U.S. patent application number 14/790383 was filed with the patent office on 2015-10-22 for vibration element, manufacturing method thereof, and vibration wave actuator.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Yutaka Maruyama.
Application Number | 20150303832 14/790383 |
Document ID | / |
Family ID | 45021502 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150303832 |
Kind Code |
A1 |
Maruyama; Yutaka |
October 22, 2015 |
VIBRATION ELEMENT, MANUFACTURING METHOD THEREOF, AND VIBRATION WAVE
ACTUATOR
Abstract
A vibration element includes a substrate, a piezoelectric
element including a piezoelectric layer and an electrode layer, and
a bonding layer provided between the piezoelectric element and the
substrate and comprising ceramic containing melted glass powder,
wherein the vibration element causes the substrate to vibrate by
vibration energy of the piezoelectric element to output the
vibration energy of the substrate, and the piezoelectric element is
fixed to the substrate via the bonding layer.
Inventors: |
Maruyama; Yutaka; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
45021502 |
Appl. No.: |
14/790383 |
Filed: |
July 2, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13118320 |
May 27, 2011 |
9083264 |
|
|
14790383 |
|
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Current U.S.
Class: |
310/323.16 |
Current CPC
Class: |
H01L 41/18 20130101;
H02N 2/0015 20130101; H02N 2/026 20130101; H04R 31/00 20130101;
H04R 17/00 20130101; H02N 2/001 20130101; H04R 2440/00 20130101;
Y10T 29/42 20150115; H01L 41/319 20130101; H01L 41/314
20130101 |
International
Class: |
H02N 2/00 20060101
H02N002/00; H01L 41/18 20060101 H01L041/18 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2010 |
JP |
2010-124711 |
Claims
1. A vibration element, comprising: a substrate; a piezoelectric
element including a piezoelectric layer and an electrode layer; and
a bonding layer provided between the piezoelectric element and the
substrate and comprising ceramic containing glass, wherein the
electrode layer is fixed to the substrate via the bonding layer,
wherein the bonding layer comprises a compound whose main component
is the same as a main component of the piezoelectric layer, wherein
a first concentration of the glass at an interface of the substrate
and the bonding layer is greater than a second concentration of
glass at a center of the bonding layer, wherein a third
concentration of glass at an interface of the bonding layer and the
electrode layer is greater than the second concentration, and
wherein the piezoelectric layer does not contain glass defused from
the bonding layer.
2. The vibration element according to claim 1, wherein silicon
oxide and boron oxide are contained in the glass and also an
additive is added to the glass.
3. The vibration element according to claim 1, wherein the main
component is a piezoelectric material.
4. The vibration element according to claim 1, wherein the
substrate comprises ceramic or metal.
5. The vibration element according to claim 4, wherein the ceramic
forming the substrate includes alumina or ceramic prepared by
adding zirconia to alumina as a main component.
6. The vibration element according to claim 4, wherein the metal
forming the substrate is stainless steel.
7. The vibration element according to claim 1, wherein the
piezoelectric layer comprises lead zirconate and lead titanate as
main components, and wherein the electrode layer comprises silver
and palladium as main components.
8. The vibration element according to claim 1, wherein the
piezoelectric layer comprises barium titanate as a main component,
and wherein the electrode layer comprises silver as a main
component.
9. The vibration element according to claim 1, wherein the
piezoelectric element comprises the piezoelectric layer and the
electrode layer being alternately stacked.
10. A vibration wave actuator, comprising the vibration element
according to claim 1 as a driving power source.
11. The vibration element according to claim 1, wherein the
vibration element causes the substrate to vibrate by vibration
energy of the piezoelectric element to output the vibration energy
of the substrate.
12. The vibration element according to claim 1, wherein material
for the electrode layer is different from material for the
substrate.
13. The vibration element according to claim 1, wherein material
for the bonding layer is different from any one of material for the
electrode layer and material for the substrate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 13/118,320 filed May 27, 2011, which claims
priority to Japanese Patent Application No. 2010-124711 filed May
31, 2010, all of which are hereby incorporated by reference herein
in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a vibration element in
which a piezoelectric element is fixed onto a substrate, a
manufacturing method thereof, and a vibration wave actuator using
the vibration element.
[0004] 2. Description of the Related Art
[0005] In a vibration wave actuator, a piezoelectric element has
commonly been used as a vibration source of a vibration element. A
single plate piezoelectric element, or a laminated piezoelectric
element obtained by stacking many piezoelectric layers and then
sintering formed/integrated layers, is used as the piezoelectric
element. Particularly, compared with the single plate piezoelectric
element, the laminated piezoelectric element has an advantage of
being able to obtain a large deformation or a large force with a
low applied voltage due to multi-layering (U.S. Pat. No.
7,109,639).
[0006] FIG. 5 is a perspective view of appearance of a linear
vibration wave (ultrasonic wave) actuator 30 discussed in U.S. Pat.
No. 7,109,639. The linear vibration wave actuator 30 includes a
vibration element 31 and a rod-shaped moving member (linear slider)
36 in pressure contact. The vibration element 31 includes a
laminated piezoelectric element 35 and a drive plate 32 and the
laminated piezoelectric element 35 has a plurality of piezoelectric
layers and electrode layers stacked alternately. The drive plate 32
is made of metal and is bonded to the laminated piezoelectric
element 35 by an adhesive. The drive plate 32 includes a plate
portion formed in a rectangular shape and two protruding portions
33a and 33b formed in a convex shape on a top surface of the plate
portion. The protruding portions 33a and 33b have contact portions
34a and 34b, respectively, formed on a tip surface thereof. The
contact portions 34a and 34b are members to come directly into
contact with the linear slider 36 as driven elements and thus have
predetermined wear resistance. The linear vibration wave actuator
30 excites two bending vibration modes to cause the protruding
portions 33a and 33b to make an elliptic motion. The elliptic
motion generates a relative movement force between the linear
slider 36 and the vibration element 31, with which the linear
slider 36 is in contact under pressure. The linear slider 36 is
linearly driven by the relative movement force.
