Multilayer piezoelectric actuator

Abstract

To provide a multilayer piezoelectric actuator that can suppress the occurrence of short circuits inside the element even when used for long periods of time in a high-temperature environment.SOLUTION: A multilayer piezoelectric actuator 100 includes a metal case 200, a stacked piezoelectric element 300 housed inside the metal case 200, a terminal 400 connected to the stacked piezoelectric element 300 and drawn out to the metal case 200, and a gas 500 sealed inside the metal case 200. The oxygen concentration in the gas 500 is 10% or more and 50% or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a multilayer piezoelectric actuator including a multilayer piezoelectric element and a metal case that houses the multilayer piezoelectric element. [Background technology]

[0002] To prevent electrical short circuits caused by migration during long-term use in a humid environment, a multilayer piezoelectric actuator is known in which the multilayer piezoelectric element is housed inside a metal case and the metal case is sealed. This type of multilayer piezoelectric actuator is disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-192832 Summary of the Invention [Problem to be solved by the invention]

[0004] Previously, this type of multilayer piezoelectric actuator was primarily used in a temperature range of -25°C to 85°C, but in recent years, it has also begun to be used in high-temperature environments of 150°C or higher, such as in semiconductor manufacturing equipment. In such applications, nitrogen is generally used as the gas sealed inside the metal case.

[0005] However, when a multilayer piezoelectric actuator is energized for a long period of time in a high-temperature environment as described above, the insulation resistance of the multilayer piezoelectric element may decrease. In particular, when a piezoelectric actuator is energized for about a year, short circuits may occur inside the element.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a multilayer piezoelectric actuator that can prevent short circuits from occurring inside the element even when used for a long period of time in a high-temperature environment. [Means for solving the problem]

[0007] The inventors of the present invention have discovered through research that the decrease in insulation resistance in high-temperature environments is due to oxygen defects in the piezoelectric ceramic layers contained in the multi-layer piezoelectric element. Therefore, when a low-humidity, oxygen-containing gas was sealed in the metal case instead of nitrogen, the decrease in insulation resistance was suppressed. The present invention was made based on this finding, and specifically has the following features.

[0008] That is, the present invention provides a first multilayer piezoelectric actuator, A multilayer piezoelectric actuator comprising a metal case, a multilayer piezoelectric element housed inside the metal case, a terminal connected to the multilayer piezoelectric element and extending outside the metal case, and gas sealed inside the metal case, The oxygen concentration in the gas is 10% or more and 50% or less. A laminated piezoelectric actuator is provided.

[0009] Furthermore, the present invention provides a second multilayer piezoelectric actuator, which is the first multilayer piezoelectric actuator, The multi-layer piezoelectric element includes a laminate in which piezoelectric ceramic layers and internal electrode layers are alternately stacked, The piezoelectric ceramic layer is PbTiO3-PbZrO3-Pb(Ni 1 / 3 Nb 2 / 3 The main component is ternary lead zirconate titanate (PZT), expressed as )O3, and contains 0 to 0.05 wt% (excluding 0) of Mn as an additive, calculated as an oxide expressed as MnO. A laminated piezoelectric actuator is provided.

[0010] Furthermore, the present invention provides a third multilayer piezoelectric actuator, which is the first or second multilayer piezoelectric actuator, The multi-layer piezoelectric element includes a laminate in which piezoelectric ceramic layers and internal electrode layers are alternately stacked, The Curie temperature of the piezoelectric ceramic layer is 200°C or higher, The terminals are shipped in a shorted state outside the metal case. A laminated piezoelectric actuator is provided.

[0011] Furthermore, the present invention provides a fourth multilayer piezoelectric actuator, which is the first or second multilayer piezoelectric actuator, The multi-layer piezoelectric element includes a laminate in which piezoelectric ceramic layers and internal electrode layers are alternately stacked, When viewed along the stacking direction, the laminate has a partial electrode structure in which the internal electrode layers are smaller than the piezoelectric ceramic layers, and some ends of the internal electrode layers coincide with the ends of the piezoelectric ceramic layers, while the remaining some ends of the internal electrode layers are spaced apart from the ends of the piezoelectric ceramic layers, The distance from the end of the remaining part of the internal electrode layer to the end of the piezoelectric ceramic layer is 0.1 mm or more. A laminated piezoelectric actuator is provided.

