Layered piezoelectric elements

Abstract

A stacked piezoelectric element includes a piezoelectric body comprising a piezoelectric ceramic material, a first electrode, and a second electrode. The piezoelectric body has a first main surface and a second main surface opposite to each other. The first electrode includes an outer electrode formed on the first main surface. The second electrode includes an inner electrode formed within the piezoelectric body opposite to the outer electrode. The piezoelectric body includes an active region between the outer electrode and the inner electrode, and an inactive region on the side opposite to the active region, separated by the inner electrode. The stress experienced by the piezoelectric body from the outer electrode is greater than the stress experienced by the piezoelectric body from the inner electrode. The polarization direction of the active region is from the outer electrode toward the inner electrode.

Description

Technical Field

[0001] This invention relates to a laminated piezoelectric element. Background Technology

[0002] Known stacked piezoelectric elements include a piezoelectric element comprising a piezoelectric ceramic material and a first electrode and a second electrode configured to apply an electric field to the piezoelectric element (see, for example, Patent Documents 1 and 2). The piezoelectric element has a first main surface and a second main surface opposite to each other. The first electrode includes an external electrode formed on the first main surface. The second electrode includes an internal electrode formed within the piezoelectric element opposite to the external electrode.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2008 / 078487

[0006] Patent Document 2: International Publication No. 2015 / 060132 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] One embodiment of the present invention aims to provide a stacked piezoelectric element that achieves large displacement and has high reliability.

[0009] Means for solving technical problems

[0010] The inventors have conducted in-depth research on stacked piezoelectric elements that achieve large displacement and high reliability. As a result, the inventors gained new insights, which led to the conception of this invention.

[0011] The piezoelectric element is polarized. Through polarization, specific ions move within the crystal structure, aligning the polarization directions of the magnetic domains within the piezoelectric element. These specific ions are, for example, composed of ABO... X The perovskite-type crystal structure represented contains boron (B) ions. In this case, the greater the total amount of B ions that migrate to the specified positions, the better the piezoelectric element is polarized. In structures where the piezoelectric element is well polarized, the piezoelectric properties are high. A suitable polarization state is achieved when B ions migrate to the specified positions in each magnetic domain, and the polarization is uniform in the specified direction.

[0012] The ease of migration of a specified ion varies depending on the stress the piezoelectric element experiences from a component different from the piezoelectric element itself. The piezoelectric element has portions subjected to stress from one component and portions subjected to stress from other components. When the stress from one component is greater than the stress from other components, the specified ion exhibits, for example, the following migration tendency: the specified ion is less likely to migrate towards the portion subjected to stress from one component and more likely to migrate towards the portion subjected to stress from other components.

[0013] Therefore, a stacked piezoelectric element with the following structure tends to achieve large polarization. The piezoelectric element has multiple parts subjected to different stresses from multiple components different from the piezoelectric element itself. The polarization direction is from the part subjected to high stress towards the part subjected to low stress. The greater the polarization achieved, the greater the displacement of the stacked piezoelectric element. The greater the polarization achieved, the less likely the stacked piezoelectric element is to lose polarization even when used with a voltage applied in the opposite direction to the polarization direction. That is, the stacked piezoelectric element has high reliability.

[0014] Due to differences in the structure and manufacturing process of the electrodes disposed on the piezoelectric element, the stress experienced by the piezoelectric element from the electrodes can vary. When the electrode is, for example, a sintered metal layer, it is typically obtained by sintering simultaneously with the piezoelectric element. When the electrode is, for example, a plating layer, it is typically obtained by forming a metal layer on the piezoelectric element using a plating method. Plating methods include, for example, sputtering, vapor deposition, or electroplating.

[0015] When the electrode is a sintered metal layer, the metal materials attract each other during the sintering process, thus tending to form multiple pores in the electrode. When the electrode is a plating layer, the electrode is dense, and there is a tendency for pores not to form in the electrode. Due to these different tendencies, the piezoelectric element experiences less stress from the electrode as a sintered metal layer than from the electrode as a plating layer.

[0016] Therefore, a structure in which a piezoelectric element has multiple parts subjected to different stresses from multiple components different from the piezoelectric element can be achieved by forming internal and external electrodes on the piezoelectric element.

[0017] One embodiment of the stacked piezoelectric element includes a piezoelectric body comprising a piezoelectric ceramic material, a first electrode, and a second electrode. The piezoelectric body has a first main surface and a second main surface opposite to each other. The first electrode includes an external electrode formed on the first main surface. The second electrode includes an internal electrode formed within the piezoelectric body opposite to the external electrode. The piezoelectric body includes an active region between the external electrode and the internal electrode, and an inactive region on the side opposite to the active region, separated by the internal electrode. The stress experienced by the piezoelectric body from the external electrode is greater than the stress experienced by the piezoelectric body from the internal electrode. The polarization direction of the active region is from the external electrode toward the internal electrode.

