Piezoelectric device, piezoelectric actuator, and ultrasonic apparatus

Abstract

To provide a piezoelectric device with high durability that is less likely to be broken even if the amount of displacement of a diaphragm increases.SOLUTION: A piezoelectric device comprises: a substrate that has an opening; a diaphragm that has a first surface and a second surface on the opposite side of the first surface, where the first surface is joined to the substrate to close the opening; and a piezoelectric element that is provided on the second surface of the diaphragm. The diaphragm includes a first area overlapping the piezoelectric element when seen from a thickness direction of the diaphragm, and a second area not overlapping the piezoelectric element. The thickness of the second area in the thickness direction of the diaphragm is smaller than the thickness of the first area. The second area is provided with a reinforcement part formed of a material with a higher fracture toughness than that of the first area of the diaphragm. The second area has a constant thickness and the reinforcement part has a constant thickness in the thickness direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a piezoelectric device, a piezoelectric actuator including the piezoelectric device, and an ultrasonic device including the piezoelectric device.

Background Art

[0002] Conventionally, a piezoelectric device in which a first electrode, a piezoelectric element, and a second electrode are laminated on a substrate is known. In the piezoelectric device described in Patent Document 1, on a diaphragm (support), the piezoelectric body covers the first electrode, and a concave portion that is recessed toward the diaphragm side is provided outside the region where the piezoelectric body overlaps the first electrode of the diaphragm. The piezoelectric body is provided so as to cover the first electrode. Further, the second electrode is provided across the diaphragm including the concave portion from the piezoelectric body. With such a configuration, the displacement characteristics of the diaphragm can be improved by the concave portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, as in Patent Document 1, when the thickness of the diaphragm is reduced to increase the displacement amount, the diaphragm may be damaged without being able to withstand the deformation of the diaphragm. For this reason, there is a limit to the displacement amount of the diaphragm that can be driven by the piezoelectric element, and there is a demand for a highly durable piezoelectric device in which the possibility of damage is low even when the displacement amount of the diaphragm is increased.

Means for Solving the Problems

[0005] The piezoelectric device according to the first aspect of the present disclosure includes a substrate having an opening, a diaphragm having a first surface and a second surface opposite to the first surface, the first surface being bonded to the substrate to close the opening, and a piezoelectric element provided on the second surface of the diaphragm. The diaphragm includes a first region overlapping the piezoelectric element and a second region not overlapping the piezoelectric element when viewed in the thickness direction of the diaphragm. The thickness of the second region in the thickness direction of the diaphragm is thinner than the thickness of the first region. A reinforcing portion made of a material having higher fracture toughness than the first region of the diaphragm is provided in the second region. The thickness of the second region in the thickness direction is constant, and the thickness of the reinforcing portion is constant.

Brief Description of the Drawings

[0006]

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Embodiments for Carrying Out the Invention

[0007] [First Embodiment] Hereinafter, an ultrasonic device provided with the piezoelectric device of the first embodiment of the present disclosure will be described. FIG. 1 is a diagram showing the schematic configuration of the ultrasonic device 1 according to this embodiment. The ultrasonic device 1 of this embodiment includes a piezoelectric device 10 that functions as an ultrasonic sensor, a housing 2 that houses the piezoelectric device 10, and a measurement terminal 3. Although not shown, various control circuits for controlling the piezoelectric device 10, a battery, a communication unit for outputting measurement results to the outside, etc. may be stored in the housing 2. This ultrasonic device 1 performs ultrasonic measurement in which ultrasonic waves are transmitted from the piezoelectric device 10 to the measurement target and the ultrasonic waves reflected by the measurement target are received. The measurement result of the ultrasonic measurement output from the ultrasonic device 1 is transmitted to the measurement terminal 3. The measurement terminal 3 is a computer constituted by, for example, a dedicated computer, a smartphone, a tablet terminal, etc. The measurement terminal 3 performs various arithmetic processes based on the measurement result of the ultrasonic measurement, and performs various processes such as generation of an internal tomographic image of a living body, observation of the state of a predetermined tissue in the living body, and thickness measurement. Hereinafter, the piezoelectric device 10 used in such an ultrasonic device 1 will be described.

[0008] FIG. 2 is a plan view showing a schematic configuration of the piezoelectric device 10. FIGS. 3 and 4 are cross-sectional views showing the schematic configuration of the piezoelectric device 10 of the present embodiment. Note that FIG. 3 shows a cross-section when the piezoelectric device 10 is cut along line A-A in FIG. 2, and FIG. 4 shows a cross-section when the piezoelectric device 10 is cut along line B-B in FIG. 2. As shown in FIGS. 3 and 4, the piezoelectric device 10 of the present embodiment includes a substrate 20, a diaphragm 30 laminated on the substrate 20, a piezoelectric element 40 laminated on the diaphragm 30, a reinforcing portion 50 provided at a predetermined portion of the diaphragm 30, and a sealing plate 60. In the present embodiment, the substrate thickness direction of the substrate 20 is defined as the Z direction, the direction orthogonal to the Z direction is defined as the X direction, and the direction orthogonal to the Z direction and the X direction is defined as the Y direction.

