Piezoelectric actuator and driving method for piezoelectric actuator

Abstract

To provide a piezoelectric actuator that reduces a displacement amount and stress of a vibration film 1 at resonance, and a driving method for the piezoelectric actuator.SOLUTION: A piezoelectric actuator 100 includes: a vibration film 1 that has a fixed end 1a and a free end 1b, and has a main surface (first main surface 1A) divided into a first area (3A) on the fixed end 1a side and a second area (3B) on the free end 1b side; a film support portion 2 to which the fixed end 1a of the vibration film 1 is connected; a first piezoelectric element 3A arranged on the first area (3A) of the main surface 1A of the vibration film 1; a second piezoelectric element 3B arranged on the second area (3B) of the main surface 1A of the vibration film 1; and driving portions 7A and 7B that apply opposite-phase AC voltages to the first piezoelectric element 3A and the second piezoelectric element 3B. The ratio (b / L) of the length b from the fixed end 1a to the boundary 3a between the first area (3A) and the second area (3B) to the length L of the vibration film 1 from the fixed end 1a to the free end 1b is set according to the resonance mode specific to the piezoelectric actuator 100.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present disclosure relates to a piezoelectric actuator and a method for driving a piezoelectric actuator. [Background technology]

[0002] Conventionally, transducers that transmit or receive sound waves or ultrasonic waves are known (see Patent Document 1). A cantilever-type piezoelectric actuator that can be used as a speaker that transmits sound waves has a piezoelectric body arranged over as wide an area as possible on the main surface of the diaphragm, from the fixed end to the free end, in order to obtain the maximum output (displacement of the diaphragm) for the applied voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-52305

[0004] [overview] If the operating frequency band of the piezoelectric actuator includes a resonance frequency specific to the piezoelectric actuator, the vibration membrane is displaced greatly at the time of resonance, and a large stress is applied.

[0005] An object of the present disclosure is to provide a piezoelectric actuator in which the displacement and stress of the vibrating membrane during resonance are reduced, and a method for driving the same.

[0006] To solve the above-mentioned problems, one aspect of the present disclosure is a piezoelectric actuator with a cantilever structure. The piezoelectric actuator includes a diaphragm having a fixed end and a free end, and a main surface divided into a first region on the fixed end side and a second region on the free end side; a diaphragm support part to which the fixed end of the diaphragm is connected; a first piezoelectric element disposed in the first region on the main surface of the diaphragm; a second piezoelectric element disposed in the second region on the main surface of the diaphragm; and a drive part that applies AC voltages of opposite phases to the first piezoelectric element and the second piezoelectric element. The ratio of the length from the fixed end to the boundary between the first and second regions to the length of the diaphragm from the fixed end to the free end is set according to a resonance mode specific to the piezoelectric actuator.

[0007] Another aspect of the present disclosure is a method for driving the piezoelectric actuator described above, which includes applying AC voltages of opposite phases to the first piezoelectric element and the second piezoelectric element. [Brief explanation of the drawings]

[0008] [Figure 1A] FIG. 1A is a plan view showing the configuration of a piezoelectric actuator 100 according to the first embodiment. [Figure 1B] FIG. 1B is a cross-sectional view showing the configuration of the piezoelectric actuator 100 taken along the IB-IB section of FIG. 1A. [Figure 2] FIG. 2 is a schematic diagram showing driving sections 7A and 7B that apply AC voltages to first piezoelectric element 3A and second piezoelectric element 3B of piezoelectric actuator 100, respectively. [Figure 3] FIG. 3 is a graph showing an example of the AC voltages applied by the driving units 7A and 7B. [Figure 4] FIG. 4 is a graph showing the results of calculating the maximum value of stress generated in the vibrating membrane 1 by changing the ratio (b / L) in the piezoelectric actuator 100 of FIGS. 1A and 1B. [Figure 5] FIG. 5 is a graph showing the results of calculating the maximum displacement of the vibrating membrane 1 by changing the ratio (b / L) in the piezoelectric actuator 100 of FIGS. 1A and 1B. [Figure 6A]FIG. 6A is a plan view showing the configuration of a piezoelectric actuator 101 according to the second embodiment. [Figure 6B] FIG. 6B is a cross-sectional view showing the configuration of piezoelectric actuator 101 taken along the VIB-VIB cross section of FIG. 6A. [Figure 6C] FIG. 6C is a cross-sectional view showing the configuration of piezoelectric actuator 101 taken along the VIC-VIC cross section of FIG. 6A. [Figure 7A] FIG. 7A is a plan view showing the configuration of a piezoelectric actuator 102 according to the third embodiment. [Figure 7B] FIG. 7B is a cross-sectional view showing the configuration of piezoelectric actuator 102 taken along the VIIB-VIIB section of FIG. 7A. [Figure 7C] FIG. 7C is a cross-sectional view showing the configuration of piezoelectric actuator 102 taken along the VIIC-VIIC cross section of FIG. 7A. [Figure 8] FIG. 8 is a graph showing the change in the amount of displacement of the tip of the vibrating membrane 1 when the vibration frequency is changed. [Figure 9] FIG. 9 is a graph showing the displacement shape of the vibrating membrane 1 when the piezoelectric actuator 100 is resonating in a plurality of resonance modes. [Figure 10] FIG. 10 is a contour diagram showing the displacement shape of the diaphragm 1 when resonating in a butterfly mode BF, which is an example of a plurality of resonance modes.

