Patent Publication Number: US-2017373242-A1

Title: Mems device, piezoelectric actuator, and ultrasonic motor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Japanese Patent Application No. 2016-125257, filed Jun. 24, 2016, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a MEMS device including a piezoelectric layer sandwiched between two electrodes, a piezoelectric actuator, and an ultrasonic motor. 
     2. Related Art 
     Piezoelectric actuators, which are a type of Micro Electro Mechanical Systems (MEMS) device including piezoelectric elements, are applied to driving portions of robots or various devices. The piezoelectric element includes two electrodes and a piezoelectric layer sandwiched therebetween and is deformed by application of a voltage to both electrodes. The piezoelectric actuator utilizes the deformation of the piezoelectric element to drive a driven object such as a rotor which is in contact with the piezoelectric actuator. For example, an ultrasonic motor to which a piezoelectric actuator is applied is formed by stacking a substrate on which a plurality of piezoelectric elements are formed and a vibrating plate on which protrusions for rotating the rotor are formed (see JP-A-2016-40993). In such an ultrasonic motor, the vibrating plate is deformed to cause the protrusions to be reciprocated or be elliptically moved, by a plurality of piezoelectric elements being selectively deformed. The rotor is rotated by transmitting the motion of the protrusion to the rotor. 
     An example of a structure of a piezoelectric actuator of the related art will be described in detail with reference to  FIG. 16  and  FIG. 17 .  FIG. 16  is a plan view illustrating the piezoelectric actuator  89 , and  FIG. 17  is a sectional view taken along line XVII-XVII in  FIG. 16 . In addition, in  FIG. 16 , a wiring layer  99  on an outermost surface (uppermost surface) is indicated by hatching. As illustrated in  FIG. 16 , a piezoelectric element  91  formed long in a longitudinal direction of the substrate  90  at a center in a width direction (that is, the transverse direction) of the substrate  90  and piezoelectric elements  91  formed on positions of four corners of the substrate  90 , which are smaller than the central piezoelectric element  91  are disposed on the substrate  90  of the piezoelectric actuator  89 . As illustrated in  FIG. 17 , these five piezoelectric elements  91  are formed by a first electrode layer  94 , a piezoelectric layer  95 , and a second electrode layer  96  being stacked in this order from an oxide film  93  side on the oxide film  93  stacked on an entire surface of the substrate  90 . The first electrode layer  94  and the second electrode layer  96  are thin-film electrodes formed by a sputtering method or the like, for example. The piezoelectric layer  95  and the second electrode layer  96  are formed for each individual piezoelectric element  91 . In other words, the piezoelectric layer  95  and the second electrode layer  96  are formed at positions corresponding to the respective piezoelectric elements  91 . On the other hand, the first electrode layer  94  is formed over substantially the entire surface of the substrate  90  as an electrode layer common to the five piezoelectric elements  91 . In addition, the insulating layer  97  made of silicon oxide or the like is formed over substantially the entire surface of the substrate  90  by a CVD method or the like, for example, so as to cover the first electrode layer  94 , the piezoelectric layer  95 , and the second electrode layer  96 . Further, a contact hole  98  from which the insulating layer  97  is removed is formed at a position corresponding to the second electrode layer  96  on each piezoelectric element  91  and at a position corresponding to the first electrode layer  94  at a position deviated from the piezoelectric element  91 . By the contact hole  98 , the wiring layer  99  stacked on the insulating layer  97  and the second electrode layer  96  or the first electrode layer  94 , which corresponds to the wiring layer  99 , are electrically connected. 
     For example, as illustrated in  FIG. 16 , the wiring layer  99  is formed on three regions. Specifically, a wiring layer  99   a  electrically connected to the piezoelectric element  91  positioned at the center of the substrate  90  and the second electrode layer  96  on the piezoelectric element  91  positioned at one diagonal (upper left and lower right in  FIG. 16 ) of the substrate  90 , a wiring layer  99   b  electrically connected to the second electrode layer  96  on the piezoelectric element  91  positioned at the other diagonal (lower left and upper right in  FIG. 16 ) of the substrate  90 , and a wiring layer  99   c  electrically connected to the first electrode layer  94  common to each piezoelectric elements  91  are formed. Accordingly, the same voltage is applied to the piezoelectric elements  91  positioned at the center and one diagonal and the piezoelectric elements  91  vibrate in the same phase. In addition, the same voltage is applied to the piezoelectric elements  91  positioned at the other diagonal and the piezoelectric elements  91  vibrate in the same phase. The protrusion  100  attached to the piezoelectric actuator  89  reciprocates and elliptically moves, by making a phase of vibration of the piezoelectric element  91  positioned at the center and one diagonal and a phase of vibration of the piezoelectric element  91  positioned at the other diagonal different from each other. 
