Abstract:
A physical quantity sensor ( 100 ), which can detect multiple physical quantities simultaneously has flexibility or bendability over the entire body thereof. The sensor ( 100 ) has a first electrode layer ( 2 ) formed on a substrate ( 1 ) and first and second piezoelectric elements ( 3   a,    3   b ) arranged in parallel on the electrode layer ( 2 ). Two additional electrode layers ( 4   a,    4   b ) are formed on the piezoelectric elements ( 3   a,    3   b ). The substrate ( 1 ), the electrode layer ( 2 ), first piezoelectric element ( 3   a ), one of the additional electrode layers ( 4   a ) and protective layers ( 5   a,    5   b,    5   c,    5   d,    5   e ) constitute a first physical quantity detection unit ( 6 ), and the substrate ( 1 ), the first electrode layer ( 2 ), the second piezoelectric element ( 3   b ) and the other additional electrode layer ( 4   b ) (a fourth electrode layer) constitute a second physical quantity detection unit ( 7 ).

Description:
This is a National Phase Application filed under 35 U.S.C. 371 as a national stage of PCT/JP2011/064308 filed Jun. 22, 2011, and claims priority benefit from Japanese Application No. 2010-141923, filed Jun. 22, 2010, the content of each of which is hereby incorporated by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a physical quantity sensor for measuring a plurality of physical quantities and a process for production thereof. 
     DESCRIPTION OF THE RELATED ART 
     As disclosed in Japanese Patent Laid-Open No. 2002-31574, a sensor is conventionally known which can detect a pressure, simultaneously detect both the sense of pressure and the sense of slip, and also detect projections and depressions on a surface. 
     However, in recent years, there has been a demand for a sensor that not only has a pressure detection function but also detects other physical quantities from an object and detects a condition of the object. For example, it is expected to simultaneously detect a pressure from the object and bending deflection of the object or the like using one sensor. 
     It is therefore an object of the present invention to provide a physical quantity sensor and process for production thereof capable of simultaneously detecting a plurality of physical quantities. 
     SUMMARY OF THE INVENTION 
     (1) A physical quantity sensor of the present invention includes a first physical quantity detection section having a first electrode layer, a first piezoelectric element provided on the first electrode layer and a second electrode layer provided on the first piezoelectric element, and a second physical quantity detection section having a third electrode layer, a second piezoelectric element provided on the third electrode layer and a fourth electrode layer provided on the second piezoelectric element, wherein the first piezoelectric element is disposed so that a center line in a thickness direction of the first piezoelectric element substantially matches or matches a center line in a thickness direction of the first physical quantity detection section, and the second piezoelectric element is disposed so that a center line in a thickness direction of the second piezoelectric element is disposed eccentrically with respect to a center line in a thickness direction of the second physical quantity detection section. 
     According to the configuration in (1) above, a plurality of physical quantities can be simultaneously detected. For example, it is possible to simultaneously detect a pressure from the object using the first piezoelectric element and bending deflection of the object using the second piezoelectric element. Therefore, the physical quantity sensor of the present invention can be used, for example, as a contact sensor. 
     (2) In the physical quantity sensor in (1) above, the first physical quantity detection section and the second physical quantity detection section are arranged side by side, and part of the first electrode layer and part of the third electrode layer may be connected together so as to form one electrode layer. 
     According to the configuration in (2) above, it is possible to reduce the thickness of the sensor and form an electrode common to the first physical quantity detection section and the second physical quantity detection section through one process, and thereby easily produce the sensor. 
     (3) In the physical quantity sensor in (1) above, the second physical quantity detection section may be laminated on at least one side of the first physical quantity detection section via a flexible insulating layer. 
     According to the configuration in (3) above, since the first physical quantity detection section and the second physical quantity detection section can be integrated into one unit, it is possible to realize a smaller physical quantity sensor. Furthermore, laminating the piezoelectric element of the second physical quantity detection section so as to be arranged on both sides of the piezoelectric element of the first physical quantity detection section may double the sensor sensitivity in the second physical quantity detection section. 
     (4) In the physical quantity sensor in (2) above, the first electrode on the first piezoelectric element side may be fixed to a substrate and the second piezoelectric element may constitute a cantilever oscillatable in a predetermined direction by external vibration. 
     According to the configuration in (4) above, it is possible to detect a pressure from the object using the first piezoelectric element and also detect vibration of the object using the second piezoelectric element. 
     (5) In the physical quantity sensor in (1) to (4) above, a polydimethyl siloxane (hereinafter, represented by “PDMS”) substrate may be preferably provided on at least part of the surface. 
     According to the configuration in (5) above, since the PDMS substrate has biocompatibility, it is possible to paste the present physical quantity sensor to the skin or the like of an animal via the PDMS substrate for a long time and thereby obtain biological information such as pulsation, heart beat and respiration. 
     (6) A process for producing a physical quantity sensor of the present invention is a process for producing the physical quantity sensor in (2) above, including a piezoelectric element forming step of laminating and then etching a piezoelectric element layer on the one electrode layer to form the first piezoelectric element and the second piezoelectric element, and an electrode layer forming step of laminating and then etching a conductive layer on the first piezoelectric element and the second piezoelectric element to form the third electrode layer on the first piezoelectric element and form the fourth electrode layer on the second piezoelectric element. 
