PATENT DOCUMENT

Publication Number: US-9612170-B2
Application Number: US-201514823910-A
Country: US
Kind Code: B2

Title: Transparent strain sensors in an electronic device

Abstract:
One or more strain sensors can be included in an electronic device. Each strain sensor includes a strain sensitive element and one or more strain signal lines connected directly to the strain sensitive element. The strain sensor(s) are used to detect a force that is applied to the electronic device, to a component in the electronic device, and/or to an input region or surface of the electronic device. A strain sensitive element is formed or processed to have a first gauge factor and the strain signal line(s) is formed or processed to have a different second gauge factor. Additionally or alternatively, a strain sensitive element is formed or processed to have a first conductance and the strain signal line(s) is formed or processed to have a different second conductance.

Claims:
What is claimed is: 
     
       1. A transparent strain sensor positioned in a visible area of an electronic device, the transparent strain sensor comprising:
 a transparent strain sensitive element comprised of a first transparent conductive material having a first gauge factor; 
 a transparent strain signal line connected directly to the transparent strain sensitive element and comprised of a different second transparent conductive material having a second gauge factor, wherein the first gauge factor is greater than the second gauge factor. 
 
     
     
       2. The transparent strain sensor of  claim 1 , wherein the first transparent conductive material has a first electrical resistance and the second transparent conductive material a second electrical resistance and the first electrical resistance is greater than the second electrical resistance. 
     
     
       3. The transparent strain sensor of  claim 1 , wherein the first transparent conductive material and the second transparent conductive material each comprise a transparent conducting oxide film. 
     
     
       4. The transparent strain sensor of  claim 3 , wherein the first transparent conductive material comprises one of a gallium doped zinc oxide film and an aluminum doped zinc oxide film. 
     
     
       5. The transparent strain sensor of  claim 3 , wherein the second transparent conductive material comprises an indium tin oxide film. 
     
     
       6. The transparent strain sensor of  claim 3 , wherein the first transparent conductive material comprises a multi-layer transparent conductive structure that includes an insulating layer disposed between two transparent conducting oxide films. 
     
     
       7. The transparent strain sensor of  claim 2 , wherein the second transparent conductive material in the strain signal line is processed to produce the second electrical resistance. 
     
     
       8. The transparent strain sensor of  claim 7 , wherein the second transparent conductive material is doped with one or more dopants to produce the second electrical resistance. 
     
     
       9. The transparent strain sensor of  claim 1 , wherein the first transparent conductive material in the strain sensitive element is processed to produce the first gauge factor. 
     
     
       10. The transparent strain sensor of  claim 8 , wherein the first transparent conductive material in the strain sensitive element is laser annealed to produce the first gauge factor. 
     
     
       11. The transparent strain sensor of  claim 1 , wherein the visible area of the electronic device comprises a display stack of the electronic device. 
     
     
       12. A transparent strain sensor positioned in a visible area of an electronic device, the transparent strain sensor comprising:
 a transparent strain sensitive element comprising a hybrid transparent conductive material that includes:
 a first transparent conductive segment having a first gauge factor and a first electrical resistance; and 
 a second transparent conductive segment connected to the first conductive segment that has a second gauge factor and a second electrical resistance, 
 
 wherein the first gauge factor is greater than the second gauge factor and the first electrical resistance is greater than the second electrical resistance. 
 
     
     
       13. The transparent strain sensor of  claim 12 , further comprising at least one transparent strain signal line connected directly to the transparent strain sensitive element, wherein the at least one transparent signal line has a third gauge factor and a third electrical resistance, wherein the third electrical resistance is less than the first and the second electrical resistances. 
     
     
       14. The transparent strain sensor of  claim 12 , wherein the visible area of the electronic device comprises a display stack of the electronic device. 
     
     
       15. A method for producing a transparent strain sensor, the method comprising:
 providing a transparent strain sensitive element on a substrate, wherein the transparent strain sensitive element comprises one or more first transparent conductive materials having a first gauge factor; and 
 providing a transparent strain signal line that is connected directly to the transparent strain sensitive element on the substrate, wherein the transparent strain signal line comprises one or more second transparent conductive materials that are different from the one or more first transparent conductive materials and have a different second gauge factor. 
 
     
     
       16. The method of  claim 15 , wherein the one or more first transparent conductive materials in the transparent strain sensitive element has a first electrical resistance and the one or more second transparent conductive materials in the transparent strain signal line has a second electrical resistance, the first electrical resistance being greater than the second electrical resistance. 
     
     
       17. A method for producing a transparent strain sensor, the method comprising:
 providing a transparent strain sensitive element on a substrate, wherein the transparent strain sensitive element comprises one or more transparent conductive materials; 
 providing a transparent strain signal line that is connected directly to the transparent strain sensitive element on the substrate; and 
 processing the one or more transparent conductive materials in the transparent strain sensitive element to adjust a property of the one or more transparent conductive materials to increase a gauge factor of the transparent strain sensitive element. 
 
     
     
       18. The method of  claim 17 , wherein the transparent strain signal line is comprised of the same one or more transparent conductive materials. 
     
     
       19. The method of  claim 18 , further comprising processing the one or more transparent conductive materials in the transparent strain signal line to increase a conductance of the transparent strain signal line. 
     
     
       20. The method of  claim 17 , wherein processing the one or more transparent conductive materials in the transparent strain sensitive element to increase the gauge factor of the transparent strain sensitive element comprises laser annealing the one or more transparent conductive materials in the transparent strain sensitive element to increase a crystallinity of the one or more transparent conductive materials to increase the gauge factor of the transparent strain sensitive element. 
     
     
       21. A method for producing a transparent strain sensor, the method comprising:
 providing a transparent strain sensitive element on a substrate; 
 providing a transparent strain signal line that is connected directly to the transparent strain sensitive element on the substrate, wherein the transparent strain signal line comprises one or more transparent conductive materials; and 
 processing the one or more transparent conductive materials in the transparent strain signal line to adjust a property of the one or more transparent conductive materials to increase a conductance of the transparent strain signal line. 
 
     
     
       22. The method of  claim 21 , wherein processing the one or more transparent conductive materials in the transparent strain signal line to increase the conductance of the transparent strain signal line comprises doping the one or more transparent conductive materials in the transparent strain signal line with one or more dopants to reduce an electrical resistance of the one or more transparent conductive materials to increase the conductance of the transparent strain signal line. 
     
