U.S. patent application number 10/200861 was filed with the patent office on 2002-12-19 for piezoelectric/electrostrictive device.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Kimura, Koji, Komazawa, Masato, Nanataki, Tsutomu, Takeuchi, Yukihisa.
Application Number | 20020190609 10/200861 |
Document ID | / |
Family ID | 27554414 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020190609 |
Kind Code |
A1 |
Takeuchi, Yukihisa ; et
al. |
December 19, 2002 |
Piezoelectric/electrostrictive device
Abstract
A piezoelectric/electrostrictive device including a driving
portion, a movable portion, and a fixing portion for holding the
driving portion and the movable portion, the fixing portion and the
movable portion being coupled via the driving portion along a
length direction of the device. It is preferred that the driving
portion, the movable portion and the fixing portion are made of
electrically insulating materials. The driving portion is composed
of a mutually opposed pair of thin plate portions and at least
first and second piezoelectric/electrostrictive elements. Each of
the piezoelectric/electrostrictive elements includes an operating
portion having a width that is substantially the same as the width
of each respective thin plate portion.
Inventors: |
Takeuchi, Yukihisa;
(Nishikamo-Gun, JP) ; Nanataki, Tsutomu;
(Toyoake-City, JP) ; Komazawa, Masato;
(Nagoya-City, JP) ; Kimura, Koji; (Nagoya-City,
JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
27554414 |
Appl. No.: |
10/200861 |
Filed: |
July 23, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10200861 |
Jul 23, 2002 |
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09642861 |
Aug 21, 2000 |
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6476539 |
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09642861 |
Aug 21, 2000 |
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09473835 |
Dec 28, 1999 |
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6323582 |
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Current U.S.
Class: |
310/330 |
Current CPC
Class: |
H01L 41/43 20130101;
H01L 41/0946 20130101 |
Class at
Publication: |
310/330 |
International
Class: |
H01L 041/09 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 1, 1999 |
JP |
11-281522 |
Oct 28, 1999 |
JP |
11-307844 |
Dec 27, 1999 |
JP |
11-371967 |
Nov 16, 1999 |
JP |
11-326195 |
Jul 6, 2000 |
JP |
2000-204758 |
Claims
1. A piezoelectric/electrostrictive device comprising a driving
portion to be driven by displacement of a
piezoelectric/electrostrictive element, a movable portion to be
operated by driving said driving portion, and a fixing portion for
holding said driving portion and said movable portion, said fixing
portion and said movable portion being coupled via said driving
portion along a length direction of said device, and a hole formed
by inner walls of the driving portion, an inner wall of the movable
portion, and an inner wall of the fixing portion, said
piezoelectric/electrostrictive device being characterized in that
said driving portion is composed of a mutually opposed pair of thin
plate portions and at least first and second
piezoelectric/electrostrictive elements each comprising one or more
pairs of electrodes and a piezoelectric/electrostrictive film;
wherein one end of said first piezoelectric/electrostrictive
element and a piezoelectric/electrostricti- ve operating portion
thereof at said end are positioned on the fixing portion and extend
in said length direction to a least a part of a first one of the
thin plate portions such that an opposite end of said
piezoelectric/electrostrictive operating portion of said first
piezoelectric/electrostrictive element is positioned on said first
thin plate portion; wherein one end of said second
piezoelectric/electrostrict- ive element and a
piezoelectric/electrostrictive operating portion thereof at said
end are positioned on the movable portion and extend in said length
direction to at least a part of the second one of said thin plate
portions such that an opposite end of said
piezoelectric/electrostrictive operating portion of said second
piezoelectric/electrostrictive element is positioned on said second
thin plate portion; and wherein the width of each
piezoelectric/electrostrictive operating portion is substantially
the same as the width of each respective thin plate portion.
2. A piezoelectric/electrostrictive device according to claim 1,
further comprising, on an outer surface of at least one of the thin
plate portions, a third piezoelectric/electrostrictive element
comprising one or more pairs of electrodes and a
piezoelectric/electrostrictive film, at least one end of the third
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion thereof at said at
least one end are arranged on the movable portion or the fixing
portion and extend to at least a part of the first or second thin
plate portions, respectively, and an opposite end of said
piezoelectric/electrostrictive operating portion of said third
piezoelectric/electrostrictive element is arranged on the first or
second thin plate portions, respectively, such that said third
piezoelectric/electrostrictive element is mutually opposed to one
of the first and second piezoelectric/electrostrictive elements in
a diagonal direction across said hole.
3. A piezoelectric/electrostrictive device according to claim 2,
wherein said third piezoelectric/electrostrictive element is formed
on said first thin plate portion.
4. A piezoelectric/electrostrictive device according to claim 2,
wherein said opposite ends of the piezoelectric/electrostrictive
operating portions of any two piezoelectric/electrostrictive
elements provided mutually opposed on the outer surface of the same
thin plate portion are arranged at positions not to exceed one half
of the length of the respective thin plate portion.
5. A piezoelectric/electrostrictive device according to claim 3,
wherein said opposite ends of the piezoelectric/electrostrictive
operating portions of any two piezoelectric/electrostrictive
elements provided mutually opposed on the outer surface of the same
thin plate portion are arranged at positions not to exceed one half
of the length of the respective thin plate portion.
6. A piezoelectric/electrostrictive device according to claim 2,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion share a piezoelectric/electrostrictive film.
7. A piezoelectric/electrostrictive device according to claim 3,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion share a piezoelectric/electrostrictive film.
8. A piezoelectric/electrostrictive device according to claim 2,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have the same function.
9. A piezoelectric/electrostrictive device according to claim 3,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have the same function.
10. A piezoelectric/electrostrictive device according to claim 2,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have different functions.
11. A piezoelectric/electrostrictive device according to claim 1,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have the same
function.
12. A piezoelectric/electrostrictive device according to claim 2,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have the same
function.
13. A piezoelectric/electrostrictive device according to claim 3,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have the same
function.
14. A piezoelectric/electrostrictive device according to claim 1,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have mutually
different functions.
15. A piezoelectric/electrostrictive device according to claim 2,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have mutually
different functions.
16. A piezoelectric/electrostrictive device according to claim 3,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have mutually
different functions.
17. A piezoelectric/electrostrictive device according to claim 1,
wherein at least one of said piezoelectric/electrostrictive
elements has a multi-layered piezoelectric/electrostrictive
operating portion.
18. A piezoelectric/electrostrictive device according to claim 2,
wherein at least one of said piezoelectric/electrostrictive
elements has a multi-layered piezoelectric/electrostrictive
operating portion.
19. A piezoelectric/electrostrictive device according to claim 3,
wherein at least one of said piezoelectric/electrostrictive
elements has a multi-layered piezoelectric/electrostrictive
operating portion.
20. A piezoelectric/electrostrictive device according to claim 2,
wherein said third piezoelectric/electrostrictive element is formed
on said second thin plate portion.
21. A piezoelectric/electrostrictive device according to claim 3,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have different functions.
22. A piezoelectric/electrostrictive device according to claim 3,
further comprising, on an outer surface of said second thin plate
portion, a fourth piezoelectric/electrostrictive element comprising
one or more pairs of electrodes and a
piezoelectric/electrostrictive film, one end of said fourth
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion thereof at said
one end are arranged on the fixing portion and extend to at least a
part of said second thin plate portion, and an opposite end of said
piezoelectric/electrostrictive operating portion of said fourth
piezoelectric/electrostrictive element is arranged on said second
thin plate portion, such that said fourth
piezoelectric/electrostrictive element is mutually opposed to said
third piezoelectric/electrostrictive element in a diagonal
direction across said hole.
23. A piezoelectric/electrostrictive device according to claim 20,
further comprising, on an outer surface of said first thin plate
portion, a fourth piezoelectric/electrostrictive element comprising
one or more pairs of electrodes and a
piezoelectric/electrostrictive film, one end of said fourth
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion thereof at said
one end are arranged on the movable portion and extend to at least
a part of said first thin plate portion, and an opposite end of
said piezoelectric/electrostrictive operating portion of said
fourth piezoelectric/electrostrictive element is arranged on said
first thin plate portion, such that said fourth
piezoelectric/electrostrictive element is mutually opposed to said
third piezoelectric/electrostrictive element in a diagonal
direction across said hole.
24. A piezoelectric/electrostrictive device comprising a driving
portion to be driven by displacement of a
piezoelectric/electrostrictive element, a movable portion to be
operated by driving said driving portion, and a fixing portion for
holding said driving portion and said movable portion, said fixing
portion and said movable portion being coupled via said driving
portion along a length direction of said device, and a hole formed
by inner walls of the driving portion, an inner wall of the movable
portion, and an inner wall of the fixing portion, said
piezoelectric/electrostrictive device being characterized in that
said driving portion is composed of a mutually opposed pair of thin
plate portions and at least first and second
piezoelectric/electrostrictive elements each comprising one or more
pairs of electrodes and a piezoelectric/electrostrictive film;
wherein one end of said first piezoelectric/electrostrictive
element and a piezoelectric/electrostricti- ve operating portion
thereof at said end are positioned on the fixing portion and extend
in said length direction to a least a part of a first one of the
thin plate portions such that an opposite end of said
piezoelectric/electrostrictive operating portion of said first
piezoelectric/electrostrictive element is positioned on said first
thin plate portion; wherein one end of said second
piezoelectric/electrostrict- ive element and a
piezoelectric/electrostrictive operating portion thereof at said
end are positioned on the movable portion and extend in said length
direction to at least a part of the second one of said thin plate
portions such that an opposite end of said
piezoelectric/electrostrictive operating portion of said second
piezoelectric/electrostrictive element is positioned on said second
thin plate portion; and wherein said driving portion, said movable
portion and said fixing portion comprise electrically insulating
materials.
25. A piezoelectric/electrostrictive device according to claim 24,
further comprising, on an outer surface of at least one of the thin
plate portions, a third piezoelectric/electrostrictive element
comprising one or more pairs of electrodes and a
piezoelectric/electrostrictive film, at least one end of the third
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion thereof at said at
least one end are arranged on the movable portion or the fixing
portion and extend to at least a part of the first or second thin
plate portions, respectively, and an opposite end of said
piezoelectric/electrostrictive operating portion of said third
piezoelectric/electrostrictive element is arranged on the first or
second thin plate portions, respectively, such that said third
piezoelectric/electrostrictive element is mutually opposed to one
of the first and second piezoelectric/electrostrictive elements in
a diagonal direction across said hole.
26. A piezoelectric/electrostrictive device according to claim 25,
wherein said third piezoelectric/electrostrictive element is formed
on said first thin plate portion.
27. A piezoelectric/electrostrictive device according to claim 25,
wherein said opposite ends of the piezoelectric/electrostrictive
operating portions of any two piezoelectric/electrostrictive
elements provided mutually opposed on the outer surface of the same
thin plate portion are arranged at positions not to exceed one half
of the length of the respective thin plate portion.
28. A piezoelectric/electrostrictive device according to claim 26,
wherein said opposite ends of the piezoelectric/electrostrictive
operating portions of any two piezoelectric/electrostrictive
elements provided mutually opposed on the outer surface of the same
thin plate portion are arranged at positions not to exceed one half
of the length of the respective thin plate portion.
29. A piezoelectric/electrostrictive device according to claim 25,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion share a piezoelectric/electrostrictive film.
30. A piezoelectric/electrostrictive device according to claim 26,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion share a piezoelectric/electrostrictive film.
31. A piezoelectric/electrostrictive device according to claim 25,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have the same function.
32. A piezoelectric/electrostrictive device according to claim 26,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have the same function.
33. A piezoelectric/electrostrictive device according to claim 25,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have different functions.
34. A piezoelectric/electrostrictive device according to claim 24,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have the same
function.
35. A piezoelectric/electrostrictive device according to claim 25,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have the same
function.
36. A piezoelectric/electrostrictive device according to claim 26,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have the same
function.
37. A piezoelectric/electrostrictive device according to claim 24,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have mutually
different functions.
38. A piezoelectric/electrostrictive device according to claim 25,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have mutually
different functions.
39. A piezoelectric/electrostrictive device according to claim 26,
wherein piezoelectric/electrostrictive elements existing in
mutually diagonal directions across said hole have mutually
different functions.
40. A piezoelectric/electrostrictive device according to claim 24,
wherein at least one of said piezoelectric/electrostrictive
elements has a multi-layered piezoelectric/electrostrictive
operating portion.
41. A piezoelectric/electrostrictive device according to claim 25,
wherein at least one of said piezoelectric/electrostrictive
elements has a multi-layered piezoelectric/electrostrictive
operating portion.
42. A piezoelectric/electrostrictive device according to claim 26,
wherein at least one of said piezoelectric/electrostrictive
elements has a multi-layered piezoelectric/electrostrictive
operating portion.
43. A piezoelectric/electrostrictive device according to claim 25,
wherein said third piezoelectric/electrostrictive element is formed
on said second thin plate portion.
44. A piezoelectric/electrostrictive device according to claim 26,
wherein two of the piezoelectric/electrostrictive elements that are
provided mutually opposed on the outer surface of the same thin
plate portion have different functions.
45. A piezoelectric/electrostrictive device according to claim 26,
further comprising, on an outer surface of said second thin plate
portion, a fourth piezoelectric/electrostrictive element comprising
one or more pairs of electrodes and a
piezoelectric/electrostrictive film, one end of said fourth
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion thereof at said
one end are arranged on the fixing portion and extend to at least a
part of said second thin plate portion, and an opposite end of said
piezoelectric/electrostrictive operating portion of said fourth
piezoelectric/electrostrictive element is arranged on said second
thin plate portion, such that said fourth
piezoelectric/electrostrictive element is mutually opposed to said
third piezoelectric/electrostrictive element in a diagonal
direction across said hole.
46. A piezoelectric/electrostrictive device according to claim 43,
further comprising, on an outer surface of said first thin plate
portion, a fourth piezoelectric/electrostrictive element comprising
one or more pairs of electrodes and a
piezoelectric/electrostrictive film, one end of said fourth
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion thereof at said
one end are arranged on the movable portion and extend to at least
a part of said first thin plate portion, and an opposite end of
said piezoelectric/electrostrictive operating portion of said
fourth piezoelectric/electrostrictive element is arranged on said
first thin plate portion, such that said fourth
piezoelectric/electrostrictive element is mutually opposed to said
third piezoelectric/electrostrictive element in a diagonal
direction across said hole.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuation-in-part application of U.S. Ser. No.
