U.S. patent application number 09/730596 was filed with the patent office on 2001-07-26 for multilayer piezoelectric element and method of producing the same.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Furukawa, Masahito, Horino, Kenji, Itoh, Syuuzi, Kudoh, Minami, Morita, Makoto.
Application Number | 20010009344 09/730596 |
Document ID | / |
Family ID | 26578814 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009344 |
Kind Code |
A1 |
Furukawa, Masahito ; et
al. |
July 26, 2001 |
Multilayer piezoelectric element and method of producing the
same
Abstract
An electronic part comprises a main part, a terminal electrode,
and a film. The main part includes a sintered piezoelectric ceramic
element, wherein a plurality of internal electrode layers and
piezoelectric layers are alternately stacked. The terminal
electrode is provided at an edge of the sintered piezoelectric
ceramic element and electrically conducting to the internal
electrodes. The film is provided on a surface of the sintered
piezoelectric ceramic element and the exposed internal electrodes,
and is made of a glass insulating material.
Inventors: |
Furukawa, Masahito; (Tokyo,
JP) ; Horino, Kenji; (Tokyo, JP) ; Morita,
Makoto; (Tokyo, JP) ; Itoh, Syuuzi; (Tokyo,
JP) ; Kudoh, Minami; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, McCLELLAND, MAIER & NEUSTADT, P.C.
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TDK CORPORATION
13-1, Nihonbashi 1-chome, Chuo-ku
Tokyo
JP
|
Family ID: |
26578814 |
Appl. No.: |
09/730596 |
Filed: |
December 7, 2000 |
Current U.S.
Class: |
310/358 ;
310/366 |
Current CPC
Class: |
H01L 41/23 20130101;
H01L 41/273 20130101; H01L 41/083 20130101; H01L 41/0533
20130101 |
Class at
Publication: |
310/358 ;
310/366 |
International
Class: |
H01L 041/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 8, 1999 |
JP |
P.HEI.11-348732 |
Jan 17, 2000 |
JP |
P2000-007904 |
Claims
What is claimed is:
1. An electronic part comprising: a main part including a sintered
piezoelectric ceramic element, wherein a plurality of internal
electrode layers and piezoelectric layers are alternately stacked;
a terminal electrode provided at an edge of the sintered
piezoelectric ceramic element and electrically conducting to the
internal electrodes; and a film provided on surfaces of the
sintered piezoelectric ceramic element and made of glass insulating
material.
2. The electronic part according to claim 1, wherein said film
includes at least two components of ceramic compounds selected from
the group consisting of all or a part of lead oxide (PbO), silicon
oxide (SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3) and the
sintered piezoelectric ceramics.
3. The electronic part according to claim 1, wherein said film is
0.5 to 7.0 .mu.m in thickness.
4. A multilayer piezoelectric element comprising: a structure
including a plurality of piezoelectric ceramic layers and internal
electrode layers, wherein a plurality of layers of internal
electrodes and piezoelectric layers are alternately stacked and
edges of the internal electrode layers are exposed; and a glass
insulating portion deposited to the exposed edges of the internal
electrode layers of said structure with particles including a glass
insulating material, wherein said glass insulating portion includes
a glass insulating layer having the glass insulating material, and
the glass insulating layer is formed at the exposed edges of the
internal electrode layers.
5. The multilayer piezoelectric element according to claim 4,
wherein the glass insulating layer is uniformly formed on the
exposed edges of the internal electrode layers and surfaces of
piezoelectric ceramic layers.
6. The multilayer piezoelectric element according to claim 4,
wherein the glass insulating layer of said glass insulating portion
is deposited with an electrophoretic deposition and heat
treatment.
7. The multilayer piezoelectric element according to claim 4,
wherein the glass insulating layer is 0.3 to 10 .mu.m in
thickness.
8. The multilayer piezoelectric element according to claim 6,
wherein a heat-treating temperature for forming the glass
insulating layer is lower than a firing temperature of the
multilayer piezoelectric element, and the glass insulating layer
includes one of: a glass component based on a single component; a
glass component based on a mixed component including a plurality of
components; a glass component based on a single component dispersed
with piezoelectric ceramic in a glass matrix thereof; and a glass
component based on a mixed component dispersed with piezoelectric
ceramic in a glass matrix thereof.
9. The multilayer piezoelectric element according to claim 8,
wherein the piezoelectric ceramic contained in the glass insulating
layer is the same piezoelectric ceramic as one of the multilayer
piezoelectric layer.
10. The multilayer piezoelectric element according to claim 4,
wherein the glass insulating layer includes PbO of 10 to 80 wt %,
SiO.sub.2 of 10 to 80 wt %, Al.sub.2O.sub.3 of 0 to 50 wt %, and
the same piezoelectric ceramic as one of the multilayer
piezoelectric layer of 0 to 50 wt %.
11. The multilayer piezoelectric element according to claim 4,
wherein the multilayer piezoelectric element is for a piezoelectric
actuator.
12. A method of producing an electronic part of multilayer
piezoelectric ceramics, comprising the steps of: mixing
piezoelectric ceramic powders in a binder solution thereby making
slurry; making a piezoelectric ceramic green sheet from the slurry;
making a multilayer piezoelectric ceramic element by alternately
stacking a plurality of layers of the piezoelectric ceramic green
sheets and internal electrodes; sintering the multilayer
piezoelectric ceramic element; forming a terminal electrode
electrically conducting to the internal electrodes at edges of the
sintered multilayer piezoelectric ceramic element; coating a glass
insulating paste including a glass insulating material on a surface
of the sintered multilayer piezoelectric ceramic element; and
heat-treating the glass insulating paste for making a film with the
glass insulating material.
13. The method according to claim 12, wherein the glass insulating
paste includes at least two components of ceramic compounds
selected from the group consisting of all or a part of lead oxide
(PbO), siliconoxide (SiO.sub.2), aluminumoxide (Al.sub.2O.sub.3)
and the sintered piezoelectric ceramic.
14. The method according to claim 12, wherein the coated glass
insulating paste is 0.5 to 7.0 .mu.m in thickness.
15. A method of producing a multilayer piezoelectric element
comprising: alternately stacking a plurality of piezoelectric
ceramic layers and internal electrode layers, edges of the internal
electrode layers being exposed; electrodepositing particles
including a glass insulating material at the exposed edges of the
internal electrode layers with an electrophoretic deposition,
thereby forming an insulating part; and heat-treating the
insulating part, wherein a glass insulating layer of the insulating
part is formed on at least one of the exposed edges of the internal
electrode layers and a surface of the piezoelectric ceramic layer
between the internal electrode layers.
16. The method according to claim 15, wherein the glass insulating
layer is 0.3 to 10 .mu.m in thickness.
17. The method according to claim 15, wherein a heat-treating
temperature for forming the glass insulating layer is lower than a
firing temperature of the multilayer piezoelectric element, and the
glass insulating layer includes one of: a glass component based on
a single component; a glass component based on a mixed component
including a plurality of components; a glass component based on the
single component dispersed with piezoelectric ceramic in a glass
matrix thereof; and a glass component based on the mixed component
dispersed with piezoelectric ceramic in a glass matrix thereof.
18. The method according to claim 17, wherein the piezoelectric
ceramic contained in the glass insulating layer is the same
piezoelectric ceramic as one of the multilayer piezoelectric
layer.
19. The method according to claim 15, wherein the glass insulating
layer includes PbO of 10 to 80 wt %, SiO.sub.2 of 10 to 80 wt %,
Al.sub.2O.sub.3 of 0 to 50 wt %, and the same piezoelectric ceramic
as one of the multilayer piezoelectric layer of 0 to 50 wt %.
20. The method according to claim 15, wherein the multilayer
piezoelectric element is for a piezoelectric actuator.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a multilayer piezoelectric
element and a method of producing the same, in particular a method
of producing such multilayer piezoelectric ceramics where
reliability has been improved.
