U.S. patent application number 10/448984 was filed with the patent office on 2004-01-29 for piezoelectric/electrostrictive device and method of manufacturing same.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Ikeda, Koji, Kimura, Koji, Nanataki, Tsutomu, Shibata, Kazuyoshi, Takeuchi, Yukihisa.
Application Number | 20040017133 10/448984 |
Document ID | / |
Family ID | 27577724 |
Filed Date | 2004-01-29 |
United States Patent
Application |
20040017133 |
Kind Code |
A1 |
Takeuchi, Yukihisa ; et
al. |
January 29, 2004 |
Piezoelectric/electrostrictive device and method of manufacturing
same
Abstract
A piezoelectric/electrostrictive device including a pair of
mutually opposing thin plate sections and a fixation section for
supporting the thin plate sections. A
piezoelectric/electrostrictive element is arranged on each of the
pair of thin plate sections. Movable sections, having mutually
opposing end surfaces, are formed proximate the ends of the thin
plate sections. A distance between the end surfaces is not less
than a length of the movable sections.
Inventors: |
Takeuchi, Yukihisa;
(Nishikamo-Gun, JP) ; Nanataki, Tsutomu;
(Toyoake-City, JP) ; Ikeda, Koji; (Kounan-City,
JP) ; Kimura, Koji; (Nagoya-City, JP) ;
Shibata, Kazuyoshi; (Mizunami-City, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
27577724 |
Appl. No.: |
10/448984 |
Filed: |
May 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10448984 |
May 30, 2003 |
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10246032 |
Sep 18, 2002 |
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6605887 |
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10246032 |
Sep 18, 2002 |
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10067958 |
Feb 5, 2002 |
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6476538 |
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10067958 |
Feb 5, 2002 |
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09671669 |
Sep 27, 2000 |
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6534898 |
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09671669 |
Sep 27, 2000 |
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09524042 |
Mar 13, 2000 |
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6498419 |
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60210246 |
Jun 8, 2000 |
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Current U.S.
Class: |
310/320 |
Current CPC
Class: |
H01L 41/0946 20130101;
H01L 41/0831 20130101; H01L 41/094 20130101; H01L 41/1132 20130101;
H01L 41/273 20130101 |
Class at
Publication: |
310/320 |
International
Class: |
H02N 002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 1999 |
JP |
11-281,522 |
Oct 28, 1999 |
JP |
11-307,844 |
Nov 16, 1999 |
JP |
11-326,195 |
Dec 27, 1999 |
JP |
11-371,967 |
Jan 21, 2000 |
JP |
2000-013,576 |
Jan 24, 2000 |
JP |
2000-015,123 |
Mar 1, 2000 |
JP |
2000-056,434 |
Jun 6, 2000 |
JP |
2000-169,584 |
Claims
We claim:
1. A piezoelectric/electrostrictive device comprising: a pair of
mutually opposing thin plate sections; a fixation section for
supporting said thin plate sections; movable sections provided at
first end portions of said pair of thin plate sections; and one or
more piezoelectric/electrostricti- ve elements arranged on at least
one thin plate section of said pair of thin plate sections, wherein
said movable sections are formed from a material which is different
from the material of said thin plate sections.
2. The piezoelectric/electrostrictive device according to claim 1,
wherein said movable sections comprise an adhesive member provided
between said first end portions of said pair of thin plate
sections.
3. The piezoelectric/electrostrictive device according to claim 1,
wherein said movable sections include mutually opposing
surfaces.
4. The piezoelectric/electrostrictive device according to claim 3,
wherein a gap is formed between said mutually opposing surfaces of
said movable sections.
5. The piezoelectric/electrostrictive device according to claim 1,
wherein said first end portions of said pair of thin plate sections
have mutually opposing end surfaces; and a distance (Lc) between
said mutually opposing end surfaces is not less than a length (Df)
of said first end portions of said thin plate sections.
6. The piezoelectric/electrostrictive device according to claim 1,
wherein said thin plate sections and said fixation section are
composed of a ceramic substrate integrated into one unit by
co-firing a ceramic green laminate and cutting off unnecessary
portions.
7. The piezoelectric/electrostrictive device according to claim 6,
wherein said piezoelectric/electrostrictive element has a
film-shaped configuration, and is integrated with said ceramic
substrate by means of sintering.
8. The piezoelectric/electrostrictive device according to claim 5,
wherein a gap is formed between said mutually opposing end surfaces
of said first end portions of said pair of thin plate sections.
9. The piezoelectric/electrostrictive device according to claim 4,
further comprising a member having substantially the same
composition as a constitutive member of said movable sections, or a
plurality of members which are compositionally different therefrom,
interposed between said mutually opposing end surfaces of said
movable sections, and an area of a surface of said member opposed
to said mutually opposing end surfaces is substantially the same as
an area of said mutually opposing end surfaces.
10. The piezoelectric/electrostrictive device according to claim 5,
wherein said device has such a structure that internal residual
stress, which has been generated in at least one of said thin plate
sections and said piezoelectric/electrostrictive element during
production, is released by forming said mutually opposing end
surfaces of said first end portions of said thin plate
sections.
11. The piezoelectric/electrostrictive device according to claim 1,
wherein said piezoelectric/electrostrictive element has a
piezoelectric/electrostrictive layer and a pair of electrodes
formed on said piezoelectric/electrostrictive layer.
12. The piezoelectric/electrostrictive device according to claim
11, wherein said piezoelectric/electrostrictive element is
constructed in a stacked form comprising a plurality of units each
including said piezoelectric/electrostrictive layer and said pair
of electrodes.
13. A piezoelectric/electrostrictive device according to claim 9,
further comprising a hole formed by both inner walls of said pair
of thin plate sections, inner walls of said movable sections, inner
walls of said plurality of members and an inner wall of said
fixation section, and said hole is filled with a gel material.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a
piezoelectric/electrostrictive device which is provided with a
movable section to be operated on the basis of a displacement
action of a piezoelectric/electrostrictive element, or a
piezoelectric/electrostrictive device which is capable of detecting
displacement of a movable section by the aid of a
piezoelectric/electrostrictive element, and a method for producing
the same. In particular, the present invention relates to a
piezoelectric/electrostrictive device which is excellent in
strength, shock resistance, and moisture resistance and which makes
it possible to efficiently operate a movable section to a great
extent, and a method for producing the same.
[0003] 2. Description of the Related Art:
[0004] Recently, a displacement element, which makes it possible to
adjust the optical path length and the position in an order of
submicron, is required, for example. in the fields of the optics,
the magnetic recording, and the precision machining. Development is
advanced for the displacement element based on the use of the
displacement Drought about by the inverse piezoelectric effect or
the electrostrictive effect caused when a voltage is applied to a
piezoelectric/electrostrictive material (for example, a
ferroelectric material).
[0005] As shown in FIG. 41, for example, those hitherto disclosed
as such a displacement element include a piezoelectric actuator
comprising a fixation section 204, a movable section 206, and a
beam section 208 for supporting them which are formed in an
integrated manner with a hole 202 provided through a plate-shaped
member 200 composed of a Piezoelectric/electrostrictive material
and with electrode layer 210 provided on the beam section 208 (see,
for example, Japanese Laid-Open Patent Publication No.
10-136665).
[0006] The piezoelectric actuator is operated such that when. a
voltage is applied to the electrode layer 210, the beam section 208
makes expansion and contraction in a direction along a line
obtained by connecting the fixation section 204 and the movable
section 206 in accordance with the inverse piezoelectric effect or
the electrostrictive effect. Therefore, the movable section 206 can
perform circular arc-shaped displacement or rotational displacement
in the plane of the plate-shaped member 200.
[0007] On the other hand, Japanese Laid-Open Patent Publication No.
63-64640 discloses a technique in relation to an actuator based on
the use of a bimorph. In this technique, electrodes for the bimorph
are provided in a divided manner. The actuator is driven due to the
selection of the divided electrodes, and thus the highly accurate
positioning is performed at a high speed. This patent document
(especially in FIG. 4) discloses a structure in which, for example,
two bimorphs are used in an opposed manner.
[0008] However. the piezoelectric actuator described above involves
such a problem that the amount of operation of the movable section
206 is small, because the displacement in the direction of
expansion and contraction of the piezoelectric/electrostrictive
material (i.e., in the in-plane direction of the plate-shaped
member 200) is transmitted to the movable section 206 as it is.
[0009] All of the parts of the piezoelectric actuator are made of
the piezoelectric/electrostrictive material which is a fragile
material having a relatively heavy weight. Therefore, the following
problems arise. That is, the mechanical strength is low, and the
piezoelectric actuator is inferior in handling performance, shock
resistance, and moisture resistance. Further, the piezoelectric
actuator itself is heavy, and its operation tends to be affected by
harmful vibrations (for example, residual vibration and noise
vibration during high speed operation).
[0010] In order to solve the problems described above, it has been
suggested that the hole 202 is filled with a filler material having
flexibility. However, it is clear that the amount of displacement,
which is brought about by the inverse piezoelectric effect or the
electrostrictive effect, is decreased even when the filler material
is merely used.
[0011] Further, the actuator described in Japanese Laid-Open Patent
Publication No. 63-64640 has such a structure that the bimorph
itself is composed of two piezoelectric elements which are
laminated with each other, in addition to the fact that the bimorph
is stuck to a fixation member or a mediating member. Therefore, the
stress tends to remain, resulting from, for example, the curing and
the shrinkage of an adhesive and the heating treatment required for
the sticking and the lamination. It is feared that the displacement
action is disturbed by the internal residual stress, and it is
impossible to realize the displacement and the resonance frequency
as designed. Especially, when the actuator is small in size, the
influence of the adhesive is increased by itself.
[0012] Accordingly, a method is conceived in order to exclude the
influence of the adhesive required to effect the sticking, in which
the actuator is composed of, for example, an integrated sintered
product made of ceramics to give a this case, it is inevitably
feared that the internal residual stress arises due to the
difference in behavior of thermal shrinkage between respective
members during the sintering.
[0013] Further, when the actuator is small in size, a problem is
involved such that the fixation property of the actuator and the
attachment property of the actuator to another Dart are
deficient.
SUMMARY OF THE INVENTION
[0014] The present invention has been made taking the foregoing
problems into consideration, an object of which is to provide a
piezoelectric/electrostrictive device and a method for producing
the same which make it possible to obtain a displacement element
that is scarcely affected by harmful vibration and capable of high
speed response with high mechanical strength while being excellent
in handling Performance, shock resistance, and moisture resistance,
making it possible to realize a light weight of the device,
especially a light weight of a movable section or a fixation
section, and improve the handling performance of the device and the
attachment performance for parts to be attached to the movable
section or the fixation performance of the device, so that the
movable section may be greatly displaced at a relatively low
voltage, and it is possible to achieve a high speed of the
displacement action of the device, especially of the movable
section (realization of a high resonance frequency), as well as a
sensor element which makes it possible to accurately detect
vibration of the movable section.
[0015] According to the present invention, there is provided a
piezoelectric/electrostrictive device comprising a pair of mutually
opposing thin plate sections and a fixation section for supporting
the thin plate sections; movable sections provided at forward end
portions of the pair of thin plate sections; and one or more
piezoelectric/electrostr- ictive elements arranged on at least one
thin plate section of the pair of thin plate sections; wherein any
one of the movable sections and the fixation section has mutually
opposing end surfaces; and a distance between the end surfaces is
not less than a length of the movable section.
[0016] The movable section, the fixation section, and the thin
plate section may be made of ceramics or metal. Alternatively each
of the components may be made of a ceramic material, or each of
them may be made of a metal material. Further, each of the
components may be constructed to have a hybrid structure obtained
by combining those produced from materials of ceramics and
metal.
[0017] It is also preferable that any one of the movable section
And the fixation section is provided with a cutoff section; and a
part of the cutoff section constitutes the mutually opposing end
surfaces. It is also preferable that the thin plate section, the
movable section, and the fixation section are composed or a ceramic
substrate integrated into one unit by co-firing a ceramic green
laminate and cutting off unnecessary portions. It is also
preferable that the piezoelectric/electrostrictive element has a
film-shaped configuration, and it is integrated with the ceramic
substrate by means of sintering.
[0018] In this arrangement, the piezoelectric/electrostrictive
element may have a piezoelectric/electrostrictive layer and a pair
of electrodes formed on the piezoelectric/electrostrictive layer.
It is also preferable that the piezoelectric/electrostrictive
element has a piezoelectric/electrostrictive layer and a pair of
electrodes formed on both sides of the
piezoelectric/electrostrictive layer and one electrode of the pair
of electrodes is formed on at least the thin plate section. In this
arrangement, the vibration caused by the piezoelectric/electrostr-
ictive element can be efficiently transmitted via the thin plate
section to the movable section or the fixation section. Thus, it is
possible to improve the response performance. Especially, it is
preferable that the piezoelectric/electrostrictive element is
constructed in a stacked form comprising a plurality of units each
including the piezoelectric/electrostrictive layer and the pair of
electrodes.
[0019] When the arrangement as described above is adopted, the
following feature is achieved. That is, the generated force of the
piezoelectric/electrostrictive element is increased, and thus it is
possible to obtain large displacement. Further, it is possible to
obtain a high resonance frequency owing to the increase in rigidity
of the device itself, making it easy to achieve the high speed of
the displacement action.
[0020] It is also preferable that a gap is formed between the
mutually opposing end surfaces. It is also preferable that a member
which is the same as a constitutive member of any one of the
movable section and the fixation section, or a plurality of members
which are different therefrom are interposed between the mutually
opposing end surfaces, the same member or the different members
including, for example, glass, cement, and organic resin,
preferably organic resin such as those based on epoxy, acrylic,
polymide, phenol, silicone, terpene, xylene, styrene, melamine,
methacrylic, and rubber, or mixture or copolymer thereof.
Especially, in view of, for example, the joining performance, the
handling performance, and the hardness, it is preferable to allow
organic resin or the like based on epoxy, acrylic, and methacrylic
to intervene. In order to further enhance the hardness, it is also
preferable to mix a filler such as an inorganic material.
[0021] Especially, it is possible to effectively realize a light
weight of the movable section or the fixation section by forming
the gap between the mutually opposing end surfaces, allowing the
member lighter than the constitutive member of the movable section
or the fixation section to intervene between the mutually opposing
end surfaces, or joining the end surfaces with small one of the
members described above. Accordingly, it is possible to increase
displacement of the movable section or the fixation section.
[0022] When the gap is formed between the mutually opposing end
surfaces, a part of the movable section or the fixation section
including one end surface and another part of the movable section
or the fixation section including the other end surface are more
flexible, resulting in strong resistance to the deformation.
Therefore, it is possible to obtain excellent handling performance
of the piezoelectric/electrostrictive device.
