Patent Publication Number: US-2022221352-A1

Title: Force sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority from Japanese Patent Application No. 2021-004305 filed on Jan. 14, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     What is disclosed herein relates to a force sensor. 
     2. Description of the Related Art 
     Force sensors are known that detect force based on switching of electrical coupling states of switches that depends on the presence or absence of the force (e.g., Japanese Patent Application Laid-open Publication No. 2018-080956). 
     A force sensor having a two-dimensional resolution on a force detection surface has a plurality of switches arranged two-dimensionally. In such a sensor, when electrical characteristics of the switches are non-uniform, technical difficulty in achieving accuracy of detecting force is increased at a position of the switch where an electrical change depending on the presence or absence of force is relatively small. 
     For the foregoing reasons, there is a need for a force sensor that can stably detect force regardless of the detection position of the force. 
     SUMMARY 
     According to an aspect, a force sensor includes: a plurality of first electrodes that are arranged along a substrate; an elastic body that is in contact with the first electrodes; a second electrode that is in contact with the elastic body, the elastic body being interposed between the second electrode and the first electrodes; and a third electrode that is provided on the substrate side of the second electrode and configured to be electrically coupled to the second electrode. The elastic body includes a conductive particle that electrically couples the first electrodes and the second electrode when force is applied that causes the first electrodes and the second electrode to be approached. The third electrode has a continuous lattice shape that separates at least the first electrodes adjacent in one direction from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a layered structure including main elements of a force sensor; 
         FIG. 2  is a diagram illustrating the force sensor that is receiving force from a second electrode side; 
         FIG. 3  is a diagram illustrating an exemplary circuit structure of the force sensor; 
         FIG. 4  is a plan view illustrating an exemplary structure of an array; 
         FIG. 5  is a plan view illustrating an exemplary positional relation between the arrays; 
         FIG. 6  is a timing chart illustrating exemplary electrical control of operation of the force sensor including the circuit illustrated in  FIG. 3 ; 
         FIG. 7  is a cross-sectional view illustrating an exemplary structure of a force sensor as a reference example; 
         FIG. 8  is a plan view exemplarily illustrating shapes of electrodes in a detection region of a force sensor in a first modification; 
         FIG. 9  is a plan view illustrating an exemplary wiring layer in which power supply lines Vbias and a signal line Sig are provided in an array Un; 
         FIG. 10  is a plan view illustrating an exemplary arrangement of contacts that couple the electrode layer illustrated in  FIG. 8  and the wiring layer illustrated in  FIG. 9  in the array Un; and 
         FIG. 11  is a cross-sectional view of a layered structure including main elements of a force sensor in a second modification. 
     
    
    
     DETAILED DESCRIPTION 
     The following describes each embodiment of the present disclosure with reference to the drawings. This disclosure is made by way of examples. All appropriate modifications that may be easily conceived by those skilled in the art within the spirit of the invention are naturally included in the scope of the present disclosure. For the purpose of clarity, the widths, thicknesses, and shapes of respective components may be schematically illustrated, and those are illustrated by way of examples and do not limit the interpretation of the present disclosure. In the present specification and the respective drawings, the same elements already described in the previous drawings are labeled with the same symbols, and detailed description thereof may be omitted as appropriate. 
     In this disclosure, when an element is described as being “on” another element, the element can be directly on the other element, or there can be one or more elements between the element and the other element. 
     Embodiment 
       FIG. 1  is a cross-sectional view of a layered structure including main elements of a force sensor  1 . The force sensor  1 , which is what is called a device substrate, includes a plurality of elements layered on a substrate  10 . The elements include field effect transistors (FETs) of semiconductor. Specifically, an insulation film  11 , a first wiring layer  12 , a first insulation layer  13 , a semiconductor layer  14 , a second wiring layer  15 , a second insulation layer  16 , a third wiring layer  17 , a third insulation layer  18 , a fourth wiring layer  19 , and the like are layered on the substrate  10  in this order from a side closer to the substrate  10 . The first wiring layer  12 , the second wiring layer  15 , the third wiring layer  17  and the fourth wiring layer  19  are formed of a conductive material like metal electrodes, for example. The first insulation layer  13 , the second insulation layer  16 , and the third insulation layer  18  are formed of insulator including silicon oxide or silicon nitride, for example. The semiconductor layer  14  is a semiconductor that functions as a channel of the FET. When the FET is a metal oxide semiconductor FET (MOSFET), the semiconductor layer  14  is of silicon (Si), for example. The FETs, such as a first element  61  illustrated in  FIG. 1 , and a second element  62 , a third element  63 , and a fourth element  64  illustrated in  FIG. 3 , which is described later, are formed on the substrate  10  by the layered structure. 
     In the following description, one direction along the substrate  10  is defined as a first direction Dx. The other direction that is along the substrate  10  and orthogonal to the first direction Dx is defined as a second direction Dy. The direction orthogonal to the first direction Dx and the second direction Dy is defined as a third direction Dz. The third direction Dz is the layering direction of the layered structure formed on the substrate  10 . 
     A covering portion HRC, an electrode layer, and the like are layered on the upper side of the fourth wiring layer  19 . The covering portion HRC is provided between the fourth wiring layer  19  and the electrode layer to insulate the fourth wiring layer  19  and the electrode layer from each other. The covering portion HRC is an organic layer that restrains force from being applied from the second electrode  30  side, which is described later, to the structure on the lower layer side of the covering portion HRC to protect the lower layer side structure. The electrode layer includes a first electrode  20  and a third electrode  40 . The first electrode  20  and the third electrode  40  are spaced apart from each other. An elastic body  50  is provided on the upper side of the electrode layer. The elastic body  50  is a thin film shaped elastic member. The elastic body  50  includes a plurality of conductive particles  51 . The elastic body  50  containing the conductive particles  51  has force sensitive conductivity. 