[0012] Furthermore, the present invention provides a fifth multilayer piezoelectric actuator, which is the first or second multilayer piezoelectric actuator, The dew point of the gas is -40°C or less A laminated piezoelectric actuator is provided. [Effects of the Invention]

[0013] According to the multilayer piezoelectric actuator of the present invention, the oxygen concentration in the gas sealed inside the metal case is set to 10% or more, so that the decrease in insulation resistance can be suppressed even when used for a long period of time in a high-temperature environment. Note that if the oxygen concentration in the gas sealed inside the metal case is higher than 50%, the metal will catch fire, so the oxygen concentration must be 50% or less. [Brief explanation of the drawings]

[0014] [Figure 1]1 is a perspective view showing a multilayer piezoelectric actuator according to an embodiment of the present invention, in which a discharge resistor is connected between terminals of the multilayer piezoelectric actuator. [Figure 2] 2 is another perspective view showing the multilayer piezoelectric actuator of FIG. 1. FIG. [Figure 3] 3 is a cross-sectional view showing the multilayer piezoelectric actuator of Fig. 2. In the figure, the internal electrode layers of the multilayer piezoelectric element are not shown. [Figure 4] 4 is a perspective view showing a multi-layer piezoelectric element included in the multi-layer piezoelectric actuator of FIG. 3. FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line A in FIG. [Figure 6] FIG. 5 is a cross-sectional view taken along line B in FIG. [Figure 7] FIG. 6 is a cross-sectional view showing a modification of FIG. 5. [Figure 8] FIG. 7 is a cross-sectional view showing a modification of FIG. 6. [Figure 9] 1 is a graph showing changes over time in DC insulation resistance values ​​of the multilayer piezoelectric actuators of Examples 1, 2, and 3. [Figure 10] 10 is a graph showing changes over time in DC insulation resistance values ​​of the multilayer piezoelectric actuators of Comparative Examples 1, 2, and 3. DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring to FIG. 3, a multilayer piezoelectric actuator 100 according to an embodiment of the present invention includes a metal case 200, a multilayer piezoelectric element 300 housed inside the metal case 200, a terminal 400 connected to the multilayer piezoelectric element 300 and extending outside the metal case 200, and a gas 500 sealed inside the metal case 200.

[0016] (metal case) As shown in FIGS. 2 and 3, the metal case 200 of this embodiment is composed of an upper lid 210, a lower lid 220, and a bellows 230. The upper lid 210 defines the upper end of the metal case 200 in the vertical direction. The lower lid 220 defines the lower end of the metal case 200 in the vertical direction. In this embodiment, the vertical direction is the Z direction. Here, the upper side is the +Z direction, and the lower side is the -Z direction. The terminal 400 is provided on the lower lid 220. The bellows 230 is hermetically joined to the upper lid 210 and the lower lid 220 by welding or brazing. In other words, the metal case 200 does not have any holes or the like that communicate with the outside. The bellows 230 is configured to be able to expand and contract in the vertical direction in accordance with the expansion and contraction of the multi-layer piezoelectric element 300. The material for the metal case 200 can be, for example, stainless steel, but any metal material that is airtight and durable against repeated expansion and contraction of the bellows 230 will do, and there is no limitation on the material.

[0017] (Layered piezoelectric element) Referring to FIG. 4, the multi-layer piezoelectric element 300 of this embodiment includes a laminate 310 in which piezoelectric ceramic layers 312 and internal electrode layers 314 are alternately stacked. The laminate 310 is formed by stacking the piezoelectric ceramic layers 312 and the internal electrode layers 314 alternately in a stacking direction and then sintering them to form an integrated body. Here, the stacking direction is the vertical direction. The multi-layer piezoelectric element 300 has an upper portion 320 and a bottom portion 330. The upper portion 320 defines the upper end of the multi-layer piezoelectric element 300 in the vertical direction. The bottom portion 330 defines the lower end of the multi-layer piezoelectric element 300 in the vertical direction. Referring to FIGS. 3 and 4, the upper lid 210 is in contact with the upper portion 320 of the multi-layer piezoelectric element 300. The lower lid 220 is in contact with the bottom portion 330 of the multi-layer piezoelectric element 300.

