Abstract:
A force sensor having a noise shielding layer is disclosed. For a first embodiment, a top noise shielding layer is configured on a top surface of a force sensor to screen noise signals which are caused by human body&#39;s touch or approaching from top of the force sensor. For a second embodiment, a bottom noise shielding layer is configured on a bottom surface of the force sensor to screen noise signals which are caused by human body&#39;s touch or approaching from bottom of the force sensor.

Description:
BACKGROUND 
     Technical Field 
       [0001]    The present invention relates to a force sensor, especially relates to a force sensor having a noise shielding layer configured on a top surface to screen noise signals caused by human body&#39;s touch. 
       Description of Related Art 
       [0002]      FIG. 1  shows a prior art. 
         [0003]      FIG. 1  shows a force sensor which has a top substrate  11  configured on a top side for a user to press. A top electrode  111  is configured on a bottom side of the top substrate  11 ; a top force sensitive layer  112  is configured on a bottom side of the top electrode  111 ; a gap  15  is configured on a bottom side of the top piezo material  112 ; a bottom force sensitive layer  122  is configured on a bottom side of the gap  15 ; a bottom electrode  121  is configured on a bottom side of the bottom force sensitive layer  122 ; and a bottom substrate  12  is configured on a bottom side of a bottom electrode  121 . 
         [0004]    The top force sensitive layer  112  and the bottom force sensitive layer  122  contact with each other when the force sensor is pressed. An electrical path is created among the top electrode  111 , the top force sensitive layer  112 , the bottom force sensitive layer  122 , and the bottom electrode  121  and a corresponding force signal is generated for a control system (not shown) to process. 
         [0005]      FIG. 2  shows an operation with the prior art. 
         [0006]      FIG. 2  shows an induced capacitance  11 C is created when a user&#39;s finger touches the force sensor. Noise signals caused by the induced capacitance  11 C are generated. The noise signals are annoying especially where a higher precision detection is required. In order to screen noise signals, a relative higher threshold voltage needs to be set. However, the higher the threshold voltage it is, the less the precision is obtained. 
         [0007]      FIG. 3  shows an equivalent circuit for the prior art. 
         [0008]      FIG. 3  shows an ideal equivalent circuit for the prior art of  FIG. 1 . Where the force sensor equivalents to a variable resistor R 1 . For example, current i 0  flows when a force presses the force sensor. Also, a same current i 0  passes through the reference resistor Rref., and an output I is obtained. However, it is not an ideal case for an actual operation. Please referring to  FIG. 4  for an actual situation, 
         [0009]      FIG. 4  shows an equivalent circuit when pressed for a prior art force sensor. 
         [0010]      FIG. 4  shows an actual situation when a user&#39;s finger presses the force sensor. Noise signals ( FIG. 5A ) are created by an induced capacitance  11 C when a user&#39;s finger touches the force sensor. The action of user&#39;s press equivalents to a resistor parallel connected to the force sensor. A fraction of current flows through the user&#39;s finger to ground.  FIG. 4  shows as an example when an input current i 0  is provided to the force sensor when the force sensor is pressed. A fraction of current i 01  flows through the finger to ground, and a fraction of current i 02  flows through the force sensor R 1  as well as the reference resistor Rref., an output II is obtained. However, the output II of  FIG. 4  shall be smaller than the ideal output I of  FIG. 3 . It means S/N ratio is relative lower for the prior art. 
         [0011]    The disadvantage for the prior art is that a relative lower “signal-to-noise ratio” (S/N ratio) causes noise signals for an electronic system. A relative higher S/N ratio is preferred which eliminate noise signals a lot for an electronic system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  shows a prior art. 
           [0013]      FIG. 2  shows an operation with the prior art. 
           [0014]      FIG. 3  shows an equivalent circuit for the prior art. 
           [0015]      FIG. 4  shows an equivalent circuit when pressed for a prior art force sensor. 
           [0016]      FIG. 5A  shows an actual test picture for the prior art. 
           [0017]      FIG. 5B  shows an actual test picture for the present invention. 
