Piezoelectric actuator

Abstract

The present invention provides a piezoelectric actuator that achieves both sufficient deformation in a cantilevered state and sufficient reliability with respect to the applied drive voltage. [Solution] In the piezoelectric actuator 1, when the piezoelectric element 3 is viewed from the stacking direction, the distance R1 from the edge 3b on the connection part 11 side of the piezoelectric element 3 to the edge 8a of the internal electrode 5 in the drive part 12 is greater than the distance R2 from the edge 3c on the drive part 12 side of the piezoelectric element 3 to the edge 8b of the internal electrode 5 in the drive part 12, and the thickness T3 of the cover layer 10 is less than the thickness T2 of the element layer 4 between the internal electrodes 5 in the drive part 12.

Description

Technical Field

[0001] The present disclosure relates to a piezoelectric actuator.

Background Art

[0002] A piezoelectric actuator provided with a drive unit in which a body portion made of a piezoelectric material is interposed between internal electrodes is known. In such a piezoelectric actuator, the drive unit is displaced by applying a drive voltage between the internal electrodes. The piezoelectric element disclosed in Patent Document 1 includes a first conductor layer provided on a surface facing an actuator base, and a second conductor layer facing the first conductor layer inside the piezoelectric body. The second conductor layer is electrically connected to an external connection portion layer provided on the surface facing the actuator base via a through-hole conductor extending along the facing direction of the first conductor layer and the second conductor layer at one end of the piezoelectric element.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the applications of a piezoelectric actuator is, for example, a piezoelectric valve. The piezoelectric valve is attached to a compressed air pipe used in, for example, a factory, and has a function of keeping the pressure in the pipe constant. In this case, the piezoelectric actuator is also called a bending element, and by applying a drive voltage in a state where a diaphragm is attached to a plate-shaped piezoelectric element, the piezoelectric element and the diaphragm are deformed into a convex or concave shape. In such a piezoelectric actuator, it is required to achieve both ensuring a sufficient deformation amount in a cantilever state and ensuring sufficient reliability with respect to the applied drive voltage.

[0005] This disclosure was made to solve the above-mentioned problems and aims to provide a piezoelectric actuator that can achieve both sufficient deformation in a cantilevered state and sufficient reliability with respect to the applied drive voltage. [Means for solving the problem]

[0006] The gist of this disclosure is as follows:

[0007] [1] A piezoelectric element having a plurality of elemental layers made of piezoelectric material and extending in a direction perpendicular to the stacking direction of the plurality of elemental layers, a plurality of internal electrodes provided inside the piezoelectric element so as to sandwich the elemental layers, and an external electrode provided on the end face of the piezoelectric element in the stacking direction, on one end side in the extending direction of the piezoelectric element, wherein one end side in the extending direction of the piezoelectric element is a connection part in which the plurality of internal electrodes are electrically connected to the external electrode, and the other end side in the extending direction of the piezoelectric element is a drive voltage provided between the internal electrodes A piezoelectric actuator comprising a drive unit that is displaced by applied pressure, wherein one or more cover layers of the piezoelectric element are arranged on the outermost layer in the stacking direction of the piezoelectric element, and when the piezoelectric element is viewed from the stacking direction, the distance from the edge of the piezoelectric element on the connection side to the edge of the internal electrode in the drive unit is greater than the distance from the edge of the piezoelectric element on the drive unit side to the edge of the internal electrode in the drive unit, and the thickness of the cover layer is less than the thickness of the element layer between the internal electrodes in the drive unit.

[0008] In this piezoelectric actuator, a cover layer consisting of one or more elemental layers is arranged as the outermost layer in the stacking direction of the piezoelectric element. The cover layer prevents the exposure of the internal electrodes in the piezoelectric element. Furthermore, in this piezoelectric actuator, the distance from the edge of the piezoelectric element on the connection side to the internal electrodes in the drive unit is greater than the distance from the edge of the piezoelectric element on the drive unit side to the edge of the internal electrodes in the drive unit, and the thickness of the cover layer is less than the thickness of the elemental layer between the internal electrodes in the drive unit. With the former configuration, the piezoelectric element can be sufficiently extended to near the edge on the drive unit side while the drive unit is biased towards the opposite side of the connection, and with the latter configuration, the thickness of the cover layer that does not contribute to driving can be suppressed in the piezoelectric element. Therefore, this piezoelectric actuator achieves both sufficient deformation in a cantilevered state and sufficient reliability with respect to the applied drive voltage.

