JPH04349675A - Piezoelectric actuator - Google Patents

Abstract

PURPOSE:To provide a laminated type piezoelectric element having high reliability by improving an initial insulating characteristic of the element by improving moisture resistance of the element. CONSTITUTION:A laminated piezoelectric element 1 is sealed in a metal can 7 provided with a driver so composed as to transmit a displacement in a displacing direction of the element 1. Desiccant 8 is sealed in the can to shut OFF invasion of moisture from the exterior and to largely reduce a humidity in the can thereby to improve reliability. As the driver of the can, a movable element such as a diaphragm 6, etc., a can formed in bellows to be driven, are indicated, but the other structure in which displacement is externally transmitted, may be used.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator for a minute positioning mechanism used in fluid control valves, semiconductor exposure equipment, and the like.

0002

[Prior Art] Conventionally, this type of piezoelectric actuator
For example, a small amount of organic binder is added to a piezoelectric material powder whose main component is lead zirconate titanate, a slurry is made by dispersing this in an organic solvent, and a piezoelectric sheet is formed into a film using the doctor blade method. Then, on one side of this piezoelectric sheet, an internal electrode conductor is formed by applying a conductive paste mainly composed of platinum powder or a mixture of silver powder and palladium powder by screen printing, etc. A plurality of sheets are stacked to form a laminate, an insulator is formed every other layer on the internal electrodes exposed on the side surfaces, and a first external electrode is formed on top of the insulator. On the other hand, on the side surface opposite to the side surface, an insulator is selectively formed on the exposed portions of the internal electrodes on which no insulator was previously formed, and a second external electrode is formed thereon. It has a structure in which lead wires are connected to external electrodes on both sides with solder.

0003

[Problems to be Solved by the Invention] In the conventional piezoelectric actuator described above, when a silver-based material is used for the metal forming the internal electrode, in a humid atmosphere, the silver migrates due to moisture adhering to the side surfaces, resulting in laminated sintering. Significantly contaminates the sides of the body. That is, since the ends of the silver-based electrode conductor layer are all exposed on the side surfaces of the laminated sintered body, migration is likely to occur, and the contaminated side surfaces of the laminated sintered body rapidly deteriorate its insulation properties. Therefore, when a moisture resistance durability test is performed, discharge occurs on the side surface one after another, which poses a problem in that it greatly impairs yield and reliability. In addition, when non-silver-based materials such as gold and platinum are used for internal electrode materials to suppress the occurrence of migration, although the reliability is greatly improved compared to the silver-based materials mentioned above, it adheres to the side surfaces of the laminated sintered body. The resulting moisture reduces the insulation resistance of the element. Therefore, when conducting the same test as above, dielectric breakdown such as electrical discharge may occur accidentally on the side. As a countermeasure against this, there is a structure in which an organic insulating material is formed only on the internal electrode exposed on the side surface and the piezoelectric material in the vicinity to prevent moisture from entering the side surface, as in JP-A No. 61-27688; Applications have been made for structures such as 16685-1983, in which the ends of the internal electrodes exposed on the side surfaces of the element, which are not provided with external electrodes, are covered with a glass film to block the intrusion of moisture, but their moisture resistance is poor. It wasn't completely satisfying.

0004

[Means for Solving the Problems] In order to solve the above problems, the present invention forms a laminate by alternately laminating a plurality of thin plates made of an electromechanical conversion material and a plurality of internal electrodes made of a conductive material. , a stacked piezoelectric device comprising a pair of external electrodes to be connected to the internal electrodes every other layer on the side surface of the stacked body, and lead wires connected with solder to apply a voltage to the external electrodes from the outside. The device is housed in a metal sealed container filled with a desiccant, and the lead wires are taken out to the outside of the container while maintaining the airtightness inside the container. A piezoelectric actuator is employed, which is characterized by forming a movable part that extends in the direction in which the piezoelectric element extends.

[0005]

[Operation] The present invention provides a stacked piezoelectric element with a lid member attached to one end in the stacking direction and a terminal member attached to the other end.
Both parts are sealed in a tube together with the laminated piezoelectric element, and after filling the space inside the tube with desiccant, the tube is sealed to prevent moisture from entering from the outside and to reduce the humidity inside the tube immediately after sealing. It is something that reduces

[0006]