[0009] The substrate 20 is a plate-like member having a predetermined thickness and has an opening 21 penetrating in the thickness direction. When the diaphragm 30 is laminated on the substrate 20, the opening 21 is closed by the diaphragm 30. As shown in FIGS. 2 to 4, the opening 21 is formed to be long in the Y direction, and a plurality of openings 21 are provided along the X direction. A partition portion 22 surrounding the opening 21 in the substrate 20 defines a vibrating portion 30A that is vibrated by driving the piezoelectric element 40 with a laminate of the diaphragm 30 and the reinforcing portion 50. In the present disclosure, a vibrating body 35 is constituted by the diaphragm 30 and the reinforcing portion 50. The vibrating portion 30A refers to a portion of the vibrating body 35 surrounded by the partition portion 22. That is, in the diaphragm 30 and the reinforcing portion 50, a portion overlapping the partition portion 22 in the Z direction becomes a base portion 30C where vibration is suppressed, and a portion surrounded by the partition portion 22 becomes a vibrating portion 30A that is vibrated by driving the piezoelectric element 40. Further, the base portion 30C refers to a portion of the vibrating body 35 overlapping the partition portion 22 in the Z direction.

[0010] The diaphragm 30 has a first surface 31 (the surface on the +Z side) facing the substrate 20 and a second surface 32 (the surface on the -Z side) opposite to the first surface 31. The first surface 31 covers and is joined to the -Z side surface of the substrate 20 to close the opening 21. This diaphragm 30 is, for example, a laminate including a first layer 301 made of SiO2 and a second layer 302 made of ZrO2, and is formed by processing an element substrate in which the first layer 301 is disposed on the +Z side and the second layer 302 is disposed on the -Z side. Specifically, when the portion of the diaphragm 30 where the piezoelectric element 40 is laminated is defined as the first region A1 and the portion other than the first region A1 is defined as the second region A2, a recess 33 is formed in at least a part of the second region A2 by processing such as etching from the second surface 32 side. That is, in the first region A1 of the diaphragm 30, it is composed of the first layer 301 and the second layer 302, and in the second region A2 of the diaphragm 30, the thickness along the Z direction is thinner than that of the first region A1, there is no second layer 302 of ZrO2, and it is composed of only the first layer 301 made of SiO2. The groove depth of the recess 33 along the Z direction is equal to or greater than half of the thickness of the first region A1. That is, the thickness of the second region A2 is less than half of the thickness of the first region A1 and has a uniform thickness. In the example shown in FIG. 3, a part of the second layer 302 is removed in the first region A1. This is a concave portion caused by over-etching when forming the piezoelectric element 40 on the diaphragm 30 in the first region A1, and the depth in the Z direction is sufficiently smaller than that of the recess 33.

[0011] In a plan view seen from the Z direction, the piezoelectric element 40 is laminated in the first region A1. The second region A2 is provided at least at a position sandwiching the first region A1 in the X direction. In the vibrating body 35, the second region A2 includes a base portion 30C overlapping the partition portion 22 of the substrate 20 and an arm portion 30B between the base portion 30C and the first region A1. The recess 33 is provided at least across the arm portion 30B to the base portion 30C, and a reinforcing portion 50 that constitutes the vibrating body 35 together with the diaphragm 30 is provided in the recess 33.

[0012] The piezoelectric element 40 is provided on the second surface 32 of the diaphragm 30 at a position overlapping the first region A1 of the diaphragm 30. This piezoelectric element 40 is constituted by, for example, a laminate in which a first electrode 41, a piezoelectric film 42, and a second electrode 43 are laminated from the diaphragm 30 toward the -Z side. The piezoelectric element 40 is formed as follows. First, an electrode film is formed on the diaphragm 30, and then the first electrode 41 is patterned by etching. Next, after forming the piezoelectric film 42 covering the first electrode 41, the piezoelectric film 42 is patterned by etching. Further, after forming an electrode film covering the piezoelectric film 42 and the first electrode 41, the second electrode 43 is patterned by etching. As a result, as shown in FIGS. 3 and 4, the side surface of the piezoelectric element 40 becomes a tapered surface inclined with respect to the Z direction.

[0013] In the present embodiment, one ultrasonic transducer is constituted by the vibrating portion 30A and the piezoelectric element 40. In such an ultrasonic transducer, a rectangular wave voltage (driving signal) of a predetermined frequency is applied between the first electrode 41 and the second electrode 43, so that the piezoelectric film 42 expands and contracts, and the vibrating portion 30A vibrates due to the expansion and contraction of the piezoelectric film 42, and ultrasonic waves are transmitted to the +Z side. Further, when the vibrating portion 30A is vibrated by ultrasonic waves, the piezoelectric film 42 bends, so that a potential difference is generated between the first electrode 41 side and the second electrode 43 side of the piezoelectric film 42. Thereby, it becomes possible to detect the reception of ultrasonic waves by detecting the potential difference generated between the first electrode 41 and the second electrode 43.

