U.S. patent application number 11/604699 was filed with the patent office on 2007-05-31 for multilayered piezoelectric element and method of manufacturing the same.
This patent application is currently assigned to FUJIFILM Corporation. Invention is credited to Tetsu Miyoshi.
Application Number | 20070120448 11/604699 |
Document ID | / |
Family ID | 38086753 |
Filed Date | 2007-05-31 |
United States Patent
Application |
20070120448 |
Kind Code |
A1 |
Miyoshi; Tetsu |
May 31, 2007 |
Multilayered piezoelectric element and method of manufacturing the
same
Abstract
In a multilayered piezoelectric element having a multilayered
structure in which electrode layers and piezoelectric material
layers are alternately stacked, an internal electrode and a side
electrode can be strongly connected. The element includes a first
electrode layer having an end portion that protrudes to an outer
side than adjacent piezoelectric material layers on a first side
surface of the multilayered structure and providing a first
insulating region between a second side surface and itself, a
second electrode layer having an end portion that protrudes to an
outer side than adjacent piezoelectric material layers on the
second side surface of the multilayered structure and providing a
second insulating region between the first side surface and itself,
a first side electrode connected to the end portion of the first
electrode layer, and a second side electrode connected to the end
portion of the second electrode layer.
Inventors: |
Miyoshi; Tetsu;
(Kaisei-machi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJIFILM Corporation
|
Family ID: |
38086753 |
Appl. No.: |
11/604699 |
Filed: |
November 28, 2006 |
Current U.S.
Class: |
310/366 |
Current CPC
Class: |
H01L 41/314 20130101;
Y10T 29/49128 20150115; H01L 41/0471 20130101; Y10T 29/42 20150115;
H01L 41/083 20130101; Y10T 29/49155 20150115; Y10T 29/49002
20150115; H01L 41/0472 20130101; H01L 41/27 20130101; Y10T 29/435
20150115 |
Class at
Publication: |
310/366 |
International
Class: |
H01L 41/083 20060101
H01L041/083 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2005 |
JP |
2005-342915 |
Claims
1. A multilayered piezoelectric element having a multilayered
structure in which at least one first electrode layer and at least
one second electrode layer are alternately stacked with a
piezoelectric material layer therebetween, said multilayered
piezoelectric element comprising: plural piezoelectric material
layers; a first electrode layer having an end portion at least a
part of which protrudes to an outer side than adjacent
piezoelectric material layers on a first side surface of said
multilayered structure, and formed such that a first insulating
region is provided between said first electrode layer and a second
side surface of said multilayered structure; a second electrode
layer having an end portion at least a part of which protrudes to
an outer side than adjacent piezoelectric material layers on the
second side surface of said multilayered structure, and formed such
that a second insulating region is provided between said second
electrode layer and the first side surface of said multilayered
structure; a first side electrode formed on the first side surface
of said multilayered structure, connected to the at least a part of
the end portion of said first electrode layer, and insulated from
said second electrode layer by said second insulating region; and a
second side electrode formed on the second side surface of said
multilayered structure, connected to the at least a part of the end
portion of said second electrode layer, and insulated from said
first electrode layer by said first insulating region.
2. A multilayered piezoelectric element having a multilayered
structure in which at least one first electrode layer and at least
one second electrode layer are alternately stacked with a
piezoelectric material layer therebetween, said multilayered
piezoelectric element comprising: plural piezoelectric material
layers; a first electrode layer having an end portion at least a
part of which protrudes to an outer side than adjacent
piezoelectric material layers on each of a first side surface and a
second side surface of said multilayered structure; a second
electrode layer having an end portion at least a part of which
protrudes to an outer side than adjacent piezoelectric material
layers on each of the first side surface and the second side
surface of said multilayered structure; a first insulating film for
covering the end portion of said first electrode layer on the
second side surface of said multilayered structure; a second
insulating film for covering the end portion of said second
electrode layer on the first side surface of said multilayered
structure; a first side electrode formed on the first side surface
of said multilayered structure, connected to the at least a part of
the end portion of said first electrode layer, and insulated from
said second electrode layer by said second insulating film; and a
second side electrode formed on the second side surface of said
multilayered structure, connected to the at least a part of the end
portion of said second electrode layer, and insulated from said
first electrode layer by said first insulating film.
3. A multilayered piezoelectric element according to claim 1,
wherein each of said plural piezoelectric material layers is formed
according to an aerosol deposition method by spraying powder of a
piezoelectric material toward one of a substrate, said first
electrode layer and said second electrode layer, and depositing the
piezoelectric material thereon.