[0018] In one of the above embodiments, the stress experienced by the piezoelectric element from the internal electrode is less than the stress experienced by the piezoelectric element from the external electrode. The active region between the external electrode and the internal electrode has portions subjected to stress from the internal electrode and portions subjected to stress from the external electrode, and the stresses experienced by these portions are different as described above. The polarization direction of the active region is from the external electrode toward the internal electrode.

[0019] Therefore, the above-described embodiment achieves the following structure. The piezoelectric element (active region) has multiple portions that are subjected to different stresses from multiple components different from the piezoelectric element itself. The polarization direction is from the portion subjected to greater stress from one of the multiple components toward the portion subjected to less stress from the other components.

[0020] As a result, the above-described embodiment achieves a large displacement and has high reliability.

[0021] In one of the above embodiments, the coverage of the external electrode can also be greater than that of the internal electrode. This structure, where the coverage of the external electrode is greater than that of the internal electrode, simply and reliably achieves a structure where the stress experienced by the piezoelectric element from the external electrode is greater than the stress experienced by the piezoelectric element from the internal electrode.

[0022] In one embodiment described above, the piezoelectric element may also have a first end face and a second end face that are opposite to each other in a second direction intersecting a first direction opposite to the first main surface and the second main surface. The internal electrode may also be exposed on the first end face and separated from the second end face in the second direction. The external electrode may also be separated from the first end face in the second direction. The spacing between the internal electrode and the second end face in the second direction may also differ from the spacing between the external electrode and the first end face in the second direction. In these cases, the deformation of the stacked piezoelectric element (piezoelectric element) resulting from the polarization treatment and the displacement of the stacked piezoelectric element (piezoelectric element) generated by the drive are well balanced.

[0023] In one embodiment described above, the second electrode may also include an external electrode formed on the second main surface and electrically connected to the internal electrode. The external electrode included in the second electrode may also be separated from the second end face in the second direction. The distance between the external electrode included in the second electrode and the second end face in the second direction may also be greater than the distance between the internal electrode and the second end face in the second direction. In these cases, the deformation of the stacked piezoelectric element (piezoelectric body) generated by the polarization process and the displacement of the stacked piezoelectric element (piezoelectric body) generated by the drive are well balanced.

[0024] The effects of the invention

[0025] One embodiment of the present invention provides a stacked piezoelectric element that achieves large displacement and has high reliability. Attached Figure Description

[0026] Figure 1 This is a perspective view showing a stacked piezoelectric element according to one embodiment.

[0027] Figure 2 It is along Figure 1 A sectional view along line II-II.

[0028] Figure 3 It is a line graph showing the relationship between electric field and polarization. Detailed Implementation

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, in the description, the same reference numerals are used for the same elements or elements having the same function, and repeated descriptions are omitted.

[0030] Reference Figure 1 as well as Figure 2 The structure of the stacked piezoelectric element 1 involved in this embodiment will be described. Figure 1 This is a perspective view showing the stacked piezoelectric element involved in this embodiment. Figure 2 It is along Figure 1 A sectional view along line II-II.

[0031] The stacked piezoelectric element 1 includes a piezoelectric element 3 and a first electrode 10 and a second electrode 20 disposed on the piezoelectric element 3. The first electrode 10 and the second electrode 20 are configured to apply an electric field to the piezoelectric element 3. The stacked piezoelectric element 1 is used, for example, in a hard disk drive. The stacked piezoelectric element 1 is used, for example, in a second actuator other than a voice coil motor in a dual-actuator hard disk drive.

[0032] The piezoelectric element 3 comprises a piezoelectric ceramic material. The piezoelectric element 3 is, for example, composed of a sintered body of the piezoelectric ceramic material. The piezoelectric ceramic material may include, for example, PZT[Pb(Zr,Ti)O3], PT(PbTiO3), PLZT[(Pb,La)(Zr,Ti)O3], or barium titanate (BaTiO3). These piezoelectric ceramic materials are perovskite oxides (general formula: ABO). X ).

