JP3077522B2 - Piezoelectric element, acceleration sensor configured using the same, and method of manufacturing piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element, an acceleration sensor using the same, and a method of manufacturing the piezoelectric element.

[0002]

2. Description of the Related Art Conventionally, some acceleration sensors used for detecting an impact or the like include a piezoelectric element incorporated therein. Among these piezoelectric elements, FIG.
Some have a bimorph structure as shown in FIG. That is, the piezoelectric element includes a plate-shaped piezoelectric ceramic body 3 in which a signal extraction electrode 1 is formed on each main surface and an internal electrode 2 in a state parallel to the signal extraction electrode 1 is embedded. Each of the signal extraction electrodes 1 has three surface electrodes 4 and connection electrodes 5 covering the three surface electrodes 4. One side (upper side in the figure) of these signal extraction electrodes 1 extends to one outer end surface (left side in the figure) of the piezoelectric ceramic body 3, while the other side (lower side in the figure). The signal extraction electrode 1 extends to the outer end surface on the other side (the right side in the figure).

Further, the longitudinal direction of each of the ceramic regions 6 and 7 constituting the piezoelectric ceramic body 3 by being opposed to each other with the internal electrode 2 interposed therebetween has three portions, that is, a change in stress generated when an acceleration is applied. The center portions 6a, 7a and the end portions 6b, 7b are separated from each other through a boundary line between the ceramic regions 6 and 7, and the center portions 6a, 7a and the end portions 6b, 7b of the ceramic regions 6, 7 are in the thickness direction. Are polarized in different directions along the central portion 6a,
The polarization process is performed in the directions opposite to each other with respect to the end 7a and the ends 6b and 7b. That is, in this case, the central portion 6a and the end portion 6b of the ceramic region 6 have different polarization directions A and B, respectively, and the central portion 7a and the end portion 7b of the ceramic region 7 have different polarization directions. The polarization process is performed so as to have C and D, and at the same time, the polarization direction A at the central portions 6a and 7a.
And C are inwardly approaching each other, while the polarization directions B and D at both ends 6b and 7b are outwardly away from each other.

Further, a pair of holding frames 8 whose both ends along the longitudinal direction of the piezoelectric element have a U-shape in side view.
Each of the signal extraction electrodes 1 formed on the main surface of the piezoelectric ceramic body 3 is fixedly supported by an external extraction electrode 9 formed on a different outer end face of the piezoelectric ceramic body 3 and the holding frame 8. 10 are connected to each other. The use of the piezoelectric element having the above configuration is based on the following reasons. That is, when acceleration acts on the piezoelectric element, the central portions 6a, 7a and the end portions 6b, 7b of the ceramic regions 6, 7 constituting the piezoelectric ceramic body 3 are deformed by the action of the inertial force. That is, these parts 6a, 7
a, 6b, and 7b receive a tensile stress or a compressive stress generated by the deformation. Therefore, these parts 6
In a, 7a, 6b, and 7b, the amount of charge generation increases due to the synergistic effect of each of the polarization directions A to D and the applied stress. As a result, the amount of charge generation in the entire piezoelectric element increases. The advantage is that the detection sensitivity of the acceleration sensor is improved.

Next, a method of manufacturing the piezoelectric element having the configuration shown in FIG. 1 will be described step by step with reference to the process perspective views shown in FIGS. In these figures, the range of the size and the shape suitable for each piezoelectric element is indicated by a virtual line.

First, as shown in FIG. 2A, a plurality of strip-shaped internal electrode layers 11 corresponding to a plurality of the internal electrodes 2 arranged in parallel are buried in a plurality of rows, and a piezoelectric ceramic element serving as a piezoelectric element is formed. A rectangular flat plate-shaped piezoelectric ceramic substrate 12 having a size and a shape suitable for a large number of the bodies 3 is prepared. On the opposing main surfaces of the piezoelectric ceramic substrate 12, the individual piezoelectric ceramic members 3, that is, the ceramic regions 6, 7 opposing each other with the internal electrode 2 interposed therebetween are separated along the longitudinal direction. A plurality of strip-shaped surface electrode layers 13 which are separately arranged at positions corresponding to the central portions 6a, 7a and the end portions 6b, 7b are formed. Therefore, in this case, three rows of surface electrode layers 13 are formed in parallel in each of the ranges corresponding to the three groups of piezoelectric ceramic bodies arranged in parallel in one row.