     
       23. An electronic device, comprising:
 a display stack for a display, comprising:
 a cover glass; and 
 a strain sensing structure positioned below the cover glass, the strain sensing structure comprising:
 a substrate; 
 a first transparent strain sensitive element positioned on a first surface of the substrate; 
 a second transparent strain sensitive element positioned on a second surface of the substrate; and 
 one or more transparent strain signal lines connected directly to each transparent strain sensitive element, wherein the first and the second transparent strain sensitive elements have a gauge factor that is greater than a gauge factor of the transparent strain signal lines, and wherein the first and the second transparent strain sensitive elements and the transparent strain signal lines are positioned in an area that is visible when viewing the display; 
 
 
 sense circuitry electrically connected to the transparent strain signal lines; and 
 a controller operably connected to the sense circuitry and configured to determine an amount of force applied to the cover glass based on the signals received from the sense circuitry. 
 
     
     
       24. The electronic device of  claim 23 , wherein the first and the second transparent strain sensitive elements are each comprised of one of a gallium doped zinc oxide film and an aluminum doped zinc oxide film and the transparent strain signal lines are comprised of a indium tin oxide film.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62/195,030, filed on Jul. 21, 2015, and entitled “Transparent Strain Sensors in an Electronic Device,” which is incorporated by reference as if fully disclosed herein. 
    