[0033] The piezoelectric element 3 is cuboid in shape. The piezoelectric element 3 has a first main surface 3a and a second main surface 3b that are opposite each other. The first main surface 3a and the second main surface 3b are opposite each other in a first direction Ax1. The first main surface 3a and the second main surface 3b are part of the outer surface of the piezoelectric element 3. The piezoelectric element 3 is, for example, constructed by stacking multiple piezoelectric layers. The piezoelectric element 3 is, for example, constructed by sintering a ceramic green sheet containing piezoelectric ceramic material. The direction in which the piezoelectric layers are stacked is, for example, along the first direction Ax1. In the actual piezoelectric element 3, the piezoelectric layers are integrated to the point that the boundaries between the piezoelectric layers are indistinguishable. The length of the piezoelectric element 3 along the first direction Ax1 is, for example, about 0.05 mm. The first direction Ax1 is, for example, the thickness direction of the piezoelectric element 3. The cuboid shape includes a cuboid shape with chamfered corners and edges, and a cuboid shape with rounded corners and edges.

[0034] The piezoelectric element 3 has a first end face 3c and a second end face 3d that are opposite to each other. The first end face 3c and the second end face 3d are opposite each other in a second direction Ax2 that intersects the first direction Ax1. The first end face 3c and the second end face 3d are part of the outer surface of the piezoelectric element 3. The second direction Ax2 is, for example, the direction of the long side of the piezoelectric element 3. The length of the piezoelectric element 3 along the second direction Ax2 is about 0.65 mm.

[0035] The piezoelectric element 3 has a first side surface 3e and a second side surface 3f that are opposite to each other. The first side surface 3e and the second side surface 3f are opposite each other on a third direction Ax3 that intersects the first direction Ax1 and the second direction Ax2. The first side surface 3e and the second side surface 3f are part of the outer surface of the piezoelectric element 3. The third direction Ax3 is, for example, the direction of the short side of the piezoelectric element 3. The length of the piezoelectric element 3 along the third direction Ax3 is, for example, about 0.25 mm.

[0036] The first main surface 3a and the second main surface 3b extend along the second direction Ax2, connecting the first end surface 3c and the second end surface 3d. The first main surface 3a and the second main surface 3b extend along the third direction Ax3, connecting the first side surface 3e and the second side surface 3f.

[0037] The first end face 3c and the second end face 3d extend along the first direction Ax1 in a manner connecting the first main face 3a and the second main face 3b. The first end face 3c and the second end face 3d extend along the third direction Ax3 in a manner connecting the first side face 3e and the second side face 3f.

[0038] The first side surface 3e and the second side surface 3f extend along the second direction Ax2 in a manner connecting the first end surface 3c and the second end surface 3d. The first side surface 3e and the second side surface 3f extend along the first direction Ax1 in a manner connecting the first main surface 3a and the second main surface 3b.

[0039] The first electrode 10 includes an external electrode. For example, the first electrode 10 includes a first external electrode 11. The first external electrode 11 is formed on the outer surface of the piezoelectric body 3. The first external electrode 11 has a first electrode portion 12 and a second electrode portion 13. The first electrode portion 12 is disposed on a first main surface 3a, and the second electrode portion 13 is disposed on a second end surface 3d. The first electrode portion 12 and the second electrode portion 13 are integrally formed on the outer surface of the piezoelectric body 3. The first electrode portion 12 and the second electrode portion 13 are connected to each other at the ridge 4a formed by the first main surface 3a and the second end surface 3d. The first electrode portion 12 extends on the first main surface 3a between the end edge of the first side surface 3e and the end edge of the second side surface 3f. The first electrode portion 12 extends on the first main surface 3a from the end edge of the second end surface 3d toward the end edge of the first end surface 3c. The first electrode portion 12 is separate from the first end surface 3c. The first electrode portion 12 has an electrode end 12c located near the first end surface 3c. The electrode end 12c is separate from the first end surface 3c. The distance S12 between the electrode end 12c on the second direction Ax2 and the first end face 3c is, for example, 90 to 250 nm. The first external electrode 11 is connected to the piezoelectric element 3. The first electrode portion 12 is connected to the first main surface 3a.

[0040] The second electrode portion 13 is configured to completely cover the second end face 3d. The first electrode 10 is not disposed on either the first side face 3e or the second side face 3f. The second electrode portion 13 is in contact with the second end face 3d.

[0041] The second electrode 20 includes an internal electrode 21. The internal electrode 21 is disposed within the piezoelectric element 3. In this embodiment, the stacked piezoelectric element 1, as the internal electrode disposed within the piezoelectric element 3, includes only the internal electrode 21. The internal electrode 21 is formed in the piezoelectric element 3 in the first direction Ax1, opposite to the first electrode portion 12 of the first external electrode 11. The spacing between the internal electrode 21 and the first electrode portion 12 in the first direction Ax1 is, for example, 5 to 100 μm. Viewed from the first direction Ax1, the internal electrode 21 is, for example, generally rectangular in shape. The internal electrode 21 is in contact with the piezoelectric element 3.