     The second electrode  30  is provided on the upper side of the elastic body  50 . The second electrode  30  is a conductive sheet. The second electrode  30  may be any sheet-shaped member as long as at least a surface of the second electrode  30  on the elastic body  50  side is conductive. More specifically, the second electrode  30  is provided with a compound thin film, such as an indium tin oxide (ITO) thin film, on the elastic body  50  side, for example. The side of the second electrode  30  opposite to the elastic body  50  side thereof may have conductivity or be covered with an insulator such as synthetic resin. 
       FIG. 2  is a diagram illustrating the force sensor  1  that is receiving force from the second electrode  30  side. When the force sensor  1  illustrated in  FIG. 1  receives force in the third direction Dz from the second electrode  30  side, the elastic body  50  is compressed in the third direction Dz, as illustrated in  FIG. 2 . As a result, some of the conductive particles  51  included in the elastic body  50  form a conduction path that makes electrical conduction between the third electrode  40  and the second electrode  30  and another conduction path that makes electrical conduction between the first electrode  20  and the second electrode  30 .  FIG. 2  schematically and exemplarily illustrates a state in which a conductive particle  51   a  couples the third electrode  40  and the second electrode  30  while a conductive particle  51   b  couples the first electrode  20  and the second electrode  30 . The conductive particles  51   a  and  51   b  are included in the conductive particles  51 . When the force in the third direction Dz onto the second electrode  30  side is disappeared, the state returns to a state illustrated in  FIG. 1  from a state illustrated in  FIG. 2 , resulting in the conduction paths being disappeared. As described above, the force sensor  1  can detect force from the second electrode  30  side on the basis of whether the conduction paths are established. The third electrode  40 , the second electrode  30 , the first electrode  20 , and the elastic body  50 , which form the conduction paths in response to force from the second electrode  30  side, function as a switch  80  that switches open and close depending on the force. When the second electrode  30  in the embodiment does not receive the force and is not coupled to the first electrode  20  and the third electrode  40 , the second electrode  30  is in a floating state. 
     More specifically, the elastic body  50  has isotropic force sensitive conductivity that establishes the conduction between the third electrode  40  and the second electrode  30  and the conduction between the first electrode  20  and the second electrode  30  in response to force along the third direction Dz and does not establish conduction in other directions (e.g., the direction along the substrate  10 ). The conductive particles  51  are provided in the elastic body  50  so as to establish such force sensitive conductivity. 
     In the embodiment, a sheet resistance of the third electrode  40  is less than that of the second electrode  30 . Specifically, the electrode layers forming the first electrode  20  and the third electrode  40  are made of metal having high conductivity such as silver (Ag). The concrete composition of the third electrode  40  is not limited to that described above. The third electrode  40  is preferably made of a material having high conductivity as much as possible and a low sheet resistance. 
       FIG. 3  is a diagram illustrating an exemplary circuit structure of the force sensor  1 . The circuit illustrated in  FIG. 3  includes an array circuit SC and a reset circuit RC. 
     The array structure SC includes the first element  61 , the second element  62 , and the third element  63 . The first element  61 , the second element  62 , and the third element  63  are FET switching elements. One of a source and a drain of the first element  61  is coupled to the switch  80  while the other is coupled to the second element  62 , the third element  63 , and a capacitor  70 . One of a source and a drain of the second element  62  is coupled to a signal line Sig while the other is coupled to the first element  61 , the third element  63 , and the capacitor  70 . One of a source and a drain of the third element  63  is coupled to an initialization potential line Vbl while the other is coupled to the first element  61 , the second element  62 , and the capacitor  70 . A gate and a back gate of the first element  61  are coupled to a detection operation signal transmission line Vs. A gate and a back gate of the second element  62  are coupled to a scan line Gate. A gate and a back gate of the third element  63  are coupled to an initialization signal transmission line Vdch. 
     One of two terminals of the capacitor  70  is coupled to a common potential line Vcom while the other is coupled to the first element  61 , the second element  62 , and the third element  63 . The switch  80  is provided such that the switch  80  can open and close the coupling between the one of the source and the drain of the first element  61 , and a power supply line Vbias. 
     The reset circuit RC includes the fourth element  64 . The fourth element  64  is an FET switching element. One of a source and a drain of the fourth element  64  is coupled to the signal line Sig while the other is coupled to a reset potential line VR 1 . A gate and a back gate of the fourth element  64  are coupled to a reset signal transmission line Vrst. 
     The array circuit SC is provided individually for each array that can detect force individually. As exemplarily illustrated in  FIG. 5 , which is described later, the force sensor  1  is provided with a plurality of arrays. The scan line Gate is shared by the array circuits SC arranged in the first direction Dx. The signal line Sig is shared by the array circuits SC arranged in the second direction Dy. The detection operation signal transmission line Vs, the power supply line Vbias, the common potential line Vcom, the initialization potential line Vbl, and the initialization signal transmission line Vdch are shared by all of the array circuits SC. 
       FIG. 4  is a plan view illustrating an exemplary structure of the array. The plan view is a front view of the first direction Dx-second direction Dy plane along the plate surface of the substrate  10 . As illustrated in  FIG. 4 , the first element  61 , the second element  62 , and the third element  63  are provided in each of the arrays. The scan line Gate, the signal line Sig, the detection operation signal transmission line Vs, the common potential line Vcom, the initialization potential line Vbl, and the initialization signal transmission line Vdch are provided such that the circuit described with reference to  FIG. 3  is achieved. The structure of the array illustrated in  FIG. 4  is achieved by the layered structure on the substrate  10  described with reference to  FIG. 1 . The first electrode  20  and the third electrode  40  illustrated in  FIG. 4  are provided in the same layer (electrode layer), as illustrated in  FIG. 1 . The first element  61 , the second element  62 , the third element  63 , the scan line Gate, the signal line Sig, the detection operation signal transmission line Vs, the common potential line Vcom, the initialization potential line Vbl, and the initialization signal transmission line Vdch are provided on the substrate  10  side of the electrode layer. 