     According to the configuration in (6) above, the physical quantity sensor in (2) above can be easily produced. Particularly since an electrode common to the first physical quantity detection section and the second physical quantity detection section can be formed through one process, it is possible to easily produce the physical quantity sensor in (2) above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a physical quantity sensor according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view along line I-I shown by an arrow in  FIG. 1 ; 
         FIG. 3  is a diagram sequentially illustrating production steps of the physical quantity sensor shown in  FIG. 1 ; 
         FIG. 4  is a cross-sectional view of a physical quantity sensor according to a second embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of a physical quantity sensor according to a third embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of a physical quantity sensor according to a fourth embodiment of the present invention; and 
         FIG. 7  is a cross-sectional view of a physical quantity sensor according to a modification example of the first embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Hereinafter, a physical quantity sensor according to a first embodiment of the present invention will be described with reference to the accompanying drawings. 
     As shown in  FIG. 1  and  FIG. 2 , a physical quantity sensor  100  according to the present embodiment is provided with a substrate  1 , an electrode layer  2  formed on the substrate  1 , a piezoelectric element  3   a  and a piezoelectric element  3   b  disposed side by side on the electrode layer  2 , electrode layers  4   a  and  4   b  formed on the piezoelectric elements  3   a  and  3   b  and protective layers  5   a ,  5   b ,  5   c ,  5   d  and  5   e  that protect the electrode layer  2 , the piezoelectric elements  3   a  and  3   b  and the electrode layers  4   a  and  4   b . Furthermore, the substrate  1 , the electrode layer  2 , the piezoelectric element  3   a  (first piezoelectric element), the electrode layer  4   a  (third electrode layer) and the protective layers  5   a ,  5   b ,  5   c ,  5   d  and  5   e  constitute a first physical quantity detection section  6 , and the substrate  1 , the electrode layer  2 , the piezoelectric element  3   b  (second piezoelectric element) and the electrode layer  4   b  (fourth electrode layer) constitute a second physical quantity detection section  7 . 
     The substrate  1  is made of a flexible insulating material. For the substrate  1 , any material may be used according to the purpose as long as it has flexibility. For example, when the physical quantity sensor  100  is used pasted to a living body, PDMS may be used in consideration of biocompatibility. 
     The electrode layers  2 ,  4   a  and  4   b  are made of a flexible conductive material and, for example, copper, silver, gold, nickel-copper alloy or conductive polymer may be used. 
     The piezoelectric elements  3   a  and  3   b  are made of a flexible piezoelectric material. An example thereof may be piezoelectric polymer of PVDF (polyvinylidene fluoride). As shown in  FIG. 2 , a center line in the thickness direction of the piezoelectric element  3   a  matches a center position (center line in the thickness direction of the first physical quantity detection section  6 ) A 3  between a bottom surface position A 1  and a top surface position A 2  of the physical quantity sensor  100 . A center line in the thickness direction of the piezoelectric element  3   b  is disposed eccentrically with respect to a center position (center line in the thickness direction of the second physical quantity detection section  7 ) A 5  between the bottom surface position A 1  and a top surface position A 4  of the second physical quantity detection section. 
     The protective layers  5   a ,  5   b ,  5   c ,  5   d  and  5   e  are made of a flexible insulating material. For the protective layers  5   a ,  5   b ,  5   c ,  5   d  and  5   e , any material may be used as long as it is flexible according to the purpose as in the case of the substrate  1 . For example, when the physical quantity sensor  100  is used as a pasted sensor to a living body, PDMS may be used in consideration of biocompatibility. 
     Next, operation of the physical quantity sensor  100  will be described. Here, for example, suppose the physical quantity sensor  100  shown in  FIG. 2  is bent so as to warp in a convex form to an extent that it is not plastically deformed with the center of the surface of the protective layer  5   c  as a vertex. In this case, although stress of bending operation is added to the piezoelectric element  3   a  in the first physical quantity detection section  6 , since the center line in the thickness direction of the piezoelectric element  3   a  matches the center position (the center line in the thickness direction of the first physical quantity detection section  6 ) A 3  between the bottom surface position A 1  and the top surface position A 2 , stress deformation of the piezoelectric element  3   a  becomes symmetric on the top surface position A 2  side and the bottom surface position A 1  side, causing surface charges generated on the top and bottom surfaces to cancel out each other. That is, the first physical quantity detection section  6  does not detect a bending force. In contrast, in the second physical quantity detection section  7 , since the center line in the thickness direction of the piezoelectric element  3   b  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section  7 ) A 5  between the bottom surface position A 1  and the top surface position A 4  of the second physical quantity detection section  7 , stress deformation of the piezoelectric element  3   b  becomes asymmetric on the top surface position A 4  side and the bottom surface position A 1  side, preventing surface charges generated on the top and bottom surfaces of the piezoelectric element  3   b  from canceling out each other. Therefore, by measuring a voltage value generated in the second physical quantity detection section  7 , it is possible to detect the degree of the bending force as a value. In the case where the physical quantity sensor  100  shown in  FIG. 2  is bent so as to warp in a concave form to an extent that it is not plastically deformed with the center of the surface of the substrate  1  as a vertex, it is likewise possible to detect the degree of the bending force as a value. 
     Next, in the physical quantity sensor  100  shown in  FIG. 2 , suppose, for example, both ends of the substrate  1  are fixed and the surfaces of the protective layers  5   a ,  5   b ,  5   c ,  5   d  and  5   e  are uniformly pressed from above downward in  FIG. 2 . In this case, the piezoelectric element  3   a  is deformed by receiving pressure from the protective layers  5   b  and  5   c , and therefore surface charges generated on the top and bottom surfaces of the piezoelectric element  3   a  do not cancel out each other. Therefore, by measuring a voltage value generated in the first physical quantity detection section  6 , it is possible to detect the degree of pressure applied to the physical quantity sensor  100  as a value. In the physical quantity sensor  100  shown in  FIG. 2 , the protective layers  5   a  and  5   e  are fixed and when the surface of the substrate  1  is uniformly pressed upward from below in  FIG. 2 , it is likewise possible to detect the degree of pressure applied to the physical quantity sensor  100  as a value. Here, the piezoelectric element  3   b  is also naturally pressed from the protective layers  5   c  and  5   d  and receives some influence. If the degree of influence of the pressure from the protective layers  5   c  and  5   d  is measured beforehand and a correction is made by subtracting a detection value about the pressure from the detection value about the force of bending operation, it is possible to make a setting so as to receive no influence from the protective layers  5   c  and  5   d.    