[0014] The reinforcing portion 50 is disposed with a uniform thickness in the recess 33 provided in the second region A2 of the diaphragm 30. The thickness of the reinforcing portion 50 at the position of the recess 33 is at least half of the thickness of the first region A1 or more. The third surface 52, which is the -Z side surface of the reinforcing portion 50, is preferably on the same surface as the second surface 32 of the first region A1 of the diaphragm 30 or located on the -Z side of the second surface 32. Also, a part of the reinforcing portion 50 is formed across the second region A2 to the first region A1. That is, the reinforcing portion 50 is formed on the diaphragm 30 on which the piezoelectric element 40 is formed by a method such as sputtering. Therefore, as shown in FIG. 3, a part of the reinforcing portion 50 extends along the tapered surface of the second electrode 43 from the second region A2 to form an extension portion 51. As shown in FIGS. 2-4, the reinforcing portion 50 may be provided so as to cover the piezoelectric element 40. In this case, as shown in FIGS. 1 and 3, the reinforcing portion 50 is removed (for example, by etching etc.) until the surface of the piezoelectric film 42 and the diaphragm 30 is exposed on the ±Y sides of the piezoelectric element 40 sandwiching the vibrating portion 30A, and an insulating groove 53 is formed. Thereby, it is possible to avoid the first electrode 41 and the second electrode 43 being electrically connected by the conductive reinforcing portion 50.

[0015] Furthermore, when driving each of the piezoelectric elements 40 arranged in the X direction individually, the reinforcing portion 50 at the ±Y side ends of the diaphragm 30 is removed so that the first electrodes 41 of the respective piezoelectric elements 40 are not electrically connected. Thereby, the ends of the first electrodes 41 of the respective piezoelectric elements 40 are exposed on the diaphragm 30 respectively.

[0016] This reinforcing portion 50 is made of a material having a higher fracture toughness than that of the diaphragm 30. More preferably, the reinforcing portion 50 is made of a material having a smaller Young's modulus than the material having the highest Young's modulus constituting the diaphragm 30. In the present embodiment, the diaphragm 30 is a laminate of a first layer 301 of SiO2 and a second layer 302 of ZrO2. When the Young's modulus of SiO2 is 70 (GPa) and the Young's modulus of the ZrO2 layer is 200 (GPa), it is preferable to use a material having a Young's modulus smaller than at least the Young's modulus of the ZrO2 layer for the reinforcing portion 50. FIG. 5 is a diagram showing the approximate Young's modulus and fracture toughness of each material. As can be seen from FIG. 5, when the first region A1 is a laminate of an SiO2 layer and a ZrO2 layer as the reinforcing portion 50, any one of Au, Cu, Al, Ir, and NiCr having higher fracture toughness is used. Among these, it is preferable to use Au, Cu, or Al having a Young's modulus smaller than that of the ZrO2 layer. Also, since Cu has a larger Young's modulus than Au and Al and is less likely to bend, and Al has a smaller fracture toughness than Au and Cu. For this reason, it is most preferable to use Au as the reinforcing portion 50.

[0017] The sealing plate 60 is provided on the side opposite to the substrate 20 of the diaphragm 30 and is joined to the diaphragm 30 or the reinforcing portion 50 via, for example, a resist resin or the like. A gap with a predetermined dimension is provided between the sealing plate 60, the diaphragm 30, and the reinforcing portion 50. Thereby, the piezoelectric element 40 etc. do not come into contact due to the vibration of the vibrating portion 30A. This sealing plate 60 is, for example, a plate-like member having a larger thickness dimension than the diaphragm 30 and the substrate 20, and reinforces the substrate 20 and the diaphragm 30 by being joined to the diaphragm 30.

[0018] [Displacement characteristics of the piezoelectric device 10] Next, the displacement characteristics of the piezoelectric device 10 of the present embodiment as described above will be described. FIG. 6 is a diagram showing the distribution of strain in the X direction applied to the vibrating body 35 when the piezoelectric device 10 of the present embodiment is driven with a driving voltage of 10 (V). FIG. 7 is a diagram showing the distribution of strain in the X direction applied to the vibrating body 35 when the piezoelectric device 10 of the present embodiment is driven with a driving voltage of 100 (V). Further, FIG. 8 is a diagram showing the strain in the X direction at each position in the X direction on the -Z side surface of the vibrating body 35 when the piezoelectric device 10 of the present embodiment is driven with driving voltages of 10 (V) and 100 (V). FIG. 9 is a diagram showing the strain in the X direction at each position in the X direction on the +Z side surface of the vibrating body 35 when the piezoelectric device 10 of the present embodiment is driven with driving voltages of 10 (V) and 100 (V). FIG. 10 is a diagram showing the strain in the X direction at each position in the thickness direction of the vibrating body 35. In FIG. 10, as an example, the central position of the arm portion 30B (the intermediate position between the first region A1 and the base portion 30C) when the driving voltage is 10 (V), the vicinity position of the first region A1 of the arm portion 30B when the driving voltage is 10 (V), and the strain measurement results at the vicinity position of the first region A1 of the arm portion 30B when the driving voltage is 100 (V) are shown.