     As illustrated in  FIG. 4 , the position of the first element  61  in a plan view and the position of the first electrode  20  in a plan view partially overlap. As illustrated in  FIG. 1 , the second wiring layer  15  stacked on the upper side of the semiconductor layer  14  of the first element  61  as a FET, includes an electrode  15   a  that is coupled to the semiconductor layer  14  and formed as one of the source and the drain of the first element  61 . The electrode  15   a  is coupled to a coupling portion  19   a  via a contact hole formed in the second insulation layer  16  and the third insulation layer  18 . The coupling portion  19   a  is formed in forming of the fourth wiring layer  19 . The coupling portion  19   a  couples the first electrode  20  and the electrode  15   a . The coupling portion  19   a  and the first electrode  20  are coupled via a contact hole formed on the upper side of the coupling portion  19   a  in the covering portion HRC. The first electrode  20  has a cross sectional shape that is curved along the contact hole as illustrated in  FIG. 1 , for example. This shape is, however, an example of the shape of the first electrode  20 . The shape of the first electrode  20  is not limited to this example and can be modified as appropriate. 
     As illustrated in  FIGS. 1 and 4 , the first electrode  20  is formed so as to be spaced apart from the third electrode  40 .  FIG. 4  exemplarily illustrates the squire-shaped first electrode  20  that has four sides including two sides facing each other along the first direction Dx and the other two sides facing each other along the second direction Dy. The shape of the first electrode  20  is not limited to this example. The first electrode  20  may have any shape that preferably allows the first electrode  20  to be spaced apart from the third electrode  40 . The shape can be modified as appropriate. As illustrated in  FIG. 4 , one array is provided with one first electrode  20 , for example. 
       FIG. 5  is a plan view illustrating a positional relation between the arrays. As illustrated in  FIG. 5 , for example, the first electrodes  20 , one of which is described with reference to  FIG. 4 , are provided. The first electrodes  20  illustrated in  FIG. 5  are arranged in a matrix of a row-column configuration along the first direction Dx and the second direction Dy. In  FIG. 5 , the first electrodes  20  are arranged in a matrix of 3×3 in the first direction Dx and the second direction Dy. The actual force sensor  1  includes a larger number of first electrodes  20  than this example. For a concrete example, the first electrodes  20  are arranged in a matrix of 80×84. A pitch between the first electrodes  20  adjacent in the first direction Dx (or the second direction Dy) is 321 μm. The concrete example is only an example. The pitch is not limited to the concrete example and can be modified as appropriate. 
     The arrays, one of which is described with reference to  FIGS. 3 and 4 , are provided corresponding to the arrangement of the first electrodes  20  described with reference to  FIG. 5 . The arrays provided corresponding to the first electrodes  20  arranged along the first direction Dx share the scan line Gate. As illustrated in  FIG. 4 , the scan line Gate is provided so as to extend along the first direction Dx. The arrays provided corresponding to the first electrodes  20  arranged along the second direction Dy share the signal line Sig. As illustrated in  FIG. 4 , the signal line Sig is provided so as to extend along the second direction Dy. In the structure of the first electrodes  20  and the arrays that are provided as described above, one signal line Sig extends along the second direction Dy between the adjacent first electrodes  20  of the first electrodes  20  arranged in the first direction Dx, in a plan view. In a plan view, one scan line Gate extends along the first direction Dx between the adjacent first electrodes  20  of the first electrodes  20  arranged in the second direction Dy. In other words, in a plane view, the signal lines Sig and the scan lines Gate separate the first electrodes  20  from each other so as to be arranged in a lattice shape. 
     As illustrated in  FIG. 5 , the third electrode  40  is formed as a continuous electrode that separates the first electrodes  20  from each other so as to be arranged in a lattice shape. The third electrode  40  (hatched part) illustrated in  FIG. 5  separates the first electrodes  20  arranged in the first direction Dx from each other, and the first electrodes  20  arranged in the second direction Dy from each other. In other words, the third electrode  40  has openings  25  each of which has the first electrode  20  therein. The third electrode  40  has the openings  25  arranged in a matrix of a row-column configuration. The opening  25  separates the first electrode  20  from the third electrode  40 . Specifically, as illustrated in  FIG. 4 , one side of the first electrode  20  and one side of the opening of the third electrode  40  facing the one side of the first electrode  20  are spaced apart with a distance Wi therebetween. The shape of the opening  25  is not limited to square and can be modified as appropriate. The distance Wi is 50 μm, for example. The distance Wi is not limited to this example and can be modified as appropriate. The distance Wi is preferably equal to or greater than the thickness of the elastic body  50  in the third direction Dz and less than 25% (e.g., about 22.5%) of smaller one of the width in the first direction Dx and the width in the second direction Dy of each of the regions separated by the signal lines Sig and the scan lines Gate in a lattice shape. Although not illustrated in  FIG. 4 , the distances between the sides of the first electrode  20  that are opposite to the sides denoted by Wi and the third electrode  40  are also the distance Wi. 
     The third electrode  40  is coupled to the power supply line Vbias that is provided outside a detection region SA in which the first electrodes  20  are provided. As illustrated in  FIG. 5 , the detection region SA is a region where the first electrodes  20  are provided and force from the second electrode  30  side can be detected. 
     As illustrated in  FIG. 5 , a surrounding region FA is provided so as to surround the outside of the detection region SA. The power supply line Vbias is provided so as to trace the surrounding region FA. The power supply line Vbias and the third electrode  40  are coupled in the third direction Dz via contacts  45 . Specifically, the third electrode  40  has an extending portion  40   a  that extends from the detection region SA to the surrounding region FA. The extending portion  40   a  overlaps with the power supply line Vbias and the contacts  45  in a plan view. The extending portion  40   a  is coupled to the power supply line Vbias via the contacts  45 . As a result, the third electrode  40  has the same potential as a potential (e.g., a constant potential C 4 , which is described later) of the power supply line Vbias. In this way, the power supply line Vbias functions as a power supply. The power supply line Vbias is formed in the same layer as any one of the wiring layers that are on or above the substrate  10  and on the lower side of the covering portion HRC (e.g., the first wiring layer  12 , the second wiring layer  15 , the third wiring layer  17 , and the fourth wiring layer  19 ). The power supply line Vbias is not limited to being formed as described above. For example, a wiring layer for the power supply line Vbias only may be stacked on or above the substrate  10 . The contacts  45  are formed in contact holes that are formed so as to penetrate the covering portion HRC and the insulation layers located on the upper side of the wiring layer in the third direction Dz so as to couple the third electrode  40  and the wiring layer in which the power supply line Vbias is formed. 
