Patent Publication Number: US-2022232328-A1

Title: Piezoelectric element, piezoelectric device, and manufacturing method of piezoelectric element

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Patent Application No. PCT/JP2020/044651 filed on Dec. 1, 2020, which designated the U.S. and claims the benefit of priority from Japanese Patent Applications No. 2019-235224 filed on Dec. 25, 2019, No. 2020-125990 filed on Jul. 24, 2020 and No. 2020-177170 filed on Oct. 22, 2020 and International Patent Application No. PCT/JP2020/040471 filed on Oct. 28, 2020. The entire disclosures of all of the above applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a piezoelectric element, a piezoelectric device, and a method for manufacturing a piezoelectric element, in which the vibration region is cantilevered. 
     BACKGROUND 
     Conventionally, a piezoelectric element in which the vibration region is cantilevered is proposed in a conceivable technique. Specifically, the vibration region is configured to have a piezoelectric film and an electrode film connected to the piezoelectric film. In such a piezoelectric element, the piezoelectric film is deformed and electric charges are generated in the piezoelectric film when the vibration region vibrates due to acoustic pressure (hereinafter, also simply referred to as sound pressure) or the like. Therefore, the sound pressure applied to the vibration region is detected by extracting the electric charge generated in the piezoelectric film through the electrode film. 
     SUMMARY 
     According to an example, a piezoelectric element may include: a vibration unit that outputs a pressure detection signal according to a pressure; a support member; and an improvement unit for improving a detection accuracy of the pressure detection signal. The vibration unit on the support member includes a piezoelectric film and an electrode film in a support region and vibration regions. Each vibration region has one end portion as a fixed end and an other end portion as a free end. A part of each vibration region on a one end portion side is a first region, and another part of each vibration region on an other end portion side is a second region. The electrode film is disposed in the first region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
         FIG. 1  is a cross-sectional view of a piezoelectric element according to the first embodiment; 
         FIG. 2  is a plan view of the piezoelectric element shown in  FIG. 1 ; 
         FIG. 3  is a plan view of a piezoelectric element in a modified example of the first embodiment; 
         FIG. 4  is a plan view of a piezoelectric element according to a second embodiment; 
         FIG. 5  is a plan view of a piezoelectric element according to a third embodiment; 
         FIG. 6  is a plan view of a piezoelectric element according to a fourth embodiment; 
         FIG. 7  is a cross-sectional view of a piezoelectric element according to a fifth embodiment; 
         FIG. 8  is a plan view of a piezoelectric element according to a sixth embodiment; 
         FIG. 9  is a plan view of a piezoelectric element according to a seventh embodiment; 
         FIG. 10  is a diagram for explaining the relationship between the frequency and the sensitivity of each sensing unit; 
         FIG. 11  is a cross-sectional view of a piezoelectric element according to an eighth embodiment; 
         FIG. 12  is a cross-sectional view of a piezoelectric element according to a ninth embodiment; 
         FIG. 13A  is a cross-sectional view showing a manufacturing process of the piezoelectric element shown in  FIG. 12 ; 
         FIG. 13B  is a cross-sectional view showing a manufacturing process of a piezoelectric element following  FIG. 13A ; 
         FIG. 14  is a cross-sectional view of a piezoelectric device according to a ninth embodiment; 
         FIG. 15  is a diagram showing the relationship between Cb/Cm and the sensitivity ratio; 
         FIG. 16  is a plan view of a piezoelectric element according to a tenth embodiment; 
         FIG. 17  is a cross-sectional view of a piezoelectric device according to the tenth embodiment; 
         FIG. 18  is a circuit diagram showing a connection relationship between a sensing unit, a parasitic capacitance, and a circuit board; 
         FIG. 19  is a plan view showing the shape of the intermediate electrode film in an eleventh embodiment; 
         FIG. 20  is a plan view showing the shape of the intermediate electrode film in the modified example of the eleventh embodiment; 
         FIG. 21  is a diagram showing a stress distribution of a piezoelectric element according to a twelfth embodiment; 
         FIG. 22  is a plan view of a piezoelectric element according to the twelfth embodiment; 
         FIG. 23  is a diagram for explaining the concept of electrostatic energy in the vibration region; 
         FIG. 24  is a schematic diagram in which a vibration region is divided into a first region and a second region based on  FIG. 23 ; 
         FIG. 25  is a schematic diagram in which a vibration region is divided into a first region and a second region according to a modified example of the twelfth embodiment; 
         FIG. 26  is a diagram for explaining the concept of electrostatic energy in the vibration region of a thirteenth embodiment; 
         FIG. 27  is a schematic diagram in which a vibration region is divided into a first region and a second region based on  FIG. 26 ; 
         FIG. 28  is a cross-sectional view of a piezoelectric element according to a fourteenth embodiment; 
         FIG. 29  is a circuit diagram when a piezoelectric device is configured; 
         FIG. 30A  is a schematic diagram when sound pressure is applied to a vibration region; 
         FIG. 30B  is a schematic diagram when sound pressure is applied to a vibration region; 
         FIG. 31  is a circuit diagram in the case where the piezoelectric device in the modified example of the fourteenth embodiment is configured; 
         FIG. 32  is a cross-sectional view of a piezoelectric element according to a fifteenth embodiment; 
         FIG. 33  is a cross-sectional view showing a manufacturing process of a piezoelectric element; 
         FIG. 34  is a cross-sectional view showing a manufacturing process of a piezoelectric element; 
         FIG. 35  is a cross-sectional view of a piezoelectric device according to a sixteenth embodiment; 
         FIG. 36  is a plan view of a piezoelectric element according to to sixteenth embodiment; 
         FIG. 37  is a circuit diagram of a piezoelectric device according to a sixteenth embodiment; 
         FIG. 38  is a diagram showing a relationship between a frequency and a resonance magnification in a vibration region; 
         FIG. 39  is a cross-sectional view of a piezoelectric element according to a seventeenth embodiment; 
         FIG. 40  is a schematic diagram when a load is applied to a vibration region; 
         FIG. 41  is a schematic diagram showing stress on the side surface corresponding to  FIG. 40 ; 
         FIG. 42  is a schematic diagram showing stress in a cross section along the line XXXXII-XXXXII in  FIG. 40 ; 
         FIG. 43A  is a diagram showing the relationship between the number of electrode regions and sensitivity when the length of the vibration region in the eighteenth embodiment is 440 μm; 
         FIG. 43B  is a diagram showing the relationship between the number of electrode regions and sensitivity when the length of the vibration region in the eighteenth embodiment is 490 μm; 
         FIG. 43C  is a diagram showing the relationship between the number of electrode regions and sensitivity when the length of the vibration region in the eighteenth embodiment is 540 μm; 
         FIG. 44  is a cross-sectional view of a piezoelectric device according to a nineteenth embodiment; 
         FIG. 45  is a diagram showing the relationship between frequency and sensitivity; 
         FIG. 46  is a diagram showing the relationship between acoustic compliance in the back space and required acoustic resistance; 
         FIG. 47  is a diagram showing the relationship between acoustic resistance and the width of a separation slit; and 
         FIG. 48  is a diagram showing the relationship between the ratio of the acoustic compliance of the back space to the acoustic compliance of the pressure receiving surface space and the signal intensity ratio. 
     
    
    