Then, as shown in FIG. 2 (b), the internal electrode layer 11 and the surface electrode layer 13 are used, and a central portion 6a of each of the ceramic regions 6 and 7 constituting each piezoelectric ceramic body 3 is used. , 7a and the end portions 6b, 7b. By the way, at this time, each part 6a, 7a, 6
The polarization processing of b and 7b is performed after setting the polarization directions A to D as shown in FIG. Then, as shown in FIG. 2C, three rows of surface electrode layers 13 formed on the same main surface of the piezoelectric ceramic base 12 and corresponding to each of the three rows of the piezoelectric ceramic bodies 3 are formed. The connection electrode layer 14 for conducting after covering is formed. Here, the surface electrode layer 13 and the connection electrode layer 1
Reference numeral 4 denotes a surface electrode 4 and a connection electrode 5 that constitute the signal extraction electrode 1 in each piezoelectric element.

Subsequently, as shown in FIG. 3 (a), a holding frame base 16 in which a concave groove 15 having a predetermined width is formed at each predetermined position on the inner surface side is prepared, and the surface electrode layer 13 and the connection are formed. Each of the holding frame bases 16 is integrated with each other on the main surface of the piezoelectric ceramic base 12 formed by laminating the electrode layers 14. Further, the piezoelectric ceramic substrate 12 is formed according to a virtual line set to delimit a range of size and shape suitable for each piezoelectric element.
When the holding frame base 16 is cut, the individual piezoelectric elements having the configuration shown in FIG.
A piezoelectric element having a piezoelectric ceramic body 3 having a pair of front electrodes 4 and a signal extraction electrode 1 composed of a connection electrode 5 covering them on the main surface and a pair of holding frames 8 is obtained. At this time, the surface electrode 4 constituting the signal extraction electrode 1 is exposed on the outer end surface of the piezoelectric element.
Therefore, when the external lead electrodes 9 and 10 are formed on the outer end surfaces of the obtained piezoelectric elements, that is, on the outer end surfaces of the piezoelectric ceramic body 3 and the holding frame 8, the piezoelectric member having the bimorph structure shown in FIG. Each of the surface electrodes 4 that are completed as elements and constitute each signal extraction electrode 1 are external extraction electrodes 9 and 10.
Are electrically connected to each other after being connected in a “T” shape.

[0009]

However, the following problems may occur in the above-described conventional piezoelectric element and the method of manufacturing the same. That is, first, the thickness of the surface electrode layer 13 formed on the main surface of the piezoelectric ceramic substrate 12 may be reduced depending on the forming conditions, and when the thickness of the surface electrode layer 13 is reduced, The connection and conduction between each of the external extraction electrodes 9 and 10 formed on the outer end surface of the piezoelectric element and the surface electrode 4 constituting each signal extraction electrode 1 become unstable.
In addition, a general method is used in which the connection electrode layer 14 for conducting the surface electrode layer 13 on the same surface of the piezoelectric ceramic substrate 12 is subjected to screen printing of a conductive paste and then printing. When formed after adoption, depolarization of the piezoelectric ceramic substrate 12, that is, the piezoelectric ceramic body 3, may occur due to the effect of heat applied during baking.
As a result, in the acceleration sensor configured using the conventional piezoelectric element, the detection sensitivity may be reduced, and the mass productivity may be reduced.

The present invention has been made in view of such inconvenience, and can stabilize connection and conduction between a surface electrode constituting a signal extraction electrode and an external extraction electrode, and provide a piezoelectric ceramic body. An object of the present invention is to provide a piezoelectric element which is free from the possibility of depolarization, an acceleration sensor configured using the same, and a method of manufacturing the piezoelectric element.

