Abstract:
A multi-touch pad having grid piezoresistor structure is disclosed. The grid structure conducts current to flow more linearly thereby allowing a more precise calculation of touch position.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a multi-touch pad, especially related to a multi-touch pad having grid piezoresistor structure. The grid structure conducts current to flow more linearly from power end to ground end. 
     2. Description of Related Art 
       FIGS. 1 ˜ 3  show a prior art. 
       FIG. 1  shows a prior art multi-touch pad  14  which is disclosed in US20090256817. The multi-touch pad  14  is used by a user&#39;s finger to input instructions to a computer  12 . A monitor  10  is electrically coupled to the computer  12  for displaying information. The multi-touch pad  14  has a top layer  18 . 
       FIG. 2  shows a section view of the input device  14 . Under the top cover  18 , there is a stack of top electrode wires  14 T, top resistor  15 T, force sensing resistor  16 , bottom resistor  15 B, and bottom electrode wires  14 B. 
       FIG. 3  shows a current pattern for the structure of  FIG. 2 . 
       FIG. 3  shows that a spot P is depressed as an example. Current  17  flows from a top wire  14 T to a bottom wire  14 B. Current  17  fans in, as shown in area  17 T, to the spot P from the top wire  14 T, and the current  17  fans out, as shown in area  17 B, to the bottom wire  14 B. 
     Since the resistance for the current fan in area and fan out area of the force sensing resistor at different pressed position equivalents to a resistance of a plurality of paralleled connected circuit path. The current is nonlinearity at different pressed position between the two electrodes. The current nonlinearity leads to a deviation of the pressed position calculation; the nearer the position is to the electrode, the larger the deviation is. For a touch pad structure, a current linearity is desirable so that the deviation of pressed position calculation can be reduced or eliminated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ˜ 3  show a prior art. 
         FIGS. 4 and 5A ˜ 5 C show a first embodiment according to the present invention. 
         FIGS. 6 and 7A ˜ 7 C show a second embodiment according to the present invention. 
         FIG. 8  shows current flow of a grid piezoresistor according to the present invention. 
         FIG. 9  shows a process for manufacturing a grid piezoresistor according to the present invention. 
         FIGS. 10 and 11A ˜ 11 C show a third embodiment according to the present invention. 
         FIGS. 12A ˜ 12 C show a first electrical connection according to the present invention. 
         FIGS. 13A ˜ 13 C show a second electrical connection according to the present invention. 
         FIGS. 14 ˜ 15  show a first application according to the present invention. 
         FIG. 16  shows a second application according to the present invention. 
         FIGS. 17 and 18A ˜ 18 C show a fourth embodiment according to the present invention. 
         FIG. 19  shows a modified stack of the present invention. 
         FIG. 20  shows a further modified stack of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention discloses a multi-touch pad with grid piezoresistor; the grid piezoresistor conducts current more linearly from top electrode to bottom electrode when the multi-touch pad is depressed. The grid piezoresistor structure also saves piezoresistor material a lot due to the holes enclosed in the grid piezoresistor. 
     The size of the hole dependents on the tool to be used. For a first example, the size for the hole is designed to be as small as 3 mm square or in diameter for a multi-touch pan with human being&#39;s finger to touch, where a human being&#39;s finger is deemed roughly to have a touch area around 5 mm square or in diameter. For a second example, the size of the hole is designed as small as 0.2˜0.4 mm square or in diameter for a multi-touch pan with a stylus to touch, where a tip of a stylus is deemed to have a touch area roughly around 0.5 mm in diameter. 
     The grid piezoresistor structure leads the current to be linearity at different pressed position between the two electrodes. The current linearity at different pressed position leads to the position calculation more correct. 
       FIGS. 4 and 5A ˜ 5 C show a first embodiment according to the present invention. 
       FIG. 4  shows an isomeric view of the first embodiment. 
       FIG. 4  shows a Multi-touch pad which has a top grid piezoresistor  20 T and a bottom grid piezoresistor  20 B with a spacer  25  sandwiched in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. The top grid piezoresistor  20 T has a plurality of hole  27 T passing through. The bottom grid piezoresistor  20 B has a plurality of hole  27 B passing through. 
