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DESCRIPTION JPH09107132

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DESCRIPTION JPH09107132
[0001]
The present invention relates to a piezoelectric / electrostrictive film type device, and more
particularly to a piezoelectric / electrostrictive film type device which can be suitably used for a
sensor, a filter or the like.
[0002]
2. Description of the Related Art In recent years, a piezoelectric / electrostrictive working unit
has been provided on the outer surface of a cavity as one of the mechanisms for detecting a
pressure change or the like of the cavity formed inside the base. There is known a piezoelectric /
electrostrictive film type element in which a piezoelectric / electrostrictive working portion acts
as a mechanical / electrical converter to detect a volume change of a hollow portion. Such a
piezoelectric / electrostrictive film type element is used as, for example, a sensor, a filter, etc., and
the pressure change of the inspection atmosphere introduced from the opening enlarges or
reduces the volume of the cavity, and the cavity at this time The distortion of the wall of the part
gives a mechanical change to the piezoelectric / electrostrictive working part, which is converted
into an electrical signal by the piezoelectric / electrostrictive working part
[0003]
FIG. 5 shows an example in which a conventionally known piezoelectric / electrostrictive film
type element is used as a sensor, and the pressure change of the inspection atmosphere
introduced by the opening 26 enlarges or reduces the volume of the cavity 30, The distortion of
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the wall of the hollow portion at this time gives a mechanical change to the piezoelectric /
electrostrictive operation unit 22, and this is converted into an electrical signal by the
piezoelectric / electrostrictive operation unit 22.
[0004]
The piezoelectric / electrostrictive film type element 20 is composed of a ceramic base 21 and a
piezoelectric / electrostrictive action part 22 integrally formed on the ceramic base 21.
The ceramic base 21 is integrally formed by stacking a thin flat cover plate 23 and a base plate
24 with the spacer plate 25 interposed therebetween.
[0005]
In the spacer plate 25, windows 28 are formed, and the spacer plate 25 and the base plate 24
are overlapped so that the openings 26 provided in the base plate 24 are opened with respect to
these windows 28. There is. Further, a closing plate 23 is overlapped on the surface of the spacer
plate 25 opposite to the side on which the base plate 24 is overlapped, and the opening of the
window 28 is covered by the closing plate 23. Thus, the hollow portion 30 is formed inside the
ceramic base 21.
[0006]
The ceramic base 21 is provided with piezoelectric / electrostrictive action parts 22 at positions
corresponding to the hollow parts 30 on the outer surface of the closing plate 23. Here, the
piezoelectric / electrostrictive operation unit 22 is composed of the lower electrode 31, the
piezoelectric / electrostrictive layer 32 and the upper electrode 33.
[0007]
The conventionally known piezoelectric / electrostrictive film type device is configured as
described above, and the planar view of the piezoelectric / electrostrictive layer 32 and the cavity
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30 is as shown in FIG. In order to emphasize the mechanical-electrical conversion efficiency, the
piezoelectric / electrostrictive layer 32 is slightly larger so that the piezoelectric / electrostrictive
layer 32 covers the entire surface of the cavity 30, and in consideration of the manufacturing
accuracy. There is. However, when the piezoelectric / electrostrictive actuating portion 22 is
formed to cover the entire planar shape of the cavity 30 as described above, the vibration mode
based on the displacement of the piezoelectric / electrostrictive actuating portion 22 is that of
the corner of the cavity 30. Due to the restraint, it is considered that the center and end of the
cavity are not uniform, and an error occurs between the characteristic simulation in designing
the sensor, the filter, the acoustic wave oscillator, etc. and the actual product.
[0008]
When the piezoelectric / electrostrictive working portion 22 is provided to cover the entire
planar shape of the hollow portion 30, the electrode films (upper and lower electrodes) 31 and
33 and the piezoelectric / electrostrictive layer 32 are formed on the outer surface of the closing
plate 23. After forming by means of a known film forming method, for example, a screen printing
method, a spray method or the like, heat treatment is performed. During this heat treatment,
each film shrinks by firing, but due to the restraint at both ends of cavity 30, both ends are less
likely to shrink compared with the central portion (that is, not burned), and the firing degree is
uniform as a whole In addition, there is a problem that a large stress remains at both ends. Such
non-uniformity of the degree of firing of the piezoelectric / electrostrictive working portion 22
adversely affects the vibration mode of the piezoelectric / electrostrictive working portion 22.