[0003] 2. Description of the Related Art
[0004] In general, electronic parts of multilayer piezoelectric
ceramic are composed by making stacked piezoelectric ceramic made
by alternately stacking a plurality of layers of piezoelectric
ceramic green sheets printed with internal electrodes of silver
(Ag) or silver-palladium (Ag--Pd) alloy, firing the stacked
piezoelectric ceramic, and coating, as shown in FIG. 11, an
electrically conductive paste of silver being a main component to
the sintered stacked ceramic 101 at edges thereof so as to form
terminal electrodes 102a, 102b, 102c.
[0005] In addition, as shown in FIG. 12, there is also a product
exposing internal electrodes 104 alternately stacked with
piezoelectric ceramic layers 103 at sides of the sintered
piezoelectric ceramic 101.
[0006] Electronic parts of the above multilayer piezoelectric
ceramic are probable to generate a lot of minute pores within
layers of sintered piezoelectric ceramic by firing, so that
moisture goes into the pores by using for a long period of time
under atmosphere at high temperature and high humidity, thereby to
create defects in insulation between internal electrodes.
[0007] As a measure therefor, as shown in FIG. 13, external films
105 of an organic resin are formed on surfaces of the sintered
piezoelectric ceramic 1 for preventing invasion or penetration of
the moisture. However, it is difficult to perfectly avoid the
invasion of the moisture with the external films 105 of the organic
resin, and an insulating property goes down by such as migration of
silver as an electrode material accompanying with use for a long
time, inevitably resulting in short circuiting.
[0008] In a case where the multilayer piezoelectric element is
miniaturized or complicated in configuration, the multilayer
piezoelectric element sometimes exposes at its sides the edges of
the internal electrode layers. If voltage is impressed to the
internal electrode layers to drive the multilayer piezoelectric
element under a condition where moisture is able to penetrate the
edges, a metal composing the internal electrode layers is ionized
and induces a so-called migration phenomena where the metal moves
between electrodes in response to an electrical field. For the
internal electrode layer, because of saving costs, alloys of silver
being a main component, for example, Ag--Pd alloy are used in
general. However, in the internal electrode layer comprising the
alloy including Ag, migration easily occurs, and in extreme cases,
metal bridges comprising Ag and the like are formed between
opposite internal electrode layers. As a result, electrical short
circuits are often caused between the opposite internal electrode
layers by the metal bridges, probably missing reliability.
[0009] The migration is accelerated particularly under high
temperature, high humidity or high electrical field. Then,
improvement of moisture resistance has been designed by the under
various measures.
[0010] (1) A method of coating an outer face of the multilayer
piezoelectric element with an insulating material of a resin film
or a glass insulating layer.
[0011] (2) A method of coating the outer face of the multilayer
piezoelectric element with an insulating material of silicon oxide
(SiO.sub.2)
[0012] For example, JP-A-61-15382 discloses a technology which
uniformly forms the silica insulating material on the exposed parts
of the internal electrode layers through a decompression CVD
method.
[0013] (3) A method of forming a glass insulating layer on the
outer face of the multilayer piezoelectric element by a dry or wet
transcribing method.
[0014] For example, JP-A-7-7193 discloses a technology which forms
the glass insulating paste on a dry transcribing paper or a wet
transcribing paper, delaminates, then sticks the glass insulating
paste to four sides of the multilayer piezoelectric element, and
heats it for coating the glass insulating material.
[0015] (4) A still further method of selectively coating the
insulating material of inorganic material or high polymer material
on only parts exposing the internal electrode layer of the
multilayer piezoelectric element.
[0016] For example, JP-A-7-176802 discloses a technology which
selectively adheres particles of inorganic materials as
piezoelectric ceramic or high polymer such as polyimide onto only
parts exposing the internal electrode layer of the multilayer
piezoelectric element by the electrophoretic deposition so as to
form the coating thereon.
[0017] (5) In the structure formed with holes in the multilayer
piezoelectric element where the holes are filled with fillers, the
coating is formed to the part exposing the edge of the internal
electrode layer inside of the holes.
[0018] For example, JP-A-10-136665 discloses a structure formed
with holes in the multilayer piezoelectric element where the holes
are filled with soft fillers as silicone resin or urethane resin,
and the coating is formed to the part exposing the edge of the
internal electrode layer of the holes, thereby to improve the
moisture resistance.
[0019] However, although depending on the above measures, the
reliability of the multilayer piezoelectric element is not yet
perfectly improved in view of the points mentioned below.
[0020] According to the above measure (1), if the multilayer
piezoelectric element is coated on its outer face with a resin
film, an effect of imparting the moisture resistance is poor, and a
problem is left in there liability. In case the multilayer
piezoelectric element is coated on its outer face with the glass
insulating layer by an ordinary method, the moisture resistance is
improved, but if elastic modulus is large different between the
glass insulating layer and the piezoelectric ceramic when the
multilayer piezoelectric element is driven, the glass insulating
layer probably hampers displacement of the piezoelectric
ceramic.
[0021] According to the above measure (2), the moisture resistance
is improved, but when the multilayer piezoelectric element is
driven so that tensile stress repeatedly acts on a silica film, the
silica film is easily cracked. When cracking appears in the silica
film, there is involved a problem that the edge of the internal
electrode layer is again exposed, resulting to spoil the
reliability.
[0022] For forming the silica film in a predetermined film
thickness, a relatively long processing time lead to increase of
the cost.
[0023] According to the above measure (3), if the outer face of the
multilayer piezoelectric element is coated with the glass
insulating layer, the moisture resistance is heightened, and
appearing rate of defects is reduced when using it at the high
humidity, but when, similarly to the measure (1), the elastic
modulus is large different between the glass insulating layer and
the piezoelectric ceramic, the glass insulating layer probably
hampers displacement of the piezoelectric ceramic.
[0024] According to the measure (4), the moisture resistance is
increased, and since the insulating material is selectively coated
to only the part exposing the internal electrode layer, when the
multilayer piezoelectric element is driven and the tensile stress
is repeatedly acted on the inorganic coating layer, appearance of
cracks can be checked. The reliability is therefore largely
increased. Further, according to the electrophoretic deposition,
comparing with the measure (2), the coating time of the insulating
material is shortened, enabling to suppress increase of the cost
more.
[0025] However, since the insulating material is formed to only
parts exposing the internal electrode layers, the moisture
resistance of the piezoelectric ceramic layer is not enough at
parts not formed with the insulating material, for example, between
the internal electrode layers, and in particular when pores exist
in the piezoelectric ceramic layer, probability of spoiling the
reliability is present.
[0026] According to the measure (5), the moisture resistance is
improved in the part exposed at the holes, but at parts exposing
the internal electrode layers outside, another coating layer should
be separately provided.
SUMMARY OF THE INVENTION
[0027] In view of the above-mentioned problems, it is an object of
the invention to offer electronic parts of the multilayer
piezoelectric ceramic enabling to compose as scarcely causing
deterioration of insulation resistance in spite of using for longer
time under atmosphere at high temperature and at high humidity as
well as a production method thereof.
[0028] It is another object of the invention to offer electronic
parts of the multilayer piezoelectric ceramic maintaining a
displacing characteristic well conditioned and enabling to compose
as scarcely causing deterioration of insulation resistance as well
as a production method thereof.
[0029] Further, it is an object of the invention to offer a method
of producing a multilayer piezoelectric element having excellent
reliability by uniformly forming the glass insulating layer at side
parts exposing edges of the internal electrode layers of the
multilayer piezoelectric element suppressing defects, and products
thereof.
[0030] Herein, a term of "glass insulating layer" is defined by a
coated layer comprising an amorphous inorganic compound and
completely checking defects for preventing penetration of
moisture.
[0031] In the electronic parts of the multilayer piezoelectric
ceramic according to a first aspect of the invention, the sintered
piezoelectric ceramic comprising a plurality of alternately stacked
layers of internal electrodes and piezoelectric layers is a main
part, provided at edges thereof with terminal electrodes conducting
electricity to the internal electrodes, and is provided on surfaces
thereof with films of glass insulating material.