     Next, a process for producing the physical quantity sensor  100  will be described using  FIG. 3 . First, a piezoelectric element layer  3  is laminated on the electrode layer  2  formed on the substrate  1  through sputtering or the like (see  FIGS. 3  ( a ) and ( b )). Next, the laminated piezoelectric element layer  3  is etched to form the piezoelectric element  3   a  and the piezoelectric element  3   b  through patterning (piezoelectric element forming step: see  FIG. 3(   c )). Next, a conductive layer  4  is laminated on the piezoelectric element  3   a  and the piezoelectric element  3   b  through sputtering or the like (see  FIG. 3(   d )) and then etched to form the electrode layer  4   a  on the piezoelectric element  3   a  and form the electrode layer  4   b  on the piezoelectric element  3   b  (electrode layer forming step: see  FIG. 3(   e )). An insulating material layer is then laminated from the electrode layer  4   a  and  4   b  sides through sputtering or the like (see  FIG. 3  ( f )) and then etched to form the protective layers  5   a ,  5   b ,  5   c ,  5   d  and  5   e  through patterning (see  FIG. 3  ( g )). This completes the physical quantity sensor  100 . 
     The physical quantity sensor  100  of the present embodiment can simultaneously detect a plurality of physical quantities. That is, the piezoelectric element  3   a  can detect pressure from an object and the piezoelectric element  3   b  can detect bending deflection of the object at the same time. Therefore, the physical quantity sensor  100  can be used, for example, as a contact sensor. 
     Furthermore, since the electrode layer  2  is commonly used for the first physical quantity detection section  6  and the second physical quantity detection section  7 , the physical quantity sensor  100  can be made thinner. Furthermore, since the electrode layer  2  commonly used for the first physical quantity detection section  6  and the second physical quantity detection section  7  can be formed through one process, the physical quantity sensor  100  can be produced easily. 
     Furthermore, when a PDMS substrate is used for the substrate  1 , since the PDMS substrate has biocompatibility, the physical quantity sensor  100  including the PDMS substrate can be pasted to the skin or the like of an animal for a long time and it is possible to obtain biological information such as pulsation, heart beat and respiration. The same applies to a case where PDMS is used for the substrate or the like in the following embodiments and modification example. 
     Second Embodiment 
     Next, a physical quantity sensor according to a second embodiment of the present invention will be described. Regions denoted by reference numerals  11 ,  12 ,  13   a  and  14   a  in the present embodiment are similar to the regions denoted by reference numerals  1 ,  2 ,  3   a  and  4   a  in the first embodiment respectively, and therefore descriptions thereof may be omitted. 
     As shown in  FIG. 4 , a physical quantity sensor  200  according to the present embodiment is provided with a substrate  11 , an electrode layer  12  formed on the substrate  11 , a piezoelectric element  13   a  formed on the electrode layer  12 , an electrode layer  14   a  formed on the piezoelectric element  13   a , an insulating layer  15  formed on the piezoelectric element  13   a  and the electrode layer  14   a , an electrode layer  16  formed on the insulating layer  15 , a piezoelectric element  13   b  formed on the electrode layer  16  and an electrode layer  14   b  formed on the piezoelectric element  13   b . A first physical quantity detection section includes the electrode layer  12  (first electrode layer), the piezoelectric element  13   a  (first piezoelectric element) and the electrode layer  14   a  (third electrode layer) as main parts, and includes the regions other than the piezoelectric element  13   a  in the physical quantity sensor  200  as a layer for adjusting the position at which the piezoelectric element  13   a  is disposed. Furthermore, a second physical quantity detection section includes the electrode layer  16  (second electrode layer), the piezoelectric element  13   b  (second piezoelectric element) and the electrode layer  14   b  (fourth electrode layer) as main parts, and includes the regions other than the piezoelectric element  13   b  in the physical quantity sensor  200  as a layer for adjusting the position at which the piezoelectric element  13   b  is disposed. 
     The insulating layer  15  is made of a flexible insulating material. For the insulating layer  15 , as in the case of the substrate  11 , any material may be used according to the purpose as long as it is flexible. 
     As in the case of the electrode layer  14   a , the electrode layer  14   b  and the electrode layer  16  are made of a flexible conductive material and, for example, copper, silver, gold, nickel-copper alloy or conductive polymer may be used. 
     As in the case of the piezoelectric element  13   a , the piezoelectric element  13   b  is made of a flexible piezoelectric material. An example thereof may be piezoelectric polymer of PVDF (polyvinylidene fluoride). As shown in  FIG. 4 , a center line in the thickness direction of the piezoelectric element  13   a  matches a center position (center line in the thickness direction of the first physical quantity detection section) B 3  between a bottom surface position B 1  and a top surface position B 2  of the first physical quantity detection section. A center line in the thickness direction B 4  of the piezoelectric element  13   b  is disposed eccentrically with respect to a center position (center line in the thickness direction of the second physical quantity detection section) B 3  between the bottom surface position B 1  and the top surface position B 2  of the second physical quantity detection section. 