[0042] The internal electrode 21 is disposed within the piezoelectric element 3, extending along the second direction Ax2 from the first end face 3c toward the second end face 3d. The internal electrode 21 is exposed at the first end face 3c but not at the second end face 3d. The internal electrode 21 is separated from the second end face 3d in the second direction Ax2. The internal electrode 21 has a pair of electrode end faces 21c and 21d that are opposite to each other in the second direction Ax2. The electrode end face 21c is exposed at the first end face 3c of the piezoelectric element 3. The electrode end face 21d is not exposed at the second end face 3d of the piezoelectric element 3 and is separated from the second end face 3d.

[0043] The distance S21 between the electrode end face 21d and the second end face 3d on the second direction Ax2 is, for example, 10 to 80 nm. Since the electrode end face 21d is separated from the second end face 3d, the stacked piezoelectric element 1 prevents the internal electrode 21 from short-circuiting with the first electrode 10.

[0044] In this embodiment, the intervals S21 and S12 are different from each other. The structure of the different intervals S21 and S12 reduces the stress generated in the piezoelectric element 3 due to the polarization treatment. Therefore, the deformation of the stacked piezoelectric element 1 (piezoelectric element 3) caused by the polarization treatment and the displacement of the stacked piezoelectric element 1 (piezoelectric element 3) generated by the drive are well balanced.

[0045] The internal electrode 21 is disposed within the piezoelectric element 3 such that it extends along a third direction Ax3 between a first side surface 3e and a second side surface 3f. The internal electrode 21 has a pair of electrode side surfaces 21e and electrode side surfaces 21f that are opposite to each other in the third direction Ax3. In this embodiment, the electrode side surface 21e is exposed on the first side surface 3e, and the electrode side surface 21f is exposed on the second side surface 3f.

[0046] The internal electrode 21 is formed, for example, by simultaneous firing with the piezoelectric element 3. The internal electrode 21 is, for example, made of Pt. In this case, the internal electrode 21 is formed of a sintered body of a conductive paste containing particles made of Pt. The internal electrode 21 may also be made of a conductive material other than Pt. The conductive material may include, for example, Ag, Pd, Au, Cu, Ni, or alloys thereof. The internal electrode 21 may also be formed of a sintered body of a conductive paste containing these conductive materials. The thickness of the internal electrode 21 is, for example, 0.2–3 μm.

[0047] The second electrode 20 includes an external electrode. For example, the second external electrode 22 is formed on the outer surface of the piezoelectric element 3. The second external electrode 22 has a third electrode portion 23, a fourth electrode portion 24, and a fifth electrode portion 25. The third electrode portion 23 is disposed on the first main surface 3a. The fourth electrode portion 24 is disposed on the first end face 3c. The fifth electrode portion 25 is disposed on the second main surface 3b. The third electrode portion 23, the fourth electrode portion 24, and the fifth electrode portion 25 are integrally formed on the outer surface. The second external electrode 22 is in contact with the piezoelectric element 3. The third electrode portion 23 is in contact with the first main surface 3a.

[0048] The third electrode portion 23 and the fourth electrode portion 24 are connected to each other at the edge 4b ​​formed by the first main surface 3a and the first end surface 3c. The fourth electrode portion 24 and the fifth electrode portion 25 are connected to each other at the edge 4c formed by the first end surface 3c and the second main surface 3b. The third electrode portion 23 extends on the first main surface 3a between the end edge of the first side surface 3e and the end edge of the second side surface 3f. The third electrode portion 23 extends on the first main surface 3a from the end edge of the first end surface 3c toward the first electrode portion 12. The third electrode portion 23 is separate from the first electrode portion 12. The third electrode portion 23 has an electrode end 23c located close to the first electrode portion 12. The electrode end 23c is separate from the electrode end 12c. The distance S23 between the electrode end 23c and the electrode end 12c in the second direction Ax2 is, for example, 50 to 200 nm. The structure with a spacing S23 in the range of 50 to 200 nm prevents short circuit between the first external electrode 11 and the second external electrode 22, and suppresses the detachment of crystal particles from the piezoelectric body 3.

[0049] The fourth electrode portion 24 is configured to cover the entire first end face 3c. The fourth electrode portion 24 is in contact with the first end face 3c. The fifth electrode portion 25 extends on the second main surface 3b between the edge of the first side surface 3e and the edge of the second side surface 3f. The fifth electrode portion 25 extends along the second direction Ax2 on the second main surface 3b from the edge of the first end face 3c toward the edge of the second end face 3d. The fifth electrode portion 25 is separate from the second end face 3d. The fifth electrode portion 25 has an electrode end 25d located near the second end face 3d. The electrode end 25d is separate from the second end face 3d. The distance S25 between the electrode end 25d in the second direction Ax2 and the second end face 3d is, for example, 90 to 200 nm. The structure with a distance S25 in the range of 90 to 200 nm prevents short circuits between the first external electrode 11 and the second external electrode 22 and suppresses the detachment of crystal particles from the piezoelectric body 3. The fifth electrode portion 25 is in contact with the second main surface 3b.

