JPH07106656A - Piezoelectric actuator and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a piezoelectric actuator having high mechanical strength and high control accuracy for microdisplacement in which cracking or chipping at the fringe on the displacement transmission plane of a laminate is prevented and a method for manufacturing the actuator with high mass-productivity without sacrifice of reliability. CONSTITUTION:Strain transmission planes 6a, 6b are rounded 20 at the peripheral part thereof. The peripheral part is rounded during the hot press step when a laminate of green sheet is pressed integrally using a metal mold having a protrusion of such profile as being fitted to the rounded part 20 on the contact face with a green sheet. The inventive method can also be employed in the manufacture of a piezoelectric actuator having beveled periphery on the strain transmitting planes 6a, 6b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator and a manufacturing method thereof, and more particularly to a piezoelectric actuator having an improved displacement transmitting surface and a manufacturing method thereof.

[0002]

2. Description of the Related Art A conventional piezoelectric actuator will be described with reference to FIG. FIG. 5 is a perspective view showing a structure of an example of a conventional laminated actuator. Referring to the figure, this actuator has a laminated structure in which a ceramic layer 2 having a piezoelectric effect and an internal electrode layer 3 are alternately laminated so that they are on top of each other. Layer 7 is provided.

The internal electrode layer 3 is exposed on four side surfaces of the laminated structure, but two side surfaces facing each other out of these four side surfaces (a front side surface and a back side surface in the figure). Then, the exposed portion of the internal electrode layer 3 and the ceramic layer 2 in the vicinity thereof
An insulator 4 such as glass is formed thereon, and an external electrode layer 5 is continuously provided thereon in a strip shape in the stacking direction (vertical direction in the drawing). In this case, the above-mentioned insulators 4 are formed so as to cover the exposed portions of the internal electrode layers 3 every other layer, and are staggered on the above-mentioned two side surfaces. Therefore, the external electrode layers 5 on the front side surface are connected so that all the even-numbered internal electrode layers from the top have the same potential, and the external electrode layers 5 on the back side surface are the odd-numbered internal electrode layers. Are connected so that they have the same potential.

With such a structure, when a driving voltage is applied from an external power supply circuit (not shown) between the two external electrode layers 5, the internal electrode layers facing each other with the ceramic layers 2 in between are opposed to each other. Since it acts as a counter electrode,
Displacement direction indicated by arrow in FIG. 5 (matches stacking direction)
In addition, a minute mechanical displacement of several microns to several tens of microns occurs. The above-mentioned protective layer 7 protects the ceramic layer 2 as a strain generation source from mechanical and physical shocks, electrically insulates it from the device using this actuator, and prevents the displacement generated in this laminated structure from occurring. It also serves as a displacement transmission surface when transmitting to the device.

As will be described later, the actuator having the above-described structure is manufactured by cutting it out from a large laminated sintered body and finishing it into a desired shape and size during the manufacturing process. The conventional actuator shown in FIG. Then, as shown in the figure, two displacement transmitting surfaces 6a and 6b perpendicular to the stacking direction are formed.
And four side faces intersect at a right angle to form a ridge.

[0006] By the way, since ceramics as a material of the actuator is a material having extremely high brittleness, if the corners of the ridge formed by the displacement transmitting surface and the side surface are left at right angles in this way, it becomes a reference for displacement transmission. Displacement transmission surface 6 to be
Cracks or breaks are likely to occur at the peripheral portions of a and 6b, and when this actuator is used, minute displacement on the order of microns may not be precisely controlled. In addition, the laminated structure may be damaged during the manufacturing process or during assembly into the device, which may cause a decrease in the yield rate of the product and the product becoming unusable.

As a method for suppressing the occurrence of cracks and chips on the displacement transmitting surfaces of such a laminated structure, as shown in FIG. 6, chamfered portions 10 are formed on the peripheral portions of the displacement transmitting surfaces 6a and 6b.
An actuator provided with is disclosed in Japanese Patent Application Laid-Open No. 4-145674 (Japanese Patent Application No. 2-269846).