    
     FIELD 
     Embodiments described herein generally relate to electronic devices. More particularly, the present embodiments relate to one or more transparent strain sensors in an electronic device. 
     BACKGROUND 
     Strain gauges or sensors are used to detect or measure strain on an object. Typically, the electrical resistance of a strain sensor varies in proportion to the compression and tension forces it is experiencing. The gauge factor of a strain sensor represents the sensitivity of the material to strain. In other words, the gauge factor indicates how much the resistance of the strain sensor changes with strain. The higher the gauge factor, the larger the change in resistance. Higher gauge factors allow a greater range of strain to be detected and measured. 
     In some situations, it is desirable for the strain sensors to be made of a transparent material. For example, transparent strain sensors may be used when the strain sensors are located in an area where the strain sensors can be detected visually by a user (e.g., though a display). However, some materials that are used to form transparent strain sensors have low or zero gauge factors. 
     SUMMARY 
     One or more transparent strain sensors can be included in an electronic device. As used herein, the term “strain sensor” refers to a strain sensitive element and the one or more strain signal lines that connect directly to the strain sensitive element. In one embodiment, the strain sensor(s) are used to detect a force that is applied to the electronic device, to a component in the electronic device, such as an input button, and/or to an input region or surface of the electronic device. In one non-limiting example, a force sensing device that includes one or more strain sensors may be incorporated into a display stack of an electronic device. The one or more strain sensors can be positioned in an area of the display stack that is visible to a user when the user is viewing the display. As such, the one or more transparent strain sensors can be formed with a transparent conductive material or two or more transparent conductive materials. 
     In some embodiments, each transparent strain sensitive element is formed or processed to have a first gauge factor and a first conductance. Each transparent strain signal line is formed or processed to have a different second gauge factor and a different first conductance. For example, in one embodiment the transparent material or materials that form a transparent strain sensitive element may have a higher gauge factor than the transparent material(s) of the at least one transparent strain signal line while the conductance of the transparent strain sensitive element may be less than the conductance of the transparent strain signal line(s). Thus, the transparent strain sensitive element is configured to be more sensitive to strain than the transparent strain signal line(s) and the transparent strain signal line(s) is configured to transmit signals more effectively. 
     In one aspect a transparent strain sensor includes a transparent strain sensitive element and a transparent strain signal line connected directly to the strain sensitive element. The transparent strain sensitive element is formed with comprised a first transparent conductive material having a first gauge factor. The transparent strain signal line is formed with a second transparent conductive material having a second gauge factor. The first gauge factor can be greater than the second gauge factor in one embodiment. Additionally or alternatively, the first transparent conductive material may have a first electrical resistance and the second transparent conductive material a second electrical resistance with the first electrical resistance being greater than the second electrical resistance. In a non-limiting example, the transparent strain sensitive element may be formed with a transparent GZO film or a transparent AZO film and the at least one transparent strain signal line is formed with a transparent ITO film. 
     In another aspect, a transparent strain sensor can be formed with a hybrid transparent conductive material that includes at least one first transparent conductive segment that has a first gauge factor and a first electrical resistance and at least one second transparent conductive segment that has a second gauge factor and a second electrical resistance. The first transparent conductive segment is connected to the second transparent conductive segment. The first gauge factor can be greater than the second gauge factor and the first electrical resistance greater than the second electrical resistance. 
     In another aspect, a transparent strain sensor can include a transparent strain sensitive element and at least one transparent strain signal line connected directly to the transparent strain sensitive element. The transparent strain sensitive element and transparent strain signal line(s) can be formed with the same a transparent conductive material or materials, but the transparent conductive material(s) in the strain sensitive element and/or in the at least one strain signal line may be doped with one or more dopants to change the gauge factor and/or the conductance of the transparent conductive material. Thus, the transparent strain sensitive element and the at least one transparent strain signal line can have different gauge factors and/or electrical conductance. In some embodiments, the gauge factor of the transparent strain sensitive element is greater than the gauge factor of the at least one strain signal line. Additionally or alternatively, the transparent strain sensitive element can have a first electrical resistance and the transparent strain signal line(s) a second overall electrical resistance where the first electrical resistance is greater than the second electrical resistance. 
     In yet another aspect, a method for producing a transparent strain sensor may include providing a transparent strain sensitive element on a substrate and providing a transparent strain signal line that is connected directly to the transparent strain sensitive element on the substrate. The transparent strain sensitive element is formed with one or more transparent conductive materials having a first gauge factor. The transparent strain signal line is formed with one or more transparent conductive materials having a different second gauge factor. 
     In another aspect, a method for producing a transparent strain sensor can include providing a transparent strain sensitive element on a substrate, where the transparent strain sensitive element comprises one or more transparent conductive materials, and providing a transparent strain signal line that is connected directly to the strain sensitive element on the substrate. The one or more transparent conductive materials of the transparent strain sensitive element is processed to increase a gauge factor of the transparent strain sensitive element. In one non-limiting example, the one or more transparent conductive materials may be can be laser annealed to increase the crystallinity of the transparent strain sensitive element, which results in a higher gauge factor. In some embodiments, the transparent strain signal line can also be formed with the same or different transparent conductive material(s), and the transparent conductive material(s) of the transparent strain signal line may be processed to increase a conductance of the transparent strain signal line. 
     In yet another aspect, a method for producing a transparent strain sensor may include providing a transparent strain sensitive element on a substrate and providing a transparent strain signal line that is connected directly to the strain sensitive element on the substrate. The transparent strain signal line is formed with one or more transparent conductive materials. The one or more transparent conductive materials of the transparent strain signal line can be processed to increase a conductance of the transparent strain signal line. In one non-limiting example, the one or more transparent conductive materials may be doped with a dopant or dopants that reduce the overall electrical resistance of the strain signal line, which in turn increases the conductance of the transparent strain signal line. 
     In yet another aspect, an electronic device can include a cover glass and a strain sensing structure positioned below the cover glass. The strain sensing structure may include a substrate, a first transparent strain sensitive element positioned on a first surface of the substrate and a second transparent strain sensitive element positioned on a second surface of the substrate. One or more transparent strain signal lines are connected to each transparent strain sensitive element. In some embodiments, the first and second transparent strain sensitive elements have a gauge factor that is greater than a gauge factor of the transparent strain signal lines. Sense circuitry is electrically connected to the transparent strain signal lines, and a controller is operably connected to the sense circuitry. The controller is configured to determine an amount of force applied to the cover glass based on the signals received from the sense circuitry. In some embodiments, the first and second transparent strain sensitive elements and the transparent strain signal lines are positioned in an area of the display stack that is visible to a user when the user is viewing the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  depicts one example of an electronic device that can include one or more strain sensors; 