     DETAILED DESCRIPTION 
     At present, it may be desired to improve the detection accuracy in a piezoelectric element having such a cantilever-supported vibration region. 
     A piezoelectric element, a piezoelectric device, and a method for manufacturing a piezoelectric element, which can improve detection accuracy, are provided in the present embodiments. 
     According to one of the present embodiments, the piezoelectric element includes: a support member; a piezoelectric film arranged on the support member; an electrode film connected to the piezoelectric film and extracting an electric charge generated by a deformation of the piezoelectric film; a support region supported by the support member; a plurality of vibration regions connected to the support region and floated from the support member; and a vibration unit for outputting a pressure detection signal based on the electric charge. The plurality of vibration regions are provided with one end portion as a fixed end and the other end portion as a free end, which provide a boundary with the support region. A region on a one end portion side is defined as a first region, and a region on an other end portion side is defined as a second region. The electrode film is formed in the first region, and an improvement unit for improving the detection accuracy of the pressure detection signal is formed therein. 
     According to this, since the improvement unit for improving the accuracy of the pressure detection signal is formed, the detection accuracy can be improved. 
     Further, according to another of the present embodiments, the piezoelectric element includes: a support member; a piezoelectric film arranged on the support member; an electrode film connected to the piezoelectric film and extracting an electric charge generated by a deformation of the piezoelectric film; a support region supported by the support member; a plurality of vibration regions connected to the support region and floated from the support member; and a vibration unit for outputting a pressure detection signal based on the electric charge. The plurality of vibration regions are provided with one end portion as a fixed end and the other end portion as a free end, which provide a boundary with the support region. A region on a one end portion side is defined as a first region, and a region on an other end portion side is defined as a second region. Resonance frequencies in at least a part of the vibration regions are formed so as to be different from each other, and the electrode film is arranged in the first region. 
     According to this, since the resonance frequencies are set to different values in at least a part of the vibration regions, the relationship between the frequency and the sensitivity becomes a different waveform. Therefore, by appropriately switching the vibration regions used for pressure detection, the frequency at which the detection sensitivity is high can be widened, and the detection sensitivity of a low frequency noise such as road noise can also be high. Therefore, the detection accuracy can be improved. 
     Further, according to another of the present embodiments, a piezoelectric device includes: the above described piezoelectric element; a mount member on which the piezoelectric element is mounted; a lid portion fixed to the mount member in a state of accommodating the piezoelectric element; and a casing in which a through hole is formed to communicate with an outside and to introduce pressure. 
     According to this, since the piezoelectric device is provided with the piezoelectric element having the improvement unit, the accuracy of the pressure detection signal can be improved. 
     Further, according to another of the present embodiments, a manufacturing method of a piezoelectric element includes: preparing a support member; forming a vibration unit on the support member. The forming of the vibration unit includes: forming a recess in the support member to float the vibration region. 
     According to this, since the piezoelectric element in which the improvement unit is formed is manufactured, the piezoelectric element capable of improving the detection accuracy is manufactured. 
     The reference numerals in parentheses attached to the components and the like indicate an example of correspondence between the components and the like and specific components and the like in an embodiment to be described below. 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each embodiment described below, same or equivalent parts are designated with the same reference numerals. 
     First Embodiment 
     The piezoelectric element  1  of the first embodiment will be described with reference to  FIGS. 1 and 2 . The piezoelectric element  1  of the present embodiment may be suitable for use as, for example, a microphone. Further,  FIG. 1  corresponds to a cross-sectional view taken along the line I-I in  FIG. 2 . In  FIG. 2 , the first electrode portion  71 , the second electrode portion  72 , and the like, which will be described later, are omitted. Further, in each drawing corresponding to  FIG. 2 , the first electrode portion  71 , the second electrode portion  72 , and the like are appropriately not shown. 
     The piezoelectric element  1  of the present embodiment includes a support member  10  and a vibration unit  20 . The support member  10  has a support substrate  11  and an insulation film  12  formed on the support substrate  11 . The support substrate  11  is made of, for example, a silicon substrate, and the insulation film  12  is made of an oxide film or the like. 
     The vibration unit  20  constitutes a sensing unit  30  that outputs a pressure detection signal corresponding to a pressure such as sound pressure, and is arranged on the support member  10 . In the support member  10 , a recess  10   a  is formed for floating an inner edge side of the vibration unit  20 . Therefore, the vibration unit  20  has a structure with a support region  21   a  arranged on the support member  10  and a floating region  21   b  connected to the support region  21   a  and floating on the recess portion  10   a . The recess portion  10   a  has a flat rectangular shape at the opening end on the vibration unit  20  side (hereinafter, also simply referred to as the opening end of the recess portion  10   a ). Therefore, the floating region  21   b  has a substantially rectangular shape in a plane. 
     The floating region  21   b  of the present embodiment is divided into a separation slit  41  and a stress increasing slit  42  so that four vibration regions  22  are configured. In the present embodiment, two separation slits  41  are formed so as to pass through the substantially center of the floating region  21   b  and extend toward the opposite corners of the floating region  21   b . Here, the separation slit  41  of the present embodiment is terminated in the floating region  21   b . The floating region  21   b , which will be described in detail later, is divided into four vibration regions  22  since the stress increasing slit  42  is connected to the separation slit  41  and extends to the end on the support region  21   a  side in the floating region. Although not particularly limited, in the present embodiment, the distance between the vibration regions  22  (that is, the width of the separation slit  41 ) is about 1 μm. 
     Since each vibration region  22  is configured by dividing the floating region  21   b  as described above, one end portion  22   a  thereof is regarded as a fixed end supported by the support member  10  (that is, the support region  21   a ), and the other end portion thereof on the other end portion  22   b  side is regarded as a free end. That is, each vibration region  22  is in a state of being connected to the support region  21 a and in a state of being cantilevered. The one end portion  22   a  in each vibration region  22  is a portion that coincides with the open end of the recess  10   a  in the normal direction (hereinafter, also simply referred to as the normal direction) with respect to the surface direction of the vibration unit  20 , and further a portion that is a boundary with the support region  21   a . Therefore, the shape of one end portion  22   a  in each vibration region  22  depends on the open end of the recess  10   a.    
     The vibration unit  20  is configured to have a piezoelectric film  50  and an electrode film  60  connected to the piezoelectric film  50 . Specifically, the piezoelectric film  50  has a lower piezoelectric film  51  and an upper piezoelectric film  52  stacked on the lower piezoelectric film  51 . Further, the electrode film  60  includes: a lower electrode film  61  arranged below the lower piezoelectric film  51 ; an intermediate electrode film  62  arranged between the lower piezoelectric film  51  and the upper piezoelectric film  52 ; and an upper electrode film  63  arranged on the upper piezoelectric film  52 . That is, in the vibration unit  20 , the lower layer piezoelectric film  51  is sandwiched between the lower electrode film  61  and the intermediate electrode film  62 , and the upper layer piezoelectric film  52  is sandwiched between the intermediate electrode film  62  and the upper electrode film  63 . The piezoelectric film  50  is formed by a sputtering method or the like. 
     Further, each vibration region  22  has a fixed end side as a first region R 1  and a free end side as a second region R 2 . The lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  are formed in the first region R 1  and the second region R 2 , respectively. Here, the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the first region R 1  and the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the second region R 2  are , separated and insulated fro each other. Further, the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the first region R 1  are appropriately extended to the support region  21   a.    
     In the support region  21   a  of the vibration unit  20 , the first electrode portion  71  electrically connected to the lower electrode film  61  and the upper electrode film  63  formed in the first region R 1  and the second electrode portion  72  electrically connected to the intermediate electrode film  62  formed in the first region R 1  are arranged. Note that  FIG. 1  is a cross-sectional view taken along the line I-I in  FIG. 2 , showing a cross section of the vibration region  22  on the right side of the drawing which is different from a cross section of the vibration region  22  on the left side of the drawing. Then, in the support region  21   a , the first electrode portion  71  electrically connected to the lower electrode film  61  and the upper electrode film  63  formed in the first region R 1 , and the second electrode portion  72  electrically connected to the intermediate electrode film  62  formed in the first region R 1  are arranged. 
     The first electrode portion  71  is formed in a hole portion  71   a  that penetrates the upper electrode film  63 , the upper piezoelectric film  52 , and the lower piezoelectric film  51  to expose the lower electrode film  61 , and includes a through hole electrode  71   b  electrically connected to the lower electrode film  61  and the upper electrode film  63 . Further, the first electrode portion  71  has a pad portion  71   c  formed on the through hole electrode  71   b  and electrically connected to the through hole electrode  71   b . The second electrode portion  72  has a through hole electrode  72   b  formed in a hole portion  72   a  that penetrates the upper piezoelectric film  52  and exposes the intermediate electrode film  62 , and the through hole electrode  72   b  is electrically connected to the intermediate electrode film  62 . Further, the second electrode portion  72  has a pad portion  72   c  formed on the through hole electrode  72   b  and electrically connected to the through hole electrode  72   b.    
     The sensing unit  30  of the present embodiment is configured to output the change in electric charge in the four vibration regions  22  as one pressure detection signal. That is, the four vibration regions  22  are electrically connected in series. More specifically, each vibration region  22  has a bimorph structure, and each lower electrode film  61 , each intermediate electrode film  62 , and each upper electrode film  63  formed in each vibration region  22  are connected in parallel to each other, and the vibration regions  22  are connected in series. 
     Further, the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the second region R 2  are not electrically connected to the respective electrode portions  71  and  72 , and are in a floating state. Therefore, the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the second region R 2  may not be always necessary. In the present embodiment, they are formed so as to protect portions of the lower piezoelectric film  51  and the upper piezoelectric film  52  arranged in the second region R 2 . 
     In the present embodiment, the lower piezoelectric film  51  and the upper piezoelectric film  52  are made of lead-free piezoelectric ceramics such as scandium nitride aluminum (ScAlN), aluminum nitride (AlN), and the like. The lower electrode film  61 , the intermediate electrode film  62 , the upper electrode film  63 , the first electrode portion  71 , the second electrode portion  72 , and the like are made of molybdenum, copper, platinum, platinum, titanium, or the like. 
     The above is the basic configuration of the piezoelectric element  1  in this embodiment. In such a piezoelectric element  1 , when sound pressure is applied to each vibration region  22  (that is, the sensing unit  30 ), each vibration region  22  vibrates. In this case, for example, when the other end portion  22   b  side (that is, the free end side) of the vibration region  22  is displaced upward, tensile stress is generated in the lower piezoelectric film  51  and compression stress is generated in the upper piezoelectric film  52 . Therefore, the sound pressure is detected by extracting the electric charge from the first electrode portion  71  and the second electrode portion  72 . 
     At this time, the stress generated in the vibration region  22  (that is, the piezoelectric film  50 ) is larger on the fixed end side than on the free end side because the stress is released on the free end side (that is, the other end portion side). That is, on the free end side, the generation of electric charges is small, and the SN ratio, which is the ratio of the signal to the noise, may tend to be small. Therefore, in the piezoelectric element  1  of the present embodiment, as described above, each vibration region  22  is divided into a first region R 1  in which the stress may tend to be large and a second region R 2  in which the stress may tend to be small. In the piezoelectric element  1 , the lower electrode film  61 , the upper electrode film  63 , and the intermediate electrode film  62  arranged in the first region R 1  are connected to the first and second electrode portions  71  and  72  to extract the electric charge generated in the lower piezoelectric film  51  and upper piezoelectric film  52  disposed in the first region R 1 . As a result, it is possible to suppress the influence of noise from becoming large. 
     In the present embodiment, each vibration region  22  is formed with a deformation promoting structure that promotes the deformation of the piezoelectric film  50  located in the first region R 1  when the sound pressure is applied. In this embodiment, the deformation promoting structure corresponds to the improvement unit. 
     In the present embodiment, each vibration region  22  is formed with a stress increasing slit  42  for increasing the stress generated in the first region R 1  when the sound pressure is applied. Specifically, the stress increasing slit  42  is formed so as to be connected to the separation slit  41  in the first region R 1  and to form a corner portion C 1  at the connecting portion with the separation slit  41 . Therefore, in the vibration region  22 , the corner portion C 1  is formed in the portion of the first region R 1  floating from the support member  10 , and the stress may tend to be concentrated on the corner portion C 1  and the stress may tend to be increased. As a result, in the vibration region  22 , the stress that can be generated on the one end portion  22   a  side also increases, and the overall deformation becomes large. Therefore, the pressure detection signal can be increased by increasing the deformation of the piezoelectric film  50 , and the detection sensitivity can be improved. The corner portion C 1  formed at the connecting portion between the separation slit  41  and the stress increasing slit  42  may have an acute angle formed between the separation slit  41  and the stress increasing slit  42 . Alternatively, it may be an obtuse angle or a right angle. 
     In the present embodiment described above, in the vibration region  22 , the corner portion C 1  is formed in a portion of the first region R 1  floating from the support member  10 . Then, in the corner portion C 1 , the stress may tend to be concentrated and the stress may tend to increase. Therefore, the deformation of the first region R 1  in the vibration region  22  can be promoted, and the pressure detection signal can be increased. Therefore, the detection sensitivity can be improved and the detection accuracy can be improved. 
     Here, in the vibration region  22  that is cantilevered as described above, the one end portion  22   a  supported by the support member  10  is supported and restrained by the support member  10 . Therefore, the stress generated in the vibration region  22  may tend to be the largest in the region of the portion slightly shifted to the inner periphery side from the one end portion  22   a . Alternatively, by forming the corner portion C 1  in the vibration region  22  as described above, the portion where the stress is maximized may be shifted to the one end portion  22   a  side. Therefore, also in this respect, in the present embodiment, the deformation of the entire vibration region  22  can be increased, and the detection sensitivity can be improved. 
     (Modification of First Embodiment) 
     The modification of the first embodiment will be described below. In the first embodiment, as shown in  FIG. 3 , the stress increasing slit  42  may be extended along the extending direction of the separation slit  41 , and the corner portion C 1  may be formed by only the stress increasing slit  42 , so that the stress increasing slit  42  has a bent shape. That is, the stress increasing slit  42  may have a so-called wavy shape. 
     Further, in the stress increasing slit  42 , when the stress generated in the corner portion C 1  formed by the stress increasing slit  42  becomes too large and the vibration unit  20  may be destroyed, the corner portion C 1  may have a curved shape having a curvature. 
     Second Embodiment 
     A second embodiment will be described. This embodiment is a modification of the first embodiment in which the configuration of the deformation promoting structure is changed. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, as shown in  FIG. 4 , the stress increasing slit  42  is not formed in the vibration region  22 , and the separation slit  41  is formed so as to reach the corner portion of the floating region  21   b . That is, the floating region  21   b  of the present embodiment is divided into four vibration regions  22  only by the separation slit  41 . In each vibration region  22 , a corner portion C 2  is formed at one end portion  22   a . In this embodiment, the corner portion C 2  corresponds to the deformation promoting structure. 
     Specifically, in the present embodiment, the open end of the recess  10   a  in the support member  10  provides a recess portion  10   b  that is located between both ends of the one end portion  22   a  of the vibration region  22 , and is formed by recessing the open end on an outer periphery side of the support member  10 . The both ends of the one end portion  22   a  of the vibration region  22  are, in other words, the portions of the one end portion  22   a  that the separation slit  41  reaches. 
     The open end of the recess portion  10   a  is in a state in which a concave-convex structure is formed by the recess portion  10   b  in the direction along the open end. As a result, the one end portion  22   a  of the vibration region  22  has a concave-convex structure depending on the shape of the open end of the recess portion  10   a , so that the corner portion C 2  is formed. 
     In the present embodiment described above, since the corner portion C 2  is configured in the one end portion  22   a  of the vibration region  22 , the stress of the one end portion  22   a  becomes large. Therefore, it is possible to promote the deformation of the one end portion  22   a  in the vicinity of the corner portion C 2  in the vibration region  22 , and it is possible to increase the pressure detection signal. Therefore, the sensitivity can be improved. 
     (Modification of Second Embodiment) 
     The modification of the second embodiment will be described below. In the second embodiment, the corner portion C 2  may be configured such that a convex portion is formed at the open end of the recess portion  10   a  so that the open end protrudes toward the inner periphery side of the support member  10 . That is, in the second embodiment, when the corner portion C 2  is formed at one end portion  22   a  which is disposed in the first region R 1  of the vibration region  22 , the shape of the recess  10   a  on the open end side can be appropriately changed. 
     Further, also in the second embodiment, as in the modification of the first embodiment, if the stress generated in the corner portion C 2  becomes too large and the vibration unit  20  may be destroyed, the corner portion C 2  may have a curved shape having a curvature. 
     Third Embodiment 
     A third embodiment will be described. This embodiment is a modification of the first embodiment in which the configuration of the deformation promoting structure is changed. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, as shown in  FIG. 5 , the open end of the recess portion  10   a  formed in the support member  10  has a planar circular shape with a center of the intersection of the two separation slits  41 . Further, the open end of the recess  10   a  is formed so as to intersect both ends of the stress increasing slit  42  in the extending direction in the normal direction. 
     Therefore, the two ends of the vibration region  22  on the support region  21   a  side in the outline of the floating region are in a state of reaching the one end portion  22   a . The vibration region  22  has a shape in which the one end portion  22   a  expands on the opposite side of the other end portion  22   b  with respect to the virtual line K 1  connecting the two ends. In the present embodiment, since the open end of the recess portion  10   a  has a planar circular shape, the one end portion  22   a  of the vibration region  22  has an arc shape. Therefore, in each vibration region  22  of the present embodiment, the open end of the recess portion  10   a  has a rectangular shape as in the first embodiment, and the first region R 1  is large, compared with a case where the one end portion  22   a  coincides with the virtual line K 1 . 
     The outline of the vibration region  22  is an end line that forms the outline of the vibration region  22 . The outline of the floating region in the vibration region  22  is a line of the portion of the outline of the vibration region  22  excluding the one end portion  22   a  supported by the support member  10 . Further, in the present embodiment, the shape of one end portion  22   a  corresponds to the deformation promoting structure. 
     In the present embodiment described above, since the vibration region  22  has a shape in which the one end portion  22   a  has a shape with a portion expanding on the opposite side of the other end portion  22   b  from the virtual line K 1 , the first region R 1  can be made larger than a case where the open end of the recess portion  10   a  has a rectangular shape. Further, as described above, since the deformation of the portion of the vibration region  22  inside the one end portion  22   a  may tend to be slightly larger, the deformation in the vicinity of the virtual line K 1  can also be large. That is, when the open end of the recess portion  10   a  has a rectangular shape, the deformation of the one end portion  22   a  can be increased. Therefore, the pressure detection signal can be increased and the sensitivity can be improved. 
     Fourth Embodiment 
     A fourth embodiment will be described. This embodiment is a modification of the third embodiment in which the configuration of the deformation promoting structure is changed. Other configurations are the same as those of the third embodiment, and therefore a description of the same configurations will be omitted. 
     In the present embodiment, as shown in  FIG. 6 , the stress increasing slit  42  is not formed in the vibration unit  20 . The open end of the recess portion  10   a  formed in the support member  10  has a planar circular shape with the intersection of the two separation slits  41  as a center. Here, in the present embodiment, the open end of the recess portion  10   a  is formed so as not to intersect with the separation slit  41 . 
     That is, the two ends of the vibration region  22  on the support region  21   a  side in the outline of the floating region are in a state of being terminated by the floating region, respectively. Therefore, in the present embodiment, each vibration region  22  is in a state where the portions of the vibration regions  22  on the one end portion  22   a  side are connected to each other. 
     The vibration region  22  has a shape in which the one end portion  22   a  expands on the opposite side of the other end portion  22   b  with respect to the virtual line K 2  connecting the two ends. Therefore, in each vibration region  22  of the present embodiment, the open end of the recess portion  10   a  has a rectangular shape as in the first embodiment, and the first region R 1  is large, compared with a case where the one end portion  22   a  coincides with the virtual line K 2 . Further, in the present embodiment, the shape of one end portion  22   a  corresponds to the deformation promoting structure. 
     In the present embodiment described above, since the vibration region  22  has a shape in which the one end portion  22   a  has a shape with a portion expanding on the opposite side of the other end portion  22   b  from the virtual line K 2 , the first region R 1  can be made larger than a case where the open end of the recess portion  10   a  has a rectangular shape. For that reason, the same effects as those of the third embodiment can be obtained. 
     Fifth Embodiment 
     A fifth embodiment will be described. This embodiment is a modification of the first embodiment in which the configuration of the deformation promoting structure is changed. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, as shown in  FIG. 7 , in the second region R 2 , the hole portion  81  is formed to penetrate the upper electrode film  63 , the upper piezoelectric film  52 , the intermediate electrode film  62 , and the lower piezoelectric film  51  and to reach the lower electrode film  61 . A hard film  82  having a Young&#39;s modulus higher than that of the piezoelectric film  50  is embedded in the hole portion  81 . 
     In the present embodiment, the hard film  82  is made of the same material as the first and second electrode portions  71  and  72  and the electrode film  60 . Since the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the second region R 2  are not electrically connected to the first and second electrode portions  71  and  72 , there is no difficulty even if they are connected to each other. And in this embodiment, the hard film  82  corresponds to the deformation promoting structure. 
     Further, in the present embodiment, the hole portion  81  and the hard film  82  are formed in the second region R 2  so that their density on the other end portion  22   b  side is denser than the first region R 1  side. More specifically, in the present embodiment, the hard film  82  is formed in the second region R 2  so as to gradually become denser from the first region R 1  side toward the other end portion  22   b  side. 
     As described above, in the present embodiment, the hard film  82  is arranged in the second region R 2 . Therefore, as compared with the case where the hard film  82  is not arranged in the second region R 2 , when the sound pressure is applied, the second region R 2  is hardened, so that the second region R 2  is less likely to be deformed. Therefore, in the present embodiment, the stress is likely to be concentrated on the first region R 1  and the first region R 1  is easily deformed. Therefore, the pressure detection signal can be increased and the sensitivity can be improved. 
     Further, in the present embodiment, the hard film  82  is formed so that the other end  22   b  side is denser than the first region R 1  side in the second region R 2 . Therefore, for example, compared with a case where the hard film  82  is formed so that the other end  22   b  side is sparser than the first region R 1  side in the second region R 2 , it is possible to suppress the inhibition of the deformation of the first region R 1  by the hard film  82 . Therefore, it is possible to easily obtain the effect of arranging the hard film  82 . 
     Further, the hard film  82  is made of the same material as the first and second electrode portions  71  and  72  and the electrode film  60 . Therefore, for example, the hard film  82  can be formed at the same time when the first and second through electrodes  71   b  and  72   b  are formed, and the manufacturing process can be simplified. 
     Sixth Embodiment 
     A sixth embodiment will be described. This embodiment provides a temperature detection element and a heat generation element in each vibration region  22  as compared with the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     First, the piezoelectric element  1  as described above may be used in a state of being exposed to the outside air or a state of being exposed to a predetermined oil. In this case, when the usage environment is low temperature, there may be a possibility such that the vibration of the vibration region  22  may be deteriorated since the vibration region  22  may be frozen when the element  1  is exposed to the outside air, or the viscosity of the oil in contact with the vibration region  22  may be reduced. That is, the piezoelectric element  1  as described above may have a possibility of reduction of the detection sensitivity when the usage environment is low temperature. 
     Therefore, in the present embodiment, as shown in  FIG. 8 , in each vibration region  22 , a temperature detection element  91  that outputs a temperature detection signal according to the temperature and a heat generation element  92  that generates heat when energized are provided. In the present embodiment, the temperature detection element  91  and the heat generation element  92  are formed in the second region R 2  in each vibration region  22 . More specifically, in the present embodiment, the intermediate electrode film  62  is not formed in the second region R 2 . The temperature detection element  91  and the heat generating element  92  are formed in a portion located between the lower piezoelectric film  51  and the upper piezoelectric film  52 . That is, the temperature detection element  91  and the heat generation element  92  are formed in the portion where the intermediate electrode film  62  in the first embodiment is formed. 
     Further, although not particularly shown, a leader wiring electrically connected to the temperature detection element  91  and the heat generation element  92  is formed in the first region R 1  and the support region  21   a . An electrode portion electrically connected to the leader wiring is formed in the support region  21   a . As a result, the temperature detection element  91  and the heat generation element  92  are connected to the external circuit. 
     In the second region R 2 , the lower electrode film  61  and the upper electrode film  63  are formed so as to sandwich the piezoelectric film  50  therebetween, as in the first embodiment. Further, the temperature detection element  91  is configured by using a temperature sensitive resistor whose resistance value changes according to the temperature, and the heat generating element  92  is configured by using a heat generating resistor that generates heat when energized. In the present embodiment, the temperature detection element  91  and the heat generation element  92  are made of, for example, platinum. Further, in the present embodiment, the temperature detection element  91  and the heat generation element  92  correspond to the improvement unit. 
     In the present embodiment described above, the temperature detection element  91  and the heat generation element  92  are arranged. Therefore, the temperature of the vibration region  22  can be maintained at a predetermined temperature by adjusting the amount of energization to the heat generation element  92  based on the temperature detected by the temperature detection element  91 . Therefore, it is possible to suppress the freezing of the vibration region  22  and the decrease in the viscosity of the oil in contact with the vibration region  22 , and it is possible to suppress the decrease in the detection sensitivity. That is, it is possible to suppress a decrease in detection accuracy. 
     Further, the temperature detection element  91  and the heat generation element  92  are formed in the second region R 2 . Therefore, as compared with the case where the temperature detection element  91  and the heat generating element  92  are formed in the first region R 1 , it is possible to suppress a decrease in the portion where the intermediate electrode film  62  for extracting the electric charge is arranged, and it is possible to utilize the second region R 2  effectively. 
     Further, the temperature detection element  91  and the heat generating element  92  are formed between the lower piezoelectric film  51  and the upper piezoelectric film  52 , and are not exposed to the outside air. Therefore, the environmental resistance of the temperature detection element  91  and the heat generation element  92  can be improved. 
     The temperature detection element  91  and the heat generating element  92  are formed between the lower piezoelectric film  51  and the upper piezoelectric film  52 , and the lower electrode film  61  and the upper electrode film  63  are formed to sandwich the piezoelectric film  50  as in the first embodiment. Therefore, it is possible to suppress the deterioration of the environmental resistance to the piezoelectric film  50 . 
     Seventh Embodiment 
     A seventh embodiment will be described. In this embodiment, a plurality of sensing units  30  are formed with respect to the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     First, the piezoelectric element  1  as described above may leak the sound pressure through a portion for partitioning each vibration region  22  (that is, a separation slit  41  and a stress increasing slit  42 ), and the acoustic resistance of the separation slit  41  that is disposed in parallel to the acoustic impedance may tend to be small. Then, as the acoustic resistance decreases, the low frequency roll-off frequency increases, so that the sensitivity at low frequencies may tend to decrease. 