     Next, operation of the physical quantity sensor  200  will be described. Here, suppose, for example, the physical quantity sensor  200  shown in  FIG. 4  is bent so as to warp in a convex form to an extent that it is not plastically deformed with the center of the surface of the electrode layer  14   b  as a vertex. In this case, although stress of bending operation is added to the piezoelectric element  13   a  in the first physical quantity detection section, since the center line in the thickness direction of the piezoelectric element  13   a  matches the center position (center line in the thickness direction of the first physical quantity detection section) B 3  between the bottom surface position B 1  and the top surface position B 2 , stress deformation of the piezoelectric element  13   a  becomes symmetric on the top surface position B 2  side and the bottom surface position B 1  side, causing surface charges generated on the top and bottom surfaces of the piezoelectric element  13   a  to cancel out each other. That is, the first physical quantity detection section does not detect a bending force. In contrast, in the second physical quantity detection section, since the center line in the thickness direction of the piezoelectric element  13   b  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section) B 3  between the bottom surface position B 1  and the top surface position B 2  of the second physical quantity detection section, stress deformation of the piezoelectric element  13   b  becomes asymmetric on the top surface position B 2  side and the bottom surface position B 1  side, preventing surface charges generated on the top and bottom surfaces of the piezoelectric element  13   b  from canceling out each other. Therefore, by measuring a voltage value generated in the second physical quantity detection section, it is possible to detect the degree of the bending force as a value. In the case where the physical quantity sensor  200  shown in  FIG. 4  is bent so as to warp in a concave form to an extent that it is not plastically deformed with the center of the surface of the substrate  11  as a vertex, it is likewise possible to detect the degree of the bending force as a value. 
     Next, in the physical quantity sensor  200  shown in  FIG. 4 , suppose, for example, both ends of the substrate  11  are fixed and the surface of the electrode layer  14   b  is uniformly pressed from above downward in  FIG. 4 . In this case, the piezoelectric element  13   a  is deformed by receiving pressure from the electrode layer  14   b  side, and therefore surface charges generated on the top and bottom surfaces of the piezoelectric element  13   a  do not cancel out each other. Therefore, by measuring a voltage value generated in the first physical quantity detection section, it is possible to detect the degree of pressure applied to the physical quantity sensor  200  as a value. In the physical quantity sensor  200  shown in  FIG. 4 , both ends of the electrode layer  14   b  are fixed and when the surface of the substrate  11  is uniformly pressed upward from below in  FIG. 4 , it is likewise possible to detect the degree of pressure applied to the physical quantity sensor  200  as a value. Here, the piezoelectric element  13   b  is also naturally pressed and receives some influence, but if the degree of influence of pressure is measured beforehand and a correction is made by subtracting a detection value about the pressure from the detection value about the force of bending operation, it is possible to make a setting so as to receive no influence of the pressure. 
     Next, a process for producing the physical quantity sensor  200  will be described. As in the case of the process for producing the physical quantity sensor  100  according to the above-described first embodiment, the respective regions are laminated on the substrate  11  through patterning using sputtering, etching or the like. To be more specific, the piezoelectric element layer is laminated on the electrode layer  12  formed on the substrate  11  through sputtering or the like first, and then etched to form the piezoelectric element  13   a  through patterning. Next, a conductive layer is laminated from the piezoelectric element  13   a  side through sputtering or the like and etched to form the electrode layer  14   a  on the piezoelectric element  13   a . Next, an insulating material layer is laminated from the electrode layer  14   a  side through sputtering or the like, and then etched to form the insulating layer  15 . Next, a conductive layer is laminated from the insulating layer  15  side through sputtering or the like, and then etched to form the electrode layer  16  on the insulating layer  15 . Next, a piezoelectric material layer is laminated from the electrode layer  16  side through sputtering or the like, and then etched to form the piezoelectric element  13   b . A conductive layer is then laminated from the piezoelectric element  13   b  side through sputtering or the like, and then etched to form the electrode layer  14   b  on the piezoelectric element  13   b , and the physical quantity sensor  200  is thereby completed. 
     The physical quantity sensor  200  of the present embodiment can simultaneously detect a plurality of physical quantities. That is, the piezoelectric element  13   a  can detect pressure from an object and the piezoelectric element  13   b  can detect bending deflection at the same time. Therefore, the physical quantity sensor  200  can be used, for example, as a contact sensor. 
     Furthermore, the first physical quantity detection section and the second physical quantity detection section can be integrated into one unit, and it is thereby possible to realize a smaller physical quantity sensor  200 . 
     Third Embodiment 
     Next, a physical quantity sensor according to a third embodiment of the present invention will be described. Since regions denoted by reference numerals  22 ,  23   a  and  24   a  in the present embodiment are similar to the regions denoted by reference numerals  2 ,  3   a  and  4   a  in the first embodiment, descriptions thereof may be omitted. 
     As shown in  FIG. 5 , a physical quantity sensor  300  according to the present embodiment is provided with a substrate  21 , an electrode layer  22  formed on the substrate  21 , a piezoelectric element  23   a  formed on the electrode layer  22 , an electrode layer  24   a  formed on the piezoelectric element  23   a , a protective layer  25  formed on the piezoelectric element  23   a  and the electrode layer  24   a , a piezoelectric element  23   b  formed below the electrode layer  22  and embedded in the substrate  21 , and an electrode layer  24   b  formed below the piezoelectric element  23   b  and embedded in the substrate  21 . A first physical quantity detection section includes the electrode layer  22 , the piezoelectric element  23   a  (first piezoelectric element) and the electrode layer  24   a  (third electrode layer) as main components and also includes regions other than the piezoelectric element  23   a  in the physical quantity sensor  300  (except the substrate  21 ) as a layer for adjusting the position at which the piezoelectric element  23   a  is disposed. Furthermore, a second physical quantity detection section includes the electrode layer  22 , the piezoelectric element  23   b  (second piezoelectric element) and the electrode layer  24   b  (fourth electrode layer) as main components and also includes regions other than the piezoelectric element  23   b  in the physical quantity sensor  300  (except the substrate  21 ) as a layer for adjusting the position at which the piezoelectric element  23   b  is disposed. 