4. A multilayered piezoelectric element according to claim 2,
wherein each of said plural piezoelectric material layers is formed
according to an aerosol deposition method by spraying powder of a
piezoelectric material toward one of a substrate, said first
electrode layer and said second electrode layer, and depositing the
piezoelectric material thereon.
5. A multilayered piezoelectric element according to claim 1,
wherein said first electrode layer and said second electrode layer
are formed by one of sputtering and plating.
6. A multilayered piezoelectric element according to claim 2,
wherein said first electrode layer and said second electrode layer
are formed by one of sputtering and plating.
7. A multilayered piezoelectric element according to claim 1,
wherein each of said first electrode layer and said second
electrode layer includes a conducting layer, and an adhesion layer
formed between said conducting layer and said piezoelectric
material layer.
8. A multilayered piezoelectric element according to claim 2,
wherein each of said first electrode layer and said second
electrode layer includes a conducting layer, and an adhesion layer
formed between said conducting layer and said piezoelectric
material layer.
9. A method of manufacturing a multilayered piezoelectric element
having a multilayered structure in which at least one first
electrode layer and at least one second electrode layer are
alternately stacked with a piezoelectric material layer
therebetween, said method comprising the steps of: (a) forming a
first piezoelectric material layer; (b) forming a first electrode
layer on said first piezoelectric material layer except for a
predetermined region; (c) forming a second piezoelectric material
layer on said first electrode layer; (d) forming a second electrode
layer on said second piezoelectric material layer except for a
predetermined region; (e) forming a third piezoelectric material
layer on said second electrode layer; (f) forming a first side
surface and a second side surface by dicing the formed multilayered
structure to protrude at least a part of an end portion of said
first electrode layer to an outer side than adjacent piezoelectric
material layers on the first side surface and secure a first
insulating region between said first electrode layer and the second
side surface, and to protrude at least a part of an end portion of
said second electrode layer to an outer side than adjacent
piezoelectric material layers on the second side surface and secure
a second insulating region between said second electrode layer and
the first side surface; (g) forming a first side electrode, which
is connected to the at least a part of the end portion of said
first electrode layer and insulated from said second electrode
layer by said second insulating region, on the first side surface
of said multilayered structure; and (h) forming a second side
electrode, which is connected to the at least a part of the end
portion of said second electrode layer and insulated from said
first electrode layer by said first insulating region, on the
second side surface of said multilayered structure.
10. A method of manufacturing a multilayered piezoelectric element
having a multilayered structure in which at least one first
electrode layer and at least one second electrode layer are
alternately stacked with a piezoelectric material layer
therebetween, said method comprising the steps of: (a) forming a
first piezoelectric material layer; (b) forming a first electrode
layer on said first piezoelectric material layer; (c) forming a
second piezoelectric material layer on said first electrode layer;
(d) forming a second electrode layer on said second piezoelectric
material layer; (e) forming a third piezoelectric material layer on
said second electrode layer; (f) forming a first side surface and a
second side surface by dicing the formed multilayered structure to
protrude at least a part of an end portion of each of said first
and second electrode layers to an outer side than adjacent
piezoelectric material layers on each of the first and second side
surfaces; (g) forming a first insulating film on the second side
surface of said multilayered structure to cover the end portion of
said first electrode layer; (h) forming a second insulating film on
the first side surface of said multilayered structure to cover the
end portion of said second electrode layer; (i) forming a first
side electrode, which is connected to the at least apart of the end
portion of said first electrode layer and insulated from said
second electrode layer by said second insulating film, on the first
side surface of said multilayered structure; and (j) forming a
second side electrode, which is connected to the at least a part of
the end portion of said second electrode layer and insulated from
said first electrode layer by said first insulating film, on the
second side surface of said multilayered structure.
11. A method according to claim 9, wherein each of steps (a), (c)
and (e) includes forming respective one of said first to third
piezoelectric material layers according to an aerosol deposition
method by spraying powder of a piezoelectric material toward
respective one of a substrate, said first electrode layer and said
second electrode layer, and depositing the piezoelectric material
thereon.
12. A method according to claim 10, wherein each of steps (a), (c)
and (e) includes forming respective one of said first to third
piezoelectric material layers according to an aerosol deposition
method by spraying powder of a piezoelectric material toward
respective one of a substrate, said first electrode layer and said
second electrode layer, and depositing the piezoelectric material
thereon.
13. A method according to claim 9, wherein each of steps (b) and
(d) includes forming respective one of said first electrode layer
and said second electrode layer by one of sputtering and
plating.
14. A method according to claim 10, wherein each of steps (b) and
(d) includes forming respective one of said first electrode layer
and said second electrode layer by one of sputtering and
plating.