     Therefore, in the present embodiment, as shown in  FIG. 9 , the piezoelectric element  1  is configured by integrating a plurality of sensing units  30  (that is, the floating regions  21   b ). Specifically, the support member  10  of the present embodiment is formed with four recesses  10   a  for floating the inner periphery side of the vibration unit  20 . That is, four floating regions  21   b  are formed in the vibration unit  20  of the present embodiment. Each of the floating regions  21   b  is separated into four vibration regions  22  by forming the separation slits  41 , respectively. 
     In this embodiment, the stress increasing slit  42  is not formed. That is, in the present embodiment, the separation slit  41  is formed so as to reach the corner portion of the floating region  21   b.    
     Further, in the present embodiment, each vibration region  22  in each sensing unit  30  is configured to have a different resonance frequency. In the present embodiment, each vibration region  22  in each sensing unit  30  is formed so that the length between one end portion  22   a  and the other end portion  22   b , that is, the length of the beam is different. Therefore, as shown in  FIG. 10 , the relationship between the frequency and the sensitivity of each sensing unit  30  has a different waveform for each sensing unit  30 . In this embodiment, the configuration of the vibration regions  22  having different resonance frequencies corresponds to the improvement unit. 
     In the present embodiment described above, the piezoelectric element  1  is configured by forming a plurality of sensing units  30 . Since the resonance frequency of each sensing unit  30  is set to a different value, the relationship between the frequency and the sensitivity has a different waveform. Therefore, according to the piezoelectric element  1  of the present embodiment, by appropriately switching the vibration region  22  used for detecting the sound pressure, the frequency at which the sensitivity becomes high can be widened, and for example, the detection sensitivity of the low frequency noise such as road noise can be increased. 
     Further, in the piezoelectric element  1  of the present embodiment, a plurality of sensing units  30  are formed, and the plurality of sensing units  30  are supported by a common support member  10 . Therefore, for example, as compared with the case where a plurality of piezoelectric elements  1  in which one sensing unit  30  is formed are arranged, it becomes easier to narrow the distance between the adjacent sensing units  30 . Here, for example, in the case of a sound wave of 20 kHz, the wavelength is about 17 mm. Therefore, by setting the plurality of sensing units  30  to be supported by the common support member  10  as in the present embodiment, it becomes easy to arrange the sensing units  30  even at intervals sufficiently narrower than the wavelength. Therefore, it is possible to suppress the attenuation of the sound pressure between the sensing units  30 , and it is also possible to suppress the decrease in the detection sensitivity of the sound pressure in the high frequency region where the sound pressure is likely to be attenuated. 
     Further, each vibration region  22  has a different resonance frequency because the length between the one end portion  22   a  and the other end portion  22   b  is different. Here, each vibration region  22  is configured by etching the floating region  21   b  or the like. In this case, the length between the one end portion  22   a  and the other end portion  22   b  can be easily changed by changing the mask for etching. Therefore, according to the present embodiment, it is possible to easily form a plurality of vibration regions  22  having different resonance frequencies while suppressing the manufacturing process from becoming complicated. 
     Eighth Embodiment 
     An eighth embodiment will be described. In this embodiment, a protection film is arranged in the recess portion  10   a  of the support member  10  as compared with the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     First, in the piezoelectric element  1  as described above, the recess portion  10   a  formed in the support member  10  is formed by etching. For example, the recess portion  10   a  is formed by repeating a step of wet etching the support member  10 , a step of forming a protection film for protecting the wet-etched wall surface, a step of further etching the wet-etched wall surface, and the like. In this case, the recess portion  10   a  may tend to have fine irregularities formed on the side surface. Therefore, in the piezoelectric element  1  as described above, the detection sensitivity may decrease due to the generation of turbulent flow due to the fine irregularities formed on the side surface of the recess portion  10   a.    
     Therefore, in the present embodiment, as shown in  FIG. 11 , in the support member  10 , a protection film  100  is formed to embed the fine irregularities in the portion for forming the side surface  10   c  of the recess portion  10   a , and to flatten the exposed surface  100   a  on the opposite side of the recess portion  10   a , which is flatter than the side surface  10   c  of recess portion  10   a . Further, in the present embodiment, the protection film  100  is also formed on a portion on the support member  10  side in each vibration region  22  and a portion facing the adjacent vibration region  22  in each vibration region  22 . 
     In the present embodiment, the protection film  100  is made of a material having water repellency and oil repellency so that foreign substances such as water droplets and oil droplets are hard to adhere to, and is made of, for example, a fluorine-based polymer. Then, the protection film  100  is arranged in a portion including the side surface  10   c  of the recess portion  10   a  by a coating method, a dipping method, a vapor deposition method, or the like. As a result, the protection film  100  is arranged in a state where the exposed surface  100   a  is flatter than the side surface  10   c  of the recess portion  10   a.    
     Further, it may be preferable that the protection film  100  is made of a material that does not easily inhibit the vibration of the vibration region  22 . For example, when the piezoelectric film  50  is made of scandium aluminum nitride, Young&#39;s modulus is about 250 GPa. Therefore, it may be preferable to use a protection film  100  having a Young&#39;s modulus of about 1/500 or less, and it may be preferable to use a protection film having a Young&#39;s modulus of about 0.1 to 0.5 GPa. 
     In the present embodiment described above, the support member  10  is provided with a protection film  100  having an exposed surface  100   a  flatter than the side surface  10   c  of the recess portion  10   a  on the side surface  10   c  of the recess portion  10   a . Therefore, it is possible to suppress the occurrence of turbulent flow in the recess portion  10   a , and it is possible to suppress the deterioration of the detection accuracy. 
     Further, the protection film  100  is also formed in the vibration region  22 , and is made of a material having water repellency and oil repellency. Therefore, it is possible to suppress the adhesion of foreign matter such as water to the protection film  100 , and it is also possible to suppress the generation of turbulent flow due to the foreign matter. 
     Further, the protection film  100  is made of a material that does not easily inhibit the vibration of the vibration region  22 . Therefore, by arranging the protection film  100 , it is possible to suppress that the vibration region  22  is less likely to vibrate, and it is possible to suppress a decrease in detection sensitivity. 
     Ninth Embodiment 
     A ninth embodiment will be described. In this embodiment, the shape of the support member  10  is changed from that of the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, the support substrate  11  is made of a silicon substrate as described above, and has one surface  11   a  on the insulation film  12  side and the other surface  11   b  on the opposite side to the one surface  11   a . As shown in  FIG. 12 , the support substrate  11  has a recessed structure on the side surface  11   c  constituting the recess portion  10   a . In this embodiment, the recessed structure of the side surface  11   c  corresponds to the improvement unit. 
     Specifically, the side surface  11   c  of the support substrate  11  has the following configuration. First, the opening on the opposite side of the insulation film  12  is referred to as the first opening  11   d , and the opening on the insulation film  12  side is referred to as the second opening  11   e . In this case, the side surface  11   c  has a structure such that a first taper portion  11   f  whose side surface is cut from the first opening  11   d  toward the second opening  11   e  and a second taper portion  11   g  whose side surface is cut from the second opening  11   e  toward the first opening  11   d  are connected to each other. That is, the side surface  11   c  of the support substrate  11  has a recess structure in which the portion between the first opening  11   d  and the second opening  11   e  is recessed with respect to the virtual line K 3  connecting the first opening  11   d  and the second opening  11   e.    
     In the present embodiment, the support substrate  11  has one surface  11   a  and the other surface  11   b  as the ( 100 ) surface, and the first opening  11   d  and the second opening  11   e  have a rectangular shape. The first taper portion  11   f  and the second taper portion  11   g  are each ( 111 ) plane. 
     The piezoelectric element  1  of the present embodiment does not have the stress increasing slit  42  formed as in the seventh embodiment. That is, in the present embodiment, the separation slit  41  is formed so as to reach the corner portion of the floating region  21   b . Further, in each embodiment described later, an example in which the stress increasing slit  42  is not formed will be described. Here, also in this embodiment and each of the embodiments described later, the stress increasing slit  42  may be appropriately formed. 
     The above is the configuration of the piezoelectric element  1  in this embodiment. Next, the method of manufacturing the piezoelectric element  1  will be described with reference to  FIGS. 13A and 13B . 
     First, as shown in  FIG. 13A , it is prepared such that the insulation film  12  is arranged on the support substrate  11 , and the piezoelectric film  50 , the electrode film  60 , the first electrode portion  71 , the second electrode portion  72 , and the like are formed on the insulation film  12 . The support substrate  11  is made of a silicon substrate, and one surface  11   a  and the other surface  11   b  are designated as ( 100 ) surfaces. Further, the piezoelectric film  50 , the electrode film  60 , the first electrode portion  71 , the second electrode portion  72 , and the like are configured by appropriately performing a general sputtering method, an etching method, or the like. 
     Then, using a mask (not shown), anisotropic dry etching is performed so as to penetrate the insulation film  12  from the other surface  11   b  of the support substrate  11 . After this step is completed, the side surface  11   c  of the support substrate  11  coincides with the virtual line K 3  connecting the first opening  11   d  and the second opening  11   e.    
     Subsequently, as shown in  FIG. 13B , an anisotropic wet etching is performed on the side surface  11   c  of the support substrate  11  using a mask (not shown) to form a recessed structure on the side surface  11   c  of the support substrate  11 . The support substrate  11  is made of a silicon substrate, and one surface  11   a  and the other surface  11   b  are designated as ( 100 ) surfaces. Therefore, by performing anisotropic wet etching, the first taper portion  11   f  and the second taper portion  11   g  formed of the ( 110 ) surface having the slowest etching rate in the surface orientation of silicon are formed. 
     After that, although not particularly shown, the piezoelectric element  1  shown in  FIG. 12  is manufactured by appropriately forming the separation slit  41 . 
     Here, as shown in  FIG. 14 , the piezoelectric element  1  as described above is accommodated in the casing  130  to form a piezoelectric device. Specifically, the casing  130  includes: a printed circuit board  131  on which the piezoelectric element  1  and the circuit board  120  that performs predetermined signal processing and the like are mounted, and a lid portion  132  that is fixed to the printed circuit board  131  so as to accommodate the piezoelectric element  1  and the circuit board  120 . In this embodiment, the printed circuit board  131  corresponds to the mount member. 
     Although not shown in particular, the printed circuit board  131  has a configuration in which wiring portions, through-hole electrodes, and the like are appropriately formed, and electronic components such as capacitors (not shown) are also mounted as needed. In the piezoelectric element  1 , the other surface  11   b  of the support substrate  11  is mounted on one surface  131   a  of the printed circuit board  131  via a bonding member  2  such as an adhesive. The circuit board  120  is mounted on the one surface  131   a  of the printed circuit board  131  via a bonding member  121  made of a conductive member. The pad portion  72   c  of the piezoelectric element  1  and the circuit board  120  are electrically connected via the bonding wire  133 . The pad portion  71 c of the piezoelectric element  1  is electrically connected to the circuit board  120  via the bonding wire  133  in a cross section different from that of  FIG. 14 . The lid portion  132  is made of metal, plastic, resin, or the like, and is fixed to the printed circuit board  131  via a bonding member such as an adhesive (not shown) so as to accommodate the piezoelectric element  1  and the circuit board  120 . Then, in the present embodiment, a through hole  132   a  is formed in a portion of the lid portion  132  facing the sensing portion  30 . 
     In such a piezoelectric device, the sound pressure is detected by applying the sound pressure (that is, pressure) to the sensing unit  30  through the space between the sensing unit  30  and the lid unit  132  through the through hole  132   a.    
     According to the present embodiment described above, the support substrate  11  has a recessed structure. Therefore, when the piezoelectric device as shown in  FIG. 14  is configured, the detection accuracy can be improved. 
     That is, in the casing  130 , the space between the portion where the through hole  132   a  for introducing the sound pressure is formed and the sensing portion  30  is referred to as the pressure receiving surface space S 1 . Further, the back space S 2  includes a space located on the opposite side of the pressure receiving surface space S 1  with the sensing unit  30  interposed therebetween, and is continuous with the space without passing through the separation slit  41 . The back space S 2  can be said to be a space inside the casing  130  that is different from the pressure receiving surface space S 1 , and can also be said to be a space excluding the pressure receiving surface space S 1 . In other words, the pressure receiving surface space S 1  can be said to be a space that affects pressing the surface on the through hole  132   a  side formed in the casing  130  in the vibration region  22 . It can be said that the back space S 2  affects the pressing of the surface of the vibration region  22  on the side opposite to the through hole  132   a  formed in the casing  130 . 
     In this case, the low frequency roll-off frequency in such a piezoelectric device is defined as 1/(2n×Rg×Cb) where the acoustic resistance (that is, air resistance) due to the separation slit  41  is defined as Rg and the acoustic compliance of the back space S 2  is defined as Cb. Therefore, in order to reduce the low frequency roll-off frequency, the acoustic resistance Rg or the acoustic compliance Cb of the back space S 2  may be increased. 
     Further, in the present embodiment, since the recessed structure is formed in the support substrate  11 , the acoustic compliance can be increased by increasing the space of the back space S 2 . Therefore, in the piezoelectric device of the present embodiment, the detection sensitivity in the low frequency band can be improved by reducing the low frequency roll-off frequency, and the detection accuracy can be improved. 
     Further, the sensitivity in such a piezoelectric device is defined as 1/{(1/Cm)+(1/Cb)}, where Cm is the acoustic compliance of the piezoelectric element  1  and Cb is the acoustic compliance of the back space S 2 . Therefore, in order to increase the sensitivity, the acoustic compliance Cb may be increased, and the acoustic compliance Cb is proportional to the size of the space of the back space S 2 . 
     Further, in the present embodiment, since the support substrate  11  has a recessed structure, the capacity can be increased by increasing the space of the back space S 2 . Therefore, in the piezoelectric device of the present embodiment, the detection accuracy can be improved by increasing the sensitivity. 
     Specifically, as shown in  FIG. 15 , it is possible to suppress a decrease in the sensitivity ratio by increasing the acoustic compliance Cb of the back space S 2 . In this case, the sensitivity ratio sharply decreases when Cb/Cm is 2 or less, but the decrease in the sensitivity ratio can be moderated by forming the recessed structure. That is, forming the recessed structure on the support substrate  11  in this way is particularly effective for a piezoelectric device having a Cb/Cm of 2 or less. Note that  FIG. 15  is based on the case where Cb/Cm is extremely large. 
     Further, the support substrate  11  is configured such that the side surface  11   c  has a first taper portion  11   f  and a second taper portion  11   g . Therefore, for example, the adhesive area between the other surface  11   b  of the support substrate  11  and the printed circuit board  131  can be improved as compared with the case where the side surface  11   c  includes only the second taper portion  11   g . That is, according to the present embodiment, it is possible to improve the detection accuracy while suppressing the deterioration of the adhesiveness to the printed circuit board  131 . The configuration that the side surface  11   c  includes only the second taper portion  11   g  means that the second taper portion  11   g  is formed up to the first opening portion  11   d.    
     Further, the side surface  11   c  of the support substrate  11  is formed by anisotropic wet etching to form a ( 111 ) surface, which suppresses variation in shape. Therefore, it is possible to suppress the variation in the stress generated in the vibration region  22 , and it is possible to suppress the variation in the detection accuracy. 
     In the present embodiment, the first opening  11   d  and the second opening  11   e  have been described as having a rectangular shape, alternatively, the shapes of the first opening  11   d  and the second opening  11   e  may be changed as appropriate. For example, one surface  11   a  and the other surface  11   b  of the support substrate  11  may be a ( 110 ) surface, and the first opening  11   d  and the second opening  11   e  may be octagonal. 
     Tenth Embodiment 
     A tenth embodiment will be described. This embodiment is a modification of the ninth embodiment in which the method of arranging the piezoelectric element  1  in the piezoelectric device is changed. Descriptions of the same configurations and processes as those of the ninth embodiment will not be repeated hereinafter. 
     In the present embodiment, as shown in  FIG. 16 , the piezoelectric element  1  is configured by forming eight pad portions  701  to  708  on the upper piezoelectric film  52 . Specifically, the two pad portions are connection pad portions  701  and  702  that are electrically connected to the sensing unit  30 . The connection pad portions  701  and  702  correspond to the pad portions  71   c  and  72   c  in the first embodiment. The remaining six pad portions are dummy pad portions  703  to  708  that are not electrically connected to the sensing portion  30 . 
     The eight pad portions  701  to  708  are arranged so as to be symmetrical with respect to the center of the piezoelectric element  1  when viewed from the normal direction. That is, the eight pad portions  701  to  708  are arranged symmetrically with respect to the center of the surface parallel to the surface direction of one surface  11   a  of the support substrate  11 . In other words, the eight pad portions  701  to  708  are arranged symmetrically with respect to the center of the plane parallel to the plane direction of the printed circuit board  131  in the piezoelectric element  1  when the piezoelectric element  1  is mounted on the printed circuit board  131 . Further, the connection pad portions  701  and  702  are arranged so as to be close to each other. 
     The above is the configuration of the piezoelectric element  1  in this embodiment. As shown in  FIG. 17 , the piezoelectric device  1  is configured by flip-chip mounting the piezoelectric element  1  on the printed circuit board  131 . Specifically, in the piezoelectric element  1 , each pad portion  701  to  708  is connected to the printed circuit board  131  via a bonding member  3  made of a conductive member such as solder. Further, the piezoelectric element  1  is arranged on the printed circuit board  131  so that the connection pad portions  701  and  702  are located on the circuit board  120  side. The piezoelectric element  1  is electrically connected to the circuit board  120  via the wiring portions  131   c  formed on the printed circuit board  131  in which the connection pad portions  701  and  702  are arranged. 
     The wiring portion  131   c  of the present embodiment is formed so as to connect the pad portions  701  and  702  and the circuit board  120  in the shortest distance. Further, in the present embodiment, all the pad portions  701  to  708  are electrically connected to the printed circuit board  131 . That is, all the pad portions  701  to  708  are prevented from being in a floating state. 
     Further, in the present embodiment, the through hole  131   b  is formed in the printed circuit board  131 . Therefore, in the present embodiment, the sound pressure is detected by applying the sound pressure to the sensing unit  30  through the through hole  131   b . Therefore, in the present embodiment, in the casing  130 , the space between the portion where the through hole  131   b  is formed and the sensing portion  30  provides the pressure receiving surface space S 1 , and the space opposite to the pressure receiving surface space S 1  with the sensing portion  30  interposed therebetween provides the back space S 2 . 
     As described above, the back space S 2  includes a space located on the opposite side of the pressure receiving surface space S 1  with the sensing unit  30  interposed therebetween, and can be said to be a continuous space with the space without passing through the separation slit  41 . Therefore, in the piezoelectric device as shown in  FIG. 17 , the space located on the opposite side of the pressure receiving surface space S 1  with the sensing unit  30  interposed therebetween, and the space including the space around the piezoelectric element  1  continuous with the space without passing through the separation slit  41  provide the back space S 2 . 
     According to the present embodiment described above, it is possible to suppress a decrease in detection accuracy by reducing the parasitic capacitance. 
     That is, as shown in  FIG. 18 , in the piezoelectric device, the total capacitance of the sensing unit  30  is defined as Co and the parasitic capacitance configured between the piezoelectric element  1  and the circuit board  120  is defined as Cp, and the parasitic capacitance Cp is arranged between the circuit board  120  and the capacitance Co. When the parasitic capacitance Cp is large, the ratio of the electric charge flowing from the sensing unit  30  to the parasitic capacitance Cp becomes large, and the detection accuracy decreases. The parasitic capacitance Cp is the sum of the capacitance of the portion connecting the piezoelectric element  1  (that is, the sensing unit  30 ) and the circuit board  120 , the capacitance generated inside the circuit board  120 , and the like. 
     Therefore, the piezoelectric element  1  of the present embodiment is flip-chip mounted on the printed circuit board  131  and connected to the circuit board  120  via the wiring portion  131   c  formed on the printed circuit board  131 . The piezoelectric element  1  is arranged on the printed circuit board  131  so that the connection pad portions  701  and  702  are disposed on the circuit board  120  side. Therefore, as compared with the case where the piezoelectric element  1  and the circuit board  120  are connected by the bonding wire  133 , the wiring portion  131   c  connecting the piezoelectric element  1  and the circuit board  120  can be easily shortened. Therefore, it is possible to suppress a decrease in detection accuracy by reducing the parasitic capacitance Cp. 
     Further, in the present embodiment, the piezoelectric element  1  is flip-chip mounted on the printed circuit board  131  to form a through hole  131   b  in the printed circuit board  131 . Therefore, as compared with the case where the through hole  132   a  is formed in the lid portion  132  as in the ninth embodiment, the pressure receiving surface space S 1  can be made smaller and the air spring in the pressure receiving surface space S 1  can be made larger. Therefore, it is possible to suppress the dispersion of the sound pressure induced from the through hole  132   a , and it is possible to improve the detection accuracy by improving the detection sensitivity. In this embodiment, the through hole  132   a  may be formed in the lid portion  132  as in the ninth embodiment. Even with such a piezoelectric device, it may be difficult to reduce the pressure receiving surface space S 1 , but it is possible to reduce the parasitic capacitance Cp. 
     Further, in the present embodiment, the pad portions  701  to  708  are arranged symmetrically with respect to the center of the piezoelectric element  1 . Therefore, when the piezoelectric element  1  is flip-chip mounted, it is possible to prevent the piezoelectric element  1  from tilting with respect to the printed circuit board  131 . 
     Since the dummy pad portions  703  to  708  are not connected to the sensing portion  30 , they may be bonded to the printed circuit board  131  with an adhesive or the like. Here, by connecting the dummy pad portions  703  to  708  to the printed circuit board  131  with a bonding member  3  such as solder, the dummy pad portions  703  to  708  can also be maintained at a predetermined potential. Therefore, it is possible to suppress the generation of unnecessary noise as compared with the case where the dummy pad portions  703  to  708  are in the floating state. Further, by arranging the same material between each pad portion  701  to  708  and the printed circuit board  131 , the piezoelectric element  1  can be made difficult to tilt. Therefore, it may be preferable to arrange the same bonding member  3  between the dummy pad portions  703  to  708  and the printed circuit board  131 . Further, the piezoelectric element  1  may be prevented from tilting by arranging an underfill material or the like instead of arranging the dummy pad portions  703  to  708 . 
     Further, in the present embodiment, the piezoelectric element  1  can be suppressed from tilting, alternatively, for example, the dummy pad portions  703  to  708  may not be arranged. Even with such a piezoelectric device, the piezoelectric element  1  may tend to tilt, but the parasitic capacitance Rp can be reduced. 
     Eleventh Embodiment 
     An eleventh embodiment will be described. In this embodiment, the shape of the intermediate electrode film  62  is changed from that of the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, as shown in  FIG. 19 , the intermediate electrode film  62  is divided into a first intermediate electrode film  62   a  formed in the first region R 1  and a second intermediate electrode film  62   b  formed in the second region R 2 . The first intermediate electrode film  62   a  is further divided into a plurality of charge regions  620  and dummy regions  624  and  625 . In this embodiment, the plurality of charge regions  620  are three charge regions  621  to  623 . Therefore, in each vibration region  22 , the piezoelectric element  1  is in a state in which a capacitance is configured between the plurality of charge regions  620  and the lower electrode film  61  and the upper electrode film  63  facing the charge regions  620 . 
     Although  FIG. 19  shows the shape of the intermediate electrode film  62  located in the vibration region  22 , the intermediate electrode film  62  is appropriately extended to the support region  21   a  as well. Further, in the present embodiment, the intermediate electrode film  62  divided into a plurality of charge regions  621  to  623  corresponds to the improvement unit. 
     The plurality of charge regions  621  to  623  have the same area. That is, the dummy regions  624  and  625  are configured so that the charge regions  621  to  623  have the same area. Although not shown in particular, the plurality of charge regions  621  to  623  are connected in series to each other via a wiring or the like (not shown) in a portion located on the support region  21   a . Therefore, in each vibration region  22 , a plurality of capacitances are connected in series. On the other hand, the dummy regions  624  and  625  are not connected to the charge regions  621  to  623  and are in a floating state. 
     Although not particularly shown, the lower electrode film  61  and the upper electrode film  63  are formed so as to face the first intermediate electrode film  62   a and the second intermediate electrode film  62   b , respectively. 
     According to the present embodiment described above, the first intermediate electrode film  62   a  is divided into a plurality of charge regions  621  to  623 . The plurality of charge regions  621  to  623  are connected in series. Therefore, in one first region R 1 , a plurality of capacitances are connected in series, and the detection sensitivity can be improved by increasing the capacitances. Further, the plurality of charge regions  621  to  623  have the same area. Therefore, the plurality of capacitances configured in one first region R 1  are equal to each other. Therefore, it is possible to suppress the generation of noise between each capacitance and suppress the deterioration of the detection accuracy. 
     In the present embodiment, an example of dividing the first intermediate electrode film  62   a  into three charge regions  621  to  623  has been described, alternatively, the charge regions  621  to  623  may be two or four or more. 
     Further, in the present embodiment, an example of dividing the first intermediate electrode film  62   a  into a plurality of charge regions  621  to  623  has been described, alternatively, the lower electrode film  61  and the upper electrode film  63  may be divided into a plurality of charge regions and dummy regions. The same effect can be obtained by dividing the lower electrode film  61  and the upper electrode film  63  into a plurality of charge regions and dummy regions. Here, as described above, the intermediate electrode film  62  is arranged between the lower electrode film  61  and the upper electrode film  63 , and when the intermediate electrode film  62  is divided, only the intermediate electrode film  62  needs to be divided. Therefore, the configuration can be simplified. 
     (Modification of Eleventh Embodiment) 
     The modification of the eleventh embodiment will be described below. In the eleventh embodiment, as shown in  FIG. 20 , the charge regions  621  and  623  may not have a rectangular shape. That is, the positions and shapes of the dummy regions  624  and  625  can be appropriately changed as long as the three charge regions  621  to  623  are equal to each other. Further, when the areas of the three charge regions  621  to  623  are equal to each other, the dummy regions  624  and  625  may not be formed. 
     Twelfth Embodiment 
     A twelfth embodiment will be described. This embodiment defines how to partition the first region R 1  and the second region R 2  with respect to the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     First, in the piezoelectric element  1  as described above, when sound pressure is applied to the sensing unit  30 , the stress distribution is as shown in  FIG. 21 . Specifically, the stress may tend to be highest in the vicinity of the central portion on the one end portion  22   a  side, and gradually decreases toward the other end portion  22   b  side. Therefore, in the present embodiment, as shown in  FIG. 22 , the first region R 1  and the second region R 2  are partitioned based on the stress distribution. 
     Hereinafter, a method of partitioning the first region R 1  and the second region R 2  in the present embodiment will be described. The method of partitioning in this embodiment may be particularly effective when the sensitivity output is expressed by voltage. First, in order to improve the sensitivity of the piezoelectric element  1 , the electrostatic energy E generated in the first region R 1  may be increased. Here, as shown in  FIG. 23 , the direction along the one end portion  22   a  in the vibration region  22  is defined as the Y direction, and the direction orthogonal to the Y direction is defined as the X direction. Then, in the minute virtual region M in which the vibration region  22  is divided into a plurality of parts along the X direction, the capacitance of the virtual region M is C, and the average value of the stress generated in the virtual region M is σ. Further, the electrostatic energy E is represented by ½×C×V 2 , where V is the voltage generated in the virtual region M. The generated voltage V is proportional to the generated stress σ. 
     Therefore, in the present embodiment, as shown in  FIGS. 23 and 24 , the area where C×σ 2  of each virtual area M is maximized is calculated, and the boundary line connecting the areas where C×σ 2  of each virtual area M is maximum is used to partition the first region R 1  and the second region R 2 . In this case, as shown in  FIG. 24 , the first region R 1  and the second region R 2  may be partitioned by using the calculation line connecting the calculated values as the boundary line, or he first region R 1  and the second region R 2  may be partitioned by using the approximate line based on the calculation line as the boundary line. 
     In this embodiment, the method of partitioning the first region R 1  and the second region R 2  corresponds to the improvement unit. Further,  FIG. 24  shows an example in which the length of one end portion  22   a  in the vibration region  22  along the Y direction is 850 μm, and the length from one end portion  22   a  to the other end portion  22   b  is 425 μm. In this case, the approximate equation is expressed by the following equation 1. 
         Y =−0.0011 X   2 +1.0387 X −41.657  (Equation 1)
 
