or more of the examples disclosed above, in some examples the component is a polarizer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the touch sensor panel stackup further comprises a conductive line electrically coupled to the second electrode layer and configured to lower an effective sheet resistance of the second electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is disposed on a surface of the polarizer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the conductive line is disposed on a surface of the second electrode layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the second electrode layer is configured to be coupled to first drive circuitry, and the third electrode layer is configured to be coupled to second drive circuitry. Additionally or alternatively to one or more of the examples disclosed above, in some examples the first drive circuitry is the second drive circuitry. Additionally or alternatively to one or more of the examples disclosed above, in some examples the first electrode layer is coupled to one or more bonding pads disposed on the first side of the first substrate layer, and the second electrode layer is coupled to one or more bonding pads disposed on the first side of the first substrate layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the one or more bonding pads coupled to the first electrode layer and the one or more bonding pads coupled to the second electrode layer comprise a same layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples one or more of the first conductive material, the second conductive material, and the third conductive material includes silver nanowire. Additionally or alternatively to one or more of the examples disclosed above, in some examples one or more of the first conductive material, the second conductive material, and the third conductive material includes indium tin oxide. Additionally or alternatively to one or more of the examples disclosed above, in some examples one or more of the first conductive material, the second conductive material, and the third conductive material includes a metal mesh. Additionally or alternatively to one or more of the examples disclosed above, in some examples the touch electrode is configured to receive a stimulation signal, one or both of the second electrode layer and the third electrode layer is configured to receive a guard signal, and the guard signal is referenced to the stimulation signal. 
     Some examples of the disclosure are directed to a method for fabricating a touch sensor panel, the method comprising: forming a first substrate layer; forming a first electrode layer, the first electrode layer located on a first side of the first substrate layer, wherein the first electrode layer comprises one or more of a touch electrode and a trace configured to couple the touch electrode to sense circuitry; forming a second electrode layer located on the first side of the first substrate layer; forming a passivation layer disposed in between the first electrode layer and the second electrode layer; and forming a third electrode layer located on a second side of the first substrate layer, different from the first side of the first substrate layer, wherein the first electrode layer is comprised of a first conductive material, the second electrode layer is comprised of a second conductive material, the third electrode layer is comprised of a third conductive material, and the touch sensor panel does not include a second substrate layer between the first substrate layer and the second substrate layer. Additionally or alternatively to one or more of the examples disclosed above, in some examples the second electrode layer is configured to shield the first electrode layer from first noise, and the third electrode layer is configured to shield the first electrode layer from second noise. 
     Although examples of this disclosure have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of examples of this disclosure as defined by the appended claims.

Metadata:
Filing Date: 20190930
Publication Date: 20210323
Grant Date: 20210323
Priority Date: 20160923
Inventors: CHEN, SZ-HSIAO
TUNG, CHUN-HAO
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/0447", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04103", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0443", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04164", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134336", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13454", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04103", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04112", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136204", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04103", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136204", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134336", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13454", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F2203/04112", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 60043298