15. A method according to claim 9, wherein each of steps (b) and
(d) includes forming respective one of said first electrode layer
and said second electrode layer by disposing a conducting layer via
an adhesion layer on respective one of said first piezoelectric
material layer and said second piezoelectric material layer.
16. A method according to claim 10, wherein each of steps (b) and
(d) includes forming respective one of said first electrode layer
and said second electrode layer by disposing a conducting layer via
an adhesion layer on respective one of said first piezoelectric
material layer and said second piezoelectric material layer.
17. A method according to claim 10, wherein each of steps (g) and
(h) includes forming respective one of said first insulating film
and said second insulating film according to an aerosol deposition
method by spraying powder of an insulating material toward
respective one of the end portion of said first electrode layer and
the end portion of said second electrode layer, and depositing the
insulating material thereon.
18. A method according to claim 10, wherein each of steps (g) and
(h) includes forming respective one of said first insulating film
and said second insulating film by electrodeposition.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a piezoelectric element
having a multilayered structure, i.e., a multilayered piezoelectric
element to be used as a piezoelectric actuator, an ultrasonic
transducer and so on, and a method of manufacturing the
multilayered piezoelectric element.
[0003] 2. Description of a Related Art
[0004] A piezoelectric material represented by a material having a
lead-based perovskite structure such as PZT (Pb (lead) zirconate
titanate) provides a piezoelectric effect of expanding and
contracting when applied with a voltage. A piezoelectric element
having the property is utilized in various uses such as
piezoelectric pumps, piezoelectric actuators and ultrasonic
transducers. The basic structure of a piezoelectric element is a
single-layer structure in which two electrodes are formed on both
ends of one piezoelectric material. Accompanied with
microfabrication and integration of piezoelectric elements with
recent developments of MEMS (micro electro mechanical systems)
related devices, multilayered piezoelectric elements each having
plural piezoelectric materials and plural electrodes alternately
stacked have been used.
[0005] FIG. 7 is a sectional view showing a structure of a
conventional multilayered piezoelectric element. This piezoelectric
element includes a multilayered structure having alternately
stacked piezoelectric material layers 100 and internal electrode
layers 101a and 101b, side electrodes 103a and 103b, an upper
electrode 104 and a lower electrode 105. Insulating regions 102a
and 102b are provided in the internal electrode layers 101a and
101b, respectively.
[0006] The side electrode 103a is connected to the internal
electrode layers 101a and insulated from the internal electrode
layers 101b by the insulating regions 102b. Further, the side
electrode 103b is connected to the internal electrode layers 101b
and insulated from the internal electrode layers 101a by the
insulating regions 102a. Furthermore, the upper electrode layer 104
is connected to the side electrode 103a, and the lower electrode
layer 105 is connected to the side electrode 103b.
[0007] By forming the electrodes of the piezoelectric element in
the above-mentioned manner, electrodes for applying electric fields
to each of the piezoelectric material layers 100 are connected in
parallel. Thereby, a capacitance between the electrodes of the
multilayered structure as a whole becomes larger, and the rise in
electrical impedance can be suppressed even when the size of the
piezoelectric element is made smaller.
[0008] Further, instead of providing the insulating regions 102a
and 102b in the internal electrode layers 101a and 101b as shown in
FIG. 7, there is known a multilayered piezoelectric element in
which each internal electrode layer is formed on an entire surface
of respective one of the piezoelectric material layers and the
internal electrode layer is insulated from either one of the side
electrodes by forming an insulating film on an end surface of the
internal electrode layer at a side surface of the multilayered
structure.
[0009] However, in the multilayered piezoelectric element as shown
in FIG. 7, there has been a problem that separation easily occurs
in the connection region between the internal electrode layer and
the side electrode. The reason is that, when the piezoelectric
material layers expand and contract, the side electrodes are unable
to follow the displacement of the piezoelectric material layers,
and therefore, distortion is produced at the interface between the
side electrode and the multilayered structure. Further, in the
multilayered piezoelectric element having the insulating films
formed on the side surfaces of the multilayered structure, the
insulating films are apt to separate from the end surfaces of the
internal electrodes for the same reason. Accordingly, there are
problems that the reliability at the time of operation of
piezoelectric element is low and the life of the element is
short.
SUMMARY OF THE INVENTION
[0010] The present invention has been achieved in view of the
above-mentioned problems. A purpose of the present invention is to
prevent, in a multilayered piezoelectric element having a
multilayered structure, separation of side electrodes or insulating
films formed on side surfaces of the multilayered structure from
end surfaces of internal electrodes.