[0018] (Laminate) As shown in Fig. 4, the laminate 310 of this embodiment has a substantially rectangular parallelepiped shape extending in the stacking direction, i.e., the up-down direction. With reference to Figs. 4 and 5, the laminate 310 has a front surface 3101 and a rear surface 3102 in the front-to-rear direction. Here, the front-to-rear direction is the Y direction. The front is the +Y direction, and the rear is the -Y direction. The laminate 310 has a right surface 3103 and a left surface 3104 in the left-to-right direction. Here, the left-to-right direction is the X direction. The right is the -X direction, and the left is the +X direction.

[0019] (piezoelectric ceramic layer) Referring to FIG. 4, piezoelectric ceramic layer 312 of this embodiment is made of PbTiO3-PbZrO3-Pb(Ni 1 / 3 Nb 2 / 3 The piezoelectric ceramic layer 312 is mainly composed of ternary lead zirconate titanate (PZT) represented by PbTiO3-PbZrO3-Pb(Ni)O3, and contains as an additive 0 to 0.05 wt% (excluding 0) of Mn calculated as an oxide represented by MnO relative to the total amount. However, the present invention is not limited to this, and the piezoelectric ceramic layer 312 may be formed of PbTiO3-PbZrO3-Pb(Ni)O3 without containing Mn. 1 / 3 Nb 2 / 3 The piezoelectric ceramic layer 312 may be made of only ternary lead zirconate titanate (PZT) represented by .)O3. The Curie temperature of the piezoelectric ceramic layer 312 is 200°C or higher. Specifically, the Curie temperature of the piezoelectric ceramic layer 312 is 260°C.

[0020] 5 and 6, the piezoelectric ceramic layer 312 has two main edges 3121 perpendicular to the left-right direction and two sub-edges 3122 perpendicular to the front-rear direction when viewed along the stacking direction. That is, the piezoelectric ceramic layer 312 has two pairs of adjacent main edges 3121 and sub-edges 3122 when viewed along the stacking direction. The two main edges 3121 are spaced apart in the front-rear direction. One of the two main edges 3121 defines the front end in the front-rear direction. The other of the two main edges 3121 defines the rear end in the front-rear direction. The two sub-edges 3122 are spaced apart in the left-right direction. One of the two sub-edges 3122 defines the right end in the left-right direction. The other of the two sub-edges 3122 defines the left end in the left-right direction.

[0021] (Internal electrode layer) Referring to FIG. 4, the material constituting the internal electrode layer 314 in this embodiment may be, for example, an alloy of silver and palladium, but any conductive metal material may be used, and the material is not limited thereto.

[0022] 5 and 6, the internal electrode layer 314 has two main sides 3141 perpendicular to the left-right direction and two sub-sides 3142 perpendicular to the front-rear direction when viewed along the stacking direction. That is, the internal electrode layer 314 has two pairs of adjacent main sides 3141 and sub-sides 3142 when viewed along the stacking direction. The two main sides 3141 are spaced apart in the front-rear direction. One of the two main sides 3141 defines the front end in the front-rear direction. The other of the two main sides 3141 defines the rear end in the front-rear direction. The two sub-sides 3142 are spaced apart in the left-right direction. One of the two sub-sides 3142 defines the right end in the left-right direction. The other of the two sub-sides 3142 defines the left end in the left-right direction.

[0023] 5 and 6, the laminate 310 of this embodiment has a partial electrode structure in which, when viewed along the lamination direction, the internal electrode layers 314 are smaller than the piezoelectric ceramic layers 312, and some ends of the internal electrode layers 314 coincide with the ends of the piezoelectric ceramic layers 312, while the remaining ends of the internal electrode layers 314 are spaced apart from the ends of the piezoelectric ceramic layers 312. In addition, the distance D from the remaining ends of the internal electrode layers 314 to the ends of the piezoelectric ceramic layers 312 is 0.1 mm or more.

[0024] 5 and 6, one of the main sides 3141 of the internal electrode layer 314 coincides with one of the main sides 3121 of the piezoelectric ceramic layer 312, and the other of the main sides 3141 of the internal electrode layer 314 is spaced a distance D in the front-to-rear direction from the other of the main sides 3121 of the piezoelectric ceramic layer 312. Furthermore, one of the sub-sides 3142 of the internal electrode layer 314 coincides with one of the sub-sides 3122 of the piezoelectric ceramic layer 312, and the other of the sub-sides 3142 of the internal electrode layer 314 is spaced a distance D in the left-to-right direction from the other of the sub-sides 3122 of the piezoelectric ceramic layer 312. One of the two pairs of adjacent combinations of main sides 3141 and sub-sides 3142 of the internal electrode layer 314 coincides with one of the two pairs of adjacent combinations of main sides 3121 and sub-sides 3122 of the piezoelectric ceramic layer 312, and the other of the two pairs of adjacent combinations of main sides 3141 and sub-sides 3142 of the internal electrode layer 314 is separated from the other of the two pairs of adjacent combinations of main sides 3121 and sub-sides 3122 of the piezoelectric ceramic layer 312.