[0009] [Detailed explanation] Piezoelectric actuators and methods for driving piezoelectric actuators according to several embodiments will be described in detail below with reference to the drawings. The embodiments described below are comprehensive or specific examples. The numerical values, shapes, materials, components, and the installation positions and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the scope of the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions. The following embodiments and their variations may include similar components, and the same reference numerals will be used to denote similar components, and redundant explanations will be omitted.

[0010] (First embodiment) Fig. 1A is a plan view showing the configuration of a piezoelectric actuator 100 according to a first embodiment. Fig. 1B is a cross-sectional view showing the configuration of the piezoelectric actuator 100 taken along the IB-IB section of Fig. 1A. Fig. 2 is a schematic diagram showing driving units 7A and 7B that apply AC voltages to a first piezoelectric element 3A and a second piezoelectric element 3B of the piezoelectric actuator 100, respectively.

[0011] As shown in Figures 1A, 1B, and 2, the piezoelectric actuator 100 according to the first embodiment has at least a vibration membrane 1, a membrane support portion 2, a first piezoelectric element 3A, a second piezoelectric element 3B, and driving portions 7A and 7B.

[0012] The diaphragm 1 has a fixed end 1a connected to the diaphragm support portion 2 and a free end 1b that is freely displaceable relative to the diaphragm support portion 2. The diaphragm 1 is a flexible thin film made of single-crystal silicon. The fixed end 1a is one end 1a of the diaphragm 1 in the longitudinal direction (X direction), and the free end 1b is the other end 1b of the diaphragm 1 that faces end 1a. The planar shape of the diaphragm 1 is not particularly limited, but may be, for example, a rectangular shape as shown in FIG. 1A. In this case, the fixed end 1a is located on one of the four sides, and the free end 1b is located on the side opposite this one side.

[0013] The direction from the fixed end 1a to the free end 1b (X direction) is the longitudinal direction of the diaphragm 1. On the main surface 1A of the diaphragm 1, the direction perpendicular to the longitudinal direction (Y direction) is the lateral direction of the diaphragm 1. The length (L) of the diaphragm 1 in the X direction and the width (W) of the diaphragm 1 in the Y direction are not particularly limited. For example, the length (L) of the diaphragm 1 is 3 mm, and the width (W) of the diaphragm 1 is 2 mm.

[0014] 1A, the membrane support part 2 has a frame-like shape that surrounds the periphery of the vibrating membrane 1. A slit 5 (gap) is formed between the outer periphery (three sides) of the vibrating membrane 1, excluding the fixed end 1a (one side) of the vibrating membrane 1, and the inner periphery of the membrane support part 2. The slit 5 allows the vibrating membrane 1, whose fixed end 1a is fixed to the membrane support part 2, to freely elastically deform relative to the membrane support part 2.

[0015] A fixed end 1a of the diaphragm 1 is connected to the diaphragm support part 2. As shown in FIG. 1B, the diaphragm support part 2 has a laminated structure of an upper layer part 2b that is positioned in the same Z direction (film thickness direction) as the diaphragm 1, and a lower layer part 2a that is connected to the upper layer part 2b. The Z direction is the normal direction to the main surface 1A of the diaphragm 1.

[0016] The diaphragm 1 and the diaphragm support portion 2 can be formed simultaneously from a single silicon substrate. The silicon substrate is etched between the periphery (three sides) of the diaphragm 1, excluding the fixed end 1a, and the upper layer portion 2b. This separates the periphery (three sides) of the diaphragm 1 from the upper layer portion 2b, forming a slit 5. Then, by etching the silicon substrate from its underside (the lower layer portion 2a side), a cavity surrounded by the lower layer portion 2a and the diaphragm 1 is formed, as shown in FIG. 1B.

[0017] When an SOI substrate is used as the silicon substrate, the Si active layer of the SOI substrate can be used as the vibrating membrane 1 and the upper layer 2b, and the Si support substrate of the SOI substrate can be used as the lower layer 2a.

[0018] The first main surface 1A of the diaphragm 1 is divided into a first region (3A) on the fixed end 1a side and a second region (3B) on the free end 1b side. The first piezoelectric element 3A is arranged in the first region (3A). The second piezoelectric element 3B is arranged in the second region (3B). Figure 1A shows an example in which the boundary 3a between the first region (3A) and the second region (3B) is a line segment along the short side direction (Y direction) of the diaphragm.

[0019] The first piezoelectric element 3A and the second piezoelectric element 3B (collectively referred to as the "piezoelectric elements 3") are disposed over the entire main surface 1A of the diaphragm 1. The first piezoelectric element 3A is disposed over the entire first region (3A), and the second piezoelectric element 3B is disposed over the entire second region (3B). In reality, the outer shapes of the diaphragm 1 and the piezoelectric elements 3 are patterned in different processes. Due to limitations on pattern processing accuracy, such as mask alignment accuracy, the maximum outer shape of the piezoelectric elements 3 formed on the main surface 1A of the diaphragm 1 is narrower than the outer shape of the diaphragm 1 by a certain margin. Protective films and the like that cover the diaphragm 1 and the piezoelectric elements 3 are omitted from Figures 1A and 1B.