[0011] In order to achieve the above-mentioned purpose, a
multilayered piezoelectric element according to one aspect of the
present invention is a multilayered piezoelectric element having a
multilayered structure in which at least one first electrode layer
and at least one second electrode layer are alternately stacked
with a piezoelectric material layer therebetween, and includes:
plural piezoelectric material layers; a first electrode layer
having an end portion at least apart of which protrudes to an outer
side than adjacent piezoelectric material layers on a first side
surface of the multilayered structure, and formed such that a first
insulating region is provided between the first electrode layer and
a second side surface of the multilayered structure; a second
electrode layer having an end portion at least a part of which
protrudes to an outer side than adjacent piezoelectric material
layers on the second side surface of the multilayered structure,
and formed such that a second insulating region is provided between
the second electrode layer and the first side surface of the
multilayered structure; a first side electrode formed on the first
side surface of the multilayered structure, connected to the at
least a part of the end portion of the first electrode layer, and
insulated from the second electrode layer by the second insulating
region; and a second side electrode formed on the second side
surface of the multilayered structure, connected to the at least a
part of the end portion of the second electrode layer, and
insulated from the first electrode layer by the first insulating
region.
[0012] Further, a method of manufacturing a multilayered
piezoelectric element according to one aspect of the present
invention is a method of manufacturing a multilayered piezoelectric
element having a multilayered structure in which at least one first
electrode layer and at least one second electrode layer are
alternately stacked with a piezoelectric material layer
therebetween, and includes the steps of: (a) forming a first
piezoelectric material layer; (b) forming a first electrode layer
on the first piezoelectric material layer except for a
predetermined region; (c) forming a second piezoelectric material
layer on the first electrode layer; (d) forming a second electrode
layer on the second piezoelectric material layer except for a
predetermined region; (e) forming a third piezoelectric material
layer on the second electrode layer; (f) forming a first side
surface and a second side surface by dicing the formed multilayered
structure to protrude at least a part of an end portion of the
first electrode layer to an outer side than adjacent piezoelectric
material layers on the first side surface and secure a first
insulating region between the first electrode layer and the second
side surface, and to protrude at least a part of an end portion of
the second electrode layer to an outer side than adjacent
piezoelectric material layers on the second side surface and secure
a second insulating region between the second electrode layer and
the first side surface; (g) forming a first side electrode, which
is connected to the at least a part of the end portion of the first
electrode layer and insulated from the second electrode layer by
the second insulating region, on the first side surface of the
multilayered structure; and (h) forming a second side electrode,
which is connected to the at least a part of the end portion of the
second electrode layer and insulated from the first electrode layer
by the first insulating region, on the second side surface of the
multilayered structure.
[0013] According to the present invention, the internal electrode
is formed to have the end portion at least a part of which
protrudes to the outer side than the adjacent piezoelectric
material layers such that the internal electrode and the side
electrode or the insulating film are connected to each other in a
broad contact area. Thereby, the connection strength between the
internal electrode and the side electrode or the insulating film is
improved, and it becomes difficult for the side electrode or the
insulating electrode to separate from the internal electrode even
when the piezoelectric material layers expand and contract. As a
result, the reliability of the operation of piezoelectric element
can be improved and the lives of the piezoelectric element and
equipment having the piezoelectric element can be made longer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a partially sectional perspective view showing a
structure of a multilayered piezoelectric element according to the
first embodiment of the present invention;
[0015] FIG. 2 is a sectional view showing internal electrode layers
formed of different plural materials;
[0016] FIGS. 3A-3C are diagrams for explanation of a method of
manufacturing the multilayered piezoelectric element according to
the first embodiment of the present invention;
[0017] FIG. 4 is a schematic diagram showing a configuration of a
film forming apparatus according to an aerosol deposition
method;
[0018] FIG. 5 is a partially sectional perspective view showing a
structure of a multilayered piezoelectric element according to the
second embodiment of the present invention;
[0019] FIGS. 6A-6D are diagrams for explanation of a method of
manufacturing the multilayered piezoelectric element according to
the second embodiment of the present invention; and
[0020] FIG. 7 is a sectional view showing a structure of a
conventional multilayered piezoelectric element.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Hereinafter, preferred embodiments of the present invention
will be explained in detail by referring to the drawings. The same
reference numerals are assigned to the same component elements and
the description thereof will be omitted.
[0022] FIG. 1 is a partially sectional perspective view showing a
structure of a multilayered piezoelectric element according to the
first embodiment of the present invention.
[0023] As shown in FIG. 1, the multilayered piezoelectric element
according to the embodiment is a columnar structure having a bottom
surface with sides of about 200 .mu.m to 1 mm and a height of about
300 .mu.m to 1 mm, for example. The multilayered piezoelectric
element has (i) a multilayered structure including plural
piezoelectric material layers 10, at least one internal electrode
layer 11a and at least one internal electrode layer 11b, and (ii)
side electrodes 13a and 13b formed on a first side surface and a
second side surface of the multilayered structure, respectively.