     The top grid piezoresistor  20 T has a plurality of latitudinal piezoresistor strip  20 TX and a plurality of longitudinal piezoresistor strip  20 TY. The latitudinal piezoresistor strips  20 TX and the longitudinal piezoresistor strips  20 TY are interwoven to be coplanar on top side and coplanar on bottom side. 
     The bottom grid piezoresistor  20 B has a plurality of latitudinal piezoresistor strip  20 BX and a plurality of longitudinal piezoresistor strip  20 BY. The latitudinal piezoresistor strips  20 BX and the longitudinal piezoresistor strips  20 BY are interwoven to be coplanar on top side and coplanar on bottom side. 
     A spacer  25  is configured in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B for maintaining a predetermined space  251  between the two grid piezoresistor. 
     At least a first latitudinal electrode  26 T is configured on a top of a first latitudinal piezoresistor  20 TX of the top grid piezoresistor  20 T. At least a second latitudinal electrode  26 T is configured on a top of a second latitudinal piezoresistor  20 TX of the top grid piezoresistor  20 T. 
     At least a first longitudinal electrode  26 B is configured on a bottom of a first longitudinal piezoresistor  20 BY of the bottom grid piezoresistor  20 B. At least a second longitudinal electrode  26 B is configured on a bottom of a second longitudinal piezoresistor  20 BY of the bottom grid piezoresistor  20 B. 
       FIG. 5A  shows a top view of the first embodiment. 
       FIG. 5A  shows that the top grid piezoresistor  20 T has a plurality of latitudinal electrode  26 T. A first latitudinal electrode  26 T is configured on a top of a first latitudinal piezoresistor  20 TX. A second latitudinal electrode  26 T is configured on a top of a second latitudinal piezoresistor  20 TX. Wherein the first latitudinal electrode is next to the second latitudinal electrode. 
       FIG. 5B  shows an elevation view of the first embodiment. A spacer  25  is configured in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. 
       FIG. 5C  shows a bottom view of the first embodiment. 
       FIG. 5C  shows that the bottom grid piezoresistor  20 B has a plurality of hole  27 B. At least a first longitudinal electrode  26 B is configured on a bottom of a first longitudinal piezoresistor  20 BY. At least a second longitudinal electrode  26 B is configured on a bottom of a second longitudinal piezoresistor  20 BY. The first longitudinal electrode is next to the second longitudinal electrode. 
       FIGS. 6 and 7A ˜ 7 C show a second embodiment according to the present invention. 
       FIG. 6  shows an isomeric view of the second embodiment. 
     As compared to the first embodiment of  FIG. 4 , the difference is that the second embodiment of  FIG. 6  has a wider distance between neighboring latitudinal electrodes  26 T. A latitudinal piezoresistor strip  265 T is located in between neighboring latitudinal electrodes  26 T. For the bottom grid piezoresistor  20 B, the second embodiment of  FIG. 6  also has a wider distance between neighboring longitudinal electrodes  26 B, a longitudinal piezoresistor strip  265 B is located in between neighboring longitudinal electrodes  26 B. 
       FIG. 7A  shows a top view of the second embodiment. 
       FIG. 7A  shows that the top grid piezoresistor  20 T has a plurality of latitudinal electrode  26 T. A latitudinal piezoresistor strip  265 T is located in between neighboring latitudinal electrodes  26 T. 
       FIG. 7B  shows an elevation view of the second embodiment. A spacer  25  is configured in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. 
       FIG. 7C  shows a bottom view of the second embodiment. 
       FIG. 7C  shows that the bottom grid piezoresistor  20 B has a plurality of longitudinal electrode  26 B. A longitudinal piezoresistor strip  265 B is located in between neighboring longitudinal electrodes  26 B. 
       FIG. 8  shows current flow of a grid piezoresistor according to the present invention. 
       FIG. 8  shows current  29  flows in a top electrode  26 T. The current flows to the depressed spot P more linearly as specified with  29 T due to the narrow wall of the grid piezoresistor structure; and the current flows to the bottom electrode  26 B from the depressed spot P more linearly as specified with  29 B due to the narrow wall of the grid piezoresistor structure. 