[0020] The piezoelectric actuator 100 may include a silicon (Si) sub-frame 4 for reinforcing the strength of the membrane support portion 2. The Si sub-frame 4 is connected to the upper end of the membrane support portion 2.

[0021] Although not shown in FIG. 1B, the piezoelectric element 3 has a laminated structure of a pair of electrodes and a piezoelectric film sandwiched between the pair of electrodes. Each of the pair of electrodes is formed of a thin film of a conductive metal such as aluminum (Al) or copper (Cu). Alternatively, the lower electrode of the pair of electrodes may have a laminated structure in which titanium (Ti) and platinum (Pt) are laminated in this order. The upper electrode of the pair of electrodes may have a laminated structure in which iridium oxide (IrO2) and iridium (Ir) are laminated in this order. The piezoelectric film is composed of, for example, a lead zirconate titanate (PZT) film. In addition to lead zirconate titanate, the piezoelectric film may also be made of aluminum nitride (AlN), zinc oxide (ZnO), lead titanate (PbTiO3), potassium sodium niobate (KNN), or the like.

[0022] FIG. 3 is a graph showing an example of AC voltages applied by the driving units 7A and 7B. As shown in FIGS. 2 and 3, the driving units (7A and 7B) apply AC voltages of opposite phases to the first piezoelectric element 3A and the second piezoelectric element 3B. Specifically, the piezoelectric actuator 100 has a first driving unit 7A that applies an AC voltage to the first piezoelectric element 3A and a second driving unit 7B that applies an AC voltage to the second piezoelectric element 3B. The first driving unit 7A and the second driving unit 7B apply AC voltages that are 180° out of phase with each other to the pair of electrodes of the first piezoelectric element 3A and the second piezoelectric element 3B, respectively. The AC voltages output by the first driving unit 7A and the second driving unit 7B have the same period and amplitude.

[0023] When an AC voltage is applied to a pair of electrodes, an electric field is generated between the pair of electrodes. This electric field causes the piezoelectric film to expand and contract in a direction parallel to the XY plane, displacing the free end 1b of the diaphragm 1 so that it warps in the Z direction or the opposite direction. By repeatedly applying a voltage, the diaphragm 1 alternately displaces in the Z direction and in the direction opposite to the Z direction. This vibration of the diaphragm 1 causes the air around the diaphragm 1 to vibrate, and the air vibrations are output as sound waves or ultrasonic waves in the audible range.

[0024] The first piezoelectric element 3A and the second piezoelectric element 3B operate independently of each other. By applying AC voltages of opposite phases to the first piezoelectric element 3A and the second piezoelectric element 3B, the first region (3A) and the second region (3B) of the vibrating membrane 1 are displaced so as to warp in opposite directions.

[0025] FIG. 8 is a graph showing the change in the amount of displacement at the tip of the vibrating membrane 1 when the vibration frequency is changed. When the frequency of the AC voltage is changed, the vibrating membrane 1 resonates at a specific frequency. The horizontal axis of FIG. 8 represents the frequency of the AC voltage, and the vertical axis represents the amount of displacement at the tip of the vibrating membrane 1. In multiple resonance modes (M1, M2, BF, M3), the amount of displacement at the tip of the vibrating membrane 1 reaches a maximum value.

[0026] These multiple resonance modes include multiple bending modes in which the diaphragm 1 bends in the longitudinal direction (X direction). FIG. 9 is a graph showing the displacement shape of the diaphragm 1 when the piezoelectric actuator 100 is resonating in multiple bending modes (M1 to M4). The horizontal axis indicates the coordinate (X coordinate) in the longitudinal direction (X direction) of the diaphragm 1, and the vertical axis indicates the Z-direction component of the displacement of the diaphragm 1. Hereinafter, the "Z-direction component of the displacement" will be simply referred to as the "amount of displacement." In all bending modes, the X-coordinate of the fixed end 1a of the diaphragm 1 is normalized to 0, and the X-coordinate of the free end 1b is normalized to 1. Furthermore, the amount of displacement of the free end 1b of the diaphragm 1 is also normalized to 1 or -1.

[0027] 9 shows a primary bending mode M1, a secondary bending mode M2, a tertiary bending mode M3, and a fourth bending mode M4 as examples of multiple bending modes. These bending modes are resonance modes characterized by the shape of the displacement in the longitudinal direction (X direction) of the diaphragm 1. The bending modes include a primary bending mode M1 in which no antinode is formed between the fixed end 1a and the free end 1b, a secondary bending mode M2 ​​in which one antinode is formed between the fixed end 1a and the free end 1b, a third bending mode M3 in which two antinodes are formed between the fixed end 1a and the free end 1b, and a fourth bending mode M4 in which three antinodes are formed between the fixed end 1a and the free end 1b.