Generally, the multilayered piezoelectric element further has an
upper electrode layer 14 and a lower electrode layer 15.
[0024] The at least one internal electrode layer 11a and at the
least one internal electrode layer 11b are alternately stacked with
the piezoelectric material layer 10 therebetween. The piezoelectric
material layer 10 has a thickness of, for example, about 100 .mu.m,
and is formed of a compound oxide having a lead-based perovskite
structure such as PZT (Pb(lead) zirconate titanate). Although five
piezoelectric material layers 10, two internal electrode layers 11a
and two internal electrode layers 11b are shown in FIG. 1, the
number of piezoelectric material layers may be at least three, or
six or more. The piezoelectric material layer 10 has a dense and
hard tissue because it has been formed according to an aerosol
deposition method, which will be described later.
[0025] Each of the internal electrode layers 11a and 11b has a
thickness of about 3 .mu.m, for example. Insulating regions 12a are
provided between the internal electrode layers 11a and the side
electrode 13b, and insulating regions 12b are provided between the
internal electrode layers 11b and the side electrode 13a. Further,
at least a part of the end portion of the internal electrode layer
11a protrudes to the outer side than the adjacent piezoelectric
material layers 10 at the side of the side electrode 13a, while at
least a part of the end portion of the internal electrode layer 11b
protrudes to the outer side than the adjacent piezoelectric
material layers 10 at the side of the side electrode 13b. As shown
in FIG. 1, those protruding parts are covered by the side
electrodes 13a and 13b so as to be buried in the side electrodes
13a and 13b, respectively. Especially, FIG. 1 shows that the entire
end portions of the internal electrode layers 11a and 11b protrude
to the outer side than the adjacent piezoelectric material layers
10.
[0026] Each of the internal electrode layers 11a and 11b may be
formed of one kind of material, or may have a multilayer structure
formed of different plural materials. As an example of the former
case, a metal material such as platinum (Pt) or an alloy (e.g.,
palladium silver) is used. On the other hand, as an example of the
latter case, as shown in FIG. 2, an electrode having a two-layer
structure containing an adhesion layer 111 formed of titanium oxide
(TiO.sub.2) and having a thickness of about 50 nm and a conducting
layer 112 formed of platinum (Pt) and having a thickness of about 3
.mu.m is used. By providing the adhesion layer 111, the
adhesiveness between the conducting layer 112 and the piezoelectric
material layer 10 can be improved.
[0027] The side electrode 13a is connected to the internal
electrode layers 11a, and insulated from the internal electrode
layers 11b by the insulating regions 12b. Further, the side
electrode 13b is connected to the internal electrode layers 11b,
and insulated from the internal electrode layers 11a by the
insulating regions 12a.
[0028] The upper electrode 14 is connected to the side electrode
13a, and insulated from the side electrode 13b. Further, the lower
electrode 15 is connected to the side electrode 13b, and insulated
from the side electrode 13a. Each of the upper electrode 14 and
lower electrode 15 may be formed of one kind of material, or may
have a multilayer structure containing an adhesion layer and a
conducting layer as well as the internal electrodes 11a and
11b.
[0029] In the multilayered piezoelectric element, when a voltage is
supplied between the upper electrode 14 and lower electrode 15, for
example, an electric field is applied to each of the piezoelectric
material layers 10. As a result, the multilayered piezoelectric
element expands and contracts as a whole due to the piezoelectric
effect in each piezoelectric material layer 10. As shown in FIG. 1,
the end portions of the internal electrode layers 11a and 11b
protruding to the outer side than the piezoelectric material layers
10 are respectively connected to the side electrodes 13a and 13b in
broader contact areas than those in the conventional multilayered
piezoelectric element as shown in FIG. 7. Thereby, the connection
strength increases in the connection portions between them, and the
side electrodes 13a and 13b can be prevented from separating from
the internal electrode layers 11a and 11b even when each
piezoelectric material layer 10 expands and contracts.
[0030] Next, a method of manufacturing the multilayered
piezoelectric element according to the first embodiment of the
present invention will be explained by referring to FIGS. 3A-3C and
4.
[0031] First, as shown in FIG. 3A, a multilayered structure 23 is
formed by repeating formation of the piezoelectric material layer
10, the internal electrode layer 11a, the piezoelectric material
layer 10, and the internal electrode layer 11b in this order on a
substrate 9.