       FIG. 5  exemplarily illustrates the surrounding region FA near one corner of the periphery of the detection region SA, but the surrounding region FA is actually provided so as to surround the detection region SA in a plan view. The power supply line Vbias is provided so as to overlap with the surrounding region FA and surround the detection region SA in a plan view. The contacts  45  are provided so as to overlap with the surrounding region FA, surround the detection region SA, and trace the power supply line Vbias in a plan view. In  FIG. 5 , the contacts  45  are provided in a single line so as to trace the power supply line Vbias. The contacts  45  may be provided in multiple lines so as to trace the power supply line Vbias. 
     The reset circuit RC illustrated in  FIG. 3 , which is not illustrated in  FIGS. 4 and 5 , is shared by the arrays that share the signal line Sig. The reset potential line VR 1  may be shared by all of the reset circuits RC. 
       FIG. 6  is a timing chart illustrating exemplary electrical control of operation of the force sensor  1  including the circuit illustrated in  FIG. 3 . In a period other than a period T 1  notably denoted in  FIG. 6 , the third element  63  is in a state (an OFF state) where signal transmission between the source and the drain is shut off. In a period other than a period T 2  notably denoted in FIG.  6 , the first element  61  is in the state (OFF state) where signal transmission between the source and the drain is shut off. In a period other than a period T 3  notably denoted in  FIG. 6 , the second element  62  is in the state (OFF state) where signal transmission between the source and the drain is shut off. In the period other than the period T 3  notably denoted in  FIG. 6 , the fourth element  64  is in a state (an ON state) where signal transmission between the source and the drain is enabled. In other words, the initialization signal transmission line Vdch, the detection operation signal transmission line Vs, the reset signal transmission line Vrst, and the scan line Gate in the periods other than the periods T 1 , T 2 , and T 3  are set to have such potentials that the states of the first element  61 , the second element  62 , the third element  63 , and the fourth element  64  are achieved as described above. Each of the potentials of the initialization potential line Vbl, the reset potential line VR 1 , the common potential line Vcom, and the power supply line Vbias is individually predetermined to be a constant potential. The constant potential C 1  of the initialization potential line Vbl, a constant potential C 2  of the reset potential line VR 1 , a constant potential C 3  of the common potential line Vcom, and a constant potential C 4  of the power supply line Vbias, which are illustrated in  FIG. 6 , may be different from one another. Some of the constant potentials C 1  to C 4  may be equal. In the embodiment, the constant potentials C 3  and C 4  are equal. 
     The scan lines Gate are provided such that the number of scan lines Gate corresponds to that of arrays arranged in the first direction Dx. In  FIG. 6 , the scan lines Gate are denoted as scan line Gate ( 1 ), . . . , and scan line Gate (n). The scan lines Gate A sequentially receives a drive signal from a scan circuit (not illustrated). The scan circuit includes a shift register, for example. The number of shift outputs of the shift register is the same as the number (n) of scan lines Gate. n is a natural number equal to or larger than two. The scan line Gate to which the shift register applies the drive signal output from the scan circuit is sequentially shifted from the scan line Gate ( 1 ) to the scan line Gate (n). 
     In the period T 1 , the potential of the initialization signal transmission line Vdch becomes high (H). This causes the circuit between the source and the drain of the third element  63  to be in a coupling state. As a result, the other of the two terminals of the capacitor  70  coupled to the other of the source and the drain of the third element  63  is electrically coupled to the initialization potential line Vbl. Upon being electrically coupled to the initialization potential line Vbl, the capacitor  70  releases a capacitance held before being coupled. That is, the capacitance held by the capacitor  70  is caused to correspond to a potential difference between the common potential line Vcom and the initialization potential line Vbl. This state is a state where the capacitor  70  is reset. As described above, the initialization signal transmission line Vdch is shared by all of the arrays. Therefore, the capacitors  70  of all of the arrays are reset in the period T 1 . 
     In the period T 2 , the potential of the detection operation signal transmission line Vs becomes high (H). This causes the circuit between the source and the drain of the first element  61  to be in a coupling state. As a result, the power supply line Vbias is coupled to or not coupled to the one of the terminals of the capacitor  70  depending on ON and OFF of the switch  80  coupled to the one of the source and the drain of the first element  61 . Specifically, when the force sensor  1  receives force from the second electrode  30  side, the power supply line Vbias is coupled to the one of the terminals of the capacitor  70 . When the force sensor  1  does not receive force from the second electrode  30  side, the power supply line Vbias is not coupled to the one of the terminals of the capacitor  70 . In this way, the capacitance stored in the capacitor  70  changes depending on whether the force sensor  1  receives force from the second electrode  30  side in the period T 2 . 
     In the period T 3 , the potential of the reset signal transmission line Vrst becomes low (L). In a period other than the period T 3  and some periods before and after the period T 3 , the fourth element  64  is in the ON state. As a result, the signal line Sig and the reset potential line VR 1  are coupled. In the period where the fourth element  64  is in the ON state, the potential of the signal line Sig is reset by the potential of the reset potential line VR 1 . Before and after the period T 3 , the potential of the reset signal transmission line Vrst is reversed (H to L and L to H). As a result, the potential of the reset signal transmission line Vrst becomes low (L) in the period T 3 . This causes the coupling between the signal line Sig and the reset potential line VR 1  to be cut off. 
