JP2850718B2 - Manufacturing method of piezoelectric actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric actuator .
More particularly, the present invention relates to a method for manufacturing a piezoelectric actuator in which the shape of a displacement transmitting surface is improved.

[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 the structure of an example of a conventional stacked-type actuator. Referring to FIG. 1, this actuator has a laminated structure in which ceramic layers 2 exhibiting a piezoelectric effect and internal electrode layers 3 are alternately laminated one above the other, and protection is provided above and below this laminated structure. A layer 7 is provided.

[0003] The internal electrode layer 3 is exposed on four side surfaces of the laminated structure, and two opposing side surfaces (the front side surface and the back side surface in the figure) of the four side surfaces. Then, the exposed portion of the internal electrode layer 3 and the ceramic layer 2
An insulator 4 such as glass is formed thereon, and an external electrode layer 5 is further provided thereon in a band-like manner in the laminating direction (vertical direction in the drawing). In this case, the insulator 4 is formed so as to cover the exposed portion of the internal electrode layer 3 alternately, and alternately on the two side surfaces. Therefore, the external electrode layer 5 on the front side is connected to all even-numbered internal electrode layers from the top so as to have the same potential, and the external electrode layer 5 on the rear side is connected to the odd internal electrode layer. Are connected so as to have the same potential.

In 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 respective ceramic layers 2 interposed therebetween are mutually connected. It acts to be a counter electrode,
Displacement direction indicated by the arrow in FIG. 5 (coincides with the stacking direction)
Then, a minute mechanical displacement of about several microns to several tens of microns occurs. The above-described protective layer 7 protects the ceramic layer 2 as a strain generating source from mechanical and physical impacts, electrically insulates the device using this actuator, and displaces the displacement generated in this laminated structure. It also serves as a displacement transmission surface when transmitting to the device.

As described later, the actuator having the above-described structure is manufactured by cutting out a large laminated sintered body in a manufacturing process and finishing it to a desired shape and dimensions. As shown in FIG. Then, as shown in the figure, two displacement transmitting surfaces 6a and 6b perpendicular to the laminating direction are provided.
And the four sides intersect at right angles to form a ridge.

Incidentally, since ceramics as a material of the actuator is a material having extremely high brittleness, if the angle of the ridge formed by the displacement transmitting surface and the side surface is kept at a right angle in this manner, the standard of displacement transmission becomes Displacement transmission surface 6 to become
Cracks or breaks are likely to occur in the peripheral portions of a and 6b, and when using this actuator, it is sometimes impossible to precisely control minute displacement on the order of microns. Further, the laminated structure may be damaged during the manufacturing process or during the incorporation into the device, which may cause a decrease in the non-defective product rate or render it unusable.

As a method for suppressing the occurrence of cracks and chips on the displacement transmitting surface of such a laminated structure, as shown in FIG. 6, a chamfered portion 10 is provided on the periphery of the displacement transmitting surfaces 6a and 6b.
Is disclosed in Japanese Patent Application Laid-Open No. 4-145,674 (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, to manufacture this actuator, first, lead zirconate titanate Pb (T
An organic binder is added to a ceramic powder such as (i, Zr) O ₃ and dispersed in an organic solvent to form a slurry (step S1), and a green sheet is formed by a slip casting method using a doctor blade (step S1). S
2). Thereafter, a layer of a conductive paste is formed on the green sheet (step S3) and cut into a predetermined size (step S4).

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

Next, a V-groove is provided at the cutting position of the upper surface and the lower surface of the laminated sintered body using a peripheral cutting machine such as a dicing saw (step S9), and further, a wire saw, a crystal cutter or an inner periphery is formed. The sintered block is cut out by a cutting machine such as a blade (step S10).

Thereafter, an insulator 4 is formed on a pair of opposing side surfaces of the sintered block (step S11). Insulator 4
A glass powder having a softening point at 500 to 700 ° C. is adhered to a desired position by an electrophoresis method.
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 opposing side surfaces of the sintered block by a screen printing method (step S12). Then, V-groove processing is performed on the cutting positions on the upper and lower surfaces of the sintered block by using a peripheral cutting machine such as a dicing saw (step S13). Thereafter, the sintered block is cut at the position of the V-groove by a cutting machine such as a wire saw, and a smaller chip-shaped piezoelectric element chip is cut out (step S14).
Is obtained. Then, a lead wire is soldered to each of the external electrode layers 5 (step S15), and an exterior is provided (step S16), thereby completing a laminated piezoelectric actuator.