[0009] [2] When the piezoelectric element is viewed from the stacking direction, the distance from the edge of the piezoelectric element on the connection side to the edge of the external electrode on the connection side is smaller than the distance from the edge of the external electrode on the drive side to the edge of the internal electrode in the drive unit, as described in [1]. With this configuration, the external electrode can be positioned closer to the edge of the piezoelectric element on the connection side. As a result, in the extending direction of the piezoelectric element, it becomes possible to form the drive unit to be sufficiently long relative to the connection unit, and the amount of deformation in the cantilever state can be more sufficiently secured.

[0010] [3] The piezoelectric actuator according to [1] or [2], wherein the external electrode is composed of a sputtered film. With such a configuration, migration can be suppressed even if the external electrode includes metal particles and resin. This further improves the reliability with respect to the applied drive voltage.

[0011] [4] In the connection portion, the internal electrode is electrically connected to the external electrode via a through-hole, the piezoelectric actuator according to any one of [1] to [3]. With such a configuration, the area occupied by the connection portion in the piezoelectric element can be made more compact, and the amount of deformation in the cantilever state can be more sufficiently secured.

[0012] [5] A piezoelectric actuator according to any one of [1] to [4], further comprising a diaphragm joined to the piezoelectric element. In this case, the diaphragm joined to the piezoelectric element can increase the power (torque) when the piezoelectric element is displaced.

[0013] [6] The piezoelectric actuator according to [5], wherein the length of the diaphragm in the extending direction is greater than the length of the piezoelectric element in the extending direction, and the center of the piezoelectric element in the extending direction is offset toward the drive unit with respect to the center of the diaphragm in the extending direction. With such a configuration, the piezoelectric element can be biased toward the drive unit in the diaphragm. Therefore, the power (torque) when the piezoelectric element is displaced can be further increased. [Effects of the Invention]

[0014] According to this disclosure, it is possible to achieve both sufficient deformation in a cantilevered state and sufficient reliability with respect to the applied drive voltage. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view of a piezoelectric actuator according to one embodiment of the present disclosure. [Figure 2] Figure 1 is a side view of the piezoelectric actuator shown. [Figure 3] This is an exploded perspective view showing the layer structure of the piezoelectric element. [Figure 4] This is a cross-sectional view showing the layer structure of the piezoelectric element. [Figure 5] This is a plan view showing the main components of a piezoelectric actuator. [Modes for carrying out the invention]

[0016] Hereinafter, with reference to the drawings, a preferred embodiment of a piezoelectric actuator according to one aspect of the present disclosure will be described in detail.

[0017] FIG. 1 is a perspective view of a piezoelectric actuator according to an embodiment of the present disclosure. Further, FIG. 2 is a side view thereof. The piezoelectric actuator 1 shown in FIGS. 1 and 2 is configured as a bending element applied to, for example, a piezoelectric valve. The piezoelectric valve is a member that is attached to a compressed air pipe used in, for example, a factory and has a function of keeping the pressure in the pipe constant. The application target of the piezoelectric actuator 1 is not limited to the piezoelectric valve, and it can also be applied to other devices such as acoustic devices such as speakers and buzzers, and print heads of inkjet printers.

[0018] The piezoelectric actuator 1 includes a diaphragm 2 and a piezoelectric body 3. In the present embodiment, both the diaphragm 2 and the piezoelectric body 3 are rectangular in plan view. In the following description, the “longitudinal direction” refers to the direction along the long side of the diaphragm 2 and the piezoelectric body 3, and the “lateral direction” refers to the direction along the short side of the diaphragm 2 and the piezoelectric body 3.

[0019] The thickness of the diaphragm 2 is approximately the same as the thickness of the piezoelectric body 3 or slightly larger than the thickness of the piezoelectric body 3. The diaphragm 2 is made of a conductive material such as metal. The material constituting the diaphragm 2 may be carbon fiber reinforced plastic, 42 alloy (an alloy containing iron and nickel), or the like. One end portion 2a in the longitudinal direction of the diaphragm 2 is a portion that is held, for example, by adhesion to other members using an adhesive, formation of a hole into which a fixing member can be inserted, or clamping by other members, when applied to the piezoelectric valve. As a result, the piezoelectric actuator 1 is in a cantilever state, with one end portion 2a side in the longitudinal direction of the diaphragm 2 being the fixed end and the other end portion 2b side in the longitudinal direction of the diaphragm 2 being the free end.