FIG. 7 shows a manufacturing process diagram of the actuator described in the above publication. Referring to the figure, in order to manufacture this actuator, first, lead zirconate titanate Pb (T
An organic binder is added to ceramic powder such as i, Zr) O ₃ and dispersed in an organic solvent to make slurry (step S1), and a green sheet is formed by a slip casting method using a doctor blade (step S
2). After that, a layer of conductive paste is adhered and formed on this green sheet (step S3), and cut into a predetermined size (step S4).

Next, a predetermined number of the cut green sheets are stacked one by one in a mold (step S5), an upper punch is placed on the green sheets, and the sheets are pressed from above and below by a press while heating to a temperature at which the binder flows. And integrated (step S6). The press die used at this time has a flat surface in contact with the green sheet. The green sheet laminated body thus obtained is heated to the decomposition temperature of the binder to remove the binder contained in the green sheet laminated body (step S7) and then sintered to obtain a laminated sintered body (step S
8).

Next, using an outer peripheral blade cutting machine such as a dicing saw, V grooves are provided at the cutting positions on the upper surface and the lower surface of the laminated sintered body (step S9), and further, a wire saw, a crystal cutter or an inner peripheral surface. The sintered block is cut out by cutting with a cutting machine such as a blade (step S10).

After that, the insulator 4 is formed on a pair of side surfaces of the sintered block which face each other (step S11). Insulator 4
For example, a glass powder having a softening point at 500 to 700 ° C. is attached to a desired position by electrophoresis, and then 600 to
A glass body fired at a temperature of 800 ° C. is used.

Next, a silver paste layer to be the external electrode layer 5 is formed on the two opposite side surfaces of the sintered block by a screen printing method (step S12). After that, V-groove processing is performed at the cutting positions on the upper surface and the lower surface of the sintered block using an outer peripheral blade cutting machine such as a dicing saw (step S13). After that, the sintered block is cut at the position of the above V groove by a cutting machine such as a wire saw, and a smaller chip-shaped piezoelectric element chip is cut out (step S14).
The actuator shown in is obtained. Then, a lead wire is soldered to each of the external electrode layers 5 (step S15), and an exterior is applied (step S16) to complete the laminated piezoelectric actuator.

[0013]

In the method of manufacturing a piezoelectric actuator disclosed in the above publication, the green sheet laminated body is sintered to form a laminated sintered body, and then the laminated sintered body is sintered. Once before cutting (step S
9) Further, the V groove is formed at the cutting position once (step S13) before cutting the sintered block into chips, twice in total. That is, because the manufacturing process is increased for chamfering,
The manufacturing cost increases accordingly. Further, since V-grooves are formed in a state where the hardness is extremely high by sintering, it is inevitable that a mechanical method such as an outer peripheral blade or an inner peripheral blade, or a laser is used. For this reason, mechanical damage such as microcracks is likely to occur at the time of groove formation, and the reliability of the actuator may be reduced. The generated microcracks can be removed to a certain extent by polishing or the like in a later step, but the number of manufacturing steps increases, which also increases the manufacturing cost. In addition, it is very difficult to completely remove the insulating material 4 such as glass without damaging the insulating material 4 and preventing the progress of the microcracks that have occurred once. There is an unavoidable decrease in.

Therefore, the present invention provides a piezoelectric actuator excellent in controllability and reliability of minute displacement, which is free from mechanical damage caused by cracking or chipping of the periphery of the displacement transmitting surface of the laminated structure, and such a piezoelectric actuator. It is an object of the present invention to provide a manufacturing method capable of manufacturing an actuator without lowering reliability and having excellent mass productivity.

[0015]

In the piezoelectric actuator of the present invention, a ceramic layer exhibiting a piezoelectric effect and an internal electrode layer for applying an electric field according to a driving voltage applied from the outside are alternately laminated. In a laminated piezoelectric actuator including a laminated structure obtained by combining and integrating the laminated structure, each of the two end faces of the laminated structure perpendicular to the laminating direction and the side faces of the laminated structure parallel to the laminating direction are formed. The ridge is rounded.