     The substrate  21  is made of a flexible insulating material. For the substrate  21 , any material may be used according to the purpose as long as it is flexible. For example, when the physical quantity sensor  300  is used pasted to a living body, PDMS may be used in consideration of biocompatibility. 
     The piezoelectric element  23   b  is formed using a material similar to that of the piezoelectric element  23   a  and disposed at a position opposite to the piezoelectric element  23   a  centered on the electrode layer  22 . As shown in  FIG. 5 , the center line in the thickness direction of the piezoelectric element  23   a  matches the center position (center line in the thickness direction of the first physical quantity detection section) C 3  between the bottom surface position C 1  and the top surface position C 2  of the first physical quantity detection section. The center line in the thickness direction C 4  of the piezoelectric element  23   b  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section) C 3  between the bottom surface position C 1  and the top surface position C 2  of the second physical quantity detection section. 
     The electrode layer  24   b  is formed using a material similar to that of the electrode layer  24   a  and is disposed at a position opposite to the electrode layer  24   a  centered on the electrode layer  22 . 
     The protective layer  25  is made of a flexible insulating material. For the protective layer  25 , any material may be used according to the purpose as long as it is flexible as in the case of the substrate  21 . 
     Next, operation of the physical quantity sensor  300  will be described. Here, suppose the physical quantity sensor  300  shown in  FIG. 5  is bent so as to warp in a convex form to an extent that it is not plastically deformed with the center of the surface of the protective layer  25  as a vertex. In this case, although stress of bending operation is added to the piezoelectric element  23   a  in the first physical quantity detection section, since the center line in the thickness direction of the piezoelectric element  23   a  matches the center position (the center line in the thickness direction of the first physical quantity detection section) C 3  between the bottom surface position C 1  and the top surface position C 2 , stress deformation of the piezoelectric element  23   a  becomes symmetric on the top surface position C 2  side and the bottom surface position C 1  side, causing surface charges generated on the top and bottom surfaces of the piezoelectric element  23   a  to cancel out each other. That is, the first physical quantity detection section does not detect a bending force. In contrast, in the second physical quantity detection section, since the center line in the thickness direction of the piezoelectric element  23   b  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section) C 3  between the bottom surface position C 1  and the top surface position C 2  of the second physical quantity detection section, stress deformation of the piezoelectric element  23   b  becomes asymmetric on the top surface position C 2  side and the bottom surface position C 1  side, preventing surface charges generated on the top and bottom surfaces of the piezoelectric element  23   b  from canceling out each other. Therefore, by measuring a voltage value generated in the second physical quantity detection section, it is possible to detect the degree of the bending force as a value. In the case where the physical quantity sensor  300  shown in  FIG. 5  is bent so as to warp in a concave form to an extent that it is not plastically deformed with the center of the surface of the electrode layer  24   b  as a vertex, it is likewise possible to detect the degree of the bending force as a value. 
     Next, in the physical quantity sensor  300  shown in  FIG. 5 , both ends of the substrate  21  are fixed and suppose the surface of the protective layer  25  is uniformly pressed from above downward in  FIG. 5 . In this case, the piezoelectric element  23   a  is deformed by receiving pressure from the protective layer  25  side, and therefore surface charges generated on the top and bottom surfaces of the piezoelectric element  23   a  do not cancel out each other. Therefore, by measuring a voltage value generated in the first physical quantity detection section, it is possible to detect the degree of pressure applied to the physical quantity sensor  300  as a value. Both ends of the protective layer  25  are fixed and when the surfaces of the substrate  21  and the electrode layer  24   b  are uniformly pressed upward from below in  FIG. 5 , it is likewise possible to detect the degree of pressure applied to the physical quantity sensor  300  as a value. Here, the piezoelectric element  23   b  is also naturally pressed and receives some influence. If the degree of influence of pressure is measured beforehand and a correction is made by subtracting a detection value about the pressure from the detection value about the force of bending operation, it is possible to make a setting so as to receive no influence of the pressure. 
     Next, a process for producing the physical quantity sensor  300  will be described. As in the case of the process for producing the physical quantity sensor  100  of the above-described first embodiment, the respective regions are laminated and formed through patterning using sputtering, etching or the like. To be more specific, the electrode layer  24   b  is formed first, the substrate  21  is laminated so as to cover one side of the electrode layer  24   b , the substrate  21  is then etched to form a dent for the piezoelectric element  23   a . Next, a piezoelectric material is embedded in the dent through sputtering to form the piezoelectric element  23   a . Next, the electrode layer  22  and the piezoelectric element layer are laminated on the substrate  21  and the piezoelectric element  23   a  respectively through sputtering or the like and etched to form the piezoelectric element  23   a  through patterning. Next, a conductive layer is laminated from the piezoelectric element  23   a  side through sputtering or the like and then etched to form the electrode layer  24   a  on the piezoelectric element  23   a  through patterning. Next, the protective layer  25  is laminated on the piezoelectric element  23   a  and the electrode layer  24   a  through sputtering or the like, and the physical quantity sensor  300  is thereby completed. 