[0020] The piezoelectric element 3 has a plurality of element layers 4 (see FIG. 3) made of a piezoelectric material such as a piezoelectric ceramic. Here, the stacking direction of the plurality of element layers 4 corresponds to the thickness direction of the piezoelectric element 3. Examples of the piezoelectric ceramic material constituting the element layer 4 include PZT [Pb(Zr,Ti)O3], PT (PbTiO3), PLZT [(Pb,La)(Zr,Ti)O3], barium titanate (BaTiO3), and the like. The element layer 4 is constituted by, for example, a sintered body of a ceramic green sheet containing the above-described piezoelectric ceramic material. In the actual piezoelectric element 3, the element layers 4 are integrated to such an extent that the boundaries between the layers cannot be recognized.

[0021] The piezoelectric element 3 is provided with a plurality of internal electrodes 5 and a plurality of external electrodes 6. The internal electrodes 5 are provided inside the piezoelectric element 3 so as to sandwich the element layers 4. The internal electrodes 5 are constituted by including, for example, electrode portions 7A, 7B for connection, electrode portions 8A, 8B for driving, and electrode portions 9A, 9B for connection (see FIG. 3). The internal electrodes 5 are made of a conductive material such as a metal. As the conductive material constituting the internal electrodes 5, for example, Ag (silver), Pd (palladium), Pt (platinum), an Ag-Pd alloy, or the like is used. The internal electrodes 5 are constituted by a sintered body of a conductive paste containing the above-described conductive material.

[0022] The external electrodes 6 are provided on one end side in the longitudinal direction (extending direction) of the piezoelectric element 3 at the end face 3a in the stacking direction of the piezoelectric element 3. The end face 3a is the end face on the opposite side to the joint face with the diaphragm 2. In the present embodiment, the external electrodes 6 are constituted by a pair of external electrodes 6A, 6B. The external electrodes 6A, 6B have the same shape as each other and, in a plan view of the piezoelectric element 3, form, for example, a rectangular shape with rounded corners. The external electrodes 6A, 6B are arranged in a state of being separated from each other in the short direction orthogonal to the longitudinal direction at one end side in the longitudinal direction of the end face 3a of the piezoelectric element 3.

[0023] The external electrode 6 is composed of a metal plating film (sputtered film) formed, for example, by sputtering. The external electrode 6 may also be composed of a multilayer metal plating film. Examples of constituent materials for the external electrode 6 include chromium (Cr) / copper-nickel alloy (Ni-Cu) / gold (Au).

[0024] Figure 3 is a cross-sectional view showing the electrode configuration of a piezoelectric element. In the example shown in Figure 3, the piezoelectric element 3 is composed of elemental layers 4A to 4D, each with a different pattern of internal electrodes 5. In the example shown in Figure 3, elemental layer 4B is positioned in the middle of the stacking direction of the piezoelectric element 3, and multiple layers (e.g., 5 layers) of elemental layer 4A are stacked on both sides of the stacking direction, flanking elemental layer 4B. Furthermore, a pair of elemental layers 4C are stacked so as to sandwich the multiple layers of elemental layer 4A on both sides of the stacking direction between elemental layer 4B and elemental layer 4C, with elemental layer 4D being the outermost layer stacked on one of the elemental layer 4C (the upper layer in the illustration in Figure 3). The other elemental layer 4C constitutes the outermost layer on the opposite side from elemental layer 4D.

[0025] The base layer 4A is a layer provided only with connecting electrode portions 7A and 7B. Connecting electrode portion 7A is the portion electrically connected to the external electrode 6A, and connecting electrode portion 7B is the portion electrically connected to the external electrode 6B. The connecting electrode portions 7A and 7B are the same shape as each other, and, like the pair of external electrodes 6A and 6B, in a plan view of the piezoelectric base 3, they form, for example, a rectangular shape with rounded corners. The planar shape of the connecting electrode portions 7A and 7B may be slightly smaller than that of the external electrodes 6A and 6B. The connecting electrode portions 7A and 7B are arranged spaced apart from each other on one end of the base layer 4A in the longitudinal direction so that they overlap with the external electrodes 6A and 6B when viewed from the stacking direction.