     In the period T 3 , the potentials of the scan lines Gate ( 1 ) to (n) are sequentially controlled to be reversed from low (L) to high (H) and from high (H) to low (L).  FIG. 6  illustrates an example where any of the potential of the scan lines Gate ( 1 ) to (n) becomes high (H) in response to the application of the drive signal. As a result, the second elements  62  of the arrays that do not share the signal line Sig but share the scan line Gate, that is, the arrays arranged in the first direction Dx, are sequentially brought into the ON state, whereby the capacitors  70  and the signal lines Sig are coupled sequentially. The potential of each of the signal lines Sig becomes the potential corresponding to the capacitance held by the capacitor  70 . This makes it possible for the force sensor  1  coupled to the signal lines Sig to detect force. The force sensor  1  is a circuit that determines whether the force sensor  1  receives force from the second electrode  30  side on the basis of the potentials of the signal lines Sig. 
     The force sensor  1  includes various circuits (not illustrated) for the electrical controlling described with reference to  FIG. 6 . Specifically, the force sensor  1  includes a power source circuit and a control circuit, for example. The power source circuit supplies the potentials corresponding to high (H) and low (L) of each of the initialization signal transmission line Vdch, the initialization potential line Vbl, the detection operation signal transmission line Vs, the reset signal transmission line Vrst, and the like, and the potentials corresponding to the constant potentials C 1 , C 2 , C 3 , and C 4 . The control circuit controls switching of high (H) and low (L) corresponding to the periods T 1 , T 2 , and T 3  described with reference to  FIG. 6 . 
     The above explanation is made based on the circuit structure illustrated in  FIG. 3 . The circuit structure of the force sensor  1  is, however, not limited to that illustrated in  FIG. 3 . In principle, the operation of the force sensor in the present disclosure is achieved by the first element  61 , the second element  62 , the capacitor  70 , the switch  80 , and potential supply to their source-drain couplings and their gates. The third element  63  and the fourth element  64  are an example of a specific element for the potential reset, and are not essential for force detection. 
     As described with reference to  FIGS. 1, 2, 4 and 5 , in the force sensor  1  of the embodiment, the first electrode  20  and the third electrode  40  are spaced apart with the opening  25  interposed therebetween. In other words, the first electrode  20  and the third electrode  40  are provided in such a positional relation that the first electrode  20  and the third electrode  40  are not in contact with each other but close to each other by being spaced apart with the distance Wi (refer to  FIG. 4 ). Wherever force from the second electrode  30  side is detected in the detection region SA including the first electrodes  20  arranged along the plate surface of the substrate  10 , electrical separation distances between the first electrodes  20  and the third electrode  40  that are electrically coupled to each other in response to the force are substantially the same. This is because the distances between the first electrodes  20  and the third electrode  40  are made uniform to be the distance Wi, and thus, the conduction path length of each second electrode  30  is substantially the same as the length of the distance Wi when the first electrode  20  and the third electrode  40  is electrically coupled to each other via the conductive particles  51  and the second electrode  30 . Furthermore, in the embodiment, the potential of the power supply line Vbias is supplied via the third electrode  40  having a lower sheet resistance than that of the second electrode  30 . As a result, a current from the power supply line Vbias to the conduction path of the second electrode  30  is almost not attenuated. Consequently, the electrical state where the conduction path is established between the first electrode  20  and the third electrode  40  and the electrical state where the conduction path therebetween is not established are clearly distinguished at any position where the force from the second electrode  30  side is applied in the detection region SA. As described above, according to the embodiment, it is possible to stably detect force regardless of the detection position of the force. 
       FIG. 7  is a cross-sectional view illustrating an exemplary structure of a force sensor as a reference example. The force sensor illustrated in  FIG. 7  differs from that of the embodiment in that the force sensor does not include the third electrode  40 . Thus, a power supply source having the same potential as the power supply line Vbias is coupled to the second electrode  30 . This reference example does not have a structure for coupling the power supply source and the second electrode  30  in the detection region SA. Thus, the second electrode  30  is necessarily coupled to the power supply source outside the detection region SA.  FIG. 7  illustrates the elastic body  50  in a state of receiving force from the second electrode  30  side. 
     The sheet resistance of the second electrode  30  is higher than that of the third electrode  40  in the embodiment. Thus, as the detection position of force is further away from the power supply source in the reference example, attenuation of the current from the power supply source is increased due to the sheet resistance of the second electrode  30 . Consequently, as the detection position of force is further away from the power supply source in the reference example, the electrical state where the conduction path between the second electrode  30  and the third electrode  40  is established as illustrated in  FIG. 7  and the electrical state where the conduction path is not established are more hardly distinguished. This is because the increase in the attenuation of the current from the power supply source due to the sheet resistance of the second electrode  30  indicates that, even when the conduction path is established, the electrical change due to the influence of the current becomes smaller. In contrast to the reference example, the force sensor of the embodiment can reduce variation in the detection accuracy depending on the positional relation between the detection position of force in the detection region SA and the power supply source. The embodiment can stably detect force regardless of the detection position of the force, as described above. 
     As described above, the force sensor  1  in the embodiment includes the first electrodes  20  arranged along the substrate  10 , the elastic body  50  that is in contact with the first electrodes  20 , the second electrode  30  that is in contact with the elastic body  50  and has the elastic body  50  interposed between the second electrode  30  and the first electrodes  20 , and the third electrode  40  that is provided on the substrate  10  side of the second electrode  30  and configured to be electrically coupled to the second electrode  30 . The elastic body  50  includes the conductive particles that electrically couple the first electrodes  20  and the second electrode  30  when force is applied that causes the first electrodes  20  and the second electrode  30  to be approached. The third electrode  40  has a continuous lattice shape that separates at least the first electrodes  20  adjacent in one direction from each other. Specifically, the third electrode  40  having the same potential as the second electrode  30  that is coupled to the first electrode  20  when force is applied is disposed near the first electrode  20  so as to separate the adjacent first electrodes  20  from each other. This allows the first electrode  20  and the third electrode  40 , which are electrically coupled when force is applied, to be put in a closer positional relation. This makes it easy to more stabilize the electrical characteristics of the switch (e.g., switch  80 ) including the first electrode  20  and the third electrode  40  regardless of the arrangement of the switch. Thus, the force sensor  1  can stably detect force regardless of the detection position of the force. 