09/473,835 filed on Dec. 28, 1999, the entirety of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0002] The present invention relates to a
piezoelectric/electrostrictive device comprising a movable portion
being operated based on a displacement of a
piezoelectric/electrostrictive element, or a
piezoelectric/electrostrictive device capable of detecting a
displacement of a movable portion by a
piezoelectric/electrostrictive element, and more particularly
relates to a piezoelectric/electrostrictive device which is
superior in mechanical strength, impact resistance, and humidity
resistance and is capable of having the movable portion efficiently
operated in a large magnitude.
[0003] In recent years, in the fields of optics and magnetic
recording, precision machining, and the like, a displacement
element capable of adjusting an optical path length and position in
sub-micron order has been required, and development has been
progressed of the displacement element utilizing displacement due
to the inverse piezoelectric effect or the electrostrictive effect
caused when a voltage is applied to a
piezoelectric/electrostrictive material (for example, a
ferroelectric substance or the like). For example, as shown in FIG.
14, a piezoelectric actuator 21, in which a fixing portion 25, a
movable portion 24, and a beam 26 connecting the two are integrally
formed by providing a hole 28 on a plate-like body composed of a
piezoelectric/electrostrictive material, and an electrode layer 22
is provided on the beam 26, is disclosed (in the official gazette
of Japanese Patent Application Laid-Open No. 10-136665). In the
actuator 21, when a voltage is applied to an electrode layer 22,
the beam 26 expands or contracts in a direction in which the fixing
portion 25 is connected with the movable portion 24 by the inverse
piezoelectric effect or the electrostrictive effect, thus making it
possible to have the movable portion 24 perform an arc-shaped
displacement or a rotational displacement in the plane of the
plate-like body.
[0004] On the other hand, JP-A-63-64640 discloses a technique with
regard to an actuator utilizing a bimorph, in which an electrode of
the bimorph is split, and by selecting the split electrodes to
drive the actuator, precise positioning is performed at a high
speed, and for example, the specification shows in FIG. 4 thereof a
structure which uses two bimorphs opposed to each other.
[0005] However, in the above-described actuator 21, as the
displacement in an expanding or contracting direction (namely, the
in-plane direction of the plate-like body) of a
piezoelectric/electrostrictive material is transmitted per se to a
movable portion, there is a problem that an operational quantity of
the movable portion 24 is small. Further, the actuator 21, having
all the members thereof being composed of a
piezoelectric/electrostrictive material which is fragile and
comparatively heavy, has another problem, in addition to being low
in mechanical strength, and inferior in handling, impact
resistance-and humidity resistance, that the actuator 21 per se is
heavy and is operationally likely to be subjected to an influence
of harmful vibrations (for example, residual vibrations or noise
vibrations when operated at a high speed).
[0006] In order to solve the above-described problems in the
actuator 21, a proposition has been made that an elastic filling
material is filled into a hole 28. However, when the filling
material is used, it is apparent that the efficiency of
displacement due to the inverse piezoelectric effect or the
electrostrictive effect is decreased.
[0007] On the other hand, what is shown in FIG. 4 of the laid-open
specification of JP-A-63-64640 is the structure wherein so-called
piezoelectric/electrostrictive portions, which generate
displacement, bridge over both of the respective bonding portions
in the bonding manner between the intermediary member and the
bimorph, and the head and the bimorph; that is, the bimorph is
formed continuously over from the intermediary member to the head.
Therefore, there is observed an interference between the displace
movement that occurs from the bonded portion between the
intermediary member and the bimorph, and the displace movement that
occurs from the bonded portion between the head and the bimorph as
a fulcrum, thereby the expression of the displacement is
prohibited. As a result, an action for effectively displacing the
head per se toward the outer space is unable to be obtained. In
addition, the actuator disclosed in JP-A-63-64640 is so structured
that a displacement generating member and a so-called frame member
(intermediary member or the like) are separately prepared, and then
adhered to be incorporated, and consequently the bonded state of
the frame with the bimorph is so structured to be likely to vary
with time in accordance with operation of the bimorph, and also to
be likely to cause drifting, exfoliation, or the like. Further, a
bonded portion of the bimorph with the intermediary member and a
bonded portion of the head with the bimorph, namely a structure
having an adhesive agent at a supporting portion of a displacement
member, is low in rigidity of the supporting portion, and is so
structured that an increase in resonant frequency which is required
in high speed operation is also difficult to be obtained.
[0008] Of a piezoelectric/electrostrictive device capable of
solving such problems, although the applicant of the present
invention and others have proposed, in the specification of the
Japanese Patent Application No. 11-375581 filed on Dec. 28, 1999, a
piezoelectric/electrostrictive device capable of obtaining a large
displacement quantity as well as maintaining mechanical strength of
a joined portion of a thin plate portion with the movable portion
above a predetermined level, a device capable of generating still
larger displacement and responding at a higher speed is sought
after particularly for precise positioning in the magnetic
recording field and optical field.
[0009] The present invention is made in view of above-described
current situation, and an object thereof is to provide a
displacement element which is capable of further increasing a
displacement quantity of a movable portion while maintaining the
mechanical strength at the joined portion of the thin plate portion
with the movable portion above a predetermined level, as well as
high in resonant frequency and superior in responsibility, and a
sensor element capable of detecting vibrations of the movable
portion in finer precision.
SUMMARY OF THE INVENTION
[0010] According to the present invention, firstly provided is a
piezoelectric/electrostrictive device comprising a driving portion
to be driven by displacement of a piezoelectric/electrostrictive
element, a movable portion to be operated based on the drive of the
driving portion, and a fixing portion for holding the driving
portion and the fixing portion, the fixing portion and the movable
portion being coupled together via the driving portion, and a hole
being formed by inner walls of the driving portion, an inner wall
of the movable portion, and an inner wall of the fixing portion, in
which the driving portion is composed of a mutually opposed pair of
thin plate portions and at least two piezoelectric/electrostrictive
elements provided on the thin plate portions; each of said
piezoelectric/electrostrictive elements being comprised of one or
more pairs of electrodes and a piezoelectric/electrostrictive film;
at least one of ends of said piezoelectric/electrostrictive element
and a piezoelectric/electrostricti- ve operating portion on said at
least one of ends are positioned on the fixing portion, and formed
as being extended to at least a part of either one of the thin
plate portions out of said pair of the thin plate portions, and an
end of said piezoelectric/electrostrictive operating portion on
another side of said piezoelectric/electrostrictive element is
positioned on said either one of the thin plate portions, in a
direction of said one of the thin plate portions from the fixing
portion toward the movable portion, in one out of at least two
piezoelectric/electrostrictiv- e elements comprising at least one
or more pairs of electrodes and a piezoelectric/electrostrictive
film, at least one of the ends of said
piezoelectric/electrostrictive element and a
piezoelectric/electrostricti- ve operating portion on said at least
one of the ends are positioned on the movable portion, and formed
being extended to at least a part of another thin plate portion out
of said pair of the thin plate portions, and an end of said
piezoelectric/electrostrictive operating portion on another side of
said piezoelectric/electrostrictive element is positioned on said
another thin plate portion, in a direction of said another thin
plate portion from the fixing portion toward the movable portion,
in one of remaining piezoelectric/electrostrictive elements among
said piezoelectric/electrostrictive elements comprising at least
one or more pairs of electrodes and a
piezoelectric/electrostrictive film.
[0011] According to the present invention, further provided is a
piezoelectric/electrostrictive device in which the
piezoelectric/electrostrictive element comprising one or more pairs
of electrodes and a piezoelectric/electrostrictive film is further
arranged on the outer surface of at least either one thin plate
portion out of a pair of mutually opposing thin plate portions and
has a structure, in a direction of the thin plate portion from a
fixing portion toward a movable portion, at least one end of the
piezoelectric/electrostrictive element and a
piezoelectric/electrostrictive operating portion of the same end
side thereof are arranged on the fixing portion or the movable
portion, and formed being extended to at least a part of the thin
plate portion, and an end of the piezoelectric/electrostrictive
operating portion of the other end side of the
piezoelectric/electrostrictive element is arranged on the thin
plate portion, and the piezoelectric/electrostrictive element is
arranged on the same thin plate portion opposing to one of the at
least two piezoelectric/electrostrictiv- e elements arranged so as
to be in diagonal directions across a hole; and a
piezoelectric/electrostrictive device in which, on respective outer
surfaces of a pair of mutually opposing thin plate portions, in a
direction of the thin plate portions from the fixing portion toward
the movable portion, a piezoelectric/electrostrictive element
comprising at least one or more pairs of electrodes and a
piezoelectric/electrostrictiv- e film, one end of the element and
one end of a piezoelectric/electrostric- tive operating portion
positioned on said one end of the element being arranged on the
fixing portion, and a piezoelectric/electrostrictive element
comprising at least one or more pairs of electrodes and a
piezoelectric/electrostrictive film, one end of the element and one
end of a piezoelectric/electrostrictive operating portion
positioned on said one end of the element being arranged on the
movable portion, are respectively arranged mutually opposed on the
same thin plate portion being extended until at least a part of
said thin plate portion, the respective
piezoelectric/electrostrictive elements having one end thereof and
piezoelectric/electrostrictive operating portions on the same end
side thereof are arranged on the fixing portion or the movable
portion, and formed being extended to at least a part of the thin
plate portion, and an end of a piezoelectric/electrostrictive
operating portion of the other end side of the
piezoelectric/electrostrictive element is arranged on the thin
plate portion.
[0012] Furthermore, according to the present invention, provided
are a piezoelectric/electrostrictive device in which ends of
piezoelectric/electrostrictive operating portions on the thin plate
portions of respective piezoelectric/electrostrictive elements
provided mutually opposed on the outer surfaces of the same thin
plate portions are arranged in positions not to exceed one half of
the lengths of respective thin plate portions; a
piezoelectric/electrostrictive device in which two
piezoelectric/electrostrictive elements provided mutually opposed
on the outer surface of the same thin plate portion share a
piezoelectric/electrostrictive film; a
piezoelectric/electrostrictive device in which two
piezoelectric/electrostrictive elements provided mutually opposed
on the outer surface of the same thin plate portion out of a pair
of mutually opposing thin plate portions are elements mutually
having the same or different functions; a
piezoelectric/electrostrictive device in which two
piezoelectric/electrostrictive elements provided mutually opposed
on the outer surface of the same thin plate portion out of a pair
of mutually opposing thin plate portions are elements having
mutually different functions; a piezoelectric/electrostrictive
device in which piezoelectric/electrostrictive elements existing
mutually in diagonal directions across a hole out of at least two
piezoelectric/electrostrictive elements provided on the outer
surface of a pair of mutually opposing thin plate portions are
elements having the same function, and a
piezoelectric/electrostrictive device in which
piezoelectric/electrostrictive elements existing in mutually
diagonal directions across a hole out of at least two
piezoelectric/electrostricti- ve elements provided on the outer
surfaces of a pair of mutually opposing thin plate portions are
elements having mutually different functions, and a
piezoelectric/electrostrictive device in which at least one
piezoelectric/electrostrictive element out of at least two
piezoelectric/electrostrictive elements provided on the outer
surfaces of a pair of mutually opposing thin plate portions has a
multi-layered piezoelectric/electrostrictive operating portion.
[0013] In the present invention, it is observed that suppression of
the rotation-mode displacement is a matter of great importance in a
structure of a unique device disclosed in this specification, in
view of enlarging displacement quantity of the movable portion and
increasing efficiency of the displacement.
[0014] The rotation-mode herein means a displacement mode of a
device as a whole; said displacement mode being obtainable by
making a radius of curvature of one thin plate portion out of a
pair of mutually opposing thin plate portions when said one thin
plate portion over a whole length there is compulsively bent
(hereinafter thus formed radius of curvature referred to as
compulsive radius of curvature) smaller than that of another thin
plate portion which is positioned on the opposite side of the
center of curvature of the compulsive radius of curvature of said
one thin plate portion when said another thin plate portion is bent
according to the compulsive bent of said one thin plate portion. In
other words, it is called a rotation-mode because a movable portion
seems as if to largely rotate about a fixing portion.
[0015] In the rotation-mode, a distance of a point of the movable
portion prior to and after the displacement is a function of the
above-described compulsive radius of curvature and separation
distance of a pair of mutually opposing thin plate portions. That
is, the smaller the compulsive radius of curvature is (namely, the
larger the bending of the thin plate portions is in the entire
length), and the smaller the separation distance is, the larger the
displacement distance becomes.
[0016] However, the separation distance cannot be made zero, as it
is required in order to secure compulsive radius of curvature. In
other words, there should be an allowance to allow one thin plate
portion out of a pair of thin plate portions to be compulsively
bent relative to the other thin plate of the pair of thin plates.
The allowance can be made practically zero by using only one thin
plate portion, however, such structure is undesirable in view of
stability of the device, and in any case there is an upper
limit.
[0017] As a movable portion displaces as if to largely rotate about
a fixing portion as described previously, inner walls of the
movable portion are made to form an angle relative to the fixing
portion prior to and after the displacement.
[0018] As to such problem, the present invention provides a method
to enable the movable portion to efficiently develop a large
displacement by changing the displacement form of a thin plate
portion to a displacement mode having a point of inflection
existing on the thin plate portion, more specifically, having the
point of inflection existing on the thin plate portion so as to
have the curvature center for the bending existing on both sides of
the thin plate portion interposed therebetween, at both portions of
the thin plate portion having the point of inflection interposing
therebetween, thus making a displacement mode for the device as the
entirety, namely a rotational symmetric mode, which is a
characteristic of the present invention.
[0019] This can be described that a method is found to deform a
thin plate portion in an S-shape with a point of inflection
existing on the thin plate portion, by bending a part of the thin
plate portion containing a connecting portion of the thin plate
portion with the fixing portion, or a connecting portion of the
thin plate portion with the movable portion.
[0020] The rotational symmetric mode used herein means a
displacement mode which can be most efficiently obtained when an
S-shape of one thin plate portion out of a pair of mutually
opposing thin plate portions is rotationally symmetric to the other
thin plate portion using a hole formed by respective inner walls of
the movable portion, driving portion, and fixing portion as the
symmetric center of the rotational symmetry.
[0021] Although a distance of a point of the movable portion prior
to and after the displacement at this time is a function of radius
of curvature of the bent portion of the thin plate portion and a
position of point of inflection on the same thin plate portion, the
degree of freedom is high as there is no limitation factor being
contrary to each other in a case of the rotational mode (whereas
the entire length of the thin plate portion is desired to be bent,
separation distance between a pair of thin plate portions which is
a space for bending thereof is preferred to be smaller). This is
better suited for efficiently developing a larger displacement, as
bending even small parts of the thin plate portions can be
utilized.