[0026] The base layer 4B is a layer provided with connecting electrode portions 7A and 7B, a driving electrode portion 8A, and a linking electrode portion 9A. The driving electrode portion 8A has a rectangular shape with rounded corners, for example, in a plan view of the piezoelectric base 3. The driving electrode portion 8A is provided with a sufficiently large area compared to the connecting electrode portions 7A and 7B, and is positioned on the other end side of the base layer 4B so as to occupy most of the area excluding the formation areas of the connecting electrode portions 7A and 7B. The linking electrode portion 9A extends in the longitudinal direction of the base layer 4B with the same width as the connecting electrode portion 7A between the connecting electrode portion 7A and the driving electrode portion 8A, and connects the connecting electrode portion 7A and the driving electrode portion 8A.

[0027] The base layer 4C is a layer provided with connecting electrode portions 7A and 7B, a driving electrode portion 8B, and a connecting electrode portion 9B. The driving electrode portion 8B has the same shape as the driving electrode portion 8A, and in a plan view of the piezoelectric base 3, it has a rectangular shape with rounded corners, for example. The driving electrode portion 8B is provided with a sufficiently large area compared to the connecting electrode portions 7A and 7B, and is positioned on the other end side of the base layer 4C so as to occupy most of the area excluding the formation areas of the connecting electrode portions 7A and 7B.

[0028] In a plan view of the piezoelectric element 3, the driving electrode portions 8A and 8B overlap at the same position without any protruding portions. The connecting electrode portion 9B extends in the longitudinal direction of the element layer 4C with the same width as the connecting electrode portion 7B between the connecting electrode portion 7B and the driving electrode portion 8B, connecting the connecting electrode portion 7B and the driving electrode portion 8B.

[0029] The outermost layer 4C, which is opposite to the element layer 4D, functions as a cover layer 10 that prevents the exposure of the internal electrodes 5 in the piezoelectric element 3. In the example in Figure 3, the element layer 4D as the cover layer 10 is a single layer, but an element layer 4 without one or more internal electrodes provided inside the element layer 4D may be arranged as the cover layer 10.

[0030] The base layer 4D is a layer in which the internal electrodes 5 are not provided. The base layer 4D is laminated on the base layer 4C as the outermost layer in the stacking direction of the piezoelectric element 3 and functions as a cover layer 10 that prevents the exposure of the internal electrodes 5 in the piezoelectric element 3. The outer surface of the base layer 4D is the surface that becomes the end face 3a in the stacking direction of the piezoelectric element 3, and the external electrodes 6A and 6B described above are arranged on one end in the longitudinal direction. When multiple cover layers 10 are arranged, the external electrodes 6A and 6B described above are arranged on the outermost cover layer 10 of the multiple cover layers 10.

[0031] Figure 4 is a cross-sectional view showing the layer structure of the piezoelectric element. As shown in Figure 4, in this embodiment, one end of the piezoelectric element 3 in the longitudinal direction (extension direction) is a connection part 11 in which a plurality of internal electrodes 5 are electrically connected to an external electrode 6. The other end of the piezoelectric element 3 in the longitudinal direction (extension direction) is a drive part 12 that is displaced by the application of a drive voltage between the internal electrodes 5. The drive voltage can be, for example, a voltage that can generate an electric field of 1 kV / mm or more.

[0032] Specifically, in the piezoelectric element 3, the portion from the edge 3b on one longitudinal end of the piezoelectric element 3 to the edge 8a on one longitudinal end of the driving electrode portions 8A and 8B belongs to the connection portion 11. Also, in the piezoelectric element 3, the portion from the edge 8a on one longitudinal end of the driving electrode portions 8A and 8B to the edge 8b on the other longitudinal end of the driving electrode portions 8A and 8B (i.e., the portion where the driving electrode portions 8A and 8B overlap in the stacking direction with the element layer 4 in between) belongs to the driving portion 12.