     The force sensor  1  has the detection region SA in which the first electrodes  20  are arranged in a matrix of a row-column configuration, and the transistors (second elements  62 ). The detection region SA includes the signal lines Sig along in one of the row direction (first direction Dx) and the column direction (second direction Dy), and the scan lines Gate along the other of the row and the column directions. One of the source and the drain of the transistor is coupled to the substrate  10  via the first element  61 , the other of the source and the drain is coupled to the signal line Sig, and the gate of the transistor is coupled to the scan line Gate. With this configuration, the transistors are operated on a scan line Gate basis. A signal indicating the electrical state of the first electrode  20  coupled to the operated transistor via the first element  61  is obtained via the signal line Sig. That is, the electrical states of the first electrodes  20  can be scanned by scanning the scan lines Gate. This makes it possible to detect the force-applied portion where the electrical coupling between the first electrode  20  and the second electrode  30  is established in the detection region SA. 
     The third electrode  40  and the first electrodes  20  are formed in the same layer. This allows the first electrodes  20  and the third electrode  40  to be formed in the same process, thereby making it possible to manufacture the force sensor  1  at a lower cost. 
     The third electrode  40  is continuous along the substrate  10  so as to surround the four sides of each first electrode  20 . This makes it possible to achieve a more qualitative positional relation between the first electrode  20  and the third electrode  40  having the same potential as the second electrode  30  coupled to the first electrode  20  when force is applied. As a result, the electrical characteristics of the switch (e.g., switch  80 ) including the first electrode  20  and the third electrode  40  can be easily more stabilized regardless of the arrangement of the switch. 
     The sheet resistance of the third electrode  40  is less than that of the second electrode  30 . With this configuration, among the first electrode  20 , the second electrode  30 , and the third electrode  40  that are coupled when force is applied, the conduction path including the first electrode  20  and the third electrode  40  nearest to the first electrode  20  is established. As a result, the electrical characteristics of the switch (e.g., switch  80 ) including the first electrode  20  and the third electrode  40  is more easily stabilized regardless of the arrangement of the switch. 
     The third electrode  40  has the extending portion  40   a  that extends to the outside (surrounding region FA) of the region (detection region SA) in which the first electrodes  20  are provided and is coupled to the power supply line Vbias. The first electrode  20  and the third electrode  40  are electrically coupled when force causing the first electrode  20  and the second electrode  30  to be approached is applied. This makes it possible to provide commonality between the structure in which the first electrode  20  and the third electrode  40  are coupled and the structure in which the first electrode  20  and the second electrode  30  are coupled. As a result, the force sensor  1  can be manufactured at a lower cost. 
     The second electrode  30  is electrically floating when the second electrode  30  is not electrically coupled to the third electrode  40 . This can eliminates a structure for externally applying a specific potential to the second electrode  30  constantly. As a result, the force sensor  1  can be manufactured at a lower cost. 
     Modifications 
     The following describes modifications having structures that differ partially from the structure of the embodiment with reference to  FIGS. 8 to 11 . The same structure as the embodiment in the modifications has the same symbol as that in the embodiment, and the description thereof is omitted in some cases. 
     First Modification 
       FIG. 8  is a plan view exemplarily illustrating the shapes of the electrodes in the detection region SA of a force sensor in a first modification. As illustrated in  FIG. 8 , in the first modification, array electrodes  20 A,  20 B,  20 C, and  20 D, and a third electrode  40 A (hatched part) are provided in an array Un.  FIG. 8  exemplarily illustrates the arrays Un arranged in a matrix of 3×3, i.e., three arrays Un arranged in the first direction Dx and three arrays Un arranged in the second direction Dy, although the symbols thereof are omitted. In the detection region SA, more arrays Un may be arranged or fewer arrays Un may be arranged. As described above, in the force sensor in the first modification, the multiple arrays Un are arranged in the detection region SA in a matrix of a row-column configuration in a plan view. 
     The array electrodes  20 A,  20 B,  20 C, and  20 D each have the same structure as the first electrode  20  in the embodiment from a functional point of view. A third electrode  40 A has the same structure as the third electrode  40  in the embodiment from a functional point of view. In the first modification, the first electrode  20  in each array in the embodiment is replaced with the array electrodes  20 A,  20 B,  20 C, and  20 D serving as the first electrodes. In the first modification, the structure of the third electrode  40  in a plan view in the embodiment is modified to that of the third electrode  40 A in accordance with the number, the shapes, and the arrangement of the first electrodes. 
     In the example illustrated in  FIG. 8 , the array electrodes  20 A and  20 B arranged in the first direction Dx in the array Un are adjacent to each other without the third electrode  40 A therebetween. The array electrodes  20 C and  20 D arranged in the first direction Dx in the array Un are adjacent to each other without the third electrode  40 A therebetween. The array electrodes  20 A and  20 C arranged in the second direction Dy in the array Un are adjacent to each other with the third electrode  40 A therebetween. The array electrodes  20 B and  20 D arranged in the second direction Dy in the array Un are adjacent to each other with the third electrode  40 A therebetween. As described above, the third electrode  40 A has a continuous lattice shape that separates at least the first electrodes adjacent in one direction (e.g., the second direction Dy) from each other out of the first electrodes adjacent in the array Un. The positional relation between the first electrodes and the third electrode  40 A in the array Un is not limited to this example. For example, the first direction Dx and the second direction Dy in  FIG. 8  may be interchanged. The third electrode  40 A may further extend so as to separate the array electrode  20 A from the array electrode  20 B, and separate the array electrode  20 C from the array electrode  20 D in the array Un. 