[0022] Further, contrary to the rotational mode, as an inner wall
surface of a movable portion prior to displacement and the inner
wall surface of the movable portion after the displacement maintain
a paralleling state prior to and after the displacement, no
unfavorable influence is given to the operation efficiency of other
elements placed on the movable portion, thus a large displacement
can be efficiently achieved.
[0023] In this way, as a concrete means for realizing the
rotationally symmetric mode, at least two
piezoelectric/electrostrictive elements and
piezoelectric/electrostrictive operating portions thereof, of which
respective ends are arranged on the movable portion or the fixing
portion, and the other ends are arranged on the thin plate
portions, are arranged so as to be in mutually diagonal directions
at least with a hole interposing therebetween, for the
above-described pair of mutually opposing thin plate portions.
Thus, a displacement of the movable portion in the rotational mode
is effectively suppressed, and as a result, a
piezoelectric/electrostrictive device which develops an extremely
large displacement in one axis direction is realized.
[0024] A piezoelectric/electrostrictive device of the present
invention preferably comprises a movable portion, thin plate
portions, and a fixing portion integrally formed in ceramics, and
more preferably is made of materials containing fully-stabilized
zirconia as the major component or materials containing partially
stabilized zirconia as the major component, and most preferably at
least the movable portion, the thin plate portions, and the fixing
portion are made in a sintered ceramic green laminated body. This
is because connecting portions with the movable portion, the thin
plate portions, and the fixing portion can be made as a borderless
structure by sintering integration, thus improving long term
reliability of such portions over time, and in addition a
phenomenon such as drifting or the like which is a variation with
time of displacement as a device can be suppressed to the minimum,
thus developing a large displacement with good reproducibility.
Fabricating methods of the device according to the present
application will be described later in detail.
[0025] By the way, when fabricating a device of a structure
according to the present application, another method in addition to
complete integration by sintering is that a laminated body divided
in a mutually opposing direction of the thin plate portions,
namely, a ceramic laminated body comprising a thin plate portion
and a member to be a rectangular fixing portion and movable portion
is prepared, a piezoelectric/electrostrictive element is formed by
screen printing so as to overlap the thin plate portions and the
fixing portion or the movable portion of the ceramic laminated
body, at least two sintered structures integrated with the ceramic
laminated body by sintering are prepared, and the sintered
structures are adhered to so as to have the thin plate portions
mutually away, that is, the above-described members that provide
the fixing portion and the movable portion are mutually adhered to
by use of an adhesive (for example, an organic adhesive such as
epoxy resin, acrylic resin, or the like, and an inorganic adhesive
such as glass, cement, or the like). However, since the device
fabricated all in one by sintering is superior in stability and
reliability even if a stress is applied to a device by operation of
a driving portion, as it has no discontinuous portion of a
so-called structured body such as a bonded portion where a third
party intervenes, it is preferable to form the device by sintering
integration where no adhesive or the like is used.
[0026] Further, in a piezoelectric/electrostrictive device
according to the present invention, it is preferable that a
piezoelectric/electrostric- tive film comprising a
piezoelectric/electrostrictive element is made of the material
whose major component is a mixture of lead zirconate, lead
titanate, and lead magnesium niobate, and also preferable is one
made of materials containing sodium bismuth titanate. Details of
materials to be used will be described later.
[0027] It should be noted that "a piezoelectric/electrostrictive
device (hereinafter referred to only as a "device")" in the present
specification is a notion to imply an element mutually converting
an electric energy and a mechanical energy by way of a
piezoelectric/electrostrictive material. Therefore, the device is
preferably used as an active element such as a variety of
actuators, vibrators, or the like, and more specifically as a
displacement element utilizing a displacement due to the inverse
piezoelectric effect or the electrostrictive effect. However, it
can also be used as a passive element such as an acceleration
sensor element, an impact sensor element, or the like. It should
also be noted that "piezoelectric" in the present specification
means "piezoelectric/electrostrictive". Further, a "length" means a
distance in a direction connecting a movable portion with a fixing
portion, namely in the Z-axis direction in the drawings, a "width"
means a distance in a direction penetrating through a hole, namely
in the Y-axis direction in the drawings, and a "thickness" means a
distance in a laminating direction of a
piezoelectric/electrostrictive element with a thin plate portion,
namely in the X-axis direction in the drawings.
[0028] A piezoelectric/electrostrictive element means an element
comprising at least one or more pairs of electrodes and a
piezoelectric/electrostrictive film to be driven based on signals
transmitted, and to perform a function of conveying the movement
thereof to a movable portion. In the element, a piezoelectric
operating portion means, the substantial operable portion of a
piezoelectric/electrostricti- ve element so as to move a movable
portion in a predetermined movement in accordance with an applied
signal to a driving portion, and comprises a portion where at least
one or more pairs of electrodes and a
piezoelectric/electrostrictive film are mutually overlapped.
Further, a base for a device means a sintered ceramic laminated
body prior to arrangement of a piezoelectric/electrostrictive
element thereon. In addition, in the present invention,
displacement quantity of a device is measured by a laser Doppler
vibrometer (made by Graphtec Corp.).
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIGS. 1(a) and (b) show front views schematically depicting
a structure of an embodiment of one of
piezoelectric/electrostrictive devices of the present invention,
and FIG. 1(a) shows a state prior to a displacement and FIG. 1(b)
shows a state after the displacement.
[0030] FIG. 2 shows a front view schematically depicting a
structure of another embodiment of a piezoelectric/electrostrictive
device of the present invention.
[0031] FIGS. 3(a) and (b) show front views schematically depicting
structures of still another embodiment of a
piezoelectric/electrostrictiv- e device of the present invention,
and FIG. 3(a) shows a state prior to a displacement and FIG. 3(b)
shows a state after the displacement.
[0032] FIG. 4 shows a schematic perspective view depicting a
structure of a base for a piezoelectric/electrostrictive device of
the present invention.
[0033] FIG. 5 shows a schematic perspective view depicting an
embodiment of a piezoelectric/electrostrictive device of the
present invention.
[0034] FIG. 6 shows a schematic perspective view depicting another
embodiment of a piezoelectric/electrostrictive device of the
present invention.
[0035] FIG. 7 shows a schematic perspective view depicting still
another embodiment of a piezoelectric/electrostrictive device of
the present invention.
[0036] FIG. 8 shows a schematic perspective view depicting an
embodiment of one of piezoelectric/electrostrictive elements
constituting a piezoelectric/electrostrictive device of the present
invention.
[0037] FIG. 9 shows a schematic perspective view depicting an
embodiment of one of piezoelectric/electrostrictive elements
constituting a piezoelectric/electrostrictive device of the present
invention.
[0038] FIG. 10 shows a schematic perspective view depicting an
embodiment of one of piezoelectric/electrostrictive elements
constituting a piezoelectric/electrostrictive device of the present
invention.
[0039] FIGS. 11(a), (b), (c), and (d) show process drawings of one
of methods of fabricating a piezoelectric/electrostrictive device
of the present invention.
[0040] FIGS. 12(a) and (b) show schematic perspective views
depicting an example of an optical shutter with a device according
to the present invention mounted thereon, and FIG. 12(a) is a
perspective view and FIG. 12(b) is a top view.
[0041] FIGS. 13(a), (b), and (c) show schematic perspective views
depicting another example of an optical shutter with a device
according to the present invention mounted thereon, and FIG. 13(a)
is a perspective view, FIG. 13(b) is a top view, and FIG. 13(c) is
an enlarged view of shields.
[0042] FIG. 14 is a schematic perspective view depicting an
embodiment of a conventional piezoelectric actuator.
[0043] FIG. 15 is a schematic perspective view depicting another
embodiment of a piezoelectric/electrostrictive device of the
present invention.
[0044] FIG. 16 shows a schematic perspective view depicting still
another embodiment of a piezoelectric/electrostrictive device of
the present invention.
[0045] FIG. 17 shows a schematic perspective view depicting still
another embodiment of a piezoelectric/electrostrictive device of
the present invention.
[0046] FIG. 18 shows a schematic perspective view depicting still
another embodiment of a piezoelectric/electrostrictive device of
the present invention.
[0047] FIG. 19 shows a schematic perspective view depicting still
another embodiment of a piezoelectric/electrostrictive device of
the present invention.
[0048] FIG. 20 schematically shows examples of respective ceramic
green sheets to be used for a ceramic green sheet laminated body in
a method of fabricating a piezoelectric/electrostrictive device
according to the present invention.
BEST MODE OF CARRYING OUT THE INVENTION
[0049] A piezoelectric/electrostrictive device according to the
present invention is hereinafter described with reference to the
drawings. It should be noted, however, that the present invention
is not limited to embodiments shown in the drawings.
[0050] Please be noted that those having the same or similar
function are, in principle, denoted by the same symbol in the
drawings.
[0051] If a device according to the present invention is classified
in accordance with arrangement of piezoelectric/electrostrictive
elements, there are three aspects as follows.
[0052] A first aspect is a device where a
piezoelectric/electrostrictive element 2 comprising a pair of
electrodes 2b, and 2c and a piezoelectric/electrostrictive film 2a
is respectively formed on each thin plate portion out of a pair of
mutually opposing thin plate portions 6, and 7, placed in diagonal
directions across a hole 8. An example of the aspect is shown in
FIGS. 1(a) and (b). Here, FIG. 1(a) shows a state prior to a
displacement, and FIG. 1(b) shows a state after the displacement.
In this aspect, it is preferable to form
piezoelectric/electrostrictive elements all having the same
functions, for example, a strain direction of a
piezoelectric/electrostrictive operating portion relative to a main
surface direction of the thin plate portion being the same. The
reason is that a large displacement can be obtained by a small
driving force in the structure. It is preferable, from a viewpoint
of obtaining a large displacement, that an end located on a thin
plate portion 6 or 7 of the piezoelectric/electrostrictive
operating portion exists in a position so as to occupy 30 to 95% of
the length of the thin plate portion 6, in a direction of the thin
plate portion 6 from a fixing portion 5 toward a movable portion 4;
40 to 90% is more preferable. Meanwhile, in a case a
piezoelectric/electrostrictive film in the above-described
piezoelectric/electrostrictive element is formed beyond the thin
plate portion and over the movable portion and the fixing portion,
the end of the operating portion preferably exists in a position
occupying 50.+-.40%, more preferably 50.+-.25%, of the length of
the thin plate portion 6, in order to obtain a large displacement
with a small driving force.
[0053] A second aspect is a device where, on a pair of mutually
opposing thin plate portions 6 and 7, one
piezoelectric/electrostrictive element is further formed in an
opposing position on the thin plate portion 6 or 7 where either one
of piezoelectric/electrostrictive elements each comprising a pair
of electrodes 2b and 2c and a piezoelectric/electrostri- ctive film
2a is respectively formed already, in diagonal directions across a
hole 8. As an example of the second aspect, FIG. 2 shows an
embodiment where one piezoelectric/electrostrictive element is
further formed in an opposing position on the thin plate portion 7.
Of course, another piezoelectric/electrostrictive element may be
further formed in an opposing position on the thin plate portion 6.
It becomes also possible to perform a more complicated displacement
by feeding mutually different instructions, for example, electric
signals, respectively to these three piezoelectric/electrostrictive
elements.
[0054] In a third embodiment, as shown in FIGS. 3(a) and (b), a
device is mounted with two each, four in total,
piezoelectric/electrostrictive elements respectively comprising a
pair of electrodes 2b, and 2c and a piezoelectric/electrostrictive
film 2a mutually opposed on the same thin plate portions 6, and 7,
and therefore four fulcrums are available for a displacement. So,
if elements positioned at least in diagonal directions across a
hole mutually have the same functions, driving force can be doubled
by simultaneously driving the same, thus the driving force can be
efficiently converted into a displacement in addition to remarkable
increase in displacement quantity. Further, by forming
piezoelectric/electrostrictive elements having mutually different
strain directions formed on the same driving portion (thin plate
portion), the displacement of the thin plate portion due to the
strain such as expansion and/or contraction can be carried by
respective piezoelectric/electrostrictive elements, thus enabling a
movable portion to operate dominantly in a lateral direction,
namely in the X-axis direction.
[0055] In addition, in this aspect, since
piezoelectric/electrostrictive operating portions of
piezoelectric/electrostrictive elements are formed on a joined
portion of a fixing portion and a movable portion with a thin plate
portion, the mechanical strength at the portion is also secured.
Further, even if the device may be so structured that all the four
piezoelectric/electrostrictive elements utilize the same effect,
using a piezoelectric material having a relatively high coercive
electric field, by driving one side of the
piezoelectric/electrostrictive elements, formed on the same driving
portion, in the electric field opposite to the polarization
direction within the coercive electric field, the
expansion/contraction relation can be made the same as the case
when positioning relation of the four
piezoelectric/electrostrictive elements is changed, which can be
preferably employed. FIG. 3(a) shows a state prior to a
displacement, and FIG. 3(b) shows a state after the displacement.
In this aspect, it can also be advantageously employed that two
piezoelectric/electrostrictive elements provided mutually opposed
on the outer surface of the same thin plate portion share a
piezoelectric/electrostrictive film. By doing in this way, a
resonant-frequency can be further increased as well as the
mechanical strength of the device can be increased.
[0056] 1. Embodiment of Device
[0057] Configuration, in the present invention, of a base 1' for a
device which is a sintered ceramic laminated body prior to
providing a piezoelectric/electrostrictive element thereon is
hereinafter described.
[0058] FIG. 4 is a schematic perspective view for describing the
composition of respective members of the base 1' to be used in a
device of the present invention. The device comprises respective
members composed of thin plate portions 6 and 7 having
piezoelectric/electrostric- tive elements (not shown) formed
thereon and constituting a driving portion (not shown) to be driven
by displacement thereof, a movable portion 4 to be displaced in
accordance with a drive of the driving portion (not shown), and a
fixing portion 5 for holding the driving portion to be formed by
the thin plate portions 6 and 7 and a
piezoelectric/electrostrictive element and the movable portion 4.
The fixing portion 5 and the movable portion 4 are coupled via the
thin plate portions 6 and 7, and a hole 8 is formed by inner walls
of the thin plate portions 6 and 7, inner wall of the movable
portion 4, and an inner wall of the fixing portion 5.
[0059] 2. Composing Members of Base
[0060] Respective members of a base composing a device of the
present invention are individually and specifically described by
way of a base 1' shown in FIG. 4.
[0061] (1) Movable Portion and Fixing Portion
[0062] A movable portion 4 is a portion to be operated based on the
driving quantity of a driving portion 3 (not shown, details thereof
to be described later), and a variety of members are mounted
thereon depending on the application of the device. For example,
when the device is used as a displacement element, a shield of an
optical shutter is mounted thereon, and when the device is used as
a positioning mechanism or ringing suppression mechanism for a hard
disk drive, members requiring positioning such as a magnetic head,
a slider with a magnetic head mounted thereon, a suspension with a
slider mounted thereon, or the like are mounted on the movable
portion.