[0007] When the laminated piezoelectric element 35 is manufactured,
first a green sheet to be a piezoelectric layer is produced from
piezoelectric material powder and an organic binder by the doctor
blade or a similar method and then an electrode material paste is
printed to predetermined positions on the green sheet to produce an
electrode layer. Then, a predetermined number of green sheets are
stacked in a plane shape and pressurized for lamination.
Subsequently, the piezoelectric layer and the electrode layer are
sintered at the same time to integrate the layers, and polarization
is performed to finish the laminated piezoelectric element 35 to
predetermined dimensions by machining in the end. Also a
piezoelectric electrostrictive film actuator having an integrated
laminated structure integrated by heat treatment of an electrode
material and a piezoelectric material alternately stacked in a
layered shape on at least one side of the ceramic substrate is
known.
[0008] FIGS. 6A and 6B illustrate a vibration element 40 integrated
by sintering a piezoelectric element 41, including a piezoelectric
layer 45 and electrode layers 44 and 46, and a ceramic substrate
42, as a vibration element, at the same time.
[0009] A piezoelectric layer 43 as a compound layer having the same
components or the same main components as the piezoelectric layer
45 is placed between the electrode layer 44 of the piezoelectric
element 41 and the ceramic substrate 42, and the piezoelectric
element 41 and the ceramic substrate 42 are joined by sintering
(Japanese Patent Application Laid-Open No. 2009-124791).
[0010] In the vibration element 31 of the linear vibration wave
actuator 30 discussed in U.S. Pat. No. 7,109,639, the laminated
piezoelectric element 35 and the drive plate 32 made of metal are
bonded by an adhesive made of resin.
[0011] However, an adhesive made of resin is relatively soft. Thus,
vibration damping of a vibration element is large and particularly
an influence of the vibration damping of a vibration element
increases with a decreasing size thereof, causing degradation of
efficiency of a small vibration wave actuator as a leading factor.
Moreover, when the vibration element is miniaturized, an influence
of variations in thickness of an adhesion layer and accuracy of
position due to adhesion on performance of a small vibration wave
actuator increases and also variations of performance of small
vibration wave actuators increase.
[0012] Further, according to the manufacturing method of a
conventional laminated piezoelectric element, the costs of plant
and equipment investment of production units for green sheet
formation from piezoelectric material powder, laminating press,
machining and the like are large, contributing to increasing
manufacturing costs as a factor. Thus, like the above piezoelectric
electrostrictive film actuator having an integrated laminated
structure, a method of directly fixing a laminated piezoelectric
element to a ceramic substrate without providing an adhesion layer
with an adhesive at the same time as the production of the
laminated piezoelectric element is used.
[0013] However, a chemical reaction is normally less likely to
occur between an electrode layer of a piezoelectric element and a
ceramic substrate, resulting in comparatively low bonding strength
between the electrode layer and the substrate. Thus, the element
may peel off from the substrate from the start or is more likely to
peel off due to vibration.
[0014] Therefore, Japanese Patent Application Laid-Open No.
2009-124791 proposes the vibration element 40 integrated by
sintering after the piezoelectric layer 43 being placed between the
electrode layer 44 of the piezoelectric element 41 and the ceramic
substrate 42.
[0015] However, while it is possible to increase bonding power with
the ceramic substrate 42 by placing the piezoelectric layer 43
therebetween, the piezoelectric element 41 may peel off from the
ceramic substrate 42 if a larger vibration amplitude is provided to
a vibration element. Thus, it becomes necessary to further increase
bonding power between the piezoelectric element 41 and the ceramic
substrate 42.
SUMMARY OF THE INVENTION
[0016] The present invention is directed to a vibration element
capable of outputting stable vibration energy by attempting to
improve bonding strength between a piezoelectric element and a
substrate with an inexpensive configuration and improving vibration
efficiency by curbing vibration damping accompanying
miniaturization, a manufacturing method thereof, and a vibration
wave actuator.
[0017] According to an aspect of the present invention, a vibration
element includes a substrate, a piezoelectric element including a
piezoelectric layer and an electrode layer, and a bonding layer
provided between the piezoelectric element and the substrate and
comprising ceramic containing melted glass powder, wherein the
vibration element causes the substrate to vibrate by vibration
energy of the piezoelectric element to output the vibration energy
of the substrate, and the piezoelectric element is fixed to the
substrate via the bonding layer.
[0018] According to another aspect of the present invention, a
method for manufacturing a vibration element by fixing a
piezoelectric element having a piezoelectric layer and an electrode
layer to a substrate includes forming a bonding layer containing
glass powder on the substrate by using the substrate formed of
ceramic or metal, forming the piezoelectric element on the formed
bonding layer, and integrating the substrate, the bonding layer,
and the piezoelectric element by simultaneous sintering
thereof.
[0019] According to yet another aspect of the present invention, a
vibration wave actuator includes the vibration element as a driving
power source.
[0020] According to an exemplary embodiment of the present
invention, a vibration element capable of outputting stable
vibration energy by attempting to improve bonding strength between
a piezoelectric element and a substrate with an inexpensive
configuration and improving vibration efficiency by curbing
vibration damping accompanying miniaturization, a manufacturing
method thereof, and a vibration wave actuator can be realized.