[0023] Further, the distance between the end surfaces is not less
than the length of the movable section. Therefore, the attachment
area can be increased, when another part is attached to the movable
section. Thus, it is possible to improve the attachment performance
or the part. It is now assumed that the part is secured, for
example, with an adhesive or the like. The part can be held by
being interposed on the both sides. Thus, it is possible to
reliably secure the part.
[0024] When the part is held by being interposed on the both sides,
the height of the part and the height of the movable section are
not simply added. Accordingly, it is possible to maintain the
height of the whole including the part to be low. Further, the
length of the movable section can be made smaller than the distance
on the side of the end surface. Therefore, the physical property of
an adhesive or the like for sticking or bonding the part
effectively makes the action. Thus, it is possible to increase the
displacement.
[0025] On the other hand, when the fixation section has the
mutually opposing end surfaces, it is possible to strongly fix the
piezoelectric/electrostrictive device according to this invention
to a predetermined fixation portion. Thus. it is possible to
improve the reliability.
[0026] As described above, according to the present invention, it
is possible to obtain the displacement element which is scarcely
affected by harmful vibration and capable of high speed response
with high mechanical strength while being excellent in handling
performance, shock resistance. and moisture resistance, making it
possible to realize a light weight of the device, especially a
light weight of the movable section or the fixation section, and
improve the handling performance of the device as well as the
attachment performance for parts to be attached to the movable
section, the miniaturization, and the fixation performance of the
device, so that the movable section may be greatly displaced, and
it is possible to achieve a high speed of the displacement action
of the movable section (realization of a high resonance frequency),
as well as the sensor element which makes it possible to accurately
detect vibration of the movable section.
[0027] In the production of the piezoelectric/electrostrictive
device, for example, when the piezoelectric/electrostrictive
element is formed on a ceramic laminate (obtained by laminating
ceramic green sheets followed by sintering into one unit), for
example, by means of the lamination or the integrated sintering
based on the use of the film formation method as described later
on, the internal residual stress is generated at a portion to be
formed into the piezoelectric/electrostrictive element and/or the
thin plate section. Especially, when the
piezoelectric/electrostrictive element is formed on the ceramic
laminate by means of the integrated sintering, the internal
residual stress tends to be generated at the portion to be
converted into the piezoelectric/electrostrictive element and/or
the thin plate section, due to the shrinkage and the difference in
coefficient of thermal expansion of the constitutive members caused
during the sintering.
[0028] If the piezoelectric/electrostrictive device is produced and
used starting from this state, the movable section does not exhibit
the desired displacement in some cases, even when a predetermined
electric field is applied to the piezoelectric/electrostrictive
layer for constructing the piezoelectric/electrostrictive element,
because of the following reason. That is, the material
characteristic of the piezoelectric/electrostrictive layer and the
displacement action of the movable section are inhibited by the
internal residual stress generated in the
piezoelectric/electrostrictive element and/or the thin plate
section.
[0029] In the present invention, the mutually opposing end surfaces
are provided on any one of the movable section and the fixation
section. Therefore, the distance between the end surfaces is, for
example, shortened by the internal residual stress generated in the
piezoelectric/electrostrictive element and/or the thin plate
section. That is, the internal residual stress, which has been
generated in the piezoelectric/electrostrictive element and/or the
thin plate section, is released by the movement of the end
surfaces.
[0030] Further, in the present invention, the distance between the
end surfaces is made to be wide. Therefore, even when the distance
between the end surfaces is narrowed due to the internal residual
stress, it is possible to give a margin sufficient to attach
another part between the end surfaces.
[0031] As described above, in the present invention, the
displacement action of the movable section is not inhibited by the
internal residual stress. It is possible to obtain the displacement
action of the movable section as approximately designed and
expected. Additionally, the release of the internal residual stress
also makes it possible to improve the mechanical strength of the
device.
[0032] When a hole is formed by both inner walls of the pair of
thin plate sections, inner walls of the movable sections, inner
walls of the plurality of members, and an inner wall of the
fixation section, it is also preferable that the hole is filled
with a gel material. In this arrangement, although the displacement
action of the movable section is usually restricted due to the
presence of the filler material, the invention described above
intends to reduce the weight as a result of the formation of the
end surfaces on the movable section or the fixation section, and
increase the displacement amount of the movable section. Therefore,
the restriction of the displacement action of the movable section
by the filler material is counteracted, and it is possible to
realize the effect owing to the presence of the filler material,
i.e., the realization of the high resonance frequency and the
maintenance of the rigidity.
[0033] According to another aspect of the present invention there
is provided a method for producing a piezoelectric/electrostrictive
device comprising a pair of mutually opposing thin plate sections
and a fixation section for supporting the thin plate sections;
movable sections provided at forward end portions of the pair of
thin plate sections; and one or more piezoelectric/electrostrictive
elements arranged on at least one thin plate section of the pair of
thin plate sections; the method comprising a step of forming the
movable sections or the fixation section having mutually opposing
end surfaces wherein a distance between the end surfaces is not
less than a length of the movable section, by cutting off a
predetermined part of any one of a portion to be formed into the
movable sections or a portion to be formed into the fixation
section after producing at least the piezoelectric/electrostrictive
element on the thin plate section.
[0034] As a result, there is provided the movable section or the
fixation section which has the mutually opposing end surfaces.
Accordingly, the internal residual stress, which has been generated
in the piezoelectric/electrostrictive element and/or the thin plate
section during the production, is released, for example, by
shortening the distance between the end surfaces. Therefore, the
displacement action of the movable section is not inhibited by the
internal residual stress.
[0035] The phrase "after producing the
piezoelectric/electrostrictive element" referred to herein
indicates a state in which at least the
piezoelectric/electrostrictive layer is formed. As for the
electrode to be formed after the formation of the
piezoelectric/electrostrictive layer, the electrode may be formed
after performing the cutoff to form the movable section or the
fixation section having the mutually opposing end surfaces.
[0036] The provision of the movable section or the fixation section
having the mutually opposing end surfaces realizes the light weight
of the movable section or the fixation section. Therefore, the
piezoelectric/electrostrictive device, which makes it possible to
increase the resonance frequency, can be efficiently produced with
ease without decreasing the amount of displacement of the movable
section. Thus, it is possible to realize the mass production of the
high performance piezoelectric/electrostrictive device.
[0037] Further, the movable section or the fixation section is bent
more flexibly, and it is strongly resistant to deformation.
Therefore, the piezoelectric/electrostrictive device is excellent
in handling performance. Owing to the presence of the mutually
opposing end surfaces and the wide distance between the end
surfaces, when another part is attached to the movable section, it
is possible to provide a large attachment area therefor. Thus, it
is possible to improve the attachment performance for the part.
When a part is interposed and bonded, it is possible to improve the
displacement.
[0038] According to still another aspect of the present invention,
there is provided a method for producing a
piezoelectric/electrostrictive device comprising a pair of mutually
opposing thin plate sections and a fixation section for supporting
the thin plate sections; movable sections provided at forward end
portions of the pair of thin plate sections; and one or more
piezoelectric/electrostrictive elements arranged on at least one
thin plate section of the pair of thin plate sections; the method
comprising a step of producing a ceramic laminate by integrally
sintering a ceramic green laminate including at least a ceramic
green sheet having a window and ceramic green sheets to be formed
into the thin plate sections thereafter to produce the ceramic
laminate; a step of forming the piezoelectric/electrostrictive
element on an outer surface of a portion of the ceramic laminate to
be formed into the thin plate section; and a cutoff step of forming
the movable sections or the fixation section having at least
mutually opposing end surfaces wherein a distance between the end
surfaces is not less than a length of the movable section, by means
of at lease one time of cutoff treatment for the ceramic laminate
formed with the piezoelectric/electrostrictive element.
[0039] Accordingly, in the production of the
piezoelectric/electrostrictiv- e device, especially when the
ceramic laminate by means of the sintering, the internal residual
stress, which is generated in the piezoelectric/electrostrictive
element and/or the thin plate piezoelectric/electrostrictive device
is produced by using the ceramic green sheet-laminating method, it
is possible to realize the light weight of the device, especially
the light weight of the movable section or the fixation section,
and improve the handling performance of the device, the attachment
performance for parts to be attached to the movable section, and
the fixation performance of the device. Thus, it is possible to
allow the movable section to make large displacement.
[0040] It is also referable that in the step of producing the
ceramic laminate, the ceramic laminate is produced by integrally
sintering a ceramic green laminate including a plurality of ceramic
green sheets each having a window for forming the movable section
or the fixation section having at least the mutually opposing end
surfaces, and the ceramic green sheets to be formed into the thin
plate sections thereafter to produce the ceramic laminate; and in
the cutoff step, the movable section or the fixation section, which
has at least the mutually opposing end surfaces and in which the
distance between the end surfaces is not less than the length of
the movable section, is formed by means of the cutoff treatment for
the ceramic laminate formed with the piezoelectric/electrostrictive
element.
[0041] It is also preferable that in the step of producing the
ceramic laminate, the ceramic laminate is produced by integrally
sintering a ceramic green laminate including a plurality of ceramic
green sheets each having a window for forming a portion to be
formed into the movable section or a portion to be formed into the
fixation section having at least the mutually opposing end surfaces
partially connected to one another, and the ceramic green sheets to
be formed into the thin plate sections thereafter to produce the
ceramic laminate; and in the cutoff step, the portion to be formed
into the movable section or the portion to be formed into the
fixation section having at least the mutually opposing end surfaces
partially connected to one another is formed by means of the cutoff
treatment for the ceramic laminate formed with the
piezoelectric/electrostrictive element, and the movable section or
the fixation section, which has the mutually opposing end surfaces
and in which the distance between the end surfaces is not less than
the length of the movable section, is formed by cutting off the
connecting portion.
[0042] It is also preferable that the production method further
comprises a step of allowing a plurality of members different from
a constitutive member of the movable section or the fixation
section to intervene between the mutually opposing end surfaces. In
this case, organic resin may be used as at least one member of the
plurality of members.
[0043] Therefore, the piezoelectric/electrostrictive device and the
method for producing the same according to the present invention
can make the use of the active device including, for example,
various transducers, various actuators, frequency region functional
parts (filters), transformers, vibrators, resonators, oscillators,
and discriminators for the communication and the power generation,
as well as the sensor element for various sensors including, for
example, ultrasonic sensors, acceleration sensors, angular velocity
sensors, shock sensors, and mass sensors. Especially, the
piezoelectric/electrostrictive device and the method for producing
the same according to the present invention can be preferably
utilized for various actuators to be used for the mechanism for
adjusting the displacement and the positioning and for adjusting
the angle for various precision parts such as those of optical
instruments and precision mechanical equipments.
[0044] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings n which a preferred embodiment of the present invention is
shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 shows a perspective view illustrating an arrangement
of a piezoelectric/electrostrictive device according to an
embodiment of the present invention;
[0046] FIG. 2 shows a magnified view illustrating a first modified
embodiment of the piezoelectric/electrostrictive element;
[0047] FIG. 3 shows a magnified view illustrating a second modified
embodiment of the piezoelectric/electrostrictive element;
[0048] FIG. 4 shows a perspective view illustrating, with partial
omission, a third modified embodiment of the
piezoelectric/electrostricti- ve element;
[0049] FIG. 5 shows a perspective view illustrating, with partial
omission, a fourth modified embodiment of the
piezoelectric/electrostrict- ive element;
[0050] FIG. 6 shows a perspective view illustrating a first
modified embodiment of the piezoelectric/electrostrictive device
according to the embodiment of the present invention;
[0051] FIG. 7 shows a perspective view illustrating a second
modified embodiment of the piezoelectric/electrostrictive device
according to the embodiment of the present invention;
[0052] FIG. 8 illustrates a situation in which both of the
piezoelectric/electrostrictive elements do not make the
displacement action in the piezoelectric/electrostrictive device
according to the second modified embodiment;
[0053] FIG. 9A shows a waveform illustrating a voltage waveform to
be applied to the first piezoelectric/electrostrictive element;
[0054] FIG. 9B shows a waveform illustrating a voltage waveform to
be applied to the second piezoelectric/electrostrictive
element;
[0055] FIG. 10 illustrates a situation in which the
piezoelectric/electrostrictive element makes the displacement
action in the piezoelectric/electrostrictive device according to
the second modified embodiment;
[0056] FIG. 11 shows a perspective view illustrating a third
modified embodiment of the piezoelectric/electrostrictive device
according to the embodiment of the present invention;
[0057] FIG. 12 shows a perspective view illustrating a fourth
modified embodiment of the piezoelectric/electrostrictive device
according to the embodiment of the present invention;
[0058] FIG. 13 shows a perspective view illustrating a fifth
modified embodiment of the piezoelectric/electrostrictive
device;
[0059] FIG. 14 shows a perspective view illustrating a sixth
modified embodiment of the piezoelectric/electrostrictive
device;
[0060] FIG. 15 shows a perspective view illustrating a seventh
modified embodiment of the piezoelectric/electrostrictive
device;
[0061] FIG. 16 illustrates a process for laminating ceramic green
sheets required for a first production method;
[0062] FIG. 17 illustrates a state in the first production method
in which a ceramic green laminate is formed;
[0063] FIG. 18 illustrates a state in the first production method
in which the ceramic green laminate is converted into a sintered
ceramic laminate, and then a piezoelectric/electrostrictive element
is formed on the ceramic laminate;
[0064] FIG. 19 illustrates an intermediate process in the first
production method in which the ceramic laminate is cut along
predetermined cutting lines to provide the
piezoelectric/electrostrictive device according to the embodiment
of the present invention;
[0065] FIG. 20A illustrates a state in which the internal residual
stress is generated in the thin plate section and the
piezoelectric/electrostric- tive layer;
[0066] FIG. 20B illustrates a state in which a central portion of a
movable section is cut off;
[0067] FIG. 21 illustrates a process for laminating ceramic green
sheets required for a second production method;
[0068] FIG. 22 illustrates a state in the second production method
in which a ceramic green laminate is formed;
[0069] FIG. 23 Illustrates a state in. the second production method
in which the ceramic green laminate is converted into a sintered
ceramic laminate, and then a piezoelectric/electrostrictive element
is formed on the ceramic laminate;
[0070] FIG. 24 illustrates a state in the second production method
in which the ceramic laminate is cut along predetermined cutting
lines to provide the piezoelectric/electrostrictive device
according to the embodiment of the present invention;
[0071] FIG. 25 illustrates a process for laminating ceramic green
sheets required for a third production method;
[0072] FIG. 26 illustrates a state in the third production method
in which a ceramic green laminate is formed;
[0073] FIG. 27 illustrates a state in the third production method
in which the ceramic green laminate is converted into a sintered
ceramic laminate, and then a piezoelectric/electrostrictive element
is formed on the ceramic laminate;
[0074] FIG. 28 illustrates an intermediate process in the third
production method in which the ceramic laminate is cut along
predetermined cutting lines to provide the
piezoelectric/electrostrictive device according to the embodiment
of the present invention;
[0075] FIG. 29 illustrates a process for laminating ceramic green
sheets required for a fourth production method;
[0076] FIG. 30 illustrates a state in the fourth production method
in which a ceramic green laminate is formed;
[0077] FIG. 31 illustrates a state in the fourth production method
in which the ceramic green laminate is converted into a sintered
ceramic laminate, and then a piezoelectric/electrostrictive element
is formed on the ceramic laminate;
[0078] FIG. 32 illustrates an intermediate process in the fourth
production method in which the ceramic laminate is cut along
predetermined cutting lines to provide the
piezoelectric/electrostrictive device according to the embodiment
of the present invention;
[0079] FIG. 33 illustrates a process for laminating ceramic green
sheets required for a fifth production method;
[0080] FIG. 34 illustrates a state in the fifth production method
in which a ceramic green laminate is formed;
[0081] FIG. 35 illustrates a state in the fifth production method
in which the ceramic green laminate is sintered into a ceramic
laminate;
[0082] FIG. 36 illustrates a state in the fifth production method
in which piezoelectric/electrostrictive elements, which are
constructed as separate members, are bonded to surfaces of metal
plates to serve as thin plate sections respectively;
[0083] FIG. 37 illustrates a state in the fifth production method
in which the metal plate is bonded to the ceramic laminate to
provide a hybrid laminate;
[0084] FIG. 38 illustrates a state in the fifth production method
in which the hybrid laminate is cut along predetermined cutting
lines to provide a piezoelectric/electrostrictive device according
to an eighth modified embodiment;
[0085] FIG. 39 illustrates a state in a sixth production method in
which a ceramic green laminate is sintered into a ceramic laminate,
and then a hole is filled with a filler material;
[0086] FIG. 40 illustrates a state in the sixth production method
in which the metal plates to serve as thin plate sections
respectively are bonded to the ceramic laminate to provide a hybrid
laminate; and
[0087] FIG. 41 shows an arrangement of a
piezoelectric/electrostrictive device concerning an illustrative
conventional technique.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0088] Explanation will be made below with reference to FIGS. 1 to
40 for illustrative embodiments of the
piezoelectric/electrostrictive device and the production method for
the same according to the present invention.