[0063] A fixing portion 5 is a portion for holding a driving
portion 3 and a movable portion 4, and a device 1 as a whole is
secured by securely holding the fixing portion 5 to any base such
as, for example, a carriage arm fixed to a VCM (voice coil motor),
or a fixing plate attached to the carriage arm, or the tip of the
suspension, or the like, when utilizing the device as the
positioning mechanism for the hard disk drive.
[0064] Further, an electrode lead or other members for controlling
a piezoelectric/electrostrictive element 2 may also be
arranged.
[0065] As materials for composing the movable portion 4 and the
fixing portion 5, although no specific limitation is there as long
as rigidity is there, ceramics which can be applied for the ceramic
green sheet laminating method to be described later can be
preferably used. More specifically, in addition to zirconia such as
fully-stabilized zirconia, partially-stabilized zirconia, or the
like, or materials containing alumina, magnesia, silicon nitride,
aluminum nitride, or titanium oxide as the major component,
materials containing a mixture of those listed may be used.
However, in view of the higher mechanical strength and toughness,
preferable are materials containing zirconia, more particularly
fully-stabilized zirconia as the major component, or materials
containing partially-stabilized zirconia as the major
component.
[0066] (2) Driving Portion
[0067] A driving portion 3 is a portion to be driven by
displacement of a piezoelectric/electrostrictive element 2, and
comprises mutually opposing thin plate portions 6 and 7, and a
predetermined number, for example, two for the first aspect, three
for the second aspect, and four for the third aspect, of the
film-like piezoelectric/electrostrictive elements 2 formed on
surfaces of the thin plate portions 6 and 7.
[0068] {circle over (1)} Thin Plate Portion
[0069] Thin plate portions 6 and 7 are flexible thin plate-like
members, and have functions to convert and amplify expanding and/or
contracting strain of a piezoelectric/electrostrictive element 2
disposed on the surface thereof into bending displacement for
transmitting to a movable portion 4.
[0070] Accordingly, forms and materials of the thin plate portions
6 and 7 suffice with those having flexibility and the mechanical
strength in the order of not being broken by flexural deformation,
and can be suitably selected considering responsibility and
operability of the movable portion.
[0071] Ordinarily, the thickness of the thin plate portion 6 or 7
is preferably around 2 to 100 .mu.m, and the total thickness of the
thin plate portion 6 or 7 and a piezoelectric/electrostrictive
element 2 combined together is preferably 7 to 500 .mu.m. The width
of the thin plate portions 6 and 7 are preferably 50 to 2000 .mu.m.
This point is further described later.
[0072] As materials composing the thin plate portions 6 and 7,
ceramics similar to the movable portion 4 and the fixing portion 5
can be preferably used, and zirconia, more particularly a material
containing fully-stabilized zirconia as the major component and a
material containing partially-stabilized zirconia as the major
component, is most preferably employed since it has larger
mechanical strength (even after machined into a thin-walled
structure), higher toughness, and smaller reactivity relative to a
piezoelectric/electrostrictive film or an electrode material. In
the meantime, with regard to the fully-stabilized and
partially-stabilized zirconia, those stabilized in the following
manner are preferable. Namely, compounds that can stabilize
zirconia are yttrium oxide, ytterbium oxide, cerium oxide, calcium
oxide, and magnesium oxide, and by adding and including at least
one of these compounds, zirconia is partially or fully stabilized,
and stabilization of zirconia is also possible not only by adding
one kind of the compounds but also by adding a combination of the
compounds.
[0073] Meanwhile, as to adding quantity of respective compounds, it
is 1 to 30 mol % (mole percent) and preferably 1.5 to 10 mol % in
case of yttrium oxide or ytterbium oxide, 6 to 50 mol % and
preferably 8 to 20 mol % in case of cerium oxide, and 5 to 40 mol %
and preferably 5 to 20 mol % in case of calcium oxide or magnesium
oxide. Among these listed, particularly use of yttrium oxide as the
stabilizer is preferable, and in this case, 1.5 to 10 mol % is
preferable, and 2 to 4 mol % is more preferable. Further, as an
additive for a sintering aid, alumina, silica, magnesia, an oxide
of transition metal, or the like may preferably be added in a range
of 0.05 to 20 weight percent. However, it is preferred to add
alumina, magnesia, an oxide of transition metal, or the like as an
additive when an integration method by sintering a green element
formed by the film forming method is employed as a means for
forming a piezoelectric/electrostrictive element.
[0074] It should be noted that, in order to obtain the desired
mechanical strength and the stable crystal phase, the average
crystal grain size of zirconia may desirably be 0.05 to 3 .mu.m,
and more desirably 0.05 to 1 .mu.m. Further, although ceramics
similar to the movable portion 4 and the fixing portion 5 may be
used for the thin plate portions 6 and 7, as described previously,
preferably desirable is that the thin plate portions 6 and 7 are
composed of substantially the same materials in view of the higher
reliability of joined portions, increased mechanical strength of
the device, and lowered complication in fabrication.
[0075] Base 1' is structured so that a ratio a/b of the thickness
of the hole 8, namely a distance a in the X-axis direction in FIG.
4 and the width of the thin plate 6 or 7, namely a distance b in
the Y-axis direction in FIG. 4 is 0.5 to 20. The ratio a/b is
preferably set at 1 to 10, and more preferably at 2 to 8. The
defined value of the a/b is prescribed based on knowledge that a
displacement of a piezoelectric/electrostrictive device according
to the present invention can be made larger and a displacement in
the X-Z plane in FIG. 4 can be dominantly obtained. On the other
hand, a ratio e/a of the length of the thin plate portion, namely a
distance e in the Z-axis direction in FIG. 4 and the thickness a of
the above-described hole is preferably set at 0.5 to 10, and more
preferably at 0.7 to 5. The defined value of the e/a is based on
knowledge that the piezoelectric/electrostrictive device according
to the present application can generate a larger displacement in
higher resonant frequency, namely at a higher speed of response.
Accordingly, it is specifically preferable to have the ratio a/b of
0.5 to 20, and the ratio e/a of 0.5 to 10; and extremely preferable
to have the ratio a/b of 1 to 10, and the ratio e/a of 0.7 to 5, so
as to make the present device have such a structure that not only
flapped displacement or vibration in the Y-axis direction can be
suppressed, but also a larger displacement at relatively low
voltage can be attained with keeping superiority in high speed
responsibility.
[0076] The length f of the movable portion 4 shown in FIG. 4 is
preferably shorter. By making the length shorter, the weight of the
movable portion can be made lighter and the resonant frequency can
be increased. However, in order to secure the rigidity of the
movable portion 4 in the X-axis direction, and to ensure a
displacement thereof, the ratio f/d with the thickness d of the
thin plate portion is made 3 or more, and preferably 10 or more. In
addition, actual dimensions of respective members are to be
determined also considering such factors as a bonding area for
mounting the members on the movable portion 4, a bonding area for
mounting the fixing portion 5 to another member, a bonding area for
mounting the terminals or the like for electrodes, mechanical
strength, durability, required displacement, and resonant frequency
of the device as a whole, a driving voltage, and the like.
Ordinarily, a is preferably 100 to 2000 .mu.m, and more preferably
200 to 1000 .mu.m. Ordinarily, b is preferably 50 to 2000 .mu.m,
and more preferably 100 to 500 .mu.m. Ordinarily, d is made to be
b>d relative to the width b of the thin plate portions 6 and 7,
and is preferably 2 to 100 .mu.m, and more preferably 4 to 60
.mu.m. Ordinarily, e is preferably 200 to 3000 .mu.m, and more
preferably 300 to 2000 .mu.m. And, ordinarily, f is preferably 50
to 2000 .mu.m, and more preferably 100 to 1000 .function.m.
[0077] It should be noted that by structuring in such a manner, the
displacement in the Y-axis direction ordinarily does not exceed 10%
relative to the displacement in the X-axis, that is the major axis,
direction. However, by suitably adjusting within a range of the
previously described preferable dimension ratios and the actual
dimensions, driving at a low voltage can be made possible, and a
displacement component in the Y-axis can be adjusted to 5% or less,
which is an extremely superior advantage. In other words, a
substantially dominant displacement is obtained only in the X-axis,
namely the major axis. Further, in addition to the characteristics
described previously, obtained is a device which can develop a
large displacement, superior in high speed responsibility, at a
relatively low voltage.
[0078] Further, positional relations of respective members in a
driving state of a device according to the present invention are
described with reference to FIG. 3(b). In FIG. 3(b), the device
according to the present invention is so structured that, by
driving two each, four in total, piezoelectric/electrostrictive
elements 2 disposed mutually opposed respectively on thin plate
portions 6 and 7, by way of functions of respective elements, the
thin plate portion 6 is, by operation of one pair of
piezoelectric/electrostrictive elements formed mutually opposed on
the same thin plate portion 6, curved toward the hole 8, on the
side of the fixing portion 5, and toward the opposite side of the
hole 8, on the side of the movable portion 4, and the thin plate
portion 7 is, by operation of one pair of
piezoelectric/electrostrictive elements formed mutually opposed on
the same thin plate portion 7, curved toward the opposite side of
the hole 8, on the side of the fixing portion 5, and toward the
hole 8, on the side of the movable portion 4, thus a large
displacement quantity as shown in FIG. 3(b) can be obtained.
Naturally, by suitably selecting functions of the four elements, a
desired displacement can be obtained. By this structure, an inner
wall of the movable portion 4 and an inner wall of the fixing
portion 5 can be maintained in parallel, thus the displacement is
efficiently increased. In other words, by eliminating rotation of
the movable portion 4, efficiency is increased.
[0079] {circle over (2)} Piezoelectric/Electrostrictive Element
[0080] A piezoelectric/electrostrictive element 2 has at least a
part thereof formed on thin plate portions 6 and 7, and constitutes
a driving portion 3 together with the thin plate portions 6 and 7,
and, for example, as shown in FIG. 3, comprises a pair of
electrodes 2b and 2c for applying a voltage to a
piezoelectric/electrostrictive film and a
piezoelectric/electrostrictive film 2a. In a device according to
the present invention, although a conventionally known
piezoelectric/electrostrictive element such as a unimorph-type, a
bimorph-type, or the like may be used, it is preferable to compose
the device described in the present application with the
unimorph-type piezoelectric/electrostrictive element, as the
unimorph-type element is superior in stability of displacement
quantity to be generated, and advantageous in reducing weight. For
example, preferably can be used are a laminated type
piezoelectric/electrostrictive element 2 or the like, with a first
electrode 2c, a piezoelectric/electrostrictive film 2a, and a
second electrode 2b laminated thereon, as shown in FIG. 8.
[0081] Generally, the piezoelectric/electrostrictive element
described in FIG. 8 has such a function that in a case that a
piezoelectric material such as a ferroelectric substance or the
like is used for a piezoelectric/electrostrictive film thereof, a
voltage is applied across the above-described electrodes (for
example, between a second electrode 2b and a first electrode 2c),
and when an electric field is exerted to the
piezoelectric/electrostrictive film 2a, based on the electric
field, an electric field induced strain is induced on the
piezoelectric/electrostrictive film 2a, and as a transverse effect
thereof, a strain in the contracting mode in a direction parallel
to the main surface of the piezoelectric/electrostrictive film is
primarily generated. Accordingly, if a
piezoelectric/electrostrictive element of this structure is applied
to the device of the present invention, the strain which contracts
in the direction of the above-described main surface is converted
into a bending displacement which bends the thin plate portion, and
the driving portion is bent for a displacement in a direction
toward the outer space (in the opposite direction of the hole) by
use of the joined portion of the thin plate portion with the
movable portion or the thin plate portion with the fixing portion
as the fulcrums, thus the movable portion can be displaced in a
predetermined direction.
[0082] It should be noted that when an antiferroelectric substance
is used instead of the ferroelectric material as the
above-described piezoelectric material, on account of a difference
in strain generating mechanism of piezoelectric/electrostrictive
materials, in other words, when an electric field is applied to a
piezoelectric/electrostrictive film, the
piezoelectric/electrostrictive film functions to generate a strain
caused by volume expansion of a crystal which is based on the phase
transition from antiferroelectric phase to ferroelectric phase,
namely a strain of expansion mode primarily in a direction of the
main surface of the piezoelectric/electrostrictive film.
Accordingly, in this case, in opposition to the
piezoelectric/electrostrictive element in which the ferroelectric
substance is used, the driving portion is bent and displaced in a
direction toward the inner space (in a direction of the hole), and
as the result, the movable portion can be displaced in a direction
opposite to the case where the ferroelectric substance is used. In
this way, while the structure is the same, different functions may
be had by applying piezoelectric/electrostrictive materials having
a different strain generating mechanism.
[0083] Further, it is also preferable, in addition to a structure
having the piezoelectric/electrostrictive film 2a interposed by a
pair of upper and lower electrodes, to form a
piezoelectric/electrostrictive film 2a further on the second
electrode, and to form a third electrode further on the
piezoelectric/electrostrictive film 2a to make a
piezoelectric/electrostrictive element having a structure of at
least two or more stairs. Furthermore, it is also preferable to
have a structure formed by repeating an electrode and a
piezoelectric/electrostrictive film in three stairs, four stairs,
five stairs, or ever more. By having piezoelectric/electrostrictive
elements in multiple stair structures in this manner, the driving
force of the driving portion is increased, and larger displacement
is made obtainable. Also, in a structure having the higher rigidity
of the device per se, for example, in a structure or the like where
the thin plate is made thicker, a larger displacement and higher
resonant frequency can be made easily compatible. A device using
piezoelectric/electrostrictive elements in a multiple stair
structure is separately described later.
[0084] Further, also usable is a piezoelectric/electrostrictive
element 2 having a structure comprising a first electrode 2b and a
second electrode 2c in a comb-shape structure, as shown in FIG. 9,
wherein the first electrode 2b and the second electrode 2c are
structured to be mutually opposed and interleaved with a gap 13 of
predetermined width between teeth of mutual combs. In FIG. 9, while
the first electrode 2b and the second electrode 2c are arranged on
the upper surface of the piezoelectric/electrostrictive film 2a,
the electrode may be formed between the thin plate portion 6 and
the piezoelectric film 2a, or the electrodes may also be formed
preferably on the upper surface of the
piezoelectric/electrostrictive film 2a and between both surfaces of
the thin plate portion 6 and the piezoelectric/electrostrictive
film 2a. In other words, in a piezoelectric/electrostrictive
element of the present structure, electrodes are formed on at least
one main surface of at least the piezoelectric/electrostrictive
film 2a. Further, a piezoelectric/electrostrictive element 2 shown
in FIG. 10 also comprises a first electrode 2b and a second
electrode 2c of the comb-shaped structure, and the first electrode
2b and the second electrode 2c are structured to be mutually
opposed and interleaved with a gap 13 of predetermined width
between teeth of mutual combs. The piezoelectric/electrostrictive
element 2 is structured to have the piezoelectric/electrostrictive
film 2a so as to be embedded in the gap 13 between the first
electrode 2b and the second electrode 2c, however, such
piezoelectric/electrostrictive element can also be preferably used
in the device of the present invention.