[0028] FIG. 10 is a contour diagram showing the displacement shape of the diaphragm 1 when resonating in butterfly mode BF, as another example of a resonance mode of the piezoelectric actuator 100. The "butterfly mode" is a resonance mode characterized by the shape of the displacement in the short-side direction (Y direction) of the diaphragm 1. As shown in FIG. 10, in butterfly mode BF, the diaphragm 1 is bent in the short-side direction (Y direction), for example, at the free end 1b. A central portion 1b-1 of one side of the diaphragm 1 that forms the free end 1b is displaced in the +Z direction / -Z direction relative to the frame 6, and both end portions 1b-2 and 1b-3 of one side of the diaphragm 1 that form the free end 1b are displaced in the -Z direction / +Z direction relative to the frame 6. Note that the frame 6 represents the position where the Y coordinate is 0, i.e., the XY plane. The central portion 1b-1 and both end portions 1b-2 and 1b-3 are displaced alternately in the -Z direction / +Z direction, causing the diaphragm 1 to resonate in butterfly mode BF.

[0029] Note that, in order to explain butterfly mode BF, a contour diagram showing diaphragm 1 bending only in the short-side direction (Y direction) is shown here. However, butterfly modes can also occur in combination with bending modes M1, M2, M3, M4, etc. in the long-side direction (X direction) shown in Figure 9. Furthermore, the position in the short-side direction of diaphragm 1 where butterfly modes occur is not limited to free end 1b. Butterfly modes can also occur at positions in the long-side direction (X direction) of diaphragm 1 other than free end 1b.

[0030] When the piezoelectric actuator 100 resonates, the diaphragm 1 is displaced significantly, and a large stress is applied to the diaphragm 1. In particular, when viewed from the normal direction (Z direction) of the XY plane, the stress on the diaphragm 1 caused by displacement in the lateral direction (Y direction) that intersects with the longitudinal direction (X direction) of the diaphragm 1 often becomes a practical problem. Therefore, it is desirable to suppress the amount of displacement of the diaphragm 1 in the lateral direction (Y direction) relative to the amount of displacement in the longitudinal direction (X direction).

[0031] When the piezoelectric actuator 100 resonates, the vibrating membrane 1 is displaced significantly, and a large stress is applied to the vibrating membrane 1. Therefore, the ratio (b / L) of the length (b) from the fixed end 1a to the boundary 3a to the length (L) of the vibrating membrane 1 from the fixed end 1a to the free end 1b is set according to the resonance mode specific to the piezoelectric actuator 100. This makes it possible to reduce the amount of displacement and stress of the vibrating membrane 1 during resonance.

[0032] A method for setting the ratio (b / L) according to the resonance mode specific to the piezoelectric actuator 100 will be described with reference to FIGS.

[0033] 4 is a graph showing the relationship between the ratio (b / L) in each resonance mode (M1, M2, M3, M4, BF) and the normalized maximum stress of the vibrating membrane 1. The horizontal axis represents the ratio (b / L). The vertical axis represents the maximum stress of the vibrating membrane 1 normalized to 1 when the ratio (b / L) is 0, i.e., when the first main surface 1A is composed only of the second region 3B.

[0034] 5 is a graph showing the relationship between the ratio (b / L) in each resonance mode (M1, M2, M3, M4, BF) and the normalized maximum displacement of the diaphragm 1. The horizontal axis represents the ratio (b / L). The vertical axis represents the maximum displacement of the diaphragm 1 normalized to 1 when the ratio (b / L) is 0, i.e., when the first main surface 1A is composed only of the second region 3B.

[0035] In the first-order bending mode M1, the maximum stress and maximum displacement reach their minimum values ​​when the ratio (b / L) is 0.233 (m11 in FIG. 4, M11 in FIG. 5). Compared to when the ratio (b / L) is 0, the minimum value of the maximum displacement is reduced to approximately 5%. Therefore, by setting the ratio (b / L) to 0.1 or more and 0.38 or less for the first-order bending mode M1, the maximum stress and maximum displacement of the vibrating membrane 1 in the first-order bending mode M1 can be reduced to approximately 50% or less. By setting the ratio (b / L) to 0.16 or more and 0.3 or less for the first-order bending mode, the maximum stress and maximum displacement of the vibrating membrane 1 in the first-order bending mode M1 can be reduced to approximately 25% or less.

[0036] In the second-order bending mode M2, the maximum stress and maximum displacement reach their minimum values ​​when the ratio (b / L) is 0.633 (m21 in FIG. 4, M21 in FIG. 5). Compared to when the ratio (b / L) is 0, the minimum value of the maximum displacement is reduced to approximately 4%. Therefore, by setting the ratio (b / L) to 0.56 or more and 0.71 or less for the second-order bending mode M2, the maximum stress and maximum displacement of the vibrating membrane 1 in the second-order bending mode M2 ​​can be reduced to approximately 50% or less. By setting the ratio (b / L) to 0.59 or more and 0.67 or less for the second-order bending mode M2, the maximum stress and maximum displacement of the vibrating membrane 1 in the second-order bending mode M2 ​​can be reduced to approximately 25% or less.