     In the first modification, the first electrodes such as the array electrodes  20 A,  20 B,  20 C, and  20 D, which are provided in one array Un, share one second element  62 . The first modification may have a structure in which the first element  61  illustrated in  FIG. 3  is excluded and the switch  80  is coupled to the second element  62 , the third element  63 , and the capacitor  70 . The open and close (ON and OFF) of the switch  80  in the first modification is switching between the conduction (ON) and non-conduction (OFF) among the third electrode  40 , the second electrode  30 , and the array electrodes  20 A,  20 B,  20 C, and  20 D. 
       FIG. 9  is a plan view illustrating an exemplary wiring layer in which the power supply lines Vbias and the signal line Sig are provided in the array Un. 
       FIG. 10  is a plan view illustrating an exemplary arrangement of contacts that couple the electrode layer illustrated in  FIG. 8  and the wiring layer illustrated in  FIG. 9  in the array Un. The contacts illustrated in  FIG. 10  are formed so as to penetrate the covering portion HRC. 
     As illustrated in  FIG. 9 , coupling portions  19   a  in the first modification extend so as to correspond to the shapes and arrangement of the array electrodes  20 A,  20 B,  20 C, and  20 D in a plan view. The coupling portions  19   a  extending as described above are coupled to the array electrodes  20 A,  20 B,  20 C, and  20 D via one or more contacts included in contact formation regions  20 P,  20 Q,  20 R, and  20 S illustrated in  FIG. 10 . Specifically, the array electrode  20 A is coupled to the coupling portion  19   a  illustrated in  FIG. 9  via contacts  451  included in the contact formation region  20 P illustrated in  FIG. 10 . The array electrode  20 B is coupled to the coupling portion  19   a  illustrated in FIG.  9  via contacts  452  included in the contact formation region  20 Q illustrated in  FIG. 10 . The array electrode  20 C is coupled to the coupling portion  19   a  illustrated in  FIG. 9  via contacts  453  included in the contact formation region  20 R illustrated in  FIG. 10 . The array electrode  20 D is coupled to the coupling portion  19   a  illustrated in  FIG. 9  via contacts  454  included in the contact formation region  20 S illustrated in  FIG. 10 . 
     The coupling portions  19   a  each of which is coupled to one of the array electrodes  20 A,  20 B,  20 C, and  20 D are mutually coupled via a common coupling portion  19   c  positioned at or near the center of the array Un, for example. The common coupling portion  19   c  is provided in the same layer as the coupling portions  19   a . The structure in which the coupling portion  19   a  and the electrode  15   a  are coupled in  FIG. 1  is replaced with the coupling between the common coupling portion  19   c  and the electrode  15   a  (refer to  FIG. 1 ) in the first modification. The concrete coupling portion form between the coupling portion  19   a  and the electrode  15   a  is not limited to this example, and can be modified as appropriate. The number and the arrangement of array electrodes such as the array electrodes  20 A,  20 B,  20 C, and  20 D are not limited to those in the example illustrated in  FIG. 9 , and can be modified as appropriate. For example, one of the array electrodes may be positioned on the upper side of the common coupling portion  19   c  in a plan view. In this case, a contact is provided that couples the array electrode and the common coupling portion  19   c . As the number of contacts that couple the coupling portion  19   a  (or the common coupling portion  19   c ) and the array electrode is increased, the number of current paths between these coupling structures is increased, thereby making it possible to further reduce an electrical resistance of each contact. The coupling between the array electrode and the common coupling portion  19   c  via the contacts may be employed from this point of view. 
     As illustrated in  FIG. 9 , the power supply lines Vbias in the first modification extend in the second direction Dy so as to be arranged without being in contact with the coupling portions  19   a  and the signal line Sig. Specifically, the power supply lines Vbias are provided along the two sides that face each other in the first direction Dx and extend in the second direction Dy among the four sides of the array Un. The power supply lines Vbias and the third electrode  40 A are coupled via contacts  455  included in contact formation regions  45 A illustrated in  FIG. 10 . A dummy electrode DF illustrated in  FIG. 9  is disposed at a portion corresponding to the space between the array electrodes  20 A and  20 C illustrated in  FIG. 8 . The dummy electrode DF is coupled to the third electrode  40 A via contacts  456  positioned between the contact formation regions  20 P and  20 R among the contacts included in the contact formation region  45 A illustrated in  FIG. 10 . The potential of the power supply line Vbias is applied to the dummy electrode DF via the contacts in the contact formation region  45 A and the third electrode  40 A. This makes it possible to make the electrical characteristics between the array electrodes  20 A and  20 C closer to the electrical characteristics between the array electrodes  20 B and  20 D, thereby making it possible to increase detection accuracy of force. In  FIG. 10 , two of the contacts (contacts  451 ,  452 ,  453 ,  454 ,  455 , and  456 ) in each region are representatively labeled with the numerals. The objects illustrated in the same shapes (e.g., square shape) as those labeled with the numerals also function as the contacts in the same manner as those labeled with the numerals. 
     In the first modification, the adjacent arrays Un in the arrays Un arranged in a matrix of a row-column configuration share the power supply line Vbias and the third electrode  40 A that are positioned between the adjacent arrays Un. 
     The wiring layer illustrated in  FIG. 9  is the fourth wiring layer  19  (refer to  FIG. 1 ) in the embodiment, for example, but is not limited to this, and may be another wiring layer. In this case, the contacts illustrated in  FIG. 10  and the contact holes for establishing couplings by the contacts extend to the other wiring layer. 
     In the first modification described with reference to  FIGS. 8 to 10 , the four first electrodes (array electrodes  20 A,  20 B,  20 C, and  20 D) in the array Un share one second element  62 . In the first modification, the number of first electrodes sharing the second element  62  is not limited to four and may be equal to or larger than two. The arrangement of the first electrodes sharing the one second element  62  in a plan view and the shape of each first electrode are not limited to specific ones. 
     The first modification is the same as the embodiment except for those notably described above. In the same manner as the embodiment, the elastic body  50  and the second electrode  30  are provided on the upper side of the electrode layer in which the array electrodes  20 A,  20 B,  20 C, and  20 D and the third electrode  40 A are formed. 