[0025] Referring to FIG. 4, the laminate 310 of this embodiment further includes an external electrode 700.

[0026] (external electrode) Referring to FIG. 4, the external electrode 700 of this embodiment can be made of silver paste, but the material is not limited thereto as long as it has the desired properties. Referring to FIGS. 5 and 6, the external electrode 700 is provided on the front surface 3101 and the rear surface 3102 of the laminate 310. One of the main edges 3141 of the internal electrode layer 314, which coincides with one of the main edges 3121 of the piezoelectric ceramic layer 312, is connected to the external electrode 700. The other of the main edges 3141 of the internal electrode layer 314, which is spaced apart in the front-rear direction from the other of the main edges 3121 of the piezoelectric ceramic layer 312, is spaced apart from the external electrode 700. In other words, the other of the main edges 3141 of the internal electrode layer 314, which is spaced apart in the front-rear direction from the other of the main edges 3121 of the piezoelectric ceramic layer 312, is not connected to the external electrode 700.

[0027] However, the present invention is not limited to this, and the internal electrode layers 314 of the laminate 310 may be modified as shown in Figures 7 and 8. In this case, neither of the two minor sides 3142 of the internal electrode layers 314 coincides with the minor sides 3122 of the piezoelectric ceramic layers 312, and both minor sides 3142 of the internal electrode layers 314 are spaced apart from the minor sides 3122 of the piezoelectric ceramic layers 312 in the left-right direction.

[0028] (Terminal) Referring to FIG. 3 , the terminals 400 of this embodiment are made of metal. Referring to FIGS. 3 and 4 , the terminals 400 are connected to the external electrodes 700 of the laminate 310 via lead wires 600. The terminals 400 are shipped in a shorted state outside the metal case 200. However, the present invention is not limited to this. As shown in FIG. 1 , the multilayer piezoelectric actuator 100 may be shipped with a discharge resistor 800 connected between the terminals 400. The multilayer piezoelectric element 300 of this embodiment includes the piezoelectric ceramic layers 312 having the above-described configuration. This increases the insulation resistance, but also increases the likelihood of pyroelectric voltage due to the pyroelectric effect. If the multilayer piezoelectric actuator 100 is shipped without the terminals 400 being shorted or without the discharge resistor 800 connected between the terminals 400, and is then installed in a device or the like by a customer, a sudden discharge may occur from the multilayer piezoelectric element 300 when the multilayer piezoelectric actuator 100 is connected to an electrical circuit of the device, causing a crack in the piezoelectric ceramic layer 312 and potentially resulting in failure of the multilayer piezoelectric element 300. For this reason, the multilayer piezoelectric actuator 100 is shipped in a state where the terminals 400 are shorted outside the metal case 200, or in a state where a discharge resistor 800 is connected between the terminals 400.

[0029] (gas) Referring to FIG. 3, the gas 500 of this embodiment is sealed in the metal case 200. The oxygen concentration of the gas 500 of this embodiment is 10% or more from the viewpoint of improving the lifespan of the multilayer piezoelectric actuator 100 when used at high temperatures of 150°C or higher. Furthermore, the oxygen concentration of the gas 500 of this embodiment is 50% or less because there is a possibility of fire spreading to the metal case 200 when the metal case 200 is welded in the same atmosphere as the gas 500. Additionally, in consideration of the lifespan of the multilayer piezoelectric actuator 100 when used at high temperatures of 150°C or higher, the strength of the metal case 200 when welded, and the gas-tightness of the metal case 200 after welding, the oxygen concentration of the gas 500 is preferably 10% or more and 21% or less. The dew point of the gas 500 of this embodiment is −40°C or lower. The gas 500 in this embodiment is preferably one that has as little moisture as possible, does not affect the internal electrode layers 314, the external electrodes 700, and other components of the multilayer piezoelectric actuator 100, has a stable oxygen concentration, is low cost, and is more preferably dry air with a controlled dew point temperature. If there are no problems with the conditions of use, cost, etc., the gas 500 in this embodiment may also be a mixed gas of oxygen gas and an inert gas such as nitrogen gas, helium gas, argon gas, or carbon dioxide gas.