[0089] It is noted that the piezoelectric/electrostrictive device
resides in a concept which includes the element for mutually
converting the electric energy and the mechanical energy by the aid
of the piezoelectric/electrostrictive element. Therefore, the
piezoelectric/electrostrictive device is most preferably used as
the active element such as various actuators and vibrators,
especially as the displacement element based on the use of the
displacement brought about by the inverse piezoelectric effect and
the electrostrictive effect. Additionally, the
piezoelectric/electrostrictive device is also preferably used as
the passive element such as acceleration sensor elements and shock
sensor elements.
[0090] As shown in FIG. 1, the piezoelectric/electrostrictive
device 10 according to this embodiment is provided with a substrate
16 which comprises, in an integrated manner, a pair of mutually
opposing thin plate sections 12a, 12b, and a fixation section 14
for supporting the thin plate sections 12a, 12b. The
piezoelectric/electrostrictive device 10 comprises
piezoelectric/electrostrictive elements 18a, 18b which are formed
at respective parts of the pair of thin plate sections 12a, 12b
respectively.
[0091] In other words, the piezoelectric/electrostrictive device 10
is constructed such that the pair of thin plate sections 12a, 12b
are displaced in accordance with the driving of the
piezoelectric/electrostri- ctive element or elements 18a and/or
18b, or the displacement of the thin plate sections 12a, 12b is
detected by the piezoelectric/electrostrictive element or elements
18a and/or 18b. Therefore in the embodiment shown in FIG. 1,
actuator sections 19a, 19b are constructed by the thin plate
sections 12a, 12b and the piezoelectric/electrostrictive elements
18a, 18b.
[0092] Further, respective forward end portions of the pair of thin
plate sections 12a, 12b are thick-walled toward the inside. The
thick-walled portions function as movable sections 20a, 20b which
are displaced in accordance with the displacement action of the
thin plate sections 12a, 12b. The forward end portions of the pair
of thin plate sections 12a, 12b will be hereinafter referred to as
"movable sections 20a, 20b".
[0093] Those usable as the substrate 16 include a structure
comprising ceramics or metal as a whole, and a hybrid structure
obtained by combining products produced with materials of ceramics
and metal.
[0094] Those adoptable for the substrate 16 include, for example, a
structure in which respective parts are bonded to one another with
an adhesive such as organic resin or glass or the like, a ceramic
integrated structure which is obtained by sintering and integrating
a ceramic green laminate into one unit, and a metal integrated
structure, integrated, for example, by brazing, soldering, eutectic
bonding, or welding into one unit. Preferably, it is desirable to
construct the substrate 16 with a ceramic laminate integrated into
one unit by sintering a ceramic green laminate.
[0095] The time-dependent change of state scarcely occurs in the
integrated product of ceramic, because no adhesive exists at joined
portions between the respective parts. Therefore, the reliability
of the joined portion is high, giving a structure which is
advantageous to ensure the rigidity. Additionally, the integrated
product of ceramic can be produced with ease by means of the method
for laminating ceramic green sheets as described later on.
[0096] The piezoelectric/electrostrictive elements 18a, 18b are
prepared as separate members as described later on, and the
prepared piezoelectric/electrostrictive elements 18a, 18b are stuck
to the substrate 16 with an adhesive such as organic resin or glass
or by means of, for example, brazing, soldering, or eutectic
bonding. Alternatively, the piezoelectric/electrostrictive elements
18a, 18b are directly formed on the substrate 16 by using the film
formation method not by using the sticking method described
above.
[0097] The piezoelectric/electrostrictive element 18a, 18b
comprises a piezoelectric/electrostrictive layer 22, and a pair of
electrodes 24, 26 which are formed on both sides of the
piezoelectric/electrostrictive layer 22. The first electrode 24 of
the pair of electrodes 24, 26 is formed at least on the pair of
thin plate sections 12a, 12b.
[0098] In the embodiment of the present invention, explanation will
be made principally for a case in which each of the
piezoelectric/electrostr- ictive layer 22 and the pair of
electrodes 24; 26 has a multilayered structure, the first electrode
24 and the second electrode 26 are alternately stacked with each
other to give a substantially comb-shaped cross section, and thus
the piezoelectric/electrostrictive element 18a, 18b is provided,
which has a multiple stage structure at a portion at which the
first electrodes 24 and the second electrodes 26 are overlapped
with each other with the piezoelectric/electrostrictive layer 22
interposed therebetween. However, there is no limitation to the
multilayered structure A single-layered structure may be available.
In this embodiment, the number of the multiple layers is not
specifically limited. However, it is preferable to use not more
than ten layers, and more preferably not more than five layers.
[0099] FIG. 1 is illustrative of a case in which the
piezoelectric/electrostrictive layer 22 has a three-layered
structure, the first electrode 24 is formed to have a comb-shaped
configuration to be located at the lower surface of the first layer
(side surface of the thin plate section 12a, 12b) and at the upper
surface of the second layer, and the second electrode 26 is formed
to have a comb-shaped configuration to be located at the upper
surface of the first layer and at the upper surface of the third
layer. In the case of this arrangement, the number of terminals 28,
30 can be decreased by mutually connecting the first electrodes 24
and the second electrodes 26 respectively to be common. Therefore,
the increase in size, which would be otherwise caused by the
multilayered structure of the piezoelectric/electrostrictive
element 18a, 18b, can be suppressed.
[0100] The voltage is applied to the pair of electrodes 24, 26 via
terminals (pads) 28, 30 of the respective electrodes 24, 26 formed
on the. both side surfaces (element formation surfaces) of the
fixation section 14 respectively. The respective terminals 28, 30
are positioned as follows. That is, the terminal 28 corresponding
to the first electrode 24 is formed at the positions deviated
toward the reward end of the fixation section 14. The terminal 30
corresponding to the second electrode 26 disposed on the side of
the external space is formed at the position deviated toward the
inner wall of the fixation section 14.
[0101] In this embodiment, the piezoelectric/electrostrictive
device 10 can be individually fixed by utilizing the surfaces
respectively different from the surfaces on which the terminals 28,
30 are arranged. As a result, it is possible to obtain the high
reliability for both of the fixation of the
piezoelectric/electrostrictive device 10 and the electric
connection between the circuit and the terminals 28, 30. In this
arrangement, the electric connection between the terminals 28, 30
and the circuit is made, for example, by means of the flexible
printed circuit (also referred to as FPC), the flexible flat cable
(also referred to as FFC), and the wire bonding.
[0102] When the piezoelectric/electrostrictive element 18a, 18b
having the multilayered structure is used as described above, then
the driving force of the actuator section 19a, l 9b is increased,
and thus it is possible to contemplate the large displacement.
Further, the rigidity of the piezoelectric/electrostrictive device
10 itself is increased, and thus it is possible to realize the high
resonance frequency, making it easy to achieve the realization of a
high speed of the displacement action.
[0103] When the number of stages is increased, it is possible to
increase the driving force of the actuator sections 19a, 19b.
However, the electric power consumption is also increased in
accordance therewith. Therefore, when the device is practically
produced and used, for example, it is preferable that the number of
stages is appropriately determined depending on the way of use and
the state of use. In the case of the piezoelectric/electrostrictive
device 10 according to this embodiment, even when the driving force
of the actuator section 19a, 19b is increased by using the
piezoelectric/electrostrictive element 13a, 18b, the width of the
thin plate section 12a, 12b (distance in the Y axis direction) is
basically unchanged. Therefore, the device is extremely preferred
to make application, for example, to the actuator for the purpose
of the ringing control and the positioning of the magnetic head for
the hard disk to be used in an extremely narrow gap.
[0104] Another example of the piezoelectric/electrostrictive
element 18a, 18b is preferably shown, for example, in FIG. 2. That
is, the piezoelectric/electrostrictive layer 22 has a five-layered
structure. The first electrode 24 is formed to have a comb-shaped
configuration to be located at the upper surface of the first
layer, the upper surface of the third layer, and the upper surface
of the fifth layer. The second electrode 26 is formed to have a
comb-shaped configuration to be located at the upper surface of the
second layer and the upper surface of the fourth layer.
[0105] Still another example is also available as shown, in FIG. 3.
That is, the piezoelectric/electrostrictive layer 22 is allowed to
have a five-layered structure as well. The first electrode 24 is
formed to have a comb-shaped configuration to be located at the
upper-surface of the first layer, the upper surface of the third
layer, and the upper surface of the fifth layer. The second
electrode 26 is formed to have a comb-shaped configuration to be
located at the lower surface of the first layer, the upper surface
of the second layer, and the upper surface of the fourth layer.
[0106] The voltage is applied to the pair of electrodes 24, 26 via
ends (hereinafter referred to as "terminal sections 24a, 26a) of
the respective electrodes 24, 26 formed on the fifth layer of the
piezoelectric/electrostrictive layer 22. The respective terminal
sections 24a, 26a are formed and separated from each other in such
a degree that they can be electrically insulated from each
other.
[0107] The piezoelectric/electrostrictive element 18a, 18b
described above is illustrative of the case of the construction of
the so-called sandwich structure in which the
piezoelectric/electrostrictive layer 22 is allowed to intervene
between the pair of electrodes 24, 26. Alternatively, as shown in
FIG. 4, a pair of comb-shaped electrodes 24, 26 may be formed on
the first principal surface of the piezoelectric/electrostrictive
layer 22 formed on at least the side surface of the thin plate
section 12a, l2b. Further alternatively, as shown in FIG. 5, a pair
of comb-shaped electrodes 24, 26 are formed and embedded in the
piezoelectric/electrostr- ictive layer 22 formed on at least the
side surface of the thin plate section 12a, 12b.
[0108] The structure shown in FIG. 4 is advantageous in that it is
possible to suppress the electric power consumption to be low. The
structure shown in FIG. 5 makes it possible to effectively utilize
the inverse piezoelectric effect in the direction of the electric
field having large generated force and strain, which is
advantageous to cause the large displacement.
[0109] Specifically, the piezoelectric/electrostrictive element
18a, 18b shown in FIG. 4 comprises the pair of electrodes 24, 26
having the comb-shaped structure formed on the first principal
surface of the piezoelectric/electrostrictive layer 22. In this
structure, the first electrode 24 and the second electrode 26 are
mutually opposed to one another in an alternate manner with a gap
32 having a constant width interposed therebetween. FIG. 4 is
illustrative of the case in which the pair of electrodes 24, 26 are
formed on the first principal surface of the
piezoelectric/electrostrictive layer 22. Alternatively, the pair of
electrodes 24, 26 may be formed between the thin plate section 12a,
12b and the piezoelectric/electrostrictive layer 22. Further
alternatively, the pair of comb-shaped electrodes 24, 26 may be
formed on the first principal surface of the
piezoelectric/electrostrictive layer 22 and between the thin plate
section 12a, 12b and the piezoelectric/electrostri- ctive layer 22
respectively.
[0110] On the other hand, in the piezoelectric/electrostrictive
element 18a, 18b shown in FIG. 5, the pair of electrodes 24, 26
having the comb-shaped structure are formed so that they are
embedded in the piezoelectric/electrostrictive layer 22. In this
structure, the first electrode 24 and the second electrode 26 are
mutually opposed to one another in an alternate manner with a gap
32 having a constant width interposed therebetween.
[0111] The piezoelectric/electrostrictive elements 18a, 18b as
shown in FIGS. 4 and 5 can be preferably used for the
piezoelectric/electrostricti- ve device 10 according to the
embodiment of the present invention as well. When the pair of
comb-shaped electrodes 24, 26 are used as in the
piezoelectric/electrostrictive elements 18a, 18b shown in FIGS. 4
and 5, the displacement of the piezoelectric/electrostrictive
element 18a, 18b can be increased by decreasing the pitch D of the
comb teeth of the respective electrodes 24, 26.
[0112] The distance Lc between the mutually opposing end surfaces
34a, 34b of the movable sections 20a, 20b is not less than the
length of the movable section 20a, 20b (correctly the length of the
movable section 20a, 20b in the Z axis direction) Df. For example,
as shown in FIG. 1, a gap (air) 36 may be lowed to intervene
between the end surfaces 34a, 34b. Alternatively, as in
piezoelectric/electrostrictive devices 10a, 10b according to first
and second modified embodiments shown in FIGS. 6 and 7, a plurality
of members, which are composed of the same material as that of the
constitutive member of the movable section 20a, 2b or which are
composed of a material different therefrom, may be allowed to
intervene between the end surfaces 34a, 34b. In this arrangement,
the mutually opposing end surfaces 34a, 34b of the respective
movable sections 20a, 20b function as attachment surfaces 34a,
34b.