Further, according to the method of manufacturing a piezoelectric actuator of the present invention, each of the two end faces perpendicular to the laminating direction of the laminated structure obtained by alternately superimposing and integrating the ceramic layers exhibiting the piezoelectric effect and the internal electrode layers. A method of manufacturing a laminated piezoelectric actuator having a chamfered portion or a rounded portion formed on a ridge portion formed by a side surface of the laminated structure and a side surface parallel to the laminating direction, the green comprising a ceramic having piezoelectricity. A step of forming a conductor layer for an internal electrode layer on the sheet to obtain a green sheet with a conductor layer; a step of sequentially stacking the green sheets with a conductor layer to form a green sheet laminate; Included in the above-mentioned laminated press body is a hot pressing step in which pressure is applied in the laminating direction to the body while heating the body to press-bond it to obtain a laminated press body A step of removing the inder and sintering to obtain a laminated sintered body; a first cutting step of cutting the laminated sintered body to obtain a sintered block; and cutting the sintered block to form a piezoelectric element chip. In the method for manufacturing a laminated piezoelectric actuator including a second cutting step, a step of fitting the chamfered portion or the rounded portion on the surface of the hot pressing step that presses the green sheet laminated body is performed. By applying the pressure to the green sheet laminated body by using a pressing die having a protrusion having a cross-sectional shape and arranged so as to pick up a large number of the piezoelectric element chips, the first laminated laminated body is formed. The groove for forming the chamfered portion or the rounded portion is provided at a position corresponding to the cutting position in the cutting step and the cutting position in the second cutting step.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. 1 is a perspective view showing a structure of a laminated piezoelectric actuator according to a first embodiment of the present invention. In addition, FIG. 2 is a process diagram for explaining the manufacturing method.

Referring to FIG. 1, the actuator of the present embodiment is different from the conventional actuator shown in FIGS. 5 and 6 in that a rounded portion 20 is formed at the peripheral edge of the displacement transmitting surfaces 6a and 6b.
Is provided. Further, referring to FIG. 2, the manufacturing method of the present embodiment is different from the conventional manufacturing method shown in FIG. 7 in that a pressing die having a protrusion is used in the hot pressing step S6A. , Twice V in the conventional manufacturing process
This is that the groove forming step (FIG. 7, step S10 and step S13) is omitted.

A plan view of the press die used in the hot pressing step S6A is shown in FIG. 3 (a). 3B is a perspective view taken along the line AA, and FIG. 3B is a perspective view taken along the line BB.
It shows in (c). With reference to FIGS. 3A to 3C, the press die 8 of this pressing die is provided with a protrusion 81A running in parallel in the vertical and horizontal directions on the surface in contact with the ceramic green sheet. The cross-sectional shape of the protrusion 81A is a shape in which two arcs of a quarter of a circle are back-to-back, and the curvature of each is the same as the curvature of the rounding portion 20 provided in the actuator shown in FIG. . The pitch of the array of the respective protrusions matches the vertical and horizontal dimensions of the cross section perpendicular to the stacking direction of the actuator.

The actuator having the rounding portion 20 shown in FIG. 1 is manufactured by the same manufacturing process as that of the conventional actuator shown in FIG. 5, but in this case, the binder flows through the green sheet laminated body which has been laminated. In the hot pressing step S6A in which pressure is applied from above and below with a press to integrate them, the pressing die of the pressing die shown in FIGS. 3A to 3C is used. At this time, as shown in FIG. 4A, the green sheet laminate 9 is placed between the upper and lower press dies 8A, and pressure is applied while heating. This way,
At the same time when each green sheet is crimped and integrated,
A groove for rounding is formed at a cutting position in a later cutting process. Moreover, at this time, the groove for the block cutting step S10 (see FIG. 2) and the groove for the element cutting step S14 (same) are simultaneously formed in one step. Since this groove is formed when the green sheet laminate 9 is in a soft and plastic state, it is different from machining by a mechanical method such as cutting after sintering to increase hardness. , Without mechanical damage. A groove forming method using such a mold is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-51292 (Japanese Patent Application No. 63-20214).
No. 2), it is conventionally used for forming a slit for division when a large number of ceramic substrates serving as insulating substrates for mounting chip-shaped electronic components are taken. Is not particularly difficult to apply.