[0032] In the embodiment, the piezoelectric material layers 10 are
formed by using an aerosol deposition (AD) method. FIG. 4 is a
schematic diagram showing a configuration of a film forming
apparatus according to the AD method. The film forming apparatus
has an aerosol generation chamber 1, a raising gas nozzle 2, a
pressure regulating gas nozzle 3, an aerosol carrier pipe 4, a film
formation chamber 5, an exhaust pipe 6, an injection nozzle 7 and a
substrate holder 8. The raising gas nozzle 2, the pressure
regulating gas nozzle 3 and the aerosol carrier pipe 4 are disposed
in the aerosol generation chamber 1.
[0033] The aerosol generation chamber 1 is a container in which raw
material powder is placed. In the aerosol generation chamber 1,
there is provided a container driving unit 1a for agitating the raw
material powder placed within the aerosol generation chamber 1 by
providing vibration or the like to the aerosol generation chamber
1.
[0034] A compressed gas cylinder for supplying a carrier gas is
connected to the raising gas nozzle 2 disposed in the aerosol
generation chamber 1. The raising gas nozzle 2 generates a cyclonic
flow by injecting the gas supplied from the compressed gas cylinder
into the aerosol generation chamber 1. Thereby, the raw material
powder placed in the aerosol generation chamber 1 is dispersed by
the gas and an aerosol is generated.
[0035] Further, a compressed gas cylinder for supplying a pressure
regulating gas for regulating the gas pressure within the aerosol
generation chamber 1 is connected to the pressure regulating gas
nozzle 3. By controlling the pressure within the aerosol generation
chamber 1 by adjusting the flow rate of the pressure regulating
gas, the speed of the air flow (raising gas) generated within the
aerosol generation chamber 1 is controlled. As the carrier gas and
the pressure regulating gas, nitrogen (N.sub.2), oxygen (O.sub.2),
helium (He) argon (Ar) or dry air is used.
[0036] The aerosol carrier pipe 4 disposed in the aerosol
generation chamber 1 carries the aerosol containing the raw
material powder raised within the aerosol generation chamber 1 to
the nozzle 7 disposed in the film formation chamber 5.
[0037] The air within the film formation chamber 5 is exhausted by
the exhaust pump 6, and thereby, a predetermined degree of vacuum
is kept. The injection nozzle 7 disposed within the film formation
chamber 5 has an opening having predetermined shape and size, and
injects the aerosol supplied from the aerosol generation chamber 1
via the aerosol carrier pipe 4 from the opening toward the
substrate 9 at a high speed.
[0038] The substrate holder 8 holds the substrate 9. Further, a
substrate holder driving unit 8a for moving the substrate holder 8
in a three-dimensional manner is provided to the substrate holder
8. Thereby, the three-dimensional relative position and relative
speed between the injection nozzle 7 and the substrate 9 are
controlled. By controlling the relative speed, the thickness of a
film formed by one reciprocating motion can be controlled.
[0039] In such a film forming apparatus, powder of a piezoelectric
material as the raw material powder is placed in the aerosol
generation chamber 1 and the substrate 9 is set on the substrate
holder 8 and kept at predetermined film formation temperature.
Then, the substrate is moved at a predetermined speed while the
film forming apparatus is driven such that the aerosol is injected
from the injection nozzle 7. Thereby, the aerosol (raw material
powder) collides with the substrate 9 and cut into the substrate 9
or a structure previously deposited on the substrate 9 (referred to
as "anchoring"). Further, the particles bind together on the newly
formed active surfaces formed by the deformation or crushing of the
raw material powder at the time of collision, and the raw material
powder is deposited on the substrate.
[0040] In an anchor part (a region formed by anchoring) formed in
the boundary region between the film and the substrate or the
internal electrode layer as an under layer, thus formed film
strongly and closely adheres to the under layer and has an
extremely dense structure because of the binding of the particles
on the newly formed surfaces (mechanochemical reaction).
[0041] Here, when the film formation is performed by using the AD
method, as the material of the substrate or the internal electrode
layer as the under layer, a material having such hardness that the
deformation or crushing of the raw material powder occurs due to
the collision is used. This is because, if the hardness of the
under layer is insufficient, the raw material powder colliding with
the under layer simply cuts into the under layer and is deposited
on the under layer without deforming or crushing, and therefore, it
becomes impossible to form a dense film by mechanochemical
reaction. Accordingly, as the substrate 9, for example, an YSZ
(yttrium-stabilized zirconia) substrate, SUS substrate or the like
is used.
[0042] Referring to FIG. 3A again, the internal electrode layers
11a are formed so as to cross a dicing line as shown by a broken
line at the side of a side surface 23a of the multilayered
structure and not to reach a dicing line at the side of a side
surface 23b of the multilayered structure. Thereby, the insulating
regions 12a are provided. Further, the internal electrode layers
11b are formed so as to cross the dicing line as shown by the
broken line at the side of the side surface 23b of the multilayered
structure and not to reach the dicing line at the side of the side
surface 23a of the multilayered structure. Thereby, the insulating
regions 12b are provided.