[0113] The piezoelectric/electrostrictive device 10a according to
the first modified embodiment shown in FIG. 6 is illustrative of
the following case. That is, the distance Lc between the attachment
surfaces 34a, 34b is set to be about 1.5-fold the length Df of the
movable section 20a, 20b. Further, three spacer members 37A, 37B,
37C, each of which has a substantially identical thickness, are
allowed to intervene between the attachment surfaces 34a, 34b.
[0114] The piezoelectric/electrostrictive device 10b according to
the second modified embodiment shown in FIG. 7 is illustrative of
the following case. That is, the distance Lc between the attachment
surfaces 34a, 34b is set to be about 1.5-fold the length Df of the
movable section 20a, 20b. Further, one large spacer member 37 is
bonded between the attachment surfaces 34a, 34b by the aid of an
adhesive 38.
[0115] Further, for example, in the piezoelectric/electrostrictive
device 10b according to the second modified embodiment, as shown in
FIG. 8, for example, it is preferable that distances La, Lb from
the central axis n of the spacer member 37 to the respective end
surfaces 34a, 34b are approximately identical to one another.
[0116] In the piezoelectric/electrostrictive devises 10a, 10b
according to the first and second modified embodiments, each of the
three spacer members 37A to 37C (see FIG. 6) and the spacer member
37 (see FIG. 7) has a substantially rectangular
parallelepiped-shaped configuration. Each of the side surfaces
(surfaces opposed to the movable sections 20a, 20b of the thin
plate sections 12a, 12b) is set to have the areal size which is
substantially the same as the areal size of each of the attachment
surfaces 3a, 34b of the movable sections 20a, 20b of the thin plate
sections 12a, 12b.
[0117] The operation of the piezoelectric/electrostrictive device
10b according to the second modified embodiment will now be
explained by way of example. At first, for example, when the two
piezoelectric/electrostri- ctive elements 18a, 18b are in the
natural state, namely when both of the
piezoelectric/electrostrictive elements 18a, 18b do not make the
displacement action, then the major axis m of the
piezoelectric/electrost- rictive device 10b (major axis of the
fixation section 14) is substantially coincident with the central
axis n of the spacer member 37 as shown in FIG. 8.
[0118] Starting from this state, for example, a sine wave Wa, which
has a predetermined bias electric potential Vb, is applied to the
pair of electrodes 24, 26 of the first
piezoelectric/electrostrictive element 18a as shown in a waveform
figure shown in FIG. 9A, while a sine wave Wb, which has a phase
different from that of the sine wave Wa by about 180.degree., is
applied to the pair of electrodes 24, 26 of the second
piezoelectric/electrostrictive element 18b as shown in FIG. 9B.
[0119] The piezoelectric/electrostrictive layer 22 of the first
piezoelectric/electrostrictive element 18a makes the contraction
displacement in the direction of the first principal surface at a
stage at which, for example, a voltage having a maximum value is
applied to the pair of electrodes 24, 26 of the first
piezoelectric/electrostrictive element 18a. Accordingly, as shown
in FIG. 10, for example, the stress is generated for the first thin
plate section 12a to bend the thin plate section 12a, for example,
in the rightward direction as shown by the arrow A. Therefore, the
first thin plate section 12a is bent in the rightward direction. At
this time, a state is given, in which no voltage is applied to the
pair of electrodes 24, 26 of the second
piezoelectric/electrostrictive element 18b. Therefore, the second
thin plate section 12b follows the bending of the first thin plate
section 12a, and it is bent in the rightward direction. As a
result, the movable sections 20a, 20b and the spacer member 37 are
displaced, for example, in the rightward direction with respect to
the major axis m of the piezoelectric/electrostrictive device 10b.
The displacement amount is changed depending on the maximum value
of the voltage applied to each of the
piezoelectric/electrostrictive elements 18a, 18b. For example, the
larger the maximum value is, the larger the displacement amount
is.
[0120] Especially, when a material having a high coercive electric
field is applied as the constitutive material for the
piezoelectric/electrostri- ctive layer 22, it is also preferable
that the bias electric potential is adjusted so that the level of
the minimum value is a slightly negative level as depicted by
waveforms indicated by dashed lines in FIGS. 9A and 9B. In this
case, for example, the stress, which is in the same direction as
the bending direction of the first thin plate section 12a, is
generated in the second thin plate section 12b by driving the
piezoelectric/electrostrictive element (for example, the second
piezoelectric/electrostrictive element 18b) to which the negative
level is applied. Accordingly, it is possible to further increase
the displacement amount of the movable sections 20a, 20b and the
spacer member 37. In other words, when the waveforms indicated by
the dashed lines in FIGS. 9A and 9B are used, the device is allowed
to have such a function that the piezoelectric/electrostrictive
element 18b or 18a, to which the negative level is applied,
supports the piezoelectric/electrost- rictive element 18a or 18b
which principally makes the displacement action.
[0121] As described above, in the piezoelectric/electrostrictive
device 10 according to the embodiment of the present invention, the
minute displacement of the piezoelectric/electrostrictive element
18a, 18b is the bending of the thin plate section 12a, 12b, and it
is transmitted to the movable sections 20a, 20b. Accordingly, it is
possible to greatly displace the movable sections 20a, 20b with
respect to the major axis m of the piezoelectric/electrostrictive
device 10b.
[0122] Especially, in this embodiment, the movable sections 20a,
20b are provided with the mutually opposing attachment surfaces
34a, 34b. In this arrangement, the space between the mutually
opposing attachment surfaces 34a, 34b is the gap 36. Alternatively,
the member, which is lighter than the constitutive member of the
movable sections 20a, 20b, is allowed to intervene between the
mutually opposing attachment surfaces 34a, 34b. Thus, it is
possible to effectively realize the light weight of the movable
sections 20a, 20b. It is possible to increase the resonance
frequency without decreasing the displacement amount of the movable
sections 20a, 20b.
[0123] The frequency herein indicates the frequency of the voltage
waveform obtained when the movable sections 20a, 20b are displaced
rightwardly and leftwardly by alternately switching the voltage
applied to the pair of electrodes 24, 26. The resonance frequency
indicates the maximum frequency at which the displacement action of
the movable sections 20a, 20b can follow in a predetermined
vibration mode.
[0124] In the piezoelectric/electrostrictive device 10 according to
this embodiment, the movable sections 20a, 20b, the thin plate
sections 12a, 12b, and the fixation section 14 are integrated into
one unit. It is unnecessary that all of the parts are formed with
the piezoelectric/electrostrictive material which is a fragile
material having a relatively heavy weight. Therefore, the device
has the following advantages. That is, the device has the high
mechanical strength, and it is excellent in handling performance,
shock resistance, and moisture resistance. Further, the operation
of the device is scarcely affected by harmful vibration (for
example, noise vibration and remaining vibration during high speed
operation).
[0125] In this embodiment, when the space between the mutually
opposing attachment surfaces 34a, 34b is the gap 36, the movable
section 20a including t first attachment surface 34a and the
movable section 20b including the second attachment surface 34b are
easily bent, and the device is highly resistant to the deformation.
Therefore, the piezoelectric/electrostrictive device 10 is
excellent in handling performance.
[0126] Owing to the presence of the mutually opposing attachment
surfaces 34a, 34b, the surface area of the movable sections 20a,
20b is increased. Therefore, when another part is attached to the
movable section 20a, 20b, it is possible to increase the attachment
area. Thus, it is possible to improve the attachment performance
for the part. For example, if it is assumed that the part is
secured with an adhesive or the like, the part is bonded by the aid
of not only the principal surface of the movable section 20a, 20b
(front surface and/or back surface) but also the mutually opposing
attachment surfaces 34a, 34b. It is possible to secure the part in
a reliable manner.
[0127] In this embodiment, the piezoelectric/electrostrictive
element 18a, 18b is constructed to have the
piezoelectric/electrostrictive layer 22 and the pair of electrodes
24, 26 formed on the both sides of the
piezoelectric/electrostrictive layer 22. The first electrode 24 of
the pair of electrodes 24, 26 is directly formed on at least the
side surface of the thin plate section 12a, 12b. Therefore, the
vibration caused by the piezoelectric/electrostrictive element 18a,
18b can be efficiently transmitted to the movable section 20a, 20b
via the thin plate section 12a, 12b. Thus, it is possible to
improve the response performance.
[0128] In this embodiment, as shown in FIG. 1, for example, the
portion (substantial driving portion 40), at which the pair of
electrodes 24, 26 are overlapped with each other with the
piezoelectric/electrostrictive layer 22 interposed therebetween, is
continuously formed over the range from the part of the fixation
section 14 to the part of the thin plate section 12a, 12b. If the
substantial driving portion 40 is formed to further extend over a
part of the movable section 20a, 20b, then it is feared that the
displacement action of the movable section 20a, 20b is inconsistent
with the deformation of the substantial driving portion 40 and the
deformation of the thin plate section 12a, 12b, and it is
impossible to obtain the large displacement. However, in this
embodiment, the substantial driving portion 40 is formed such that
it does not range over both of the movable section 20a, 20b and the
fixation section 14. Therefore, it is possible to avoid the
inconvenience of the restriction of the displacement action of the
movable section 20a, 20b, and it is possible to increase the
displacement amount of the movable section 20a, 20b.
[0129] On the other hand, when the piezoelectric/electrostrictive
element 18a, 18b is formed on the part of the movable section 20a,
20b, it is preferable that the substantial driving portion 40 is
located over the range from the part of the movable section 20a,
20b to the part of the thin plate section 12a, 12b, because of the
following reason. That is, if the substantial driving portion 40 is
formed to extend up to a part of the fixation section 14, the
displacement action of the movable section 20a, 20b is restricted
as described above.
[0130] The embodiment described above is illustrative of the case
in which the attachment surfaces 34a, 34b are provided for the
movable sections 20a, 20b. Alternatively, as in a
piezoelectric/electrostrictive device 10c according to a third
modified embodiment shown in FIG. 11, end surfaces 34a, 34b may be
provided for the fixation section 14. In this case, for example,
the movable sections 20a, 20b, which are provided at the forward
end portions of the pair of thin plate sections 12a, 12b, have an
integrally connected configuration. The mutually opposing end
surfaces 34a, 34b are provided for the fixation section 14.
[0131] Accordingly, in addition to the effect obtained when the
mutually opposing attachment surfaces 34a, 34b are provided for the
movable sections 20a, 20b as described above, the
piezoelectric/electrostrictive device 10c according to the third
modified embodiment can be tightly fixed to a predetermined
fixation portion. Thus, it is possible to improve the reliability.
The length of the substantial driving portion 40 is preferably 20%
to 95% of the length of the thin plate section 12a, 12b, and more
preferably 40% to 80% thereof.
[0132] Next, explanation will be made for preferred illustrative
constructions of the piezoelectric/electrostrictive device 10
according to the embodiment of the present invention.
[0133] At first, in order to ensure the displacement action of the
movable section 20a, 20b, it is preferable that the distance Dg, by
which the substantial driving portion 40 of the
piezoelectric/electrostrictive element 18a, 18b is overlapped with
the fixation section 14 or the movable section 20a, 20b, is not
less than 1/2 of the thickness Dd of the thin plate section 12a,
12b.
[0134] The device is constructed such that the ratio Da/Db between
the distance (distance in the X axis direction) Da between the
inner walls of the thin plate sections 12a, 12b and the width
(distance in the Y axis direction) Db of the thin plate section
12a, 12b is 0.5 to 20. The ratio Da/Db is preferably 1 to 15 and
more preferably 1 to 10. The prescribed value of the ratio Da/Db is
prescribed on the basis of the discovery that the displacement
amount of the movable section 20a, 20b can be increased, and the
displacement in the X-Z plane can be dominantly obtained.
[0135] On the other hand, it is desirable that the ratio De/Da
between the length (distance in the Z axis direction) De of the
thin plate section 12a, 12b and the distance Da between the inner
walls of the thin plate sections 12a, 12b is preferably 0.5 to 10
and more preferably 0.5 to 5. The prescribed value or the ratio
De/Da is prescribed on the basis or the discovery that the
displacement amount of the movable sections 20a, 20b with the
spacer members (37A to 37C or 37) intervening therebetween can be
increased, and the displacement action can be performed at a high
resonance frequency (high response speed can be achieved).
[0136] Therefore, in order to suppress the flapping displacement in
the Y axis direction or the vibration of the
piezoelectric/electrostrictive device 10 according to this
embodiment and provide the structure in which the high speed
response performance is excellent and the large displacement is
simultaneously obtained at a relatively low voltage, it is
preferable that the ratio Da/Db is 0.5 to 20 and the ratio De/Da is
0.5 to 10, and it is more preferable that the ratio Da/Db is 1 to
10 and the ratio De/Da is 0.5 to 5.
[0137] Further, for example, in the case of the
piezoelectric/electrostric- tive device 10b according to the second
embodiment, the hole 42 is formed by the both inner walls of the
pair of thin plate sections 12a, 12b, the inner walls of the
movable sections 20a, 20b, and the inner wall of the spacer member
37 (and the inner wall of the adhesive 38), and the inner wall of
the fixation section 14. It is preferable that the hole 42 is
filled with a gel material for example, silicone gel. Usually, the
displacement action of the movable section 20a, 20b is restricted
by the presence of such a filler material. However, in the second
modified embodiment, it is intended to realize the light weight
brought about by the formation of the end surface 34a, 34b for the
movable section 20a, 20b and increase the displacement amount of
the movable section 20a, 20b. Therefore, the restriction of the
displacement action of the movable section 20a, 20b due to the
filler material is counteracted. Accordingly, it is possible to
realize the effect owing to the presence of the filler material,
namely the realization of the high resonance frequency and the
maintenance of the rigidity.
[0138] It is preferable that the length (distance in the Z axis
direction) Df of the movable section 20a, 20b is short, because of
the following reason. That is, it is possible to realize the light
weight and increase the resonance frequency by shortening the
length. Further, when an articles is interposed, it is possible to
improve the displacement. However, in order to ensure the rigidity
of the movable section 20a, 20b in the X axis direction and obtain
its reliable displacement, it is desirable that the ratio Df/Dd
with respect to the thickness Dd of the thin plate section 12a, 12b
is not less than 2 and preferably not less than 5.
[0139] The actual size of each component is determined considering,
for example, the joining area for attaching the part to the movable
section 20a, 20b, the joining area for attaching the fixation
section 14 to another member, the joining area for attaching the
electrode terminal or the like, and the strength, the durability,
the necessary displacement amount, the resonance frequency, and the
driving voltage of the entire piezoelectric/electrostrictive device
10.