[0050] In this embodiment, the interval S25 is larger than the interval S21. The structure with an interval S25 greater than the interval S21 achieves a balance of stress existing within the piezoelectric element 3. The structure with an interval S25 greater than the interval S21 effectively balances the deformation of the stacked piezoelectric element 1 (piezoelectric element 3) caused by polarization treatment and the displacement of the stacked piezoelectric element 1 (piezoelectric element 3) caused by driving.

[0051] In the second direction Ax2, the position of the electrode end face 21d of the internal electrode 21 is closer to the second end face 3d than the position of the electrode end 25d of the fifth electrode portion 25. The distance D21 between the position of the electrode end face 21d and the position of the electrode end 25d in the second direction Ax2 is, for example, 10 to 190 nm.

[0052] The fourth electrode portion 24 is configured to completely cover the electrode end face 21c of the internal electrode 21 exposed on the first end face 3c. The internal electrode 21 is connected to the fourth electrode portion 24 on the first end face 3c. The internal electrode 21 is electrically connected to the second external electrode 22. The fifth electrode portion 25 is opposite to the internal electrode 21 in the first direction Ax1. The distance between the fifth electrode portion 25 of the second external electrode 22 and the internal electrode 21 in the first direction Ax1 is, for example, 5 to 100 μm. The second electrode 20 is not disposed on either the first side surface 3e or the second side surface 3f. In this embodiment, the first side surface 3e and the second side surface 3f are exposed from the first electrode 10 and the second electrode 20.

[0053] The first external electrode 11 and the second external electrode 22, for example, each have a stacked Ni-Cr alloy layer and an Au layer, respectively. In this case, the Ni-Cr alloy layer is formed on the piezoelectric element 3, and the Au layer is formed on the Ni-Cr alloy layer. The Ni-Cr alloy layer is the lower layer, and the Au layer is the upper layer. The first external electrode 11 and the second external electrode 22 each have a Ni-Cr / Au stacked structure. The first external electrode 11 and the second external electrode 22 may also each have a single-layer structure. In this case, the first external electrode 11 and the second external electrode 22 may also be, for example, a Ni-Cr alloy layer, an Au layer, a Cr layer, or a Ni layer. Alternatively, either the first external electrode 11 or the second external electrode 22 may have a Ni-Cr / Au stacked structure, and the other may have a single-layer structure. The first external electrode 11 and the second external electrode 22 may also be formed, for example, by a plating method. Plating methods include sputtering, vapor deposition, or electroplating. In this embodiment, the first external electrode 11 and the second external electrode 22 are respectively coatings.

[0054] When the first external electrode 11 and the second external electrode 22 have a stacked structure, for example, the thickness of the Ni-Cr alloy layer is 20–400 nm, and the thickness of the Au layer is 50–200 nm. When the first external electrode 11 and the second external electrode 22 have a single-layer structure, for example, the thickness of each of the first external electrode 11 and the second external electrode 22 is 70–600 nm. In this embodiment, the piezoelectric element 3 is held between the first external electrode 11 and the second external electrode 22. The structure in which the first external electrode 11 and the second external electrode 22 hold the piezoelectric element 3, for example, suppresses deformation of the piezoelectric element 3.

[0055] The first external electrode 11 and the internal electrode 21 of the second electrode 20 are configured to apply an electric field to the piezoelectric element 3. The second external electrode 22 of the second electrode 20 is electrically connected to the internal electrode 21 of the second electrode 20. Therefore, it is difficult for the second external electrode 22 and the internal electrode 21 to be configured to apply an electric field to the piezoelectric element 3. The stacked piezoelectric element 1, as a pair of electrodes configured to apply an electric field to the piezoelectric element 3, includes the first external electrode 11 and the internal electrode 21.

[0056] In the stacked piezoelectric element 1, the piezoelectric element 3 includes an active region EA1. The active region EA1 is located between the first external electrode 11 and the internal electrode 21. The active region EA1 is displaced according to the electric field applied to the stacked piezoelectric element 1. In this embodiment, the active region EA1 is located between the first electrode portion 12 of the first external electrode 11 and the internal electrode 21. The piezoelectric element 3 includes an inactive region EN1. The inactive region EN1 is located on the opposite side of the active region EA1, separated by the internal electrode 21. The inactive region EN1 is located between the internal electrode 21 and the second external electrode 22. The active region EA1 and the inactive region EN1 are located on opposite sides of one internal electrode 21.