           [0018]      FIG. 6  shows a first embodiment according to the present invention. 
           [0019]      FIG. 7  shows an operation with the first embodiment according to the present invention. 
           [0020]      FIG. 8  shows a second embodiment according to the present invention. 
           [0021]      FIG. 9  shows a third embodiment according to the present invention. 
           [0022]      FIG. 10  shows a fourth embodiment according to the present invention. 
           [0023]      FIGS. 11A-11C  show force sensors categorized by electrodes configuration applied with noise shielding layer according to the present invention. 
           [0024]      FIG. 12A  shows a fifth embodiment according to the present invention. 
           [0025]      FIG. 12B  shows a modified embodiment to  FIG. 12A  according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 5A  shows an actual test picture for the prior art. 
         [0027]      FIG. 5A  shows a test picture for a multi-touch force sensor according to the prior art which does not have any shielding layer.  FIG. 5A  shows a plurality of noise signals generated in an area  115  besides normal signals for the palm when a user&#39;s palm touches the multi-touch force sensor. 
         [0028]    A material for the shielding layer is an electrical conductive material such as metal, conductive polymer, or ito (Indium Tin Oxide). The shielding layer can be formed with network or grid to save the conductive material. 
         [0029]      FIG. 5B  shows an actual test picture for the present invention. 
         [0030]      FIG. 5B  shows a test picture for a multi-touch force sensor according to the present invention which has a noise shielding layer  21  ( FIG. 6 ) configured on top.  FIG. 5B  shows no significant noise signals generated in an area  115  besides normal signals for the palm when the user&#39;s palm touches the force sensor. 
         [0031]      FIG. 6  shows a first embodiment according to the present invention. 
         [0032]      FIG. 6  shows a force sensor according to the present invention which has a noise shielding layer  21  configured on a top side of a force sensor.  FIG. 6  shows a force sensor has a noise shielding layer  21 . A top substrate  11  is configured on a bottom side of the top noise shielding layer  21 ; a top electrode  111  is configured on a bottom side of the top substrate  11 ; a bottom substrate  12  is configured on a bottom side of a bottom electrode  121 ; and a pair of force sensitive layers  112 ,  122  are configured between the top electrode  111  and the bottom electrode  121 . 
         [0033]    For a modified force sensor (not shown), single layer of force sensitive layer can be adopted and configured between the top electrode  111  and the bottom electrode  121 . 
         [0034]    The force sensitive layer can be used for the present invention is made of a material selected from a group consisting of piezo-electric material, dielectric material, semi-conductive material, piezo-resistive material and piezo-capacitive material. 
         [0035]      FIG. 7  shows an operation with the first embodiment according to the present invention. 
         [0036]      FIG. 7  shows an operation for the first embodiment of  FIG. 6 . Referring to  FIG. 7 , an induced capacitor  11 C is created when a finger of a user touches the force sensor. Since the noise shielding layer  21  is electrically coupled to system ground, therefore the induced capacitance  11 C gives no significant influence to the force sensor. No noise signals shall be generated when the user&#39;s finger touches the force sensor. 
         [0037]      FIG. 8  shows a second embodiment according to the present invention. 
         [0038]      FIG. 8  shows a second embodiment according to the present invention. In addition to the top noise shielding layer  21  configured on top, a bottom noise shielding layer  22  is configured on a bottom side of the bottom substrate  12 . Both the top noise shielding layer  21  and the bottom noise shielding layer  22  are electrically coupled to ground. For the bottom of the force sensor, noise signals can be eliminated under conditions where electrical conductive material may be configured on a bottom side of the force sensor. 
         [0039]      FIG. 9  shows a third embodiment according to the present invention. 
         [0040]      FIG. 9  shows a modification version from the second embodiment according to the present invention. Where the top substrate  11  and the bottom substrate  12  are integrated into a single substrate  13  (11+12). In other words, the top substrate  11  and the bottom substrate  12  are made as partial elements of a single flexible circuit substrate  13 . 