[0019] As shown in FIGS. 6 and 7, when the driving voltage input to the piezoelectric device 10 is 100 (V), the strain in the X direction becomes larger than when the driving voltage is 10 (V). In particular, the strain also becomes large in the first region A1 of the diaphragm 30. By the way, when such strain in the X direction is balanced between the +Z side (the first surface 31 side) and the -Z side (the side of the second surface 32 of the diaphragm 30 and the third surface 52 of the reinforcing portion 50) of the vibrating body 35, the strains of each other are absorbed and canceled, and the influence on the breakage of the diaphragm 30 due to the strain is small. When the driving voltage is 10 (V), as shown in FIGS. 6, 8, and 9, the strain at the position of the arm portion 30B of the diaphragm 30 becomes larger than the strain in the first region A1, but the difference in strain is relatively small. In this case, as shown in FIG. 10, the strain becomes "0" near the midpoint in the thickness direction (Z direction) of the diaphragm 30. The position where the strain becomes "0" is the neutral point where the strain on the +Z side of the vibrating body 35 and the strain on the -Z side cancel each other out. When the driving voltage is 10 (V), the neutral point is near the midpoint position in the thickness direction (Z direction) of the diaphragm 30.

[0020] On the other hand, when the driving voltage of the diaphragm 30 is increased, as shown in FIGS. 7-9, not only the arm portion 30B but also the strain in the X direction in the first region A1 increases. Particularly, on the +Z side surface of the vibrating body 35, the strain within the first region A1 increases, and also the direction of the strain (compression or elongation) reverses near the boundary between the first region A1 and the second region A2 (arm portion 30B). Also, on the -Z side surface of the vibrating body 35, although the strain within the first region A1 is small, the strain at the arm portion 30B becomes extremely large. Due to the occurrence of such strain, as shown in FIG. 10, the balance of the strain between the +Z side and the -Z side of the vibrating body 35 is disrupted, and the neutral point shifts to the first surface 31 side (+Z side).

[0021] As described above, the strain when the diaphragm 30 is displaced is not only a problem on the surface of the diaphragm 30 but also changes at each position in the thickness direction (Z direction) of the diaphragm 30. Particularly, when the driving voltage is increased, since the neutral point moves to the first surface 31 side, the strain becomes larger in the portion on the second surface 32 side than the neutral point.

[0022] In contrast, in the present embodiment, the diaphragm 30 is provided with a recess 33 extending from the arm portion 30B outside the outer edge of the first region A1 to the base portion 30C and having a depth equal to or greater than half of the thickness dimension of the diaphragm 30. A reinforcing portion 50 is laminated on the recess 33, and the third surface 52 of the reinforcing portion 50 is flush with the second surface 32 of the first region A1 of the diaphragm 30. As described above, the reinforcing portion 50 is made of a material having a fracture toughness greater than that of the first region A1 of the diaphragm 30. The depth of the recess 33 and the thickness of the reinforcing portion 50 are preferably appropriately set according to the maximum driving power input to the piezoelectric device 10 so that the neutral point is located within the reinforcing portion 50. Thereby, when a larger driving voltage, such as 100 (V), is input to the piezoelectric device 10, the side of the second surface 32 (third surface 52) from the neutral point where the strain in the X direction becomes larger is within the reinforcing portion 50, and damage due to the strain can be suppressed.

[0023] In addition, the reinforcing portion 50 has a Young's modulus smaller than that of the second layer 302 constituting the first region A1 of the diaphragm 30. Thereby, it is easily displaced when a driving voltage is input, and the vibration displacement amount of the diaphragm 30 can be increased. FIG. 11 is a diagram showing the displacement amount of the vibrating portion 30A when the driving voltage is changed in the conventional example and the present embodiment, and FIG. 12 is a diagram showing the displacement amount of the vibrating portion 30A when the frequency of the ultrasonic wave output from the piezoelectric device 10 is changed. Note that, in the conventional example, a piezoelectric device is used in which the diaphragm 30 of the present embodiment is not provided with the recess 33 or the reinforcing portion 50, and the entire diaphragm 30 has the same configuration (a laminate of SiO2 and ZrO2) as the first region A1.

[0024] In the conventional piezoelectric device, the entire diaphragm is composed of a laminate of SiO2 and ZrO2. In this case, ZrO2 with a large Young's modulus is provided in the portion corresponding to the arm portion 30B that contributes to displacement, and the displacement amount cannot be made sufficiently large. On the other hand, in the present embodiment, in the arm portion 30B, there is no ZrO2 due to the concave portion 33, and instead, a reinforcing portion 50 with a small Young's modulus is used. Therefore, as shown in FIG. 11, in the piezoelectric device 10 of the present embodiment, the vibrating portion 30A can be displaced with a larger displacement amount than the conventional piezoelectric device with respect to the input driving voltage. Further, as described above, even when the driving voltage is increased, damage to the diaphragm 30 can be suppressed.