     By the way, in the structure described above, a layout (that is, routing) of a wiring layer  99  is restricted, since a plurality of wiring layers  99  are formed on one surface of the substrate  90 . Therefore, wiring resistance (also referred to as electric resistance) is likely to increase up to the piezoelectric element  91  through the wiring layer  99 . Specifically, as illustrated in  FIG. 17 , since the wiring layer  99   c  electrically connected to the first electrode layer  94  is formed at a position deviated from the piezoelectric element  91  by avoiding the wiring layer  99   a  electrically connected to the second electrode layer  96 , the first electrode layer  94  is extended to an outside of the piezoelectric element  91 . In other words, a wiring which is made of only the first electrode layer  94  and is to be thin and have high resistance is formed. There are risk that voltage drop increases at a portion including only the first electrode layer  94  and that a sufficient voltage cannot be supplied to the piezoelectric element  91 . In addition, since the wiring layer  99  at the position deviating from the piezoelectric element  91  such as between the piezoelectric elements  91  in the wiring layers  99  electrically connected to the second electrode layer  96  faces to the first electrode layer  94  with the thin insulating layer  97  interposed therebetween, a parasitic capacitance is formed on the portion. As a result, there is a risk that a problem such as noise or delay of a drive signal is generated. In addition, there is a risk that electric field intensity between the second electrode layer  96  and the first electrode layer  94  in the portion is increased and that a problem such as dielectric breakdown is generated. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a MEMS device in which voltage drop or the like is suppressed, a piezoelectric actuator, and an ultrasonic motor. 
     According to an aspect of the invention, in a MEMS device in which a first electrode layer, a piezoelectric layer, and a second electrode layer are stacked in this order from a first surface side of a substrate, a first wiring layer is stacked on a second surface on a side opposite to a first surface of the substrate and the first electrode layer and the first wiring layer are connected to each other via a through wiring passing through the substrate. 
     According to the invention, since the first wiring layer is formed on the second surface on the side opposite to the first surface on which the piezoelectric layer is formed, a degree of freedom in design increases. In other words, the first wiring layer can be formed without interfering with wirings such as the second electrode layer formed on the first surface and the second wiring layer electrically connected to the second electrode layer. Accordingly, a region in which the first wiring layer is formed or the like can be increased as much as possible and wiring resistance (electric resistance) of the first wiring layer can be suppressed. As a result, voltage drop is suppressed in the first electrode layer overlapping the piezoelectric layer. 
     In the configuration, it is preferable that the through wiring overlap the piezoelectric layer in a stacking direction of the first electrode layer, the piezoelectric layer, and the second electrode layer. 
     According to the configuration, since the first electrode layer may not be routed to an outside of the piezoelectric layer, the wiring resistance can be suppressed. In other words, film thickness is unlikely to be increased and the region (wiring portion) made only of the first electrode layer of which the wiring resistance is likely to be increased can be reduced. As a result, the voltage drop is further suppressed in the first electrode layer overlapping the piezoelectric layer. 
     In addition, in each configuration described above, it is preferable that the through wiring overlap a region in which the first electrode layer, the piezoelectric layer, and the second electrode layer overlap each other in the stacking direction. 
     According to the configuration, the wiring resistance can be suppressed since the first electrode layer may be not routed to the outside of a region in which the first electrode layer, the piezoelectric layer, and the second electrode layer overlap each other. 
     Further, in any of the above configurations, it is preferable that at least a portion of the first wiring layer be buried in the substrate. 
     According to the configuration, the wiring resistance of the first wiring layer can be suppressed while increase in the thickness of the MEMS device is suppressed. 
     In any of the above configurations, it is preferable that the first electrode layer and the first wiring layer be connected via a plurality of through wirings. 
     According to the configuration, the adhesion of the first wiring layer can be improved as compared with a case where the first electrode layer and the first wiring layer are connected by one through wiring. Accordingly, peeling of the first wiring layer from the substrate can be suppressed. 
     In addition, according to another aspect of the invention, in a MEMS device in which a first electrode layer, a piezoelectric layer, and a second electrode layer are stacked in this order from a first surface side of a substrate, a resin layer covering the first electrode layer, the piezoelectric layer, and the second electrode layer and a second wiring layer stacked at least on a portion of the resin layer are formed on the first surface of the substrate, and the second electrode layer and the second wiring layer are connected to each other via a contact hole formed on the resin layer. 
     According to the configuration, the first electrode layer and the second wiring layer can be separated from each other by the resin layer. Therefore, parasitic capacitance formed between the first electrode layer and the second wiring layer can be suppressed. In addition, electric field strength between the first electrode layer and the second wiring layer can be suppressed. Accordingly, the second wiring layer can be disposed without the pattern of the first electrode layer being avoided and the degree of freedom in design increases. As a result, a region in which the second wiring layer is formed or the like can be increased as much as possible, and wiring resistance of the second wiring layer can be suppressed. 
     In addition, in the configuration, it is preferable that the contact hole overlap the piezoelectric layer in a stacking direction of the first electrode layer, the piezoelectric layer, and the second electrode layer. 
     According to the configuration, since the second electrode layer may not be routed to the outside of the piezoelectric layer, the wiring resistance can be suppressed. In other words, film thickness is unlikely to be increased and the region (wiring portion) made only of the second electrode layer of which the wiring resistance is likely to be increased can be reduced. 
     Further, in any of the above configurations, it is preferable that at least a portion of the second wiring layer be buried in the resin layer. 
     According to the configuration, the wiring resistance of the second wiring layer can be suppressed while increase in the thickness of the MEMS device is suppressed. 
     In any of the above configurations, it is preferable that the second electrode layer and the second wiring layer be connected via the plurality of contact holes. 
     According to the configuration, the adhesion of the second wiring layer can be improved as compared with a case where the second electrode layer and the second wiring layer are connected by one contact hole. Accordingly, peeling of the second wiring layer from the resin layer can be suppressed. 