         [0041]      FIG. 10  shows a fourth embodiment according to the present invention. 
         [0042]      FIG. 10  shows a modification version from the third embodiment according to present invention. Where the bottom noise shielding layer  22  and the top noise shielding layer  21  are integrated into a single shielding layer. In other words, the bottom noise shielding layer  22  and the top noise shielding layer  21  are made as partial elements of a single flexible circuit substrate  13 . After assembly, the integrated bottom noise shielding layer  22  and the top noise shielding layer  21  is electrically coupled to system ground. 
         [0043]      FIGS. 11A ˜ 11 C show force sensors categorized by electrodes configuration applied with noise shielding layer according to the present invention. 
         [0044]      FIG. 11A  shows a force sensor has a top electrode  31 A and a bottom electrode  31 B. The top electrode  31 A is configured on a bottom surface of a top substrate  32 A. The bottom electrode  31 B is configured on a top surface of a bottom substrate  32 B. A top noise shielding layer  33 A is configured on a top surface of the top substrate  32 A. A bottom noise shielding layer  33 B is optionally configured on a bottom surface of the bottom substrate  32 B. An intermediate layer  35  can be inserted between the top electrode  31 A and the bottom electrode  31 B. 
         [0045]    A material for the intermediate layer  35  is selected from a group consisting of an air space, piezo-capacitive material, and compressive-restorable dielectric material, so that the force sensor functions as a variable capacitor with AC power. Alternatively, a material for the intermediate layer  35  is selected from a group consisting of piezo-electric material, piezo-resistive material, compressible-restorable semiconductor polymer, so that that the force sensor functions as a variable resistor with DC power. 
         [0046]      FIG. 11B  shows a force sensor has a coplanar electrodes  41 A,  41 B. The coplanar electrodes  41 A,  41 B are configured on a top surface of a bottom substrate  42 B. A top noise shielding layer  43 A is configured on a top surface of a top substrate  42 A. A bottom noise shielding layer  43 B is optionally configured on a bottom surface of the bottom substrate  42 B. An intermedia layer  45  is inserted between the top substrate  42 A and the bottom substrate  42 B. 
         [0047]    A material for the intermedia layer  45  is selected from a group consisting of piezo-capacitive material, and compressive-restorable dielectric material, so that the force sensor functions as a variable capacitor with AC power. 
         [0048]    Alternatively, a material for the intermedia layer  45  is selected from a group consisting of piezo-electric material, piezo-resistive material, compressible-restorable semiconductor polymer, so that the force sensor functions as a variable resistor with DC power. 
         [0049]      FIG. 11C  shows a force sensor has a coplanar electrodes  51 A,  51 B, and an auxiliary metal  512 . The coplanar electrodes  51 A,  51 B are configured on a top surface of a bottom substrate  52 B. The auxiliary metal  512  is configured on a bottom surface of the top substrate  52 A. A top noise shielding layer  53 A is configured on a top surface of a top substrate  52 A. A bottom noise shielding layer  53 B is optionally configured on a bottom surface of the bottom substrate  52 B. An intermediate layer  55  can be inserted between the auxiliary metal  512  and the bottom substrate  42 B. 
         [0050]    The auxiliary metal  512  is an independent metal layer to enhance an even distribution for electric field, and without connecting to any electrode. 
         [0051]    A material for the intermediate layer  55  is selected from a group consisting of an air space, piezo-capacitive material, and compressive-restorable dielectric material. So that the force sensor functions as a variable capacitor with AC power. 
         [0052]    Alternatively, a material for the intermediate layer  55  is selected from a group consisting of piezo-electric material, piezo-resistive material, compressible-restorable semiconductor polymer. So that the force sensor functions as a variable resistor with DC power. 
         [0053]    Table 1 shows Electrode Configuration v Intermediate Layer choices for the force sensor of  FIGS. 11A ˜ 11 C. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Electrode configuration v Intermediate layer choices. 
               