       FIG. 9  shows a process for manufacturing a grid piezoresistor according to the present invention. 
       FIG. 9  shows a process for manufacturing a grid piezoresistor with silk screen printing, including the following steps: 
     printing a plurality of latitudinal electrode; 
     printing a top grid piezoresistor which has a plurality of latitudinal strip and a plurality of longitudinal strip; each latitudinal electrode is configured on a top of a corresponding one latitudinal strip; 
     printing a plurality of longitudinal electrode; 
     printing a bottom grid piezoresistor which has a plurality of latitudinal strip and a plurality of longitudinal strip; each longitudinal electrode is configured on a bottom of a corresponding one longitudinal strip; 
     stacking the top grid piezoresistor and the bottom grid piezoresistor with a space or slight contact in between; 
     a top protection layer is configured for the top grid piezoresistor to be attached on a bottom of the top protection layer; 
     a bottom protection layer is configured for the bottom grid piezoresistor to be attached on a top of the bottom protection layer; and 
     a spacer is configured for maintaining a space or slight contact between the two grid piezoresistors. 
       FIGS. 10 and 11A ˜ 11 C show a third embodiment according to the present invention. 
       FIG. 10  shows an isomeric view of the third embodiment. 
     As compared to the second embodiment of  FIG. 6 , the difference is that the third embodiment of  FIG. 10  has an even wider distance between neighboring latitudinal electrodes  26 T. Two latitudinal piezoresistor strips  265 T are located in between neighboring latitudinal electrodes  26 T as an example. For the bottom grid piezoresistor  20 B, the third embodiment of  FIG. 10  also has an even wider distance between neighboring longitudinal electrodes  26 B, two longitudinal piezoresistor strips  265 B are located in between neighboring longitudinal electrodes  26 B as an example. 
       FIG. 11A  shows a top view of the third embodiment. 
       FIG. 11A  shows that the top grid piezoresistor  20 T has a plurality of latitudinal electrode  26 T. Two latitudinal piezoresistor strips  265 T are located in between neighboring latitudinal electrodes  26 T. 
       FIG. 11B  shows an elevation view of the third embodiment. A spacer  25  is configured in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. 
       FIG. 11C  shows a bottom view of the third embodiment. 
       FIG. 11C  shows that the bottom grid piezoresistor  20 B has a plurality of longitudinal electrode  26 B. Two longitudinal piezoresistor strips  265 B are located in between neighboring longitudinal electrodes  26 B. 
       FIGS. 12A ˜ 12 C show a first electrical connection according to the present invention. 
       FIG. 12A  shows that one of the latitudinal electrodes, for example,  2611 T is electrically coupled to power end and the rest are electrically coupled to ground end at a single moment. 
       FIG. 12B  shows an elevation view of the third embodiment. A spacer  25  is configured in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. 
       FIG. 12C  shows that one of the longitudinal electrodes, for example,  2611 B is electrically coupled to ADC and the rest three electrodes  2613 B,  2615 B,  2017 B are electrically coupled to ground end at a single moment. 
       FIGS. 13A ˜ 13 C show a second electrical connection according to the present invention. 
       FIG. 13A  shows that four latitudinal electrodes  2611 T,  2613 T,  2615 T,  2617 T are alternately electrically coupled to power end; however, only one of the latitudinal electrodes, for example,  2611 T is electrically coupled to power end and the rest three electrodes  2613 T,  2615 T,  2617 T are electrically coupled to ground end at a single moment. 
     There are three independent metal wires  2612 T,  2614 T,  2616 T; each is interleaved in between neighboring latitudinal electrodes  26 T. The independent metal wire function as a conductivity enhancing metal (CEM) to enhance lateral conductivity between the neighboring latitudinal piezoresistor strips. The higher the lateral conductivity is, the higher the reading resolution/sensitivity is for the signal detection. 
       FIG. 13B  shows an elevation view of the third embodiment. A spacer  25  is configured in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. 