[0037] In the third-order bending mode M3, the maximum stress and maximum displacement reach their minimum values ​​when the ratio (b / L) is 0.133 or 0.766 (m31 and m32 in FIG. 4, M31 and M32 in FIG. 5). Compared to when the ratio (b / L) is 0, the minimum value of the maximum displacement is reduced to approximately 7%. Therefore, by setting the ratio (b / L) for the third-order bending mode M3 to 0.06 to 0.22 or 0.7 to 0.82, the maximum stress and maximum displacement of the diaphragm 1 in the third-order bending mode M3 can be reduced to approximately 50% or less. By setting the ratio (b / L) for the third-order bending mode M3 to 0.73 to 0.79, the maximum stress and maximum displacement of the diaphragm 1 in the third-order bending mode M3 can be reduced to approximately 25% or less.

[0038] In the fourth-order bending mode M4, the maximum stress and maximum displacement reach their minimum values ​​when the ratio (b / L) is 0.300, 0.400, or 0.833 (m41, m42, and m43 in FIG. 4; M41 to M43 in FIG. 5). Compared to when the ratio (b / L) is 0, the minimum value of the maximum displacement is reduced to approximately 2 to 16%. Therefore, by setting the ratio (b / L) for the fourth-order bending mode M4 to 0.24 to 0.46 or 0.81 to 0.88, the maximum stress and maximum displacement of the diaphragm 1 in the fourth-order bending mode M4 can be reduced to approximately 50% or less. By setting the ratio (b / L) for the fourth-order bending mode M4 to 0.27 to 0.32, 0.38 to 0.44, or 0.83 to 0.85, the maximum stress and maximum displacement of the diaphragm 1 in the fourth-order bending mode M4 can be reduced to approximately 25% or less.

[0039] In butterfly mode BF, the maximum stress and maximum displacement reach their minimum values ​​when the ratio (b / L) is 0.633 (b11 in FIG. 4, B11 in FIG. 5). Compared to when the ratio (b / L) is 0, the minimum value of the maximum displacement is reduced to approximately 0.6%. Therefore, by setting the ratio (b / L) to 0.44 or more and 0.84 or less for butterfly mode BF, the maximum stress and maximum displacement of the diaphragm 1 in butterfly mode BF can be reduced to approximately 50% or less. By setting the ratio (b / L) to 0.53 or more and 0.74 or less for butterfly mode BF, the maximum stress and maximum displacement of the diaphragm 1 in butterfly mode BF can be reduced to approximately 25% or less.

[0040] (Second embodiment) In the second embodiment, specific examples of the planar arrangement of wiring connected to the upper electrodes of the first piezoelectric element 3A and the second piezoelectric element 3B will be described with reference to Figures 6A to 6C. Figure 6A is a plan view showing the configuration of a piezoelectric actuator 101 according to the second embodiment. Figure 6B is a cross-sectional view showing the configuration of the piezoelectric actuator 101 taken along the VIB-VIB cross section of Figure 6A. Figure 6C is a cross-sectional view showing the configuration of the piezoelectric actuator 101 taken along the VIC-VIC cross section of Figure 6A.

[0041] As described above, the first piezoelectric element 3A has a laminated structure of a pair of electrodes (31, 33A) and a piezoelectric film 32A sandwiched between the pair of electrodes. The second piezoelectric element 3B has a laminated structure of a pair of electrodes (31, 33B) and a piezoelectric film 32B sandwiched between the pair of electrodes. The electrode on the vibration film 1 side is called the lower electrode (31), and the other electrode is called the upper electrode (33A, 33B). The first piezoelectric element 3A and the second piezoelectric element 3B have a common lower electrode (31). The lower electrode (31) is connected to, for example, a ground potential.

[0042] The first wiring 8A is connected to the upper electrode 33A via a contact plug 9A. The contact plug 9A is located at the end of the upper electrode 33A on the fixed end 1a side. This allows the length of the first wiring 8A from the contact plug 9A to the fixed end 1a to be shortened. When viewed from the Z direction, the contact plug 9A has a thin and elongated shape in the short direction (Y direction) of the vibration membrane 1. This increases the contact area with the upper electrode 33A and reduces the electrical resistance of the contact plug 9A. The first wiring 8A passes from the contact plug 9A above the fixed end 1a and is led to the membrane support member 2. As shown in FIG. 6A, the first wiring 8A is led to the membrane support member 2 from one end (right side) of the fixed end 1a (one side) in the Y direction. Note that the first wiring 8A on the membrane support member 2 is not shown.

[0043] The second wiring 8B is connected to the upper electrode 33B via a contact plug 9B. The contact plug 9B is located at the end of the upper electrode 33B on the fixed end 1a side. This allows the length of the second wiring 8B from the contact plug 9B to the fixed end 1a to be shortened. When viewed from the Z direction, the contact plug 9B has a thin and elongated shape in the short direction (Y direction) of the vibration membrane 1. This increases the contact area with the upper electrode 33B and reduces the electrical resistance of the contact plug 9B. The second wiring 8B is led from the contact plug 9B, passing above the first piezoelectric element 3A and the fixed end 1a, to the membrane support member 2. As shown in FIG. 6A, the second wiring 8B is led from the other (left) end of the fixed end 1a (one side) in the Y direction to the membrane support member 2. Note that the second wiring 8B is not shown in the membrane support member 2.