[0021] Further features and aspects of the present invention will
become apparent from the following detailed description of
exemplary embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate exemplary
embodiments, features, and aspects of the invention and, together
with the description, serve to explain the principles of the
invention.
[0023] FIGS. 1A to 1C are block diagrams illustrating a
configuration of a vibration element according to a first exemplary
embodiment of the present invention. FIG. 1A is a front view, FIG.
1B is a side view, and FIG. 1C is a plan view.
[0024] FIGS. 2A to 2C are block diagrams illustrating the
configuration of a vibration element according to a second
exemplary embodiment of the present invention. FIG. 2A is a front
view, FIG. 2B is a side view, and FIG. 2C is a plan view.
[0025] FIGS. 3A to 3C are block diagrams illustrating the
configuration of a vibration element according to a third exemplary
embodiment of the present invention. FIG. 3A is a front view, FIG.
3B is a side view, and FIG. 3C is a plan view.
[0026] FIG. 4 is a diagram illustrating a drive mechanism of a
linear vibration wave actuator into which the vibration element
according to the first to third exemplary embodiments of the
present invention is incorporated.
[0027] FIG. 5 is a diagram illustrating the configuration of a
conventional linear vibration wave actuator.
[0028] FIGS. 6A and 6B are diagrams illustrating the configuration
of a conventional vibration element.
DESCRIPTION OF THE EMBODIMENTS
[0029] Various exemplary embodiments, features, and aspects of the
invention will be described in detail below with reference to the
drawings.
[0030] A configuration example of a vibration element according to
a first exemplary embodiment of the present invention will be
described with reference to FIGS. 1A to 1C. FIGS. 1A to 1C are a
front view, a side view, and a plan view of the vibration element,
respectively. FIG. 1B illustrates a section in a broken line
position indicated by arrows in FIG. 1C.
[0031] A vibration element 1a illustrated in FIGS. 1A to 1C is
assumed to be applied to a linearly driven vibration wave actuator.
The vibration element 1a includes a substrate 2 in a plate shape, a
piezoelectric element 15, and a bonding layer 3. As described
below, the substrate 2 and the piezoelectric element 15 are bonded
(fixed) and integrated by simultaneous sintering. That is, the
piezoelectric element 15 functioning as a vibration energy source
and the substrate 2 functioning as a vibration element that
accumulates the vibration energy are fixed and integrated via the
bonding layer 3. In the piezoelectric element 15, an electrode
layer 4, a piezoelectric layer 5, an electrode layer 6, and a
piezoelectric layer 7 are sequentially stacked. The electrode layer
4 is divided into two portions and the divided portions are
arranged in a spaced state. Similarly, the electrode layer 6 is
divided into two portions and the divided portions are arranged in
a spaced state.
[0032] The piezoelectric layer 5 covers the entire surface of the
electrode layer 4, and the piezoelectric layer 7 covers the entire
surface of the electrode layer 6. Electric conduction between the
electrode layers 4 and 6 and external portions (such as a control
unit) is realized by forming a hole 8 in the piezoelectric layers 5
and 7 and introducing a conductive wire 9 onto the electrode layers
4 and 6 via the hole 8 to fix the conductor wire 9 to solder or the
like. Alternatively, a through-hole filled with a conductor may be
formed in the hole 8 to realize conduction to the conductor
wire.
[0033] An alternating signal is supplied to the electrode layers 4
and 6 from the control unit that controls the vibration of the
piezoelectric element 15, and the piezoelectric layer 5 expands and
contracts (distortion) due to the alternating signal so that the
expansion and contraction is output to the outside as vibration
energy. The substrate 2 vibrates due to the vibration energy, and
the vibration of the substrate 2 is used as a driving force to
drive a driven element (see a linear slider 14 in FIG. 4).
[0034] The substrate 2 has a length of 12 mm, a width of 5 mm, and
a thickness of 0.3 mm. The thickness of the bonding layer 3 is
about 6 .mu.m, the thickness of the piezoelectric layer 5 is about
12 .mu.m, the thickness of the piezoelectric layer 7 is about 6
.mu.m, and the thickness of the electrode layers 4, 6 is about 5
.mu.m. The hole 8 for conduction has a diameter of 1 mm.
[0035] Next, the manufacturing method of the vibration element 1a
will be described.
[0036] First, alumina (aluminum oxide) that is sintered ceramic in
a plate shape is ground and cut to finish the substrate 2 to
predetermined dimensions. Next, a piezoelectric material paste
prepared by mixing piezoelectric material powder, glass powder, and
an organic vehicle made up of an organic solvent and an organic
binder and containing glass powder capable of forming a thick film
is applied to the surface on one side of the ceramic plate by
screen printing. Then, the organic solvent is removed by heating
the applied piezoelectric material paste containing glass powder at
about 150.degree. C. for 10 min to dry the paste to form the
bonding layer 3. Then, a conductive material paste is prepared by
mixing conductive material powder containing silver and palladium
as main components and an organic vehicle made up of an organic
solvent and an organic binder. The conductive material paste is
applied onto the dried bonding layer 3 by screen printing, and the
paste is dried by heating at about 150.degree. C. for 10 min to
form the electrode layer 4.
[0037] Next, a piezoelectric material paste prepared by mixing
piezoelectric material powder and an organic vehicle made up of an
organic solvent and an organic binder and capable of forming a
thick film is applied to the surface of the electrode layer 4 by
screen printing. Then, the organic solvent is removed by heating
the applied piezoelectric material paste at about 150.degree. C.
for 10 min to dry the paste to form the piezoelectric layer 5. By
repeating the application and drying in this manner, the electrode
layer 6 and the piezoelectric layer 7 are formed.