         FIG. 2  depicts a plan view of an example strain sensitive structure that is suitable for use in a display stack of an electronic device; 
         FIG. 3  depicts a plan view of one example of an optically transparent serpentine strain sensitive element which may be used in the example strain sensitive structure depicted in  FIG. 2 ; 
         FIG. 4  is an enlarged view of the area shown in  FIG. 2 ; 
         FIG. 5  is a flowchart of a first method for producing a strain sensor; 
         FIG. 6  is a simplified cross-sectional view taken along line A-A in  FIG. 4  of a first strain sensitive structure that is suitable for use as the strain sensitive structure shown in  FIG. 2 ; 
         FIG. 7  is a simplified cross-sectional view taken along line A-A in  FIG. 4  of a second strain sensitive structure that is suitable for use as the strain sensitive structure shown in  FIG. 2 ; 
         FIG. 8  is a plan view of a third example of a strain sensitive element that is suitable for use as the strain sensitive element shown in  FIGS. 2 and 4 ; 
         FIG. 9  is a flowchart of a second method for producing a strain sensor; 
         FIG. 10  is a flowchart of a third method for producing a strain sensor; 
         FIG. 11  is a flowchart of a fourth method for producing a strain sensor; 
         FIG. 12  is a illustrative block diagram of an electronic device that can include one or more strain sensors; 
         FIG. 13  is a cross-sectional view of an example display stack that includes strain sensors; 
         FIG. 14  is a simplified cross-sectional view of the strain sensitive structure responding to force; and 
         FIG. 15  is a simplified schematic diagram of sense circuitry operably connected to a strain sensor. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The following disclosure relates to an electronic device that includes one or more strain sensors configured to detect strain based on an amount of force applied to the electronic device, a component in the electronic device, and/or an input region of the electronic device. As one example, the one or more strain sensors can be incorporated into a display stack of an electronic device, and at least a portion of the top surface of the display screen may be an input region. In some embodiments, the one or more transparent strain sensors are located in an area of the display stack that is visible to a user when the user is viewing the display. As used herein, the term “strain sensor” includes a strain sensitive element and at least one strain signal line physically or directly connected to the strain sensitive element. Additionally, “optically transparent” and “transparent” are defined broadly to include a material that is transparent, translucent, or not visibly discernable by the human eye. 
     In some embodiments, each strain sensitive element is formed or processed to have a first gauge factor and a first conductance. Each strain signal line is formed or processed to have a different second gauge factor and a different first conductance. For example, in one embodiment the material or materials that form a strain sensitive element may have a higher gauge factor than the material(s) of the at least one strain signal line while the conductance of the strain sensitive element may be less than the conductance of the strain signal line(s). Thus, the strain sensitive element is configured to be more sensitive to strain than the strain signal line(s) and the strain signal line(s) is configured to transmit signals more effectively. In a non-limiting example, the strain sensitive element may be formed with a transparent GZO film or a transparent AZO film and the at least one strain signal line formed with a transparent ITO film. 
     In some embodiments, a gauge factor and/or a conductance of a strain sensitive element or a strain signal line can be based at least in part on the structure and/or the operating conditions of the electronic device or a component in the electronic device that includes one or more strain sensors. 
     In another embodiment, a strain sensitive element and/or the one or more strain signal lines connected to the strain sensitive element may be processed after the strain sensitive elements and the strain signal line(s) are formed. In a non-limiting example, the material used to form the strain sensitive element and the strain signal line(s) can be the same material or materials, and the material(s) in the strain sensitive element and/or the material(s) in the strain signal lines is processed to adjust the conductance and/or the gauge factor of the processed component. In one embodiment, the strain sensitive element can be laser annealed to increase the crystallinity of the strain sensitive element, which results in a higher gauge factor. Additionally or alternatively, the one or more strain signal lines may be doped with a dopant or dopants that reduce the overall electrical resistance of the strain signal line(s), which in turn increases the conductance of the strain signal line(s). 
     And in yet another embodiment, one or more parameters of the fabrication process that is used to form the strain sensitive element and/or the strain signal line(s) may be adjusted to increase the gauge factor and/or the conductance of the component. For example, in one embodiment the flow rate of oxygen can be increased when the strain sensitive element is deposited onto the substrate. The higher oxygen flow rate can reduce the carrier concentration and/or mobility of the carriers in the strain sensitive element. In another embodiment, the thickness of the material used to form the strain sensitive element and/or the strain signal line(s) may be adjusted to increase the gauge factor or the conductance of the component. 
     Directional terminology, such as “top”, “bottom”, “front”, “back”, “leading”, “trailing”, etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments described herein can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration only and is in no way limiting. When used in conjunction with layers of a display or device, the directional terminology is intended to be construed broadly, and therefore should not be interpreted to preclude the presence of one or more intervening layers or other intervening features or elements. Thus, a given layer that is described as being formed, positioned, disposed on or over another layer, or that is described as being formed, positioned, disposed below or under another layer may be separated from the latter layer by one or more additional layers or elements. 
     These and other embodiments are discussed below with reference to  FIGS. 1-15 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  shows one example of an electronic device that can include one or more strain sensors. In the illustrated embodiment, the electronic device  100  is implemented as a smart telephone. Other embodiments can implement the electronic device differently. For example, an electronic device can be a laptop computer, a tablet computing device, a wearable computing device, a smart watch, a digital music player, a display input device, a remote control device, and other types of electronic devices that include a strain sensor or sensors. 
     The electronic device  100  includes an enclosure  102  surrounding a display  104  and one or more input/output (I/O) devices  106  (shown as button). The enclosure  102  can form an outer surface or partial outer surface for the internal components of the electronic device  100 , and may at least partially surround the display  104 . The enclosure  102  can be formed of one or more components operably connected together, such as a front piece and a back piece. Alternatively, the enclosure  102  can be formed of a single piece operably connected to the display  104 . 
     The display  104  can be implemented with any suitable display, including, but not limited to, a multi-touch sensing touchscreen device that uses liquid crystal display (LCD) technology, light emitting diode (LED) technology, organic light-emitting display (OLED) technology, or organic electro luminescence (OEL) technology. 
     In some embodiments, the I/O device  106  can take the form of a home button, which may be a mechanical button, a soft button (e.g., a button that does not physically move but still accepts inputs), an icon or image on a display, and so on. Further, in some embodiments, the button can be integrated as part of a cover glass of the electronic device. Although not shown in  FIG. 1 , the electronic device  100  can include other types of I/O devices, such as a microphone, a speaker, a camera, and one or more ports such as a network communication port and/or a power cord port. 
     Strain sensors can be included in one or more locations of the electronic device  100 . For example, in one embodiment one or more strains sensors may be included in the I/O device  106 . The strain sensor(s) can be used to measure an amount of force and/or a change in force that is applied to the I/O device  106 . In another embodiment, one or more strain sensors can be positioned under at least a portion of the enclosure to detect a force and/or a change in force that is applied to the enclosure. Additionally or alternatively, one or more strains sensors may be included in a display stack for the display  104 . The strain sensor(s) can be used to measure an amount of force and/or a change in force that is applied to the display or to a portion of the display. As described earlier, a strain sensor includes a strain sensitive element and at least one strain signal line physically or directly connected to the strain sensitive element. 