[0044] An interlayer insulating film 12 is formed between the upper electrodes 33A, 33B and the first wiring 8A and second wiring 8B. Contact plugs 9A, 9B penetrate the interlayer insulating film 12 to electrically connect the upper electrode 33A and the first wiring 8A or the upper electrode 33B and the second wiring 8B, respectively. A protective film 13 is formed on the first wiring 8A, the second wiring 8B, and the interlayer insulating film 12. The interlayer insulating film 12 is made of, for example, SiO2 (silicon oxide). The protective film 13 is made of, for example, Si3N4 (silicon nitride).

[0045] 2 vibrates the diaphragm 1 by applying AC voltages of opposite phases shown in Fig. 3 to the upper electrodes (33A, 33B). Also, by setting the ratio (b / L) in the same manner as in the first embodiment, the maximum stress and maximum displacement of the diaphragm 1 can be reduced.

[0046] (Third embodiment) In the third embodiment, another embodiment of the planar arrangement of wiring connected to the upper electrodes of the first piezoelectric element 3A and the second piezoelectric element 3B will be described with reference to Figures 7A to 7C. Figure 7A is a plan view showing the configuration of a piezoelectric actuator 102 according to the third embodiment. Figure 7B is a cross-sectional view showing the configuration of the piezoelectric actuator 102 taken along the VIIB-VIIB section of Figure 7A. Figure 7C is a cross-sectional view showing the configuration of the piezoelectric actuator 102 taken along the VIIC-VIIC section of Figure 7A.

[0047] The first wiring 10A is connected to the upper electrode 33A via a contact plug 11A. The contact plug 11A is disposed at the end of the upper electrode 33A on the fixed end 1a side. This allows the length of the first wiring 10A from the contact plug 11A to the fixed end 1a to be shortened. When viewed from the Z direction, the contact plug 11A has a shape that is thin and long in the short direction (Y direction) of the vibration membrane 1. This increases the contact area with the upper electrode 33A and reduces the electrical resistance of the contact plug 11A. The first wiring 10A passes above the fixed end 1a and is led out to the membrane support part 2.

[0048] The first wiring 10A extends beyond the contact plug 11A to the free end 1b side. The first wiring 10A passes above the second piezoelectric element 3B and extends to the free end 1b.

[0049] The second wiring 10B is connected to the upper electrode 33B via a contact plug 11B. The contact plug 11B is disposed at the end of the upper electrode 33B on the fixed end 1a side. This allows the length of the second wiring 10B from the contact plug 11B to the fixed end 1a to be shortened. When viewed from the Z direction, the contact plug 11B has a shape that is thin and long in the short direction (Y direction) of the vibration membrane 1. This increases the contact area with the upper electrode 33B and reduces the electrical resistance of the contact plug 11B. The second wiring 10B passes above the first piezoelectric element 3A and the fixed end 1a and is led out to the membrane support part 2.

[0050] The second wiring 10B extends toward the free end 1b beyond the contact plug 11B. The second wiring 10B extends to the free end 1b.

[0051] An interlayer insulating film 12 is formed between the upper electrodes 33A, 33B and the first wiring 10A and second wiring 10B. Contact plugs 11A, 11B penetrate the interlayer insulating film 12 to electrically connect the upper electrode 33A and the first wiring 10A or the upper electrode 33B and the second wiring 10B, respectively. A protective film 13 is formed on the first wiring 10A, the second wiring 10B, and the interlayer insulating film 12.

[0052] As described above, in the piezoelectric actuator 102 of the third embodiment, the length of the first wiring 10A in the longitudinal direction (X direction) of the vibrating membrane 1 is equal to the length of the second wiring 10B in the longitudinal direction (X direction) of the vibrating membrane 1. This makes it possible to improve the symmetry of the arrangement of the wirings 10A and 10B on the vibrating membrane 1.

[0053] In a modified example of the third embodiment, the second wiring 10B does not have to extend beyond the contact plug 11B toward the free end 1b. In this case, the first wiring 10A extends to the contact plug 11B. This allows the length of the first wiring 10A in the longitudinal direction (X direction) of the vibrating membrane 1 to be equal to the length of the second wiring 10B in the longitudinal direction (X direction) of the vibrating membrane 1.

[0054] Although the present disclosure has been described in detail above, it will be apparent to those skilled in the art that the present disclosure is not limited to the embodiments described herein. One or more elements of one embodiment may be combined with one or more elements of another embodiment. The present disclosure can be implemented in modified and altered forms without departing from the spirit and scope of the present disclosure, as defined by the claims. Therefore, the description of the present disclosure is intended to be illustrative and explanatory and is not intended to be limiting of the present disclosure.

[0055] (Addendum) The technical ideas that can be understood from this disclosure are described below. The components described in the appendices are given the reference numerals of the corresponding components in the embodiments. The reference numerals are provided as examples to aid understanding, and the components described in each appendix should not be limited to the components indicated by the reference numerals.