[0140] Specifically, for example, the distance Da between the inner
walls of the thin plate sections 2a, 12b is preferably 100 .mu.m to
2000 .mu.m and more preferably 200 .mu.m to 1600 .mu.m. The width
Db of the thin plate section 12a, 12b is preferably 50 .mu.m to
2000 .mu.m and more preferably 100 .mu.m to 500 .mu.m. The
thickness Dd of the thin elate section 12a, 12b is preferably 2
.mu.m to 100 .mu.m and more preferably 10 .mu.m to 80 .mu.m, while
it satisfies Db>Dd in relation to the width Db of the thin plate
section 12a, 12b, in order to make it possible to effectively
suppress the flapping displacement which is the displacement
component in the Y axis direction.
[0141] The length De of the thin plate section 12a, 12b is
preferably 200 .mu.m to 3000 .mu.m and more preferably 300 .mu.m to
2000 .mu.m. The length Df of the movable section 20a, 20b is
preferably 50 .mu.m to 2000 .mu.m, more preferably 100 .mu.m to
1000 .mu.m, and especially preferably 200 .mu.m to 600 .mu.m.
[0142] The arrangement as described above exhibits such an
extremely excellent effect that the displacement in the Y axis
direction does not exceeds 10% with respect to the displacement in
the X axis direction, while the device can be driven at a low
voltage by appropriately making adjustment within the range of the
size ratio and the actual size, and it is possible to suppress the
displacement component in the Y axis direction to be not more than
5%. In other words, the movable section 20a, 20b is displaced in
one axis direction., i.e., substantially in the X axis direction.
Further, the high speed response is excellent, and it is possible
to obtain the large displacement at a relatively low voltage.
[0143] In the piezoelectric/electrostrictive device 10, the shape
of the device is not the plate-shaped configuration (the thickness
in the direction perpendicular to the displacement direction is
small) unlike conventional one. Each of the movable section 20a,
20b and the fixation section 14 has the rectangular
parallelepiped-shaped configuration (the thickness in the direction
perpendicular to the displacement direction is large). The pair of
thin plate sections 12a, 12b are provided so that the side surface
of the movable section 20a 20b is continuous to the side surface of
the fixation section 14. Therefore, it is possible to selectively
increase the rigidity of piezoelectric/electrostrictive device 10
in the Y axis direction.
[0144] That is, in the piezoelectric/electrostrictive device 10, it
impossible to selectively generate only the operation of the
movable section 20a, 20b in the plane (XZ plane). It is possible to
suppress the operation of the movable section 20a, 20b in the YZ
plane (operation in the so-called flapping direction).
[0145] Next, explanation will be made for the respective
constitutive components of the piezoelectric/electrostrictive
device 10 according to this embodiment.
[0146] As described above, the movable section 20a, 20b is the
portion which is operated on the basis of the driving amount of the
thin plate section 12a, 12b, and a variety of members are attached
thereto depending on the purpose of use or the
piezoelectric/electrostrictive device 10. For example, when the
piezoelectric/electrostrictive device 10 is used as a displacement
element, a shield plate for an optical shutter or the like is
attached thereto. Especially, when the
piezoelectric/electrostrictive device 10 is used for the mechanism
for positioning a magnetic head of a hard disk drive or for
suppressing the ringing, a member required to be positioned is
attached thereto, including, for example, the magnetic head, a
slider provided with the magnetic hand, and a suspension provided
with the slider.
[0147] As described above, the fixation section 14 is the portion
for supporting the thin plate sections 12a, 12b and the movable
section 20a, 20b. For example, when the fixation section 14 is
utilized to position the magnetic head of the hard disk drive, the
entire piezoelectric/electrostrictive device 10 is fixed by
supporting and securing the fixation section 14, for example, to a
carriage arm attached to VCM (voice coil motor) or a fixation plate
or a suspension attached to the carriage arm. As shown in FIG. 1,
the terminals 28, 30 for driving the piezoelectric/electrostrictive
elements 18a, 18b and other members are arranged on the fixation
section 14 in some cases.
[0148] The material for constructing the movable section 20a, 20b
and the fixation section 14 is not specifically limited preferably
use ceramics to which the ceramic green sheet-laminating method is
applicable as described later on. Specifically, the material
includes, for example, materials containing a major component of
zirconia represented by fully stabilized zirconia and partially
stabilized zirconia, alumina, magnesia, silicon nitride, aluminum
nitride, and titanium oxide, as well as materials containing a
major component of a mixture of them. However, in view of the high
mechanical strength and the high toughness, it is preferable to use
a material containing a major component of zirconia, especially
fully stabilized zirconia and a material containing a major
component of partially stabilized zirconia. The metal material is
not limited provided that it has rigidity. However, the metal
material includes, for example, stainless steel and nickel.
[0149] As described above, the thin plate section 12a, 12b is the
portion which is driven in accordance with the displacement of the
piezoelectric/electrostrictive element 18a, 18b. The thin plate
section 12a, 12b is the thin plate-shaped member having
flexibility, and it functions to amplify the expansion and
contracting displacement of the piezoelectric/electrostrictive
element 18a, 18b arranged on the surface as the bending
displacement and transmit the displacement to the movable section
20a, 20b. Therefore, it is enough that the shape or the material of
the thin plate section 12a, 12b provides the flexibility with the
mechanical strength of such a degree that it is not broken by the
bending displacement. it is possible to make appropriate selection
considering the response performance and the operability of the
movable section 20a, 20b.
[0150] It is preferable that the thickness Dd of the thin plate
section 12a, 12b is preferably about 2 .mu.m to 100 .mu.m. It is
preferable that the combined thickness of the thin plate section
12a, 12b and the piezoelectric/electrostrictive element 18a, 18b is
7 .mu.m to 500 .mu.m. It is preferable that the thickness of the
electrode 24. 26 is 0.1 .mu.m to 50 .mu.m, and the thickness of the
piezoelectric/electrostrictive layer 22 is 3 .mu.m to 300
.mu.m.
[0151] Ceramics, which is similarly used for the movable section
20a, 20b and the fixation section 14 can be preferably used as the
material for constructing the thin plate section 12a, 12b. A
material containing a major component of zirconia, especially fully
stabilized zirconia and a material containing a major component of
partially stabilized zirconia are most preferably used, because the
mechanical strength is large even in c case of a thin wall
thickness, the toughness is high, and the reactivity with the
piezoelectric/electrostrictive layer and the electrode material is
small.
[0152] When the thin plate section 12a, 12b is made or a metal
material, it is enough that the metal material has flexibility and
the metal material is capable of bending displacement as described
above. However, preferably it is desirable that the thin plate
section 12a, 12b is made of an iron-based material such as various
stainless steel materials and various spring steel materials.
Alternatively, it is desirable that the thin plate section 12a, 12b
is made of a non-ferrous material such as beryllium copper,
phosphor bronze, nickel, and nickel-iron alloy.
[0153] Those which are fully stabilized or partially stabilized as
follows are preferably used as fully stabilized zirconia or
partially stabilized zirconia as described above. That is, the
compound to be used for fully stabilizing or partially stabilizing
zirconia includes yttrium oxide, ytterbium oxide, cerium oxide,
calcium oxide, and magnesium oxide. When at least one compound of
them is added and contained, the objective zirconia can be
stabilized. Alternatively, the objective zirconia can be stabilized
as well, not only by adding one type of the compound but also by
adding a combination of the compounds.
[0154] The amount of addition of each of the compounds is desirably
as follows. That is, yttrium oxide or ytterbium oxide is added by 1
to 30 mole %, preferably 1.5 to 10 mole %. Cerium oxide is added by
6 to 50 mole %, preferably 8 to 20 mole %. Calcium oxide or
magnesium oxide is added by 5 to 40 mole %, preferably 5 to 20 mole
%. Especially, it is referable to use yttrium oxide as a
stabilizer. In this case, yttrium oxide is desirably added by 1.5
to 10 mole %, more preferably 2 to 4 mole %. For example, alumina,
silica, or transition metal oxide may be added as an additive of
sintering aid or the like in a range of 0.05 to 20% by weight.
However, when the sintering integration based on the film formation
method is adopted as a technique for forming the
piezoelectric/electrostrictive element 18a, 18b, it is also
preferable to add, for example, alumina, magnesia, and transition
metal oxide as an additive.
[0155] In order to obtain the mechanical strength and the stable
crystal phase, it is desirable that the average crystal grain size
of zirconia is 0.05 to 3 .mu.m, preferably 0.05 to 1 .mu.m. As
described above, ceramics can be used for the thin plate section
12a, 12b in the same manner as in the movable section 20a, 20b and
the fixation section 14. Preferably, it is advantageous to
construct the thin plate sections 12a, 12b with a substantially
identical material in view of the reliability of the joined portion
and the strength of the piezoelectric/electrostrictive device 10,
in order to reduce any complicated procedure of the production.
[0156] The piezoelectric/electrostrictive element 18a, 18b has at
least the piezoelectric/electrostrictive layer 22 and the pair of
electrodes 24, 26 for applying the electric field to the
piezoelectric/electrostrict- ive layer 22. It is possible to use,
for example, piezoelectric/electrostr- ictive elements of the
unimorph type and the bimorph type. However, those of the unimorph
type combined with the thin plate section 12a, 12b are suitable for
the piezoelectric/electrostrictive device 10 as described above,
because they are excellent in stability of the generated
displacement amount and they are advantageous to realize the light
weight.
[0157] As shown in FIG. 1, the piezoelectric/electrostrictive
element 18a, 18b is preferably formed on the side surface side of
the thin pate section 12a, 12b in view of the fact that the thin
plate section 12a, 12b can be driven to a greater extent.
[0158] Piezoelectric ceramics is preferably used for the
piezoelectric/electrostrictive layer 22. However, it is also
possible to use electrostrictive ceramics, ferroelectric ceramics,
or anti-ferroelectric ceramics However, when the
piezoelectric/electrostrict- ive device 10 is used, for example, to
position the magnetic head of the hard disk drive, it is important
to provide the linearity concerning the displacement amount of the
movable section 20a, 20b and the driving voltage or the output
voltage. Therefore, it is preferable to use a material having small
strain hysteresis. It is preferable to use a material having a
coercive electric field of not more than 10 kV/mm.
[0159] Specified materials include ceramics containing, for
example, lead zirconate lead titanate, lead magnesium niobate, lead
nickel niobate, lead zinc niobate, lead manganese niobate, lead
antimony stannate, lead manganese tungstate, lead cobalt niobate,
barium titanate, sodium bismuth titanate, potassium sodium niobate,
and strontium bismuth tantalate singly or in mixture.
[0160] Especially, a material containing a major component of lead
zirconate, lead titanate, and lead magnesium niobate, or a material
containing a major component of sodium bismuth titanate is
preferably used, in order to obtain the product having a stable
composition with a high electromechanical coupling factor and a
piezoelectric constant and with small reactivity with the thin
plate sections 12a, 12b (ceramics) during the sintering of the
piezoelectric/electrostrictive layer 22.
[0161] It is also preferable to use ceramics obtained by adding, to
the material described above, for example, oxides of lanthanum,
calcium, strontium, molybdenum, tungsten. barium, niobium, zinc,
nickel, manganese, cerium, cadmium, chromium, cobalt, antimony,
iron, yttrium, tantalum, lithium, bismuth, and stannum singly or in
mixture.
[0162] For example. when lanthanum and/or strontium is contained in
the major components of lead zirconate, lead titanate, and lead
magnesium niobate, an advantage is obtained in some cases, for
example, in such a way that the coercive electric field and the
piezoelectric characteristic can be adjusted.
[0163] It is desirable to avoid the addition of a material such as
silica which tends to form glass, because of the following reason.
That is, the material such as silica tends to react with the
piezoelectric/electrostri- ctive material during the heat treatment
for the piezoelectric/electrostri- ctive layer 22. As a result, the
composition is varied, and the piezoelectric characteristic is
deteriorated.
[0164] On the other hand, it is preferable that the pair of
electrodes 24, 26 of the piezoelectric/electrostrictive element
18a, 18b are made of metal which is solid at room temperature and
which is excellent in electrical conductivity. For example, it is
possible to use elemental substance or alloy of, for example,
aluminum, titanium, chromium, iron, cobalt, nickel, copper, zinc,
niobium, molybdenum, ruthenium, palladium, rhodium, silver,
stannum, tantalum, tungsten, iridium, platinum, gold, and lead. It
is also preferable to use a cermet material obtained by dispersing,
in the metal described above, the same material as that of the
piezoelectric/electrostrictive layer 22 or the thin plate section
12a, 12b.
[0165] The material for the electrodes 24, 26 of the
piezoelectric/electrostrictive element 18a, 18b is selected and
determined depending on the method for forming the
piezoelectric/electrostrictive layer 22. For example, when the
piezoelectric/electrostrictive layer 22 is formed by sintering on
the first electrode 24 after the first electrode 24 is formed on
the thin plate section 12a, 12b, it is necessary for the first
electrode 24 to use high melting point metal such as platinum,
palladium, platinum-palladium alloy, and silver-palladium alloy
which does not change at the sintering temperature for the
piezoelectric/electrostrictive layer 22. However, the electrode
formation can be performed at a low temperature for the second
electrode 26 which is formed on the piezoelectric/electrostrictive
layer 22 after forming the piezoelectric/electrostrictive layer 22.
Therefore, it is possible for the second electrode 26 to use low
melting point metal such as aluminum, gold, and silver.
[0166] The thickness of the electrode 24, 26 also serves as a
factor to considerably decrease the displacement of the
piezoelectric/electrostrict- ive element 18a, 18b. Therefore, it is
preferable, especially for the electrode formed after the sintering
of the piezoelectric/electrostrictiv- e layer 22, to use organic
metal paste capable of obtaining a dense and thinner film after the
sintering, for example, a material such as gold resinate paste,
platinum resinate paste, and silver resinate paste.
[0167] The embodiment described above is illustrative of the case
in which the thickness of the movable section 20a, 20b formed
integrally at the forward end portion of the thin plate section
12a, 12b is thicker than the thickness Dd of the thin plate section
12a, 12b. Alternatively, as in a piezoelectric/electrostrictive
device 10d according to a fourth modified embodiment shown in FIG.
12, it is also preferable that the thickness of the movable section
20a, 20b is approximately the same as the thickness Dd of the thin
plate section 12a, 12b. Accordingly, when a part or an article is
attached to the movable section 20a, 20b, the part having a size
corresponding to the distance between the thin plate sections 12a,
12b can be attached between the movable section 20a, 20b so that
the part is interposed thereby. In this case, an adhesive area for
attaching the part (for example, the adhesive 38 shown in FIG. 7)
corresponds to the movable section 20a, 20b.