[0043] As the material of the internal electrode layers 11a and
11b, a material having ductility and hardness to some degree is
used. In the embodiment, ductility is required because the end
portions of the internal electrode layers 11a and 11b are protruded
to the side surfaces by dicing the multilayered structure 23 as
described below. Further, hardness is required because the internal
electrode layers 11a and 11b become under layers when the
piezoelectric material layers 10 are formed and need sufficient
hardness enough to endure the collision of the raw material powder
as described above. The property of the material may somewhat
differ depending on the dicing condition or the like, and a metal
thin film of platinum (Pt), copper (Cu), nickel (Ni) or the like
formed by using a film formation technology such as sputtering,
plating or the like may be used as the internal electrode layers
11a and 11b. In the embodiment, a platinum thin film formed by
sputtering is used.
[0044] Then, the multilayered structure 23 is diced along the
dicing lines as shown in FIG. 3A. Thereby, as shown in FIG. 3B, the
end portions 25 of the internal electrode layers 11a and 11b
protrude to the outer side than the piezoelectric material layers
10 at the side surfaces of the diced multilayered structure 24. The
reason why the end portions 25 protrude is that the internal
electrode layers 11a and 11b have higher hardness than that of the
piezoelectric material layers 10, and they remains more easily than
the piezoelectric material layers 10 when the multilayered
structure 24 is cut. At this step, the substrate 9 may be separated
from the multilayered structure 24.
[0045] Then, as shown in FIG. 3C, the side electrodes 13a and 13b
are formed in the regions other than insulating regions 27 on the
side surfaces of the diced multilayered structure 24. The
insulating regions 27 are provided for insulting the side
electrodes 13a and 13b from the lower electrode layer 15 and the
upper electrode layer 14 (FIG. 1), respectively. The side
electrodes 13a and 13b are formed by forming a resist mask on the
insulating regions 27 and performing sputtering or plating. BY
using such a method of forming a film, the side electrodes 13a and
13b can be formed so as to cover the protruding end portions
25.
[0046] Further, the upper electrode layer 14 and the lower
electrode layer 15 as shown in FIG. 1 may be formed simultaneously
with or after the formation of the side electrodes 13a and 13b. As
described above, the multilayered piezoelectric element according
to the embodiment is completed.
[0047] An experiment of fabricating the multilayered piezoelectric
element according to the embodiment and separating the side
electrodes from the multilayered structure was made. As the
internal electrode layer, a two-layer structure containing an
adhesion layer of titanium oxide (TiO.sub.2) having a thickness of
about 50 nm and a conducting layer of platinum (Pt) having a
thickness of about 3 .mu.m was formed. Further, as dicing
conditions of the multilayered structure, a dicing blade NBC-ZS
type manufactured by DISCO CORPORATION was used and the number of
revolutions was set to 12,000 rpm.
[0048] As a result, the tensile strength of the side electrodes was
improved about twice the case of forming the internal electrode
layers by screen printing. In the conventional multilayered
piezoelectric element, the screen printing is general as a method
of forming electrodes. Since the formed electrodes are soft, the
end portions of the internal electrode layers do not protrude to
the outside from the multilayered part even when the multilayered
structure is diced.
[0049] Next, a multilayered piezoelectric element according to the
second embodiment of the present invention will be explained. FIG.
5 is a partially sectional perspective view showing a structure of
the multilayered piezoelectric element according to the second
embodiment.
[0050] The second embodiment is different from the first embodiment
in the point where the internal electrode layers are insulated from
the side electrodes by covering the end portions of the internal
electrode layers with insulating films, while the internal
electrode layers are insulated from the side electrodes by
providing the insulating regions in the first embodiment.
[0051] As shown in FIG. 5, the multilayered piezoelectric element
according to the embodiment has (i) a multilayered structure
including plural piezoelectric material layers 30, at least one
internal electrode layer 31a and at least one internal electrode
layer 31b, (ii) insulating films 32a and 32b formed on the first
and second side surfaces of the multilayered structure,
respectively, and (iii) side electrodes 33a and 33b further formed
thereon. Generally, the multilayered piezoelectric element further
has an upper electrode layer 34 and a lower electrode layer 35.
[0052] The at least one internal electrode layer 31a and the at
least one internal electrode layer 31b are alternately stacked with
the piezoelectric material layer 30 therebetween. Here, the
internal electrode layers 31a and 31b are formed on the entire
surfaces of the piezoelectric material layers 30. Further, at least
apart of the end portions of the internal electrode layers 31a and
31b protrude to the outer side than the adjacent piezoelectric
material layers 30 at the sides of the side electrodes 33a and 33b.