     According to the present embodiment described above, the first region R 1  and the second region R 2  are partitioned so that the electrostatic energy E of the first region R 1  is high. Therefore, the detection sensitivity can be improved and the detection accuracy can be improved. 
     (Modified Example of Twelfth Embodiment) 
     The modification of the twelfth embodiment will be described below. The first region R 1  and the second region R 2  may be divided as shown in  FIG. 25 . That is, since the vibration region  22  has a planar triangular shape, the triangle is divided so as to divide one end portion  22   a  into three equal parts, and the first region R 1  and the second region R 2  may be divided by the boundary line connecting each center of gravity position C of the three triangles and both ends of the one end portion  22   a . Even when the first region R 1  and the second region R 2  are partitioned in this way, the first region R 1  and the second region R 2  are partitioned in a region close to the approximate line of the twelfth embodiment to include the region where the electrostatic energy E becomes high. Therefore, the detection sensitivity can be improved and the detection accuracy can be improved. 
     Further, in the twelfth embodiment, the example in which the vibration region  22  has a planar triangular shape has been described, alternatively, the shape of the vibration region  22  can be changed as appropriate. For example, the vibration region  22  may have a planar rectangular shape or a planar fan shape. Even in the vibration region  22  as described above, the same effect as that of the twelfth embodiment can be obtained by partitioning the first region R 1  and the second region R 2  by the same method as that of the twelfth embodiment. 
     Thirteenth Embodiment 
     A thirteenth embodiment will be described. This embodiment defines how to partition the first region R 1  and the second region R 2  with respect to the twelfth embodiment. Descriptions of the same configurations and processes as those of the twelfth embodiment will not be repeated hereinafter. 
     Hereinafter, a method of partitioning the first region R 1  and the second region R 2  in the present embodiment will be described. The method of partitioning in this embodiment may be particularly effective when the sensitivity output is expressed by electric charge. In this embodiment, the area of the virtual area M is defined as S, and the sum of the stresses generated in the virtual area M is defined as σsum, as compared to the twelfth embodiment. Then, ½×C×V 2  is proportional to S×(σsum/S) 2 . That is, ½×C×V 2  is proportional to the generated stress per unit area. Therefore, in the present embodiment, as shown in  FIGS. 26 and 27 , the area where C×σ 2  of each virtual area M is maximized is calculated, and the boundary line connecting the areas where C×σ 2  of each virtual area M is maximum is used to partition the first region R 1  and the second region R 2 . In this case, as shown in  FIG. 27 , the first region R 1  and the second region R 2  may be partitioned by using the calculation line connecting the calculated values as the boundary line, or he first region R 1  and the second region R 2  may be partitioned by using the approximate line based on the calculation line as the boundary line. Further,  FIG. 27  shows an example in which the length of one end portion  22   a  in the vibration region  22  along the Y direction is 850 μm, and the length from one end portion  22   a  to the other end portion  22   b  is 425 μm. In this case, the approximate equation is expressed by the following equation 2. 
       Y=241.11  (Equation 2)
 