[0009]
Accordingly, the object of the present invention is to make the vibration mode of the piezoelectric
/ electrostrictive working part as designed, and to minimize the noise during sensing, filtering
and sound wave transmission as much as possible. It is an object of the present invention to
provide a piezoelectric / electrostrictive film type device that can That is, according to the
present invention, a spacer plate having at least one window, a ceramic base in which a thin
closing plate for covering the window is integrated, and the opening of the window on the outer
surface of the closing plate A piezoelectric / electrostrictive film type element comprising: a
piezoelectric / electrostrictive working portion comprising a lower electrode, a piezoelectric /
electrostrictive layer, and an upper electrode sequentially provided in a layer by a film forming
method at a cover portion; The piezoelectric / electrostrictive film type element is provided,
wherein the electrostrictive layer is provided so as to cover only a part of the planar shape of the
window portion.
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[0010]
Also according to the invention, a ceramic plate in which a spacer plate having at least one
window and a thin closing plate covering the window are integrated, and the covering of the
window on the outer surface of the closing plate. A piezoelectric / electrostrictive film type
element comprising: a lower electrode sequentially provided in a layer by a film forming method
at a portion; and a piezoelectric / electrostrictive working portion constituted of a piezoelectric /
electrostrictive layer having a substantially rectangular planar shape and an upper electrode. In
plan view, the shape of the window portion of the spacer plate and the shape of the piezoelectric
/ electrostrictive layer respectively have two symmetry axes common to the directions, and one
of the symmetry axes The intersecting sides of the substantially rectangular piezoelectric /
electrostrictive layer are the intersection points of the two symmetry axes by a distance of 5
times or more of the plate thickness of the closed plate from the intersection point of the
symmetry axis and the planar shape of the window. In particular that it has a shape that has The
piezoelectric / electrostrictive film element according to, is provided.
[0011]
In the present invention, the piezoelectric / electrostrictive layer may cover only the central
portion of the window (cavity), and the piezoelectric / electrostrictive layer may be formed in one
of the windows (cavity). It may cover except for the both ends.
In the present invention, the term “piezoelectric / electrostrictive film type element” refers to
any element having only a piezoelectric film, an element having only an electrostrictive film, and
an element having both a piezoelectric film and an electrostrictive film. It is a thing.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a piezoelectric / electrostrictive
film type device according to the present invention will be described in detail with reference to
the drawings. FIG. 1 is a sectional view showing an embodiment of the piezoelectric /
electrostrictive film type device according to the present invention, and FIG. 2 is an exploded
perspective view showing the piezoelectric / electrostrictive film type device of FIG. It shows the
case applied to the sensor. The piezoelectric / electrostrictive film type device 40 is composed of
a ceramic base 41 and a piezoelectric / electrostrictive operation unit 42 integrally formed on
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the ceramic base 41. In the ceramic base 41, a thin flat plate-like closed plate 43 and a base plate
44 are overlapped with the spacer plate 45 interposed therebetween, and are integrally
configured. Here, the opening 46 is formed in the base plate 44 as in FIG. 5.
[0013]
The spacer plate 45 and the base plate 44 are overlapped so that at least one window 48 is
formed in the spacer plate 45, and the opening 46 provided in the base plate 44 is opened with
respect to these windows 48. ing. In addition, the closing plate 43 is overlapped on the surface of
the spacer plate 45 opposite to the side on which the base plate 44 is overlapped, and the
opening of the window 48 is covered by the closing plate 43. The cavity 50 is formed.
[0014]
Then, on the outer surface of the closing plate 43, the piezoelectric / electrostrictive operation
portion 42 is provided on the ceramic substrate 41 so as to cover only a part of the planar shape
of the hollow portion 50. Here, the piezoelectric / electrostrictive operation unit 42 includes the
lower electrode 51, the piezoelectric / electrostrictive layer 52, and the upper electrode 53. 3 to
4 are plan explanatory views showing the covering state of the piezoelectric / electrostrictive
layer with respect to the planar shape of the hollow portion (window portion), without covering
the entire planar shape of the hollow portion 50. A piezoelectric / electrostrictive layer 52 is
provided on the outer surface of the closure plate 43 so as to cover only a part of the shape.