     Further, according to still another aspect of the invention, a piezoelectric actuator which deforms the piezoelectric layer by forming an electric field between the first electrode layer and the second electrode layer and deforms the substrate by deformation of the piezoelectric layer includes the structure of the MEMS device according to any of the above configurations. 
     According to the configuration, output of the piezoelectric actuator can be increased. 
     Further, according to still another aspect of the invention, an ultrasonic motor including a protrusion of which position changes according to the deformation of the substrate; and a rotating object which abuts against the protrusion and rotates according to a change of the protrusion includes the structure of the piezoelectric actuator according to the configuration. 
     According to the configuration, output of the ultrasonic motor can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a plan view illustrating a configuration of an ultrasonic motor. 
         FIG. 2  is a front view illustrating the configuration of the ultrasonic motor. 
         FIG. 3  is an exploded perspective view illustrating a driving device. 
         FIG. 4  is a plan view illustrating a piezoelectric actuator as viewed from a piezoelectric element side. 
         FIG. 5  is a plan view illustrating the piezoelectric actuator viewed from the side opposite to the piezoelectric element. 
         FIG. 6  is a schematic sectional view taken along line VI-VI. 
         FIG. 7  is a schematic diagram illustrating an operation of the ultrasonic motor. 
         FIG. 8  is a process diagram illustrating a method for manufacturing a piezoelectric actuator. 
         FIG. 9  is a process diagram illustrating the method for manufacturing the piezoelectric actuator. 
         FIG. 10  is a process diagram illustrating the method for manufacturing the piezoelectric actuator. 
         FIG. 11  is a process diagram illustrating the method for manufacturing the piezoelectric actuator. 
         FIG. 12  is a schematic sectional view of a piezoelectric actuator according to a second embodiment. 
         FIG. 13  is a process diagram illustrating a method of manufacturing the piezoelectric actuator according to the second embodiment. 
         FIG. 14  is a process diagram illustrating the method of manufacturing the piezoelectric actuator according to the second embodiment. 
         FIG. 15  is a process diagram illustrating a method for manufacturing a piezoelectric actuator according to a third embodiment. 
         FIG. 16  is a plan view illustrating a configuration of a piezoelectric actuator of the related art. 
         FIG. 17  is a schematic sectional view taken along line XVII-XVII. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, aspects for realizing the invention will be described with reference to the attached drawings. In the embodiments described below, although various limitations have been made as preferred specific examples of the invention, the scope of the invention is not limited to the aspects unless specifically stated to limit the invention in the following description. In addition, in the following description, an ultrasonic motor  1  including a piezoelectric actuator  17 , which is one type of MEMS device of the invention, will be described as an example.  FIG. 1  is a plan view illustrating a configuration of the ultrasonic motor  1 . In addition,  FIG. 2  is a front view illustrating the configuration of the ultrasonic motor  1 . 
     The ultrasonic motor  1  is configured by a base  2 , a rotor  3  which is a kind of rotating object, a driving device  4  which rotates the rotor  3 , a holding mechanism  5  which holds the driving device  4 , and the like. The rotor  3  has a columnar shape and is rotatably supported by a shaft on one surface (surface on which driving device  4  is disposed) of the base  2 . The holding mechanism  5  includes a slide member  7  to which the driving device  4  is attached, a biasing member  8  such as a coil spring of which one end is fixed to the slide member  7 , and a support pin  9  which protrudes from a surface of the base  2  and to which the other end of the biasing member  8  is fixed. 
     The slide member  7  includes a base portion  11  which is slidably supported with respect to the base  2  and a pair of supporting portions  12  which stand on a side opposite to the base  2  from the base portion  11 . In the present embodiment, the base portion  11  includes two slide holes (not illustrated) long in a sliding direction. A slide pin  13  fixed to the base  2  is inserted through the slide hole. In other words, the slide member  7  is held in a slidable state in a longitudinal direction by the slide pin  13  inserted through the slide hole. The supporting portion  12  is formed at both ends of the base  2  in a direction orthogonal to the sliding direction (transverse direction). A screw fixing hole  14  corresponding to screw insertion holes (specifically, a vibrating plate-side screw insertion hole  20  and an actuator-side screw insertion hole  22 ) of the driving device  4  (which will be described below) is formed on a tip side (that is, side opposite to base  2 ) of the supporting portion  12 . The driving device  4  is fixed to the supporting portion  12  by screwing a screw  15  inserted through the screw insertion hole of the driving device  4  into the screw fixing hole  14 . The biasing member  8  is disposed in the sliding direction of the slide member  7  between the supporting portion  12  and the support pin  9 . One end of the biasing member  8  is fixed to the supporting portion  12  and the other end thereof is fixed to the support pin  9  to bias the slide member  7  toward the rotor  3 . Accordingly, a protrusion  23  (which will be described below) of the driving device  4  attached to the slide member  7  becomes a state of being pressed against the rotor  3 . 
     Next, the driving device  4  will be described.  FIG. 3  is an exploded perspective view illustrating the driving device  4 .  FIG. 4  is a plan view illustrating the piezoelectric actuator  17  as viewed from the piezoelectric element  27  side.  FIG. 5  is a plan view illustrating the piezoelectric actuator  17  as viewed from a side opposite to the piezoelectric element  27 .  FIG. 6  is a schematic sectional view taken along line VI-VI in  FIG. 4  and  FIG. 5 . In  FIG. 4  and  FIG. 5 , an uppermost surface of the wiring layer (specifically, first wiring layer  34  or second wiring layer  35 ) is illustrated by hatching. 