[0038] The piezoelectric material powder used to form the bonding
layer 3 has lead zirconate and lead titanate
(PbZrO.sub.3--PbTiO.sub.3) having a perovs kite crystal structure
as main components. Moreover, three-component or multi-component
piezoelectric material powder prepared by adding and dissolving a
small amount of a compound made of a plurality of metals is used.
The same piezoelectric material powder is used for the
piezoelectric layers 5 and 7.
[0039] Further, silicon oxide and boron oxide are contained as the
glass powder and in addition, an additive such as bismuth oxide,
alumina, alkali metal oxide, alkali earth metal oxide, and other
metallic oxide is mixed and formulated so that a glass softening
point appropriate for a burning temperature is achieved.
[0040] Then, glass powder (also called glass frit) prepared by
pulverizing glass once melted into an average grain size of 1 to 2
.mu.m is used. The glass powder is added by 0.2% to several
percentage points by weight of the piezoelectric material powder to
prepare a paste.
[0041] By changing the mixing ratio of silicon oxide and boron
oxide, the softening point of glass can be changed. Also, the
reaction with the substrate 2 can be increased by selecting the
additive element.
[0042] The piezoelectric material powder of the bonding layer 3 is
sintered during sintering and the glass powder softens and flows to
gather in the respective interfaces of the substrate 2 and the
electrode layer 4 so that the bonding layer 3 can strongly be bound
to the substrate 2 and the electrode layer 4.
[0043] The piezoelectric layer 5 sandwiched between the electrode
layers 4 and 6 is a layer that causes a displacement according to
the applied voltage as a piezoelectric active portion with
polarization treatment. The bonding layer 3 and the piezoelectric
layer 7, on the other hand, are not piezoelectric active portions
and instead, piezoelectric inactive portions that do not actually
cause a displacement.
[0044] Incidentally, the piezoelectric layers 5 and 7 and the
bonding layer 3 may be compounds in which the mixing ratio of main
components of lead zirconate and lead titanate
(PbZrO.sub.3--PbTiO.sub.3) is changed or components other than the
main components are changed. In addition, the thickness of the
piezoelectric layers 5 and 7 and the thickness of the bonding layer
3 may be made different.
[0045] A paste prepared by adding piezoelectric material powder by
10% by weight in advance in addition to a conductive material is
used as the conductive material paste to form the electrode layers
4 and 6.
[0046] However, the same effect can be obtained if the
piezoelectric material powder to be added contains the same
components as those of the piezoelectric layer 5 or the same lead
zirconate and lead titanate (PbZrO.sub.3--PbTiO.sub.3) as the main
components. The piezoelectric layers 5 and 7 have a plate of screen
printing worked with in advance so that the hole 8 (unprinted
portion) can be formed and the electrode layers 4 and 6 are each
divided into two portions via the unprinted portion to be arranged
by being spaced.
[0047] The bonding layer 3, the piezoelectric layers 5 and 7, and
the electrode layers 4 and 6 stacked alternately on the substrate 2
in this manner are in an unsintered state.
[0048] After the organic binder being removed first by heating
using a furnace at temperature of 500.degree. C. or below, the
laminated layer is sintered in an atmosphere of lead at the highest
temperature of 1100.degree. C. in a retention time of two hours.
That is, the bonding layer 3, the piezoelectric layers 5 and 7, the
electrode layers 4 and 6, and the substrate 2 are sintered at the
same time and integrated. In other words, the manufacture of a
piezoelectric element and bonding (fixing) of the piezoelectric
element and the substrate 2 occurred at the same time.
[0049] The bonding layer 3 made of ceramic is provided to bond the
substrate 2 and the electrode layer 4. Silver and palladium forming
the electrode layer 4 and used as conductive materials have weak
bonding power with the substrate 2. Thus, if there is no bonding
layer 3, the electrode layer 4 may be peeled off from the substrate
2 from the start, or the electrode layer 4 of the piezoelectric
element 15 is more likely to be separated from the substrate 2 due
to vibration.
[0050] The piezoelectric material powder of the bonding layer 3
whose main components are the same as those of the piezoelectric
material is most desirable in terms of the thermal expansion
coefficient, mechanical properties, and costs, but the powder
material may have components similar to those of the substrate, in
addition to those of the piezoelectric material.
[0051] In the present exemplary embodiment, for example, alumina
powder mixed with glass powder may be used. Particularly, alumina
is easily available and inexpensive, has high heat resistance, and
is less likely to chemically react with other materials and thus,
alumina powder having glass powder mixed therewith is
appropriate.
[0052] If alumina is used for the substrate described below, above
all, alumina is a material of the same kind and is more likely to
bond through diffusion, making alumina suitable for bonding with
the substrate.
[0053] Other material powder that can be sintered at the same time
when the piezoelectric element is sintered during sintering can be
used.
[0054] The electrode layer 4 uses conductive material powder made
of noble metals containing silver as a main component and palladium
by about 20% to 30% by weight of the whole powder. Thus, the
electrode layer 4 starts to sinter at a lower temperature than the
bonding layer 3 and the piezoelectric layer 5 and contraction
caused by sintering is large so that a more compact layer is
formed. Thus, melted glass is present only between the substrate 2
and the electrode layer 4, and there is almost no diffusion or
penetration into the piezoelectric layer 5.
[0055] If glass diffuses or penetrates into the piezoelectric layer
5, piezoelectric characteristics of the piezoelectric layer 5
normally deteriorate and thus, the electrode layer 4 can prevent
glass from diffusing or penetrating into the piezoelectric layer 5.