[0056] <Appendix 1> Each of the piezoelectric actuators 100-102 has a cantilever structure and includes a vibrating membrane 1 having a fixed end 1a and a free end 1b, the vibrating membrane 1 having a main surface (first main surface 1A) divided into a first region (3A) on the fixed end 1a side and a second region (3B) on the free end 1b side, a membrane support 2 to which the fixed end 1a of the vibrating membrane 1 is connected, a first piezoelectric element 3A arranged in the first region (3A) of the main surface 1A of the vibrating membrane 1, a second piezoelectric element 3B arranged in the second region (3B) of the main surface 1A of the vibrating membrane 1, and drive units 7A and 7B that apply AC voltages of opposite phases to the first piezoelectric element 3A and the second piezoelectric element 3B. The ratio (b / L) of the length b from the fixed end 1a to the boundary 3a between the first region (3A) and the second region (3B) to the length L of the vibrating membrane 1 from the fixed end 1a to the free end 1b is set according to a resonance mode specific to the piezoelectric actuators 100-102. This makes it possible to reduce the amount of displacement and stress of the vibrating membrane 1 during resonance.

[0057] <Appendix 2> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a first-order bending mode M1 in which no antinode is formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.1 or more and 0.38 or less for the first-order bending mode M1. This makes it possible to reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the first-order bending mode M1.

[0058] <Appendix 3> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a first-order bending mode M1 in which no antinode is formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.16 or more and 0.3 or less for the first-order bending mode. This makes it possible to further reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the first-order bending mode M1.

[0059] <Appendix 4> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a second-order bending mode M2 ​​in which one antinode is formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.56 or more and 0.71 or less for the second-order bending mode M2. This makes it possible to reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the second-order bending mode M2.

[0060] <Appendix 5> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a second-order bending mode M2 ​​in which one antinode is formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.59 or more and 0.67 or less for the second-order bending mode M2. This makes it possible to further reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the second-order bending mode M2.

[0061] <Appendix 6> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a third-order bending mode M3 in which two antinodes are formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.06 or more and 0.22 or less, or 0.7 or more and 0.82 or less, for the third-order bending mode M3. This makes it possible to reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the third-order bending mode M3.

[0062] <Appendix 7> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a third-order bending mode M3 in which two antinodes are formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.73 or more and 0.79 or less for the third-order bending mode M3. This makes it possible to further reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the third-order bending mode M3.

[0063] <Appendix 8> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a fourth-order bending mode M4 in which three antinodes are formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.24 or more and 0.46 or less, or 0.81 or more and 0.88 or less, for the fourth-order bending mode M4. This makes it possible to reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the fourth-order bending mode M4.

[0064] <Appendix 9> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a fourth-order bending mode M4 in which three antinodes are formed between the fixed end 1a and the free end 1b. The ratio b / L is set to 0.27 to 0.32, 0.38 to 0.44, or 0.83 to 0.85 for the fourth-order bending mode M4. This makes it possible to further reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the fourth-order bending mode M4.

[0065] <Appendix 10> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a vibration mode BF characterized by a displacement shape in a direction intersecting the direction connecting the fixed end 1a and the free end 1b. The ratio b / L is set to 0.44 or more and 0.84 or less for the vibration mode BF. This makes it possible to reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the vibration mode BF.

[0066] <Appendix 11> In the piezoelectric actuators 100 to 102 described in Supplementary Note 1, the natural resonance modes include a vibration mode BF characterized by a displacement shape in a direction intersecting the direction connecting the fixed end 1a and the free end 1b. The ratio b / L is set to 0.53 or more and 0.74 or less for the vibration mode BF. This makes it possible to further reduce the maximum stress and maximum displacement of the vibrating membrane 1 in the vibration mode BF.

[0067] <Appendix 12> The piezoelectric actuator 102 described in any one of Supplementary Notes 1 to 11 further includes a first wiring 10A connected to the first piezoelectric element 3A and a second wiring 10B connected to the second piezoelectric element 3B. On the vibrating membrane 1, the length of the first wiring 10A in the longitudinal direction (X direction) of the vibrating membrane 1 is equal to the length of the second wiring 10B in the longitudinal direction (X direction). This can improve the symmetry of the arrangement of the wirings 10A and 10B on the vibrating membrane 1.

[0068] <Appendix 13> In a method for driving piezoelectric actuators 100-102 having a cantilever structure, the piezoelectric actuators 100-102 each include a vibrating membrane 1 having a fixed end 1a and a free end 1b, and a main surface (first main surface 1A) divided into a first region (3A) on the fixed end 1a side and a second region (3B) on the free end 1b side, a membrane support 2 to which the fixed end 1a of the vibrating membrane 1 is connected, a first piezoelectric element 3A arranged in the first region (3A) of the main surface 1A of the vibrating membrane 1, and a second piezoelectric element 3B arranged in the second region (3B) of the main surface 1A of the vibrating membrane 1. A ratio b / L of a length b from the fixed end 1a to a boundary 3a between the first region (3A) and the second region (3B) to a length L of the vibrating membrane 1 from the fixed end 1a to the free end 1b is set in accordance with a resonance mode specific to the piezoelectric actuators 100-102. The driving method of the piezoelectric actuators 100 to 102 includes applying AC voltages of opposite phases to the first piezoelectric element 3A and the second piezoelectric element 3B, thereby reducing the displacement and stress of the vibrating membrane 1 during resonance. [Explanation of symbols]