     As illustrated in  FIG. 3 , according to the embodiment, the driving device  4  includes a metallic vibrating plate  18  and a piezoelectric actuator  17  in which a piezoelectric element  27  or the like is formed on a silicon substrate  24 . In the embodiment, the vibrating plate  18  is a plate member which is adhered to a surface (first surface  39  which is will be described below) of a side on which the piezoelectric element  27  of the piezoelectric actuator  17  is formed and has a rectangular shape in a plan view. The piezoelectric actuator  17  can be reinforced by the vibrating plate  18 . In addition, a vibrating plate connecting portion  19  is formed at both ends in a direction orthogonal to the sliding direction of the vibrating plate  18 . A vibrating plate-side screw insertion hole  20  corresponding to the screw fixing hole  14  of the supporting portion  12  is opened in the vibrating plate connecting portion  19 . Further, a protrusion  23  which abuts against (is in contact with) the rotor  3  is formed on a central portion of a direction orthogonal to the sliding direction in a side of the rotor  3 -side of the vibrating plate  18 . The protrusion  23  is a member for abutting against the rotor  3  and applying rotating force to the rotor  3 . The vibrating plate  18  can be formed of a metal material such as stainless steel, aluminum, aluminum alloy, titanium, a titanium alloy, copper, a copper alloy, an iron-nickel alloy, or the like. In addition, the protrusion  23  can be integrally formed with the vibrating plate  18  or can be formed of a more durable member. 
     In the embodiment, the piezoelectric actuator  17  is a rectangular plate member which has substantially the same shape as the vibrating plate  18  except for the protrusion  23  in a plan view. Like the vibrating plate  18 , actuator connecting portions  21  are formed at both ends of the vibrating plate  18  in a direction orthogonal to the sliding direction. An actuator-side screw insertion hole  22  corresponding to the vibrating plate-side screw insertion hole  20  is opened in the actuator connecting portion  21 . In other words, in a state where the vibrating plate  18  and the piezoelectric actuator  17  overlap each other, the vibrating plate-side screw insertion hole  20  and the actuator-side screw insertion hole  22  communicate with each other. The driving device  4  is fixed to the slide member  7  by fixing the screw  15  to the screw fixing hole  14  of the supporting portion  12  through the vibrating plate-side screw insertion hole  20  and the actuator-side screw insertion hole  22 . 
     A piezoelectric element  27  is formed on a surface (hereinafter referred to as first surface  39 ) of a side facing the vibrating plate  18  of the substrate  24  constituting the piezoelectric actuator  17 . In the embodiment, five piezoelectric elements  27   a  to  27   e  are formed. Specifically, the piezoelectric element  27   e  formed long in the longitudinal direction (that is, in sliding direction) of the piezoelectric actuator  17  in the center of the piezoelectric actuator  17  (that is, direction orthogonal to sliding direction) in the transverse direction and the piezoelectric elements  27   a  to  27   d  in which the dimension in the longitudinal direction is formed to be smaller than the central piezoelectric element  27   e  are disposed on four corners of the electric actuator. 
     As illustrated in  FIG. 6 , in each of the piezoelectric elements  27   a  to  27   e , a first electrode layer  28 , a piezoelectric layer  29  and a second electrode layer  30  are sequentially stacked from a first surface  39  side of the substrate  24  (more specifically, oxide film  25  side formed on the first surface  39  of substrate  24 ) in this order. The first electrode layer  28  is an electrode common to the piezoelectric elements  27   a  to  27   e  and is formed substantially on an entire surface of the substrate  24 , as illustrated in  FIG. 4 . On the other hand, the piezoelectric layer  29  and the second electrode layer  30  are individual electrodes for each of the piezoelectric elements  27   a  to  27   e , and are formed on a region on which the piezoelectric elements  27  are disposed. In other words, the piezoelectric layer  29  and the second electrode layer  30  define a shape of each of the piezoelectric elements  27   a  to  27   e . The first electrode layer  28  can be an individual electrode and the second electrode layer  30  can be a common electrode depending on circumstances of a driving circuit and wiring. When an electric field corresponding to a potential difference between both the electrodes is applied between the first electrode layer  28  and the second electrode layer  30 , the piezoelectric element  27  configured described above vibrates to be expanded and contracted (that is, moves to be expanded and contracted) in the longitudinal direction due to the piezoelectric transverse effect. 
     In addition, as illustrated in  FIG. 6 , an inorganic protective film  31  so as to cover the entirety of the first electrode layer  28 , the piezoelectric layer  29 , and the second electrode layer  30 , including the piezoelectric element  27  and a first resin layer  32  (corresponding to a resin layer in the invention) covering the inorganic protective film  31  are stacked in this order. A second wiring layer  35  electrically connected to the second electrode layer  30  is buried in an inside portion of the first resin layer  32 . In the embodiment, the first resin layer  32  is formed on an upper surface and a lower surface of the second wiring layer  35 . In other words, the second wiring layer  35  is stacked between the first resin layers  32 . Therefore, the inorganic protective film  31  and the first resin layer  32  are disposed between the first electrode layer  28 , the piezoelectric layer  29 , and the second electrode layer  30  and the second wiring layer  35 . In addition, a plurality of contact holes  36  are formed on a position corresponding to the piezoelectric element  27  (specifically, a region overlapping the piezoelectric layer  29  in a stacking direction of the first electrode layer  28 , the piezoelectric layer  29 , and the second electrode layer  30 ) which connect the second electrode layer  30  and the second wiring layer  35  to each other by removing the inorganic protective film  31  and the first resin layer  32  between the second electrode layer  30  and the second wiring layer  35 . In the embodiment, a diameter of the contact hole  36  is formed to be sufficiently smaller than a dimension of the piezoelectric element  27  in the longitudinal direction and the transverse direction. As illustrated in  FIG. 4 , the contact hole  36  is evenly (in other words, uniformly) disposed on the entirety of an region on which the second electrode layer  30  is formed, that is, an region on which the piezoelectric layer  29  is formed. 