[0032] In the electronic parts of the multilayer piezoelectric
ceramic according to a second aspect of the invention, the sintered
piezoelectric ceramic is provided on the surfaces thereof with
films of the glass insulating material comprising any two or more
components of ceramic compounds selected from elements composing
all or a part of lead oxide (PbO), silicon oxide (SiO.sub.2),
aluminum oxide (Al.sub.2O.sub.3) and the sintered piezoelectric
ceramic.
[0033] In the electronic parts of the multilayer piezoelectric
ceramic according to a third aspect of the invention, the sintered
piezoelectric ceramic is provided on the surfaces thereof with the
film of the glass insulating material having thickness of 0.5 to
7.0 .mu.m.
[0034] In the method of producing electronic parts of the
multilayer piezoelectric ceramic according to a fourth aspect of
the invention, the method comprises mixing piezoelectric ceramic
powder in a binder solution so as to make slurry, making
piezoelectric ceramic green sheets from the slurry, making a
multilayer piezoelectric ceramic by alternately stacking a
plurality of layers of the piezoelectric ceramic green sheets and
internal electrodes, sintering the multilayer piezoelectric ceramic
layers, followed by forming at edges of the sintered ceramic
terminal electrodes electrically conducting to internal electrodes
of the sintered piezoelectric ceramic, sintering the multilayer
piezoelectric ceramics, followed by coating glass insulating paste
on the surfaces of the sintered piezoelectric ceramic, and
heat-treating the paste for making films with the glass insulating
material.
[0035] In the method of producing electronic parts of the
multilayer piezoelectric ceramic according to a fifth aspect of the
invention, the sintered piezoelectric ceramic is coated on the
surfaces thereof with the glass insulating paste comprising any two
or more components of ceramic compounds selected from elements
composing all or a part of lead oxide (PbO), silicon oxide
(SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3) and the sintered
piezoelectric ceramics.
[0036] In the method of producing electronic parts of the
multilayer piezoelectric ceramic according to a sixth aspect of the
invention, the sintered piezoelectric ceramic is coated on the
surfaces thereof with the film of the glass insulating material in
thickness of 0.5 to 7.0 .mu.m.
[0037] Further, inventors have found the following constitution for
accomplishing the above object so as to solve the problems.
[0038] In a method of producing a multilayer piezoelectric element
which has a structure having an arrangement of a plurality of
alternate stacking layers of piezoelectric ceramic layers and
internal electrode layers and exposing the edges of the internal
electrode layers, a seventh aspect of the invention comprises the
steps of electrodepositing particles comprising a glass insulating
material to the exposed sides through an electrophoretic
deposition; and then carrying out a heat treatment at a
predetermined temperature, thereby forming the glass insulating
layer of the glass insulating material to the exposed parts only or
both of the exposed parts and the surface of the piezoelectric
layers of the internal electrode layers.
[0039] A eighth aspect of the invention is preferable in that the
glass insulating layer has a thickness of 0.3 to 10 .mu.m in the
seventh aspect.
[0040] A ninth aspect of the invention is preferable in that, in
the seventh or eighth aspect, the heat-treating temperature of the
glass insulating layer is lower than a firing temperature of the
multilayer piezoelectric element, and the glass insulating layer is
composed of any one selected from the components of the glass
component which is a single one, the glass component which is a
plurality of mixed substances, the single component which is
dispersed with piezoelectric ceramic in the glass matrix thereof,
and the plurality of mixed component which is dispersed with the
piezoelectric ceramic in the glass matrix thereof.
[0041] The softening points of these glass insulating materials are
preferably 500 to 900.degree. C.
[0042] A tenth aspect of the invention is convenient in that, in
the ninth aspect, when the piezoelectric ceramic is contained in
the glass insulating layer, this piezoelectric ceramic is the same
as the piezoelectric ceramic composing the multilayer piezoelectric
element.
[0043] An eleventh aspect of the invention is structured such that,
in any one of the seventh to the ninth aspects, the glass
insulating layer may contain PbO: 10 to 80 wt %, SiO.sub.2: 10 to
80 wt %, Al.sub.2O.sub.3: 0 to 50 wt %, and one of the same
piezoelectric ceramic as the piezoelectric ceramic of the
multilayer piezoelectric element: 0 to 50 wt %.
[0044] A twelfth aspect of the invention is that the multilayer
piezoelectric element as set forth in the seventh to eleventh
aspects may be for a piezoelectric actuator.
[0045] A thirteenth aspect of the invention is the multilayer
piezoelectric element produced by the seventh to eleventh
aspects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a perspective view showing internal electrodes
composing the electronic parts of the multilayer piezoelectric
ceramic not exposing the internal electrodes according to the
invention and ceramic green sheets.
[0047] FIG. 2 is a cross sectional view showing the electronic
parts of the multilayer piezoelectric ceramic according to those of
FIG. 1.
[0048] FIG. 3 is a perspective view showing internal electrodes
composing the electronic parts of the multilayer piezoelectric
ceramic exposing the internal electrodes according to the invention
and ceramic green sheets.
[0049] FIG. 4 is a cross sectional view showing the electronic
parts of the multilayer piezoelectric ceramic according to those of
FIG. 3.
[0050] FIG. 5 is a schematically perspective view showing the
structure of the multilayer piezoelectric element.
[0051] FIG. 6(a) is a cross sectional view along A-A line of FIG.
5.
[0052] FIG. 6(b) is a cross sectional view along B-B line of FIG.
5.
[0053] FIG. 7 is a flow chart showing a procedure for processing
the multilayer piezoelectric element according to the
invention;
[0054] FIG. 8 is a schematic view showing element parts according
to the invention;
[0055] FIG. 9 is a schematic view showing one example of the
electrophoretic deposition according to the invention; and
[0056] FIG. 10(a) is a view showing a process of the glass
particles electrodeposited to the internal electrode layers by the
electrophoretic deposition according to the invention; and
[0057] FIGS. 10(b1) and 10(b2) are schematic views showing the
glass insulating layers formed by performing the heat treatment to
the glass electrodeposited layers by the electrophoretic deposition
of the invention.
[0058] FIG. 11 is a perspective view showing the electronic parts
of the multilayer piezoelectric ceramic not exposing the internal
electrodes according to the conventional example.
[0059] FIG. 12 is a perspective view showing the electronic parts
of the multilayer piezoelectric ceramic exposing the internal
electrodes according to the conventional example.
[0060] FIG. 13 is a cross sectional view showing electronic parts
of the multilayer piezoelectric ceramic provided with films of the
insulating resin according to the conventional example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] Hereinafter, a first embodiment of the invention is
described with reference to FIGS. 1 to 4. The shown electronic
parts of the multilayer piezoelectric ceramic are, as shown in FIG.
1, composed of the sintered multilayer ceramic produced by drawing
out from the electrically conductive paste of Ag or Ag--Pd alloy,
printed to form the internal electrodes 110, 111, 112 with
differently positioned electrodes within the surfaces of the
piezoelectric ceramic green sheets 113, alternately stacking a
plurality of layers of the piezoelectric ceramic green sheets 113
and the internal electrodes 110, 111, 112 to produce multilayer
piezoelectric ceramics, and firing the multilayer piezoelectric
ceramic.
[0062] In the sintered multilayer ceramics, the electrically
conductive paste of Ag being the main component is coated to the
sintered multilayer ceramic 101 at edges thereof to form the
terminal electrodes 114 which electrically conduct to the internal
electrodes 110, 111, 112. The terminal electrodes 114 are formed as
shown in 102a, 102b and 102c of FIG. 12. Further, the sintered
piezoelectric ceramic is coated on the surfaces thereof with films
115 of the glass insulating material comprising any two or more
components of ceramic compounds selected from elements composing
all or a part of lead oxide (PbO), silicon oxide (SiO.sub.2),
aluminum oxide (Al.sub.2O.sub.3) and the sintered piezoelectric
ceramic.