     In this way, even when the first region R 1  and the second region R 2  are partitioned based on the generated stress per unit area, the same effect as that of the twelfth embodiment can be obtained. 
     Fourteenth Embodiment 
     A fourteenth embodiment will be described. In this embodiment, each vibration region  22  is connected in parallel to each other to be bent with respect to the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, as shown in  FIG. 28 , the piezoelectric element  1  is in a state where the other end portion  22   b  (that is, the free end) in each vibration region  22  is warped. In the present embodiment, the other end portion  22   b  in each vibration region  22  is in a state the portion  22   b  is disposed along the side opposite to the support substrate  11  side. The amount of warpage in each vibration region  22  is the same, and is configured to warp at least the thickness of the piezoelectric film  50  or more, for example. 
     Further, each vibration region  22  has a bimorph structure in which the lower piezoelectric film  51  and the upper piezoelectric film  52  are stacked as described above, and can be regarded as the circuit configuration shown in  FIG. 29 . When the piezoelectric device is configured, each electrode film  60  in each vibration region  22  is connected in parallel to the circuit board  120 . That is, in the present embodiment, the pressure detection signal is output to the circuit board  120  from each vibration region  22 . In this embodiment, the vibration region  22  has a warpage shape, and the pressure detection signal is output from each vibration region  22  to the circuit board  120 , which corresponds to the improvement unit. 
     The above is the configuration of the piezoelectric element  1  in this embodiment. The piezoelectric element  1  is manufactured as follows. That is, when the piezoelectric film  50  is formed on the insulation film  12  by a sputtering method or the like, a predetermined voltage is applied to the piezoelectric film  50  through the support substrate  11 , and a predetermined residual stress is generated to be applied to the formed piezoelectric film  50 . After that, the piezoelectric element  1  shown in  FIG. 28  is manufactured by forming a separation slit  41  to separate each vibration region  22  and bending the other end portion  22   b  of each vibration region  22  by residual stress. 
     Such a piezoelectric element  1  outputs a pressure detection signal from each vibration region  22  as described above. At this time, for example, as shown in  FIG. 30A , when the sound pressure is applied to each vibration region  22  from a direction corresponding to the normal direction, the deformation of each vibration region  22  becomes the same and the pressure detection signals output from the vibration regions  22  are also equal to each other. On the other hand, for example, as shown in  FIG. 30B , when the sound pressure is applied to each vibration region  22  from a direction intersecting the normal direction, the deformation of each vibration region  22  is different, and the pressure detection signals output from the vibration regions  22  are different. That is, a pressure detection signal corresponding to the direction in which the sound pressure is applied is output from each vibration region  22 . Therefore, in the piezoelectric element  1  of the present embodiment, the direction in which the sound pressure is applied can also be detected. That is, the piezoelectric element  1  of the present embodiment is configured to have directivity. 
     At this time, in the present embodiment, the vibration region  22  is in a warped state. Therefore, in each vibration region  22 , the difference in deformation depending on the direction in which the sound pressure is applied may tend to be large. Therefore, it is possible to improve the sensitivity regarding directivity. 
     According to the present embodiment described above, the piezoelectric element  1  is arranged in a state in which each vibration region  22  is warped. When connected to the circuit board  120 , each vibration region  22  is connected in parallel with the circuit board  120 . Therefore, it is possible to further improve the sensitivity regarding directivity while providing directivity. 
     (Modified Example of Fourteenth Embodiment) 
     The modification of the fourteenth embodiment will be described below. In the fourteenth embodiment, as shown in  FIG. 31 , each vibration region  22  may be connected in parallel to the circuit board  120  and also connected in series with each other. 
     Fifteenth Embodiment 
     A fifteenth embodiment will be described. In this embodiment, a reflection film is formed in the vibration region  22  as compared with the first embodiment. The remaining configuration is similar to that according to the first embodiment and will thus not be described repeatedly. 
     In the present embodiment, as shown in  FIG. 32 , in each vibration region  22 , a reflection film  140  having a higher reflectance than the piezoelectric film  50 , the electrode film  60 , and the pad portions  71   c  and  72   c  is formed on the outermost layer. In the present embodiment, the reflection film  140  is formed on the upper electrode film  63 . In other words, a high reflectance means a low absorption rate. Further, in the present embodiment, the reflection film  140  is made of a material having a Young&#39;s modulus smaller than that of the piezoelectric film  50 , and is made of, for example, an aluminum single-layer film or a multilayer film. The reflection film  140  is formed in the second region R 2 . In this embodiment, the reflection film  140  corresponds to the improvement unit. 
     The above is the configuration of the piezoelectric element  1  in this embodiment. Next, the method of manufacturing the piezoelectric element  1  in the present embodiment will be described. 
     When the piezoelectric element  1  is manufactured, an insulation film  12 , a piezoelectric film  50 , an electrode film  60 , a reflection film  140 , and the like are formed in this order on the support substrate  11  and appropriately patterned. Then, after forming the recess portion  10   a , the separation slit  41  is formed. 
     After that, in the present embodiment, a determination of a good or bad quality is made. Specifically, as shown in  FIG. 33 , a detection device  150  including a laser light source  151  for irradiating the laser beam L and a detector  152  for detecting the intensity of the received laser beam L is prepared. The detector  152  has a control unit (not shown) that makes a determination based on a threshold value, and the control unit includes a microcomputer and the like having a CPU and a memory equipped with a non-transitory tangible storage medium such as a ROM, a RAM, a flash memory, and a HDD. CPU is an abbreviation for Central Processing Unit, ROM is an abbreviation for Read Only Memory, RAM is an abbreviation for Random Access Memory, and HDD is an abbreviation for Hard Disk Drive. The storage medium such as the ROM is a non-transitory tangible storage medium. 
     In the memory, the intensity when the laser beam L is received under a condition that the vibration region  22  is not warped is stored as a threshold value. Then, the control unit compares the intensity of the laser beam L received by the detector  152  with the threshold value and makes a determination of a good or bad quality. 
     Specifically, the surface along the normal direction with respect to the reflection film  140  arranged in the vibration region  22  is set as the reference surface T, and the laser beam L is irradiated to the reflection film  140  from the direction inclined with respect to the reference surface T. Then, the laser beam L reflected is detected by the detector  152 . After that, the detector  152  compares the intensity of the detected laser beam L with the threshold value to make a determination of a good or bad quality. For example, when the intensity of the detected laser beam L is less than 50% of the threshold value, the detector  152  makes a quality determination to determine that the state of the vibration region  22  is abnormal. In this case, for example, as shown in  FIG. 34 , even when the warp of the vibration region  22  is large and the laser beam L is not detected by the detector  152 , it is determined that the state of the vibration region  22  is abnormal. It may be preferable to select a laser beam L having the largest reflectance. For example, when the reflection film  140  is made of aluminum, it may be preferable to use a wavelength in the visible light region of 1 μm or less. When the reflection film  140  is made of another metal film, it may be preferable to use a wavelength in the infrared region. 
     According to the present embodiment described above, since the reflection film  140  is arranged in the vibration region  22 , it is possible to determine the quality of the vibration region  22 . Therefore, it is possible to manufacture the piezoelectric element  1  that can suppress the deterioration of the detection accuracy. Further, in the present embodiment, since the quality determination is performed by irradiating the reflection film  140  with the laser beam L, the quality determination can be performed without contact. 
     Further, the reflection film  140  is made of a material having a Young&#39;s modulus smaller than that of the piezoelectric film  50 . Therefore, it is possible to suppress the reflection film  140  from inhibiting the deformation of the piezoelectric film  50 , and it is possible to suppress the deterioration of the detection accuracy. 
     Further, the reflection film  140  is arranged in the second region R 2 . Therefore, it is possible to suppress the influence of the reflection film  140  on the first region R 1  in the vibration region  22  where the stress may tend to be large. 
     This embodiment can also be applied to the fourteenth embodiment. In this case, the threshold value used for the determination may be set to the strength when the amount of warpage of the vibration region  22  becomes a predetermined value. 
     Sixteenth Embodiment 
     A sixteenth embodiment will be described. In this embodiment, self-diagnosis is performed when the piezoelectric device is configured as in the ninth embodiment. Descriptions of the same configurations and processes as those of the ninth embodiment will not be repeated hereinafter. 
     In the piezoelectric device of the present embodiment, as shown in  FIG. 35 , in the piezoelectric element  1 , the other surface  11   b  of the support substrate  11  is mounted on one surface  131   a  of the printed circuit board  131  via the bonding member  2 . Then, in the present embodiment, the through hole  131   b  is formed in the printed circuit board  131  as in the piezoelectric device described with reference to  FIG. 17  of the tenth embodiment. Therefore, in the present embodiment, the sound pressure is detected by applying the sound pressure to the sensing unit  30  through the through hole  131   b . Then, in the present embodiment, the space between the portion where the through hole  131   b  is formed and the sensing portion  30  in the casing  130  is the pressure receiving surface space S 1 . Further, the back space S 2  includes a space located on the opposite side of the pressure receiving surface space S 1  with the sensing unit  30  interposed therebetween, and is continuous with the space without passing through the separation slit  41 . 
     In this embodiment, the piezoelectric device configured as shown in  FIG. 35  will be described as an example, alternatively, the following configuration may also be applied to the piezoelectric device configured as in the ninth embodiment and the tenth embodiment. 
     As shown in  FIGS. 36 and 37 , the piezoelectric element  1  of the present embodiment has first to fifth pad portions  701  to  705  that are electrically connected to each vibration region  22 . The first to fifth pad portions  701  to  705  correspond to the pad portions  71   c  and  72   c  in the first embodiment. Then, in the piezoelectric element  1 , each vibration region  22  is connected in parallel to the circuit board  120  via the first to fifth pad portions  701  to  705 , as in  FIG. 31  described in the modified example of the fourteenth embodiment, and is connected in series with each other. 
     The circuit board  120  performs predetermined signal processing, and in the present embodiment, the control unit  120   a  is arranged. The control unit  120   a  may be arranged separately from the circuit board  120 . 
     Similar to the control unit of the fifteenth embodiment, the control unit  120   a  is a microcomputer or the like including a CPU, a memory having a non-transitory tangible storage medium such as a ROM, a RAM, a flash memory, and an HDD. Then, the control unit  120   a  of the present embodiment performs a self-diagnosis of the piezoelectric device. 
     Specifically, the control unit  120   a  of the present embodiment determines the abnormality of the piezoelectric element  1 . Specifically, the control unit  120   a  vibrates each vibration region  22  by applying a predetermined voltage between the first pad unit  701  and the fifth pad unit  705  for the abnormality determination signal. More specifically, the control unit  120   a  normally vibrates each vibration region  22  at a frequency of sound pressure that can be applied to the vibration region  22  in actual sound pressure detection. In the present embodiment, as shown in  FIG. 38 , the vibration region  22  is formed so that the resonance frequency is 13 kHz, and it is assumed that the frequency of the sound pressure that can be applied to the piezoelectric element  1  is several kHz. 
     Therefore, the control unit  120   a  applies a predetermined voltage between the first pad unit  701  and the fifth pad unit  705  so that each vibration region  22  normally vibrates at several kHz. In this embodiment, it is assumed that the resonance frequency is 13 kHz and the frequency of the sound pressure that can be applied to the piezoelectric element  1  is several kHz. Therefore, the control unit  120   a  applies a predetermined voltage between the first pad unit  701  and the fifth pad unit  705  so as to normally vibrate at a frequency lower than the resonance frequency. 
     As a result, when each vibration region  22  is normal, a partial voltage corresponding to a predetermined voltage is applied from the second to fourth pad portions  702  to  704 . On the other hand, when an abnormality such as a short circuit occurs between the vibration regions  22 , the voltage output from the second to fourth pad portions  702  to  704  changes. Further, when an abnormality such as a disconnection occurs between the vibration regions  22 , no voltage is output from the second to fourth pad portions  702  to  704 . Therefore, the control unit  120   a  compares the voltages of the second to fourth pad units  702  to  704  with a predetermined threshold range to determine the abnormality. 
     Further, the control unit  120   a  of the present embodiment performs a self-diagnosis for estimating the pressure in the back space S 2 . Then, the control unit  120   a  corrects the pressure detection signal output from the piezoelectric element  1  based on the estimated pressure. 
     That is, in the above-mentioned piezoelectric device, the way of vibration of the vibration region  22  changes due to the fluctuation of the pressure in the back space S 2 . Specifically, the pressure in the back space S 2  varies depending on the ambient temperature, humidity, altitude (i.e., location) and the like to be used. The higher the pressure in the back space S 2 , the more difficult it is for the vibration region  22  to vibrate, and the lower the pressure in the back space S 2 , the easier it is to vibrate. That is, in the above-mentioned piezoelectric device, the detection sensitivity may change depending on the usage environment. Therefore, in the present embodiment, the pressure in the back space S 2  is estimated, and the pressure detection signal output from the piezoelectric element  1  is corrected based on the estimated pressure. 
     Specifically, the control unit  120   a  applies a pressure estimation signal to the piezoelectric element  1  to estimate and vibrate each vibration region  22  in order to estimate the pressure in the back space S 2 . In this case, the control unit  120   a  vibrates each vibration region  22  at the maximum vibration at the resonance frequency so that the vibration of each vibration region  22  becomes large. Then, the control unit  120   a  executes the following operations based on the difference between the voltage of the second to fourth pad units  702  to  704  when the pressure estimation signal is applied and the voltage of the second to fourth pad units  702  to  704  when the abnormality determination signal is applied. That is, the control unit  120   a  calculates the Q value as the resonance magnification and performs self-diagnosis to estimate the pressure in the back space S 2  from the Q value. 
     When calculating the Q value, the specific calculation method may be changed as appropriate. For example, based on one of the differences between the voltage of the second to fourth pad portions  702  to  704  when the pressure estimation signal is applied and the voltage of the second to fourth pad portions  702  to  704  when the abnormality determination signal is applied, the Q value may be calculated. Further, the Q value may be calculated based on the average of the differences between the voltage of the second to fourth pad portions  702  to  704  when the pressure estimation signal is applied and the voltage of the second to fourth pad portions  702  to  704  when the abnormality determination signal is applied. 
     Then, when detecting the sound pressure, the control unit  120   a  corrects the pressure detection signal output from the piezoelectric element  1  based on the estimated pressure in the back space S 2 . Specifically, the control unit  120   a  multiplies the pressure detection signal by a correction coefficient corresponding to the pressure in the back space S 2 , based on the case where the pressure in the back space S 2  is atmospheric pressure, as a reference. For example, when the pressure in the back space S 2  is larger than the atmospheric pressure, the vibration region  22  is less likely to vibrate, so that the control unit  120   a  corrects by multiplying the pressure detection signal by a value larger than 1 as a correction coefficient. On the other hand, when the pressure in the back space S 2  is smaller than the atmospheric pressure, the vibration region  22  tends to vibrate easily, so that the control unit  120   a  corrects by multiplying the pressure detection signal by a value smaller than 1 as a correction coefficient. As a result, the pressure detection signal becomes a value corresponding to the pressure in the back space S 2  (that is, the ease of vibration of the vibration region  22 ). The correction coefficient is derived in advance by an experiment or the like, and is stored in the control unit  120   a  in association with the pressure in the back space S 2 . 
     According to the present embodiment described above, since the self-diagnosis is performed, the detection accuracy can be improved. Specifically, since the abnormality determination of the piezoelectric element  1  is performed, the detection accuracy can be improved by stopping the detection of the sound pressure when there is an abnormality. Further, since the pressure in the back space S 2  is estimated, the detection accuracy can be improved by performing the correction based on the estimated pressure. 
     (Modified Example of Sixteenth Embodiment) 
     The modification of the sixteenth embodiment will be described below. In the sixteenth embodiment, the control unit  120   a  may perform only one of the abnormality determination and the estimation of the pressure in the back space S 2  as the self-diagnosis. Further, in the sixteenth embodiment, when estimating the pressure of the back space S 2 , the control unit  120   a  does not have to vibrate each vibration region  22  at the resonance frequency as long as the vibration is different from the normal vibration. Here, by vibrating each vibration region  22  at the maximum vibration at the resonance frequency, the difference from the normal vibration can be increased, and the estimation accuracy of the pressure in the back space S 2  can be improved. 
     Seventeenth Embodiment 
     A seventeenth embodiment will be described. This embodiment defines the film thicknesses of the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  with respect to the first embodiment. Descriptions of the same configurations and processes as those of the ninth embodiment will not be repeated hereinafter. 
     As shown in  FIG. 39 , the piezoelectric element  1  in the present embodiment has the same configuration as that of the first embodiment. Here, in the present embodiment, the stress increasing slit  42  is not formed in the piezoelectric element  1 . 
     In the present embodiment, the film thickness of the lower electrode film  61  and the film thickness of the upper electrode film  63  are thinner than the film thickness of the intermediate electrode film  62 . For example, in the present embodiment, the film thickness of the lower electrode film  61  and the film thickness of the upper electrode film  63  are 25 nm, and the film thickness of the intermediate electrode film  62  is 100 nm. The film thickness of the lower piezoelectric film  51  between the lower electrode film  61  and the intermediate electrode film  62  and the film thickness of the upper layer piezoelectric film  52  between the intermediate electrode film  62  and the upper electrode film  63  are the same in the first implementations described above, and for example, 50 μm. 
     Further, the lower electrode film  61  and the upper electrode film  63  have the same rigidity. In the present embodiment, the lower electrode film  61  and the upper electrode film  63  are made of the same material, and the rigidity is made equal by making the film thickness equal. 
     In this embodiment, each of the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  arranged in the first region R 1  and the second region R 2  has the above configuration. Here, at least portions of the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  formed in the first region R 1  may have the above described configuration. Further, in the present embodiment, the configurations of the lower electrode film  61 , the intermediate electrode film  62 , and the upper electrode film  63  correspond to the improvement unit. 
     As described above, in the present embodiment, the film thickness of the lower electrode film  61  and the film thickness of the upper electrode film  63  are thinner than the film thickness of the intermediate electrode film  62 , and the rigidity of the lower electrode film  61  and the rigidity of the upper electrode film  63  are equalized. Therefore, the detection accuracy can be improved by improving the sensitivity. 
     That is, in each vibration region  22 , the one end portion  22   a  is a fixed end and the other end portion  22   b  is a free end as described above. Therefore, as shown in  FIG. 40 , for example, in each vibration region  22 , when a load (that is, sound pressure) is applied from the upper electrode film  63  side to the lower electrode film  61  side, the compression stress is applied to the lower piezoelectric film  51  side, and the tensile stress is applied to the upper piezoelectric film  52  side. The center portion of each vibration region  22  in the thickness direction is a neutral surface Cs to which neither the compression stress nor the tensile stress is applied. 
     In this case, as shown in  FIGS. 41 and 42 , the compression stress applied to the lower piezoelectric film  51  increases as the distance from the neutral plane Cs increases. Similarly, the tensile stress applied to the upper piezoelectric film  52  increases as the distance from the neutral surface Cs increases. Therefore, the lower piezoelectric film  51  and the upper piezoelectric film  52  are formed so as to include a position away from the neutral surface Cs, so that a portion having a large stress can be included. That is, the lower piezoelectric film  51  and the upper piezoelectric film  52  are formed so as to include a position away from the neutral surface Cs, so that a portion in which an electric charge is likely to be generated can be included. Here, when the film thickness of the lower piezoelectric film  51  is simply increased to include a position away from the neutral surface Cs, the distance between the lower electrode film  61  and the intermediate electrode film  62  becomes wider, so that the capacitance between the lower electrode film  61  and the intermediate electrode film  62  is reduced. Similarly, when the film thickness of the upper piezoelectric film  52  is simply increased to include a position away from the neutral surface Cs, the distance between the intermediate electrode film  62  and the upper electrode film  63  becomes wider, so that the capacitance between the intermediate electrode film  62  and the upper electrode film  63  is reduced. 
     Therefore, as in the present embodiment, by making the lower electrode film  61  thinner while making the intermediate electrode film  62  thicker, the lower piezoelectric film  51  can be formed to include a portion away from the neutral surface Cs without changing the film thickness of the lower piezoelectric film  51 . Similarly, by making the upper electrode film  63  thinner while making the intermediate electrode film  62  thicker, the upper piezoelectric film  52  can be formed to include a portion away from the neutral surface Cs without changing the film thickness of the upper piezoelectric film  52 . Therefore, the electric charge generated in the lower piezoelectric film  51  and the upper piezoelectric film  52  can be increased, and the detection accuracy can be improved by improving the sensitivity. 
     Further, the lower electrode film  61  and the upper electrode film  63  are made of molybdenum, copper, platinum, platinum, titanium or the like, and have Young&#39;s modulus larger than that of the scandium aluminum nitride and the like constituting the lower piezoelectric film  51  and the upper piezoelectric film  52 . Therefore, the thicker the lower electrode film  61  and the upper electrode film  63 , the more easily the deformation of the lower piezoelectric film  51  and the upper piezoelectric film  52  is inhibited. Therefore, as in the present embodiment, by making the film thicknesses of the lower electrode film  61  and the upper electrode film  63  thinner than the film thickness of the intermediate electrode film  62 , it is possible to suppress the inhibition of deformation of the lower piezoelectric film  51  and the upper piezoelectric film  52 , compared with a case where the film thicknesses of the lower electrode film  61  and the upper electrode film  63  are equal to the film thickness of the intermediate electrode film  62 . Therefore, it is possible to suppress the decrease in sensitivity and improve the detection accuracy. 
     Further, the lower electrode film  61  and the upper electrode film  63  have the same rigidity. Therefore, it is possible to prevent the lower piezoelectric film  51  and the upper piezoelectric film  52  from being deformed differently when sound pressure is applied, and it is possible to suppress the overall deformation from being deteriorated. 
     (Modified Example of Seventeenth Embodiment) 
     The modification of the seventeenth embodiment will be described below. In the seventeenth embodiment, the lower electrode film  61  and the upper electrode film  63  may be configured as follows as long as the film thickness thereof is thinner than the intermediate electrode film  62 , and the rigidity is equal to that of the intermediate electrode film  62 . That is, the lower electrode film  61  and the upper electrode film  63  may be made of different materials and may be configured so that the rigidity becomes equal by adjusting the film thickness. 
     Eighteenth Embodiment 
     An eighteenth embodiment will be described. This embodiment defines the number of charge regions  620  based on the parasitic capacitance Cp with respect to the eleventh embodiment. Descriptions of the same configurations and processes as those of the eleventh embodiment will not be repeated hereinafter. 
     In the piezoelectric element  1  of the present embodiment, as in the eleventh embodiment, the first intermediate electrode film  62   a  is divided into a plurality of charge regions  620 , and each charge region  620  is connected in series. Further, each charge region  620  has the same area and is connected in series with each other. 
     Here, the sensitivity (that is, the output voltage) of the piezoelectric element  1  is defined as ΔV, the total capacitance of the sensing unit  30  is defined as Co, the parasitic capacitance is defined as Cp, and the acoustic-electricity conversion coefficient when converting the sound pressure into a voltage is defined as ┌, and the number of charge regions  620  is defined ss n. The following equation 3 is established. 
       Δ V =┌×{Co/(Co+Cp)}  (Equation 3)
 