[0085] The piezoelectric/electrostrictive element described in FIG.
9 and FIG. 10 has functions different from the
piezoelectric/electrostrictive element shown in FIG. 8. The
piezoelectric/electrostrictive element of the structure shown in
FIGS. 9 and 10 has such a function that the electric field-induced
strain is induced on the piezoelectric/electrostri- ctive film 2a
based on an electric field, thereby a strain of the mode expanding
in a direction parallel to the main face of the
piezoelectric/electrostrictive film is generated as a longitudinal
effect thereof, when a voltage is applied across the
comb-teeth-shaped electrodes, and the electric field acts on the
piezoelectric/electrostric- tive film 2a.
[0086] Accordingly, if the piezoelectric/electrostrictive element
of this structure is applied to the device of the present
invention, the strain expanding in the direction of the main
surface described above is converted into a bending displacement
which bends the thin plate portion, and the driving portion is bent
for displacement in a direction toward the inner space (in the
direction of the hole) by use of the joined portion of the thin
plate portion with the movable portion or the thin plate portion
with the fixing portion as fulcrum, and as the result the movable
portion can be displaced in a predetermined direction. In the
meantime, ordinarily an element having a comb-teeth-shaped
electrode structure according to FIG. 9 and FIG. 10 is arranged
such that a pitch direction of the comb teeth is oriented to a
direction of the thin plate portion from the fixing portion toward
the movable portion. By arranging in this manner, the expansion
strain based on the longitudinal effect of the electric field
induced strain can be effectively utilized as the bending
displacement. In this way, the structure of FIG. 8 and the
structures of FIG. 9 and FIG. 10 are different in the directions of
strain of the piezoelectric/electrostrictive operating portions in
the direction of the main surface of the thin plate portion as the
ground, and come to have mutually different functions in the
point.
[0087] When piezoelectric/electrostrictive elements having
comb-shaped electrodes such as piezoelectric/electrostrictive
elements as shown in FIG. 9 and FIG. 10 are used, the displacement
of the piezoelectric/electrostrictive element can be made larger by
reducing the pitch D of the teeth of the combs.
[0088] Further, for example, in a third aspect of the device
according to the present invention, as shown in FIGS. 3(a) and (b),
whereas, on respective thin plate portions 6 and 7, a
piezoelectric/electrostrictive element 2 having at least one end
thereof being arranged on a part of a fixing portion 5 comprising a
pair of electrodes 2b and 2c, and a piezoelectric/electrostrictive
film 2a, and a piezoelectric/electrostrict- ive element 2 having at
least one end thereof being arranged on a part of the movable
portion 4 comprising a pair of electrodes 2b and 2c, and a
piezoelectric film 2a, are respectively provided on the thin plate
portions 6 and 7, respectively opposing one each, and four in
total, two piezoelectric/electrostrictive elements 2 provided
mutually opposed on the outer surfaces of the same thin plate
portion 6 or 7 may share either one of at least a second electrode
2b or a first electrode 2c. Further, two
piezoelectric/electrostrictive elements 2 provided mutually opposed
on the outer surface of the same thin plate portion 6 or 7 may
share only the piezoelectric/electrostrictive film 2a. On the other
hand, two piezoelectric/electrostrictive elements provided mutually
opposed on an outer surface of the same thin plate portion out of a
pair of mutually opposing thin plate portions may have an element
having the same or mutually different functions arranged
thereon.
[0089] An example of arranging elements having mutually different
functions as two piezoelectric/electrostrictive elements provided
mutually opposed on the outer surfaces of the same thin plate
portions is an aspect wherein either one of the
piezoelectric/electrostrictive elements is made of a type to
utilize the longitudinal effect of the electric field induced
strain and the other of the piezoelectric/electrostrictive elements
is made of another type to utilize the transverse effect of the
electric field induced strain. More specifically, one of the
elements may be structured as a piezoelectric/electrostrictive
element having the structure as shown in FIG. 9 or FIG. 10, and the
other of the elements may be structured as a
piezoelectric/electrostrictive element having the structure as
shown in FIG. 8. Further, for example, as respective two
piezoelectric/electrostri- ctive elements existing mutually in the
diagonal directions across a hole out of four
piezoelectric/electrostrictive elements provided on the outer
surfaces of a pair of mutually opposing thin plate portions,
elements respectively having the same function, for example, a type
utilizing the longitudinal effect of the electric field induced
strain, may be arranged. At this time, by arranging elements having
mutually different functions as two piezoelectric/electrostrictive
elements provided mutually opposed on the outer surface of the same
thin plate portion, all the four piezoelectric/electrostrictive
elements can be made simultaneously driven, and a remarkably large
displacement is obtained.
[0090] Furthermore, when two piezoelectric/electrostrictive
elements exist mutually in-the diagonal directions relative to the
center of the hole out of four piezoelectric/electrostrictive
elements provided on the outer surfaces of a pair of mutually
opposing thin plate portions, elements having mutually different
functions, for example, a type to utilize the longitudinal effect
of the electric field induced strain and another type to utilize
the transverse effect of the electric field induced strain, may be
respectively arranged. In this case, two piezoelectric/electrostri-
ctive elements provided mutually opposed on an outer surface of the
same thin plate portion out of a pair of mutually opposing thin
plate portions may have an element having the same or mutually
different functions arranged thereon.
[0091] As specific ceramics for forming a
piezoelectric/electrostrictive film, ceramics containing,
individually or as a mixture, 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, strontium bismuth tantalate, or
the like may be listed. More specifically, in view of providing
materials having a high electromechanical coupling factor and
piezoelectric constant, smaller reactivity with the thin plate
portion (ceramics) at the time of sintering the
piezoelectric/electrostrictive film, and stable composition, the
material whose major component is a mixture of lead zirconate, lead
titanate, and lead magnesium niobate, or materials containing
sodium bismuth titanate as the major component may be preferably
used. Additionally, it is possible to add a glass component to the
major component described previously, however, it is not preferable
in view of securing larger displacement. The reason being that the
reaction of the glass with the above-described major components
makes it impossible to obtain a feature intrinsic to the
piezoelectric/electrostri- ctive materials.
[0092] Further, one may use, as the above-described ceramics for
the piezoelectric/electrostrictive film, the ceramics obtainable by
adding thereto, singularly or as a mixture, oxides of lanthanum,
calcium, strontium, molybdenum, tungsten, barium, niobium, zinc,
nickel, manganese, cerium, cadmium, chromium, cobalt, antimony,
iron, yttrium, tantalum, lithium, bismuth, tin, and the like. For
example, by having a mixture of lead zirconate and lead titanate
and lead magnesium niobate, being the major components, contained
with lanthanum or strontium, there may an occasion when an
advantage is obtained that the coercive electric field or the
piezoelectric feature may be made adjustable. Other minor additives
may be added as required.
[0093] On the other hand, an electrode of a
piezoelectric/electrostrictive element is solid at room
temperature, and is preferably composed of a metal superior in
conductivity, for example, such as aluminum, titanium, chromium,
iron, cobalt, nickel, copper, zinc, niobium, molybdenum, ruthenium,
palladium, rhodium, silver, tin, tantalum, tungsten, iridium,
platinum, gold, lead, or the like, is used singularly or as an
alloy, and further, a cermet material made by dispersing the same
materials as used for the piezoelectric/electrostrictive films
and/or the thin plate portions may be used in those materials
listed above.
[0094] Selection of materials for an electrode in a
piezoelectric/electrostrictive element is determined in accordance
with a sequence, a method, or the like in forming the electrode and
the piezoelectric/electrostrictive film. For example, when a
piezoelectric/electrostrictive film is formed on a first electrode
by sintering after the first electrode is formed on a thin plate
portion, it is necessary to use a metal of high melting point such
as platinum or the like for the first electrode which is not
subjected to change at the sintering temperature of the
piezoelectric/electrostrictive film, and when a second electrode is
formed on a piezoelectric/electrostrictive film after the
piezoelectric/electrostrictive film is formed, the electrode can be
formed at a low temperature, thus a metal of low melting point such
as aluminum, gold, silver, or the like may be used.
[0095] As the thickness of an electrode may also decrease a
displacement of the piezoelectric/electrostrictive element,
specifically the second electrode described in FIG. 8 to be formed
after sintering the piezoelectric/electrostrictive film, the
comb-shaped electrode described in FIG. 9, or the like, it is
preferable to use organic metal paste, thereby a finer and thinner
film is obtainable after firing. For example, materials such as
gold resinate paste, platinum resinate paste, silver resinate
paste, or the like can be used.
[0096] Specific configuration of respective members of a device
according to the present invention, namely structure of a
piezoelectric/electrostri- ctive element, arrangement of a terminal
to apply a driving signal, drawing-out of an electrode lead from
the piezoelectric/electrostrictive element, or the like is
described with reference to the accompanying drawings. FIG. 5 shows
a schematic perspective view illustrating a device 1 according to
the above-described third aspect of the present invention. The
device 1 comprises, as a fundamental structure, respective members
of a driving portion 3 to be driven by the displacement of a
piezoelectric/electrostrictive element 2, a movable portion 4 to be
operated based on the drive of the driving portion 3, and a fixing
portion 5 for holding the driving portion 3 and the movable portion
4. The fixing portion 5 and the movable portion 4 are coupled
together via the driving portion 3, and a hole 8 is formed by inner
walls of the driving portion 3, movable portion 4, and fixing
portion 5. The driving portion 3 is a pair of mutually opposing
thin plate portions, and on both outer surfaces of the thin plate
portions, piezoelectric/electrostrictive elements 2 of the
structure of FIG. 8 composed by four of a pair of electrodes and a
piezoelectric film, respective one ends thereof being arranged on
parts of the fixing portion 5 or the movable portion 4. By
employing such structure, the mechanical strength of joined
portions of the thin plate portions with the movable portion, and
the thin plate portion with the fixing portion is raised, and
operation at a high speed is made possible, as well as displacement
quantity of the movable portion can be increased by employing
suitable methods for driving in accordance with a desired operating
aspect. In the aspect shown in FIG. 5, between one pair of the
piezoelectric/electrostrictive element 2 formed mutually opposed
respectively on the outer surface of the same thin plate portion, a
first electrode 2c and a piezoelectric/electrostrictive film 2a are
shared. And for the first electrode 2c, shared and made for common
use, electrode leads are drawn out at, and a terminal 10B is
arranged on, the vicinity of ends of the fixing portion 5 on the
faces where respective piezoelectric/electrostrictive elements 2
are formed. As for the second electrode 2b, electrode leads are
respectively drawn out to, and terminals 10C, 10D are respectively
arranged on, the side of the fixing portion 5 and the side of the
movable portion 4 on the faces where respective
piezoelectric/electrostrictive elements 2 are formed. Such aspect
has no electrode formed at a portion of the fixing portion 5 side
of the face where the hole 8 is apertured, and according to this
structure, the device can be fixed independently of the face where
terminals are arranged. As a result, high reliability can be
obtained in securing the device and bonding of a circuit with the
terminals. By the way, in this aspect, a terminal and a circuit are
joined together by a flexible print circuit (also called FPC), a
flexible flat cable (also called FFC), a wire bonding, or the
like.
[0097] Elements are driven through terminals 10B, 10C, and 10D, and
a voltage is applied across respective sets of the terminals 10B
and 10C, and 10B and 10D. In the device in FIG. 5, the
piezoelectric/electrostatic elements 2 existing in mutually
diagonal directions across the hole 8 are driven simultaneously,
but not simultaneously with the piezoelectric/electrostrictive
elements 2 existing mutually opposed on the same the same thin
plate portion. For example, when a voltage is applied across
respective terminals of the piezoelectric/electrostrictive element
2 of the fixing portion side on the thin plate portion 6 and of the
piezoelectric/electrostrictive element 2 of the movable portion
side on the thin plate portion 7 in diagonal directions thereof, an
electric field is exerted on respective
piezoelectric/electrostrictive films, and the electric field
induced strain is induced on respective
piezoelectric/electrostrictive films by the electric field, strain
due to the transverse effect thereof is converted into bending
displacement of the thin plate portions, and the movable portion is
displaced toward the right-hand side in FIG. 5. Displacement shape
at this time of both the thin plate portions is characterized in
that the shape thereof is mutually rotationally symmetric, the
movable portion displaces in great magnitude, and operation is at
high speed. When the movable portion is made to displace toward the
left-hand side in FIG. 5, another set of elements in diagonal
directions different from the above-described set may be driven in
the same manner.
[0098] On the other hand, a device shown in FIG. 6 is a
modification of the device shown in FIG. 5, and is different
therefrom in the point that a first electrode is not shared among a
pair of the piezoelectric/electrostrictive elements formed mutually
opposed on the outer surface of the same thin plate portion.
[0099] Further, as shown in FIG. 7, three through-holes (11)
provided on a fixing portion 5 may be utilized. In this case, the
through-holes (11) are provided in advance on the fixing portion 5,
and after the through-holes are filled with conductive materials, a
piezoelectric/electrostrictive element pattern is formed so as to
have respective electrodes joined with the through-holes (11), then
the filled surfaces of the through-holes are exposed by machining,
and terminals 10 to apply driving signals are formed thereon. A
conducting wire may be embedded as a conductive material. It should
be noted that, in this example, a through-hole provided in the
vicinity of the hole 8 out of the three through-holes is used as a
common terminal. Meanwhile, the device shown in FIG. 7 is an
example of the device belonging to the third aspect of the present
invention.