     In one non-limiting example, the entire top surface of a display may be an input region that is configured to receive one or more force inputs from a user.  FIG. 2  depicts a plan view of an example strain sensitive structure that is suitable for use in a display stack. The strain sensitive structure  200  can include a grid of independent optically transparent strain sensitive elements  204  that are formed in or on a substrate  202 . The strain sensitive elements  204  may be formed in or on at least a portion of one or both surfaces of the substrate  202 . The substrate  202  can be formed of any suitable material or materials. In one embodiment, the substrate  202  is formed with an optically transparent material, such as polyethylene terephthalate (PET). 
     As discussed earlier, the strain sensitive elements  204  are configured to detect strain based on an amount of force applied to an input region of the display. The strain sensitive elements  204  may be formed with a transparent conductive material or materials such as, for example, polyethylenedioxythiophene (PEDOT), a tin doped indium oxide (ITO) film, a gallium doped zinc oxide (GZO) film, an aluminum doped zinc oxide (AZO) film, carbon nanotubes, graphene, silver nanowire, other metallic nanowires, and the like. In certain embodiments, the strain sensitive elements  204  may be selected at least in part on temperature characteristics. For example, the material selected for transparent strain sensitive elements  204  may have a negative temperature coefficient of resistance such that, as temperature increases, the electrical resistance decreases. 
     In this example, the transparent strain sensitive elements  204  are formed as an array of rectilinear sensing elements, although other shapes and array patterns can also be used. In many examples, each individual strain sensitive element  204  may have a selected shape and/or pattern. For example, in certain embodiments, a strain sensitive element  204  may be deposited in a serpentine pattern, such as the pattern shown in  FIG. 3 . A strain sensitive element  204  can have a different pattern or configuration in other embodiments. 
     The strain sensitive element  204  may include at least two electrodes  300 ,  302  that are configured to be physically or directly connected to one or more strain signal lines (not shown). The strain signal line(s) can be connected to a conductive contact  206 , which operably connects the strain sensitive element  204  to sense circuitry (not shown). The conductive contact  206  may be a continuous contact or can be formed in segments that surround or partially surround the array of strain sensitive elements  204 . In other embodiments, a strain sensitive element  204  may be electrically connected to sense circuitry without the use of electrodes. For example, a strain sensitive element  204  may be connected to the sense circuitry using conductive traces that are formed as part of a film layer. 
     Referring now to  FIG. 4 , there is shown an enlarged view of the area  208  shown in  FIG. 2 . The electrodes  300 ,  302  of each strain sensitive element  204  are connected to the conductive contact  206  using strain signal lines  400 ,  402 , respectively. Together the strain sensitive element  204  and the strain signal lines  400 ,  402  physically or directly connected to the strain sensitive element  204  form a strain sensor  404 . In some embodiments, a gauge factor and/or a conductance of the strain sensitive element  204  and/or the strain signal line(s)  400 ,  402  can be based at least in part on the configuration of the strain sensitive structure  200 , on the operating conditions of the electronic device, and/or on the operating conditions of the component (e.g., display) in the electronic device that includes one or more strain sensors. 
       FIG. 5  is a flowchart of a first method for producing a strain sensor. Initially, one or more strain sensitive elements are provided that have a material or combination of materials that have been formed or processed to have a first conductance and a first gauge factor (block  500 ). Next, as shown in block  502 , one or more strain signal lines that are directly connected to each strain sensitive element are provided, where the strain signal line(s) include a material or combination of materials that have been formed or processed to have a different second conductance and a different second gauge factor. Various embodiments of such strain sensitive elements and strain signal line(s) are described in more detail in conjunction with  FIGS. 6-11 . 
     In one embodiment, the material(s) of each strain sensitive element has a lower conductance than the conductance of the material(s) of the at least one strain signal line. For example, the material(s) of each strain sensitive element may have a higher electrical resistance than the material(s) of the at least one strain signal line. Additionally, the first gauge factor of the strain sensitive element is higher than the second gauge factor of the at least one strain signal line that is connected to the strain sensitive element. Thus, the strain sensitive element is more sensitive to strain than the strain signal line(s) and the strain signal line(s) is configured to transmit signals more effectively. In a non-limiting example, the strain sensitive element may be formed with a transparent GZO film or a transparent AZO film and the at least one strain signal line formed with a transparent ITO film. 
     Referring now to  FIG. 6 , there is shown a simplified cross-sectional view taken along line A-A in  FIG. 4  of a first strain sensitive structure that is suitable for use as the strain sensitive structure  200  shown in  FIG. 2 . The strain sensitive structure  600  includes a strain sensitive element  204  disposed on a surface of the substrate  202 . The strain sensitive element  204  is connected to at least one strain signal line  400 . As described earlier, the strain sensitive element  204  is made of a material or combination of materials that has a first conductance and a first gauge factor and the at least one strain signal line  400  is made of a material or combination of materials having a different second conductance and a different second gauge factor. 
     The at least one strain signal line  400  is connected to the conductive contact  206 . In some embodiments, the conductive contact is made of copper and is positioned in a non-visible area of an electronic device (e.g., in a non-visible area of a display). A dielectric or insulating layer  602  may be disposed over at least a portion of the at least one strain signal line  400  and the strain sensitive element  204 . The insulating layer  602  may act as a protective layer for the strain signal line  400  and the strain sensitive element  204 . In embodiments where the strain sensitive element and the strain signal line(s) are formed with a substantially transparent material or materials, the insulating layer  602  can be made of a material or combination of materials that has an index of refraction that substantially matches the index of refraction of the strain sensitive element  204  and/or the at least one strain signal line  400 . 
       FIG. 7  is a simplified cross-sectional view taken along line A-A in  FIG. 4  of a second strain sensitive structure that is suitable for use as the strain sensitive structure  200  shown in  FIG. 2 . The strain sensitive structure  700  is similar to the strain sensitive structure  600  shown in  FIG. 6 , with the exception of the strain sensitive element  204 . In the embodiment of  FIG. 7 , the strain sensitive element  204  is an alternating multi-layer transparent conductive structure that includes a layer of insulating material  702  positioned between two layers of conductive material  704 . Each layer of conductive material  704  can be made of a material or combination of materials that has a first conductance and a first gauge factor. In some embodiments, the multi-layer structure of the strain sensitive element  204  is configured to have an overall electrical resistance that is lower than the strain sensitive element  204  in  FIG. 6  (e.g., a solid layer of conductive material) while still providing a higher gauge factor. In one non-limiting example, each layer of transparent conductive material can be formed with a transparent GZO film or a transparent AZO film. 
     The strain signal line  400  that is connected to the strain sensitive element  204  can be formed with a material or combination of materials that has a conductance and a gauge factor that are different from the overall conductance and the gauge factor of the multi-layer structure of the strain sensitive element  204 . As described earlier, the overall conductance of the strain sensitive element  204  may be less than the conductance of the strain signal line(s), while the gauge factor of the strain sensitive element  204  can be greater than the gauge factor of the strain signal line(s). 
     In the embodiments illustrated in  FIGS. 6 and 7 , the strain sensitive element has a higher gauge factor than the gauge factor of the at least one strain signal line connected to the strain sensitive element. The higher gauge factor allows the strain sensitive element to be more sensitive to strain than the strain signal line(s). Additionally, in some embodiments the electrical conductance of the strain signal line(s) is higher than the conductance of the strain sensitive element. Due to the higher conductance, the strain signal line or lines efficiently transmit signals produced by the strain sensitive element to the conductive contact  206 . 