     The parasitic capacitance Cp is the sum of the capacitance of the portion connecting the piezoelectric element  1  (that is, the sensing unit  30 ) and the circuit board  120 , the capacitance generated inside the circuit board  120 , and the like. Further, the capacitance Co of the sensing unit  30  is proportional to 1/n 2  because each charge region  620  is connected in series. 
     Therefore, as shown in  FIGS. 43A to 43C , the length from the one end portion  22   a  to the other end portion  22   b  in the vibration region  22  is defined as the length d, the sensitivity is changed according to the length d, the number of charge regions  620 , and the parasitic capacitance Cp. At present, it may be desired to increase the sensitivity, and the range from the maximum sensitivity to about 90% may be practical. Therefore, in the present embodiment, the number of charge regions  620  is set so as to set the maximum sensitivity to be 90% or more. For example, as shown in  FIG. 43B , when the length d from one end portion  22   a  to the other end portion  22   b  in the vibration region  22  is 490 μm and the parasitic capacitance Cp is 2.0×10 −12  F, and the number of the charge regions  620  is 8 to 16, the sensitivity can be lowered. That is, the sensitivity can be lowered by setting the number of the charge regions  620  in each vibration region  22  in a range between 2 and 4. 
     In the present embodiment described above, the number of charge regions  620  is defined to set the maximum sensitivity to be 90% or more. Therefore, the detection accuracy can be improved by improving the sensitivity. 
     Nineteenth Embodiment 
     A nineteenth embodiment will be described. In this embodiment, the acoustic compliance Cf of the pressure receiving surface space S 1 , the acoustic compliance Cb of the back space S 2 , the acoustic resistance Rg of the separation slit  41 , and the like are adjusted when the piezoelectric device is configured as in the ninth embodiment. Descriptions of the same configurations and processes as those of the ninth embodiment will not be repeated hereinafter. 
     As shown in  FIG. 44 , the piezoelectric device of the present embodiment is configured such that the other surface  11   b  of the support substrate  11  in the piezoelectric element  1  is mounted on one surface  131   a  of the printed circuit board  131  via the bonding member  2 . Then, in the present embodiment, the through hole  131   b  is formed in the printed circuit board  131  as in the piezoelectric device described with reference to  FIG. 17  of the tenth embodiment. Therefore, in the present embodiment, the sound pressure is detected by applying the sound pressure to the sensing unit  30  through the through hole  131   b . Then, in the present embodiment, the space between the portion where the through hole  131   b  is formed and the sensing portion  30  in the casing  130  is the pressure receiving surface space S 1 . Further, the back space S 2  includes a space located on the opposite side of the pressure receiving surface space S 1  with the sensing unit  30  interposed therebetween, and is continuous with the space without passing through the separation slit  41 . 
     In this embodiment, the recessed structure is not formed on the support substrate  11  of the piezoelectric element  1 , but the recessed structure may be formed on the support substrate  11 . Further, although the piezoelectric element  1  of the present embodiment does not have the stress increasing slit  42  as in the first embodiment, the stress increasing slit  42  or the like may be formed. Hereinafter, the piezoelectric device configured as shown in  FIG. 44  will be described as an example, but the following configuration can also be applied to the piezoelectric device using the piezoelectric element  1  of each of the above embodiments. 
     First, the sensitivity of the piezoelectric device depends on the low frequency roll-off frequency, the resonance frequency of the piezoelectric element  1 , and the Helmholtz frequency. Specifically, the low frequency roll-off frequency is defined as fr, and the low frequency roll-off frequency fr is expressed by the following equation 4. The resonance frequency of the piezoelectric element  1  is defined as fmb, the resonance frequency fmb is expressed by the following equation 5. The Helmholtz frequency is defined as fh, the Helmholtz frequency fh is expressed by the following equation 6. 
     