[0030] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples.

[0031] 3, a multilayer piezoelectric actuator 100 was prepared according to Examples 1, 2, and 3, including a stainless steel metal case 200, a multilayer piezoelectric element 300, metal terminals 400, and dry air (oxygen concentration 21 vol%, dew point -40°C or lower) as gas 500. The multilayer piezoelectric element 300 of the multilayer piezoelectric actuator 100 according to Example 1 was made of 0.42PbTiO3-0.33PbZrO3-0.25Pb(Ni 1 / 3 Nb 2 / 3)O3 as a main component, and containing 0.05 wt% of Mn as an additive, calculated as an oxide expressed as MnO relative to the total amount, an internal electrode layer 314 made of an alloy of silver and palladium, and an external electrode 700 made of silver paste. The multilayer piezoelectric element 300 of the multilayer piezoelectric actuator 100 of Example 2 is composed of 0.42PbTiO3-0.33PbZrO3-0.25Pb(Ni 1 / 3 Nb 2 / 3 )O3 as a main component, and containing 0.01 wt% of Mn as an additive, calculated as an oxide expressed as MnO relative to the total amount, an internal electrode layer 314 made of an alloy of silver and palladium, and an external electrode 700 made of silver paste. In addition, the multilayer piezoelectric element 300 of the multilayer piezoelectric actuator 100 of Example 3 is made of 0.42PbTiO3-0.33PbZrO3-0.25Pb(Ni 1 / 3 Nb 2 / 3 The piezoelectric element is composed of a piezoelectric ceramic layer 312 made of O3, an internal electrode layer 314 made of an alloy of silver and palladium, and an external electrode 700 made of silver paste.

[0032] Similarly, multilayer piezoelectric actuators of Comparative Examples 1, 2, and 3 were prepared. The multilayer piezoelectric actuator of Comparative Example 1 has the same configuration as Example 1, except that the gas sealed inside the metal case is pure nitrogen gas. The multilayer piezoelectric actuator of Comparative Example 2 has the same configuration as Example 2, except that the gas sealed inside the metal case is pure nitrogen gas. Additionally, the multilayer piezoelectric actuator of Comparative Example 3 has the same configuration as Example 3, except that the gas sealed inside the metal case is pure nitrogen gas.

[0033] For the multilayer piezoelectric actuators 100 of Examples 1, 2, and 3 and the multilayer piezoelectric actuators of Comparative Examples 1, 2, and 3, the insulation resistance values ​​were measured over time at 150° C. under application of 150 VDC.

[0034] FIG. 9 shows the change over time in the DC insulation resistance of the multilayer piezoelectric actuators 100 of Examples 1, 2, and 3. This indicates that in Examples 1, 2, and 3, almost no decrease in the DC insulation resistance was observed even after approximately 6,000 hours had passed since the start of measurement. Specifically, in Examples 1, 2, and 3, where R1 is the DC insulation resistance at the start of measurement and R2 is the insulation resistance after 6,000 hours from the start of measurement, it was found that R2 / R1≧0.50. Furthermore, in Examples 1 and 2, in which Mn was added to the piezoelectric ceramic layer 312, almost no decrease in the DC insulation resistance was observed even after 12,000 hours had passed since the start of measurement. Specifically, in Examples 1 and 2, in which Mn was added to the piezoelectric ceramic layer 312, where R3 is the insulation resistance after 12,000 hours from the start of measurement, it was found that R3 / R1>0.999.

[0035] FIG. 10 shows the change over time in the DC insulation resistance values ​​of the multilayer piezoelectric actuators of Comparative Examples 1, 2, and 3. This shows that after about 10,000 hours have passed since the start of measurement, the DC insulation resistance value of Comparative Example 3 has dropped significantly, and a drop in the DC insulation resistance value was also observed in Comparative Example 2. Furthermore, it was found that the DC insulation resistance value of Comparative Example 1 has dropped after 16,000 hours have passed since the start of measurement. Specifically, in Comparative Examples 1, 2, and 3, the DC insulation resistance value at the start of measurement was R 1r The insulation resistance value after 16,000 hours from the start of measurement is R 2r Then, R 2r / R 1r It was found to be ≦0.2.

