Metal working – Piezoelectric device making
Reexamination Certificate
2003-07-31
2004-11-09
Tugbang, A. Dexter (Department: 3729)
Metal working
Piezoelectric device making
C029S830000, C029S831000, C029S426100, C029S426200, C029S762000, C029S851000, C310S367000
Reexamination Certificate
active
06813815
ABSTRACT:
USE FIELD OF THE INVENTION
The present invention relates generally to a piezoelectric/electrostrictive element, a piezoelectric/electrostrictive device and a production method thereof, and more particularly to a laminated piezoelectric/electrostrictive element and a laminated piezoelectric/electrostrictive device made up of piezoelectric/electrostrictive layers and internal electrode layers laminated alternately, and a production method thereof.
PRIOR ART
In recent years, a variety of fields such as optics, magnetic recording, precision machining, and printing demand a displacement element for controlling, for example, the length or position of an optical path in the order of a submicron or vibrations precisely. As such a displacement element meeting the above demand, there is one employing displacement provided by a reverse piezoelectric effect or an electrostrictive effect taken place when the voltage is applied to a piezoelectric/electrostrictive material made of, for example, a ferroelectric substance.
Conventionally, as such a displacement element, a laminated piezoelectric element
100
, as shown in
FIG. 34
, which is disclosed in Japanese Patent First Publication No. 4-309274 is known. The piezoelectric/electrostrictive element
100
includes, as shown in
FIG. 34
, a lamination
104
formed by laminating a plurality of piezoelectric ceramic layers
101
and electrode layers
102
alternately and a pair of electrically insulated external electrodes
104
and
105
which connect the electrode layers
102
alternately on opposed side surfaces of the laminate
103
and are so formed as to extend to upper and lower surfaces of the laminate
103
. In the laminated piezoelectric element
100
, ridges defined by the side surfaces and the upper and lower surfaces of the laminate
103
are rounded to an extent where the radius of curvature of the ridges exceeds half the thickness of the piezoelectric ceramic layers
101
.
The production of the laminated piezoelectric element
100
shown in
FIG. 34
is accomplished by first weighing and grinding raw material, mixing it with binder, and defoaming the mixture, after which the mixture is shaped into a sheet from which rectangular green sheets
101
A are punched (which will be the piezoelectric ceramic layers
101
by baking). A conductive paste is printed over a given area of one surface of the green sheet
101
A to form the electrode layer
102
. Next, the green sheets
101
A on which the electrode layers
102
are printed properly are, as shown in
FIG. 35
, laminated and bonded by pressure and cut as needed after which it is baked to produce the laminate
103
as shown in FIG.
36
. As a result, the green sheets
101
A are, as mentioned above, baked to produce the piezoelectric ceramic layers
101
. In the laminate
103
, arrangement positions of the electrode layers
102
are predetermined on a pair of opposed side surfaces thereof so that the electrode layers
102
may be exposed alternately. Afterwards, on given areas of upper and lower surfaces of the thus produced laminate
103
, an external upper surface electrode
104
A, and an external lower surface electrode
105
A are formed. Next, on a pair of opposed side surfaces
106
and
107
to which the electrode layers
102
of the laminate
103
are exposed alternately, external side surface electrodes (thick film electrodes)
104
B and
105
B are formed to make the laminated piezoelectric element
100
show in FIG.
34
. The external side surface electrode
104
B is so formed as to connect with the external upper surface electrode
104
A, while the external side surface electrode
105
B is so formed as to connect with the external lower surface electrode
105
A. As a method of forming the above mentioned external electrodes
104
and
105
, there is a dipping method or an evaporation method.
FIG. 37
shows an actuator
200
utilizing the thus constructed laminated piezoelectric element
100
. The actuator
200
has the laminated piezoelectric element
100
secured on a movable plate (diaphragm)
110
by an adhesive
111
.
As another displacement element, a piezoelectric displacement element, as disclosed in Japanese Patent First Publication No. 63-295269, is known which is equipped with a plurality of opposed inner electrode layers in a ceramic thin plate exhibiting the piezoelectric effect. Corners that are boundaries of side surfaces and upper and lower surfaces of the ceramic thin plate are chamfered mechanically. On front and reverse surfaces and the opposed side surfaces of the ceramic thin plate, a pair of opposed surface electrodes connecting with internal electrode layers is so formed that the electrodes are electrically insulated from each other. The opposed surface electrodes are formed on the surfaces of the ceramic thin plate by a physical vapor deposition method such as a sputtering method or a vapor deposition method or a film forming method such as plating.
SUMMARY OF THE INVENTION
The laminated piezoelectric element
100
, as shown in
FIG. 34
, has problems in that the possibility that edges of the green sheets
101
A (shown in
FIG. 35
) are deformed, damaged, or broken by handling is high. Particularly, a thin piezoelectric element in which a total film thickness (thickness) of the laminate
103
is 100 &mgr;m or less has a high possibility that the green sheets
101
A are broken by handling. The conventional laminated piezoelectric element
100
, thus, has a problem that the fabrication yield is low.
The piezoelectric displacement element, as disclosed in Japanese Patent First Publication No. 63-295269 is chamfered by mechanically cutting end portions of the ceramic thin film diagonally, which results in an increase in production processes. The mechanical cutting may also cause damage to the ceramic thin film.
The invention was made in order to solve the above problems. It is, thus, an object of the invention to provide a piezoelectric/electrostrictive element and a piezoelectric/electrostrictive device which are excellent in strength, shock resistance, handling, dimensional accuracy, positional accuracy, stability of element characteristics, and fabrication yield, and to provide a production method thereof.
In order to solve the above problems, the first feature of the invention lies in a piezoelectric/electrostrictive element including a substantially trapezoidal laminate having narrower and wider surfaces lying substantially in parallel to each other and first and second surfaces opposed to each other between the narrower and wider surfaces. The first and second surfaces are inclined at given angles with respect to one of the narrower and wider surfaces. The trapezoidal laminate is made up of a plurality of piezoelectric/electrostrictive layers and a plurality of internal electrodes, each of which is disposed between an adjacent two of the piezoelectric/electrostrictive layers. The internal electrodes are divided into a first and a second group, each of the first group internal electrodes lying over one of the second group internal electrodes through one of the piezoelectric/electrostrictive layers. A first external electrode is formed on the first surface of the laminate, and is coupled to the first group internal electrodes; and a second external electrode formed on the second surface of said laminate, said second external electrodes being coupled to the second group internal electrodes.
The thus constructed piezoelectric/electrostrictive element is of a substantially trapezoidal shape which decreases in width from one of the bottom surfaces to the other bottom surface, so that the angle which the slant surfaces of both sides make with the other bottom surface is obtuse, thus resulting in an increase in strength of a ridge portion (a corner) defined by the other bottom surface and the slant surfaces. Therefore, for example, when the other (narrower) bottom surface is secured on a movable plate (diaphragm), the breakage or damage of the ridge portion caused by an external force or vibrations of the piezoelectric/electrostrictive element itself is av
Iwamoto Masaki
Namerikawa Masahiko
Shibata Kazuyoshi
Burr & Brown
NGK Insulators Ltd.
Nguyen Tai
Tugbang A. Dexter
LandOfFree
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