     Referring now to  FIG. 8 , there is shown a plan view of a third example of a strain sensitive element that is suitable for use as the strain sensitive element  204  shown in  FIGS. 2 and 4 . The strain sensitive element  800  is a hybrid strain sensitive element that is formed with two or more materials having different properties. In the illustrated embodiment, one segment  802  in the hybrid strain sensitive element  800  is made of a first conductive material that has a first conductance and first gauge factor and another segment  804  is made of a second conductive material that has a different second conductance and a different second gauge factor, where the first conductance is greater than the second conductance and the second gauge factor is greater than the first gauge factor. 
     The one or more strain signal lines that are directly connected to the hybrid strain sensitive element is formed or processed to have a gauge factor and a conductance that is different from the overall gauge factor and overall conductance of the strain sensitive element. For example, the strain sensitive element has a greater overall gauge factor than the gauge factor of the at least one strain signal line. The higher overall gauge factor allows the strain sensitive element to be more sensitive to strain than the strain signal line(s). Additionally, in some embodiments the electrical conductance of the strain signal line(s) is higher than the overall conductance of the strain sensitive element. Based on the higher conductance, the strain signal line(s) can effectively transmit signals produced by the strain sensitive element to the conductive contact  206  (see  FIGS. 2 and 4 ). 
     The segments  802 ,  804  can have the same dimensions or one segment (e.g., segment  802 ) can have dimensions that are different from the dimensions of the other segment (e.g., segment  804 ). For example, one segment can be longer than another segment, which may result in a given gauge factor and/or conductance. In some embodiments, the given gauge factor can be a gauge factor that is equal to or greater than a threshold gauge factor. The given gauge factor and/or conductance can be based at least in part on the structure and/or operating conditions of the electronic device or a component in the electronic device that includes one or more hybrid strain sensors. In one embodiment, at least two same segments (e.g., at least two segments  802 ) can have different dimensions. Thus, at least one segment  802  can have dimensions that differ from another segment  802  and/or at least one segment  804  can have dimensions that differ from another segment  804 . In another embodiment, all of the segments can have different dimensions. And in some embodiments, the hybrid strain sensitive element  800  may be formed with three or more materials having different properties. 
     The embodiments of a strain sensor shown in  FIGS. 6-8  are formed with two or more different materials. The materials are selected for a given gauge factor and/or an electrical conductance. Other embodiments can produce a strain sensor by processing either the strain sensitive elements and/or the one or more strain signal lines connected to the strain sensitive elements after the strain sensitive elements and the strain signal line(s) are formed. For example, in some embodiments the material used to form the strain sensitive elements and the strain signal lines is the same material, and the strain sensitive elements and/or the strain signal lines are processed to adjust the conductance and/or the gauge factor of the processed component. The methods depicted in  FIGS. 9 and 10  process the strain sensitive element and the strain signal line(s) respectively. 
       FIG. 9  is a flowchart of a second method for producing a strain sensor. Initially, as shown in block  900 , the strain sensitive element and the strain signal line(s) that is connected to the strain sensitive element are provided. Both the strain sensitive element and the strain signal line(s) are formed with one or more suitable materials. As described earlier, in some embodiments the strain sensitive element and the one or more strain signal lines are formed with the same material, such as, for example, a transparent conducting oxide film. Next, as shown in block  902 , the strain sensitive element is processed to increase the gauge factor of the strain sensitive element. The strain sensitive element may be processed using any suitable technique that increases the gauge factor of the strain sensitive element. For example, in one embodiment the strain sensitive element is laser annealed to increase the crystallinity of the strain sensitive element, which results in a higher gauge factor. 
       FIG. 10  is a flowchart of a third method for producing a strain sensor. Initially, as shown in block  900 , the strain sensitive element and the strain signal line(s) that is connected to the strain sensitive element are provided. Both the strain sensitive element and the strain signal line(s) are formed with one or more suitable materials. As described earlier, in some embodiments the strain sensitive element and the one or more strain signal lines are formed with the same material, such as, for example, a transparent conducting oxide film. 
     Next, as shown in block  1000 , the strain signal line(s) are processed to increase the conductance of the one or more strain signal lines. The strain signal line(s) may be processed using any suitable technique that increases the conductance of the strain signal line(s). For example, in one embodiment the one or more strain signal lines are doped with a dopant or dopants that reduce the overall electrical resistance of the strain signal line(s), which in turn increases the conductance of the strain signal line(s). For example, the one or more dopants can be diffused into the strain signal line(s) to increase the conductance of the strain signal line(s). 
     In still other embodiments, one or more parameters of the fabrication process that is used to form the strain sensitive elements and/or the strain signal line(s) can be adjusted to increase the gauge factor and/or the conductance of the component.  FIG. 11  is a flowchart of a fourth exemplar method for producing a strain sensor. Initially, one or more parameters of the process used to form a strain sensitive element on a substrate is adjusted to produce a strain sensitive element that has a higher gauge factor. For example, in one embodiment the flow rate of oxygen is increased when the strain sensitive element is deposited onto the substrate. The higher oxygen flow rate can reduce the carrier concentration and/or mobility of the carriers in the strain sensitive element. In another embodiment, the thickness of the material used to form the strain sensitive element is adjusted to increase the gauge factor and/or to reduce the electrical resistance of the strain sensitive element. For example, the material in a strain sensitive element can be formed as a thinner layer to result in a lower resistivity. 
     Next, as shown in block  1102 , one or more strain signal lines are formed on the substrate and connected to the strain sensitive element. One or more parameters of the fabrication process used to form the strain signal line(s) may be altered to increase the conductance of the strain signal line(s). Additionally or alternatively, the one or more strain signal lines can be processed after formation to increase the conductance of the strain signal line(s). 
     In some embodiments, a full sheet of a transparent conducting oxide film can be formed over and extend across the surface of a substrate (e.g., substrate  202  in  FIG. 2 ) and select regions or areas of the film processed to produce the strain sensitive elements and/or the strain signal lines. For example, a mask can be formed over a transparent conducting oxide film, where select areas of the mask that correspond to the locations of the strain sensitive elements are removed. The exposed select regions of the transparent conducting oxide film can then be doped to produce the strain sensitive elements in the full sheet of the transparent conducting oxide film. The dopant or dopants can be selected to produce strain sensitive elements that have a given gauge factor, or that have a gauge factor that is equal to or greater than a threshold gauge factor. Similarly, select areas of a mask that correspond to the locations of the strain signal lines can be removed, and the exposed select regions of the transparent conducting oxide film can be doped to produce the strain signal lines in the full sheet of the transparent conducting oxide film. The dopant or dopants can be selected to produce strain signal lines that have a given conductance, or that have a conductance that is equal to or greater than a threshold conductance. 
     In other embodiments, two or more sheets of a transparent conducting oxide film can be formed over the surface of a substrate (e.g., substrate  202  in  FIG. 2 ) and select regions or areas of the films processed to produce the strain sensitive elements and/or the strain signal lines. For example, one mask having openings that correspond to the locations of the strain sensitive elements can be formed over at least a portion of a transparent conducting oxide film. The exposed regions of the transparent conducting oxide film can then be doped to produce the strain sensitive elements in the full sheet of the transparent conducting oxide film. A second mask can be formed over at least a portion of a sheet of a conducting oxide film. The second mask can have openings at locations that correspond to the locations of the strain signal lines. The exposed select regions of the transparent conducting oxide film can be doped to produce the strain signal lines. 