[0063] In the thus composed electronic parts of the multilayer
piezoelectric ceramic, the surfaces of the sintered piezo-electric
ceramic are protected with the films 115 of the non-permeable fine
glass insulating material of moisture, so that it is possible to
avoid defects of insulation between the internal electrodes and
defects of insulation by migration, to work for a longer time under
such atmosphere at high temperature and high humidity, and to
secure the displacement amount, thereby enabling to compose
products of high reliability and durability.
[0064] Other than those not exposing the internal electrodes as
shown in FIGS. 1 and 2, the electronic parts of the multilayer
piezoelectric ceramic may be composed with the sintered
piezoelectric ceramic where the internal electrodes 110', 111',
112' are printed all over except parts to both edges in length of
the piezoelectric ceramic green sheets 113 as shown in FIG. 3, and
the internal electrodes 110', 111', 112' are exposed at the edges
as shown in FIG. 4.
[0065] The electric parts of the multilayer piezoelectric ceramics
are produced by at first adding an organic binder of a
predetermined amount as a main component of calcined powders of the
piezoelectric ceramic, further adding solvent, fully mixing in a
ball mill, and making slurry of the piezoelectric ceramics, and
subsequently forming a thin film from the slurry on polyester film
by a roll coater, heating to dry the thin film up to 80 to
100.degree. C. on the polyester film, and punching it out to
produce the green sheet of 20 .mu.m thickness.
[0066] For forming the internal electrodes, Ag powders, Pd powders
and ethyl cellulose are solved in butyl carbitol and terpineol, and
agitated to mix to produce the electrically conductive paste. This
electrically conductive paste is used to print on one side of the
piezoelectric ceramic green sheets by the screen having desired
patterns and dried to form the internal electrodes.
[0067] Next, a plurality of piezoelectric ceramic green sheets and
internal electrodes are alternately stacked, and 20 sheets of the
ceramic green sheets not printed with the internal electrodes
(sheet thickness: 15 .mu.m) are stacked on the upper and lower
outermost layers. Subsequently, the stacked piezoelectric ceramic
is being heated at about 60.degree. C. while pressure is given to
the stacking direction for pressure bonding.
[0068] The stacked piezoelectric ceramic is inserted in a furnace
to burn out the organic binder and fired for two hours as holding
the heating temperature at 1060.degree. C., brought down to
600.degree. C. at a rate of 200.degree. C./hour, and cooled to room
temperature to produce the sintered piezoelectric ceramics. Through
this procedure, the organic binder is burned out, and the pores are
dotted in the layers of the sintered piezoelectric ceramic.
[0069] For forming the film of the sintered piezoelectric ceramic,
powders of any two or more components of ceramic compounds (called
as "the same materials as element" hereafter) selected from
elements composing all or a part of lead oxide (PbO), silicon oxide
(SiO.sub.2), aluminum oxide (Al.sub.2O.sub.3) and the sintered
piezoelectric ceramic, are dispersed by synthetic resins such as
ethyl cellulose or acrylic resin and solvent of methyl ethyl ketone
(MEK), thereby to produce the glass insulating paste adjusted to be
moderate viscosity.
[0070] The glass insulating paste is uniformly coated and dried on
the surfaces of the sintered piezoelectric ceramic by such as a dip
or spin coat, and heat-treated in the furnace of an air atmosphere
at temperature of about 800.degree. C. for 20 minutes. Through this
procedure, the surfaces of the sintered piezoelectric ceramic can
be formed with the film of the glass insulating material, and a
glass content penetrates the layer of the sintered piezoelectric
ceramic and diffuses to fill the pores.
[0071] The sintered piezoelectric ceramic is thereafter subjected
to a dicing process to produce a piezoelectric ceramic chip, and
finally the piezoelectric ceramic chip exposing the internal
electrodes is coated at the edges thereof with the electrically
conductive paste composed of Ag powders, Pd powders, glass frits
and vehicle, and after drying the paste, the interior of the
furnace is made the air atmosphere for baking at about 720.degree.
C. for 20 minutes so as to form the terminal electrodes.
[0072] In those structures not exposing the internal electrodes at
the sides thereof, with respect to 100 pieces of the inventive
products and the conventional products which have the film of the
glass insulating material from composition of PbO: 30 wt %, SiO: 10
wt %, Al.sub.2O.sub.3: 10 wt %, the same materials as the element:
50 wt %, the comparison was evaluated by the high temperature high
humidity test (test conditions: temperature: 85.degree. C.,
relative humidity: 85% RH). The results are shown in Table 1.
1 TABLE 1 Testing Time and Percentage Thickness of of Accumulated
Defects (%) Reference No. film (.sup..mu.m) Displacement 10 h 24 h
50 h 100 h 250 h 500 h 1000 h Percentage of Defects in Electric 1
0.3 .largecircle. 0 0 0 0 0 50 100 Parts of the Multilayer
Piezoelectric 2 0.5 .largecircle. 0 0 0 0 0 0 0 Ceramic according
to the Invention 3 1 .largecircle. 0 0 0 0 0 0 0 4 3 .largecircle.
0 0 0 0 0 0 0 5 5 .largecircle. 0 0 0 0 0 0 0 6 7 .largecircle. 0 0
0 0 0 0 0 7 10 X 0 0 0 0 0 0 0 Percentage of Defects in Electric
Parts of 8 -- X 100 the Multilayer Piezoelectric Ceramic according
to the Conventional Products
[0073] The inventive products can be composed enabling to prevent
penetration of the moisture and reduce occurrence of
[0074] defects in insulation and to have high reliability and
durability by forming the film of the glass insulating material
having thickness of 0.5 to 7.0 .mu.m on the surface of the sintered
piezoelectric ceramic. If the film thickness of the glass
insulating material is around 0.3 .mu.m, as it is thin, the
durability is up to the high temperature and high humidity test for
1000 hours at the most. If the film thickness of the glass
insulating material is about 10 .mu.m, as it is thick, such a
product is not desirable because of giving influences to the
displacing characteristics of the sintered piezoelectric
ceramic.
[0075] On the other hand, the external film of the organic resin of
the conventional products cannot perfectly avoid invasion of the
moisture, and such a product is only durable to the high
temperature and high humidity test for 10 hours.
[0076] In those structures exposing the internal electrodes at the
sides thereof, with respect to the inventive products and the
conventional products which have the film of the glass insulating
material from the same composition as above mentioned, the
comparison was evaluated by the high temperature high humidity test
(test conditions: temperature: 85.degree. C., relative humidity:
85% RH). The results are shown in Table 2.
2 TABLE 2 Testing Time and Percentage Thickness of of Accumulated
Defects (%) Reference No. film (.sup..mu.m) Displacement 10 h 24 h
50 h 100 h 250 h 500 h 1000 h Percentage of Defects in Electric 9
0.3 .largecircle. 100 Parts of the Multilayer Piezoelectric 10 0.5
.largecircle. 0 0 0 0 0 10 50 Ceramic according to the Invention 11
1 .largecircle. 0 0 0 0 0 0 0 12 3 .largecircle. 0 0 0 0 0 0 0 13 5
.largecircle. 0 0 0 0 0 0 0 14 7 .largecircle. 0 0 0 0 0 0 0 15 10
X 0 0 0 0 0 0 0 Percentage of Defects in Electric Parts of 16 -- X
the Multilayer Piezoelectric Ceramic according to the Conventional
Products
[0077] Though the inventive products are those exposing the
internal electrodes at the sides, if applying the film of the
[0078] glass insulating material having thickness of 0.5 to 7.0
.mu.m to the sintered piezoelectric ceramic on the surfaces
thereof, such structure is available enabling to avoid invasion of
the moisture, reduce occurrence of defects in insulation and have
the high reliability and high durability. If the film thickness of
the glass insulating material is around 0.3 .mu.m, durability is up
to the high temperature and high humidity test for around 10 hours.