[0057] In the second electrode 20, the inner electrode 21 is made of Pt, for example, as described above. Therefore, the hardness of the inner electrode 21 is low. The inner electrode 21 is fired simultaneously with the piezoelectric element 3. Therefore, the stress on the piezoelectric element 3 from the inner electrode 21 is relatively small. As a result, the inner electrode 21 is less likely to impede the displacement of the piezoelectric element 3. The displacement of the active region EA1 near the inner electrode 21 tends to become relatively large.

[0058] In the first electrode 10, the first external electrode 11 is composed of a Ni-Cr alloy layer. Therefore, the first external electrode 11 has high hardness. The first external electrode 11 is formed by plating after the piezoelectric body 3 is sintered. Therefore, the stress on the piezoelectric body 3 from the first external electrode 11 is relatively large. As a result, the first external electrode 11 easily hinders the displacement of the piezoelectric body 3. There is a tendency for the displacement of the active region EA1 near the first external electrode 11 to become smaller.

[0059] In this embodiment, the stress experienced by the piezoelectric element 3 from the first external electrode 11 is greater than the stress experienced by the piezoelectric element 3 from the internal electrode 21. In this embodiment, the internal electrode 21 is a sintered metal layer. In this embodiment, the structure of the piezoelectric element 3 having multiple parts with different stresses experienced from multiple components different from the piezoelectric element 3 is achieved by forming the internal electrode 21 and the first external electrode 11 on the piezoelectric element 3.

[0060] Prescribed ions that move within the crystal structure due to polarization treatment move more easily from the first external electrode 11 to the internal electrode 21 than those moving from the internal electrode 21 towards the first external electrode 11. Therefore, during the fabrication of the stacked piezoelectric element 1, an electric field is applied to the piezoelectric body 3 such that the polarization direction of the active region EA1 is from the first external electrode 11 towards the internal electrode 21. Prescribed ions are, for example, perovskite oxides (general formula: ABO). X The positive ion at the B site in ).

[0061] The polarization treatment is performed, for example, at room temperature. Besides room temperature, the polarization treatment can also be performed at temperatures around 80°C to 150°C. That is, the piezoelectric element 3 can also be heated. When the polarization treatment is performed while the piezoelectric element 3 is heated, the temperature of the piezoelectric element 3 can also be kept at room temperature when the polarization electric field is changed from an applied state to an unapplied state. In this case, polarization degradation is suppressed. Polarization degradation can be caused, for example, by aging or by driving the stacked piezoelectric element 1. When the stacked piezoelectric element 1 is driven, an electric field is applied to the stacked piezoelectric element 1 (piezoelectric element 3) with the first electrode 10, including the first external electrode 11, set as the positive electrode and the second electrode 20, including the internal electrode 21, set as the negative electrode.

[0062] In this embodiment, the stress experienced by the piezoelectric element 3 from the internal electrode 21 is less than the stress experienced by the piezoelectric element 3 from the first external electrode 11. The active region EA1 between the first external electrode 11 and the internal electrode 21 has a portion subjected to stress from the internal electrode 21 and a portion subjected to stress from the first external electrode 11, and the stresses experienced by these portions are different as described above. The polarization direction of the active region EA1 is from the first external electrode 11 toward the internal electrode 21.

[0063] Therefore, in this embodiment, the piezoelectric element 3 (active region EA1) has multiple portions that receive different stresses from multiple components different from the piezoelectric element 3. The polarization direction is from the portion where the stress received from one of the multiple components is greater towards the portion where the stress received from the other components is less. That is, the polarization direction is from the portion where the stress received from the first external electrode 11 is greater towards the portion where the stress received from the internal electrode 21 is less.

[0064] As a result, the stacked piezoelectric element 1 exhibits a large displacement and high reliability.

[0065] The internal electrode 21 of the second electrode 20 is formed, for example, by simultaneous firing with the piezoelectric element 3. In this case, the internal electrode 21 is formed by a sintering reaction. As a result of the sintering reaction, regions not covered by the internal electrode 21 are randomly generated in the piezoelectric element 3 (the piezoelectric layer adjacent to the internal electrode 21). That is, openings are randomly formed in the internal electrode 21. As a result, there is a tendency for the coverage of the internal electrode 21 to decrease.

[0066] The first external electrode 11 of the first electrode 10 is formed, for example, by plating after the piezoelectric body 3 is fired. In this case, it is difficult to create areas not covered by the first external electrode 11 in the region of the piezoelectric body 3 where the first external electrode 11 is formed. As a result, there is a tendency for the coverage of the first external electrode 11 to become higher.