     In the embodiment, the second wiring layer  35  is divided into two systems and different voltages are applied to both systems. A second wiring layer  35   a  on a side is formed across the piezoelectric elements  27   a  and  27   d  disposed on one diagonal position (upper left and lower right in  FIG. 4 ) of the substrate  24 . Specifically, as illustrated in  FIG. 4 , the second wiring layers  35   a  on a side is disposed so as to connect the second electrode layer  30  of the piezoelectric element  27   a  disposed in an upper left corner, the second electrode layer  30  of the piezoelectric element  27   e  disposed on the center, and the second electrode layer  30  of the piezoelectric element  27   d  disposed in a lower right corner with each other. A second wiring layer  35   b  on the other side is formed across the piezoelectric elements  27   c  and  27   b  disposed at the other diagonal position (lower left and upper right in  FIG. 4 ) of the substrate  24 . Specifically, the second wiring layer  35   b  on the other side is disposed to connect the second electrode layer  30  of the piezoelectric element  27   c  disposed at a lower left corner, the second electrode layer  30  of the piezoelectric element  27   b  disposed at an upper right corner to each other while avoiding the second wiring layer  35   a  which is positioned on a side. In other words, the second wiring layer  35   b  on the other side extends from a position corresponding to the piezoelectric element  27   c  disposed on the lower left corner to a position corresponding to the piezoelectric element  27   b  disposed on the upper right corner while being routed around an outside of the second wiring layer  35   a  on a side on the piezoelectric element  27   d  disposed at the lower right corner. The second wiring layer  35  is connected to an external wiring (not illustrated) at the end portion of the substrate  24  such as the actuator connecting portion  21  or the like. 
     In addition, as illustrated in  FIG. 6 , a first wiring layer  34  connected to the first electrode layer  28  is stacked on a surface (hereinafter, referred to as second surface  40 ) of a side opposite to a surface (first surface  39 ) on which the piezoelectric element  27  of the substrate  24  constitutes the piezoelectric actuator  17  is formed. As illustrated in  FIG. 5 , in the embodiment, the first wiring layer  34  is substantially formed on an entire surface of the second surface  40  of the substrate  24 . Further, as illustrated in  FIG. 6 , the first wiring layer  34  is connected to the first electrode layer  28  via the through wiring  37  passing through the substrate  24 . The through wiring  37  forms a conductor similar to the first wiring layer  34  in an inside portion of the through hole  42  passing through the substrate  24  in a thickness direction. In the embodiment, an inner diameter of the through hole  42 , that is, an diameter of the through wiring  37  is formed to be sufficiently smaller than the dimension of the piezoelectric element  27  in the longitudinal direction and the transverse direction. In addition, a plurality of through wirings  37  are formed on a region corresponding to the piezoelectric element  27 . Specifically, as illustrated in  FIG. 5 , in the embodiment, the through wiring  37  is disposed to be evenly (that is, uniformly) over the entire region overlapping the piezoelectric element  27  (that is, piezoelectric layer  29 ) in the stacking direction of the first electrode layer  28 , the piezoelectric layer  29  and the second electrode layer  30 . The first wiring layer  34  is connected to the external wiring (not illustrated) at the end portion of the substrate  24  such as the actuator connecting portion  21  or the like. 
     Further, as illustrated in  FIG. 6 , a second resin layer  33  covering the first wiring layer  34  is formed on the second surface  40  of the substrate  24 . The second resin layer  33  is formed integrally with the first resin layer  32  covering the second wiring layer  35 . In other words, the entire piezoelectric actuator  17  is covered by the first resin layer  32  and the second resin layer  33 . Accordingly, the wirings formed on a surface and a back surface of the substrate  24 , the piezoelectric element  27 , or the like can be protected. 
     As the oxide film  25 , silicon oxide, zirconium oxide, laminates thereof, or the like can be used. In addition, as the first electrode layer  28  and the second electrode layer  30 , various metals such as iridium, platinum, titanium, tungsten, nickel, chromium, palladium, and gold, alloys thereof, laminates thereof, or the like are used. Further, as the piezoelectric layer  29 , a ferroelectric piezoelectric material such as lead zirconate titanate (PZT), a relaxor ferroelectric added with a metal such as niobium, nickel, magnesium, bismuth, yttrium is used. In addition, a non-lead material such as barium titanate can also be used. In addition, as the inorganic protective film  31 , silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, a laminate thereof, or the like can be used. Further, as the resin layer, a photosensitive resin containing epoxy resin, acrylic resin, phenol resin, polyimide resin, silicone resin, styrene resin or the like as a main component, or the like can be used. As the first wiring layer  34  and the second wiring layer  35 , copper, titanium, tungsten, an alloy thereof, a laminate thereof, or the like is used. 