Next, the green sheet laminated body in which the grooves for rounding are formed and integrated on the upper and lower surfaces as described above, the binder is removed (step S7), and the green sheet laminated body is sintered (step S).
8) After that, cut with a wire saw at the groove position formed in the hot pressing step S6A, and cut into a sintered block (step S1
0). Further, an insulator 4 (see FIG. 1) is formed on this sintered block (step S11), an external electrode layer 5 (see FIG. 1) is formed (step S12), and then formed again in the previous step S6A. Cut with a wire saw at the groove position (step S
14), obtaining the individual actuators shown in FIG. After that, a lead wire is soldered to the external electrode layer 5 and an exterior is applied to complete the piezoelectric actuator.

The results of reliability tests carried out on the laminated piezoelectric actuator of this embodiment produced as described above and the conventional piezoelectric actuator shown in FIG. 5 will be described below. In the sample, the thickness of the ceramic layer 2 is 105 μm, the number of internal electrode layers 3 is 126, the thicknesses of the upper and lower two protective layers 7 are 2 mm and 4 mm, respectively, and the shape of the cross section perpendicular to the displacement direction is 5 mm × 5 mm. The structure has a length of 20 mm in the displacement direction. The ceramic layer 2 is Pb
(Ni _1/3 Nb _2/3 ) _0.50 Zr _0.15 Ti _0.35 O ₃ based perovskite structure composite oxide, and the internal electrode layer 3 is
This is a silver / palladium mixed electrode containing 70% silver and 30% palladium. The insulator 4 is made of ZnO 60%, B ₂ O ₃ 25
% And other oxides are 15% zinc-based glass. The external electrode layer 5 was formed by baking silver at a temperature of 700 ° C.

In the sample according to this embodiment, the level of the size of the rounding portion 20 of the displacement transmitting surfaces 6a and 6b is
There were three levels of R0.5, R1.0 and R1.5. The number of samples is 50 for each level according to the present embodiment and the conventional one.

The reliability test is a moisture resistance load test, in which a DC voltage of 15 is applied to each sample in an environment of a temperature of 40 ° C. and a humidity of 90 to 95% while applying a compressive force of 5000 N in the displacement direction.
0V is continuously applied.

Table 1 shows the results of the reliability test.

[0026]

[Table 1]

In Table 1, the relative average life is the time until failure in each sample is obtained by the above-mentioned test, and this is plotted on a Weibull probability sheet, and the result is obtained for each level. The average life (MTTF) is standardized with the average life of the conventional actuator being 1.

Referring to Table 1, the rounding size is R
When 1.0 or more, the average life of the actuator is about 1
It can be seen that it has been extended to 0 times and greatly improved. When the manufacturing process of the actuator of this embodiment is compared with the manufacturing process of the actuator shown in FIG. 5, it is considered that they are substantially equivalent in that mechanical damage such as microcracks due to groove formation at the cutting position does not occur. Therefore, the extension of the average life in the above-mentioned present embodiment is caused by the chipping or cracking of the displacement transmitting surface peripheral portion which has been conventionally generated during manufacturing or handling of the actuator. It is considered that this is because the rounding has almost eliminated the occurrence. Moreover, when manufacturing the actuator of this embodiment, no new process is required and the manufacturing capability in each process is not sacrificed, so that the manufacturing cost of this embodiment is the same as that of the conventional actuator. Is.

Although the description so far has been made on the actuator in which the peripheral portion of the displacement transmitting surface is rounded,
Next, a second embodiment in which the present invention is applied to an actuator having a chamfered portion will be described.