[0025] Further, in the piezoelectric device 10, by changing the frequency of the input driving voltage, the frequency of the ultrasonic wave output from the piezoelectric device 10 can be made variable. As shown in FIG. 12, even when the frequency of the ultrasonic wave is changed, the piezoelectric device 10 of the present embodiment can make the displacement amount of the diaphragm 30 larger than that of the piezoelectric device of the comparative example. Note that by matching the natural frequency of the piezoelectric device 10 with the frequency of the driving voltage, the displacement amount can be made larger due to the resonance effect of the diaphragm 30.

[0026] [Operational Effects of the Present Embodiment] The piezoelectric device 10 of the present embodiment includes a substrate 20 having an opening 21, a diaphragm 30 having a first surface 31 and a second surface 32, the first surface 31 being joined to the substrate 20 to close the opening 21, and a piezoelectric element 40 provided on the second surface 32 of the diaphragm 30. The diaphragm 30 includes a first region A1 that overlaps the piezoelectric element 40 when viewed in the Z direction and a second region A2 that does not overlap the piezoelectric element 40, and the thickness of the second region A2 in the Z direction is thinner than the thickness of the first region A1. And in the second region A2, a reinforcing portion 50 made of a material having a higher fracture toughness than the first region A1 of the diaphragm 30 is provided. The thickness of the second region A2 of the diaphragm 30 in the Z direction is constant, and the thickness of the reinforcing portion 50 is also constant.

[0027] As a result, in the piezoelectric device 10 of the present embodiment, since the reinforcing portion 50 having high fracture toughness is disposed in the second region A2 that is displaced more than the first region A1, breakage of the vibrating body 35 in the second region A2 can be suppressed.

[0028] In the present embodiment, the diaphragm 30 includes a concave portion 33 that is concave from the second surface 32 side in the second region A2. The groove depth of the concave portion 33 is equal to or greater than half of the thickness of the first region A1, and the reinforcing portion 50 is disposed in the concave portion 33. In the piezoelectric device 10 as in the present embodiment, when the drive voltage input to the piezoelectric element 40 is increased, the strain of the vibrating body 35 in the X direction becomes different in magnitude in the Z direction, and the neutral point shifts to the first surface 31 side instead of being at the center of the vibrating body 35 in the Z direction. Therefore, the strain in the X direction on the second surface 32 side of the vibrating body 35 becomes larger than that at the neutral point. On the other hand, in the present embodiment, the thickness of the reinforcing portion 50 is equal to or greater than half of the thickness of the first region A1. That is, in the Z direction, in the second region A2 of the vibrating body 35, the reinforcing portion 50 having high fracture toughness occupies a thickness equal to or greater than half. Thereby, breakage in the second region A2 can be more effectively suppressed.

[0029] In the present embodiment, when viewed from the Z direction, the reinforcing portion 50 extends to a position straddling the boundary between the first region A1 and the second region A2. That is, the reinforcing portion 50 includes an extending portion 51 that extends along the tapered surface of the second electrode 43. When the vibrating portion 30A is displaced, since the arm portion 30B is displaced greatly, a load concentrates on the boundary between the first region A1 and the arm portion 30B (second region A2). On the other hand, since the extending portion 51 of the reinforcing portion 50 having high fracture toughness is disposed across the boundary, breakage of the vibrating body 35 at the boundary between the first region A1 and the arm portion 30B (second region A2) can be suppressed.

[0030] In the present embodiment, in the second region A2, a portion overlapping with the partition portion 22 surrounding the opening 21 of the substrate 20 is defined as a base portion 30C, and a portion between the base portion 30C and the first region A1 is defined as an arm portion 30B. The reinforcing portion 50 is provided from the base portion 30C to the arm portion 30B. When driving power is input to the piezoelectric element 40 to vibrate the vibrating portion 30A, the arm portion 30B is greatly displaced, and the strain in the X direction also increases. Further, the strain in the X direction spreads not only in the arm portion 30B but also from the arm portion 30B to the base portion 30C as shown in FIGS. 6 and 7. In the present embodiment, since the reinforcing portion 50 is provided from the arm portion 30B to the base portion 30C, it is possible to resist the strain in the X direction as described above, and further suppress the breakage of the vibrating body 35.

[0031] The diaphragm 30 of the present embodiment is composed of a plurality of different materials, and the Young's modulus of the reinforcing portion 50 is smaller than the Young's modulus of the material having the highest Young's modulus among the materials constituting the diaphragm 30. For example, when the diaphragm 30 is a laminate of SiO2 and ZrO2, the Young's modulus of SiO2 is about 70 (GPa), and the Young's modulus of ZrO2 is about 200 (GPa). In the second region A2, there is no ZrO2 with a high Young's modulus, and the reinforcing portion 50 is provided on SiO2, and the reinforcing portion 50 is smaller than the Young's modulus of ZrO2. Thereby, the displacement amount of the vibrating portion 30A can be increased as compared with the case where the second region A2 is composed of SiO2 and ZrO2.