[0069] 1. Vibration membrane 1a fixed end 1A First principal surface (principal surface) 1b free end 2 Membrane support part 3a boundary 3A First piezoelectric element (first area) 3B Second piezoelectric element (second region) 5 Slits 7A First drive unit (drive unit) 7B Second drive unit (drive unit) 8A, 10A 1st wiring 8B, 10B second wiring 31 Lower electrode 32A, 32B Piezoelectric film 33A, 33B Upper electrode 100~102 Piezoelectric actuator b / L ratio BF Butterfly Mode M1 bending mode M2 bending secondary mode M3 third bending mode M4 fourth bending mode

Claims

1. A piezoelectric actuator having a cantilever structure, a vibration membrane having a fixed end and a free end, the main surface of the vibration membrane being divided into a first region on the fixed end side and a second region on the free end side; a membrane support part to which a fixed end of the vibration membrane is connected; a first piezoelectric element disposed in the first region of the main surface of the vibration membrane; a second piezoelectric element disposed in the second region of the main surface of the vibration membrane; a driving unit that applies AC voltages of opposite phases to the first piezoelectric element and the second piezoelectric element; and a ratio of a length from the fixed end to a boundary between the first region and the second region to a length of the vibration membrane from the fixed end to the free end is set according to a resonance mode specific to the piezoelectric actuator. Piezoelectric actuator.

2. the natural resonance mode includes a first-order bending mode in which no antinode is formed between the fixed end and the free end; The piezoelectric actuator according to claim 1 , wherein the ratio is set to be equal to or greater than 0.1 and equal to or less than 0.38 for the first-order bending mode.

3. the natural resonance mode includes a first-order bending mode in which no antinode is formed between the fixed end and the free end; The piezoelectric actuator according to claim 1 , wherein the ratio is set to be equal to or greater than 0.16 and equal to or less than 0.3 for the first bending mode.

4. the natural resonance mode includes a bending second-order mode in which one antinode is formed between the fixed end and the free end; The piezoelectric actuator according to claim 1 , wherein the ratio is set to be equal to or greater than 0.56 and equal to or less than 0.71 for the second-order bending mode.

5. the natural resonance mode includes a bending second-order mode in which one antinode is formed between the fixed end and the free end; The piezoelectric actuator according to claim 1 , wherein the ratio is set to be equal to or greater than 0.59 and equal to or less than 0.67 for the second bending mode.

6. the natural resonance mode includes a third-order bending mode in which two antinodes are formed between the fixed end and the free end; The piezoelectric actuator according to claim 1 , wherein the ratio is set to 0.06 or more and 0.22 or less, or 0.7 or more and 0.82 or less, for the third bending mode.

7. the natural resonance mode includes a third-order bending mode in which two antinodes are formed between the fixed end and the free end; The piezoelectric actuator according to claim 1 , wherein the ratio is set to be equal to or greater than 0.73 and equal to or less than 0.79 for the third bending mode.

8. the natural resonance mode includes a fourth-order bending mode in which three antinodes are formed between the fixed end and the free end; 2. The piezoelectric actuator according to claim 1, wherein the ratio is set to 0.24 or more and 0.46 or less, or 0.81 or more and 0.88 or less, for the fourth bending mode.

9. the natural resonance mode includes a fourth-order bending mode in which three antinodes are formed between the fixed end and the free end; 2. The piezoelectric actuator according to claim 1, wherein the ratio is set to 0.27 or more and 0.32 or less, 0.38 or more and 0.44 or less, or 0.83 or more and 0.85 or less for the fourth bending mode.

10. the natural resonance mode includes a vibration mode characterized by a displacement shape in a direction intersecting a direction connecting the fixed end and the free end, 2. The piezoelectric actuator according to claim 1, wherein the ratio is set to be equal to or greater than 0.44 and equal to or less than 0.84 for the vibration mode.

11. the natural resonance mode includes a vibration mode characterized by a displacement shape in a direction intersecting a direction connecting the fixed end and the free end, 2. The piezoelectric actuator according to claim 1, wherein the ratio is set to be equal to or greater than 0.53 and equal to or less than 0.74 for the vibration mode.

12. a first wiring connected to the first piezoelectric element; a second wiring connected to the second piezoelectric element, The piezoelectric actuator according to claim 1 , wherein, on the vibration membrane, a length of the first wiring in the longitudinal direction of the vibration membrane is equal to a length of the second wiring in the longitudinal direction.

13. A method for driving a piezoelectric actuator having a cantilever structure, comprising: The piezoelectric actuator is a vibration membrane having a fixed end and a free end, the main surface of the vibration membrane being divided into a first region on the fixed end side and a second region on the free end side; a membrane support part to which a fixed end of the vibration membrane is connected; a first piezoelectric element disposed in the first region of the main surface of the vibration membrane; a second piezoelectric element disposed in the second region of the main surface of the vibration membrane; and a ratio of a length from the fixed end to a boundary between the first region and the second region to a length of the vibration membrane from the fixed end to the free end is set in accordance with a resonance mode specific to the piezoelectric actuator, Applying AC voltages of opposite phases to the first and second piezoelectric elements A method for driving a piezoelectric actuator.

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