The actuator of this embodiment has two displacement transmitting surfaces 6a and 6b as shown in the perspective view of FIG.
The chamfered portion 10 is provided at the peripheral edge of the. This actuator is manufactured by the same process as the manufacturing process of the first embodiment (see FIG. 2), but the hot pressing process (the same as step S6).
The press dies used in A) are different. A plan view of the press die used in this embodiment is shown in FIG. 3 (a), and a sectional view taken along the line AA is shown in FIG. 3 (d). Further, a cross-sectional perspective view taken along line BB is shown in FIG. Referring to these figures, the press die 8B used in this embodiment has an inverted V-shaped projection 81B that runs parallel to the vertical and horizontal directions on the surface in contact with the green sheet laminate.
Is provided. The cross-sectional shape of the inverted V-shaped protrusion 81B is a shape that fits into the chamfered portion 10 of the actuator shown in FIG. In this embodiment, the green sheet laminated body 9 that has been laminated in the hot pressing step S6A is
As shown in FIG. 4B, it is sandwiched between the upper and lower press dies 8B and heated while applying pressure in the stacking direction to be integrated.

The following is a description of the results of reliability tests carried out on the actuator of the present embodiment manufactured as described above and the conventional chamfered actuator manufactured by the conventional manufacturing method shown in FIG. To do. The structure, material, and reliability test conditions of the manufactured sample are all the same as those in the first embodiment except that the peripheral portion of the displacement transmitting surface has a chamfered structure. Table 2 shows the test results. The results shown in Table 2 are standardized with the average life at each level set to 1 as the average life of the conventional actuator used in the first embodiment (the ridge of the peripheral edge of the displacement transmitting surface is a right angle). There is.

[0032]

[Table 2]

Referring to Table 2, both the actuator of this embodiment and the conventional actuator with the chamfer show the effect of extending the average life when the chamfer size is C0.8 or more. This indicates that the occurrence of cracks and chips at the peripheral edge of the displacement transmitting surface is suppressed. Further, when comparing with the same chamfer size, as in C1.2, for example, it is found that the degree of extension of the average life in this example is larger than that in the actuator with a chamfer by the conventional manufacturing method. It It is considered that this is because when the chamfering is performed by the manufacturing method of the present embodiment, the occurrence of microcracks or the like is less during the formation of the chamfering groove.

Although the above-described embodiments have been described with reference to a piezoelectric actuator using a ceramic exhibiting a piezoelectric effect, it is well known that a phenomenon in which a strain occurs in response to an applied electric field is well known. In addition to the piezoelectric effect, there is an electrostrictive effect. There is a difference between the piezoelectric effect and the electrostrictive effect whether the generated strain amount is proportional to the electric field (piezoelectric effect) or proportional to the square of the electric field (electrostrictive effect). In addition, the difference does not have any different action and effect when the configuration of the present invention is adopted. Therefore, in the above description, "piezoelectric" can be read as "electrostrictive". In the present invention, the “piezoelectric actuator” means “an actuator that utilizes a phenomenon of generating a strain by an electric field”, and is defined to include a “piezoelectric actuator” and an “electrostrictive actuator”.

[0035]

As described above, in the piezoelectric actuator of the present invention, the peripheral edge portion of the displacement transmitting surface is rounded. This prevents mechanical damage such as cracks and chips at the peripheral edge of the displacement transmitting surface during the manufacturing process and during assembly into the device, so even minute displacements on the order of microns can be accurately controlled and transmitted. As a result, the mechanical strength and reliability of the actuator are improved.

Further, in the method for manufacturing a piezoelectric actuator of the present invention, when the green sheet laminated body is hot pressed and integrated, a groove for forming a rounded portion is simultaneously formed by using a pressing die. To do. As a result, according to the present invention, it is possible to eliminate the groove forming step before the cutting step, which has conventionally been required twice, without adding a new step, thereby improving mass productivity. Moreover, in the manufacturing method of the present invention, the above-described groove formation is performed in the largest state before the laminated body is divided in the initial manufacturing process, so that the mass production effect is very large.