[0011]

According to the piezoelectric element of the present invention, a signal extraction electrode is provided on each of opposing main surfaces of a plate-shaped piezoelectric ceramic body in which internal electrodes are embedded. The signal extraction electrode is formed on the same main surface as a thick-film-shaped surface electrode formed separately at each position corresponding to each of the central portion and the end portion divided along the longitudinal direction of the piezoelectric ceramic body. It is characterized in that it is formed by laminating thin-film connection electrodes formed so as to cover the formed surface electrodes. Further, an acceleration sensor according to the present invention is configured using the above-described piezoelectric element.

In a first method of manufacturing a piezoelectric element according to the present invention, a plate-like piezoelectric ceramic body having an internal electrode embedded therein is prepared, and a piezoelectric ceramic body is provided on each of opposing main surfaces. A step of forming a thick-film-shaped surface electrode separately disposed at each position corresponding to each of a center portion and an end portion along the longitudinal direction by baking a conductive paste, and using an internal electrode and a surface electrode. And a step of forming by sputtering a thin film-shaped connection electrode covering a surface electrode formed on the same main surface. I have.

Further, in a second manufacturing method, a pair of piezoelectric ceramic plates which are bonded to one main surface on which the internal electrodes are formed to form a plate-shaped piezoelectric ceramic body are prepared, and the other side of each piezoelectric ceramic plate is provided. Forming a thick-film-shaped polarizing electrode, which is separately arranged at a position corresponding to each of a center portion and an end portion along the longitudinal direction of the piezoelectric ceramic plate on the main surface, by baking a conductive paste; Performing a polarization process on the central portion and the end portion of each piezoelectric ceramic plate using the internal electrode and the surface electrode, and connecting the thin film shape covering the surface electrode formed on the other main surface of each piezoelectric ceramic plate. The method further includes a step of forming an electrode by a sputtering process and a step of bonding one main surface of each piezoelectric ceramic plate to each other to form a piezoelectric ceramic body. It is.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially cutaway perspective view showing a simplified structure of a piezoelectric element according to this embodiment, FIG. 2 is a process perspective view showing a previous stage of the manufacturing method, and FIG. FIG. 4 is a process perspective view showing a stage. Here, the present embodiment will be described with reference to FIGS. 1 to 3 showing a conventional example.

The piezoelectric element according to this embodiment has a bimorph structure which is basically the same as that of the conventional example. As shown in FIG. 1, a plate-shaped piezoelectric ceramic body 3 in which internal electrodes 2 are embedded is used. I have it. At this time, the internal electrodes 2
Each of the central portions 6a, 7a and the end portions 6b, 7b divided along the longitudinal direction of each of the ceramic regions 6, 7 facing each other after being interposed is polarized in different directions along the thickness direction, and , Central part 6a, 7a and end part 6
Each of b and 7b is polarized according to directions opposite to each other. Further, signal extraction electrodes 1 are provided on main surfaces of the piezoelectric ceramic body 3 facing each other, and each signal extraction electrode 1
7, a central portion 6a divided along each longitudinal direction,
Three thick-film-shaped surface electrodes 4 formed separately at respective positions corresponding to each of the end portions 7a and the end portions 6b, 7b;
The thin film-shaped connection electrode 5 formed so as to cover the surface electrodes 4 formed on the same main surface is laminated.