[0100] In FIG. 7, electrode leads 2d are respectively formed on the
inner walls of a pair of thin plate portions 6 and 7, which is one
of the factors defining the hole 8. The two electrode leads 2d are
connected with respective through-holes 11 formed on the lower part
of the fixing portion 5 out of the above-described three
through-holes. Second electrodes 2b respectively provided in two
piezoelectric/electrostrictive elements 2 having one end portion on
the movable portion 4 on respectively provided mutually opposed on
the outer surfaces of a pair of thin plate portions 6 and 7 are
respectively made conductive with the above-described electrode
leads 2d via the through-holes in the movable portion 4. Thus, the
second electrodes 2b in the piezoelectric/electrostr- ictive
elements 2 having one end portion on the movable portion 4 are
connected with respective through-holes 11 formed at the lower part
of the fixing portion 5 via the electrode lead 2d. Meanwhile, first
electrode 2c in the two piezoelectric/electrostrictive elements
respectively provided mutually opposed on the outer surfaces of a
pair of thin plate portions 6 and 7 are respectively made to be
commonly used, and use a terminal provided on the through-hole 11
provided in the vicinity of the hole 8 out of the three
through-holes as a common terminal. In this aspect, a face of the
fixing portion 5 where the through-holes are not formed, namely, a
back side face 9 in FIG. 7, can be used for securing elements.
[0101] Although not shown, for example, in the device shown in FIG.
5, a terminal may be arranged on the main surface, namely on one of
the faces where the hole 8 is apertured. In other words, aspects
for electrode lead drawing out or aspects for terminal arrangement
are not specifically limited to the above-described aspects, and it
is important to determine them in accordance with a variety of
conditions such as use application of a device, method of
fabricating thereof, function of a piezoelectric/electrostrictive
element, method of driving, and the like.
[0102] For example, a device described in FIG. 15 has, in the
structure according to the third aspect of the present invention,
piezoelectric/electrostrictive elements in three stairs. More in
detail, respective piezoelectric/electrostrictive elements 2,
basing on the structure described in FIG. 8, are formed by
sequentially laminating a first electrode 2c, a
piezoelectric/electrostrictive film 2a, a second electrode 2b, a
piezoelectric/electrostrictive film 2a, a first electrode 2c, a
piezoelectric/electrostrictive film 2a, and a second electrode 2b,
and members comprising a pair of electrodes and a
piezoelectric/electrost- rictive film are laminated in three stairs
in a direction in which composing films of the elements are formed
in layers. Further, a piezoelectric/electrostrictive film is shared
among respective piezoelectric/electrostrictive elements arranged
mutually opposed on the same thin plate portion, and in addition, a
second electrode is also shared among the above-described elements.
The elements are driven by conducting electric signals to be
transmitted to terminals 10A, 10B, and 10C. The terminal 10A is
connected with the electrode 2c of the
piezoelectric/electrostrictive element 2 formed on the movable
portion side of the thin plate portion 6, the terminal 10B is
connected with the electrode 2c of the
piezoelectric/electrostrictive element 2 formed on the fixing
portion side on the thin plate portion 6, and the terminal 10C is
connected with the electrode 2b of both the
piezoelectric/electrostric- tive elements 2 on the thin plate
portion 6, respectively, and a voltage is applied respectively to
sets of the terminals 10A and 10C, and 10B and 10C. The structure
of and the relations with the terminals of these respective
piezoelectric/electrostrictive elements are the same also for the
respective piezoelectric/electrostrictive elements of the thin
plate portion 7. Further, respective electrodes denoted by the same
symbol in the same element are to be applied with a voltage of the
same potential.
[0103] Such a device as shown in FIG. 15 is driven such that, for
example, two piezoelectric/electrostrictive elements 2 mutually
existing in diagonal direction across the hole 8 are simultaneously
driven, while respective piezoelectric/electrostrictive elements 2
existing mutually opposed on the same thin plate portion are not
simultaneously driven. In other words, when a voltage is applied to
respective terminals of the piezoelectric/electrostrictive elements
2 of the fixed portion side on the thin plate portion 6 and the
piezoelectric/electrostrictive elements 2 of the movable portion
side on the thin plate portion 7 in the diagonal directions
thereof, an electric field is exerted to respective
piezoelectric/electrostrictive films, the electric field induced
strain is induced on respective piezoelectric/electrostrictive
films by the electric field, strain due to the transverse effect
thereof is converted into a bending displacement of the thin plate
portions, thus the movable portion is displaced toward the
right-hand side in FIG. 15. At this time, the displacement shape of
both the thin plate portions is characterized in that a shape is
mutually rotationally symmetric, the movable portion has a very
large displacement because of large driving force due to
piezoelectric operating portions which are made in three stairs
(three layers), and operation is performed in a high speed. When
the movable portion is made to displace toward the left-hand side
in FIG. 15, ordinarily, the elements related with another
combination of the diagonal directions different from the
above-described combination may be driven in the similar
manner.
[0104] The device shown in FIG. 16 is different from the device
shown in the above-described FIG. 15, and
piezoelectric/electrostrictive elements arranged so as to be
mutually opposed on the same thin plate portion share both one
layer of the piezoelectric/electrostrictive film 2a at the closest
side of the thin plate portions 6 and 7 and a second electrode 2b,
in the laminating direction of the composing films of the elements.
Other structures and methods of driving thereof are the same as for
the device shown in FIG. 15. In comparison with the device shown in
FIG. 15, the device shown in FIG. 16 is characterized in that a
displacement of the movable portion can be made larger since a
portion, where thickness is thinner, exists between the
piezoelectric/electrostrictive elements 2 arranged mutually opposed
on the same thin plate portion.
[0105] A device shown in FIG. 17, different from the
above-described device shown in FIG. 15, comprises respective
piezoelectric/electrostrict- ive elements 2 arranged so as to be
mutually opposed on the same thin plate portion, wherein any of
composing films of respective elements are made not to be shared,
and respectively arranged independently, and terminals 10 (10 A,
10D) for driving elements of the movable portion 4 side on the thin
plate portions 6 and 7 are respectively formed on the movable
portion 4 on the face where the hole 8 is apertured, with terminals
10B, and 10C for respective piezoelectric/electrostrictive elements
2 of the fixing portion 5 side on both the thin plate portions 6
and 7 formed on the face where elements of the fixing portion 5 are
formed. Terminals 10A are terminals for conducting electric signals
to second electrodes 2b of the elements of the movable portion side
on the thin plate portions 6 and 7, while terminals 10D are
terminals for conducting electric signals to first electrodes 2c of
the same elements described above. The basic structure and the
method of driving of the other elements thereof are also the same
as for the device shown in FIG. 15. In comparison with the device
shown in FIG. 15, the device shown in FIG. 17 is characterized in
that the movable portion thereof can displaces in further greater
magnitude, of course, than the device shown in FIG. 15 and also
even than the device shown in FIG. 16, as the device shown in FIG.
17 is so structured that only the thin plate portions 6 and 7 exist
between the piezoelectric/electrostrictive elements 2 arranged
mutually opposed on the same thin plate portions.
[0106] The device shown in FIG. 18 is a device having a structure
that a member comprising a pair of electrodes and a
piezoelectric/electrostricti- ve film is laminated in two stairs in
a laminating direction of the composing films of elements. Further,
respective piezoelectric/electrostr- ictive elements arranged
mutually opposed on the same thin plate portions 6 and 7 are,
similarly with the device shown in FIG. 17, not sharing any
composing films, which are respectively arranged independently, and
any terminals for conducting electric signals to respective
electrodes are formed on the face of the movable portion 4 and the
fixing portion 5 where the elements are formed. Structure of
elements being different from that of the devices shown in FIGS.
15, 16, and 17, and in two-stair structure, the device shown in
FIG. 18 has a characteristic that it is superior in lighter weight
and smaller power consumption, while a bit inferior in driving
force.
[0107] A device shown in FIG. 19 is shown as an example wherein one
end of the first electrode 2c which is used an electrode commonly
shared between the respective four elements and one end of
terminals 10A and 10B for applying a signal for driving its first
electrode 2c are formed on the same position as the ends of the
movable portion and the fixing portion. This structure has such a
characteristic that it can be produced easily because the patterns
of the first electrode 2c and the terminals 10 in addition to the
movable portion and the fixing portion are formed simultaneously by
the mechanical processing mentioned hereinafter. Additionally, it
is possible to keep always the relationship in the position between
the relative position of the terminals 10 for the first electrode
2c and the present device itself constant. Therefore, one may
easily fit the position between the terminals and the outer
apparatuses at the time of setting the present device by taking,
for example, the end portion of the fixing portion as a
reference.
[0108] In the present invention as such, it is also preferable that
a piezoelectric/electrostrictive element in a device is composed as
a multi-stair structure. The number of the stairs is suitably
determined depending on the use application and the specification
of the device. As a device according to the present invention has,
as can be understood from the embodiments illustrated in the
drawings, the distance in the width direction of the thin plate
portion basically unchanged, the device has an extremely preferable
structure in applying the device to such controlling devices for
positioning or suppressing ringing, and the like, a magnetic head
for a hard disk drive to be used, for example, in a extremely
narrow gap.
[0109] By the way, in the second aspect and the third aspect
according to the present invention, more specifically in the third
aspect, as illustrated in FIGS. 3(a) and (b), by separating
(parting) piezoelectric/electrostrictive elements substantially at
the center of respective thin plate portions, the thin plate
portions become liable to be bent at the separated (parted)
positions, and thus individual piezoelectric/electrostrictive
elements are made easier to displace. As a result, the displacement
of the piezoelectric/electrostrictive element is enabled to be
efficiently transferred to the movable portion, which is an
advantage. Naturally, depending on the use of the device, the
separation may be performed at a position closer to either the
movable portion or the fixing portion.
[0110] (3) Hole
[0111] The shape of a hole 8 formed by inner walls of the driving
portion 3, movable portion 4, and fixing portion 5 can be optional
as long as it does not hamper operation of the driving portion. As
described previously, electrode leads may be provided on the inner
walls of a pair of the thin plate portions defining the hole 8.
[0112] Further, since a device of the present invention is not
necessarily required to compose the entirety thereof with
piezoelectric/electrostrict- ive materials, it has an advantage
that members other than the piezoelectric/electrostrictive elements
can select materials thereof depending on required features of
respective materials. Namely, by composing the members other than
the piezoelectric/electrostrictive elements with materials of
lighter weight, on operation, the influence of harmful vibration
can be reduced, and similarly the mechanical strength, the handling
property, the impact resistance, and the humidity resistance
thereof can be improved with ease.
[0113] Furthermore, as filling materials are not required to be
used, the efficiency of a displacement due to the inverse
piezoelectric effect or the electrostrictive effect also cannot be
reduced.
[0114] 3. Method of Fabricating Device
[0115] Now, a method of fabricating a device according to the
present invention is described.
[0116] The device according to the present invention comprises
respective members composed of ceramic materials, and as comprising
members of the device, a base portion except a
piezoelectric/electrostrictive element, namely thin plate portions,
a fixing portion, and a movable portion are preferably fabricated
by use of the ceramic green sheet laminating method, while
respective terminals and the piezoelectric/electrostrictive element
are preferably fabricated by use of the film forming methods for
thin films, thick films, or the like. The ceramic green sheet
laminating method which can integrally form respective members,
described previously, of the base of the device is an easy method
of fabrication which can bring about a joined portion of high
reliability and secure the rigidity of the device, as variation
with time of the state of the joined portions of respective members
is seldom caused. As the device according to the present invention
uses the joined portions of thin plate portions, comprising the
driving portion, with the fixing portion and the movable portion,
as fulcrums for developing displacements, reliability of the joined
portions is critically important such that the feature of the
device is dominated thereby. As the method is also superior in
productivity and formability, a device of a predetermined shape can
be obtained in a shorter time and in better reproducibility. It
should be noted that, although expressions of a thin plate and a
thin plate portion are used in the present specification, in
principle, the former indicates a member related with the green
sheet in the method of fabrication, while the latter indicates a
portion comprising the driving portion together with the
piezoelectric/electrostrictive element in a laminated body.
[0117] (1) Fabrication of Laminate
[0118] Firstly, a slurry is prepared by adding and mixing a binder,
a solvent, a dispersant, a plasticizer, and the like into a ceramic
powder such as zirconia, or the like, then the slurry is processed
for degassing, and then the slurry is used in forming a ceramic
green sheet having a predetermined thickness by way of the reverse
roll coater method, the doctor blade method, or the like.
[0119] Then, by way of die-cutting using a die (punching), laser
processing, or the like, the ceramic green sheet is processed into
a desired shape. A laminate can be fabricated, in principle, in
accordance with a method disclosed in the specification of U.S.
Ser. No. 09/441,914 filed on Nov. 17, 1999. The contents of the
aforementioned application are incorporated herein by
reference.
[0120] FIG. 11(a) schematically illustrates a ceramic green sheet
101 which is a ceramic green sheet mainly constituting a thin plate
after being sintered, and a ceramic green sheet 102 with at least
one rectangular hole 103 formed thereon which is a ceramic green
sheet to be used for members constituting the movable portion and
the fixing portion. With the ceramic green sheet 102, by forming
the holes 103 so as to be parallel in one or more rows, a plurality
of devices can be obtained at a time, or at least one device having
a plurality of movable portions can be obtained. By use of at least
two ceramic green sheets constituting the thin plate and at least
one ceramic green sheet having at least one hole formed thereon,
prepared in advance, for example, between at least two ceramic
green sheets constituting the thin plate, at least one ceramic
green sheet having the at least one hole formed thereon is
laminated to make a ceramic green laminated body comprising a
ceramic green sheet constituting a pair of thin plates and a series
of ceramic green sheets each having at least one hole formed
thereon.
[0121] As a matter of course, there is no limitation whatsoever on
the preparing method of a ceramic green laminated body, in other
words, on laminating sequence of a ceramic green sheet constituting
the thin plate, and the ceramic green sheet having the at least one
hole formed thereon, and ordinarily lamination is possible at an
optional sequence so long as the laminated body causes no
inconvenience to the processing steps to follow.
[0122] For example, steps for preparing the above-described ceramic
green laminated body include a step to laminate -ceramic green
sheets constituting a pair of thin plates mutually opposed,
respectively a step to laminate ceramic green sheets constituting a
pair of thin plates mutually opposed on the outermost layer, a step
to laminate a ceramic green sheet constituting the thin plate with
at least one ceramic green sheet having at least one hole formed
thereon, a step to laminate a ceramic green sheet constituting the
thin plate with desired number of ceramic green sheets each having
at least one hole formed thereon, a step to laminate at least one
ceramic green sheet having at least one hole formed thereon with
ceramic green sheets constituting a pair of thin plates on the
outermost layer mutually opposed, a step wherein two laminates A
comprising a ceramic green sheet constituting a thin plate
laminated with at least one ceramic green sheet having at least one
hole formed thereon are prepared, and a laminated B laminated with
one or a plurality of ceramic green sheet each having at least one
hole formed thereon is prepared, and when the two laminated bodies
A are laminated so that respective thin plates mutually form the
outermost layer, the lamination is performed with an intervention
of a ceramic green sheet having at least one hole formed thereon or
the laminate B, and the like.