       FIG. 13C  shows that four longitudinal electrodes  2611 B,  2613 B,  2615 B,  2617 B are alternately electrically coupled to ADC; however, only one of the longitudinal electrodes, for example,  2611 B is electrically coupled to ADC and the rest three electrodes  2613 B,  2615 B,  2617 B are electrically coupled to ground end at a single moment. 
     There are three independent metal wires  2612 B,  2614 B,  2616 B; each is interleaved in between neighboring longitudinal electrodes  26 B. The independent metal wire function as a conductivity enhancing metal (CEM) to enhance lateral conductivity between the neighboring longitudinal piezoresistor strips. 
       FIGS. 14 ˜ 15  show a first application according to the present invention. 
       FIG. 14  shows that the present invention, multi-touch pad  31 , can be configured on a backside of a flexible display  32 .  FIG. 14  shows that a display  32  shows, for example, an icon flower as a first button B 1  which is depressible, and an icon cow as a second button B 2  which is also depressible. When either button B 1  or B 2  displayed on the flexible display  32  is depressed, the pressure transmits to the underlain multi-touch pad  31  due to the flexibility of the flexible display  32 . A force sensing area corresponding to the button configured on the multi-touch pad  31  senses the pressure and then a corresponding signal is sent to a control unit (not shown). 
       FIG. 15  shows a section view of partial area of  FIG. 14 . 
       FIG. 15  shows the flexible display  32  facing viewer for displaying information. The depressed pressure on the button B 1  transmits to the underlain multi-touch pad  31 . The bottom configured multi-touch pad  31  senses the button pressure of B 1  and a corresponding signal is sent to a control unit (not shown). 
       FIG. 16  shows a second application according to the present invention. 
       FIG. 16  shows that the present invention is configured to be an extended keyboard for a touch screen of a smart phone  35 .  FIG. 16  show a top layer  37  having a plurality of button; a multi-touch pad  31  is configured under the top layer  37 ; a force sensing area corresponding to each button is configured on the multi-touch pad  31 . The multi-touch pad  31  senses a pressure and a corresponding signal is sent to a control unit when one of the buttons is depressed. 
       FIGS. 17 and 18A ˜ 18 C show a fourth embodiment according to the present invention. 
       FIG. 17  shows a fourth embodiment according to the present invention. 
     As compared to the third embodiment of  FIG. 10 , the difference is that the fourth embodiment of  FIG. 17  does not have a spacer in between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. The top grid piezoresistor  20 T is directly stacked on the top of the bottom grid piezoresistor  20 B. Though the slight contact between the two grid piezoresistors may cause a little current leakage between the top electrode and the bottom electrode, it can be regarded as circuit open through threshold current setting in the control unit. All the modifications applied to the third embodiment can also be applied to the fourth embodiment. 
       FIG. 18A  shows that the top grid piezoresistor  20 T is the same as that of the third embodiment of  FIG. 11A . 
       FIG. 18B  shows an elevation view of the fourth embodiment. The top grid piezoresistor  20 T stack on the top of the bottom grid piezoresistor  20 B directly with having any spacer configured in between. 
       FIG. 18C  shows that the bottom grid piezoresistor  20 B is the same as that of the third embodiment of  FIG. 11C . 
       FIG. 19  shows a modified stack of the present invention. 
       FIG. 19  shows that the spacer  252  is configured in between top protection layer  38 T and bottom protection layer  38 B. The top grid piezoresistor  20 T is attached on a bottom of the top protection layer  38 T and the bottom grid piezoresistor  20 B is attached on a top of the bottom protection layer  38 B. A space  251  is configured between the top grid piezoresistor  20 T and the bottom grid piezoresistor  20 B. 
       FIG. 20  shows a further modified stack of the present invention. 
       FIG. 20  shows that the spacer  252  is configured within one of the grid hole  27 T,  27 B in between top protection layer  38 T. 
     While several embodiments have been described by way of example, it will be apparent to those skilled in the art that various modifications may be configured without departs from the spirit of the present invention. Such modifications are all within the scope of the present invention, as defined by the appended claims.