     Referring now to  FIG. 12 , there is shown an illustrative block diagram of an electronic device that can include one or more strain sensors. As discussed earlier, one or more strain sensors can be located on a variety of components and/or at one or more different locations in an electronic device to detect a force applied on the component or on the electronic device. The illustrated electronic device  1200  can include one or more processing devices  1202 , memory  1204 , one or more input/output (I/O) devices  1206 , a power source  1208 , one or more sensors  1210 , a network communication interface  1212 , and a display  1214 , each of which will be discussed in more detail. 
     The one or more processing devices  1202  can control some or all of the operations of the electronic device  1200 . The processing device(s)  1202  can communicate, either directly or indirectly, with substantially all of the components of the device. For example, one or more system buses  1216  or other communication mechanisms can provide communication between the processing device(s)  1202 , the memory  1204 , the I/O device(s)  1206 , the power source  1208 , the one or more sensors  1210 , the network communication interface  1212 , and/or the display  1214 . At least one processing device can be configured to determine an amount of force and/or a change in force applied to an I/O device  1206 , the display, and/or the electronic device  1200  based on a signal received from one or more strain sensors. 
     The processing device(s)  1202  can be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions. For example, the one or more processing devices  1202  can be a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), or combinations of multiple such devices. As described herein, the term “processing device” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. 
     The memory  1204  can store electronic data that can be used by the electronic device  1200 . For example, the memory  1204  can store electrical data or content such as audio files, document files, timing and control signals, operational settings and data, and image data. The memory  1204  can be configured as any type of memory. By way of example only, memory  1204  can be implemented as random access memory, read-only memory, Flash memory, removable memory, or other types of storage elements, in any combination. 
     The one or more I/O devices  1206  can transmit and/or receive data to and from a user or another electronic device. Example I/O device(s)  1206  include, but are not limited to, a touch sensing device such as a touchscreen or track pad, one or more buttons, a microphone, a haptic device, a speaker, and/or a force sensing device  1218 . The force sensing device  1218  can include one or more strain sensors. The strain sensor(s) can be configured as one of the strain sensors discussed earlier in conjunction with  FIGS. 2-11 . 
     As one example, the I/O device  106  shown in  FIG. 1  may include a force sensing device  1218 . As described earlier, the force sensing device  1218  can include one or more strain sensors that are configured according to one of the embodiments shown in  FIGS. 2-11 . An amount of force that is applied to the I/O device  106 , and/or a change in an amount of applied force can be determined based on the signal(s) received from the strain sensor(s). 
     The power source  1208  can be implemented with any device capable of providing energy to the electronic device  1200 . For example, the power source  1208  can be one or more batteries or rechargeable batteries, or a connection cable that connects the electronic device to another power source such as a wall outlet. 
     The electronic device  1200  may also include one or more sensors  1210  positioned substantially anywhere on or in the electronic device  1200 . The sensor or sensors  1210  may be configured to sense substantially any type of characteristic, such as but not limited to, images, pressure, light, heat, touch, force, temperature, humidity, movement, relative motion, biometric data, and so on. For example, the sensor(s)  1210  may be an image sensor, a temperature sensor, a light or optical sensor, an accelerometer, an environmental sensor, a gyroscope, a magnet, a health monitoring sensor, and so on. In some embodiments, the one or more sensors  1210  can include a force sensing device that includes one or more strain sensors. The strain sensor(s) can be configured as one of the strain sensors discussed earlier in conjunction with  FIGS. 2-11 . 
     As one example, the electronic device shown in  FIG. 1  may include a force sensing device  1220  in or under at least a portion of the enclosure  102 . The force sensing device  1220  can include one or more strain sensors that may be configured as one of the strain sensors discussed earlier in conjunction with  FIGS. 2-11 . An amount of force that is applied to the enclosure  102 , and/or a change in an amount of applied force can be determined based on the signal(s) received from the strain sensor(s). 
     The network communication interface  1212  can facilitate transmission of data to or from other electronic devices. For example, a network communication interface can transmit electronic signals via a wireless and/or wired network connection. Examples of wireless and wired network connections include, but are not limited to, cellular, Wi-Fi, Bluetooth, infrared, RFID, Ethernet, and NFC. 
     The display  1214  can provide a visual output to the user. The display  1214  can be implemented with any suitable technology, including, but not limited to, a multi-touch sensing touchscreen that uses liquid crystal display (LCD) technology, light emitting diode (LED) technology, organic light-emitting display (OLED) technology, organic electroluminescence (OEL) technology, or another type of display technology. In some embodiments, the display  1214  can function as an input device that allows the user to interact with the electronic device  1200 . For example, the display can include a touch sensing device  1222 . The touch sensing device  1222  can allow the display to function as a touch or multi-touch display. 
     Additionally or alternatively, the display  1214  may include a force sensing device  1224 . In some embodiments, the force sensing device  1224  is included in a display stack of the display  1214 . The force sensing device  1224  can include one or more strain sensors. An amount of force that is applied to the display  1214 , or to a cover glass disposed over the display, and/or a change in an amount of applied force can be determined based on the signal(s) received from the strain sensor(s). The strain sensor(s) can be configured as one of the strain sensors discussed earlier in conjunction with  FIGS. 2-11 . 
     It should be noted that  FIG. 12  is exemplary only. In other examples, the electronic device may include fewer or more components than those shown in  FIG. 12 . Additionally or alternatively, the electronic device can be included in a system and one or more components shown in  FIG. 12  is separate from the electronic device but in communication with the electronic device. For example, an electronic device may be operatively connected to, or in communication with a separate display. As another example, one or more applications or data can be stored in a memory separate from the electronic device. In some embodiments, the separate memory can be in a cloud-based system or in an associated electronic device. 
     As described earlier, a force sensing device that includes one or more strain sensors can be included in a display stack of a display (e.g., display  104  in  FIG. 1 ).  FIG. 13  depicts a cross-sectional view of an example display stack that includes strain sensors. The display stack  1300  includes a cover glass  1301  positioned over a front polarizer  1302 . The cover glass  1301  can be a flexible touchable surface that is made of any suitable material, such as, for example, glass, plastic, sapphire, or combinations thereof. The cover glass  1301  can act as an input region for a touch sensing device and a force sensing device by receiving touch and force inputs from a user. The user can touch and/or apply force to the cover glass  1301  with one or more fingers or with another element such as a stylus. 
     An adhesive layer  1304  can be disposed between the cover glass  1301  and the front polarizer  1302 . Any suitable adhesive can be used for the adhesive layer, such as, for example, an optically clear adhesive. A display layer  1306  can be positioned below the front polarizer  1302 . As described previously, the display layer  1306  may take a variety of forms, including a liquid crystal display (LCD), a light-emitting diode (LED) display, and an organic light-emitting diode (OLED) display. In some embodiments, the display layer  1306  can be formed from glass or have a glass substrate. Embodiments described herein include a multi-touch touchscreen LCD display layer. 
     Additionally, the display layer  406  can include one or more layers. For example, a display layer  406  can include a VCOM buffer layer, a LCD display layer, and a conductive layer disposed over and/or under the display layer. In one embodiment, the conductive layer may comprise an indium tin oxide (ITO) layer. 