[0013]

In the method of manufacturing a piezoelectric actuator disclosed in the above-mentioned publication, a green sheet laminate is sintered into a laminated sintered body, and then the laminated sintered body is sintered. Once (step S
9) Further, before cutting this sintered block into chips, once (step S13), a V-groove is formed at the cutting position twice in total. In other words, the manufacturing process increases for chamfering,
The manufacturing cost increases accordingly. In addition, since the V-groove is formed in a state in which the hardness is extremely increased by sintering, a mechanical method such as an outer peripheral blade or an inner peripheral blade, or a laser must be used. For this reason, mechanical damage such as microcracks is likely to occur during the formation of the groove, and the reliability as an actuator may be reduced. Although the generated microcracks can be removed to some extent by polishing or the like in a later step, the number of manufacturing steps increases, and this also increases the manufacturing cost. In addition, it is very difficult to completely remove the insulator 4 such as glass without damaging the insulator 4 and preventing the micro-crack once generated from proceeding. A slight decrease in is inevitable.

Accordingly, the present invention provides a piezoelectric actuator which is excellent in controllability and reliability of micro-displacement without mechanical damage due to cracking, chipping or the like of the periphery of the displacement transmitting surface of the laminated structure.
It is an object of the present invention to provide a manufacturing method that can manufacture an eta without lowering reliability and that is excellent in mass productivity.

[0015]

According to the present invention, there is provided a piezoelectric actuator.
The method of manufacturing the data consists of a ceramic layer exhibiting the piezoelectric effect and an internal
Laminated structure obtained by alternately stacking and integrating electrode layers
Each of the two end faces perpendicular to the stacking direction of the body and the stacking
On the ridges formed by the sides of the structure parallel to the lamination direction
Laminated piezoelectric actuator with chamfered or rounded part
A method for manufacturing an eta, comprising a ceramic having piezoelectricity
Conduction for internal electrode layer on green sheet
Forming a body layer to obtain a green sheet with a conductor layer
And the green sheets with the conductive layers are sequentially stacked.
Forming a lean sheet laminate;
Apply pressure in the stacking direction to the stack while heating it.
Hot press process to obtain a laminated press body by pressing and crimping and integrating
Removing the binder contained in the laminated press body and sintering
And obtaining a laminated sintered body, and cutting the laminated sintered body
A first cutting step of obtaining a sintered block by
Cutting step to obtain a piezoelectric element chip by cutting
In manufacturing method of laminated piezoelectric actuator containing
In the hot pressing step, the green sheet laminate
The chamfered portion or the rounded portion on the side on which the
The protrusion having a cross-sectional shape to be fitted to the piezoelectric element
Press-type stamping metal arranged to take multiple chips
Applying the pressure to the green sheet laminate using a mold
The first cutting step of the laminated press body
In the cutting position and cutting in the second cutting step
At the position corresponding to the position, the chamfer or the rounding
It is characterized in that a groove for forming a portion is provided.

In the method of manufacturing a piezoelectric actuator according to the present invention, the chamfer of the chamfered portion may have a size of C0.8 or more.
Or, the size of rounding of the rounding portion is R1.0 or more.
It is also characterized by

[0017]

Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing the structure of a multilayer piezoelectric actuator according to a first embodiment of the present invention. FIG. 2 is a process chart for explaining the manufacturing method.

Referring to FIG. 1, the actuator of this embodiment is different from the conventional actuator shown in FIGS. 5 and 6 in that the rounding portions 20 are provided at the peripheral edges of the displacement transmitting surfaces 6a and 6b.
Is provided. Referring to FIG. 2, the manufacturing method of this embodiment is different from the conventional manufacturing method shown in FIG. 7 in that a pressing die having a projection is used in the hot pressing step S6A. Twice in the conventional manufacturing process.
The point is that the groove forming step (FIG. 7, step S10 and step S13) is omitted.