Moreover, the force of peeling off from the bonding layer 3 or the
piezoelectric layer 5 is made smaller by mixing piezoelectric
powder in the electrode layer 4 to curb contraction caused by
sintering of the conductive material powder.
[0056] As the material of the substrate 2, on the other hand,
alumina, which is, as described above, sintered ceramic in a plate
shape, is selected as a preferable material for the substrate as a
vibration element. Compared with other ceramics, alumina is easily
available and inexpensive. Moreover, vibration damping is
relatively smaller when alumina is used as a vibration element.
[0057] However, mechanical strength deteriorates and vibration
damping as a vibration element grows when purity thereof becomes
lower and thus, alumina of higher purity is more desirable. Alumina
is rather brittle as a mechanical component and so a small amount
of other components may be added. For example, zirconia oxide can
improve mechanical strength and electric insulation properties and
so can be an additive. In this case, as discussed in Japanese
Patent Application Laid-Open No. 2006-74850, zirconia oxide can be
added by 5 to 40% by weight.
[0058] Any material that forms stable bonding with the bonding
layer 3 having glass powder mixed therewith in advance may be used
for the substrate 2. In addition to alumina, zirconia, silicon
carbide, and silicon nitride, which are normal ceramics, but can
easily bond to the substrate because glass powder is mixed in the
bonding layer 3 in advance, can be used for the substrate. It is
desirable to consider additive elements in addition to silicon
oxide and boron oxide as glass powder components by fitting to
various kinds of ceramics.
[0059] Further, the bonding layer 3 functions as a buffer of stress
generated due to contraction when the substrate 2, the electrode
layers 4 and 6, and the piezoelectric layers 5 and 7 are sintered
or a difference of thermal expansion coefficients when the
temperature drops after sintering so that an effect of preventing
peeling of the substrate 2 and the electrode layer 4 is gained.
When the vibration element vibrates, the bonding layer 3 functions
also as a buffer for the substrate 2 of stress generated due to a
displacement of the piezoelectric layer 5 acting as a piezoelectric
active layer.
[0060] What is different from the conventional configuration is the
use of the bonding layer 3 mixed with glass powder, whereby
particularly glass molten solid material melted by sintering
increases strength of close contact between the substrate 2 and the
electrode layer 4 so that bonding power between the substrate 2 and
the electrode layer 4 can be increased.
[0061] The piezoelectric layer 5 covers the electrode layer 4 and
the piezoelectric layer 7 covers the electrode layer 6, and
particularly the electrode layers 4 and 6 are completely covered up
to edges thereof so that the electrode layers 4 and 6 are not
exposed to the surface as protective layers of insulation
properties. By providing the protective layers of the electrode
layers 4 and 6 with the piezoelectric layers 5 and 7 in this
manner, peeling of the electrode layers 4 and 6 caused by a
mechanical force from outside can be prevented.
[0062] Moreover, peeling of the electrode layers 4 and 6 can be
prevented by preventing, for example, a short circuit when foreign
matter comes into contact, a current leak at high humidity, and
infiltration of moisture into a gap between the electrode layers 4
and 6 and the piezoelectric layers 5 and 7.
[0063] After, as described above, the bonding layer 3, which is
ceramic, the piezoelectric layers 5 and 7, the electrode layers 4
and 6, and the substrate 2 being sintered at the same time and
integrated, the conductor wire 9 is bonded to the electrode layers
4 and 6 via the hole 8 of the piezoelectric layers 5 and 7 using
solder or the like and a voltage is applied between the electrode
layers 4 and 6 to perform polarization of the piezoelectric layer
5.
[0064] Polarization is performed under polarization conditions of
applying a predetermined voltage of about 35 V (corresponding to 3
KV/mm) between the grounded (G) electrode layer 4 and the positive
(+) electrode layer 6 in oil at temperature of 120 to 150.degree.
C. for about 30 min.
[0065] Pastes to form the bonding layer 3, the piezoelectric layers
5 and 7, and the electrode layers 4 and 6 are created by adding a
small amount of additives and kneading an organic vehicle using an
organic binder such as ethyl cellulose and an organic solvent such
as terpineol using a three-roll mill.
[0066] While the thickness of a piezoelectric layer is set to 12
.mu.m for screen printing in the present exemplary embodiment,
piezoelectric layers and electrode layers whose thickness ranges
from about 2 to 3 .mu.m to 30 .mu.m can be created with high
precision. Divided electrodes and piezoelectric layers with a hole
(unprinted portion) can be provided in a plate. Compared with
lamination by the green sheets described above, the screen printing
cannot only forma thinner and more precise film easily, but also
control an application position with high precision without the
need of machining after sintering.
[0067] Further, manufacturing equipment becomes more inexpensive.
As a result of the above, the manufacturing cost also becomes more
inexpensive.
[0068] A configuration example of a vibration element according to
a second exemplary embodiment of the present invention will be
described with reference to FIGS. 2A to 2C. FIGS. 2A to 2C are a
front view, a side view, and a plan view of the vibration element,
respectively. FIG. 2B illustrates a section in a broken line
position indicated by arrows in FIG. 2C.
[0069] While there is one piezoelectric layer sandwiched by
electrode layers in the first exemplary embodiment, there are two
piezoelectric layers sandwiched by electrode layers in the present
exemplary embodiment. That is, compared with the first exemplary
embodiment, a laminated piezoelectric element 16 in the present
exemplary embodiment has one piezoelectric layer and one electrode
layer added thereto. In other words, in the second exemplary
embodiment, the voltage is made lower than in the first exemplary
embodiment by increasing the layers to two piezoelectric layers
acting as piezoelectric active portions.