[0032] In the present embodiment, the reinforcing portion 50 is composed of any one of Au, Cu, and Al. The reinforcing portion 50 composed of these materials has a higher fracture toughness than SiO2 and ZrO2 constituting the first region A1, and has a Young's modulus smaller than that of ZrO2. Therefore, with the reinforcing portion 50 composed of such a material, the displacement amount at the time of displacement of the vibrating portion 30A can be increased, and even when greatly mutated, the breakage of the vibrating body 35 can be suppressed by the high fracture toughness.

[0033] [Second Embodiment] Next, the second embodiment will be described. In the above-described first embodiment, the diaphragm 30 is laminated on the substrate 20 having the opening 21, and the region of the vibrating portion 30A in the vibrating body 35 is defined by the partition portion 22 that forms the opening 21. However, in the present embodiment, it is different from the first embodiment in that the vibrating portion 30A is defined by a suppressing portion provided on the side opposite to the substrate 20.

[0034] FIG. 13 is a plan view showing a schematic configuration of the piezoelectric device 10A according to the second embodiment, FIG. 14 is a schematic cross-sectional view of the piezoelectric device 10A taken along line C-C in FIG. 13, and FIG. 15 is a schematic cross-sectional view of the piezoelectric device 10A taken along line D-D in FIG. 13. In the following description, the same reference numerals are given to the configurations already described, and the description thereof is omitted or simplified.

[0035] In the present embodiment, as shown in FIGS. 13 to 15, the opening 21A of the substrate 20 is formed in a substantially rectangular shape, and a plurality of piezoelectric elements 40 having a longitudinal direction in the Y direction are arranged along the X direction in a region overlapping with one opening 21A. And in the present embodiment, a wall portion 61 as a suppressing portion is provided on the -Z side surface of the vibrating body 35 so as to surround each piezoelectric element 40. This wall portion 61 has the same function as the partition portion 22 of the substrate 20 in the first embodiment. That is, in the vibrating body 35 composed of the diaphragm 30 and the reinforcing portion 50, the portion overlapping the wall portion 61 in the Z direction becomes the base portion 30C where vibration is suppressed. Also, the portion from the first region A1 to the base portion 30C becomes the arm portion 30B. Note that the configurations of the diaphragm 30, the piezoelectric element 40, and the reinforcing portion 50 are the same as those in the first embodiment.

[0036] Even in such an embodiment, displacement characteristics as shown in FIGS. 6 to 10 described in the first embodiment can be obtained. That is, compared with the case where the driving voltage is 10 (V), when a driving voltage of 100 (V) is input to the piezoelectric device 10A, the vibration displacement amount of the vibrating portion 30A becomes larger, but the strain in the X direction also increases accordingly. As shown in FIGS. 8 to 10, the strain in the X direction shifts toward the first surface 31 as the driving voltage increases, and thereby, the strain in the X direction on the second surface 32 side of the vibrating body 35 becomes larger. On the other hand, also in this embodiment, a reinforcing portion 50 similar to that of the first embodiment is provided. Thereby, the influence of the increase in the strain in the X direction can be suppressed. That is, even when a high driving voltage is input to the piezoelectric device 10A, breakage of the vibrating body 35 can be suppressed, and as shown in FIGS. 11 and 12, the vibration displacement amount of the vibrating portion 30A can also be increased.

[0037] [Operational Effects of this Embodiment] The piezoelectric device 10A of this embodiment is provided at a position sandwiching the piezoelectric element 40 on the second surface 32 side of the diaphragm 30, and includes a wall portion 61 (restraining portion) that suppresses the vibration of the diaphragm 30 (vibrating body 35). Even with such a piezoelectric device 10A, similar to the first embodiment, the regions of the respective vibrating portions 30A in the vibrating body 35 can be defined. Also, similar to the first embodiment, the breakage of the vibrating body 35 can be suppressed by the reinforcing portion 50, and the displacement amount of the vibrating portion 30A can be increased.

[0038] In this embodiment, the reinforcing portion 50 has a base portion 30C that overlaps with a partition wall portion surrounding the opening of the substrate 20, and is provided extending from the base portion 30C to the arm portion 30B. In this embodiment, since the reinforcing portion 50 is provided extending from the arm portion 30B to the base portion 30C, similar to the first embodiment, it can resist the strain in the X direction and suppress breakage of the vibrating body 35.

[0039] [Third Embodiment] The piezoelectric devices 10, 10A of the present disclosure can be used not only as the ultrasonic device as shown in the first embodiment but also as various piezoelectric actuators. In the third embodiment, a liquid ejection device as a piezoelectric actuator using the piezoelectric device 10 will be exemplified. FIG. 16 is a diagram showing an example of the liquid ejection device. In FIG. 16, the liquid ejection device 7 of the present embodiment includes a pressure chamber 70 in which the piezoelectric device 10 is disposed, a nozzle 71 disposed in a part of the pressure chamber 70, and an introduction part 72 for introducing liquid into the pressure chamber 70. In the present embodiment, liquid such as ink is introduced into the pressure chamber 70 from the introduction part 72, and the pressure chamber 70 is filled with the liquid. Then, when a drive voltage is input to the piezoelectric device 10, the vibration part 30A is displacement-driven, so that the pressure in the pressure chamber 70 increases and liquid is ejected from the nozzle 71. Note that the piezoelectric device 10A described in the second embodiment may be used instead of the piezoelectric device 10.