If the film thickness of the glass insulating material is about 10
.mu.m, as it is thick, similarly to the structures not exposing the
internal electrodes, such a product is not desirable because of
giving influences to the displacing characteristics of the sintered
piezoelectric ceramic.
[0079] On the other hand, the external film of the organic resin of
the conventional products cannot avoid invasion of the moisture,
and such a product is only durable to the high temperature and high
humidity test for 10 hours.
[0080] Other embodiments of the invention will be specifically
explained with reference to FIGS. 5 to 10(b2). FIG. 5 is a
schematically perspective view showing the structure of the
multilayer piezoelectric element 1 according to the invention, FIG.
6(a) is a cross sectional view along A-A line of FIG. 5, FIG. 6(b)
is a cross sectional view along B-B line of FIG. 5. As shown in
FIGS. 5, 6(a), and 6(b), the multilayer piezoelectric element 1 is
composed of a piezoelectric ceramic layer 2, internal electrode
layers 3 for impressing an electric field to the piezoelectric
ceramic layer 2, glass insulating layers 4 for insulating the
exposed edges of the internal electrode layers 3 and the
piezoelectric ceramic layer 2 between the internal electrode layers
3, and terminal electrodes (not shown) for applying voltage to the
internal electrode layers 3, and is structured such that the edges
of the internal electrode layers 3 are exposed outside of the
piezoelectric ceramic layer 2 every other layer.
[0081] FIG. 7 is a flow chart showing a procedure for making the
multilayer piezoelectric element 1 according to the invention, and
FIG. 8 is a schematic view showing element parts of FIG. 7. As
shown in FIG. 7, raw materials for the piezoelectric ceramic are
weighed and mixed (S1) in a water with ZrO.sub.2 balls, dried and
calcined (S2). Subsequently, this is grinded (S3) in the water with
ZrO.sub.2 balls, dried, and kneaded with organic solvent and resin
ingredients so as to make paste (S4). The paste is thereafter
coated on a polyester film and shaped into sheet thereby forming a
green sheet (S5).
[0082] On the green sheet including the piezoelectric ceramic,
conductive paste of main components being Ag and Pd is used to form
the internal electrode layers 3 by such as a printing method (S6)
into desired patterns, and process (S10) green sheets stacked with
predetermined layers (S7 to S9). The stacked green sheets are
subjected to burn-out organic binder (S11) and a firing (S12), and
to a processing (S13) for forming a formed element 7 of a desired
shape. The formed element 7 exposes the sides of the internal
electrode layer 3 as shown in FIG. 8. The formed element 7 is
provided with the terminal electrodes 5 (S14), and then
predetermined glass particles are electrodeposited (S15) to the
exposed sides of the internal electrode layers 3 by the
electrophoretic deposition, dried (S16), heat-treated (S17) for
making the multilayer piezoelectric element 1 (S18).
[0083] (Glass Insulating Layer)
[0084] The glass insulating layer 4 formed on the multilayer
piezoelectric element 1 of the invention may be carried only on the
exposed parts of the edges of the internal electrode layers 3
outside of the piezoelectric ceramic layers 2. Similarly, as shown
in FIGS. 5, 6(a), and 6(b), it is preferable that the glass
insulating layer 4 is carried on both of the exposed parts of the
edges of the internal electrode layers 3 outside of the
piezoelectric ceramic layers 2 and the surface of the piezoelectric
ceramic layer between the internal electrode layers 3. The glass
insulating layer 4 increases the moisture resistance of the
multilayer piezoelectric element 1 and heighten the reliability. In
addition, the glass insulating layer 4 enough lowly suppresses
hindrance of displacement caused at driving the multilayer
piezoelectric element 1.
[0085] (A Forming Method of the Glass Insulating Layer)
[0086] The method of forming such a glass insulating layer 4
requires the following items.
[0087] (A) The glass insulating layer 4 can be formed at least on
the exposed parts of the internal electrode layer 3 outside of the
piezoelectric ceramic layer 2.
[0088] (B) The glass insulating layer 4 can be formed uniformly in
a predetermined thickness with good controllability and excellent
precision in thickness.
[0089] (C) A speed of forming the glass insulating layer 4 is
enough fast to an extent of not hampering productivity.
[0090] As the method of forming the glass insulating layer 4
satisfying such requirements, a method of combining the
electrophoretic deposition and the heat treatment is taken up.
Explanation will be made to the forming method of the glass
insulating layer 4 using the electrophoretic deposition, referring
to FIGS. 9, 10(a), 10(b1), and 10(b2).
[0091] (The Electrophoretic Deposition)
[0092] The electrophoretic deposition to be used in the invention
is not especially limited, and a known method may be served. This
electrophoretic deposition comprises, as exemplified in FIG. 9, at
first immersing a formed element 7 provided with terminal
electrodes 5 for the electrophoretic deposition at the exposed
parts of the internal electrode layer 3 and an opposite electrode 6
in a suspension 11 dispersed with predetermined glass particles 10.
The terminal electrodes 5 and the opposite electrode 6 are
electrically connected. Subsequently a predetermined voltage is
impressed from a power source provided between the opposite
electrode 6 and the terminal electrodes 5. In such a manner, the
glass particles 10 dispersed in the suspension 11 are moved toward
the exposed parts of the internal electrode layer 3 along the
electric field, so that it is possible to form a glass
electrodeposit formed element 8 deposited selectively with the
glass particles 10 on the exposed edges of the internal electrodes
3.
[0093] Subsequently, the glass electrodeposit formed element 8 is
heat-treated in an air at a predetermined temperature so as to form
uniform glass insulating layers 4. At this time, the heat-treating
temperature is determined to be above the softening point of the
glass particle 10 and below the firing temperature of the
multilayer piezoelectric element in order to soften the glass
particles 10 to be moderately fluidized, so that it is possible to
form the uniform glass insulating layer 4 with suppressing defects
enough. If then the heat treatment is carried out at a relatively
low temperature as being above the fluidizing range of the softened
glass particle 10 and for a relatively short time, it is possible
as shown in, for example, FIG. 10 (b1) to uniformly form the glass
insulating layer 4 only in the vicinity of exposed part of the
internal electrode layer 3.
[0094] On the other hand, if the heat-treating temperature is
determined to be above the softening point of the glass particle 10
and the heat treatment is performed at the relatively high
temperature as moderately expanding the fluidizing range of the
softened glass particle 10 and for the relatively long time, it is
possible as shown in, for example, FIG. 10(b2) to form the glass
insulating layer 4 on both of the exposed part of the internal
electrode layer 3 and the surface of the piezoelectric ceramic
layer 2 between the internal electrode layers 3.
[0095] In case the glass insulating layer 4 is formed on both the
internal electrode layer 3 and the piezoelectric ceramic layer 2
between the internal electrode layers 3, if fine pores exist in the
surface of the piezoelectric ceramic layer 2, the softened glass
particle 10 goes into and fills the pores, thereby enabling to
prevent the moisture penetrating the interior of the multilayer
piezoelectric element 1 from the surface of the piezoelectric
ceramic layer 2.
[0096] The glass particle 10 is electrodeposited on the exposed
part of the internal electrode layer 3 of the formed element 7 by
the electrophoretic deposition, and the heat treatment is carried
out at the temperature above the softening point of the glass
particle 10 and below the firing temperature of the multilayer
piezoelectric element, thereby enabling to form the glass
insulating layer 4 on either of the only exposed part of the
internal electrode layer 3 or on both of the exposed part of the
internal electrode layer 3 and the piezoelectric ceramic layer 2
between the internal electrode layers 3. In such manners, as the
glass insulating layer 4 can be formed in response to properties of
the formed element 7 or requisite characteristics of the multilayer
piezoelectric element 1, the characteristics and cost can be
satisfied in preferable harmonies.
[0097] (The Electrodeposition of the Glass Particles by the
Electrophoretic Deposition)
[0098] FIG. 10(a) schematically shows a process of the glass
particles 10 being electrodeposited to the formed element 7 by the
electrophoretic deposition, and FIGS. 10(b1) and 10(b2)
schematically shows a process that the glass insulating layer is
formed by performing the heat treatment to the glass
electrodeposited layers as FIG. 10(a).