[0033] In the connection section 11, the connecting electrode portions 7A in the aforementioned base layers 4A to 4C are electrically connected to each other via through-holes 13. Each of the connecting electrode portions 7A is electrically connected to the external electrode 6A via through-holes 13. Similarly, in the connection section 11, the connecting electrode portions 7B in the aforementioned base layers 4A to 4C are electrically connected to each other via through-holes 13. Each of the connecting electrode portions 7B is electrically connected to the external electrode 6B via through-holes 13.

[0034] In the example shown in Figure 4, multiple (two in this case) through-holes 13 are used for the electrical connection between adjacent connecting electrode portions 7A in the stacking direction, and for the electrical connection between adjacent connecting electrode portions 7B in the stacking direction. By using multiple through-holes 13 in this way, it is possible to increase the withstand voltage against the driving voltage. Also, in the example shown in Figure 4, the positions of adjacent through-holes 13 in the stacking direction are the same when viewed from the stacking direction. This simplifies the pattern of the base layer 4.

[0035] Furthermore, a single through-hole 13 may be used for the electrical connection between adjacent connecting electrode portions 7A in the stacking direction, and for the electrical connection between adjacent connecting electrode portions 7B in the stacking direction. In this case, the internal structure of the piezoelectric element 3 can be simplified. The positions of adjacent through-holes 13 in the stacking direction may be different from each other when viewed from the stacking direction. For example, by staggering the positions of adjacent through-holes 13 in the stacking direction for each element layer 4, it is possible to suppress the occurrence of conductivity defects.

[0036] In the drive unit 12, the drive electrode portions 8A and 8B are stacked in the stacking direction with multiple elemental layers 4 in between. When a drive voltage is applied to the drive electrode portions 8A and 8B via a pair of external electrodes 6A and 6B, the drive unit 12 is displaced in a way that it bends to one side or the other side in the stacking direction, with the connection portion 11 side as the fixed end. The direction of displacement of the drive unit 12 is controlled by a prior polarization treatment of the piezoelectric element 3.

[0037] In this embodiment, as described above, the connecting electrode portions 7A and 7B are arranged in the base layers 4A to 4C, respectively. On the other hand, between the base layer 4B on which the driving electrode portion 8A is arranged and the base layer 4C on which the driving electrode portion 8B is arranged, there are multiple base layers 4A that do not have the driving electrode portions 8A and 8B. Therefore, the length T1 of each through-hole 13 in the connecting portion 11 is smaller than the thickness T2 of the base layer 4 between the driving electrode portions 8A and 8B in the driving portion 12.

[0038] Furthermore, in this embodiment, as described above, the cover layer 10 consists of two separate base layers 4C and 4D, and multiple base layers 4A without drive electrode portions 8A and 8B are arranged between the base layer 4B on which the drive electrode portion 8A is located and the base layer 4C on which the drive electrode portion 8B is located. Therefore, the thickness T3 of the cover layer 10 is smaller than the thickness T2 of the base layer 4 between the drive electrode portions 8A and 8B in the drive unit 12. The thickness T3 of the cover layer 10 is not particularly limited, but it may be set to be, for example, 0.05 to 0.3 times the thickness T2 of the base layer 4 between the drive electrode portions 8A and 8B in the drive unit 12.

[0039] In this embodiment, it is also possible that there are multiple cover layers 10. In this case, the number of cover layers 10 should be adjusted so that the total thickness T3 of the multiple cover layers 10 is less than the thickness T2 of the base layer 4 between the driving electrode portions 8A and 8B in the drive unit 12.

[0040] Figure 5 is a plan view showing the main components of a piezoelectric actuator. As shown in Figure 5, in the piezoelectric actuator 1, the arrangement of the internal electrodes 5 in the piezoelectric element 3 is designed such that the drive unit 12 is located on the other end of the piezoelectric element 3 in the longitudinal direction, i.e., on the free end side of the vibration.