[0015]
Thus, when the piezoelectric / electrostrictive layer 52 is formed so as to cover a part of the
planar shape of the cavity 50, the piezoelectric / electrostrictive layer 52 is not formed at both
ends in the longitudinal direction of the cavity 50. Therefore, there is no displacement and
vibration at both ends of the cavity 50. Therefore, the vibration mode becomes uniform at the
center and at the end of the cavity 50, and noise during sensing, filtering and sound wave
transmission can be minimized. .
[0016]
Here, the planar shape of the hollow portion 50 is not particularly limited, and a rectangular
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(rectangular), a square, an oval, an oval, or a polygon having both ends as shown in FIGS. ,
Various shapes can be mentioned.
The aspect in which the piezoelectric / electrostrictive layer 52 covers a part of the planar shape
of the cavity 50 is not particularly limited. For example, when only the central part of the cavity
50 is covered, both ends of the cavity 50 in the longitudinal direction The case where it coat |
covers except a part (refer FIG. 3), or the case where it coat | covers except the both ends of a
transversal direction (refer FIG. 4) etc. can be mentioned.
[0017]
In the present invention, as shown in FIG. 3, when the piezoelectric / electrostrictive layer 52 is
substantially rectangular and is coated except for both end portions in the longitudinal direction
of the hollow portion 50, in order to escape restraint from both end portions, Assuming that the
length not covered by the piezoelectric / electrostrictive layer 52 is L and the plate thickness of
the closing plate 43 is t on the hollow portion 50, it is preferable that L55t. That is, in the present
invention, the shape of the window 48 (the cavity 50) of the spacer plate 45 and the shape of the
piezoelectric / electrostrictive layer 52 have two symmetrical axes X and Y in common in the
direction, respectively. The side of the substantially rectangular piezoelectric / electrostrictive
layer 52 intersecting with one of the symmetry axes (Y in FIG. 3) is an intersection (FIG. 3) of the
plane of the symmetry axis and the window 48 (cavity 50). 55), it is preferable that the shape is a
shape that is recessed in the direction of the point of intersection of the two symmetry axes (56
in FIG. 3) by a distance of 5 times or more of the plate thickness of the closing plate 43.
[0018]
In the present invention, the ceramic base 41 is formed as an integral sintered product of
ceramics. Specifically, first, a green sheet is formed from a ceramic slurry prepared from a
ceramic raw material, a binder, a solvent and the like using a general apparatus such as a doctor
blade apparatus. Then, as necessary, the green sheet is subjected to processing such as cutting,
cutting, punching, etc., to form the window 48 and at least one opening 46, and to form a
precursor of each plate 43, 44, 45 . Then, by laminating and baking the respective precursors, an
integral ceramic substrate 41 is obtained.
[0019]
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The material constituting the ceramic base 41 is not particularly limited, but alumina and
zirconia are preferably used from the viewpoint of formability and the like. The plate thickness of
the closing plate 43 is preferably 50 μm or less, the plate thickness of the orifice plate 44 is
preferably 10 μm or more, and the plate thickness of the spacer plate 45 is preferably 50 μm
or more.
[0020]
The piezoelectric / electrostrictive working unit 42 is composed of the lower electrode 51, the
piezoelectric / electrostrictive layer 52, and the upper electrode 53 on the closing plate 43, and
the piezoelectric / electrostrictive working unit 42 is usually formed by a film forming method.
Formed by That is, on the outer surface of the closing plate 43, the lower electrode 51, the
piezoelectric / electrostrictive layer 52 and the upper electrode 53 are formed by various known
film forming methods, for example, thick film forming methods such as screen printing and
spray, ion beam And thin film formation methods such as sputtering and CVD.