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

The actuator having the rounded 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 laminate after the lamination. In the hot press step S6A of heating to a temperature and applying pressure from above and below by a press to integrate, a press die of a pressing die shown in FIGS. 3A to 3C is used. At this time, as shown in FIG. 4A, the green sheet laminate 9 is arranged between the upper and lower press dies 8A, and pressure is applied while heating. This way,
When each green sheet is pressed and integrated,
A rounding groove is formed at a cutting position in a subsequent cutting step. Moreover, at this time, a groove for the block cutting step S10 (see FIG. 2) and a 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 kept soft and plastic, it is different from the case where the green sheet laminate 9 is processed by a mechanical method such as cutting after the hardness is increased by sintering. Without mechanical damage. A groove forming method using such a mold is described in, for example, Japanese Patent Application Laid-Open No. 2-51292 (Japanese Patent Application No. 63-20214).
As disclosed in Japanese Unexamined Patent Application Publication No. 2 (1993) -195, it has been conventionally used for forming slits for dividing when a large number of ceramic substrates serving as insulating substrates for mounting chip-shaped electronic components are taken. There is no particular difficulty in applying the method.

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

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

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

The reliability test is a humidity resistance load test, in which a DC voltage of 15 is applied to each sample while applying a compressive force of 5000 N in a displacement direction in an environment of a temperature of 40 ° C. and a humidity of 90 to 95%.
0 V 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 required to reach a failure for each sample by the above-described test, which is plotted on a Weibull probability sheet, and the relative average life for each level obtained from the result is obtained. The average life (MTTF) is standardized by setting the average life of a conventional actuator to 1.

Referring to Table 1, if the size of the rounding is R
When it is 1.0 or more, the average life of the actuator is about 1
It can be seen that it has expanded to 0 times and has been greatly improved. Comparing the manufacturing process of the actuator of the present embodiment with the manufacturing process of the actuator shown in FIG. 5, it is considered to be substantially equivalent in that there is no mechanical damage such as microcracks caused by the formation of a groove at the cutting position. Therefore, the increase in the average life in the present embodiment is caused by the chipping or cracking of the displacement transmitting surface peripheral portion which has conventionally occurred during the manufacture or handling of the actuator. This is considered to be because almost no occurrence occurred due to rounding. In addition, the manufacturing cost of the present embodiment is the same as that of the conventional actuator, since no new process is required to manufacture the actuator of the present embodiment, and the manufacturing capability in each process is not sacrificed. It is.

Although the description so far has been made with respect to an actuator in which the periphery of the displacement transmitting surface is rounded,
Next, a description will be given of a second embodiment in which the present invention is applied to an actuator having a chamfer.

The actuator of this embodiment has two displacement transmitting surfaces 6a and 6b as shown in a perspective perspective view of FIG.
Is provided with a chamfered portion 10 at the periphery. This actuator is manufactured in the same process as the manufacturing process of the first embodiment (see FIG. 2), but is subjected to a hot pressing process (the same as process S6).
The press mold used in A) is different. FIG. 3A is a plan view of a press die used in the present embodiment, and FIG. FIG. 3E is a perspective view taken along the line BB. Referring to these drawings, a press die 8B used in the present embodiment has an inverted V-shaped protrusion 81B running in parallel vertically and horizontally on a surface in contact with a green sheet laminate.
Is provided. The cross-sectional shape of the inverted V-shaped projection 81B is a shape fitted to the chamfered portion 10 of the actuator shown in FIG. In the present embodiment, the green sheet laminate 9 having been laminated in the hot pressing step S6A is
As shown in FIG. 4 (b), the sheet is sandwiched between upper and lower press dies 8B and is heated and integrated while applying pressure in the laminating direction.

Hereinafter, the results of reliability tests performed on the actuator of the present embodiment manufactured as described above and the conventional actuator with a chamfer manufactured by the conventional manufacturing method shown in FIG. 7 will be described. I do. The structure, material and reliability test conditions of the manufactured sample are all the same as those of the first embodiment, except that the structure of the periphery of the displacement transmitting surface is chamfered. Table 2 shows the test results. The results shown in Table 2 are obtained by standardizing the average life for each level with the average life of the conventional actuator (in which the ridge of the peripheral edge of the displacement transmitting surface is a right angle) used in the first embodiment as 1. It is.

[0032]

[Table 2]

Referring to Table 2, both the actuator of this embodiment and the conventional actuator with a chamfered portion show an effect of prolonging the average life when the chamfer size is C0.8 or more. This indicates that the occurrence of cracks, chips, and the like at the periphery of the displacement transmission surface is suppressed. Further, when compared with the same chamfer size as in, for example, C1.2, it can be seen that the extent of the average life extension in the present embodiment is larger than that in the actuator with the chamfered portion according to the conventional manufacturing method. You. This is considered to be because the occurrence of microcracks and the like during the formation of the chamfering groove is smaller when chamfering is performed by the manufacturing method of this embodiment.