[0123] It should be noted that when a device according to the
present invention is fabricated in such ceramic green sheet
laminating method, in some cases, specifically when a hole is
formed by laminating a thick sheet, difference in dimensions of
lengths of a pair of thin plate portions, which govern the driving
portion, is likely to occur because of shrinkage of a ceramic green
sheet, deterioration of machining accuracy due to differences in
dimension accuracy attributable to machining of a thicker ceramic
green sheet, shifting of position due to deformation of a sheet
while laminating, or the like. The differences in dimension of a
pair of the thin plate portions affects displacement in the right
and left directions (the X-axis direction), and in addition a
displacement shape of the movable portion is liable to include a
component in the rotating direction, thus making the movable
portion difficult to dominantly displace toward the major axis
direction.
[0124] For such problems, a countermeasure includes a step wherein
a ceramic green sheet having at least one hole formed thereon
mounted on a plastic film is, when laminating at least a plurality
of ceramic green sheet with the at least one hole formed thereon,
laminated on a surface to be the outermost layer of the ceramic
green laminate having the at least one hole formed thereon so the
plastic film forms a new outermost layer thereof, and after the
hole is accurately positioned, the plastic film is removed. Another
countermeasure is a step wherein a ceramic green sheet having at
least one hole formed thereon mounted on a plastic film is
laminated with a ceramic green sheet constituting the thin plate so
that the plastic film forms an outer layer thereof, and after the
hole is accurately positioned, the plastic film is removed, and by
employing the step, not only deformation while handling the ceramic
green sheet is substantially avoided, but also both surfaces
constituting the outermost layers are made in the same shape, thus
enabling accurate positioning of the hole. As a result, precision
in lamination is improved, dimension is stable due to improved
manufacturing precision, and a feature as a device, for example,
displacement feature, is improved.
[0125] Further, of the methods of fabricating using a plastic film
described previously, the former method is high in laminating
efficiency required in obtaining the final laminate, and is also an
effective method in reducing the number of steps required in
fabricating. While, the latter method is also an advantageous
method in providing a bonding assistant layer to be described later
for securing bonding properties of laminating interface.
[0126] With regard to the number of laminating steps, the former is
an efficient method, as lamination of a ceramic green sheet formed
on a plastic film with another ceramic green sheet having a hole
thereon can be performed in one step, and respective lamination of
mutually opposing surfaces where a plastic film is peeled off and
removed after lamination with a ceramic green sheet constituting a
thin plate can be performed in one step, and for example, total
number of lamination required can be in two steps in the minimum.
However, with the latter, mutually opposing thin plate portions are
formed by laminating a ceramic green sheet constituting the thin
plate with a ceramic green sheet having a hole thereon mounted on a
plastic film respectively by separated steps, and thereafter to be
laminated with a ceramic green sheet having a hole formed thereon.
Therefore, the total number of laminating steps required is a
minimum of three, and more lamination steps are required than the
former method.
[0127] On the other hand, a bonding assistant layer for improving
the laminating property of a ceramic green sheet is ordinarily
formed over a substantially entire area of the ceramic green sheet
prior to processing of a hole and the like, and thereafter a
predetermined hole is formed by the punching or the like by use of
a die, then a predetermined number of the ceramic green sheets are
laminated. If this is applied to the former method, the bonding
assistant layer is required to be formed on a laminating surface
with the thin plate after the film is removed. At this time, in
spite of the fact that shaping is exactly done by way of mold
machining or the like, there is a great possibility that the
shaping precision is deteriorated by formation of the bonding
assistant layer. Although there is also a means to provide a
bonding assistant layer for a green sheet constituting a thin
plate, this causes deterioration of the feature as the device, not
only by the variation in total thickness which is increased because
the ordinary variation in thickness of a bonding assistant layer is
larger than the variation in thickness of the ceramic green sheet
constituting the thin plate, but also by the thickness of the thin
plate which is increased as much the thickness of the bonding
assistant layer. Contrarily, when the bonding assistant layer is
applied to the latter method, high reliability in lamination and
high dimension precision can be compatible, since the bonding
assistant layer can be formed on the ceramic green sheet in a state
mounted on a plastic film, and a hole can be processed after the
bonding assistant layer is formed. Thus, the precision of the hole
can be secured by the precision of the die, and the ceramic green
sheet constituting the thin plate is untouched in any way. The
surface where the plastic film is peeled off and removed is secured
of the reliability in lamination by the bonding assistant layer
formed on another ceramic green sheet, having a hole formed
thereon, to be laminated on the surface.
[0128] Although the former method and the latter method have a
common object to obtain stability of the shape of the thin plate
portions, they have respective characteristics in their processes
of fabricating, and the methods are subjected to suitable selection
depending upon the structure and the like of a laminate.
[0129] It should be noted that a ceramic green sheet having at
least one hole formed thereon mounted on a plastic film and is not
only a ceramic green sheet having at least one hole formed thereon
prepared by the die cutting machining or the laser machining of the
ceramic green sheet on a plastic film, but also includes a ceramic
green sheet having at least one hole formed thereon formed in
advance in a predetermined shape, and further prepared by attaching
a plastic film thereon. The plastic film is, in view of exfoliating
property, strength, or the like, preferably a poly(ethylene
terephthalate) film. Further, a ceramic green sheet mounting
surface of the plastic film is preferably a film coated with a
release agent containing silicone or the like as components, with
an object of increasing the releasing property of the green sheet.
Furthermore, the thickness of the ceramic green sheet on the
plastic film is preferably thinner, and desirably the thickness
being equivalent to the thickness of the ceramic green sheet for
the thin plate, which is more preferable. The reason being that by
thinning the thickness of the ceramic green sheet, the machining
precision of the ceramic green sheet per se is increased. It should
be noted that in order to make easier the handling of respective
ceramic green sheets, more specifically a ceramic green sheet
constituting the thin plate, to prevent elongation and the surface
waviness of a sheet, and to secure stability of the shape of the
thin plate portion, it is preferable to handle a ceramic green
sheet in a form attached to the plastic film described
previously.
[0130] Hereinafter, some descriptions are made about specific
examples of the cases where a ceramic green laminate is prepared.
Naturally, the examples hereinafter illustrated are merely
examples, and the cases where a ceramic green sheet is prepared are
not limited thereto.
LAMINATION EXAMPLE 1
[0131] After sequentially laminating a ceramic green sheet
(hereinafter referred to as "GS") 1 for the thin plate, GS1 having
a hole formed thereon (hereinafter referred to as "with a hole"),
GS2 with a hole, GS3 with a hole, GS4 with a hole, and GS2 for the
thin plate, all shown in FIG. 20, the lamination is subjected to a
compression to produce an integrally laminated ceramic green
body.
LAMINATION EXAMPLE 2
[0132] Step 1: After laminating GS1 for the thin plate over GS1
with a hole, the lamination is subjected to compression to produce
an integrally laminated ceramic green body.
[0133] Step 2: After laminating GS4 with a hole over GS2 for the
thin plate, the lamination is subjected to compression to produce
an integrally laminated ceramic green body.
[0134] Step 3: After sequentially laminating the integrally
laminated ceramic green body obtained in step 1, GS2 with a hole,
GS3 with a hole, and an integrally laminated ceramic green body
obtained in step 2, the lamination is subjected to compression to
produce an integrally laminated ceramic green body.
LAMINATION EXAMPLE 3
[0135] Step 1: After sequentially laminating GS1 with a hole, GS2
with a hole, GS3 with a hole, and GS4 with a hole, the lamination
is subjected to compression to produce an integrally laminated
ceramic green body.
[0136] Step 2: After sequentially laminating GS1 for the thin
plate, an integrally laminated ceramic green body obtained in step
1, and GS2 for the thin plate, the lamination is subjected to
compression to produce an integrally laminated ceramic green
body.
LAMINATION EXAMPLE 4
[0137] Step 1: After laminating GS2 with a hole over GS3 with a
hole, and the lamination is subjected to compression to produce an
integrally laminated ceramic green body.
[0138] Step 2: After sequentially laminating GS1 for the thin
plate, GS1 with a hole, an integrally laminated ceramic green body
obtained in step 1, GS4 with a hole, and GS2 for the thin plate,
the lamination is subjected to compression to produce an integrally
laminated ceramic green body.
[0139] The integrally laminated ceramic bodies obtained in the
above-described lamination examples 1 to 4 are sintered to produce
integrated sintered bodies. However, examples described above do
not represent all methods of fabrication of the present invention,
and there is no specific limitation whatsoever for the number and
the sequence for the integrating lamination.
[0140] Depending on a structure, for example, the shape of the
hole, the number of the ceramic green sheets with a hole, the
number of the ceramic green sheets for the thin plate, and the
like, the number and the sequence for the integrating lamination
are suitably determined so that an integrated sintered body of
desired structure can be obtained.
[0141] Naturally, the shape of a hole is not necessarily the same,
and is determined depending on a desired function. Further, there
are also no specific limitation whatsoever on the number and the
thickness of respective ceramic green sheets.
[0142] The above-described compression can further improve the
laminating properties by heating, thus compression under heating
atmosphere can be advantageously employed. As the laminating
property of a ceramic green sheet interface can be improved by
applying a paste, slurry, or the like containing a ceramic powder
(preferably, of composition the same as or similar to the ceramic
powder used for the ceramic green sheet, in view of securing
reliability), and a binder as the major component, on the ceramic
green sheet, and printing thereon, thus a bonding assistant layer
can be made, it is also desirable to use the bonding assistant
layer.
[0143] Further, a protrusion may be provided on the outermost layer
of the ceramic green sheet laminate, at a portion except for at
least the thin plate portion on at least one side of the outer
layer surface thereof. Although the device according to the present
application is to be formed of a piezoelectric/electrostrictive
element on the outer surface of mutually opposing thin plate
portions ordinarily by known means such as the screen printing
method, when, for example, the piezoelectric/electrostrictive
element is formed by the screen printing method, the element is
prevented from a damage, since the surface of the element formed on
an opposite surface has no chance to directly touch a stand such as
a printing stage, a sintering setter, or the like, because of the
protrusion formed. Furthermore, by suitably selecting the height of
the protrusion, the thickness of the element can also be
controlled. Whereas the protrusion can be formed also for a
sintered body of green laminate, namely a ceramic laminate, it is
preferable to form the protrusion for a green laminate, and then to
sinter for integration, in view of the stability as a structure and
the stability in dimensions.
[0144] As shown in FIG. 11(a), a green laminate can be obtained by
sequentially laminating, while positioning by use of a reference
hole 104, a ceramic green sheet 101 constituting a thin plate, a
ceramic green laminate 102 prepared by laminating a desired number
of ceramic green sheets each having at least one hole formed
thereon, and a ceramic green sheet constituting a thin plate, in
this order, and then integrating by means of above-described
compression under heating, or the like. Although not shown, when
the thickness of the ceramic green laminate is too thick, a green
laminate having the thickness thereof halved in advance into upper
and lower portions is first formed, and the final green laminate
may be obtained by bonding the portions together so as to have the
holes facing each other.
[0145] With regard to a laminate 108, it is necessary to have
communicating holes 106 for communicating with the outside space
and portions to be holes 103 on a ceramic green sheet 102 and
formed in advance on the ceramic green sheet 102, or the
communicating holes 106 are to be bored after the laminate is made.
However, as long as respective holes 103 are communicated with the
outside space, the shape of the communicating holes 106 is not
specifically limited, and in addition to shapes penetrating through
a plurality of holes 103 as shown in FIGS. 11(a), and (b), it may
be structured so that respective holes 103 are individually
communicated with the outside space as shown in FIG. 11(d). Then,
the ceramic green laminate thus integrated by one of these methods
is sintered at a temperature around 1200 to 16000.degree. C. as to
be described hereinafter. A ceramic laminate thus obtained by the
sintering, however, may have an unintended warping. In such case,
it is preferable to flatten by refiring (hereinafter referred to as
"warping correction") at a temperature close to the previously
described sintering temperature with a weight placed thereon. When
performing the warping correction, a porous ceramic plate such as a
planar alumina, or the like may be preferably used as the weight.
Further, in addition to the warping correction following the
sintering, it can be preferably performed simultaneously with
sintering with the weight placed in advance at the sintering.
[0146] (2) Formation of Piezoelectric/Electrostrictive Element
[0147] A piezoelectric/electrostrictive element 107 can be formed
on a surface of a thin plate of a ceramic laminate in the required
number, when fabricating the device of the present invention, by
the thick film forming method, such as the screen printing method,
the dipping method, the coating method, the electrophoresis method,
or the like, or the thin film forming method, such as the ion beam
method, the sputtering method, the vacuum deposition method, the
ion plating method, the chemical vapor deposition method (CVD),
plating, or the like (refer FIG. 11(b). Meanwhile, FIG. 11(b)
schematically shows a piezoelectric/electrostrictiv- e element 107,
however, it does not exactly show the arrangement of the
piezoelectric/electrostrictive element 107 in the device of the
present application.).
[0148] By forming the piezoelectric/electrostrictive element by the
film forming methods, the piezoelectric/electrostrictive elements
and the thin plate portions can be integrally joined and provided
without using an adhesive, thus enabling reliability and
reproducibility to be secured, and integration to be made easy.
However, in the method of fabrication in the present invention, it
is preferable to form the piezoelectric/electrostrictive element
107 by the thick film method. The reason being that, by use of the
method, a piezoelectric/electrostrictive film can be formed by use
of a paste, slurry, or suspension, emulsion, sol, or the like of
piezoelectric ceramic particles of average particle size of 0.01 to
5 .mu.m, preferably 0.05 to 3 .mu.m as the major component, and a
favorable piezoelectric operating feature is obtained therefrom.
Specifically, the electrophoresis method is advantageous in that a
film can be formed in high density and in high shape precision.
Further, being capable of simultaneously forming a film and a
pattern, the screen printing method is preferably employed as a
method of fabricating the device according to the present
invention.
[0149] Specifically, after sintering a ceramic green laminate 108
at predetermined conditions, preferably at 1200 to 16000.degree.
C., on a predetermined position of a surface of a thin plate (a
sintered ceramic green sheet 101), respectively at predetermined
portions, in accordance with the three aspects of the device
according to the present invention, sequentially printed and
sintered are a first electrode, then a
piezoelectric/electrostrictive film, and further a second
electrode, thus a piezoelectric/electrostrictive element is formed.