[0168] The piezoelectric/electrostrictive device 10 can be
preferably utilized for various sensors including, for example,
ultrasonic sensors, acceleration sensors, angular velocity sensors,
and mass sensors. A further advantage is obtained such that the
sensitivity of the sensor can be adjusted with ease by
appropriately adjusting the size of the object to be attached
between the end surfaces 34a, 34b or between the thin plate
sections 12a, 12b.
[0169] Next, piezoelectric/electrostrictive devices 10e to 10g
according to fifth to seventh embodiments will be explained as more
preferred embodiments of the present invention with reference to
FIGS. 13 to 15.
[0170] At first, as shown in FIG. 13, the
piezoelectric/electrostrictive device 10e according to the fifth
modified embodiment is constructed in approximately the same manner
as the piezoelectric/electrostrictive device 10 explained above.
However, for example, the arrangement of the
piezoelectric/electrostrictive element 18a, 18b differs in the
following points.
[0171] That is, the piezoelectric/electrostrictive element 18a, 18b
comprises the piezoelectric/electrostrictive layer 22 which has a
four-layered structure. The first electrode 24 is formed to have a
comb-shaped configuration to be located at the upper surface of the
first layer and the upper surface of the third layer. The second
electrode 26 is formed to have a comb-shaped configuration to be
located at the lower surface of the first layer, the upper surface
of the second layer, and the upper surface of the fourth layer.
[0172] Especially, the second electrode 26, which is located at the
lower surface of the first layer, is formed substantially
continuously ranging over the respective side surfaces of the thin
plate section 12a, 12b, the movable section 20a, 20b, and the
fixation section 14. Further, a part of the second electrode 26 is
separated at the side surface of the fixation section 14 to form a
slit 70.
[0173] The slit 70 is provided taking the following facts into
consideration. That is, (1) the actuator is not driven at the
rearward end portion 72 of the piezoelectric/electrostrictive
element 18a, 18b (portion ranging from the end of the slit 70 at
the rearward end side to the rearward end of the fixation section
14), (2) any short circuit is scarcely formed at the end of the
first terminal 28, and (3) the electrode material is arranged on
the lower surface of the piezoelectric/electrostrictive layer 22 at
the rearward end portion of the piezoelectric/electrostrictive
element 18a, 18b.
[0174] If the provision of the slit 70 is inversely unfavorable, it
is not necessarily indispensable to provide the slit 70. The slit
70 may be omitted.
[0175] In this embodiment, FIG. 13 is illustrative of the following
case. That is, the thickness Dd of the thin plate section 12a, 12b
is 0.05 mm. The distance Dh from the side surface of the first thin
plate section 12a to the second thin plate section as 12b is 1.3
mm. The length Di of the fixation section 14 (length of the
fixation section 14 in the axial direction of the
piezoelectric/electrostrictive device 10f) is 0.4 mm. The length Df
of the movable section 20a, 20b is 0.3 mm. The width Dj of the
movable section 20a, 20b is 0.25 mm. The protruding amount Dk of
the movable section 20a, 20b is 0.05 mm. The entire length Dm of
the piezoelectric/electrostrictive device 10f (distance from the
forward end of the movable section 20a, 20b to the rearward end of
the fixation section 14) is 1.9 mm. The minimum distance between
the end surfaces 34a, 34b (corresponding to the distance Lc shown
in FIG. 1) is 1.04 mm.
[0176] The dimension of each of the components is regulated within
a range of .+-.10% with respect to each of the dimensions described
above. In this embodiment, when the movable sections 20a, 20b are
connected to one another with a spacer member 37 composed of the
same material as that of the constitutive member as shown in FIG. 7
between the end surfaces 34a, 34b, it is possible to obtain the
piezoelectric/electrostrictive device having a resonance frequency
of 45.+-.10 Hz and a displacement of not less than 0. 5 .mu.m (30
Vpp).
[0177] FIG. 3 is illustrative of the case in which the respective
end surfaces of the piezoelectric/electrostrictive layer 22 having
the four-layered structure are aligned. However, it is preferable
that the end surfaces of the piezoelectric/electrostrictive layer
22 are disposed so that upper layers are gradually directed
inwardly to provide steps.
[0178] Next, as shown in FIG. 14, the
piezoelectric/electrostrictive device 10f according to the sixth
modified embodiment is constructed in approximately the same manner
as the piezoelectric/electrostrictive device 10e according to the
fifth modified embodiment. However, the arrangement of the
piezoelectric/electrostrictive element 18a, 18b differs in the
following points.
[0179] That is, the piezoelectric/electrostrictive element 18a, 18b
comprises the piezoelectric/electrostrictive layer 22 which has a
three-layered structure. The first electrode 24 is formed to have a
comb-shaped configuration to be located at a part of the lower
surface of the first layer and the upper surface of the second
layer. The second electrode 26 is formed to have a comb-shaped
configuration to be located at a part of the lower surface of the
first layer, the upper surface of the first layer, and the upper
surface of the third layer.
[0180] Especially, the first electrode 24 and the second electrode
26, which are located at the lower surface of the first layer, are
separated from each other at a part of the thin plate section 12a,
12b by the aid of a slit 70. The second electrode, which is located
at the lower surface of the first layer, is formed continuously
over a range from the slit 70 to the upper end of the movable
section 20a, 20b. The first electrode 24, which is located at the
lower surface of the first layer, is formed continuously over a
range from the slit 70 to the rearward end of the fixation section
14.
[0181] Next, as shown in FIG. 15, the
piezoelectric/electrostrictive device 10g according to the seventh
modified embodiment is constructed in approximately the same manner
as the piezoelectric/electrostrictive device 10f according to the
sixth modified embodiment. However, the formation pattern of the
pair of electrodes 24, 26 differs in the following points.
[0182] That is, the first electrode 24 is formed to have a
comb-shaped configuration to be located at the lower surface of the
first layer and the upper surface of the second layer of the
piezoelectric/electrostricti- ve layer 22. The second electrode 26
is formed to have a comb-shaped configuration to be located at the
upper surface of the first layer and the upper surface of the third
layer of the piezoelectric/electrostrictiv- e layer 22.
[0183] Especially, the first electrode 24, which is located at the
lower surface of the first layer, is formed continuously over the
respective side surfaces of the thin plate section 12a, 12b, the
movable section 20a, 20b, and the fixation section 14.
[0184] The difference from the piezoelectric/electrostrictive
device 10f according to the sixth modified embodiment will now be
explained. As shown in FIG. 14, in the
piezoelectric/electrostrictive device 10f according to the sixth
modified embodiment, both of the first electrode 24 and the second
electrode 26 are formed on the thin plate section 12a. Therefore,
the electrodes 24, 26, which have the mutually opposite polarities,
are located at the both ends of the piezoelectric/electrostri-
ctive element 18, 18b (the end corresponding to the forward end of
the movable section 20a, 20b and the end corresponding to the
rearward end of the fixation section 14).
[0185] On the other hand, as shown in FIG. 15, in the
piezoelectric/electrostrictive device 10g according to the seventh
modified embodiment, only the first electrode 24 is formed on the
thin plate section 12a, 12b. Therefore, the electrodes 24, which
have the mutually identical polarity are located at the both ends
of the piezoelectric/electrostrictive element 18a, 18b. The feature
of the polarity at the end as described above is utilized by
appropriately making combination with a circuit for which the
piezoelectric/electrostri- ctive device 10g is utilized.
[0186] The substantial driving portion of the
piezoelectric/electrostricti- ve element 18a, 18b is the portion at
which the pair of electrodes 24, 26 are overlapped with each other.
In the piezoelectric/electrostrictive device 10f according to the
sixth modified embodiment, as shown in FIG. 14, the substantial
driving portion is the portion at which the electrodes 24, 26
formed at the respective layers of the
piezoelectric/electrostrictive layer 22 are overlapped with each
other, which resides in one part corresponding to the portion
indicated by the range C.
[0187] On the other hand, the substantial driving portion of the
piezoelectric/electrostrictive device 10g according to the seventh
modified embodiment resides in two parts, i.e., the portion
(portion indicated by the range C) at which the electrodes 24, 26
formed at the respective layers of the
piezoelectric/electrostrictive layer 22 are overlapped with each
other, and the portion (portion indicated by the range D) which is
disposed at the position deviated toward the movable section 20a,
20b with respect to the end of the first electrode 24 formed at the
upper surface of the second layer of the piezoelectric/electrostri-
ctive layer 22 and at which the pair of electrodes 24, 26 are
overlapped with each other with the first layer of the
piezoelectric/electrostrictiv- e layer 22 intervening therebetween.
The piezoelectric/electrostrictive device 10g according to the
seventh modified embodiment is characterized in that the portion
indicated by the range D also serves as the driving source.
[0188] Next, explanation will be made with reference to FIGS. 16 to
40 for several methods for producing the
piezoelectric/electrostrictive device 10 according to the
embodiment of the present invention.
[0189] Ceramics is preferably used for the constitutive material
for each of the members of the piezoelectric/electrostrictive
device 10 according to the embodiment of the present invention. It
is preferable that the constitutive elements of the
piezoelectric/electrostrictive device 10 concerning the substrate
16 except for the piezoelectric/electrostrictive elements 18a, 18b,
i.e., the thin plate sections 12a, 12b, the fixation section 14,
and the movable sections 20a, 20b are produced by using the ceramic
green sheet-laminating method. On the other hand, it is preferable
that the piezoelectric/electrostrictive elements 18a, 18b as well
as the respective terminals 28, 30 are produced by using the film
formation method, for example, for the thin film and the thick
film.
[0190] According to the ceramic green sheet-laminating method in
which the respective members of the substrate 16 of the
piezoelectric/electrostrict- ive device 10 can be formed in an
integrated manner, the time-dependent change of state scarcely
occurs at the joined portions of the respective members. Therefore,
this method provides the high reliability of the joined portion,
and it is advantageous to ensure the rigidity.
[0191] In the piezoelectric/electrostrictive device 10 according to
this embodiment, the boundary portion (joined portion) between the
thin plate section 12a, l2b and the fixation section 14 and the
boundary portion (joined portion) between the thin plate section
12a, 12b and the movable section 20a, 20b function as supporting
points for expressing the displacement. Therefore, the reliability
of the joined portion is an important point which dominates the
characteristic of the piezoelectric/electrostrictive device 10.
[0192] The production methods described below are excellent in
reproducibility and formability. Therefore, it is possible to
obtain the piezoelectric/electrostrictive device 10 having a
predetermined shape within a short period of time with good
reproducibility.
[0193] A first production method for the
piezoelectric/electrostrictive device 10 according to the
embodiment of the present invention will be specifically explained
below. The following definitions are now made. The laminate, high
is obtained by laminating the ceramic green sheets, is defined to
be the ceramic green laminate 58 (see, for example, FIG. 17). The
integrated matter, which is obtained by sintering the ceramic green
laminate 58, is defined to be the ceramic laminate 60 (see, for
example, FIG. 18). The integrated matter comprising the movable
sections 20a, 20b, the thin plate sections 12a, 12b, and the
fixation section 14, which is obtained by cutting off unnecessary
portions from the ceramic laminate 60, is defined to be the ceramic
substrate 16C (see FIG. 19).
[0194] In the first production method, the ceramic laminate 60 is
finally cut into chip units in a form in which a plurality of
piezoelectric/electrostrictive devices 10 are arranged in the
vertical direction and in the lateral direction respectively on an
identical substrate to produce a large number of
piezoelectric/electrostrictive devices 10 in accordance with
identical steps. However, in order to simplify the explanation,
description will be made principally for the case in which one
individual of piezoelectric/electrostrictive device 10 is
produced.
[0195] At first, for example, a binder, a solvent, a dispersing
agent, and a plasticizer are added and mixed with a ceramic powder
such as zirconia to prepare a slurry. The slurry is subjected to a
degassing treatment, and then a ceramic green sheet having a
predetermined thickness is prepared in accordance with, for
example, the reverse roll coater method and the doctor blade
method.
[0196] Subsequently, the ceramic green sheet is processed into
those having various shapes as shown in FIG. 16 in accordance with,
for example, a method such as the punching out based on the mold
and the laser machining to obtain a plurality of ceramic green
sheets 50A to 50I, 52A, 52B for forming the substrate.
[0197] The ceramic green sheets 50A to 50I, 52A, 52B include the
plurality (for example, nine) of ceramic green sheets 50A to 50I
each of which is formed with at least a window 54 for forming the
space between the thin plate sections 12a, 12b, and the plurality
(for example, two) of ceramic green sheets 52A, 52B to be formed
into the thin plate sections 12a, 12b thereafter. The numbers of
ceramic green sheets referred to above are persistently by way of
example.
[0198] After that, as shown in FIG. 17, the ceramic green sheets
50A to 50I, 52A, 52B are laminated and secured under pressure so
that the ceramic green sheets 50A to 50I are interposed between the
ceramic green sheets 52A, 52B to form a ceramic green laminate 58.
Subsequently, the ceramic green laminate 58 is sintered to obtain a
ceramic laminate 60 (see FIG. 18).
[0199] It is noted that there is no limitation for the number of
pressure-securing process or processes and the sequence for the
purpose of the lamination and integration into one unit. These
factors can be appropriately determined depending on the structure,
for example, so that the desired structure is obtained on the basis
of, for example, the shape of the window 54 and the number of
ceramic green sheets.
[0200] It is unnecessary that the shape of the window 54 is
identical in all cases.. The shape of the window 54 can be
determined depending on the desired function. There is also no
limitation for the number of ceramic green sheets and the thickness
of each of the ceramic green sheets.
[0201] In the pressure-securing process, it is possible to further
improve the laminating performance by applying the heat. The
laminating performance at the boundary of the ceramic green sheet
can be improved by providing an auxiliary joining layer, for
example, by applying and printing, onto the ceramic green sheet, a
paste or a slurry principally containing a ceramic powder (it is
preferable to use a composition which is the same as or similar to
that of the ceramics used for the ceramic green sheet in order to
ensure the reliability), and a binder. When the ceramic green
sheets 52A, 52B are thin, it is preferable to handle them with a
plastic film, especially with a polyethylene terephthalate film
coated with a releasing agent based on silicone on the surface.
[0202] Subsequently, as shown in FIG. 18, the
piezoelectric/electrostricti- ve elements 18a, 18b are formed
respectively on the both surfaces of the ceramic laminate 60, i.e.,
on the surfaces corresponding to the surfaces at which the ceramic
green sheets 52A, 52B are laminated. Those usable as the method for
forming the piezoelectric/electrostrictive elements 18a, 18b
include the thick film formation method such as the screen printing
method the dipping method, the coating method, and the
electrophoresis method, and the thin film formation method such as
the ion beam method, the sputtering method, the vacuum vapor
deposition, the ion plating method, the chemical vapor deposition
method (CVD), and the plating.