[Example] Next, an example of the present invention will be described. Figure 1
1 is a sectional view of an embodiment of a piezoelectric actuator of the present invention. The piezoelectric actuator of this embodiment includes a multilayer piezoelectric element 1 and an external electrode 3 connected to one end surface in the stacking direction via a lead wire 2, and a lead wire provided to seal against outside air. 2, a diaphragm 6 fixed to the other end surface, and a tube 7 that seals and holds the laminated piezoelectric element 1 with these terminal members 5 and diaphragm 6. A desiccant 8 is filled in the blank space. The laminated piezoelectric element 1 of this embodiment is basically a piezoelectric element having the same structure as that described in the conventional example, and the conductive paste material used for the internal electrode 9 and the external electrode 3 of this laminated piezoelectric element 1 is were formed as shown in the table below for comparative experiments. Although the laminated piezoelectric element is schematically shown in FIG. 1, the laminated piezoelectric element described below was actually used. The method for manufacturing this piezoelectric element will be briefly described below.

[0007]

[Table 1] First, a piezoelectric thin plate containing lead zirconate titanate as a main component is formed using the doctor blade method, and then the above internal electrodes are formed by screen printing, and a plurality of these sheets are laminated and sintered to form a laminate. Formed. A glass insulating film (hereinafter referred to as an insulating film) is formed on one side surface of the laminated piezoelectric element thus obtained so as to be at least smaller in area than the side surface and in contact with all layers of the exposed internal electrodes of each layer. was formed. Next, grooves were formed using a dicing machine so that the internal electrodes were exposed every other layer on the insulating film from the upper part of the insulating film. On the other hand, a glass insulating film was similarly formed on the side surface perpendicular to that surface, and then grooves were formed in the layer that had not been grooved using a dicing machine. This resulted in a structure in which the internal electrodes were alternately exposed on the insulating films on the orthogonal surfaces on which the insulating films were formed. Next, external electrodes were formed on the grooves by screen printing. Then, lead wires (non-silver core material, tin plated) were connected to the external electrodes on both sides with solder (non-silver). The laminated piezoelectric element obtained through the above steps has a cross section of 5 mm.
×5 mm, length 10 mm, and number of stacked sheets was 90. The side surfaces of this laminated piezoelectric element were uniformly coated with resin by powder coating. After the terminal member 5 shown in FIG. After the terminal member 5 is inserted into the tube 7, the terminal member 5 is glued to the tube 7. At this time, since the terminal member 5 is provided with a taper, the terminal member 5 and the tube 7 can be easily positioned. tube 7
In this example, nickel steel (N
i: 42%), and the surface was nickel plated for rust prevention. Further, since the tube 7 is cylindrical as shown in the figure, a space is created around the laminated piezoelectric element 1. After filling the space with drying material 8, the diaphragm 6 was glued to the end of the laminated piezoelectric element 1 from the other end of the tube 7 in order to efficiently transmit the displacement of the laminated piezoelectric element to the outside of the tube 7. later,
Fix and seal the pipe 7. In the present invention, silica gel was used as the desiccant and epoxy resin was used for adhesion, but it is clear that similar effects can be obtained with other desiccants and adhesives. Note that the terminal member 5 and the diaphragm 6 are made of metal, and although stainless steel is used in the present invention, metals such as aluminum may also be used. The piezoelectric actuator thus completed was heated at a temperature of 40°C and a humidity of 90 to 95% RH.
A durability test was conducted in an atmosphere. The results will be explained below. First, in order to demonstrate the superiority of the present invention, the conditions shown in the table below were set for a laminated piezoelectric element.

[0008]

[Table 2] After the samples under each condition were left for about 2 hours in the above atmosphere with no voltage applied, the insulation resistance value at 100 VDC was measured. The results are shown in the table below.

[0009]