Further, at this time, one side (the upper side in the figure) of the signal extracting electrode 1 extends to one outer end face (the left side in the figure) of the piezoelectric ceramic body 3, while the other side (the upper side in the figure). The signal extraction electrode 1 on the lower side extends to the outer end face on the other side (the right side in the figure). Furthermore, both end edges along the longitudinal direction of the piezoelectric element are sandwiched and fixedly supported by a pair of holding frames 8 each having a “U” shape in a side view. Each of the signal extraction electrodes 1 formed thereon is connected in a “T” shape to each of the external extraction electrodes 9 and 10 formed on different outer end surfaces of the piezoelectric ceramic body 3 and the holding frame 8. On the top. That is, the piezoelectric element according to the present embodiment is different from the conventional example in that each of the surface electrodes 4 separately formed on the same main surface of the piezoelectric ceramic body 3 has a thick film shape, and The connection electrode 5 formed so as to cover them is in a thin film shape. Therefore, in this piezoelectric element, since each of the surface electrodes 4 constituting the signal extraction electrode 1 is formed in a thick film shape, connection and conduction between the surface electrode 4 and each of the external extraction electrodes 9 and 10 are established. It will not be destabilized. An acceleration sensor according to the present invention is configured using the piezoelectric element according to the present embodiment.

Next, a method of manufacturing the piezoelectric element according to the present embodiment will be described with reference to FIGS.

First, as shown in FIG. 2A, a piezoelectric ceramic substrate 12 made of PZT, which is a piezoelectric ceramic, that is, a strip-like internal electrode layer 11 is buried in a plurality of rows, and a large number is embedded. A rectangular flat piezoelectric ceramic substrate 12 having a size and shape suitable for each of the piezoelectric ceramic bodies 3 is prepared, and a conductive paste containing silver or silver / palladium (not shown) is provided.
Prepare Thereafter, the prepared conductive paste is used, and the ceramic regions 6 and 7 of the piezoelectric ceramic body 3 constituting the piezoelectric element, that is, the internal electrodes 2 are formed on the opposing main surfaces of the piezoelectric ceramic base 12 respectively.
Central portions 6a, 7a and end portions 6 divided along the longitudinal direction of each of the ceramic regions 6, 7 opposed to each other via
A plurality of strip-shaped surface electrode layers 13 which are separately arranged at positions corresponding to each of b and 7b are formed.

In this case, a conductive paste is applied to each of the main surfaces of the piezoelectric ceramic substrate 12 by screen printing, and then the applied conductive paste is dried and baked at a temperature of about 800 ° C. The surface electrode layer 13 having a thickness of about 3 to 10 μm is formed by the treatment. As a result, three rows of surface electrode layers 13 are formed in parallel in each of the ranges corresponding to the three groups of piezoelectric ceramic bodies arranged in parallel as one row. The Curie point of the PZT constituting the piezoelectric ceramic substrate 12 is about 300 ° C.
It is.

Subsequently, as shown in FIG. 2B, after using the internal electrode layer 11 and the surface electrode layer 13, the central portions 6a, 7a and the ends of the respective ceramic regions 6, 7 in each piezoelectric ceramic body 3 are formed. The polarization processing is performed on the portions 6b and 7b, that is, the polarization processing is performed by applying a required electric field. That is, in this case, each part 6a, 7a, 6
b and 7b are polarization directions A as shown in FIG.
ＤD is performed. Thereafter, as shown in FIG.
The connection electrode layer 14 formed on the same main surface of the above and covered by three rows of the surface electrode layers 13 corresponding to the three rows of the piezoelectric ceramic bodies 3 and conducting the connection.
Is formed by a sputtering process, for example, monel sputtering. Therefore, the connection electrode layer 14 formed at this time has a thin film shape. The sputtering process here is Monel (nickel / copper alloy)
The present invention is not limited to this, and may be nickel or silver. Further, the temperature of the piezoelectric ceramic substrate 12 during this sputtering process is about 100 to 200 ° C.,
Since it is lower than the Curie point of PZT, there is no possibility that depolarization will occur.