[0021]
Each film thus formed (lower electrode 51, piezoelectric / electrostrictive layer 52 and upper
electrode 53) is then subjected to heat treatment (baking), and such heat treatment is carried out
each time each film is formed. Alternatively, it may be performed simultaneously after forming
the whole film. The material of the lower electrode 51 and the upper electrode 53 constituting
the piezoelectric / electrostrictive working portion 42 is not particularly limited as long as the
conductor can withstand a high temperature oxidizing atmosphere at about the heat treatment
(baking) temperature. It may be an alloy. It may be conductive ceramics. Specifically, high
melting point noble metals such as platinum and palladium can be mentioned as preferable ones.
[0022]
Further, as a material of the piezoelectric / electrostrictive layer 52 constituting the piezoelectric
/ electrostrictive operation unit 42, any material may be used as long as the material exhibits an
electric field induced strain such as a piezoelectric or an electrostrictive effect. Specifically, a
material mainly composed of lead zirconate titanate (PZT system), a material mainly composed of
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lead magnesium niobate (PMN system), a material mainly composed of lead nickel niobate (PNN
system) Are preferably used. The thickness of the piezoelectric / electrostrictive working portion
42 is generally 100 μm or less, the thickness of the lower electrode 51 and the upper electrode
53 is generally 20 μm or less, preferably 5 μm or less, and the thickness of the piezoelectric /
electrostrictive layer 52 is In order to obtain a large displacement at a low operating voltage, it is
preferably 50 μm or less, more preferably 3 μm to 40 μm.
[0023]
Although the embodiments of the present invention have been described in detail above, it goes
without saying that the present invention is not limited by these embodiments either, and for the
purpose of explanation, the function of the piezoelectric / electrostrictive working unit is
machined. Although the explanation has been made by means of the displacement → electrical
signal, it is a matter of course that the effect of the present invention can be exhibited when
using the electrical signal → mechanical displacement. Further, it is understood that various
changes, modifications, improvements, etc. can be added to the present invention based on the
knowledge of those skilled in the art, in addition to the above embodiments, without departing
from the spirit of the present invention. It should be.
[0024]
As described above, according to the piezoelectric / electrostrictive film type element of the
present invention, the piezoelectric / electrostrictive layer is formed so as to cover only a part of
the planar shape of the cavity portion, so that the cavity is formed. At the end of the part, the
piezoelectric / electrostrictive action part does not pick up displacements and vibrations that
would contain much noise at the end, and as a result noise during sensing, filtering and sound
transmission can be minimized, or There is a remarkable effect that the error between the
characteristic simulation of and the actual product can be reduced. The piezoelectric /
electrostrictive film type element of the present invention is suitably used for speakers, actuators,
filters, sensors, capacitor arrays, displays, transformers, microphones, various vibrators,
resonators, oscillators, gyros, discriminators, etc. be able to.
[0025]
Brief description of the drawings
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[0026]
FIG. 1 is a cross-sectional view showing an embodiment of a piezoelectric / electrostrictive film
type device according to the present invention.
[0027]
FIG. 2 is an exploded perspective view showing the piezoelectric / electrostrictive film type
device of FIG. 1 in an exploded manner.
[0028]
FIG. 3 is an explanatory plan view showing a state in which the piezoelectric / electrostrictive
layer is coated except for both end portions in the longitudinal direction of the hollow portion.
[0029]
FIG. 4 is an explanatory plan view showing a state in which the piezoelectric / electrostrictive
layer is coated except for both end portions in the width direction of the hollow portion.
[0030]
FIG. 5 is a cross-sectional view showing an example in which a conventionally known
piezoelectric / electrostrictive film type device is used as a sensor.
[0031]
FIG. 6 is an explanatory view showing a planar state of a piezoelectric / electrostrictive layer and
a hollow portion in the piezoelectric / electrostrictive film type device of FIG. 5;
[0032]
Explanation of sign
[0033]
DESCRIPTION OF SYMBOLS 40 ... Piezoelectric / electrostrictive film type element, 41 ...
Ceramics base, 42 ... Piezoelectric / electrostrictive action | operation part, 43 ... Blocking plate,
44 ... Base plate, 45 ... Spacer plate, 46 ... Opening part, 48 ... Window part, 50 ... Cavity 51, lower
electrode 52, piezoelectric / electrostrictive layer 53, upper electrode.
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