     According to the physical quantity sensor  300  of the present embodiment, it is possible to simultaneously detect a plurality of physical quantities. That is, it is possible to detect pressure from the object through the piezoelectric element  23   a  and detect bending operation displacement of the object through the piezoelectric element  23   b  at the same time. Therefore, the physical quantity sensor  300  can be used, for example, as a contact sensor. 
     Furthermore, since the first physical quantity detection section and the second physical quantity detection section can be integrated into one unit, it is possible to realize a smaller physical quantity sensor  300 . Furthermore, since the electrode layer  22  is shared between the first physical quantity detection section and the second physical quantity detection section, the physical quantity sensor  300  can be made thinner. Furthermore, since the electrode layer  22  commonly used for the first physical quantity detection section and the second physical quantity detection section can be formed through one process, the physical quantity sensor  300  can be produced easily. 
     Fourth Embodiment 
     Next, a physical quantity sensor according to a fourth embodiment of the present invention will be described. Since regions denoted by reference numerals  32 ,  33   a  and  34   a  in the present embodiment are similar to the regions denoted by reference numerals  2 ,  3   a  and  4   a  in the first embodiment, descriptions thereof may be omitted. Furthermore, regions denoted by reference numerals  33   b  and  34   b  in the present embodiment are similar to the regions denoted by reference numerals  23   a  and  24   b  in the third embodiment respectively, descriptions thereof may be omitted. 
     As shown in  FIG. 6 , a physical quantity sensor  400  according to the present embodiment is provided with a substrate  31 , an electrode layer  32  formed on the substrate  31 , a piezoelectric element  33   a  formed on electrode layer  32 , an electrode layer  34   a  formed on the piezoelectric element  33   a , an insulating layer  35  formed on the piezoelectric element  33   a  and the electrode layer  34   a , an electrode layer  36  formed on the insulating layer  35 , a piezoelectric element  37  formed on the electrode layer  36 , an electrode layer  38  formed on the piezoelectric element  37 , a piezoelectric element  33   b  formed below the electrode layer  32  and embedded in the substrate  31  and an electrode layer  34   b  formed below the piezoelectric element  33   b  and embedded in the substrate  31 . A first physical quantity detection section includes the electrode layer  32 , the piezoelectric element  33   a  (first piezoelectric element) and the electrode layer  34   a  (third electrode layer) as main components and also includes regions other than the piezoelectric element  33   a  in the physical quantity sensor  400  (except the substrate  21 ) as a layer for adjusting a position at which the piezoelectric element  33   a  is disposed. Furthermore, a second physical quantity detection section includes the electrode layer  32 , the piezoelectric element  33   b  and the electrode layer  34   b  as a first main section and includes the electrode layer  36 , the piezoelectric element  37  (second piezoelectric element) and the electrode layer  38  (fourth electrode layer) as a second main section. Furthermore, the piezoelectric element  33   b  in the first main section uses regions other than the piezoelectric element  33   b  in the physical quantity sensor  400  as a layer for adjusting a position at which the piezoelectric element  33   b  is disposed. Furthermore, the piezoelectric element  37  in the second main section uses regions other than the piezoelectric element  37  in the physical quantity sensor  400  as a layer for adjusting a position at which the piezoelectric element  37  is disposed. 
     The substrate  31  is made of a flexible insulating material. For the substrate  31 , any material may be used according to the purpose as long as it is flexible. For example, when the physical quantity sensor  400  is used pasted to a living body, PDMS may be used in consideration of biocompatibility. 
     The piezoelectric element  33   b  is formed using a material similar to that of the piezoelectric element  33   a  and disposed at a position opposite to the piezoelectric element  33   a  centered on the electrode layer  32 . As shown in  FIG. 6 , the center line in the thickness direction of the piezoelectric element  33   a  matches the center position (center line in the thickness direction of the first physical quantity detection section) D 3  between the bottom surface position D 1  and the top surface position D 2  of the first physical quantity detection section. The center line in the thickness direction D 4  of the piezoelectric element  37  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section) D 3  between the bottom surface position D 1  and the top surface position D 2  of the second physical quantity detection section. Furthermore, the center line in the thickness direction D 5  of the piezoelectric element  33   b  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section) D 3  between the bottom surface position D 1  and the top surface position D 2  of the second physical quantity detection section. 
     The insulating layer  35  is made of a flexible insulating material. For the insulating layer  35 , any material may be used according to the purpose as long as it is flexible as in the case of the substrate  31 . 
     Next, operation of the physical quantity sensor  400  will be described. Here, suppose the physical quantity sensor  400  shown in  FIG. 6  is bent so as to warp in a convex form to an extent that it is not plastically deformed with the center of the surface of the electrode layer  38  as a vertex. In this case, although stress of bending operation is added to the piezoelectric element  33   a  in the first physical quantity detection section, since the center line in the thickness direction of the piezoelectric element  33   a  matches the center position (the center line in the thickness direction of the first physical quantity detection section) D 3  between the bottom surface position D 1  and the top surface position D 2 , stress deformation of the piezoelectric element  33   a  becomes symmetric on the top surface position D 2  side and the bottom surface position D 1  side, causing surface charges generated on the top and bottom surfaces of the piezoelectric element  33   a  to cancel out each other. That is, the first physical quantity detection section does not detect a bending force. In contrast, in the second physical quantity detection section, since the center line in the thickness direction of the piezoelectric element  33   b  is disposed eccentrically with respect to the center position (center line in the thickness direction of the second physical quantity detection section) D 3  between the bottom surface position D 1  and the top surface position D 2  of the second physical quantity detection section, stress deformation of the piezoelectric element  33   b  becomes asymmetric on the top surface position D 2  side and the bottom surface position D 1  side, preventing surface charges generated on the top and bottom surfaces of the piezoelectric element  33   b  from canceling out each other. Therefore, by measuring a voltage value generated in the second physical quantity detection section, it is possible to detect the degree of the bending force as a value. In the case where the physical quantity sensor  400  shown in  FIG. 6  is bent so as to warp in a concave form to an extent that it is not plastically deformed with the center of the surface of the electrode layer  34   b  as a vertex, it is likewise possible to detect the degree of the bending force as a value. 