[0041] More specifically, in the piezoelectric actuator 1, when the piezoelectric element 3 is viewed from the stacking direction, the distance R1 from the edge of the piezoelectric element 3 on the connection part 11 side (i.e., the edge on one longitudinal end of the piezoelectric element 3) 3b to the edge of the internal electrode 5 in the drive unit 12 (i.e., the edge on one longitudinal end of the drive electrode portions 8A and 8B) 8a is greater than the distance R2 from the edge of the piezoelectric element 3 on the drive unit 12 side (i.e., the edge on the other longitudinal end of the piezoelectric element 3) 3c to the edge of the internal electrode 5 in the drive unit 12 (i.e., the edge on the other longitudinal end of the drive electrode portions 8A and 8B) 8b. This indicates that, in the longitudinal direction of the piezoelectric element 3, the drive unit 12 extends to a position close to the edge 3c of the piezoelectric element 3 on the drive unit 12 side. There are no particular restrictions on the distance R1, but it may be set to be, for example, 5 to 15 times the distance R2.

[0042] Furthermore, in the piezoelectric actuator 1, when the piezoelectric element 3 is viewed from the stacking direction, the distance R3 from the edge 3b on the connection portion 11 side of the piezoelectric element 3 (i.e., the edge on one longitudinal end of the piezoelectric element 3) to the edge 6a on the connection portion 11 side (the edge 3b side of the piezoelectric element 3) of the external electrode 6 is smaller than the distance R4 from the edge 6b on the drive unit 12 side (the edge 3b side of the piezoelectric element 3) of the external electrode 6 to the edge 8a of the internal electrode 5 of the drive unit 12. This indicates that when the piezoelectric element 3 is viewed from the stacking direction, the pair of external electrodes 6A and 6B are located closer to the edge 3b on the connection portion 11 side of the piezoelectric element 3. There are no particular restrictions on the distance R3, but it may be set to be, for example, greater than 1 times and less than or equal to 2 times the distance R4.

[0043] As shown in Figures 1 and 2, an adhesive portion 14 is provided for joining the diaphragm 2 and the piezoelectric element 3. The adhesive portion 14 may be arranged over the entire joining surface between the piezoelectric element 3 and the diaphragm 2. From the viewpoint of preventing short circuits, the adhesive portion 14 is made of an adhesive material that does not contain conductive components such as conductive particles. Examples of adhesive materials that make up the adhesive portion 14 include thermosetting epoxy resin.

[0044] In this embodiment, as shown in Figures 1 and 2, the length of the diaphragm 2 in the longitudinal direction is greater than the length of the piezoelectric element 3 in the longitudinal direction. Furthermore, when joining the diaphragm 2 and the piezoelectric element 3, the distance R5 from one longitudinal edge 2c of the diaphragm 2 to one longitudinal end edge 3b of the piezoelectric element 3 is greater than the distance R6 from the other longitudinal edge 2d of the diaphragm 2 to the other longitudinal end edge 3c of the piezoelectric element 3 in the longitudinal direction. As a result, the center C1 of the piezoelectric element 3 in the longitudinal direction is shifted toward the drive unit 12 side relative to the center C2 of the diaphragm 2 in the longitudinal direction, and the center of gravity of the piezoelectric actuator 1 is located on the free end side of the vibration.

[0045] As explained above, in the piezoelectric actuator 1, a cover layer 10 made of one or more elemental layers 4 is arranged as the outermost layer in the stacking direction of the piezoelectric element 3. The cover layer 10 prevents the exposure of the internal electrodes 5 in the piezoelectric element 3. In addition, in the piezoelectric actuator 1, the distance R1 from the edge 3b on the connection part 11 side of the piezoelectric element 3 to the internal electrodes 5 in the drive part 12 is greater than the distance R2 from the edge 3c on the drive part 12 side of the piezoelectric element 3 to the internal electrodes 5 in the drive part 12, and the thickness T3 of the cover layer 10 is smaller than the thickness T2 of the elemental layer 4 between the internal electrodes 5 in the drive part 12.

[0046] According to the former configuration, the piezoelectric element 3 can be sufficiently extended to near the edge on the side of the drive unit 12 while the drive unit 12 is located on the opposite side of the connection unit 11. According to the latter configuration, the thickness T3 of the cover layer 10 that does not contribute to the drive can be suppressed in the piezoelectric element 3. Therefore, the piezoelectric actuator 1 can achieve both sufficient deformation in a cantilevered state and sufficient reliability with respect to the applied drive voltage.