Although the embodiments have been described with reference to a piezoelectric actuator using ceramics exhibiting a piezoelectric effect, it is well known that a phenomenon in which a strain is caused by an applied electric field is generated. In addition to the piezoelectric effect, there is an electrostrictive effect. The piezoelectric effect and the electrostrictive effect have a difference whether the amount of generated strain 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 effect when the configuration is made as in the present invention. Therefore, in the above description, “piezoelectric” can be read as “electrostrictive”. In the present invention, the “piezoelectric actuator” means “an actuator utilizing a phenomenon that generates a strain by an electric field”, and is defined to include “piezoelectric actuator” and “electrostrictive actuator”.

[0035]

As described above, the production method of the present invention
In the piezoelectric actuator obtained by (1), the periphery of the displacement transmitting surface is rounded. This prevents mechanical damage such as cracks and chips at the periphery of the displacement transmission surface during the manufacturing process and during assembly into the device, so that 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.

In the method of manufacturing a piezoelectric actuator according to the present invention, when the green sheet laminate is integrated by hot pressing, a groove for forming a rounded portion is simultaneously formed using a pressing die. I do. As a result, according to the present invention, the step of forming a groove before the cutting step, which was conventionally required twice, can be omitted without adding a new step, thereby improving mass productivity. Moreover, in the manufacturing method of the present invention, since the above-described groove formation is performed in the largest state before the laminate is divided in the initial manufacturing process, 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 according to the conventional manufacturing method in which the laminate is sintered and the hardness is increased and then the green sheet is still soft and plastic. Is formed by the pressing mold while maintaining the value, there is no generation of microcracks which have conventionally occurred due to the mechanical processing at the time of forming the groove. Further, the manufacturing method of the present invention can be applied not only to an actuator having a rounded portion but also to an actuator having a chamfered portion.

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

[Brief description of the drawings]

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

FIG. 2 is a process chart for explaining a manufacturing method according to a 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 embodiment and the second embodiment 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 embodiment and the second embodiment of the present invention.

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

FIG. 6 is a perspective view showing the structure of a laminated piezoelectric actuator in which the periphery of a displacement transmitting surface is chamfered.

FIG. 7 is a process diagram showing a conventional manufacturing process for manufacturing the piezoelectric actuator with a chamfer shown in FIG.

[Explanation of symbols]

 Reference Signs List 2 ceramic layer 3 internal electrode layer 4 insulator 5 external electrode layer 6a, 6b displacement transmitting surface 7 protective layer 8A, 8B press die 9 green sheet laminate 10 chamfered portion 20 rounded portion 81A, 81B protrusion

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-57610 (JP, A) JP-A-5-75175 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 41/083 H01L 41/09 H01L 41/22

Claims (2)

(57) [Claims] 1. A ceramic layer exhibiting a piezoelectric effect and an internal electrode
Layered structure obtained by alternately stacking and integrating layers
Each of two end faces perpendicular to the stacking direction and the stack structure
Chamfers on the ridges formed by the sides of the body parallel to the lamination direction
Stacked piezoelectric actuator with a rounded or rounded portion
A method of manufacturing a ceramic comprising piezoelectric ceramic
Conductor layer for internal electrode layer on green sheet made of
Forming a green sheet with a conductor layer by forming
Green sheets with the conductor layer are sequentially stacked
Forming a green sheet laminate, and the green sheet
While heating the laminate, apply pressure in the stacking direction
Hot press process to obtain a laminated press body
Remove the binder contained in the laminated press
A step of obtaining a layered sintered body, and cutting and sintering the laminated sintered body
A first cutting step of obtaining a block;
Cutting to obtain a piezoelectric element chip
In the method for manufacturing a laminated piezoelectric actuator, in the hot pressing step, the green sheet laminate is pressed.
The chamfered part or the rounded part is fitted on the surface to be pressed
A protrusion having a cross-sectional shape that matches
Press die that is arranged to take multiple
And applying the pressure to the green sheet laminate.
With this, in the first cutting step of the laminated press body,
Cutting position in the second cutting step
At the position corresponding to the chamfered part or the rounded part shape
Piezoelectric actuator characterized by providing a groove for forming
Manufacturing method. 2. The size of the chamfer of the chamfered portion is C0.8.
As described above, the rounding size of the rounding portion is R1.0
2. The piezoelectric actuator according to claim 1, wherein
Manufacturing method of the heater.