[0203] When the piezoelectric/electrostrictive elements 18a, 18b
are formed by using the film formation method as described above,
the piezoelectric/electrostrictive elements 18a, 18b and the thin
plate sections 12a, 12b can be integrally joined and arranged
without using any adhesive. It is possible to ensure the
reliability and the reproducibility, and it is easy to form the
stack.
[0204] In this case, it is preferable that the
piezoelectric/electrostrict- ive elements 18a, 18b are formed by
means of the thick film formation method, because of the following
reason. That is, especially, when the
piezoelectric/electrostrictive layer 22 is formed by using the
thick film formation method, the film can be formed by using, for
example, a paste, a slurry, a suspension, an emulsion, or a sol
containing a major component of particles or powder of
piezoelectric ceramics having an average particle size of 0.01 to 5
.mu.m, preferably 0.05 to 3 .mu.m. It is possible to obtain good
piezoelectric/electrostrictive characteristics by sintering the
formed film.
[0205] The electrophoresis method is advantageous in that the film
can be formed at a high density with a high shape accuracy. The
screen printing method is advantageous to simplify the production
step, because it is possible to simultaneously perform the film
formation and the pattern formation.
[0206] Explanation will be specifically made for the formation of
the piezoelectric/electrostrictive elements 18a, 18b. At first, the
ceramic green laminate 58 is sintered and integrated into one unit
at a temperature of 1200.degree. C. to 1600.degree. C. to obtain
the ceramic laminate 60. After that, the first ones of the first
electrodes 24 for the thin plate sections 12a, 12b are printed and
sintered at predetermined positions on the both surfaces of the
ceramic laminate 60. Subsequently, the
piezoelectric/electrostrictive layers 22 are printed and sintered.
Further, the second electrodes 26, which form the pairs with the
first ones of the first electrodes 24, are printed and sintered to
form the piezoelectric/electrostrictive elements 18a, 18b by
repeating the foregoing steps in a predetermined number of times
(when the piezoelectric/electrostrictive element 18a, 18b is
composed of the multilayered piezoelectric/electrostrictive layer
22). After that, the terminals 28, 30 are printed and sintered in
order to electrically connect the respective electrodes 24, 26 to
the driving circuit.
[0207] Alternatively, the following process may be available. That
is, the first one of the first electrode 24 at the lowermost layer
is printed and sintered. The piezoelectric/electrostrictive layer
22 and the first one of the second electrode 26 which forms the
pair with the first one of the first electrode 24 are printed and
sintered. The printing and the sintering are repeated in a
predetermined number of times with the foregoing process unit to
form the piezoelectric/electrostrictive element 18a, 18b.
[0208] In this process, when the materials are selected so that the
sintering temperature for each of the members is lowered in
accordance with the stacking sequence, for example, when platinum
(Pt) is used for the first electrode 24, lead zirconate titanate
(PZT) is used for the piezoelectric/electrostrictive layer 22, gold
(Au) is used for the second electrode 26, and silver (Ag) is used
for the terminals 28, 30, then the material, which has been already
sintered beforehand, is not sintered again at a certain sintering
stage. Thus, it is possible to avoid the occurrence of
inconvenience such as peeling off and aggregation of the electrode
material or the like.
[0209] When appropriate materials are selected, it is also possible
to successively print the respective members of the
piezoelectric/electrostr- ictive elements 18a, 18b and the
terminals 28, 30, followed by the sintering one time. Further, it
is also possible to provide, for example, the electrode 26 at the
outermost layer at a low temperature after forming the
piezoelectric/electrostrictive layer 22 at the outermost layer.
[0210] Alternatively, the respective members of the
piezoelectric/electrostrictive elements 18a, 18b and the terminals
28, 30 may be formed by means of the thin film formation method
such as the sputtering method and the vapor deposition method. In
this case, it is not necessarily indispensable to perform the heat
treatment.
[0211] When the piezoelectric/electrostrictive elements 18a, 18b
are formed, it is also preferable that the
piezoelectric/electrostrictive elements 18a, 18b are previously
formed on the both surfaces of the ceramic green laminate 58, i.e.,
on the respective surfaces of the ceramic green sheets 52A, 52B,
and the ceramic green laminate 58 and the
piezoelectric/electrostrictive elements 18a, 18b are simultaneously
sintered or co-fired. For example, the following methods are
available to perform the co-firing. That is, the sintering may be
performed for all of the constitutive films of the ceramic green
laminate 58 and the piezoelectric/electrostrictive elements 18a,
18b. The first electrodes 24 and the ceramic green laminate 58 may
be co-fired, or the other constitutive films except for the second
electrodes 26 and the ceramic green laminate 58 may be
co-fired.
[0212] The following method is available to co-fire the
piezoelectric/electrostrictive elements 18a, 18b and the ceramic
green laminate 58. That is, precursors of the
piezoelectric/electrostrictive layers 22 are formed, for example,
in accordance with the tape formation method based on the use of a
slurry material. The precursors of the
piezoelectric/electrostrictive layers 22 before the sintering are
laminated on the surfaces of the ceramic green laminate 58, for
example, by means of the thermal securing process under pressure,
followed by the co-firing to simultaneously produce the movable
sections 20a, 20b, the thin plate sections 12a, 12b, the
piezoelectric/electrostrictive layers 22, and the fixation section
14. However, in this method, it is necessary to form the electrodes
24 beforehand on the surfaces of the ceramic green laminate 58
and/or on the piezoelectric/electrostrictive layers 22 by using the
film formation method described above.
[0213] Another method is also available. That is, the electrodes
24, 26 and the piezoelectric/electrostrictive layers 22, which are
the respective constitutive layers of the
piezoelectric/electrostrictive elements 18a, 18b, are formed by
means of the screen printing on portions to be finally formed into
at least the thin plate sections 12a, 12b of the ceramic green
laminate 58, followed by co-firing.
[0214] The sintering temperature for the constitutive film of the
piezoelectric/electrostrictive element 18a, 18b is appropriately
determined depending on the material for constructing the same.
However, the sintering temperature is generally 500.degree. C. to
1500.degree. C. The sintering temperature is preferably
1000.degree. C. to 1400.degree. C. for the
piezoelectric/electrostrictive layer 22. In this case, in order to
control the composition of the piezoelectric/electrostrictive layer
22, the sintering is preferably performed in the presence of an
evaporation source of the material of the
piezoelectric/electrostrictive layer 22. When the
piezoelectric/electrostrictive layers 22 and the ceramic green
laminate 58 are co-fired, it is necessary to conform the sintering
conditions of the both. The piezoelectric/electrostrictive element
18a, 18b is not necessarily formed on the both surfaces of the
ceramic laminate 60 or the ceramic green laminate 58. It is of
course allowable to form the piezoelectric/electrostrictive element
18a, 18b on only one surface.
[0215] Subsequently, unnecessary portions are cut off from the
ceramic laminate 60 formed with the piezoelectric/electrostrictive
elements 18a, 18b as described above. The cutoff positions are
located at side portions of the ceramic laminate 60, especially at
portions at which the hole 42 based on the window 54 is formed on
the side surfaces of the ceramic laminate 60 by means of the cutoff
(see cutting lines C1 and C2).
[0216] Subsequently, as shown in FIG. 19, a central portion 20c of
the portion to be formed into the movable sections 20a, 20b is cut
and removed along cutting lines C3 and C4 to produce the
piezoelectric/electrostrictive device 10 comprising the
piezoelectric/electrostrictive elements 18a, 18b formed on the
ceramic substrate 16C integrated with the movable sections 20a,
20b, the thin plate sections 12a, 12b, and the fixation section 14.
Those applicable as the cutoff method include the mechanical
machining such as the dicing machining and the wire saw machining
as well as the electron beam machining and the laser machining
based on the use of, for example, the YAG laser and the excimer
laser.
[0217] When the ceramic substrate 16C is cut off, the machining may
be performed by combining the machining methods described above.
For example, the wire saw machining is preferably performed for the
cutting lines C1 and C2 (see FIG. 18). The dicing machining is
preferably performed for the end surfaces 34a, 34b of the movable
sections 20a, 20b and the fixation section 14 perpendicular to the
cutting lines C1 and C2.
[0218] In the first production method for the
piezoelectric/electrostricti- ve device 10 described above, the
piezoelectric/electrostrictive elements 18a, 18b are formed on the
thin plate sections 12a, 12b by means of the integrated sintering.
Therefore, as shown in FIG. 20A, for example, the thin plate
sections 12a, 12b and the piezoelectric/electrostrictive elements
18a, 18b are slightly displaced to be convex toward the hole 42,
giving a state in which the strain is generated in shape, for
example, due to the shrinkage of the piezoelectric/electrostrictive
layers 22 caused during the sintering and the difference in
coefficient of thermal expansion among the pair of electrodes 24,
26, the piezoelectric/electrostrictive layers 22, and the thin
plate sections 12a, 12b. As a result, the internal residual stress
tends to arise in the piezoelectric/electrostrictive elements 18a,
18b (especially in the piezoelectric/electrostrictive layers 22)
and in the thin plate sections 12a, 12b.
[0219] The internal residual stress in the thin plate sections 12a,
12b and the piezoelectric/electrostrictive layers 22 is generated
when the integrated sintering is performed as described above as
well as when separate members of the piezoelectric/electrostrictive
elements 18a, 18b are bonded to the thin plate sections 12a, 12b,
for example, with an adhesive. That is, the internal residual
stress is generated in the thin plate sections 12a, 12b and the
piezoelectric/electrostrictive layers 22 due to the curing and
shrinkage of the adhesive or the like when the adhesive is
immobilized or cured. When the heating is required for the
immobilization or the curing, the internal residual stress is
increased.
[0220] If the piezoelectric/electrostrictive device 10 is used in
this state, the movable sections 20a, 20b do not exhibit any
desired displacement in some cases, even when the predetermined
electric field is applied to the piezoelectric/electrostrictive
layers 22, because of the following reason. That is, the material
characteristic of the piezoelectric/electrostrictive layers 22 and
the displacement action of the movable sections 20a, 20b are
inhibited by the internal residual stress generated in the thin
plate sections 12a, 12b and the piezoelectric/electrostrictive
layers 22.
[0221] In the first production method, as shown in FIG. 20A, the
central portion 20c of the movable section 20a, 20b is cut off by a
predetermined width W1 (for example, 100 km). When the central
portion 20c is cut off, the mutually opposing end surfaces 34a, 34b
are formed for the movable sections 20a, 20b as shown in FIG. 20B.
The end surfaces 34a, 34b are moved to make approach to one another
by the internal residual stress having been generated in the thin
plate sections 12a, 12b and the piezoelectric/electrostrictive
layers 22. The width between the respective end surfaces 34a, 34b
after the movement is, for example, a second predetermined width W2
(for example, 30 .mu.m) which is shorter than the predetermined
width W1. More specifically, the second predetermined width W2 is
shorter at forward end portions.
[0222] The movement of the end surfaces 34a, 34b results from the
release of the internal residual stress having been generated in
the thin plate sections 12a, 12b and the
piezoelectric/electrostrictive layers 22. When the
piezoelectric/electrostrictive device 10 is used in a state in
which the internal residual stress is released, then the movable
sections 20a, 20b exhibit the displacement action as approximately
designed, and the good device characteristic is exhibited. This
effect is equivalently obtained when a part of the portion to be
formed into the fixation section 14 is cut off to form the mutually
opposing end surfaces 34a, 34b for the fixation section 14, For
example, as shown in FIG. 11. In this case, the internal residual
stress, which has been generated in the thin plate sections 12a,
12b and the piezoelectric/electrostrictive layers 22, is released
by the movement of the mutually opposing end surfaces 34a, 34b
formed for the fixation section 14. The mutually opposing end
surfaces 34a, 34b are not necessarily section 20a, 20b or the
fixation section 14. An equivalent effect is also obtained even
when the mutually opposing end surfaces 34a, 34b are formed by
cutting a portion deviated from the center.
[0223] When the cutoff as shown in FIG. 18 and the cutoff as shown
in FIG. 19 are performed, it is preferable that the heat treatment
is performed at 300.degree. C. to 800.degree. C. after the cutoff,
because of the following reason. That is, any defect such as
microcrack tends to occur in the piezoelectric/electrostrictive
device 10 as a result of the machining, while the defect can be
removed by means of the heat treatment described above, and the
reliability is improved. Further, it is preferable to apply the
aging treatment by being left to stand for at least about 10 hours
at a temperature of about 80.degree. C. after the heat treatment,
because of the following reason. That is, when the aging treatment
is performed, for example, the various stresses, which have been
exerted during the production process, can be further mitigated to
contribute to the improvement in characteristic.
[0224] Next, a second production method will be explained with
reference to FIGS. 21 to 24. At first, as shown in FIG. 21, a
plurality (for example, four) of ceramic green sheets 50A to 50D
each of which is formed with a window 54 for forming at least the
space between the thin plate sections 12a, 12b, a plurality (for
example, seven) of ceramic green sheets 102A to 102G each of which
is continuously formed with a window 54 for forming the space
between the thin plate sections 12a, 12b and a window 100 for
forming the movable sections 20a, 20b having the mutually opposing
end surfaces 34a, 34b, and a plurality (for example, two) of
ceramic green sheets 52A, 52B to be formed into the thin plate
sections 12a, 12b thereafter are prepared.
[0225] After that, as shown in FIG. 22, the ceramic green sheets
50A to 50D, 52A, 52B, 102A to 102G are laminated and secured under
pressure so that the ceramic green sheets 50A to 50D, 102A to 102G
are interposed between the ceramic green sheets 52A, 52B to form a
ceramic green laminate 58. The lamination is performed while the
ceramic green sheets 102A to 102G are positioned at the center.
During this process, there may be portions on which no pressure is
applied during the securing under pressure, due to the presence of
the window 100. Therefore, for example, it is necessary that the
order of the lamination and the pressure-securing is changed so
that such portions do not appear. This procedure is also
significant in third and fourth production methods described later
on. After that, the ceramic green laminate 58 is sintered to obtain
a ceramic laminate 60 (see FIG. 23).
[0226] Subsequently, as shown in FIG. 23, the
piezoelectric/electrostricti- ve elements 18a, 18b having the
multilayered structure are formed respectively on the both surfaces
of the ceramic laminate 60, i.e., on the surfaces corresponding to
the surfaces at which the ceramic green sheets 52A, 52B are
laminated respectively. The piezoelectric/electrostri- ctive
elements 18a, 18b are integrated into the ceramic laminate 60 by
means of the sintering. Of course, it is allowable to form the
piezoelectric/electrostrictive element 18 on only one side surface.
This fact also holds for the third and fourth production methods
described later on.