[0040] In such a liquid ejection device 7, for example, the pressure applied to the pressure chamber 70 may be increased according to the volume of the pressure chamber 70 or the distance from the liquid ejection device 7 to the ejection target. In this case, the pressure in the pressure chamber 70 can be made larger by increasing the drive voltage input to the piezoelectric device 10. However, as described above, when the drive power is increased, the strain in the X direction of the vibrating body 35 increases. On the other hand, by using the piezoelectric device 10, breakage of the vibrating body 35 by the reinforcing part 50 can be suppressed. Further, since the displacement amount can be made larger than that of a conventional piezoelectric device with respect to the input drive voltage, the pressure in the pressure chamber 70 can also be increased with a smaller voltage.

[0041] [Modification Example] Note that the present invention is not limited to the above-described embodiments, and configurations obtained by deformation, improvement, and appropriate combination of the embodiments within the range capable of achieving the object of the present invention are included in the present invention.

[0042] (Modification Example 1) In the second embodiment, the configuration in which the diaphragm 30 is disposed on the substrate 20 has been illustrated, but a configuration in which the substrate 20 is not provided may also be adopted. That is, in the second embodiment, even if the substrate 20 is not provided, the vibrating portion 30A can be partitioned by the wall portion 61 which is a suppressing portion.

[0043] (Modification 2) In the above-described embodiment, the reinforcing portion 50 is provided such that the upper surface (third surface 52) of the reinforcing portion 50 and the second surface 32 of the diaphragm 30 are flush with each other, but the present invention is not limited thereto. The thickness of the reinforcing portion 50 may be thin and the third surface 52 may be located closer to the first surface 31 side than the second surface 32. Alternatively, the thickness of the reinforcing portion 50 may be thick and the third surface 52 may be located closer to the sealing plate 60 side than the second surface 32.

[0044] [Summary of the Present Disclosure] The piezoelectric device according to the first aspect of the present disclosure includes a substrate having an opening, a diaphragm having a first surface and a second surface opposite to the first surface, the first surface being joined to the substrate to close the opening, and a piezoelectric element provided on the second surface of the diaphragm. The diaphragm includes a first region that overlaps the piezoelectric element and a second region that does not overlap the piezoelectric element when viewed in the thickness direction of the diaphragm. The thickness of the second region in the thickness direction of the diaphragm is thinner than the thickness of the first region. A reinforcing portion made of a material having higher fracture toughness than the first region of the diaphragm is provided in the second region. The thickness of the second region in the thickness direction is constant, and the thickness of the reinforcing portion is constant.

[0045] Thereby, even when a high driving power is input to the piezoelectric device, breakage of the diaphragm and the reinforcing portion can be suppressed, and the diaphragm and the reinforcing portion can be displaced by a large displacement amount.

[0046] In the piezoelectric device of the present aspect, the diaphragm includes a concave portion that is concave from the second surface side in the second region, a groove depth in the thickness direction of the concave portion is equal to or more than half of the thickness of the first region, and the reinforcing portion is disposed in the concave portion, and it is preferable that a thickness in the thickness direction of the reinforcing portion is equal to or more than the groove depth. As a result, when a high driving power is input to the piezoelectric device, a reinforcing portion with high fracture toughness is provided on the second surface side where the strain becomes large, and damage to the diaphragm and the reinforcing portion can be suppressed.

[0047] In the piezoelectric device of this aspect, when viewed from the thickness direction, it is preferable that the reinforcing portion extends to a position straddling the boundary between the first region and the second region. As a result, the boundary between the first region and the second region where the load is likely to concentrate can be covered with a reinforcing portion having high fracture toughness, and damage to the diaphragm and the reinforcing portion at the boundary can be suppressed.

[0048] In the piezoelectric device of this aspect, in the second region, a portion overlapping with the partition wall portion surrounding the opening of the substrate is used as a base portion, and a portion between the base portion and the first region is used as an arm portion. It is preferable that the reinforcing portion is provided from the base portion to the arm portion. As a result, even when a high driving power is input to the piezoelectric device and the strain increases from the arm portion to the base portion, the reinforcing portion can suppress damage due to the strain.

[0049] In the piezoelectric device of this aspect, on the second surface side of the diaphragm, a suppressing portion is provided at a position sandwiching the piezoelectric element to suppress the vibration of the diaphragm. Even in the configuration where the suppressing portion is provided on the second surface side of the diaphragm as in this aspect, the vibration region where the piezoelectric element of the diaphragm is arranged can be defined.

[0050] In the piezoelectric device of this aspect, in the second region, a portion overlapping with the suppressing portion of the substrate is used as a base portion, and a portion between the base portion and the first region is used as an arm portion. It is preferable that the reinforcing portion is provided from the base portion to the arm portion. As a result, similar to the above aspect, even when a high driving power is input to the piezoelectric device and the strain increases from the arm portion to the base portion, the reinforcing portion can suppress damage due to the strain.