Further, the groove formation in the manufacturing method of the present invention is different from the groove formation by the conventional manufacturing method in which the laminated body is sintered and then hardened and then cut. Since it is formed by a pressing mold while maintaining the above, there is no occurrence of microcracks that have been conventionally generated due to mechanical processing during groove formation. Further, the manufacturing method of the present invention can be applied not only to the actuator with the rounded portion but also to the actuator with the chamfered portion.

Therefore, according to the present invention, there is no failure or reliability at the peripheral portion of the displacement transmitting surface, and there is no failure due to mechanical damage such as micro cracks at the time of forming the groove for the chamfered portion or the rounded portion. A high piezoelectric actuator can be efficiently manufactured.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a piezoelectric actuator with a rounding portion according to a first embodiment of the present invention.

FIG. 2 is a process drawing for explaining the manufacturing method according to the first embodiment of the present invention.

FIG. 3 is a plan view and a cross-sectional perspective view of a press die used for manufacturing the first and second embodiments of the present invention.

FIG. 4 is a cross-sectional view for explaining a method of forming a groove in a hot pressing process according to the first and second embodiments of the present invention.

FIG. 5 is a perspective view showing a structure of an example of a conventional laminated piezoelectric actuator.

FIG. 6 is a perspective view showing a structure of a laminated piezoelectric actuator in which a peripheral edge portion of a displacement transmitting surface is chamfered.

7A to 7C are process diagrams showing a conventional manufacturing process for manufacturing the piezoelectric actuator with a chamfered portion shown in FIG.

[Explanation of symbols]

 2 Ceramic Layer 3 Internal Electrode Layer 4 Insulator 5 External Electrode Layer 6a, 6b Displacement Transmission Surface 7 Protective Layer 8A, 8B Press Die 9 Green Sheet Laminate 10 Chamfer 20 Rounding 81A, 81B Projection

Claims (2)

[Claims] 1. A laminated structure obtained by alternately superimposing and integrating a ceramic layer exhibiting a piezoelectric effect and an internal electrode layer for applying an electric field according to a driving voltage applied from the outside to the ceramic layer. In the laminated piezoelectric actuator, a ridge formed by each of two end surfaces of the laminated structure perpendicular to the laminating direction and a side surface of the laminated structure parallel to the laminating direction is rounded. And a laminated piezoelectric actuator. 2. A ceramic structure having a piezoelectric effect and an internal electrode layer are alternately superposed and integrated, and two end faces of the laminated structure which are perpendicular to the laminating direction are formed in the laminating direction of the laminated structure. A method for manufacturing a laminated piezoelectric actuator having a chamfered portion or a rounded portion at a ridge formed by parallel side surfaces, wherein a conductor for an internal electrode layer is provided on a green sheet made of piezoelectric ceramics. Forming a layer to obtain a green sheet with a conductor layer,
A step of sequentially stacking the green sheets with the conductor layers to form a green sheet laminate, and a heat press for obtaining a laminated press body by heating the green sheet laminate and applying pressure in a laminating direction to the green sheet laminate for pressure bonding and integration. A step of removing a binder contained in the laminated press body and sintering the laminated press body to obtain a laminated sintered body; a first cutting step of cutting the laminated sintered body to obtain a sintered block; A method of manufacturing a laminated piezoelectric actuator including a second cutting step of cutting the connection block to obtain a piezoelectric element chip, wherein the chamfered portion is provided on a surface on a side of pressing the green sheet laminated body in the hot pressing step. Alternatively, the green sheet is formed by using a pressing die having a projection having a cross-sectional shape that fits with the rounded portion so as to pick up a large number of the piezoelectric element chips. By applying the pressure to the laminated sheet body, the chamfered portion or the rounded portion is formed at a position corresponding to the cutting position in the first cutting step and the cutting position in the second cutting step of the laminated press body. A method of manufacturing a piezoelectric actuator, comprising forming a groove for forming the piezoelectric actuator.