[0227] Subsequently, the ceramic laminate 60, which is formed with
the piezoelectric/electrostrictive elements 18a, 18b, is cut along
cutting lines C1, C2, C5 to thereby cut off side portions and
forward end portions of the ceramic laminate 60. As a result of the
cutoff, as shown in FIG. 24, the piezoelectric/electrostrictive
device 10 is obtained, which is formed with the movable sections
20a, 20b having the mutually opposing end surfaces 34a, 34b in
which the piezoelectric/electrostrictiv- e elements 18a, 18b are
formed on the ceramic substrate 16C. The following cutting timing
is available. That is, the ceramic laminate 60 may be cut along the
cutting lines C1 and C2, and then it may be cut along the cutting
line C5. Alternatively, the ceramic laminate 60 may be cut along
the cutting line C5, and then it may be cut along the cutting lines
C1 and C2. Of course, it is also preferable to perform the
foregoing cutting procedures at the same time. The end of the
fixation section 14, which is opposed to the cutting line C5, may
be appropriately cut.
[0228] In the second production method, the
piezoelectric/electrostrictive elements 18a, 18b are formed on the
ceramic substrate 16C simultaneously with the cutoff of the
unnecessary portions from the ceramic laminate 60, making it
possible to obtain the piezoelectric/electrostrictive device 10
formed with the movable sections 20a, 20b having the mutually
opposing end surfaces 34a, 34b. Accordingly, it is possible to
simplify the production steps. Further, it is possible to improve
the yield of the piezoelectric/electrostrictive device 10. In this
procedure, it is especially preferable that a plurality of
piezoelectric/electrostrictive devices 10 are arranged in the
vertical direction and in the lateral direction respectively on an
identical substrate to produce a large number of
piezoelectric/electrostrictive devices 10 in accordance with
identical steps, because of the following reason. That is, a large
number of individuals are easily dealt with in the identical step
concerning the formation of the end surfaces 34a, 34b as compared
with the first production method.
[0229] Next, a third production method will be explained with
reference to FIGS. 25 to 28. At first, as shown in FIG. 25, a
plurality (for example, four) of ceramic green sheets 50A to 50D
each of which is formed with a window 54 for forming at least the
space between the thin plate sections 12a, 12b, a plurality (for
example, seven) of ceramic green sheets 108A to 108G each of which
is continuously formed with a window 54 for forming the space
between the thin plate sections 12a, 12b and a window 104 for
forming a portion 20D (see FIG. 28) to be formed into the movable
sections 20a, 20b with the mutually opposing end surfaces 34a, 34b
partially connected to one another and which is formed with a
projection 106 partially protruding toward the window 54, and a
plurality (for example, two) of ceramic green sheets 52A, 52B to be
formed into the thin plate sections l2a, 12b thereafter are
prepared.
[0230] After that, as shown in FIG. 26, the ceramic green sheets
50A to 50D, 52A, 52B, 198A to 108G are laminated and secured under
pressure so that the ceramic green sheets 50A to 50D, 108A to 108G
are interposed between the ceramic green sheets 52A, 52B to form a
ceramic green laminate 58. The lamination is performed while the
ceramic green sheets 108A to 108G are positioned at the center.
After that, the ceramic green laminate 58 is sintered to obtain a
ceramic laminate 60 (see FIG. 27).
[0231] Subsequently, as shown in FIG. 27, the
piezoelectric/electrostricti- ve elements 18a, 18b having the
multilayered structure are formed respectively on the both surfaces
of the ceramic laminate 60, i.e., on the surfaces corresponding to
the surfaces at which the ceramic green sheets 52A, 52B are
laminated. The piezoelectric/electrostrictive elements 18a, 18b are
integrated into the ceramic laminate 60 by means of the
sintering.
[0232] Subsequently, the. ceramic laminate 60 , which is formed
with the piezoelectric/electrostrictive elements 18a, 18b, is cut
along cutting lines C1, C2, C5 to thereby cut off side portions and
forward end portions of the ceramic laminate 60. As a result of the
cutoff, as shown in FIG. 28, the fixation section 14, the thin
plate sections 12a, 12b, and the piezoelectric/electrostrictive
elements 18a, 18b are formed. However the portion 20D to be formed
into the movable sections 20a, 20b is in a state in which the
mutually opposing end surfaces 34a, 34b are partially connected to
one another by the projection 106.
[0233] Subsequently, the projection 106, which partially connects
the mutually opposing end surfaces 34a, 34b, is cut off to produce
the piezoelectric/electrostrictive device 10 in which the
piezoelectric/electrostrictive elements 18a, 18b are formed on the
ceramic substrate 16C integrated with the movable sections 20a,
20b, the thin plate sections 12a, 12b, and the fixation section
14.
[0234] In the third production method, it is enough that the
slender projection 106, which partially connects the mutually
opposing end surfaces 34a, 34b, is cut off at the final stage.
Accordingly, the cutoff procedure can be performed easily and
reliably, and thus it is possible to simplify the production steps.
Further, it is possible to improve the yield of the
piezoelectric/electrostrictive device 10.
[0235] Next, a fourth production method will be explained with
reference to FIGS. 29 to 32. At first, as shown in FIG. 29, a
plurality (for example, four) of ceramic green sheets 50A to 50D
each of which is formed with a window 54 for forming at least the
space between the thin plate sections 12a, 12b, a plurality (for
example, seven) ceramic green sheets 114A to 114G each of which is
formed with a window 54 for forming the space between the thin
plate sections 12a, 12b and a window 104 for forming a portion 20D
(see FIG. 32) to be formed into the movable sections 20a, 20b with
the mutually opposing end surfaces 34a, 34b partially connected to
one another and which is formed with a crosspiece 112 to separate
the window 54 and the window 104 from each other, and a plurality
(for example, two) of ceramic green sheets 52A, 52B to be formed
into the thin plate sections 12a, 12b thereafter are prepared.
[0236] After that, as shown in FIG. 30, the ceramic green sheets
50A to 50D, 52A, 52B, 114A to 114G are laminated and secured under
pressure so that the ceramic green sheets 50A to 50D, 114A to 114G
are interposed between the ceramic green sheets 52A, 52B to form a
ceramic green laminate 58. The lamination is performed while the
ceramic green sheets 114A to 114G are positioned at the center.
After that, the ceramic green laminate 58 is sintered to obtain a
ceramic laminate 60 (see FIG. 31).
[0237] Subsequently, as shown in FIG. 31, the
piezoelectric/electrostricti- ve elements 18a, 18b having the
multilayered structure are formed respectively on the both surfaces
of the ceramic laminate 60, i.e., on the surfaces corresponding to
the surfaces at which the ceramic green sheets 52A, 52B are
laminated. The piezoelectric/electrostrictive elements 18a, 18b are
integrated into the ceramic laminate 60 by means of the
sintering.
[0238] Subsequently, the ceramic laminate 60, which is formed with
the piezoelectric/electrostrictive elements 18a, 18b, is cut along
cutting lines C1, C2, C5 to thereby cut off side portions and
forward end portions of the ceramic laminate 60. As a result of the
cutoff, as shown in FIG. 32, the fixation section 14, the thin
plate sections 12a, 12b, and the piezoelectric/electrostrictive
elements 18a, 18b are formed. However, the portion 20D to be formed
into the movable sections 20a, 20b is in a state in which the
mutually opposing end surfaces 34a, 34bare partially connected to
one another by the crosspiece 112.
[0239] Subsequently, the crosspiece 112, which partially connects
the mutually opposing end surfaces 34a, 34b, is cut off to produce
the piezoelectric/electrostrictive device 10 in which
piezoelectric/electrost- rictive elements 18a, 18b are formed on
the ceramic substrate 16C integrated with the movable sections 20a
20b, thin plate sections 12a, 12b, and the fixation section 14.
[0240] In the fourth production method, it is enough that the
crosspiece 112, which partially connects the mutually opposing end
surfaces 34a, 34b, is cut off at the final stage. Accordingly, the
cutoff procedure can be performed easily and reliably, and thus it
is possible to simplify the production steps. Further, it is
possible to improve the yield of the piezoelectric/electrostrictive
device 10.
[0241] The embodiments described above are illustrative of the case
in which the movable sections 20a, 20b, the fixation section 14,
and the thin plate sections 12a, 12b are constructed by the ceramic
substrate 16C. Alternatively, each of the parts may be made of a
metal material. Further alternatively, each of the parts may be
made to provide a hybrid structure obtained by combining those
produced with materials of ceramics and metal. In this case, in
order to join the metal materials to one another and/or join the
ceramic and metal materials to one another, it is possible to use
adhesion with organic resin or glass, brazing, soldering, eutectic
bonding, or welding.
[0242] Explanation will be made with reference to FIGS. 33 to 40,
for example, for production methods (fifth and sixth production
methods) for a piezoelectric/electrostrictive device
(piezoelectric/electrostrictive device 10h according to an eighth
modified embodiment) having the hybrid structure in which the
movable sections 20a, 20b and the fixation section 14 are made of
ceramics, and the thin plate sections 12a, 12b are made of metal.
Therefore, the substrate containing metal and ceramics, which is
produced by the fifth and sixth production methods, is referred to
as the substrate 16D.
[0243] In the fifth production method, at first, as shown in FIG.
33, a plurality (for example, four) of ceramic green sheets 50A to
50D each of which is formed with a window 54 for forming at least
the space between the thin plate sections 12a, 12b, and a plurality
(for example, seven) ceramic green sheets 102A to 102G each of
which is continuously formed with a window 54 for forming the space
between the thin plate sections 12a, 12b and a window 100 for
forming the movable sections 20a, 20b having the mutually opposing
end surfaces 34a, 34b are prepared.
[0244] After that, as shown in FIG. 34, the ceramic green sheets
50A to 50D, 102A to 102G are laminated and secured under pressure
to form a ceramic green laminate 158. The lamination is performed
while the ceramic green sheets 102A to 102G are positioned at the
center. After that, as shown in FIG. 35, the ceramic green laminate
158 is sintered to obtain a ceramic laminate 160. At this stage,
the ceramic laminate 160 is formed such that the hole 130 is formed
by the windows 54, 100.
[0245] Subsequently, as shown in FIG. 36, the
piezoelectric/electrostricti- ve elements 18a, 18b, which are
constructed as separate members, are respectively bonded with an
epoxy adhesive to the surfaces of metal plates 152A, 152B to serve
as the thin plate sections 12a, l2b. The separate members of the
piezoelectric/electrostrictive elements 18a, 18b can be formed, for
example, in accordance with the ceramic green sheet-laminating
method.
[0246] Subsequently, the metal plates 152A, 152B are bonded to the
ceramic laminate 160 with the epoxy adhesive so that the ceramic
laminate 160 is interposed between the metal plates 152A. 152B and
the hole 130 is closed thereby to provide a hybrid laminate 162
(see FIG. 37).
[0247] Subsequently, as shown in FIG. 37, the hybrid laminate 162,
which is formed with the piezoelectric/electrostrictive elements
18a, 18b, is cut along cutting lines C1, C2, C5 to thereby cut off
side portions and forward end portions of the hybrid laminate 162.
As a result of the cutoff, as shown in FIG. 38, the
piezoelectric/electrostrictive device 10h according to the eighth
modified embodiment is obtained, in which the
piezoelectric/electrostrictive elements 18a, 18b are formed on the
thin plate sections 12a, 12b constituted by the metal plates, of
the substrate 16D, and the movable sections 20a, 20b having the
mutually opposing end surfaces 34a, 34b are formed.
[0248] On the other hand, in the sixth production method, at first,
as shown in FIG. 34, ceramic green sheets 50A to 50D, 102A to 102G
are laminated and secured under pressure to form a ceramic green
laminate 158. After that, the ceramic green laminate 158 is
sintered to obtain a ceramic laminate 160 as shown in FIG. 39. At
this stage, the ceramic laminate 160 is formed such that the hole
130 is formed by the windows 54, 100.
[0249] Subsequently, as shown in FIG. 40, the metal plates 152A,
152B are bonded to the ceramic laminate 160 with an epoxy adhesive
so that the ceramic laminate 160 as interposed between the metal
plates 152A, 152B and the hole 130 is closed thereby to provide a
hybrid laminate 162. In this procedure, when the
piezoelectric/electrostrictive elements 18a, 18b are stuck to the
surfaces of the bonded metal plates 152A, 152B, the hole 130 is
optionally filled with a filler material 164 as shown in FIG. 39 so
that a sufficient bonding pressure may be applied.
[0250] It is necessary to finally remove the filler material 164.
Therefore, it is preferable to use a hard material which is easily
dissolved in a solvent or the like. The material includes, for
example, organic resin, wax, and brazing filler material. It is
also possible to adopt a material obtained by mixing ceramic powder
as a filler with organic resin such as acrylic.
[0251] Subsequently, as shown in FIG. 40, the
piezoelectric/electrostricti- ve elements 18a, 18b, which are
constructed as separate members, are bonded with an epoxy adhesive
to the surfaces of the metal plates 152A, 152B of the hybrid
laminate 162. The separate members of the
piezoelectric/electrostrictive elements 18a, 18b can be formed, for
example, in accordance with the ceramic green sheet-laminating
method.
[0252] Subsequently, the same steps as those illustrated in FIGS.
37 and 38 are performed as described above to obtain the
piezoelectric/electrost- rictive device 10h according to the eighth
modified embodiment in which the piezoelectric/electrostrictive
elements 18a, 18b are formed on the thin plate sections 12a, 12b
constituted by the metal plates 152A, 152B, of the substrate 16D,
and the movable sections 20a, 20b having the mutually opposing end
surfaces 34a, 34b are formed.
[0253] When all of the substrate 16D is made of metal, for example,
the portions corresponding to the ceramic laminate 160 shown in
FIG. 35 are formed by means of molding. Further, thin metal
materials may be laminated to form the substrate 16D in accordance
with the cladding method.
[0254] The piezoelectric/electrostrictive device described above
can be utilized as the active device including, for example,
various transducers, various actuators, frequency region functional
parts (filters), transformers, vibrators, resonators, oscillators,
and discriminators for the communication and the power generation,
as well as the sensor element for various sensors including, for
example, ultrasonic sensors, acceleration sensors, angular velocity
sensors, shock sensors, and mass sensors. Especially, the
piezoelectric/electrostrictive device described above can be
preferably utilized for various actuators to be used for the
mechanism for adjusting the displacement and the positioning and
for adjusting the angle for various precision parts such as those
of optical instruments and precision mechanical equipments.
[0255] It is a matter of course that the
piezoelectric/electrostrictive device and the method for producing
the same according to the present invention are not limited to the
embodiments described above, which may be embodied in other various
forms without deviating from the gist or essential characteristics
of the present invention.
* * * * *