       FIG. 7  is a schematic view illustrating an operation of the ultrasonic motor  1  configured as described above.  FIG. 7  is a plan view viewed from a surface (that is, second surface  40 ) aide of a side opposite to the surface on which the piezoelectric element  27  of the piezoelectric actuator  17  is formed. Since the same driving voltage is supplied to the piezoelectric elements  27   a  and  27   d  disposed on one diagonal position (a lower left and an upper right in  FIG. 7 ) of the substrate  24  and the piezoelectric element  27   e  disposed at the center via the second wiring layer  35   a , the same electric field is applied to the piezoelectric layers  29  thereof. On the other hand, since the same driving voltage is supplied to the piezoelectric elements  27   b  and  27   c  disposed on the other diagonal position (an upper left and a lower right in  FIG. 7 ) of the substrate  24  via the second wiring layer  35   b , the same electric field is applied to the piezoelectric layers  29  thereof. In other words, the piezoelectric element groups  27   a ,  27   d ,  27   e  on a side vibrate to be expanded and contracted in the same phase (refer to arrow in  FIG. 7 ) and the piezoelectric element groups  27   b  and  27   c  on the other side vibrate to be expanded and contracted with the same phase (see dashed arrows in  FIG. 7 ). The piezoelectric actuator  17  and the vibrating plate  18  adhered thereto are deformed and distorted (refer to dashed line in  FIG. 7 ) and the protrusion  23  provided on the vibrating plate  18  reciprocate or elliptically move, by making the phases of vibration of piezoelectric element groups  27   a ,  27   d , and  27   e  on a side and the other piezoelectric element groups  27   b  and  27   c  on the other side different. As a result, the rotor  3  rotates about axis thereof in a predetermined direction (see arrow in  FIG. 7 ). The rotating direction of the rotor  3  can be reversed from the illustrated direction by the piezoelectric element groups  27   b  and  27   c  which are positioned on the other side being driven and either the piezoelectric element groups  27   a ,  27   d , and  27   e  on a side being not driven or being driven to be weaker than the piezoelectric element groups  27   b ,  27   c  on the other side. 
     As described above, in the embodiment, since the first wiring layer  34  is formed on the second surface  40  of a side opposite to the first surface  39  on which the piezoelectric layer  29  is formed, the degree of freedom in design increases. In other words, the first wiring layer  34  can be formed without interfering with the wirings of the second electrode layer  30 , the second wiring layer  35 , or the like formed on the first surface  39 . Accordingly, a region on which the first wiring layer  34  is formed or the like can be increased as much as possible and wiring resistance (electric resistance) of the first wiring layer  34  can be suppressed. As a result, the voltage drop in the first electrode layer  28  overlapping the piezoelectric layer  29  is suppressed, and the output of the piezoelectric actuator  17 , eventually the ultrasonic motor  1 , can be increased. In addition, since the through wiring  37  is formed so as to overlap the piezoelectric layer  29  (in the embodiment, region in which first electrode layer  28 , piezoelectric layer  29 , and second electrode layer  30  overlap each other, that is, piezoelectric element  27 ), the first electrode layer  28  and the first wiring layer  34  can be connected to each other without routing the first electrode layer  28  to the outside of the piezoelectric layer  29 . Accordingly, the film thickness is unlikely to be increased, and a region (wiring portion) formed only of the first electrode layer  28  of which the wiring resistance is likely to be increased can be reduced. As a result, the wiring resistance up to the first electrode layer  28  overlapping the piezoelectric layer  29  can be suppressed, and the voltage drop in the first electrode layer  28  overlapping the piezoelectric layer  29  is further suppressed. Further, since the plurality of through wirings  37  are provided, the adhesion of the first wiring layer  34  can be improved as compared with a case where the first electrode layer  28  and the first wiring layer  34  are connected by one through wiring  37 . Accordingly, peeling of the first wiring layer  34  from the substrate  24  can be suppressed. 
     In addition, since the first electrode layer  28  and the second wiring layer  35  are separated by the first resin layer  32 , parasitic capacitance formed between the first electrode layer  28  and the second wiring layer  35  can be suppressed. Furthermore, electric field intensity can be suppressed between the first electrode layer  28  and the second wiring layer  35 . Accordingly, the second wiring layer  35  can be disposed without avoiding the pattern of the first electrode layer  28  and thus the degree of freedom in design increases. As a result, the region on which the second wiring layer  35  is formed or the like can be increased as much as possible, and the wiring resistance of the second wiring layer  35  can be suppressed. In addition, since the contact hole  36  is formed so as to overlap the piezoelectric layer  29 , the second electrode layer  30  and the second wiring layer  35  can be connected to each other without routing the second electrode layer  30  to the outside of the piezoelectric layer  29 . Accordingly, the film thickness is unlikely to be increased, and a region (wiring portion) formed only of the second electrode layer  30  of which the wiring resistance is likely to be increased can be reduced. As a result, the wiring resistance up to the second electrode layer  30  overlapping the piezoelectric layer  29  can be suppressed. Further, since at least a portion of the second wiring layer  35  is buried in the first resin layer  32 , the wiring resistance of the second wiring layer  35  can be suppressed while thickening of the plate thickness of the piezoelectric actuator  17  is suppressed. In addition, since the plurality of contact holes  36  are provided, the adhesion of the second wiring layer  35  can be improved as compared with a case where the first electrode layer  28  and the first wiring layer  34  are connected to each other by one contact hole  36 . Accordingly, peeling of the second wiring layer  35  from the first resin layer  32  can be suppressed. 