             
          
           
               
                 Electrode 
                 Intermediate 
                 Force sensor 
                   
               
               
                 Configuration 
                 Layer Choices 
                 equivalent to 
                 Power 
               
               
                   
               
               
                 Top, bottom electrodes 
                 Air space; 
                 variable 
                 AC 
               
               
                 (FIG. 11A) 
                 piezo-capacitive material; 
                 capacitor 
               
               
                   
                 dielectric material; 
               
               
                   
                 Piezo-electric material; 
                 variable 
                 DC 
               
               
                   
                 Piezo-resistive material; 
                 resistor 
               
               
                   
                 Semiconductor polymer; 
               
               
                 Coplanar electrodes 
                 piezo-capacitive material; 
                 variable 
                 AC 
               
               
                 (FIG. 11B) 
                 dielectric material; 
                 capacitor 
               
               
                   
                 Piezo-electric material; 
                 variable 
                 DC 
               
               
                   
                 Piezo-resistive material; 
                 resistor 
               
               
                   
                 Semiconductor polymer; 
               
               
                 Coplanar electrodes 
                 Air space; 
                 variable 
                 AC 
               
               
                 plus 
                 piezo-capacitive material; 
                 capacitor 
               
               
                 Enhancing metal layer 
                 dielectric material; 
               
               
                 (FIG. 11C) 
                 Piezo-electric material; 
                 variable 
                 DC 
               
               
                   
                 Piezo-resistive material; 
                 resistor 
               
               
                   
                 Semiconductor polymer; 
               
               
                   
               
             
          
         
       
     
         [0054]      FIG. 12A  shows a fifth embodiment according to the present invention. 
         [0055]      FIG. 12A  shows that a variable capacitor force sensor is formed by a configuration where a top electrode  61  is prepared. A top substrate  62 A is configured on a bottom surface of the top electrode  61 A. A piezo capacitive material  62 P is configured on a bottom of the top substrate  62 A. A bottom electrode  61 B is configured on a bottom of the piezo capacitive material  62 P. A bottom substrate  62 B is configured on a bottom surface of the bottom electrode  61 B. 
         [0056]    The top electrode  61 A is electrically coupled to ground, so that the top electrode  61 A functions as a shielding layer and, in the meanwhile, functions as a counter electrode with respect to the bottom electrode  61 B. i.e. the top electrode  61 A and the bottom electrode  61 B forms a variable capacitor force sensor. Capacitance exists between the top electrode  61 A and the bottom electrode  61 B as shown in heavy arrow in the  FIGS. 12A-12B . 
         [0057]    The variable resistor force sensor of  FIG. 13A  can be pressed from top side, as shown by the finger on top, with noise shielding protection. 
         [0058]    An air space or a compressible-restorable material can be used to replace the piezo capacitive material  62 P. 
         [0059]      FIG. 12B  shows a modified embodiment to  FIG. 12A  according to the present invention. 
         [0060]      FIG. 13B  shows a bottom shielding layer  63 , electrically coupled to ground, is optionally configured on a bottom surface of the bottom substrate  62 B so that the variable resistor force sensor of  FIG. 13B  can be pressed from either top side or bottom side, as shown by the fingers on top and bottom, with noise shielding protection. 
         [0061]    While several embodiments have been described by way of examples, 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. 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 Numerical system 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 top substrate 11 
               
               
                   
                 top electrode 111 
               
               
                   
                 force sensitive layers 112, 122 
               
               
                   
                 Area 115 
               
               
                   
                 induced capacitor 11C 
               
               
                   
                 bottom substrate 12 
               
               
                   
                 substrate 13 (11 + 12) 
               
               
                   
                 noise shielding layer 21 
               
               
                   
                 noise shielding layer 22 
               
               
                   
                 electrode 31A, 31B 
               
               
                   
                 substrate 32A, 32B 
               
               
                   
                 noise shielding layer 33A, 33B 
               
               
                   
                 intermediate layer 35, 45, 55 
               
               
                   
                 electrode 41A, 41B 
               
               
                   
                 substrate 42A, 42B 
               
               
                   
                 noise shielding layer 43A, 43B 
               
               
                   
                 electrode 51A, 51B 
               
               
                   
                 substrate 52A, 52B 
               
               
                   
                 noise shielding layer 53A, 53B 
               
               
                   
                 top electrode 61A (top shielding layer 61A) 
               
               
                   
                 bottom electrode 61B 
               
               
                   
                 top substrate 62A 
               
               
                   
                 bottom substrate 62B 
               
               
                   
                 piezo capacitive material 62P 
               
               
                   
                 bottom shielding layer 63