[0067] In this embodiment, the coverage of the first external electrode 11 is greater than the coverage of the internal electrode 21. For example, the coverage of the first external electrode 11 is 95-100%, and the coverage of the internal electrode 21 is 60-95%. Therefore, the structure in which the coverage of the first external electrode 11 is greater than the coverage of the internal electrode 21 is simple and reliably implemented, resulting in a structure in which the stress on the piezoelectric element 3 from the first external electrode 11 is greater than the stress on the piezoelectric element 3 from the internal electrode 21.

[0068] The embodiments of the present invention have been described above, but the present invention is not necessarily limited to the above embodiments, and various modifications can be made without departing from its spirit.

[0069] Example

[0070] Next, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

[0071] (Example 1)

[0072] (Fabrication of laminated piezoelectric elements)

[0073] The fabrication process of the laminated piezoelectric element involved in Example 1 is as follows.

[0074] First, a green sheet containing piezoelectric ceramic material is prepared. The piezoelectric ceramic material contains PZT.

[0075] Next, an electrode pattern for obtaining the internal electrodes is formed on the green sheet. The electrode pattern is formed by applying a conductive paste containing Pt to the green sheet.

[0076] Next, a stacked green body is formed. A stacked green body is a structure consisting of green sheets with electrode patterns and green sheets without electrode patterns.

[0077] Next, the laminated green body is fired. This yields a piezoelectric substrate. The piezoelectric substrate includes an electrode film. The electrode film constitutes the internal electrodes. The thickness of the piezoelectric substrate is 0.05 mm. The thickness of the electrode film is approximately 1 μm.

[0078] Next, the piezoelectric substrate is cut into strips. Then, a stacked electrode film is formed on the outer surface of the strip-shaped piezoelectric substrate. The stacked electrode film is formed by sputtering. The stacked electrode film includes a lower electrode film made of a Ni-Cr alloy and an upper electrode film made of Au. The upper electrode film is formed on the lower electrode film. That is, the stacked electrode film has a Ni-Cr / Au stacked structure. The thickness of the lower electrode film is approximately 100 nm. The thickness of the upper electrode film is approximately 100 nm. The stacked electrode film constitutes the first external electrode and the second external electrode. That is, the stacked electrode film has a first external electrode and a second external electrode that are separated from each other. The electrode film constituting the second external electrode is connected to the electrode film constituting the internal electrode (the electrode film located within the piezoelectric substrate).

[0079] After forming the stacked electrode films, the piezoelectric substrate is subjected to a polarization treatment. During the polarization treatment, the electrode film constituting the first external electrode is the positive electrode, and the electrode film constituting the second external electrode is the negative electrode; an electric field is applied to the piezoelectric substrate. The polarization treatment is performed at room temperature.

[0080] After polarization treatment, the elongated piezoelectric substrate is cut. Through the above process, a stacked piezoelectric element is obtained. The stacked piezoelectric element has approximately 0.65mm × 0.25mm × 0.05mm dimensions.

[0081] (Evaluation of component characteristics)

[0082] The evaluation of component characteristics is carried out in the following process.

[0083] The polarization (P [μC / cm²)) in 20 multilayer piezoelectric elements obtained through the above fabrication process was measured. 2The magnitude of the electric field was determined. In this case, an alternating electric field (V [kV / mm]) was applied to the multilayer piezoelectric element. The alternating electric field was applied to the multilayer piezoelectric element with the first external electrode set as positive and the second external electrode set as negative. Measurements were performed at room temperature.

[0084] The measurement results are shown in Figure 3 . Figure 3 This is a line graph showing the relationship between electric field and polarization. In Example 1, a larger polarization was obtained compared to Comparative Example 1 described later. In Example 1, the piezoelectric characteristics of 20 stacked piezoelectric elements were also measured. An impedance analyzer was used to measure the piezoelectric characteristics. The results showed that the difference in piezoelectric characteristics among the 20 stacked piezoelectric elements was within approximately 5%.

[0085] (Reliability evaluation)

[0086] The reliability assessment is conducted in the following process.

[0087] Ten laminated piezoelectric elements obtained through the above fabrication process were subjected to driving tests. During the driving tests, a rectangular wave voltage (alternating voltage) with a frequency of 500 Hz was applied to the laminated piezoelectric elements at 60°C. The peak value of the applied voltage was ±20V. The voltage was applied to the laminated piezoelectric elements with the first external electrode set as the positive electrode and the second external electrode set as the negative electrode. The piezoelectric characteristics were measured before and after 500 hours of driving tests to confirm the changes in piezoelectric characteristics after the driving tests.