     Next, a method for manufacturing the piezoelectric actuator  17  will be described.  FIG. 8  to  FIG. 11  are process diagrams illustrating the method for manufacturing the piezoelectric actuator  17 . First, an oxide film  25  is formed on the first surface  39  of the substrate  24 . Next, the first electrode layer  28 , the piezoelectric layer  29 , the second electrode layer  30 , or the like are patterned in this order and the piezoelectric elements  27  is formed by a semiconductor process (that is, film formation process, photolithography process, etching process, and the like). In addition, the inorganic protective film  31  is formed so as to cover the piezoelectric elements  27  or the like other than a portion corresponding to the contact hole  36  by the semiconductor process. Further, a portion (lower layer portion) of the first resin layer  32  from which a portion corresponding to the contact hole  36  is removed is formed by a liquid photosensitive adhesive having photosensitivity and thermosetting property being applied to the first surface  39  on which the inorganic protective film  31  is formed by using a spin coater or the like and exposure and development being performed after heating. Accordingly, as illustrated in  FIG. 8 , the piezoelectric element  27  is covered by the inorganic protective film  31  and the first resin layer  32 , and the contact hole  36  is formed on a portion corresponding to the piezoelectric element  27 . 
     Next, as illustrated in  FIG. 9 , a second wiring layer  35  is formed on the first resin layer  32  by the semiconductor process or the electroplating method. Here, the second wiring layer  35  and the second electrode layer  30  are electrically connected via the contact hole  36 . Next, through wiring  37  is formed from the second surface  40  side. First, as illustrated in  FIG. 10 , a through hole  42  passing through the substrate  24  and the oxide film  25  is formed. The through hole  42  can be opened for example, by dry etching, laser or the like. Once the through hole  42  is formed, as illustrated in  FIG. 11 , by the electroplating method, a conductor is formed in the through hole  42  and thus the through wiring  37  is formed therein. The first wiring layer  34  is formed on the second surface  40  by the semiconductor process or the electroplating method. Accordingly, the first wiring layer  34  and the first electrode layer  28  are electrically connected via the through wiring  37 . In a case where the first wiring layer  34  is formed by the electroplating method, the through wiring  37  and the first wiring layer  34  can be formed by a single electroplating method. In addition, in a case where the second wiring layer  35  is also formed by the electroplating method, the through wiring  37 , the first wiring layer  34  and the second wiring layer  35  can be formed by a single electroplating method. In this case, after the first resin layer  32  is formed, the through hole  42  is formed, and the through wiring  37 , the first wiring layer  34 , and the second wiring layer  35  are collectively formed by the electroplating method. 
     Finally, a resin is applied to the entirety including the first surface  39  and the second surface  40  of the substrate  24 . In other words, the first resin layer  32  covering the second wiring layer  35  and the second resin layer  33  covering the first wiring layer  34  are formed. Accordingly, the piezoelectric actuator  17  is produced as illustrated in  FIG. 6 . 
     Incidentally, the piezoelectric actuator  17  is not limited to the first embodiment described above. In a piezoelectric actuator  17 ′ according to a second embodiment illustrated in  FIG. 12  to  FIG. 14 , a first wiring layer  34 ′ is buried in the substrate  24 . Hereinafter, the configuration of the second embodiment will be described in detail.  FIG. 12  is a schematic sectional view illustrating the piezoelectric actuator  17 ′ in the second embodiment, specifically, a sectional view corresponding to a sectional view taken along line VI-VI in the first embodiment.  FIG. 13  and  FIG. 14  are process diagrams illustrating a method for manufacturing the piezoelectric actuator  17 ′ in the second embodiment. 
     As illustrated in  FIG. 12 , the piezoelectric actuator  17 ′ in the embodiment has a recessed portion  44  recessed on the second surface  40  of the substrate  24  in a plate thickness direction. A first wiring layer  34 ′ is formed on the recessed portion  44 . The recessed portion  44  in the embodiment is substantially formed on the entire surface except for an outer peripheral edge of the substrate  24  on the second surface  40 . Therefore, similar to the first embodiment, the first wiring layer  34 ′ is substantially formed on the entire surface of the second surface  40 . In addition, since the through wiring  37 ′ passes through the substrate  24  in the region corresponding to the recessed portion  44  and connects the first wiring layer  34 ′ and the first electrode layer  28  to each other, the distance is decreased compared to the through wiring  37 ′ of the first embodiment. Therefore, the wiring resistance is decreased than that in the first embodiment. The entirety of the first wiring layer  34 ′ can be formed so as to be buried in the recessed portion  44 , or a portion of the first wiring layer  34 ′ can be formed to protrude from the recessed portion  44  to an outside (side opposite to piezoelectric element  27 ) of the second surface  40 . Since at least a portion of the first wiring layer  34 ′ described above is buried in the substrate  24 , the wiring resistance of the first wiring layer  34 ′ can be suppressed while increase in the thickness of the piezoelectric actuator  17 ′ is suppressed. Since other configurations are the same as those of the first embodiment described above, description thereof will be omitted. 