[0036] As described above, Example 1 and Comparative Example 1 differ only in the gas sealed inside the metal case, but a comparison of the measurement results for Example 1 in Figure 7 and Comparative Example 1 in Figure 8 reveals that even 20,000 hours after the start of measurement, there is almost no decrease in the DC insulation resistance value in Example 1, while the DC insulation resistance value at the start of measurement has decreased to 1 / 10,000 of the value at the start of measurement in Comparative Example 1. Furthermore, as described above, Example 2 and Comparative Example 2 differ only in the gas sealed inside the metal case, but a comparison of the measurement results for Example 2 in Figure 7 and Comparative Example 2 in Figure 8 reveals that even 12,000 hours after the start of measurement, there is almost no decrease in the DC insulation resistance value in Example 2, while the DC insulation resistance value at the start of measurement has decreased to 1 / 50 of the value at the start of measurement in Comparative Example 2. In addition, although Example 3 and Comparative Example 3 differ only in the gas sealed inside the metal case as described above, a comparison of the measurement results of Example 3 in Fig. 7 and Comparative Example 3 in Fig. 8 reveals that even 4000 hours after the start of measurement, there is almost no decrease in the DC insulation resistance value in Example 3, while the DC insulation resistance value at the start of measurement has decreased to 3 / 10 of the value at the start of measurement in Comparative Example 3. These results demonstrate that in the multilayer piezoelectric actuators 100 of Examples 1, 2, and 3, by setting the oxygen concentration in the gas 500 sealed inside the metal case 200 to 10% or more, a decrease in insulation resistance is suppressed even when used for a long period of time in a high-temperature environment of 150°C.

[0037] Although the embodiments of the present invention have been described above using the drawings, the present invention is not limited to these embodiments, and even if the materials and configuration are changed within the scope of the gist of the present invention, it is included in the present invention. In other words, various modifications and alterations that would naturally be made by a person skilled in the art are also included in the present invention. [Explanation of symbols]

[0038] 100 Multilayer Piezoelectric Actuator 200 Metal Case 210 Top lid 220 Lower lid 230 Bellows 300 Multilayer Piezoelectric Element 310 Laminate 3101 Front 3102 Rear 3103 Right side 3104 Left side 312 Piezoelectric ceramic layer 3121 Main side 3122 Subside 314 Internal electrode layer 3141 Main side 3142 Subside 320 Upper 330 Bottom 400 terminals 500 gas 600 leads 700 external electrode 800 Discharge resistor D distance

Claims

1. A multilayer piezoelectric actuator comprising a metal case, a multilayer piezoelectric element housed inside the metal case, a terminal connected to the multilayer piezoelectric element and extending outside the metal case, and gas sealed inside the metal case, The oxygen concentration in the gas is 10% or more and 50% or less. Multilayer piezoelectric actuator.

2. 2. The multilayer piezoelectric actuator according to claim 1, The multi-layer piezoelectric element includes a laminate in which piezoelectric ceramic layers and internal electrode layers are alternately stacked, The piezoelectric ceramic layer is made of PbTiO ３ -PbZrO ３ -Pb(Ni １／３ Nb ２／３ ) O ３ The main component is ternary lead zirconate titanate (PZT), which is expressed as Multilayer piezoelectric actuator.

3. 3. The multilayer piezoelectric actuator according to claim 1, The multi-layer piezoelectric element includes a laminate in which piezoelectric ceramic layers and internal electrode layers are alternately stacked, The Curie temperature of the piezoelectric ceramic layer is 200°C or higher, The terminals are shipped in a shorted state outside the metal case. Multilayer piezoelectric actuator.

4. 3. The multilayer piezoelectric actuator according to claim 1, The multi-layer piezoelectric element includes a laminate in which piezoelectric ceramic layers and internal electrode layers are alternately stacked, When viewed along the stacking direction, the laminate has a partial electrode structure in which the internal electrode layers are smaller than the piezoelectric ceramic layers, and some ends of the internal electrode layers coincide with the ends of the piezoelectric ceramic layers, while the remaining some ends of the internal electrode layers are spaced apart from the ends of the piezoelectric ceramic layers, The distance from the end of the remaining part of the internal electrode layer to the end of the piezoelectric ceramic layer is 0.1 mm or more. Multilayer piezoelectric actuator.

5. 3. The multilayer piezoelectric actuator according to claim 1, The dew point of the gas is −40° C. or less. Multilayer piezoelectric actuator.

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