Further, as shown in FIG. 3 (a), after holding a holding frame base 16 in which a concave groove 15 having a predetermined width is formed at each predetermined position on the inner surface side, these holding frame bases 1 are formed.
6 are bonded together on the main surface of the piezoelectric ceramic substrate 12 by using an adhesive (not shown). Thereafter, the piezoelectric ceramic base 12 and the holding frame base 1 are set in accordance with virtual lines set to delimit the range of size and shape suitable for each piezoelectric element.
6 is cut, a piezoelectric element having a configuration as shown in FIG. 3B, ie, three surface electrodes 4 having a thick film shape
And a piezoelectric ceramic body 3 having a signal extraction electrode 1 formed on the main surface, each of which is formed by laminating a thin-film connection electrode 5 formed so as to cover a surface electrode 4 formed on the same main surface. A piezoelectric element including the pair of holding frames 8 is obtained. Therefore, when the external extraction electrodes 9 and 10 are formed on the outer end surfaces of the piezoelectric ceramic body 3 and the holding frame 8 in each of the obtained piezoelectric elements by a required sputtering process or plating process, the bimorph structure shown in FIG. Is completed as a piezoelectric element having a surface electrode 4 which is formed into a thick film and constitutes each signal extraction electrode 1.
Are connected to each of the external extraction electrodes 9 and 10 in a “T” -shaped state.

By the way, in the method of manufacturing the piezoelectric element shown in FIG. 2, a rectangular flat plate-shaped piezoelectric ceramic substrate 12 in which the internal electrode layer 11 is embedded in advance is prepared. It is also possible to manufacture the piezoelectric element according to a process procedure as shown in FIG. FIG. 4 is a perspective view of a process showing a previous stage of the manufacturing method and corresponds to FIG. 2, and therefore detailed description of items common to FIG. 2 will be omitted.

In this modification, as shown in FIG. 4A, a plurality of rows of internal electrode layers 11 are formed on one main surface, and each of the ceramic regions 6 and 7 of the piezoelectric ceramic body 3 has First, a pair of piezoelectric ceramic substrates 18 corresponding to a number of matching piezoelectric ceramic plates 17 and a conductive paste (not shown) containing silver or silver / palladium are prepared in advance. That is, the piezoelectric ceramic plate 17 in this modified example is bonded to one side main surface on which the internal electrode 2 is formed to form the piezoelectric ceramic body 3, and the piezoelectric ceramic substrate 18 is formed on the one side main surface on which the internal electrode layer 11 is formed. When the surfaces are bonded, they correspond to the piezoelectric ceramic base 12. Therefore, first, on the other main surface of each of the piezoelectric ceramic substrates 18, a central portion 17 a and an end portion 17 divided along the longitudinal direction of each piezoelectric ceramic plate 17.
In addition, a plurality of rows of the surface electrode layers 13 which are separately arranged at positions corresponding to each of the b and have a thick film shape are formed by printing and baking a conductive paste. In this case, the central portion 17 of the piezoelectric ceramic plate 17 is used.
The a and the end 17b correspond to the center 6a, 7a and the end 6b, 7b of the piezoelectric ceramic body 3, respectively.

Next, as shown in FIG. 4B, a polarization process is performed on the central portion 17a and the end portion 17b of each piezoelectric ceramic plate 17 using the internal electrode layer 11 and the surface electrode layer 13. After that, as shown in FIG. 4C, three rows of surfaces are formed on the other main surface of each piezoelectric ceramic substrate 18 and correspond to each row of the piezoelectric ceramic plates 17 group. The connection electrode layer 14 that covers the electrode layer 13 and conducts electricity is formed by a sputtering process. Further, thereafter, each piezoelectric ceramic substrate 1
When the one main surfaces on which the internal electrode layers 11 are formed are bonded together by bonding with an adhesive (not shown), the same structure as shown in FIG. 2C is obtained.
Therefore, according to the procedure at a later stage of the manufacturing method shown in FIG. 3, the piezoelectric element having the bimorph structure shown in FIG. 1 is completed.