       
         
           
             
               
                 
                   fr 
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       π 
                       × 
                       Rg 
                       × 
                       Cb 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ) 
                 
               
             
             
               
                 
                   fmb 
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       π 
                       × 
                       
                         
                           { 
                           
                             Lm 
                             × 
                             
                               1 
                               
                                 ( 
                                 
                                   
                                     1 
                                     Cb 
                                   
                                   + 
                                   
                                     1 
                                     Cm 
                                   
                                 
                                 ) 
                               
                             
                           
                           } 
                         
                         0.5 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ) 
                 
               
             
             
               
                 
                   fh 
                   = 
                   
                     1 
                     
                       2 
                       ⁢ 
                       π 
                       × 
                       
                         
                           ( 
                           
                             Lf 
                             × 
                             Cf 
                           
                           ) 
                         
                         0.5 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
     In addition, Lm in the equation 5 is a constant proportional to the total mass in each vibration region  22  of the piezoelectric element  1 . Lf in Equation 6 is the inertance of the through hole  132   a.    
     The inertance Lf of the through hole  132   a  is represented by the following equation 7. Further, the acoustic compliance Cf of the pressure receiving surface space S 1  is expressed by the following equation 8. The acoustic compliance Cb of the back space S 2  is expressed by the following equation 9. The acoustic resistance Rg of the separation slit  41  is expressed by the following equation 10. 
     