[0088] As a confirmation, the changes in the piezoelectric properties of the 10 stacked piezoelectric elements before and after the drive test were within 2%.

[0089] (Comparative Example 1)

[0090] (Fabrication of laminated piezoelectric elements)

[0091] The fabrication process of the laminated piezoelectric element involved in Comparative Example 1 is described below.

[0092] In Comparative Example 1, a multilayer piezoelectric element was fabricated using the same process as in Example 1, except for the polarization treatment conditions. During the polarization treatment, the electrode film constituting the first external electrode was the negative electrode, and the electrode film constituting the second external electrode was the positive electrode; an electric field was applied to the piezoelectric substrate. The polarization treatment was performed at room temperature.

[0093] (Evaluation of component characteristics)

[0094] The evaluation of component characteristics is carried out in the following process.

[0095] Similar to the evaluation of the component characteristics in Example 1, the polarization (P [μC / cm²] of the 20 stacked piezoelectric elements obtained through the above-described fabrication process was measured. 2 The magnitude of the electric field is determined. In this case, an alternating electric field (V [kV / mm]) is also applied to the laminated piezoelectric element. With the first external electrode set as the positive electrode and the second external electrode set as the negative electrode, an alternating electric field is applied to the laminated piezoelectric element. Measurements are performed at room temperature.

[0096] The measurement results are shown in Figure 3 In Comparative Example 1, the polarization obtained was smaller compared to Example 1. In Comparative Example 1, the piezoelectric characteristics of 20 stacked piezoelectric elements were also measured. An impedance analyzer was used to measure the piezoelectric characteristics. The results showed that the difference in piezoelectric characteristics among the 20 stacked piezoelectric elements was approximately 15%.

[0097] (Reliability evaluation)

[0098] The reliability assessment is conducted in the following process.

[0099] Similar to the reliability evaluation in Example 1, a driving test was conducted on 10 stacked piezoelectric elements obtained through the above-described manufacturing process. In the driving test, with the first external electrode set as the positive electrode and the second external electrode set as the negative electrode, the aforementioned voltage was applied to the stacked piezoelectric element. The piezoelectric characteristics were measured before and after the 500-hour driving test to confirm the changes in piezoelectric characteristics after the driving test.

[0100] As a confirmation, the piezoelectric characteristics of the 10 stacked piezoelectric elements after the drive test decreased by 15% to 20% compared with the piezoelectric characteristics of the 10 stacked piezoelectric elements before the drive test.

[0101] Industrial applications

[0102] This invention can be used in stacked piezoelectric components.

[0103] Explanation of symbols:

[0104] 1…Layered piezoelectric element, 3…Piezoelectric element, 3a…First main surface, 3b…Second main surface, 3c…First end face, 3d…Second end face, 10…First electrode, 11…First external electrode, 20…Second electrode, 21…Internal electrode, 22…Second external electrode, Ax1…First direction, Ax2…Second direction, EA1…Active region, EN1…Inactive region.

Claims

1. A stacked piezoelectric element, wherein, have: A piezoelectric element comprising a piezoelectric ceramic material and having a first principal surface and a second principal surface opposite to each other; A first electrode, comprising a first external electrode formed on the first main surface; as well as The second electrode includes an internal electrode formed in the piezoelectric element opposite to the first external electrode, and a second external electrode formed on the second main surface and electrically connected to the internal electrode. The piezoelectric element includes an active region between the first external electrode and the internal electrode, and an inactive region on the opposite side of the active region, separated by the internal electrode, between the second external electrode and the internal electrode. The stress experienced by the piezoelectric element from the first external electrode is greater than the stress experienced by the piezoelectric element from the internal electrode. The polarization direction of the active region is from the first external electrode toward the internal electrode.

2. The laminated piezoelectric element according to claim 1, wherein, The coverage of the first external electrode relative to the piezoelectric element is greater than the coverage of the internal electrode relative to the piezoelectric layer constituting the piezoelectric element.

3. The laminated piezoelectric element according to claim 1 or 2, wherein, The piezoelectric element further has a first end face and a second end face that are opposite to each other in a second direction intersecting a first direction opposite to the first main face and the second main face. The internal electrode is exposed on the first end face and separated from the second end face in the second direction. The first external electrode is separated from the first end face in the second direction. The spacing between the internal electrode and the second end face in the second direction is different from the spacing between the first external electrode and the first end face in the second direction.

4. The stacked piezoelectric element according to claim 3, wherein, The second external electrode is separated from the second end face in the second direction. The distance between the second external electrode and the second end face in the second direction is greater than the distance between the internal electrode and the second end face in the second direction.

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