[0047] In this embodiment, when the piezoelectric element 3 is viewed from the stacking direction, the distance R3 from the edge 3b on the connection portion 11 side of the piezoelectric element 3 to the edge 6a on the connection portion 11 side of the external electrode 6 is smaller than the distance R4 from the edge 6b on the drive portion 12 side of the external electrode 6 to the edge 8a of the internal electrode 5 in the drive portion 12. With this configuration, the external electrodes 6A and 6B can be positioned closer to the edge 3b on the connection portion 11 side of the piezoelectric element 3. As a result, in the extending direction of the piezoelectric element 3, it becomes possible to form the drive portion 12 to be sufficiently long relative to the connection portion 11, thereby ensuring a more sufficient amount of deformation in the cantilever state.

[0048] In this embodiment, the external electrode 6 is made of a sputtered film. With this configuration, migration can be suppressed even if the external electrode 6 contains metal particles and resin. This further improves the reliability with respect to the applied drive voltage.

[0049] In this embodiment, the internal electrode 5 (connection electrode portions 7A, 7B) in the connection portion 11 is electrically connected to the external electrode 6 via the through-hole 13. With this configuration, the area occupied by the connection portion 11 in the piezoelectric element 3 can be made more compact, and the amount of deformation in the cantilever state can be more sufficiently secured.

[0050] In this embodiment, the piezoelectric actuator 1 further includes a diaphragm 2 joined to the piezoelectric element 3. In this case, the diaphragm 2 joined to the piezoelectric element 3 can increase the power (torque) when the piezoelectric element 3 is displaced.

[0051] In this embodiment, the length of the diaphragm 2 in the extending direction is greater than the length of the piezoelectric element 3 in the extending direction, and the center C1 of the piezoelectric element 3 in the extending direction is shifted toward the drive unit 12 side relative to the center C2 of the diaphragm 2 in the extending direction. With this configuration, the piezoelectric element 3 can be biased toward the drive unit 12 side in the diaphragm 2. Therefore, the power (torque) when the piezoelectric element 3 is displaced can be further increased. [Explanation of symbols]

[0052] 1...Piezoelectric actuator, 2...Diaphragm, 3...Piezoelectric element, 3a...End face, 4...Element layer, 5...Internal electrode, 6...External electrode, 10...Cover layer, 11...Connection part, 12...Drive part, 13...Through hole.

Claims

1. A piezoelectric element having multiple layers of piezoelectric material and extending in a direction perpendicular to the stacking direction of the multiple layers, Inside the piezoelectric element, a plurality of internal electrodes are provided so as to sandwich the element layer, The piezoelectric element comprises an external electrode provided on one end side in the extending direction of the piezoelectric element at the end face in the stacking direction of the piezoelectric element, One end of the piezoelectric element in the extending direction is a connection portion where the plurality of internal electrodes are electrically connected to the external electrodes. The other end of the piezoelectric element in the extending direction is a drive unit that is displaced by the application of a drive voltage between the internal electrodes. The outermost layer in the stacking direction of the piezoelectric element is covered with one or more of the element layers. When the piezoelectric element is viewed from the stacking direction, the distance from the edge of the piezoelectric element on the connection side to the edge of the internal electrode in the drive unit is greater than the distance from the edge of the piezoelectric element on the drive unit side to the edge of the internal electrode in the drive unit. A piezoelectric actuator wherein the thickness of the cover layer is smaller than the thickness of the base layer between the internal electrodes in the drive unit.

2. The piezoelectric actuator according to claim 1, wherein, when the piezoelectric element is viewed from the stacking direction, the distance from the edge of the piezoelectric element on the connection side to the edge of the external electrode on the connection side is smaller than the distance from the edge of the external electrode on the drive side to the edge of the internal electrode in the drive unit.

3. The piezoelectric actuator according to claim 1, wherein the external electrode is made of a sputtered film.

4. The piezoelectric actuator according to claim 1, wherein in the connection portion, the internal electrode is electrically connected to the external electrode via a through-hole.

5. The piezoelectric actuator according to any one of claims 1 to 4, further comprising a diaphragm joined to the piezoelectric element.

6. The length of the diaphragm in the extending direction is greater than the length of the piezoelectric element in the extending direction. The piezoelectric actuator according to claim 5, wherein the center of the piezoelectric element in the extending direction is offset toward the drive unit side with respect to the center of the diaphragm in the extending direction.

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