     In the structure where the first electrodes share one second element  62  such as that in the first modification, the same conduction as the conduction between the first electrode  20  and the second electrode  30  (refer to  FIG. 2 ) in the embodiment occurs individually for each of the first electrodes in response to force from the second electrode  30  side. Therefore, the conduction between the second electrode  30  and some of the first electrodes and the conduction between the second electrode  30  and all of the first electrodes occur. That is, the conduction can occur between the second electrode  30  and at least one of the first electrodes. For example, the structure as illustrated in  FIG. 8  in which the array electrodes  20 A,  20 B,  20 C, and  20 D share one second element  62  allows the following cases. In a first case, none of the array electrodes  20 A,  20 B,  20 C, and  20 D is electrically coupled to the second electrode  30 . In a second case, one of the array electrodes  20 A,  20 B,  20 C, and  20 D is electrically coupled to the second electrode  30 . In a third case, two of the array electrodes  20 A,  20 B,  20 C, and  20 D are electrically coupled to the second electrode  30 . In a fourth case, three of the array electrodes  20 A,  20 B,  20 C, and  20 D are electrically coupled to the second electrode  30 . In a fifth case, four of the array electrodes  20 A,  20 B,  20 C, and  20 D are electrically coupled to the second electrode  30 . The detection circuit that is coupled to the signal lines Sig and has electrical resolution with which each of the first to the fifth cases can be identified, allows force detection by each array of the force sensor to have gradation. In other words, the first to the fifth cases that occur depending on strength of force from the second electrode  30  side are allowed to be detected individually, whereby a level of the strength of force can be detected in addition to presence or absence of the force. The first to the fifth cases are exemplified in this modification. The electrical resolution of the detection circuit simply needs to correspond to the number of first electrodes sharing one second element  62 . 
     In the first modification, one transistor (second element  62 ) is coupled to two or more of the first electrodes (e.g., the array electrodes  20 A,  20 B,  20 C, and  20 D). As a result, the intensity of the signal output to the signal line Sig via the transistor can be changed according to the number of first electrodes coupled to the second electrode  30  among the two or more of the first electrodes. In other words, the intensity of the signal can have the gradation according to the number of first electrodes coupled to the one transistor via the first element  61 . This makes it possible to increase the detection accuracy of the force-applied portion and the force in the detection region SA. 
     The third electrode  40 A separates at least the first electrodes adjacent in one direction from each other among the two or more of the first electrodes (e.g., the array electrodes  20 A,  20 B,  20 C, and  20 D) coupled to the one transistor (second element  62 ). This makes it easier to stabilize the electrical characteristics depending on the positional relation between the third electrode  40  and the two or more of the first electrodes coupled to the one transistor (second element  62 ) via the first element  61 . 
     The third electrode  40 A is electrically coupled to the power supply line Vbias stacked on the substrate  10  side of the third electrode  40 A. This structure makes it possible to dispose the power supply line Vbias in the detection region SA to couple the power supply line Vbias to the third electrode  40 A. 
     The power supply lines Vbias and the signal lines Sig are in the same layer. This allows the power supply lines Vbias and the signal lines Sig to be formed in the same process, thereby making it possible to manufacture the force sensor  1  at a lower cost. 
     Second Modification 
       FIG. 11  is a cross-sectional view illustrating a layered structure including main elements of a force sensor  1 B according to a second modification.  FIG. 11  illustrates the elastic body  50  that is receiving force from the second electrode  30  side. The force sensor  1 B includes a conductive portion  90  in addition to the structure of the embodiment. As illustrated in  FIG. 11 , the force sensor  1 B in the second modification includes the power supply line Vbias that is provided on the upper side of the covering portion HRC and exposed externally. The power supply line Vbias that is provided on the upper side of the covering portion HRC and exposed externally may be a retrofitted electrode that is coupled to an external power supply source supplying the same potential as the power supply line Vbias in the embodiment, or may be the third electrode  40  that extends externally. 
     The conductive portion  90  is a conductive tape that has conductivity and adhesiveness on its surface facing the second electrode  30  and on its surface facing the power supply line Vbias that is provided on the upper side of the covering portion HRC and exposed externally, for example. As illustrated in  FIG. 11 , the conductive portion  90  couples the second electrode  30  and the power supply line Vbias that is provided on the upper side of the covering portion HRC and exposed externally. As a result, the potential of the power supply line Vbias is applied to the second electrode  30 . The conductive portion  90  may have another structure having the same functions. 
     In the second modification, the conduction is not established between the first electrode  20  and the second electrode  30  when the force sensor  1 B does not receive force from the second electrode  30  side, in the same manner as the embodiment. Consequently, the presence and absence of the application of the potential of the power supply line Vbias from one side of the first element  61  is switched depending on the presence and absence of force. Thus, the force sensor of the second modification can also detect force in the same manner as the embodiment. In the second modification, the potential of the power supply line Vbias is consistently applied to the second electrode  30 . This makes it possible to further stabilize the potential of the power supply line Vbias applied to the capacitor  70  (refer to  FIG. 3 ) via the first element  61  when the force sensor  1 B receives force from the second electrode  30  side. Furthermore, in the same manner as the embodiment, the first electrode  20  and the third electrode  40  are arranged close to each other with the opening  25  therebetween. This makes the electric characteristics of the array quite stable regardless of the position of the array in the row and column directions in the detection region SA. As a result, according to the second modification, it is possible to detect force with high accuracy under more stable conditions. 
     As described above, in the second modification, the second electrode  30  is coupled to the power supply (power supply line Vbias) provided outside the region where the first electrodes  20  are provided. This structure can preset the potential of the second electrode  30  to be equal to that of the third electrode  40 , thereby making it easy to more stabilize the electrical characteristics of the switch (e.g., switch  80 ) including the first electrode  20 , the second electrode  30 , and the third electrode  40  regardless of the disposition of the switch. 
     Other advantageous effects brought about by the modes described in the embodiment and the modifications are understood to be naturally brought about by the present disclosure to the extent that are apparent from the description of the present specification or achieved by those skilled in the art as appropriate.