     Next, the method for manufacturing the piezoelectric actuator  17 ′ according to the embodiment will be described. Since formation of the piezoelectric element  27  or the like on the first surface  39  side is the same as that in the first embodiment described above, description thereof will be omitted. When the piezoelectric element  27 , the inorganic protective film  31 , a portion of the first resin layer  32 , the second wiring, and the like are formed on the first surface  39 , as illustrated in  FIG. 13 , the recessed portion  44  and a through hole  42 ′ are formed on the second surface  40 . Specifically, the recessed portion  44  is formed by the anisotropic etching or the like, and then the through holes  42 ′ are formed by the dry etching, laser or the like. First, the through hole  42 ′ can be formed by dry etching, laser, or the like and then the recessed portion  44  can be formed by the anisotropic etching or the like. Once the through hole  42 ′ and the recessed portion  44  are formed, as illustrated in  FIG. 14 , by the electroplating method, a conductor is formed in the through hole  42 ′ and the recessed portion  44  and thus the through wiring  37 ′ and the first wiring layer  34 ′ are formed therein. The first wiring layer  34 ′ can be formed separately from the through wiring  37 ′ by the semiconductor process or the electroplating method. Finally, a resin is applied to the entirety including the first surface  39  and the second surface  40  of the substrate  24 . In other words, the first resin layer  32  covering the second wiring layer  35  and the second resin layer  33  covering first wiring layer  34 ′ are formed. Accordingly, the piezoelectric actuator  17 ′ as illustrated in  FIG. 12  is produced. 
     In each embodiment described above, although only the first wiring layer electrically connected to the first electrode layer  28  is disposed on the second surface  40 , the invention is not limited thereto. In a piezoelectric actuator  17 ″ according to a third embodiment illustrated in  FIG. 15 , a third wiring layer  45  is formed on the second surface  40  which is electrically connected to the second wiring layer  35  in addition to the first wiring layer  34 ′. 
     Specifically, in the embodiment, in a region deviated from the piezoelectric element  27 , a region A in which the first wiring layer  34 ′ is not formed is formed on a portion of the second surface  40 . A third wiring layer  45  is formed on the region A. Like the first wiring layer  34 ′, in the embodiment, the third wiring layer  45  is formed on a recessed portion  47  in which the substrate  24  is recessed in the plate thickness direction. In other words, the third wiring layer  45  is buried in the recessed portion  47  formed at a position different from the recessed portion  44  in which the first wiring layer  34 ′ is buried. In addition, in the first surface  39  side, the second wiring layer  35 ′ extends to a position corresponding to the region facing the third wiring layer  45 , that is, the region A. The second wiring layer  35 ′ and the third wiring layer  45  are connected to each other by the through wiring  46  passing through the substrate  24  and the first resin layer  32  between the substrate  24  and the second wiring layer  35 ′. In other words, the third wiring layer  45  is connected to the second electrode layer  30  via the through wiring  46  and the second wiring layer  35 ′. A diameter of the through wiring  46  is formed to be sufficiently smaller than the dimension of the piezoelectric element  27  in the longitudinal direction and the transverse direction, similarly to the through wiring  37 ′ connecting the first wiring layer  34 ′ and the first electrode layer  28 . In addition, a plurality of through wirings  46  are formed on the region A. Accordingly, wiring resistance of the wiring can be suppressed by the wiring connected to the second electrode layer  30  being formed on the second surface  40  side. For example, on the circumstances of layout, in a case where wiring resistance of the second wiring layer  35 ′ is increased due to narrowing of the wiring width or thinning of the film thickness of a portion of the second wiring layer  35 ′, as in the embodiment, it is preferable that the second wiring layer  35 ′ be connected to the third wiring layer  45  and route in the second surface  40 . Since other configurations are the same as those of the second embodiment described above, description thereof will be omitted. In addition, in the method for manufacturing the piezoelectric actuator  17 ″ according to the embodiment, since it is the same as in the second embodiment described above except that the through hole of the through wiring  46  is formed when the through hole  42 ′ of the through wiring  37 ′ is formed, the recessed portion  47  of the third wiring layer  45  is formed when the recessed portion  44  of the first wiring layer  34 ′ is formed, and the through wiring  46  and the third wiring layer  45  are formed when the through wiring  37 ′ and the first wiring layer  34 ′ are formed, the description thereof is omitted. 
     Incidentally, in each the embodiment described above, although the through wiring  37  connecting the first wiring layer  34  and the first electrode layer  28  and the contact hole  36  connecting the second electrode layer  30  and the second wiring layer  35  are uniformly disposed on a region overlapping the piezoelectric element  27  (that is, piezoelectric layer  29 ), the invention is not limited thereto. For example, these through wirings and contact holes may be gathered and disposed on a center portion of a region overlapping the piezoelectric element. In addition, a portion of the through wirings and the contact holes is formed on a region deviated from the piezoelectric element. 
     In addition, in each embodiment described above, although the piezoelectric actuator  17  used for the ultrasonic motor  1  is described as an example, the invention is not limited thereto. The present invention can also be applied to other piezoelectric actuators which have a piezoelectric element including the first electrode layer, the piezoelectric layer, and the second electrode layer, and deform the piezoelectric element. Further, the invention is not limited to the piezoelectric actuator, and the invention can be applied to any MEMS device in which the first electrode layer, the piezoelectric layer, and the second electrode layer are stacked. For example, the present invention can be also applied to a case where a piezoelectric element including the first electrode layer, the piezoelectric layer, and the second electrode layer is applied to a sensor for detecting pressure change, vibration, displacement, or the like.