[0026]

As described above, according to the piezoelectric element and the method of manufacturing the same according to the present invention, the surface electrodes constituting the signal extraction electrodes are formed to have a thick film shape. The connection and conduction between the surface electrode to be formed and the external lead electrode formed on the outer end surface of the piezoelectric element can be stabilized. In addition, since the connection electrodes forming the signal extraction electrodes covering the surface electrodes are formed in a thin film shape, and since these connection electrodes are formed by a sputtering process, the temperature of the piezoelectric ceramic body at the time of electrode formation is reduced. As a result, the depolarization cannot occur. Therefore, in the acceleration sensor constituted by using the piezoelectric element according to the present invention, it is possible to obtain an effect that it is possible to improve the detection sensitivity and the mass productivity.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a simplified configuration of a piezoelectric element according to the present embodiment and a conventional example.

FIG. 2 is a process perspective view showing a previous stage of a method for manufacturing a piezoelectric element according to the present embodiment and a conventional example.

FIG. 3 is a process perspective view showing a later stage of a method for manufacturing a piezoelectric element according to the present embodiment and a conventional example.

FIG. 4 is a process perspective view showing a modified example of the method for manufacturing a piezoelectric element according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Signal extraction electrode 2 Internal electrode 3 Piezoelectric ceramic body 4 Surface electrode 5 Connection electrode 6 Ceramic region 7 Ceramic region 6a Central portion of ceramic region 6b Edge of ceramic region 7a Central portion of ceramic region 7b Edge of ceramic region

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-112547 (JP, A) JP-A-61-1279 (JP, A) JP-A-5-90859 (JP, A) JP-A-4- 26212 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01P 15/09 H01L 29/84 H01L 41/08-41/113 H01L 41/22

Claims (4)

(57) [Claims] 1. A piezoelectric element comprising a plate-shaped piezoelectric ceramic body in which an internal electrode is embedded, and a central part and an end part along a longitudinal direction thereof are polarized in different directions along a thickness direction. A signal extraction electrode is provided on each of the opposing main surfaces of the piezoelectric ceramic body, and each signal extraction electrode is
A thick-film surface electrode formed separately at each position corresponding to the center and end of the piezoelectric ceramic body, and a thin-film shape formed covering the surface electrode formed on the same main surface A piezoelectric element characterized in that the piezoelectric element is formed by laminating the above connection electrodes. 2. A plate-like piezoelectric ceramic body in which internal electrodes are buried, each having a main surface facing each other, which is separated by a position corresponding to each of a central portion and an end portion along the longitudinal direction of the piezoelectric ceramic body. Body provided with a signal extraction electrode formed by laminating a thick-film-shaped surface electrode formed by the above-mentioned method and a thin-film-shaped connection electrode formed by covering the surface electrode formed on the same main surface. An acceleration sensor comprising an element. 3. A plate-shaped piezoelectric ceramic body in which an internal electrode is embedded is prepared, and the opposing main surfaces of the plate-shaped piezoelectric ceramic body respectively correspond to a central portion and an end portion along the longitudinal direction of the piezoelectric ceramic body. A step of forming a thick film-shaped surface electrode separately arranged for each position by printing and baking a conductive paste; and a polarization treatment for a central portion and an end portion of the piezoelectric ceramic body using the internal electrode and the surface electrode. And a step of forming, by sputtering, a thin-film-shaped connection electrode that covers the surface electrode formed on the same main surface. Production method. 4. A pair of piezoelectric ceramic plates, each of which has a main surface on which an internal electrode is formed and which is bonded to form a plate-shaped piezoelectric ceramic body, are provided on the other main surface of each piezoelectric ceramic plate. A step of forming thick-film-shaped polarizing electrodes, which are separately arranged at positions corresponding to each of a central portion and an end portion along the longitudinal direction of the ceramic plate, by printing and baking a conductive paste; A step of performing a polarization process on the central portion and the end portion of each piezoelectric ceramic plate using the electrodes, and a thin film-shaped connection electrode covering the surface electrode formed on the other main surface of each piezoelectric ceramic plate by a sputtering process. 2. The method according to claim 1, further comprising a step of forming and a step of bonding one main surface of each piezoelectric ceramic plate together to form a piezoelectric ceramic body. Manufacturing method of the mounted piezoelectric element.