     Next, in the physical quantity sensor  400  shown in  FIG. 6 , suppose, for example, both ends of the substrate  31  are fixed and the surface of the electrode layer  38  is uniformly pressed downward from above in  FIG. 6 . In this case, the piezoelectric element  33   a  is deformed by receiving pressure from the electrode layer  38  side, and therefore surface charges generated on the top and bottom surfaces of the piezoelectric element  33   a  do not cancel out each other. Therefore, by measuring a voltage value generated in the first physical quantity detection section, it is possible to detect the degree of pressure applied to the physical quantity sensor  400  as a value. Both ends of the electrode layer  38  are fixed and when the surface of the substrate  31  is uniformly pressed upward from below in  FIG. 6 , it is likewise possible to detect the degree of pressure applied to the physical quantity sensor  400  as a value. Here, the piezoelectric elements  33   b  and  37  are also naturally pressed and receive some influence. If the degree of influence of the pressure is measured beforehand and a correction is made by subtracting a detection value about the pressure from the detection value about the force of bending operation, it is possible to make a setting so as to receive no influence of the pressure. 
     Next, a process for producing the physical quantity sensor  400  will be described. As in the case of the process for producing the physical quantity sensor  100  in the above-described first embodiment, the respective regions are laminated and formed through patterning using sputtering, etching or the like. To be more specific, the substrate  31  is etched first to form a dent for the electrode layer  34   b  and the piezoelectric element  33   a . Next, a conductive material and a piezoelectric material are sequentially embedded in the above-described predetermined dent through sputtering to form the electrode layer  34   b  and the piezoelectric element  23   a  in that order. Next, the electrode layer  32  and the piezoelectric element layer are laminated on the substrate  31  and the piezoelectric element  33   a  respectively through sputtering or the like, and then etched to form the piezoelectric element  33   a  through patterning. Next, a conductive layer is laminated from the piezoelectric element  33   a  side through sputtering or the like, then etched to form the electrode layer  34   a  on the piezoelectric element  33   a  through patterning. Next, the insulating layer  35  is laminated on the piezoelectric element  33   a  and the electrode layer  34   a  through sputtering or the like and then the electrode layer  36  is laminated on the insulating layer  35 . Next, the piezoelectric element  37  is laminated on the electrode layer  36  through sputtering or the like and then a conductive layer is laminated from the piezoelectric element  33   a  side through sputtering or the like. Then, the conductive layer is etched to form the electrode layer  38  on the piezoelectric element  37  through patterning, and the physical quantity sensor  400  is thereby completed. 
     According to the physical quantity sensor  400  of the present embodiment, a plurality of physical quantities can be simultaneously detected. That is, the piezoelectric element  33   a  can detect pressure from the object and the piezoelectric elements  33   b  and  37  can simultaneously detect bending operation displacement. Therefore, the physical quantity sensor  400  can be used, for example, as a contact sensor. 
     Furthermore, since the first physical quantity detection section and the second physical quantity detection section can be integrated into one unit, it is possible to realize a smaller physical quantity sensor  400 . Particularly, since the piezoelectric elements  33   b  and  37  of the second physical quantity detection section are laminated so as to be disposed on both sides of the piezoelectric element  33   a  of the first physical quantity detection section, it is possible to double the sensor sensitivity with respect to the bending force in the second physical quantity detection section despite being a small device. 
     Furthermore, since the electrode layer  32  is shared between the first physical quantity detection section and the second physical quantity detection section, the physical quantity sensor  400  can be made thinner. Furthermore, since the electrode layer  32  commonly used for the first physical quantity detection section and the second physical quantity detection section can be formed through one process, it is possible to easily produce the physical quantity sensor  400 . 
     Modification Example 
     The present invention is not limited to the above-described embodiments and examples, but can be modified in various ways based on the spirit and scope of the present invention, and these are not excluded from the scope of the present invention. For example, the first physical quantity detection section  6  and the second physical quantity detection section  7  in the first embodiment share the electrode layer  2 , but instead of the electrode layer  2 , a first electrode layer and a second electrode layer independently formed for the first physical quantity detection section and the second physical quantity detection section respectively may be used. 
     Furthermore, the first physical quantity detection section and the second physical quantity detection section in the third embodiment above share the electrode layer  22 , but a configuration may also be adopted in which an insulating layer and an electrode layer are formed sequentially from the top between the electrode layer  22  and the piezoelectric element  23   b  so that the electrode layer  22  is not shared. Similarly, a configuration may also be adopted in which an insulating layer and an electrode layer are formed sequentially from the top between the electrode layer  32  and the piezoelectric element  33   b  in the physical quantity sensor according to the fourth embodiment so that the electrode layer  32  is not shared between the first physical quantity detection section and the second physical quantity detection section. 