[0070] The voltage can further be lowered by increasing the layers
to three or more piezoelectric layers which are piezoelectric
active portions.
[0071] In a vibration element 1b according to the present exemplary
embodiment, the bonding layer 3, the electrode layer 4, a
piezoelectric layer 5a, an electrode layer 6a, a piezoelectric
layer 5b, an electrode layer 6b, and the piezoelectric layer 7 are
sequentially stacked as the laminated piezoelectric element 16 on
the sintered substrate 2 in a plate shape.
[0072] The piezoelectric layer 5a wholly covers the electrode layer
4, the piezoelectric layer 5b wholly covers the electrode layer 6a,
and the piezoelectric layer 7 wholly covers the electrode layer 6b.
The electrode layers 4 and 6b realize electric conduction through a
hole 10 filled with a conductive paste (conductive material), and
electric conduction to an external power supply can be established
by the conductor wire 9 bonded to a hole 11. The electrode layer 6a
can establish electric conduction to the outside (such as a control
unit) via the conductor wire 9 bonded to a hole 12 filled with a
conductive paste.
[0073] In the vibration element 1b, for example, the substrate 2
has the length of 12 mm, the width of 5 mm, and the thickness of
0.3 mm. The thickness of the ceramic layer 3 is about 6 .mu.m, the
thickness of the piezoelectric layers 5a and 5b is about 12 .mu.m,
the thickness of the piezoelectric layer 7 is about 6 .mu.m, and
the thickness of the electrode layers 4, 6a, and 6b is about 5
.mu.m. The diameter of the holes 10 and 11 is 1 mm in consideration
of wiring. In the present exemplary embodiment, the piezoelectric
layers 5a and 5b become piezoelectric active portions.
[0074] In contrast to the first exemplary embodiment, the holes 10,
11, and 12 are filled with the conductive paste having almost the
same components as the conductive paste forming the electrode
layers 4, 6a, and 6b. In this case, after the holes 10, 11, and 12
being formed, the holes 10, 11, and 12 are filled with the
conductive paste by the screen printing or the like before or after
the electrode layers 4, 6a, and 6b are formed, and the substrate 2
is sintered simultaneously with the laminated piezoelectric element
16 for integration.
[0075] According to another manufacturing method, after the
laminated piezoelectric element 16 being sintered, the holes 10,
11, and 12 may be filled with a conductive paste mixed with a
heat-hardening adhesive and conductive powder.
[0076] FIG. 4 is a diagram illustrating the configuration of a
linear vibration wave actuator into which the vibration element 1a
according to the first exemplary embodiment or the vibration
element 1b according to the second exemplary embodiment is
incorporated.
[0077] The principle of linear driving is the same as that in a
conventional example. The vibration element 1a or the vibration
element 1b is provided with a protruding portion 13.
[0078] The linear slider 14 under pressure comes into contact with
the protruding portion 13 and the linear slider 14 moves due to an
elliptic motion excited in the protruding portion 13 by the
vibration of the piezoelectric element 15 or 16. That is, the
linear vibration wave actuator makes a reciprocating motion of the
linear slider 14 using the piezoelectric element 15 or 16 as a
driving power source.
[0079] Incidentally, the present invention is not limited to the
configurations of the first exemplary embodiment and the second
exemplary embodiment and, for example, while a conductor wire is
used for conduction between electrode layers and an external power
supply, a flexible circuit board or a conductive paste may be used
to establish electric conduction between electrode layers and the
external power supply, instead of the conductor wire.
[0080] A configuration example of a vibration element according to
a third exemplary embodiment of the present invention will be
described with reference to FIGS. 3A to 3C. FIGS. 3A to 3C are a
front view, a side view, and a plan view of the vibration element,
respectively. FIG. 3B illustrates a section in a broken line
position indicated by arrows in FIG. 3C.
[0081] A vibration element 1c illustrated in FIGS. 3A to 3C is
assumed to be applied to a linearly driven vibration wave
actuator.
[0082] The vibration element 1c includes a substrate 2-2 and a
piezoelectric element 15-2 in a plate shape. Materials of the
substrate and a piezoelectric element are different from those in
the first exemplary embodiment. The substrate 2-2 and the
piezoelectric element 15-2 are bonded (fixed) and integrated by, as
described above, simultaneous sintering.
[0083] That is, the piezoelectric element 15-2 functioning as a
vibration energy source and the substrate 2-2 functioning as a
vibration element that accumulates the vibration energy are fixed
and integrated via a bonding layer 3-2.
[0084] In the piezoelectric element 15-2, an electrode layer 4-2, a
piezoelectric layer 5-2, an electrode layer 6-2, and a
piezoelectric layer 7-2 are sequentially stacked.
[0085] The electrode layer 4-2 is divided into two portions, and
the divided portions are arranged in a spaced state. Similarly, the
electrode layer 6-2 is divided into two portions, and the divided
portions are arranged in a spaced state. The piezoelectric layer
5-2 covers the entire surface of the electrode layer 4-2, and the
piezoelectric layer 7-2 covers the entire surface of the electrode
layer 6-2. Electric conduction between the electrode layers 4-2 and
6-2 and external portions (such as a control unit) is realized by
forming a hole 8-2 in the piezoelectric layers 5-2 and 7-2 and
introducing a conductive wire 9-2 onto the electrode layers 4-2 and
6-2 via the hole 8-2 to fix the conductor wire 9-2 with solder or
the like. An alternating signal is supplied to the electrode layers
4-2 and 6-2 from the control unit that controls the vibration of
the piezoelectric element 15-2, and the piezoelectric layer 5-2
expands and contracts (distortion) due to the alternating signal so
that the expansion and contraction is discharged to the outside as
mechanical vibration energy. The substrate 2-2 vibrates due to the
vibration energy, and the vibration of the substrate 2-2 is used as
a driving force to drive a driven element (see the linear slider 14
in FIG. 4).