FIG. 5 shows that the entire end portions of the internal electrode
layers 31a and 31b protrude to the outer side than the adjacent
piezoelectric material layers 30.
[0053] At the side of the side electrode 33a, the end portions of
the internal electrode layers 31a are covered so as to be buried in
the side electrode 33a, while the insulating films 32b are formed
so as to cover the end portions of the internal electrode layers
31b. Similarly, at the side of the side electrode 33b, the end
portions of the internal electrode layers 31b are covered so as to
be buried in the side electrode 33b, while the insulating films 32a
are formed so as to cover the end portions of the internal
electrode layers 31a.
[0054] By thus forming the insulating films 32a and 32b, the side
electrodes 33a are connected to the internal electrode layers 31a,
and insulated from the internal electrode layers 31b. On the other
hand, the side electrodes 33b are connected to the internal
electrode layers 31b, and insulated from the internal electrode
layers 31a.
[0055] In the embodiment, the side electrodes 33a and 33b or
insulating films 32a and 32b are formed on the end portions of the
internal electrode layers 31a and 31b that protrude to the outer
side than the adjacent piezoelectric material layers 30,
respectively, and therefore, the contact areas between the internal
electrode layers and the side electrodes or insulating films become
broader. As a result, the contact strength between them increases,
and the side electrodes 33a and 33b or insulating films 32a and 32b
can be prevented from separating from the internal electrode layers
31a and 31b even when the piezoelectric material layers 30 expand
and contract when the piezoelectric element is driven.
[0056] Next, a method of manufacturing the multilayered
piezoelectric element according to the second embodiment of the
present invention will be explained by referring to FIGS.
6A-6D.
[0057] First, as shown in FIG. 6A, a multilayered structure 42 is
formed by alternately stacking the piezoelectric material layers 30
and the internal electrode layers 31 on the substrate 9. The
piezoelectric material layers 30 are formed by using the AD method
as well as in the first embodiment. Further, the internal electrode
layers 31 are formed by employing the same material as that
explained in the first embodiment by sputtering or plating.
[0058] Then, the multilayered structure 42 is diced along dicing
lines as shown in FIG. 6A. Thereby, as shown in FIG. 6B, a shaped
multilayered structure 43 is obtained. End portions 44 of the
internal electrode layers 31 protruding to the outer side than the
piezoelectric material layers 30 are formed at the side surfaces of
the diced multilayered structure 43. At this step, the substrate 9
may be separated from the multilayered structure 43.
[0059] Then, as shown in FIG. 6C, the insulating films 32a are
formed so as to cover every other end portion 44 of the internal
electrode layers 31 on the side surface 43b of the diced
multilayered structure 43. Further, the insulating films 32b are
formed so as to cover every other end portion 44 of the internal
electrode layers 31 on the side surface 43a of the diced
multilayered structure 43. Here, the insulating films 32a and 32b
are formed in a staggered manner. The internal electrode layers 31
having the end portions 44 covered by the insulating films 32a
correspond to internal electrode layers 31a as shown in FIG. 5,
while the internal electrode layers 31 having the end portions 44
covered by the insulating films 32b correspond to internal
electrode layers 31b as shown in FIG. 5.
[0060] These insulating films 32a and 32b are formed by attaching
glass powder having a softening point of, for example, about
500.degree. C. to about 700.degree. C. to the end portions 44 by
electrophoresis (electrodeposition), or depositing paste containing
glass powder onto the end portions 44 by screen printing.
Alternatively, the insulating films 32a and 32b may be formed
according to the AD method by spraying an aerosol in which powder
of an insulating material is dispersed toward the end portions 44
of the internal electrode layers 31.
[0061] Then, as shown in FIG. 6D, the side electrodes 33a and 33b
are formed in the regions other than insulating regions 47 on the
side surfaces of the diced multilayered structure 43 by sputtering
or plating. Furthermore, the upper electrode layer 34 and lower
electrode layer 35 as shown in FIG. 5 may be formed. As described
above, the multilayered piezoelectric element according to the
embodiment is completed.
[0062] The above explained multilayered piezoelectric elements
according to the first and second embodiments are used as
piezoelectric pumps, piezoelectric actuators, ultrasonic
transducers for transmitting and receiving ultrasonic waves in an
ultrasonic probe, and so on. In this regard, a multilayered
piezoelectric element may be singly used, or multilayered
piezoelectric elements may be arranged in a one- or two-dimensional
manner for use as a piezoelectric element array.
* * * * *