[0051] In the piezoelectric device of this aspect, the diaphragm is composed of a plurality of different materials, and the Young's modulus of the reinforcing portion is smaller than the Young's modulus of the material having the highest Young's modulus among the materials constituting the diaphragm. Accordingly, as in the above aspect, while suppressing breakage of the diaphragm, the displacement amount of the diaphragm can be made larger.

[0052] In the piezoelectric device of this aspect, it is preferable that the reinforcing portion is any one of Au, Cu, and Al. Accordingly, as in the above aspect, while suppressing breakage of the diaphragm, the displacement amount of the diaphragm can be made larger. Further, by forming the reinforcing portion with these conductive materials, the reinforcing portion can function as a wiring electrode or an electromagnetic shield.

[0053] In the piezoelectric device of this aspect, the piezoelectric element is a laminate in which a first electrode, a piezoelectric film, and a second electrode are laminated in this order from the diaphragm. By arranging such a piezoelectric element, the diaphragm can be vibrated and driven.

[0054] The piezoelectric actuator according to the second aspect of the present disclosure includes the piezoelectric device according to the first aspect. As described above, the piezoelectric device can suppress breakage of the diaphragm even when the displacement amount of the diaphragm is increased, and as a result, a piezoelectric actuator capable of outputting a large driving force can be provided.

[0055] The ultrasonic device according to the third aspect of the present disclosure includes the piezoelectric device according to the first aspect. As described above, the piezoelectric device can suppress breakage of the diaphragm even when the displacement amount of the diaphragm is increased, and as a result, an ultrasonic device capable of outputting a large sound pressure can be provided.

Description of Reference Numerals

[0056] 1... Ultrasonic device, 2... Housing, 3... Measurement terminal, 7... Liquid ejection device (piezoelectric actuator), 10, 10A... Piezoelectric device, 20... Substrate, 21, 21A... Opening, 22... Partition part, 30... Diaphragm, 30A... Vibration part, 30B... Arm part, 30C... Base part, 31... First surface, 32... Second surface, 33... Concave part, 35... Vibration body, 40... Piezoelectric element, 41... First electrode, 42... Piezoelectric body film, 43... Second electrode, 50... Reinforcement part, 51... Extension part, 52... Third surface, 53... Insulation groove, 60... Sealing plate, 61... Wall part, 70... Pressure chamber, 71... Nozzle, 72... Introduction part, 301... First layer, 302... Second layer, A1... First region, A2... Second region.

Claims

1. A substrate having an opening, A diaphragm having a first surface and a second surface opposite to the first surface, wherein the first surface is joined to the substrate to close the opening, A piezoelectric element provided on the second surface of the diaphragm, and comprising, The diaphragm includes a first region overlapping the piezoelectric element and a second region not overlapping the piezoelectric element when viewed from the thickness direction of the diaphragm, The thickness of the second region in the thickness direction of the diaphragm is thinner than the thickness of the first region, A reinforcing portion made of a material having a higher fracture toughness than that of the first region of the diaphragm is provided in the second region, A piezoelectric device in which the thickness of the second region in the thickness direction is constant and the thickness of the reinforcing portion is constant.

2. The diaphragm includes a concave portion that is concave from the second surface side in the second region, The groove depth of the concave portion in the thickness direction is equal to or greater than half of the thickness of the first region, The reinforcing portion is disposed in the concave portion, and the thickness of the reinforcing portion in the thickness direction is equal to or greater than the groove depth, The piezoelectric device according to claim 1.

3. When viewed from the thickness direction, the reinforcing portion extends to a position straddling the boundary between the first region and the second region, The piezoelectric device according to claim 1.

4. Of the second region, a portion overlapping a partition wall portion surrounding the opening of the substrate is used as a base portion, and a portion between the base portion and the first region is used as an arm portion. The reinforcing portion is provided from the base portion to the arm portion, The piezoelectric device according to claim 1.

5. On the second surface side of the diaphragm, a suppression portion is provided at a position sandwiching the piezoelectric element to suppress the vibration of the diaphragm, The piezoelectric device according to claim 1.

6. Of the second region, a portion overlapping the suppression portion of the substrate is used as a base portion, and a portion between the base portion and the first region is used as an arm portion. The reinforcing portion is provided from the base portion to the arm portion, The piezoelectric device according to claim 5.

7. The diaphragm is composed of a plurality of different materials, and the Young's modulus of the reinforcing portion is smaller than the Young's modulus of the material having the highest Young's modulus constituting the diaphragm, The piezoelectric device according to claim 1.

8. The reinforcing portion is any one of Au, Cu, and Al, The piezoelectric device according to claim 1.

9. The piezoelectric element is a laminate in which a first electrode, a piezoelectric film, and a second electrode are laminated in this order from the diaphragm, The piezoelectric device according to claim 1.

10. A piezoelectric actuator comprising the piezoelectric device according to claim 1.

11. An ultrasonic device comprising the piezoelectric device according to claim 1.

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