[0099] As shown in FIG. 10(a), in the electrophoretic deposition,
the electrodeposited matter such as the glass particle 10 moves
along the electric field from the opposite electrode to the
terminal electrode, gets to the exposed part of the internal
electrode layer 3, and forms an initial nucleus (not shown). Then,
the initial nucleus grows to be a hemispherical land shaped layer N
having, e.g., a radius r. It has been known that the radius r of
this land shaped layer N gradually grows, contacts to combine a
neighbor land shaped layer N, and at last forms a relatively flat
layer (not shown).
[0100] A structure of the land shaped layer N formed by the
electrophoretic deposition or a land shaped structure composed of a
relatively flat layer are herein called as "glass electrodeposited
layer".
[0101] According to the invention, as shown in FIG. 10(a), the
formed element 7 is processed with the electrophoretic deposition
and the glass electrodeposited layer is heat-treated at a
predetermined temperature. With these processes, the glass
insulating layer 4 of uniform thickness is efficiently formed with
suppressing defects enough.
[0102] With such a heat treatment to the glass electrodeposited
layer, glass particles are melted and uniform amorphous glass
insulating layer 4 is formed. A shape of thus formed glass
insulating layer 4 is formed as one of the following two types by
appropriately setting temperature and time of the heat treatment.
That is, by setting the heat-treating temperature to be relatively
low, or setting the time to be relatively short, the glass
electrodeposited layer 4 can be formed only in the vicinity of the
exposed part of the internal electrode layer 4 as shown in FIG.
10(b1). On the other hand, by setting the heat-treating temperature
to be relatively high, or setting the time to be relatively long,
the glass electrodeposited layer 4 can be, as shown in FIG. 10(b2),
formed on both of the exposed part of the internal electrode layer
3 and the piezoelectric ceramic layer 2 between the internal
electrode layers 3. As having explained above, by appropriately
setting the heat-treating conditions, the shapes of the glass
insulating layers 4 can be adopted to qualities or characteristics
required in the multilayer piezoelectric element 1.
[0103] In the invention, it is preferable that the glass
electrodeposited layer 4 is formed on both of the piezoelectric
ceramic surface of the upper face of the uppermost internal
electrode layer 3 and the piezoelectric ceramic surface of the
lower face of the lowermost internal electrode layer 3 or at least
either one of them, other than the exposed parts of the internal
electrode layers 3 and the surface of the piezoelectric ceramic
layer 2 between the internal electrode layers 3.
[0104] (The Heat-Treating Temperature for Forming the Glass
Insulating Layer)
[0105] The conditions of the heat-treating temperature for forming
the glass insulating layer 4 according to the invention are ranges
where the heat-treating temperature does not give bad influences to
the piezoelectric ceramic layer 2 and the internal electrode layer
3, and to soften the electrodeposited glass particles and to form
uniform layers. In case the piezoelectric ceramic layer 2 is
composed of PZT {Pb(Zr, Ti)O.sub.3} based ceramic materials, and
the internal electrode layer 3 is composed of the above mentioned
Ag--Pd alloy, it is preferable that the heat-treating temperature
for forming the glass insulating layer 4 from the glass
electrodeposited layer is 1000.degree. C. or lower, which is lower
than the firing temperature of the multilayer piezoelectric
element.
[0106] (Thickness of the Glass Insulating Layer)
[0107] The conditions for the thickness of the glass insulating
layer 4 are for the glass insulating layer 4 to sufficiently and
lowly suppress hindrance of displacement when the multilayer
piezoelectric element 1 is driven, and for the internal electrode
layer 3 of the multilayer piezoelectric element 1 to insulate the
exposed part from the outside and to impart sufficient moisture
resistance. As the glass insulating layer 4 satisfying such
conditions, the thickness is preferably 0.3 to 10 .mu.m. Being less
than 0.3 .mu.m, the imparted moisture resistance is not enough,
while being larger than 10 .mu.m, the hindrance by displacement
when driving the multilayer piezoelectric element 1 is excessive,
and inconveniences will probably arise when it is served as a
piezoelectric actuator.
[0108] Further, the thickness of the glass insulating layer 4 is
more preferably 0.5 to 7 .mu.m in view of more stably exhibiting
the performance of the multilayer piezoelectric element 1 or
dispersion in quality of products to be less.
[0109] (Chemical Composition of the Glass Insulating Layer)
[0110] With respect to the chemical composition of the glass
insulating layer 4 of the multilayer piezoelectric element 1
according to the invention, it is necessary to perform the heat
treatment at the temperature and for the time not giving bad
influences to the internal electrode layer 3, and to form one with
thickness not hindering the displacement when the multilayer
piezoelectric element is driven.
[0111] As materials of composing the glass insulating layer 4
having the above mentioned preferable range of the heat-treating
temperature and the moderately large elastic modulus, glass
insulating materials such as PbO, SiO.sub.2 or Al.sub.2O.sub.3 may
be enumerated.
[0112] For approaching the elastic modulus of the glass insulating
layer 4 to the elastic modulus of the multilayer piezoelectric
element 1, it is preferable to add the piezoelectric ceramic into a
glass matrix having the above mentioned glass component in a range
not to obstructing the amorphous nature of the glass insulating
layer 4.
[0113] The glass insulating layer 4 satisfying the above mentioned
conditions is preferably composed of components as below.
[0114] (1) the glass component is based on a single component.
[0115] (2) the glass component is based on a mixed component
including a plurality of components
[0116] (3) the single component is dispersed with piezoelectric
ceramic in the glass matrix thereof, and
[0117] (4) the mixed component is dispersed with the piezoelectric
ceramic in the glass matrix thereof.
[0118] In the above (3) and (4), if the piezoelectric ceramic is
the same as the piezoelectric ceramic 2 of the multilayer
piezoelectric element 1, the elastic modulus of the glass
insulating layer 4 comes preferably nearer to the elastic modulus
of the multilayer piezoelectric element 1.
[0119] In a case where the glass insulating layer 4 is composed of
PbO: 10 to 80 wt %, SiO.sub.2: 10 to 80 wt %, Al.sub.2O.sub.3: 0 to
50 wt % and the same piezoelectric ceramic as the piezoelectric
ceramic of the multilayer piezoelectric element 1: 0 to 50 wt %,
the multilayer piezoelectric element 1 will be one which enough
lowly suppresses the hindrance of displacement when the multilayer
piezoelectric element 1 is driven, heightens the moisture
resistance, improves the reliability and the durability, and costs
down relatively.
[0120] (The Internal Electrode Layer)
[0121] The internal electrode layer 3 of the multilayer
piezoelectric element 1 of the invention generates displacement in
the piezoelectric ceramic layer 2 by impressing a predetermined
voltage, and drives the multilayer piezoelectric element 1. The
internal electrode layer 3 is formed in film shape having a
predetermined pattern on a green sheet comprising the piezoelectric
ceramic, and the piezoelectric ceramic layers 2 and the internal
electrode layers 3 are alternately stacked by stacking the green
sheets to be an opposite electrode for exerting the electric field
to the piezoelectric ceramic layer 2.
[0122] (Requirements of the Internal Electrode Layer)
[0123] As the requirements of the internal electrode layer 3, the
following items will be enumerated.
[0124] (a) The layer can be easily formed at a predetermined
position on the green sheet.
[0125] (b) The layer can be formed on the green sheet with a good
adhesion.
[0126] (c) The layer can hold the function as the electrode after
fired at a predetermined temperature.
[0127] (d) The layer can displace in response to the displacement
of the piezoelectric ceramic layer 2 as holding a predetermined
structure of the electrode.