[Table 3] First, under condition (1), the insulation resistance of the internal electrode using a silver-based conductive material is slightly lower than that of a non-silver-based material. Next, when comparing condition (3), it is clear that the value is larger in the case of the metal tube sealed than in the case of leaving it naturally. Moreover, the superiority of non-silver metals is more pronounced than in condition (■). Furthermore, comparing conditions (2) and (2) clearly shows the effect of filling the desiccant. From the above results, it can be seen that the initial value of the insulation resistance of both silver-based materials and non-silver-based materials decreases in a high humidity atmosphere, which is clearly due to the influence of moisture adhering to the side surfaces of the element. Furthermore, even when sealed inside a tube, the insulation resistance is higher when the desiccant is filled. This is thought to be due to the moisture remaining in the tube when it was sealed. That is, in order to improve the initial value of insulation resistance and provide a more reliable element, it is suitable to enclose a desiccant in the tube, and at the same time, this proves the superiority of the present invention. . Next, a voltage of 150 VDC was continuously applied to each of the above materials, and 10
A durability test was conducted for 00 hours. The time dependence of insulation resistance deterioration at that time was measured. The results are shown in FIGS. 2 to 4. FIG. 2 shows actuator No. This shows the characteristics of No. 1. Since silver is used as the electrode material for both the internal and external electrodes, those left unattended began to deteriorate immediately after the start of the test and were completely short-circuited in about 100 hours. Note that after the test, this actuator was taken out and thoroughly dried, and then the insulation resistance was measured again, but the short circuit remained. Compared to this, those sealed in cans experience significantly less deterioration. However, it can be seen that those not filled with desiccant deteriorate slowly. FIG. 3 shows actuator No. 2 shows the deterioration characteristics of the insulation resistance of No. 2. Silver as electrode material
Because it uses a palladium alloy, migration is less likely to occur than when using pure silver. A short circuit occurred after about 200 hours after being left alone. After the test, it was taken out and thoroughly dried in the same manner as above, and then the insulation resistance was measured, but it remained short-circuited. It can be seen that the cans sealed in cans showed the same tendency as described above, and among them, those not filled with a desiccant were clearly deteriorated. FIG. 4 shows actuator No. This is the characteristic of 3. Since a non-silver-based material is used for the electrode material, the degree of deterioration is extremely small. However, as shown in the figure, those that have been left to naturally deteriorate gradually with insulation resistance values fluctuating greatly. This actuator was also taken out after the test and after being thoroughly dried, the insulation resistance was measured and the result was 2.
．． It became 0x1010 Ω and almost returned to its original state. Therefore, it can be seen that the deterioration of this element is not due to migration of the electrode metal, but due to insulation deterioration due to moisture adhesion. In addition, when enclosed in a tube, actuators using non-silver materials have shown very stable characteristics. In this embodiment, actuator No. Although only the deterioration characteristics of Nos. 1 to 3 are shown, the other actuators, which were sealed in a metal tube and filled with desiccant, showed extremely stable characteristics. As a result of the above, it has become clear that in order to obtain high reliability of a piezoelectric actuator, it is sufficient to encapsulate a laminated piezoelectric element inside a metal tube and fill it with a desiccant. Next, other embodiments of the present invention will be described. FIG. 5 is a cross-sectional view of another embodiment. This embodiment differs from the previous embodiments in that the laminated piezoelectric element is sealed with a lid member 4, and the side surface of the metal tube is processed into a bellows shape, so that the displacement of the laminated piezoelectric element is transmitted to the outside via the bellows. This is the point where it can be done. The assembly method is the same as the one described above, but since the tube becomes bellows-like and the gap inside the tube becomes smaller, it becomes difficult to fill with desiccant, so in this example, powdered phosphorus pentoxide was used as the desiccant. there was. The piezoelectric actuator thus produced was tested under the same conditions as in the previous example, and almost the same results were obtained, with no problems occurring. In addition, in the above-mentioned embodiment, an example was described in which silica gel and phosphorus pentoxide were used as the desiccant material 8 filled in the metal tube, but other desiccant agents such as magnesium perchlorate, activated alumina, and calcium chloride may also be used. The same can be done.

0010

[Effects of the Invention] As explained above, the present invention hermetically encapsulates a laminated piezoelectric element in a metal tube filled with a desiccant, thereby preventing moisture from entering from the outside and reducing the humidity inside the tube. This has the effect of greatly improving the insulation reliability of the piezoelectric actuator.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a piezoelectric actuator of the present invention.

FIG. 2 is a diagram showing deterioration characteristics of a piezoelectric actuator according to an embodiment of the present invention.

FIG. 3 is a diagram showing deterioration characteristics of a piezoelectric actuator according to an embodiment of the present invention.

FIG. 4 is a diagram showing the deterioration characteristics of a piezoelectric actuator according to an embodiment of the present invention.

FIG. 5 is a sectional view showing another embodiment of the invention.

[Explanation of symbols]

1 Piezoelectric actuator 2 Lead wire 3 External electrode 4 Lid member 5 Terminal member 6 Diaphragm 7 Metal pipe 8. Desiccant 9 Internal electrode 10 Internal terminal

Claims (1)

[Claims] 1. A laminate is formed by alternately stacking a plurality of thin plates made of an electromechanical conversion material and a plurality of internal electrodes made of a conductive material, and a plurality of thin plates made of an electromechanical conversion material and internal electrodes made of a conductive material are connected to the side surfaces of the laminate every other layer. 1. A piezoelectric actuator characterized in that a laminated piezoelectric element provided with a pair of external electrodes is housed in a sealed metal container filled with a desiccant.