[0086] The substrate 2-2 has the length of 12 mm, the width of 5
mm, and the thickness of 0.3 mm. The thickness of the bonding layer
3-2 is about 6 .mu.m, the thickness of the piezoelectric layer 5-2
is about 12 .mu.m, the thickness of the piezoelectric layer 7-2 is
about 6 .mu.m, and the thickness of the electrode layers 4-2 and
6-2 is about 5 .mu.m. The hole 8-2 for conduction has a diameter of
1 mm.
[0087] Next, the manufacturing method of the vibration element 1c
will be described.
[0088] First, martensitic stainless steel (SUS420J2), which is
excellent in vibration characteristics and easy to machine, is
ground and cut to finish the substrate 2-2 to predetermined
dimensions. Next, a piezoelectric material paste prepared by mixing
piezoelectric material powder, glass powder, and an organic vehicle
made up of an organic solvent and an organic binder and containing
glass powder capable of forming a thick film is applied to the
surface on one side of the substrate 2-2 by screen printing. Then,
the organic solvent is removed by heating the applied piezoelectric
material paste containing glass powder at about 150.degree. C. for
10 min to dry the paste to form the bonding layer 3-2.
[0089] Piezoelectric material powder prepared by adding a small
amount of compound made of one or a plurality of metallic elements
to barium titanate (BaTiO.sub.3) as the main component is used as
the piezoelectric material powder of the bonding layer 3-2.
[0090] Silicon oxide and boron oxide are contained as the glass
powder and in addition, bismuth oxide, alumina, alkali metal oxide,
and alkali earth metal oxide are mixed. Then, glass powder (also
called glass frit) prepared by pulverizing glass once melted into
an average grain size of 1 to 2 .mu.m is used. The glass powder is
added by 0.2% to several percentage points by weight of the
piezoelectric material powder to prepare a paste.
[0091] By changing the mixing ratio of silicon oxide and boron
oxide, the softening point of glass can be changed. Also by
selecting the additive element, reactions with the substrate can be
increased. Then, a conductive material paste is prepared by mixing
conductive material powder made of silver and an organic vehicle
made up of an organic solvent and an organic binder.
[0092] The conductive material paste is applied onto the dried
bonding layer 3-2 by screen printing and the paste is dried by
heating at about 150.degree. C. for 10 min to form the electrode
layer 4-2. Silver in the conductive material powder may contain a
slight amount of platinum or palladium.
[0093] Next, a piezoelectric material paste prepared by mixing
piezoelectric material powder, glass powder as a sintering
assistant, and an organic vehicle made up of an organic solvent and
an organic binder and capable of forming a thick film is applied to
the surface on one side of the substrate by screen printing. Then,
the organic solvent is removed by heating the applied piezoelectric
material paste at about 150.degree. C. for 10 min to dry the paste
to form the piezoelectric layer 5-2.
[0094] A piezoelectric material prepared by adding a small amount
of compound made of one or a plurality of metallic elements to
barium titanate (BaTiO.sub.3) as the main component is used for the
piezoelectric layer 5-2. The sintering temperature of barium
titanate (BaTiO.sub.3) is normally high and thus, glass powder as a
sintering assistant is mixed in the present exemplary embodiment so
that the piezoelectric layers 5-2 and 7-2 can be sintered at
700.degree. C. The glass powder as a sintering assistant is silicon
oxide or boron oxide that is basically the same as the glass powder
mixed in the bonding layer 3-2, but it is desirable to prevent
deterioration of piezoelectric characteristics when possible by
appropriately selecting the mixing ratio or additive elements
thereof.
[0095] By repeating the application and drying in this manner, the
electrode layer 6-2 and the piezoelectric layer 7-2 are formed.
[0096] If glass powder is mixed with piezoelectric material powder,
original piezoelectric characteristics generally deteriorate due to
involvement of a glass phase having no ferroelectricity
(piezoelectricity), but a certain level of piezoelectric
characteristics is present and thus, glass powder can be used under
conditions where inclusion of lead is not desirable.
[0097] The piezoelectric layer 5-2 is a layer that causes a
displacement as a piezoelectric active portion on which
polarization is performed and its chemical composition directly
affects performance of a vibration wave actuator. On the other
hand, the bonding layer 3-2 and the piezoelectric layer 7-2 are not
piezoelectric active portions and instead, piezoelectric inactive
portions.
[0098] As will described below, at least the piezoelectric element
15-2 is formed of the piezoelectric layer 7-2 as an inactive
portion on the side opposite to the side fixed to the substrate
2-2.
[0099] Components other than the main component of barium titanate
(BaTiO.sub.3) of the piezoelectric layer 5-2, and the bonding layer
3-2, and the piezoelectric layer 7-2 can be changed to fit each
purpose. Moreover, the thickness of the piezoelectric layer 5-2 and
the thickness of the bonding layer 3-2 and the piezoelectric layer
7-2 may be made different.
[0100] A conductive material paste prepared by adding barium
titanate powder by 10% by weight in addition to a conductive
material is used to form the electrode layers 4-2 and 6-2. A
similar effect is obtained if piezoelectric material powder to be
added has the same component as that of the piezoelectric layer 5-2
or the main component thereof is the same barium titanate.