Further, electrode leads are printed and sintered for connecting
electrodes with a driving circuit. Here, if materials are selected
so as to have sintering temperatures for respective members
gradually becoming lower, such as platinum (Pt) for the first
electrode, lead zirconate titanate (PZT) for the
piezoelectric/electrostrictive film, gold (Au) for the second
electrode, and silver (Ag) for the electrode leads, re-sintering of
the materials once sintered is avoided at any sintering stages, and
occurrence of troubles such as exfoliation or aggregation of
electrode materials or the like can be avoided.
[0150] In addition, by suitably selecting materials, respective
members and electrode leads of the piezoelectric/electrostrictive
element 107 can be sequentially printed to be integrally sintered
at one time, while respective electrodes and the like can be
provided at a lower temperature after the
piezoelectric/electrostrictive film is formed. Further, there is no
problem that respective members and electrode leads of the
piezoelectric/electrostrictive element are also formed by the thin
film forming method such as the sputtering method, the vapor
deposition method, or the like, and in such case, a heat treatment
is not necessarily required. In addition, it is also preferable
that a piezoelectric/electrostrictive element 107 is formed in
advance on a ceramic green sheet 101 at a position at least finally
to be a thin plate portion, and a ceramic green laminate 108 and
the piezoelectric/electrost- rictive element are co-fired. When
co-firing, one method is to co-fire all composing films of a
piezoelectric/electrostrictive element, another method is to
co-fire only a first electrode and a ceramic green sheet 101, and
still another method is to co-fire the composing films except a
second electrode and the ceramic green sheet 101, or the like. As a
method for co-firing the piezoelectric/electrostrictive element 107
and the ceramic green laminate 108, a method is that a
piezoelectric/electrostrictive film is formed by the press molding
method by use of a mold, the tape forming method by use of a slurry
material, or the like, the piezoelectric/electrostrictive film
still to be sintered is laminated at a predetermined position on
the ceramic green sheet 101 by the compression under heating or the
like, then co-fired to produce a movable portion, a driving
portion, thin plate portions, and piezoelectric/electrostrictive
films at the same time. However, in this method, electrodes are
required to be formed in advance on the thin plates or the
piezoelectric/electrostrictive films by use of the film forming
methods described previously. Further, in addition to the
above-described method, it is also possible to form electrodes and
piezoelectric/electrostrictive films, which being respective
composing layers of the piezoelectric/electrostrictive element, on
a ceramic green sheet 101 at a position at least finally to be a
thin plate portion by the screen printing method, to be
co-fired.
[0151] A sintering temperature of a piezoelectric/electrostrictive
film is suitably determined by materials composing the same, and it
is generally 800 to 1400.degree. C., and preferably 1000 to
1400.degree. C. In this case, in order to control composition of
the piezoelectric/electrostricti- ve film, it is preferable to
sinter under the presence of an evaporating source of materials of
the piezoelectric/electrostrictive film. In addition, when a
piezoelectric/electrostrictive film and a ceramic green laminated
body 108 are co-fired, sintering conditions of the both are to be
matched.
[0152] Further, when a device having a
piezoelectric/electrostrictive element respectively on both
portions of a pair of opposing thin plate portions is fabricated, a
piezoelectric/electrostrictive film, an electrode, and the like are
respectively printed on both sides of a ceramic laminate. In such
case, it is necessary to take a measure lest
piezoelectric/electrostrictive films, electrodes, and the like,
printed on the ceramic laminated body should attach to, or come in
contact with, a printing stage by {circle over (1)} printing on a
printing stage having a cavity thereon, or {circle over (2)}
firstly forming a convex in a frame-form on the periphery of a
printing position on at least one of the printing surfaces of a
ceramic laminate, then the surface with the convex formed thereon
is printed, and then the other surface is printed, or the like.
Further, particularly when a piezoelectric/electrostrictive element
is respectively formed on both surfaces of a ceramic laminate, it
is preferable to have the same sintering atmosphere on both
surfaces at sintering the piezoelectric/electrostrictive film
described previously. For example, ordinarily a ceramic laminate
with a piezoelectric/electrost- rictive element (film) formed
thereon is placed on a board such as a setter or the like for
sintering, and in this case, intervals between setters to be piled
up are adjusted so that spacing between a
piezoelectric/electrostrictive film and a setter is the same for
respective stages.
[0153] (3) Cutting Laminated Body
[0154] A sintered laminate with the above-described
piezoelectric/electrostrictive element formed thereon is, after a
notch is formed thereon, and a piezoelectric/electrostrictive
element and electrode leads are treated for coating, shielding, or
the like, depending on requirements, cut in a laminating direction
of a ceramic green sheet, such that a rectangular hole 103
apertures on the side of a laminate. Thus, a plurality of devices
can be simultaneously obtained (FIG. 11(c)). As a method of
cutting, in addition to dicing machining, wire-saw machining, or
the like (mechanical machining), laser beam machining by use of YAG
laser, excimer laser, or the like, and electron-beam machining can
be applied. When cutting into respective desired units, it is
preferable to have the cut bodies subjected to heat treatment at
300 to 800.degree. C. The reason being that whereas defects such as
micro-cracks or the like are likely to be caused inside a sintered
body by the machining, the defects can be removed by the heat
treatment, thus improving reliability. Further, it is also
preferable to have the sintered body subjected to aging treatment
by leaving it at least for about 10 hours at about 80.degree. C.
after the above-described heat treatment. By this treatment,
various stresses and the like suffered during the fabricating
process are mitigated to contribute to improvement of the
features.
[0155] In the method of fabricating a device of the present
invention, a hole of a desired shape, for example, a hole 103 in
the rectangular shape, is cut so as to aperture on a side of a
laminate. Such cutting has advantages not only in separating a
plurality of devices, but also being capable of simultaneously
forming thin plate portions and a hole (in the device 1 of FIG.
3(a), the thin plate portions 6 and 7 and the hole 8), and it is
desirable that a structure where two or more rectangular solids are
coupled by thin plates, the structure being complicated and
difficult to be fabricated, can be obtained with ease.
[0156] Further, by suitably changing the number and the position of
formation of holes 103 in a ceramic green sheet 102, or the cutting
position of a laminate 108, a device with a plurality of driving
portions formed thereon and a device having driving portions in
different lengths can be formed with extreme ease. Furthermore, by
simultaneously cutting a laminate 108 and a
piezoelectric/electrostrictive element 107, devices with thin plate
portions and piezoelectric/electrostrictive elements in the same
width can be made with ease, which is preferable. Although these
cuttings can be performed in a green state prior to sintering, in
order to increase dimension precision and to prevent grain release
of respective ceramic powders, it is preferable to cut a sintered
body.
[0157] Further, a device according to the present invention can be
made by the press molding method or the casting method, the
injection molding, the photolithography, or the like, in addition
to the methods of preparation described above by use of a ceramic
green sheet. Alternatively, the device can be made by bonding
respective members prepared as separate bodies, but this method has
a problem also in reliability as damages are likely to occur at
joined portions, in addition to the low productivity.
[0158] 4. Application Example of Device
[0159] Lastly, as one of application examples of a device of the
present invention, an example where the device of the present
invention is applied to a displacement element for an optical
shutter is described with reference to drawings. FIGS. 12(a) and
(b), and FIGS. 13(a), (b), and (c), show schematically examples
where devices of the present invention are applied to displacement
elements for optical shutters, and it can be easily understood that
the examples do not exactly represent structures according to the
present application. By the way, an "optical shutter" in the
present application means a functional element for controlling
transmission and shielding of the light by relative movement of two
shielding plates, and as it can perform ON/OFF control and quantity
control of the light, it can be functioned as an optical switch or
an optical diaphragm.
[0160] When a device of the present invention is mounted on an
optical shutter, at least one of two shielding plates is mounted on
a movable portion of the device of the present invention.
[0161] For example, an optical shutter 110 shown in FIGS. 12(a) and
(b) comprises two units 111A and 111B each provided with a device
of the present invention and a shielding plate. Two shielding
plates 113A and 113B are respectively mounted on movable portions
114A and 114B, and arranged so that mutual planar surfaces are in
parallel, and parts of the surfaces of the respective planar plates
mutually overlap toward the incident direction of the light L.
[0162] The optical shutter 110 shields the light L in the state
shown. However, by applying voltages of the same phase to
piezoelectric/electrostrictive elements 112A and 112B respectively
formed on driving portions of the devices, the shielding plate 113A
moves to the left-hand side in FIG. 12(a), and the shielding plate
113B moves to the right-hand side in FIG. 12(a), causing to change
the overlapping condition of the shielding plates 113A and 113B,
thus ON/OFF control and quantity control of the light can be
performed.
[0163] Further, an optical shutter 120 shown in FIG. 13(a)
comprises two units 121A and 121B respectively comprising a device
of the present invention and a shielding plate, two shielding
plates 123A and 123B are respectively mounted on movable portions
124A and 124B of respective devices, and arranged so that mutual
planar surfaces are in parallel, and the surfaces of the planar
plates are totally overlapped toward the incident direction of the
light. At opposing positions of the shielding plates 123A and 123B,
slits 125A and 125B are respectively formed.
[0164] Although the optical shutter 120 transmits the light L
through the slits 125A and 125B in the state shown in FIGS. 13 (a)
and (b), by applying voltages of the same phase to
piezoelectric/electrostrictive elements 122A and 122B respectively
formed on driving portions of the devices, the shielding plate 123A
moves to the left-hand side in FIG. 13(b), and the shielding plate
123B moves to the right-hand side in FIG. 13(b), causing to change
the overlapping condition of the slits 125A and 125B, thus ON/OFF
control and quantity control of the light can be performed. Whereas
FIG. 13(c) shows a state where a part of the light is transmitted,
by changing shapes and formation positions of the slits 123A and
123B, the light can also be completely shielded.
[0165] Contrarily, in a state of FIGS. 13(a) and (b), the slits
125A and 125B may be structured not to be mutually overlapped and
to shield the light L, and by moving the shielding plates 123A and
123B, the slits 125A and 125B are overlapped to transmit the light
L. Although, in examples of FIGS. 12(a) and (b), and FIGS. 13(a),
(b), and (c), illustrated are examples where two shielding plates
are respectively mounted on the devices, the optical shutter of the
present invention has at least one shielding plate mounted on a
device, and only by moving the one shielding plate, transmission
and shielding of the light can be controlled. However, it is
preferable to have both shielding plates mounted, as this enables
an increase in the relative moving quantity of the shielding
plates. Further, although examples in FIGS. 12(a) and (b), and
FIGS. 13(a), (b), and (c) illustrate optical shutters each composed
of two units, an optical shutter may be composed of three or more
units. In this case, by setting movement of a plurality of
shielding plates in a variety of directions, the optical shutter
may be used as an optical diaphragm or the like having overlapped
portion in varied degrees of aperture. As the optical shutter of
the present invention has a shielding plate mounted on the movable
portion of the device of the present invention, operation of the
shielding plate in a flapped direction is suppressed. In other
words, as the shielding plate always moves facing straight to the
incident direction of the light, it can be preferably used in view
of ON/OFF control and quantity control of the light in improved
precision, which are made possible by the present invention.
[0166] A device according to the present invention can firstly
increase a driving force and displacement quantity by
simultaneously driving elements at least positioned in diagonal
directions across a hole and having the same functions. Further, as
the device can suppress displacement in the rotational mode of a
movable portion, and can be displacement shapes of a pair of thin
plate portions, into rotationally symmetric in the mutual relation,
which are displacement mechanism capable of largely displacing in
the X-axis direction, secondly the conversion efficiency of a
driving force into a displacement can be increased, thus a larger
displacement dominantly to a specific axis, namely the x-axis, is
made possible.
[0167] In addition, as a piezoelectric/electrostrictive element is
formed on a joined portion of a fixing portion and a movable
portion with thin plate portions in the aspect, the mechanical
strength at the portion is secured and a device with a higher
responsive speed at higher resonant frequency can be realized.
[0168] Since a device according to the present invention is
characterized by having high rigidity in the width-wise direction,
that is, Y-axis direction of the thin plates, it is a structure
that enables solid bonding in mounting thereon functional members
such as a sensor, a magnetic head, or the like, and further in
mounting the present device per se to another structure. In
addition, on account of the rigidity, the device also has another
characteristic that a member of relatively larger mass can be
mounted. Further, since the rigidity is relatively smaller in the
thickness direction than in the width direction of the
above-described thin plate portions, exhibited is an effect that a
component in the Y-axis direction or a flapped component, which is
a displacement component when the device is operated, is
effectively suppressed, based on the directional property of the
rigidity. Furthermore, since the device of the present invention is
so structured that a piezoelectric/electrostrictive operating
portion for developing displacement is overlapped not only with
thin plate portions but also with a fixing portion or movable
portion, displacement shape of a driving portion is different from
the disclosure in JP-A-63-64640. Namely, instead of a configuration
where only the vicinity of the center in a direction of the thin
plate portions from a movable portion toward the fixing portion is
directed toward a direction of the hole of the device of the
invention of the present application, and the joined portions of
thin plate portions with a fixing portion and thin plate portions
with a movable portion are scarcely displaced, the device of the
present invention is structured to have such a configuration that
enables the joined portion of a movable portion with the thin plate
portions to displace toward the outside space, thus the present
application can have a displacement mechanism permitting the
movable portion to largely displace.
[0169] Further, a fixing portion and a movable portion and thin
plate portions of the present device are sintered into an
integrated body of ceramics, and a piezoelectric/electrostrictive
element has a structure integrated by sintering with the thin plate
portions, the fixing portion, and the movable portion, by the film
forming method, without use of any adhesives, and thus the present
device has a structure which is free from variations such as
displacement drifting with time caused by the presence of
adhesives, or the like. As described previously, joined portions of
the driving portion or the thin plate portions with the fixing
portion and the driving portion or the thin plate portions with the
movable portion are structured to be borderless without any
intervention by the third substances/materials, and therefore are
of a structure having high rigidity, and can be easily made to make
high resonant frequency permitting high speed operation. Thus, the
device according to the present invention is structurally and
functionally entirely different from an actuator disclosed in the
official gazette of Japanese Patent Application Laid-Open No.
63-64640, and is high in reliability.
[0170] Accordingly, the device according to the present invention
can be utilized not only as active elements such as a variety of
transducers, a variety of actuators, frequency domain functional
components (filters), transformers, vibrators and resonators for
communications and powers, oscillators, discriminators, and the
like, but also as sensor elements for a variety of sensors such as
ultrasonic sensors and acceleration sensors, angular velocity
sensors and impact sensors, mass sensors, and the like. More
specifically, the device can be preferably utilized for a variety
of actuators used for mechanisms for adjusting displacement,
positioning and angle of a variety of precision parts and the like
of optical apparatuses, precision apparatuses, and the like.
* * * * *