     A rear polarizer  1308  may be positioned below the display layer  1306 , and a strain sensitive structure  1310  below the rear polarizer  1308 . The strain sensitive structure  1310  includes a substrate  1312  having a first set of independent transparent strain sensors  1314  on a first surface  1316  of the substrate  1312  and a second set of independent transparent strain sensors  1318  on a second surface  1320  of the substrate  1312 . In the illustrated embodiment, the first and second sets of transparent strain sensors are located in an area of the display stack that is visible to a user. As described earlier, a strain sensor includes a strain sensitive element and the one or more strain signal lines physically or directly connected to the strain sensitive element. In the illustrated embodiment, the first and second surfaces  1316 ,  1320  are opposing top and bottom surfaces of the substrate  1312 , respectively. An adhesive layer  1322  may attach the substrate  1312  to the rear polarizer  1308 . 
     As described earlier, the strain sensors may be formed as an array of rectilinear strain sensors. Each strain sensitive element in the first set of independent strain sensors  1314  is aligned vertically with a respective one of the strain sensitive elements in the second set of independent strain sensors  1318 . In many embodiments, each individual strain sensitive element may take a selected shape. For example, in certain embodiments, the strain sensitive elements may be deposited in a serpentine pattern, similar to the serpentine pattern shown in  FIG. 3 . 
     A back light unit  1324  can be disposed below (e.g., attached to) the strain sensitive structure  1310 . The back light unit  1324  may be configured to support one or more portions of the substrate  1312  that do not include strain sensitive elements. For example, as shown in  FIG. 13 , the back light unit  1324  can support the ends of the substrate  1312 . Other embodiments may configure a back light unit differently. 
     The strain sensors are typically connected to sense circuitry  1326  through conductive connectors  1328 . The sense circuitry  1326  is configured to detect changes in an electrical property of each of the strain sensitive elements. In this example, the sense circuitry  1326  may be configured to detect changes in the electrical resistance of the strain sensitive elements, which can be correlated to a force that is applied to the cover glass  1301 . In some embodiments, the sense circuitry  1326  may also be configured to provide information about the location of a touch based on the relative difference in the change of electrical resistance of the strain sensors  1314 ,  1318 . 
     As described earlier, in some embodiments the strain sensitive elements are formed with a transparent conducting oxide film. When a force is applied to an input region (e.g., the cover glass  1301 ), the planar strain sensitive structure  1310  is strained and the electrical resistance of the transparent conducting oxide film changes in proportion to the strain. As shown in  FIG. 14 , the force can cause the strain sensitive structure  1310  to bend slightly. The bottom surface  1400  of the strain sensitive structure  1310  elongates while the top surface  1402  compresses. The strain sensitive elements measure the elongation or compression of the surface, and these measurements can be correlated to the amount of force applied to the input region. 
     Two vertically aligned strain sensitive elements (e.g.,  1330  and  1332 ) form a strain sensing device  1334 . The sense circuitry  1326  may be adapted to receive signals from each strain sensing device  1334  and determine a difference in an electrical property of each strain sensing device. For example, as described above, a force may be received at the cover glass  1301 , which in turn causes the strain sensitive structure  1310  to bend. The sense circuitry  1326  is configured to detect changes in an electrical property (e.g., electrical resistance) of the one or more strain sensing devices based on signals received from the strain sensing device(s)  1334 , and these changes are correlated to the amount of force applied to the cover glass  1301 . 
     In the illustrated embodiment, a gap  1336  exists between the strain sensitive structure  1310  and the back light unit  1324 . Strain measurements intrinsically measure the force at a point on the top surface  1316  of the substrate  1312  plus the force from the bottom at that point on the bottom surface  1320  of the substrate  1312 . When the gap  1336  is present, there are no forces on the bottom surface  1320 . Thus, the forces on the top surface  1316  can be measured independently of the forces on the bottom surface  1320 . In alternate embodiments, the strain sensitive structure  1310  may be positioned above the display layer when the display stack  1300  does not include the gap  1336 . 
     Other embodiments can configure a strain sensitive structure differently. For example, a strain sensitive structure can include only one set of strain sensitive elements on a surface of the substrate. A processing device may be configured to determine an amount of force, or a change in force, applied to an input region based on signals received from the set of strain sensitive elements. 
     Referring now to  FIG. 15 , there is shown a simplified schematic diagram of sense circuitry operably connected to a strain sensing device. The strain sensing device  1334  (see  FIG. 13 ) that includes two-vertically aligned strain sensitive elements can be modeled as two resistors R SENSE  configured as a voltage divider. A reference voltage divider  1502  includes two reference resistors R REF . As one example, the strain sensing device  1334  and the reference voltage divider  1502  may be modeled as a Wheatstone bridge circuit, with the strain sensing device  1334  forming one half bridge of the Wheatstone bridge circuit and the reference voltage divider  1502  forming the other half bridge of the Wheatstone bridge circuit. Other embodiments can model the strain sensor and the reference resistors differently. For example, a strain sensitive structure may include only one set of strain sensitive elements and a particular strain sensitive element and a reference resistor can be modeled as a Wheatstone half bridge circuit. 
     A first reference voltage (V REF   _   TOP ) is received at node  1504  and a second reference voltage (V REF   _   BOT ) is received at node  1506 . A force signal at node  1508  of the strain sensing device  1334  and a reference signal at node  1510  of the reference voltage divider  1502  are received by the sense circuitry  1512 . The sense circuitry  1512  is configured to detect changes in an electrical property (e.g., electrical resistance) of the strain sensing device  1334  based on the differences in the force and reference signals of the two voltage dividers. The changes can be correlated to the amount of force applied to a respective input region of an electronic device (e.g., the cover glass  1201  in  FIG. 12 ). 
     Various embodiments have been described in detail with particular reference to certain features thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the disclosure. For example, the one or more strain sensitive elements can be formed with a non-metal opaque material. Additionally or alternatively, the one or more strain sensitive elements can be formed on one layer and the strain signal line(s) on another layer such that a strain sensitive element and corresponding strain signal line(s) are not co-planar (on different planar surfaces). A via can be formed through the interposing layer or layers to produce an electrical contact between the strain sensitive element and the strain signal lines. 
     Even though specific embodiments have been described herein, it should be noted that the application is not limited to these embodiments. In particular, any features described with respect to one embodiment may also be used in other embodiments, where compatible. Likewise, the features of the different embodiments may be exchanged, where compatible.

Metadata:
Filing Date: 20150811
Publication Date: 20170404
Grant Date: 20170404
Priority Date: 20150721
Inventors: VOSGUERITCHIAN MICHAEL
SMITH JOHN STEPHEN
FILIZ SINAN
PEDDER JAMES E.
XU TINGJUN
WEN XIAONAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F3/045", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01L1/225", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/0488", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0414", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01L1/2287", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/205", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04144", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/225", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/205", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F3/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0488", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01L1/2287", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/205", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01L1/2287", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/045", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/225", "inventive": true, "first": true, "tree": "[]"}, {"code": "G01L1/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01L1/22", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 56204051