     Furthermore, in the first embodiment, if the electrode layer  2  has sufficient strength, a configuration without the substrate  1  may also be possible. Even in the case of the physical quantity sensor in a configuration without the substrate  1 , it goes without saying that the configuration is maintained in which the thicknesses of the respective sections are adjusted so that the center line in the thickness direction of the first piezoelectric element matches the center line in the thickness direction of the first physical quantity detection section and at the same time the center line in the thickness direction of the second piezoelectric element does not match the center line in the thickness direction of the second physical quantity detection section. 
     Furthermore, a protective layer made of PDMS or the like may be provided on the surface of the electrode layer  14   b  in the second embodiment, the electrode layer  24   b  in the third embodiment or the electrode layer  38  in the fourth embodiment. Even in the case of the physical quantity sensor provided with the above-described protective layer, it goes without saying that the configuration is maintained in which the thicknesses of the respective sections are adjusted so that the center line in the thickness direction of the first piezoelectric element matches the center line in the thickness direction of the first physical quantity detection section and at the same time the center line in the thickness direction of the second piezoelectric element does not match the center line in the thickness direction of the second physical quantity detection section. 
     Furthermore, as shown in  FIG. 7 , one end of a physical quantity sensor  500  having the same configuration as that of the first embodiment is attached to a base  48  to form a cantilever and an object  49  is placed so as to come into contact with protective layers  45   a ,  45   b  and  45   c  of a first physical quantity detection section  46  and when a force in a direction shown by a white arrow in  FIG. 7  is applied to the object  49 , it is possible to detect pressure from the object  49  using a piezoelectric element  43   a . Furthermore, when the object  49  vibrates in the vertical direction in  FIG. 7 , it is possible not only to detect pressure from the object  49  using the piezoelectric element  43   a  but also to detect vibration of the object  49  since a second physical quantity detection section  47  (piezoelectric element  43   b ) vibrates. Here, since regions denoted by reference numerals  41  to  47  are similar to the regions denoted by reference numerals  1  to  7  in the first embodiment respectively, descriptions thereof will be omitted. Furthermore, since positions E 1  to E 5  are similar to the positions A 1  to A 5  in the first embodiment respectively, descriptions thereof will be omitted. In the present modification example, if an electrode layer  42  has sufficient strength, the electrode layer  42  without using the substrate  41  may be used instead of the substrate, the electrode layer  42  may be directly attached to a base  48  to support the physical quantity sensor. However, even when the physical quantity sensor in the configuration without the electrode layer  42  is adopted, it goes without saying that the configuration is maintained in which the thicknesses of the respective sections are adjusted so that the center line in the thickness direction of the first piezoelectric element matches the center line in the thickness direction of the first physical quantity detection section and at the same time the center line in the thickness direction of the second piezoelectric element does not match the center line in the thickness direction of the second physical quantity detection section. 
     Furthermore, in the physical quantity sensors according to the above-described embodiments and modification example, regarding the degree of match between the center line in the thickness direction of the first piezoelectric element and the center line in the thickness direction of the first physical quantity detection section, a case with a complete match has been described above, but if not that high degree of detection accuracy of the respective physical quantities may be expected, the degree of match between the center line in the thickness direction of the first piezoelectric element and the center line in the thickness direction of the first physical quantity detection section may be a quasi-match (substantial match) level. 
     Furthermore, the physical quantity sensor according to the above-described embodiments and modification example is provided with a protective layer, but a protective layer need not be particularly provided if the electrode layer and piezoelectric element are made of a material sufficiently resistant to external forces. However, even in the case of the physical quantity sensor in the configuration with no protective layer, it goes without saying that the configuration is maintained in which the thicknesses of the respective sections are adjusted so that the center line in the thickness direction of the first piezoelectric element matches the center line in the thickness direction of the first physical quantity detection section and at the same time the center line in the thickness direction of the second piezoelectric element does not match the center line in the thickness direction of the second physical quantity detection section. 
     Furthermore, the second physical quantity detection section in the fourth embodiment is configured to have two piezoelectric elements  33   b  and  37  so as to have the sensor sensitivity with respect to bending double that in the case with one piezoelectric element, but the second physical quantity detection section may also be configured to have three or more piezoelectric elements so as to have the sensor sensitivity with respect to bending triple or more that in the case with one piezoelectric element. However, in the case of the physical quantity sensor in the configuration using three or more piezoelectric elements, it goes without saying that the configuration is maintained in which the thicknesses of the respective sections are adjusted so that the center line in the thickness direction of the first piezoelectric element matches the center line in the thickness direction of the first physical quantity detection section and at the same time the center line in the thickness direction of the second piezoelectric element does not match the center line in the thickness direction of the second physical quantity detection section. 
     DESCRIPTION OF SYMBOLS 
     
         
           1 ,  11 ,  21 ,  31 ,  41  Substrate 
           2 ,  4   a ,  4   b ,  12 ,  14   a ,  14   b ,  16 ,  22 ,  24   a ,  24   b ,  32 ,  34   a ,  34   b ,  36 ,  38 ,  42 ,  44   a ,  44   b  Electrode layer 
           3  Piezoelectric element layer 
           4  Conductive layer 
           3   a ,  3   b ,  13   a ,  13   b ,  23   a ,  23   b ,  33   a ,  33   b ,  33   a ,  37 ,  43   a ,  43   b  Piezoelectric element 
           5   a ,  5   b ,  5   c ,  5   d ,  5   e ,  25 ,  45   a ,  45   b ,  45   c ,  45   d ,  45   e  Protective layer 
           6 ,  46  First physical quantity detection section 
           7 ,  47  Second physical quantity detection section 
           15 ,  35  Insulating layer 
           48  Base 
           49  Object 
           100 ,  200 ,  300 ,  400 ,  500  Physical quantity sensor