[0128] As the internal electrode layer satisfying the above
requirements (a) to (d), including economics, and fulfilling them
as soon as possible at preferable harmonies, Ag--Pd alloy is
generally used where Ag is based and Pd is added at an appropriate
amount. The thus composed internal electrode layer 3 may be added
with at least one kind of other metals than the paste Ag--Pd alloy,
metallic oxides or organic metallic compounds. On a yet more
outside of the internal electrode layer 3 positioned at the
outermost position of the multilayer piezoelectric element 1, the
piezoelectric ceramic layer 2 is formed.
[0129] (The Forming Method of the Internal Electrode Layer)
[0130] No limitation is especially made to the forming method of
the internal electrode layer, and conventionally known methods may
be used. For example, when forming the internal electrode layer
with an electric conductive paste, it may depends on a so-called
printing method of coating on the green sheet by means of a stamp,
roller, screen or mask. Further, when forming the internal
electrode layer 3 by a dry film forming method such as a spattering
method or a vapor deposition method, at first a photo resist film
is formed on the surface of the green sheet, and the photo resist
film is formed in a predetermined pattern shape by a photo
lithographic method including an exposure treatment using a
predetermined mask, and then the internal electrode layer 3 may be
formed with the dry film forming method. Otherwise it may be formed
with a non-electrolysis plating method immersing the green sheet in
an electrolytic solution containing a predetermined metal.
[0131] The multilayer piezoelectric element 1 according to the
invention is provided with the terminal electrodes connected to
predetermined positions of the edges of the internal electrode
layers 3, the terminal electrodes being led to an external source
via lead terminals (not shown).
[0132] The multilayer piezoelectric element 1 of the invention is
not especially limited with respect to stacking number of the
piezoelectric ceramic layers 2 and the internal electrode layers 3
(area, thickness, width), and such a multilayer piezoelectric
element composed of at least two layers is sufficient.
[0133] Further, the multilayer piezoelectric element 1 of the
invention is not especially limited with respect to shapes, and it
is enough if the above structured glass insulating layer 4 is
formable. For example, such a shape is permitted which is provided
with holes in the interior of the multilayer piezoelectric element
1.
[0134] Besides, the multilayer piezoelectric element 1 of the
invention is not especially limited with respect to displacing
orientations when driving, and either piezoelectric effect is
sufficient for a so-called piezoelectric vertical effect displacing
in a vertical direction in in-place of each layer or a so-called
piezoelectric lateral effect displacing in a horizontal direction
in in-place of each layer.
EXAMPLES
[0135] Examples of the invention and Comparative examples will be
explained referring to the attached drawings. FIG. 5 is a
schematically perspective view showing the structure of the
multilayer piezoelectric element 1 of the present example, FIG.
6(a) is a cross sectional view along A-A line of FIG. 5, and FIG.
6(b) is a cross sectional view along B-B line of FIG. 5. As shown
in FIG. 5 and FIGS. 6(a) and 6(b), the multilayer piezoelectric
element 1 comprises the piezoelectric ceramic layers 2, the
internal electrode layers 3 for impressing the electric field to
the piezoelectric ceramic layer 2, the glass insulating layers 4
for insulating the piezoelectric ceramic layers between the exposed
edges of the internal electrode layers 3 and the internal electrode
layers 3, and terminal electrodes (not shown) for supplying voltage
to the internal electrode layers 3, and is structured such that the
edge faces of the internal electrode layers 3 are exposed every
other layer at the sides.
[0136] (Method of Producing the Multilayer Piezoelectric
Element)
[0137] FIG. 7 is a flow chart showing a procedure for making the
multilayer piezoelectric element 1 according to the invention, and
FIG. 8 is a schematic view showing element parts of FIG. 7. In
FIGS. 7 and 8, the piezoelectric ceramic powders, binder and
organic solvent were mixed, and the paste was prepared (S1 to S4),
and was shaped into the green sheet (S5). Separately, the electric
conductive material, binder and organic solvent were kneaded to
prepare the paste for the internal electrode layers.
[0138] On the green sheet, the paste for the internal electrode
layers in a desired shape was printed (S6), then cut into a desired
size (S7), stacked 30 sheets (S8), pressed (S9) so as to form the
green sheet stacked element (S10), burned out organic binder (S11),
a firing (S12), and to a processing (S13) for forming a formed
element 7 of a desired shape exposing the sides of the internal
electrode layer 3. The shaped element 7 was formed with the
terminal electrodes 5 at the desired positions of the exposed parts
of the internal electrode layers 3 (S14), and then processed by the
electrophoretic deposition as shown in FIG. 9.
[0139] Namely, the multilayer piezoelectric element was immersed in
the suspension 11 dispersed with the glass particles 10, and the
terminal electrodes 5, the opposite electrode 6 and the power
source were connected and impressed with voltage, whereby the glass
particles 10 were moved along the electric field and
electrodeposited to the exposed parts of the internal electrodes 3
and the vicinity thereof (S15), and the glass electrodeposit formed
element 8 having the terminal electrodes 5 and the glass deposited
layers were formed. The glass electrodeposit formed element 8 was
thereafter dried (S16), heat-treated at the predetermined
temperatures (S17) to form the glass insulating layers 4 and make
test samples of the multilayer piezoelectric element 1 (S18).
[0140] In the electrophoretic deposition, the impressed voltage was
given appropriate leveling for making test samples (S17 to S18) of
the Examples (1 to 7) whose thickness of the glass insulating layer
4 was within the specified range of the invention, the Comparative
example 8 without forming the glass insulating layer 4, and the
Comparative example 9 where the thickness of the glass insulating
layer 4 was out of the specified range of the invention.
[0141] With respect to each of the test samples, initial electric
characteristics such as the insulating resistance and capacity were
measured and evaluated (S19), while the reliability was evaluated
by the moisture resisting test (S20) under high temperature and
high humidity in order to accelerate the migration phenomena from
the internal electrode layer 3, and accumulated defects rate at
each testing time (10 to 1000 hours) was investigated.
[0142] For studying the dependency of the thickness of the glass
insulating layer 4 upon the restraining rate of hindrance of the
displacement which is a ratio of controlling hindrance of the
displacement when driving the multilayer piezoelectric element 1, a
polarization treatment was carried out on each of the test samples,
and the displacement was measured by the eddy current typed
displacement measuring apparatus. The construction of the test
samples and the conditions of the moisture resisting tests are
shown below. Table 3 shows the tested results.
[0143] (Construction of the Testing Samples)
[0144] Outward size:
[0145] 5.0.times.5.0.times.3.0 mm
[0146] Piezoelectric ceramic layer:
[0147] Chemical composition;
[0148]
Pb.sub.0.96Sr.sub.0.04{(Co.sub.1/3Nb.sub.2/3).sub.0.01Ti.sub.0.46Zr-
.sub.0.53}O.sub.3+WO.sub.3
[0149] Thickness; 25 .mu.m
[0150] Internal electrode layer:
[0151] Ag--Pd alloy (Ratio of the chemical composition; Ag/Pd=70 wt
%/30 wt %)
[0152] Thickness; 2 .mu.m
[0153] Number of stacked layers:
[0154] 30 (1 layer is a combination of one piezoelectric ceramic
layer and one internal electrode layer)
[0155] Terminal electrode:
[0156] Ag--Pd alloy
[0157] (Conditions of Producing Test Samples)
[0158] Firing temperature of the green sheet:
[0159] 1100.degree. C.
[0160] (Conditions of the Electrophoretic Deposition)
[0161] Construction of the suspension:
[0162] Glass particles+dispersion medium
[0163] (Dispersion medium:acetic anhydride)
[0164] Chemical composition of glass particles:
[0165] PbO; 60 wt %
[0166] SiO.sub.2; 20 wt %
[0167] Al.sub.2O.sub.3; 20 wt %
[0168] Concentration of glass particles in the suspension; 1 wt
%
[0169] Treating conditions:
[0170] Impressed voltage; D.C. 10 to 100 V
[0171] Treating time; 30 seconds
[0172] Treating temperature; 25.degree. C.