       
         
           
             
               
                 
                   Lf 
                   = 
                   
                     ρ0 
                     × 
                     
                       
                         ( 
                         
                           
                             L 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           + 
                           
                             1.7 
                             × 
                             a 
                           
                         
                         ) 
                       
                       
                         ( 
                         
                           π 
                           × 
                           
                             a 
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ) 
                 
               
             
             
               
                 
                   Cf 
                   = 
                   
                     Vf 
                     
                       ρ0 
                       × 
                       
                         c 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ) 
                 
               
             
             
               
                 
                   Cb 
                   = 
                   
                     Vb 
                     
                       ρ0 
                       × 
                       
                         c 
                         2 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ) 
                 
               
             
             
               
                 
                   Rg 
                   = 
                   
                     
                       3 
                       × 
                       μ 
                       × 
                       h 
                     
                     
                       
                         2 
                       
                       × 
                       
                         g 
                         3 
                       
                       × 
                       L 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ) 
                 
               
             
           
         
       
     
     In Equations 7 to 10, ρ0 is the air density, a is the radius of the through hole  132   a , and L 1  is the thickness of the printed circuit board  131  (that is, the length of the through hole  132   a ). Further, Vf is the volume of the pressure receiving surface space S 1 , Vb is the volume of the back space S 2 , and c is the speed of sound. μ is the frictional resistance of air, h is the thickness of the vibration region  22 , g is the width of the separation slit  41 , and L 2  is the length of the separation slit  41  in each vibration region  22 . The width g of the separation slit  41  is the distance between the portions where the side surfaces of the vibration regions  22  face each other, and is, for example, the width of the portions shown in  FIG. 36 . The length L 2  of the separation slit  41  is, for example, the length of the portion shown in  FIG. 36 . 
     As shown in  FIG. 45 , the piezoelectric device of the present embodiment is configured such that the frequency increases in the order of the low frequency roll-off frequency fr, the resonance frequency fmb of the piezoelectric element  1 , and the Helmholtz frequency fh. Specifically, each frequency has a value based on the acoustic compliance Cf of the pressure receiving surface space S 1 , the acoustic compliance Cb of the back space S 2 , and the acoustic resistance Rg of the separation slit  41 , as shown in the above equations 4 to 6. Therefore, the values of each frequency are adjusted by adjusting the acoustic compliance Cf of the pressure receiving surface space S 1 , the acoustic compliance Cb of the back space S 2 , and the acoustic resistance Rg of the separation slit  41 . 
     More specifically, the low frequency roll-off frequency fr becomes smaller as the acoustic compliance Cb and the acoustic resistance Rg are increased. The resonance frequency fmb of the piezoelectric element  1  becomes smaller as the acoustic compliance Cm and the acoustic compliance Cb are increased. In the present embodiment, the resonance frequency fmb of the piezoelectric element  1  is adjusted by adjusting the acoustic compliance Cb. The Helmholtz frequency fh becomes smaller as the inertance Lf and the acoustic compliance Cf are increased. In this embodiment, the Helmholtz frequency fh is adjusted by adjusting the acoustic compliance Cf. As a result, the piezoelectric device is generally used for detecting the sound pressure of the frequency between the low frequency roll-off frequency fr and the resonance frequency fmb, so that the frequency at which sensitivity can be maintained is increased, compared with the case where the Helmholtz frequency fh is made smaller than the resonance frequency fmb of the piezoelectric element  1 . 
     Further, in the present embodiment, the acoustic compliance Cf, the acoustic compliance Cb, and the acoustic resistance Rg are adjusted so that the low frequency roll-off frequency is 20 Hz or less and the Helmholtz frequency is 20 kHz. That is, in the present embodiment, the low frequency roll-off frequency fr and the Helmholtz frequency fh are set to values outside the audible range. Therefore, in the piezoelectric device of the present embodiment, it is possible to increase the frequency at which the sensitivity in the audible range can be maintained. The resonance frequency fmb of the piezoelectric element  1  is, for example, 13 kHz. 
     Here, in order to reduce the low frequency roll-off frequency to 20 Hz or less, the following may be performed. That is, the acoustic resistance Rg that affects the low frequency roll-off frequency fr is expressed by the above equation 10. Therefore, in order to set the low frequency roll-off frequency to 20 Hz or less, the above equation 4 may be set to 20 Hz or less, and the acoustic resistance Rg should satisfy Rg≥1/(40n×Cb). Therefore, the width g of the separation slit  41  may be formed so as to satisfy the following equation  11 . 
     
       
         
           
             
               
                 
                   
                     g 
                     3 
                   
                   ≦ 
                   
                     
                       3 
                       × 
                       μ 
                       × 
                       h 
                       × 
                       40 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       × 
                       Cb 
                     
                     
                       
                         
                           2 
                         
                         · 
                         L 
                       
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     11 
                   
                   ) 
                 
               
             
           
         
       
     
     Then, the acoustic resistance Rg required to set the low frequency roll-off frequency fr to 20 Hz or less is shown in  FIG. 46  in relation to the acoustic compliance Cb of the back space S 2 . In this case, the relationship between the realistic thickness h of the vibration region  22  and the length L 2  of the separation slit  41  and the width g of the separation slit  41  is shown in  FIG. 47 . Therefore, as shown in  FIG. 47 , when the width g of the separation slit  41  is 3 μm or less, the low frequency roll-off frequency can be set to 20 Hz or less. 
     Further, in the above-mentioned piezoelectric device, when sound pressure is introduced into the pressure receiving surface space S 1 , the larger the volume of the back space S 2 , the higher the sensitivity may tend to be, and the SN ratio, which is the ratio of the signal and noise, may tend to increase. In this case, as shown in  FIG. 48 , the signal intensity ratio (dB) is − 3 dB or less, which is generally noisy with respect to the reference, when Cb/Cf, which is the ratio of the acoustic compliance Cb to the acoustic compliance Cf, is 14 or less. The reference here is based on the SN ratio when the signal is the largest. Further, −3 dB or less with respect to the reference is a range in which it is difficult for human hearing to perceive a change. Therefore, in this embodiment, Cb/Cf is set to 14 or less. This makes it possible to reduce noise. 
     Further, in the piezoelectric device as described above, the detection is performed by vibrating the vibration region  22 . Further, in the above-mentioned piezoelectric device, even in a state where sound pressure is not introduced into the pressure receiving surface space S 1 , air molecules collide with the vibration region  22  from the pressure receiving surface space S 1  side and the back space S 2  side due to Brownian motion. In this case, if the collision of the air molecules from the pressure receiving surface space S 1  side and the collision of the air molecules from the back space S 2  side are different, the vibration region  22  vibrates unnecessarily and causes noise. 
     Therefore, in order to reduce noise related to unnecessary vibration, it may be preferable to make the volume of the pressure receiving surface space S 1  equal to the volume of the back space S 2 . This makes it possible to reduce noise related to unnecessary vibration. 
     As described above, in the present embodiment, the acoustic compliance Cf, the acoustic compliance Cb, and the acoustic resistance Rg are adjusted so that the low frequency roll-off frequency fr, the resonance frequency fmb of the piezoelectric element  1 , and the Helmholtz frequency fh increase in this order. Therefore, the frequency at which the sensitivity can be maintained can be increased as compared with the case where the Helmholtz frequency fh is smaller than the resonance frequency fmb of the piezoelectric element  1 . 
     Further, in the present embodiment, the low frequency roll-off frequency fr is set to 20 Hz or less, and the Helmholtz frequency fh is set to 20 kHz or more. Therefore, the sensitivity in the audible range can be maintained. In this case, since the width g of the separation slit  41  is 3 μm or less, the low frequency roll-off frequency fr can be set to 20 Hz or less. 
     Further, in the present embodiment, the ratio of Cb/Cf is set to 14 or less. Therefore, noise can be reduced. 
     Further, in the present embodiment, by making the volume of the pressure receiving surface space S 1  equal to the volume of the back space S 2 , it is possible to reduce noise related to unnecessary vibration. 
     (Other Embodiments) 
     Although the present disclosure has been described in accordance with embodiments, it is understood that the present disclosure is not limited to such embodiments or structures. The present disclosure encompasses various modifications and variations within the scope of equivalents. In addition, various combinations and configurations, as well as other combinations and configurations that include only one element, more, or less, are within the scope and spirit of the present disclosure. 
     For example, in each of the above embodiments, the vibration unit  20  may be configured to have at least one layer of the piezoelectric film  50  and at least one layer of the electrode film  60 . 
     Further, in each of the above embodiments, the floating region  21   b  of the vibration unit  20  may be divided into three or less vibrating regions  22  instead of being divided into four vibrating regions  22 . Alternatively, the region  21   b  may be divided into five or more vibration regions  22 . 
     Then, in each of the above embodiments, the sensing unit  30  may include only one vibration region  22 . That is, for example, in the first embodiment, the four sensing units  30  may be configured by the four vibration regions  22  provided by one floating region  21   b . In this case, in the seventh embodiment, the configuration has only one floating region  21   b , and a plurality of vibration regions  22  are configured in the floating region  21   b , so that the resonance frequencies of the respective vibration regions  22  are different. 
     Further, in the first embodiment, the separation slit  41  may be formed so as to reach the corner portion of the floating region  21   b  without forming the stress increasing slit  42 , and the corner portion C 1  may be configured by recessing the separation slit  41  in the first region R 1  inward. 
     Further, in the third embodiment, the one end portion  22   a  of the vibration region  22  may have a shape having a portion expanding on the opposite side to the other end portion  22   b  side with respect to the virtual line K 1 , and may be formed not to have an arc shape. Similarly, in the fourth embodiment, the one end portion  22   a  of the vibration region  22  may have a shape having a portion expanding on the opposite side to the other end portion  22   b  side with respect to the virtual line K 2 , and may be formed not to have an arc shape. 
     Further, in the fifth embodiment, the hard film  82  may be uniformly formed between the first region R 1  side and the other end portion  22   b  side in the second region R 2 , or may be formed more densely in the first region R 1  side than the other end portion  22   b  side. Further, in the fifth embodiment, the hole portion  81  in which the hard film  82  is embedded may not be formed so as to penetrate the upper electrode film  63 , the upper piezoelectric film  52 , the intermediate electrode film  62 , and the lower piezoelectric film  51 . For example, the hole portion  81  may be formed so as to penetrate only the upper electrode film  63  and the upper piezoelectric film  52 . That is, the depth of the hard film  82  formed in the second region R 2  may be appropriately changed. Further, in the fifth embodiment, the hard film  82  may not be made of the same material as the first and second electrode portions  71  and  72 , and the material thereof may be not particularly limited as long as the material has a Young&#39;s modulus higher than that of the piezoelectric film  50 . 
     Further, in the sixth embodiment, the stress increasing slit  42  may not be formed. Even with such a piezoelectric element  1 , it is possible to suppress a decrease in detection accuracy. Further, in the sixth embodiment, the temperature detection element  91  and the heat generating element  92  may be arranged in the portion where the lower electrode film  61  is formed, or may be arranged in the portion where the upper electrode film  63  is formed. Further, in the sixth embodiment, the temperature detection element  91  and the heat generation element  92  may be formed in the first region R 1 . Further, as described in the seventh embodiment and the like, the stress increasing slit  42  is not formed in each of the seventh and subsequent embodiments. Here, the stress increasing slit  42  may be appropriately formed in each embodiment. Further, in the sixteenth embodiment, the detection accuracy can be improved by operating the control unit  120   a . Therefore, in the sixteenth embodiment, the improvement unit may not be formed on the piezoelectric element  1 . 
     Further, in the seventh embodiment, when the resonance frequency of each vibration region  22  in each sensing unit  30  is different, the configuration of the vibration region  22  may be appropriately changed. For example, the resonance frequency of each vibration region  22  in each sensing unit  30  may be different depending on the film thickness and the material. 
     When the film thickness and the material of each vibration region  22  in each sensing unit  30  are different, for example, a mask is appropriately arranged when forming the piezoelectric film  50  constituting the vibration region  22 , so that the film thickness and the material may be changed. Further, for example, the film thickness and the material are made different by adjusting the film thickness by etching or the like after forming the piezoelectric film  50 , or by forming another piezoelectric film  50  on the etched portion again. Here, when another piezoelectric film  50  is formed again on the etched portion, for example, by tapering the side surface of the etched portion, it may be preferable because it is difficult to form a void between the etched portion and another piezoelectric film  50  to be newly formed. In this way, when the film thickness and the material are different, it is possible to easily select the optimum one according to the intended use. Further, the film thickness and the material of each vibration region  22  may be changed while having different lengths between the one end portion  22   a  and the other end portion  22   b.    
     In addition, each of the above embodiments can be combined as appropriate. For example, the first embodiment may be appropriately combined with each of the above embodiments so that the corner portion C 1  is formed in a portion of the first region R 1  floating from the support member  10 . The second embodiment may be appropriately combined with each of the above embodiments so that the corner portion C 2  is formed at one end portion of the first region R 1 . The third embodiment may be appropriately combined with each of the above embodiments so that the open end of the recess portion  10   a  has a circular shape. The fourth embodiment is appropriately combined with each of the above embodiments, the open end of the recess portion  10   a  is formed into a circular shape, a separation slit  41  is formed in the floating region  21   b , and the separation slit  41  is terminated in the floating region  21   b . The fifth embodiment may be appropriately combined with each of the above embodiments, and the hard film  82  may be arranged in the second region R 2 . The sixth embodiment may be appropriately combined with each of the above embodiments, and the temperature detection element  91  and the heat generating element  92  may be arranged. The seventh embodiment may be appropriately combined with each of the above embodiments to include a plurality of sensing units  30 . The eighth embodiment may be appropriately combined with each of the above embodiments so that the protection film  100  is provided on the side surface of the recess portion  10   a . The ninth embodiment may be appropriately combined with each of the above embodiments to form a recessed structure on the side surface  11   c  of the support substrate  11 . The tenth embodiment may be combined with each of the above embodiments so that the piezoelectric element  1  is flip-chip mounted on the printed circuit board  131 . The eleventh embodiment may be appropriately combined with each of the above embodiments to change the shape of the intermediate electrode film  62 . The twelfth and thirteenth embodiments may be combined with each of the above embodiments, and the method of partitioning the first region R 1  and the second region R 2  may be changed. The fourteenth embodiment may be combined with each of the above embodiments so that each vibration region  22  is connected in parallel to the circuit board  120  while warping each vibration region  22 . The fifteenth embodiment may be combined with each of the above embodiments to include a reflection film  140 . The sixteenth embodiment may be combined with each of the above embodiments to perform self-diagnosis when the piezoelectric device is configured. By combining the seventeenth embodiment with each embodiment, the lower electrode film  61  and the upper electrode film  63  are thinner than the intermediate electrode film  62 , and the rigidity of the lower electrode film  61  and the rigidity of the upper layer electrode film  63  are made equal to each other. The eighteenth embodiment may be combined with each embodiment and the number of charge regions  620  may be adjusted to set the maximum sensitivity to be 90% or more. The nineteenth embodiment may be combined with each embodiment and so that the low frequency roll-off frequency fr, the resonance frequency fmb of the piezoelectric element  1 , and the Helmholtz frequency fh are adjusted to increase in this order. Then, the combination of the above embodiments can be further combined. In addition, in each of the above-mentioned embodiments and combinations of each embodiment, it is possible to make a configuration excluding a part of the configuration requirements as necessary. For example, as described above, the stress increasing slit  42  may not be formed in the sixth embodiment or the like. 
     While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.