[0101] The piezoelectric layers 5-2 and 7-2 have a plate of screen
printing worked with in advance so that the hole 8-2 (unprinted
portion) can be formed and the electrode layers 4-2 and 6-2 are
each divided into two portions via the unprinted portion to be
arranged in a spaced state. A plurality of the bonding layer 3-2,
the piezoelectric layers 5-2 and 7-2, and the electrode layers 4-2
and 6-2 stacked alternately on the substrate 2-2 in this manner is
in an unsintered state.
[0102] After the organic binder being removed by heating using a
furnace at temperature of 500.degree. C. or below, the laminated
layer is sintered in the atmosphere at temperature 700.degree. C.
That is, the bonding layer 3-2, the piezoelectric layers 5-2 and
7-2, the electrode layers 4-2 and 6-2, and the substrate 2-2 are
sintered at the same time and integrated. In other words, the
manufacture of a piezoelectric element and bonding (fixing) of the
piezoelectric element and a substrate occurred at the same
time.
[0103] The bonding layer 3-2 is provided to bond the substrate 2-2
and the electrode layer 4-2.
[0104] Silver forming the electrode layer 4-2 and used as a
conductive material has weak bonding power with the substrate 2-2.
Thus, if there is no bonding layer 3-2, the electrode layer 4-2 may
be peeled off from the substrate 2-2 from the start due to
contraction caused by powder sintering when conductive material
powder is sintered and thermal expansion after the sintering is
more likely to peel off due to vibration of the piezoelectric
element 15-2.
[0105] Material powder whose main component is the same as that of
the piezoelectric material is desirable for the bonding later 3-2
in terms of the thermal expansion coefficient and mechanical
properties, but in addition to the piezoelectric material, the
material powder may be alumina powder in which glass powder is
mixed. Above all, alumina is appropriate because alumina has a
thermal expansion coefficient similar to the thermal expansion
coefficients of stainless steel and barium titanate described above
and is less likely to react with other materials.
[0106] Other ceramic powder that can be sintered at the same time
when piezoelectric elements are sintered during sintering can be
used.
[0107] By mixing piezoelectric powder in the electrode layer 4-2 in
advance, contraction caused by sintering of the conductive material
powder is curbed to weaken a peeling force.
[0108] Further, glass powder is mixed in the bonding layer 3-2 in
advance and the glass powder melts and gathers in the respective
interface of the substrate 2-2 and the electrode layer 4-2 during
sintering so that the bonding layer 3-2 can strongly be bound to
the substrate 2-2 and the electrode layer 4-2 after sintering.
[0109] As the metal of the substrate 2-2, on the other hand, in
addition to the above stainless steel, other chrome or
chromium-nickel stainless steel may be selected as a further
preferable material of the substrate (vibration element). This is
because such metals of all metals are easily available and
inexpensive, has high heat resistance, and vibration damping as a
vibration element is small.
[0110] Compared with ceramic, stainless steel has oxide formed on
the surface thereof and so stable bonding is likely to be formed
with the bonding layer 3-2 in which glass powder is mixed in
advance so that bonding occurs easily.
[0111] Further, thermal expansion coefficients of barium titanate,
alumina, and stainless steel are close and can be used.
[0112] The bonding layer 3-2 functions also as a buffer of stress
generated during vibration so that peeling of the substrate 2-2 and
the electrode layer 4-2 can be prevented.
[0113] Like in the first exemplary embodiment, the piezoelectric
layer 5-2 covers the electrode layer 4-2, the piezoelectric layer
7-2 covers the electrode layer 6-2, and particularly the electrode
layers 4-2 and 6-2 are completely covered up to edges thereof, so
that the electrode layers 4-2 and 6-2 are not exposed to the
surface as protective layers of insulation properties.
[0114] By providing the protective layers of the electrode layers
4-2 and 6-2 with the piezoelectric layers 5-2 and 7-2 in this
manner, peeling of the electrode layers 4-2 and 6-2 caused by a
mechanical force from outside can be prevented.
[0115] Moreover, peeling of the electrode layers 4-2 and 6-2 can be
prevented by preventing, for example, a short circuit when foreign
matter comes into contact, a current leak at high humidity, and
infiltration of moisture into a gap between the electrode layers
4-2 and 6-2 and the piezoelectric layers 5-2 and 7-2.
[0116] As described above, the bonding layer 3-2, the piezoelectric
layers 5-2 and 7-2, the electrode layers 4-2 and 6-2, and the
substrate 2-2 are sintered at the same time and integrated. Then,
the conductor wire 9-2 is bonded to the electrode layers 4-2 and
6-2 via the hole 8-2 of the piezoelectric layers 5-2 and 7-2 using
solder or the like, and a voltage is applied between the electrode
layers 4-2 and 6-2 to perform polarization of the piezoelectric
layer 5-2.
[0117] Polarization is performed under polarization conditions of
applying a predetermined voltage of about 35 V (corresponding to 3
KV/mm) between the grounded (G) electrode layer 4-2 and the
positive (+) electrode layer 6-2 in oil at temperature 80.degree.
C. for about 30 min.
[0118] FIG. 4 is a diagram illustrating the configuration of a
linear vibration wave actuator into which the vibration element 1c
according to the present exemplary embodiment is incorporated.
[0119] According to the exemplary embodiments of the present
invention, as described above, glass powder is used for bonding so
that the present invention can be applied to a variety of
substrates and a variety of piezoelectric materials, enabling an
occurrence of stable bonding power. Moreover, the manufacturing
cost becomes more inexpensive.
[0120] Such configurations of the exemplary embodiments of the
present invention are useful for development of vibration actuators
in the future.
[0121] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all modifications, equivalent
structures, and functions.
* * * * *