[0173] Heat treating conditions of glass deposited layer;
[0174] 800.degree. C., 20 minutes
[0175] (Test of Evaluating Reliability)
[0176] Conditions of the moisture resisting test:
[0177] Atmosphere of testing chamber; 85.degree. C./85% RH
[0178] Impressed voltage when driving test samples; D.C. 50 V (2
kV/mm)
[0179] Evaluating reference of the reliability; Comparing with an
initial value with respect to the insulating resistance,
evaluations were performed in that defects was defined as a case
where an order was lowered by three figures, and success was
defined as a case where an order was lowered by two figures or
less.
[0180] Displacement measuring conditions; The voltage of 50 V (2
kV/mm) was impressed at room temperature.
3TABLE 3 Measurements of test samples and evaluated results
Percentage of accumulated defects with respect to high temperature
and high humidity tests (%) Thickness of glass Amount of
Controlling percentage of 10 20 50 100 250 500 1000 Division Number
insulating layers (.sup..mu.m) displacement (.sup..mu.m) hampering
displacement (%) hours hours hours hours hours hours hours Examples
1 0.3 0.81 95.3 0 0 0 0 0 60 100 2 0.5 0.80 94.1 0 0 0 0 0 0 0 3
1.0 0.80 94.1 0 0 0 0 0 0 0 4 3.0 0.77 90.6 0 0 0 0 0 0 0 5 5.0
0.74 87.1 0 0 0 0 0 0 0 6 7.0 0.73 85.9 0 0 0 0 0 0 0 7 10.0 0.68
80.0 0 0 0 0 0 0 0 Comparative 8 none 0.85 -- 60 80 100 -- -- -- --
Examples 9 15.0 0.61 71.8 0 0 0 0 0 0 0 1) Displacement measuring
method: Displacements in thickness were measured by the eddy
current displacement measuring apparatus (DC 50 V(2 kV/mm)) 2) In
reference to the displacement of Comparative Example 8, percentage
of displacement in each test sample was calculated. (Results of
measuring the displacement and evaluating the reliability test)
[0181] Table 3 shows, in the Examples (1 to 7) and the Comparative
examples (8 and 9), thickness (.mu.m) of each glass insulating
layer 4, displacement (.mu.m), controlling percentage of hampering
displacement which expresses degree of controlling obstacle of
displacement, and percentage of accumulated defects when the
moisture resisting tests were carried out for 10 to 1000 hours. The
controlling percentage is calculated by making the displacement
(0.85 .mu.m) of the Comparative example 8 as the standard (100%).
Note that the Comparative example 8 is a bare multilayer
piezoelectric element without forming the glass layer 4.
[0182] From Table 3, in the Comparative example 8 without forming
the glass insulating layer 4, the accumulated defects is 60% after
10 hours and 100% after 50 hours, and the reliability is remarkably
low. In the Comparative example 9 where the thickness of the glass
insulating layer 4 is 15 .mu.m, the accumulated defects after 1000
hours is 0%, and although the reliability is remarkably heightened,
the controlling percentage of hampering displacement stands still
72% of the Comparative example 8, without forming the glass
insulating layer 4, and the function of the displacement as the
piezoelectric actuator is largely lowered.
[0183] On the other hand, in the Examples 1 to 7 where the
thickness of the glass insulating layer 4 is 0.3 to 10 .mu.m, the
displacement is prevented from hampering as the controlling
percentage of hampering displacement is 80 to 95%, and the
accumulated defects is 60% after 500 hours in the Example 1
(thickness of the glass insulating layer 4: 0.3 .mu.m), and 0%
after 1000 hours in the Examples 2 to 7 (thickness of the glass
insulating layer: 0.5 to 10 .mu.m). Thus, the reliability and the
durability are improved in leaps.
[0184] As seen in the results of the Examples (1 to 7) and the
Comparative examples (8, 9), the multilayer piezoelectric element 1
of the invention can display a satisfied displacing function when
driving by the formed glass insulating layer 4 which sufficiently
controls obstacle of displacement, and while the reliability and
the durability are enough secured even at high temperature and high
humidity by the glass insulating layer 4, an expected performance
can be exhibited to the full.
[0185] The invention is not limited to the Examples but various
modifications are available as far as displaying the effects of the
invention. In the composition of the piezoelectric element, as long
as causing displacement, no limitation is made to only PZT based
ceramic materials, and the piezoelectric element can be composed
with discretionary modifications of PZT or with a composition
without lead.
[0186] If a matter contains metallic components causing migration
in the internal electrode, it is a suitable object of the
invention. If a material can sufficiently secure the function also
in the terminal electrode after heat treating the glass, it is
satisfied, and the internal electrode may be composed of chemical
compositions other than in the Example. The invention is not
applied to only the actuator, and if applying the invention to
those of relatively low impressed voltage such as multilayer
piezoelectric transformers, the moisture resistance can be improved
with the same structure and the reliability can be heightened.
[0187] As mentioned above, depending on the electronic parts of the
multilayer piezoelectric ceramic according to the invention and the
production method thereof, if the film of the glass insulating
material having the predetermined thickness is provided to the
sintered piezoelectric ceramic on the surfaces thereof, invasion of
the moisture can be prevented, and it is possible to avoid defects
in insulation between the internal electrodes caused by the
invasion of the moisture and defects in insulation caused by
migration, to work for a long time under the atmosphere at high
temperature and high humidity, and to secure reliability and
durability.
[0188] Further, by the above explained structure, the invention
displays the following effects.
[0189] First, since the glass insulating layer is formed to only
the exposed parts of the internal electrode layers, or both of the
exposed parts of the internal electrode layers and the surface of
the piezoelectric ceramic layers between the internal electrode
layers, the moisture resistance is improved, and it is possible to
offer the multilayer piezoelectric element having the excellent
reliability and durability.
[0190] By combining the electrophoretic deposition and the heat
treatment to be carried out at the predetermined temperature, the
glass insulating layer can be precisely formed in uniform thickness
also in the piezoelectric ceramic layer between the internal
electrode layers, and if fine pores exist in the piezoelectric
ceramic layer, since the glass layer can be penetrated also into
the interiors of the pores, it is possible to offer the multilayer
piezoelectric element preventing the moisture from going into the
interior.
[0191] Second, since the thickness of the glass insulating layer is
specified, in addition to the above mentioned effect, it is
possible to exactly control defects of the glass insulating layer
and hindrance of displacement of the multilayer piezoelectric
element and to heighten the reliability and the durability of the
multilayer piezoelectric element.
[0192] Third, the heat treatment at forming the glass insulating
layer does not give bad influences to the internal electrode layer,
and the heat treating temperature of the glass insulating layer is
specified so that the glass insulating layer controls hindrance of
displacement when driving the multilayer piezoelectric element, and
the components of the glass insulating layer are prepared such that
various needs of the multilayer piezoelectric element are
satisfied. In addition to the above mentioned effects, the expected
functions are fully displayed, and it is possible to offer the
multilayer piezoelectric element more suited to needs.
[0193] Fourth, since the piezoelectric ceramic to be added to the
glass insulating layer is composed with the same components as the
piezoelectric ceramic of the multilayer piezoelectric element, the
glass insulating layer can displace substantially in the same
displacement of the multilayer piezoelectric element at driving it,
and in addition to the above mentioned effects, it is possible to
control hindrance of displacement of the multilayer piezoelectric
element as soon as possible.
[0194] Fifth, since the glass insulating layer is composed of PbO,
SiO.sub.2, Al.sub.2O.sub.3 and the same piezoelectric ceramic as
the multilayer piezoelectric element, and the respective contents
are specified, it is possible to offer the multilayer piezoelectric
element satisfying the above mentioned effects and costs at
desirable harmonies.
[0195] Sixth, it is possible to offer the piezoelectric actuator
having the above mentioned effects.
[0196] Seventh, since it is possible to obtain such multilayer
piezoelectric element improving the reliability, function, cost,
precision and durability, the application of the multilayer
piezoelectric element can be broadened.
* * * * *