U.S. patent application number 11/464565 was filed with the patent office on 2007-03-01 for piezoelectric substrate, piezoelectric element, liquid discharge head and liquid discharge apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Toshihiro Ifuku, Takanori Matsuda.
Application Number | 20070046153 11/464565 |
Document ID | / |
Family ID | 37803128 |
Filed Date | 2007-03-01 |
United States Patent
Application |
20070046153 |
Kind Code |
A1 |
Matsuda; Takanori ; et
al. |
March 1, 2007 |
PIEZOELECTRIC SUBSTRATE, PIEZOELECTRIC ELEMENT, LIQUID DISCHARGE
HEAD AND LIQUID DISCHARGE APPARATUS
Abstract
A piezoelectric substrate of a perovskite-type oxide is
expressed by a general formula of ABO.sub.3 having a laminate
structure of a single crystal structure or a uniaxial crystal
structure expressed by
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W)
and the laminate structure has a layered first crystal phase having
a crystal structure selected from the tetragonal structure, the
rhombohedral structure, the pseudocubic structure and the
monoclinic structure, a layered second crystal phase having a
crystal structure different from the crystal structure of said
first crystal phase and a boundary layer arranged between said
first crystal phase and said second crystal phase with a crystal
structure gradually changing in a width direction of layer.
Inventors: |
Matsuda; Takanori; (Tokyo,
JP) ; Ifuku; Toshihiro; (Yokohama-shi, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
3-30-2, Shimomaruko, Ohta-ku
Tokyo
JP
|
Family ID: |
37803128 |
Appl. No.: |
11/464565 |
Filed: |
August 15, 2006 |
Current U.S.
Class: |
310/358 |
Current CPC
Class: |
C04B 2235/3298 20130101;
B41J 2/1642 20130101; C04B 2235/3227 20130101; C04B 2235/3258
20130101; C04B 2235/3215 20130101; B41J 2/161 20130101; C04B
2235/3208 20130101; C04B 2235/762 20130101; B41J 2/1646 20130101;
C04B 35/491 20130101; B41J 2/1634 20130101; B41J 2202/03 20130101;
C04B 2235/768 20130101; C04B 2235/765 20130101; H01L 41/1876
20130101; C04B 2235/3294 20130101; C04B 2235/76 20130101; Y10T
29/42 20150115; H01L 41/18 20130101 |
Class at
Publication: |
310/358 |
International
Class: |
H01L 41/187 20070101
H01L041/187 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2005 |
JP |
2005-241378(PAT.) |
Claims
1. A piezoelectric substrate of a perovskite-type oxide expressed
by a general formula of ABO.sub.3 having a laminate structure of a
single crystal structure or a uniaxial crystal structure expressed
by (Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W),
the laminate structure having: a layered first crystal phase having
a crystal structure selected from a tetragonal structure, a
rhombohedral structure, a pseudocubic structure and a monoclinic
structure; a layered second crystal phase having a crystal
structure selected from the tetragonal structure, the rhombohedral
structure, the pseudocubic structure and the monoclinic structure
but different from the crystal structure of said first crystal
phase; and a boundary layer arranged between said first crystal
phase and said second crystal phase with a crystal structure
gradually changing in a width direction of layer.
2. The piezoelectric substrate according to claim 1, wherein the
requirement of 0.45.ltoreq.y.ltoreq.1 is satisfied.
3. A piezoelectric element comprising a piezoelectric substrate and
a pair of electrodes; said piezoelectric substrate being a
perovskite-type oxide expressed by a general formula of ABO.sub.3
having a laminate structure of a single crystal structure or a
uniaxial crystal structure expressed by
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W),
the laminate structure having: a layered first crystal phase having
a crystal structure selected from a tetragonal structure, a
rhombohedral structure, a pseudocubic structure and a monoclinic
structure; a layered second crystal phase having a crystal
structure selected from the tetragonal structure, the rhombohedral
structure, the pseudocubic structure and the monoclinic structure
but different from the crystal structure of said first crystal
phase; and a boundary layer arranged between said first crystal
phase and said second crystal phase with a crystal structure
gradually changing in a width direction of layer.
4. A liquid discharge head comprising separate liquid chambers
communicating to respective discharge ports and piezoelectric
elements arranged respectively in the separate liquid chambers and
having a piezoelectric substrate and a pair of electrodes and the
head discharging liquid in the separate liquid chambers from the
respective discharge ports; said piezoelectric substrate being a
perovskite-type oxide expressed by a general formula of ABO.sub.3
having a laminate structure of a single crystal structure or a
uniaxial crystal structure expressed by
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W),
the laminate structure having: a layered first crystal phase having
a crystal structure selected from a tetragonal structure, a
rhombohedral structure, a pseudocubic structure and a monoclinic
structure; a layered second crystal phase having a crystal
structure selected from the tetragonal structure, the rhombohedral
structure, the pseudocubic structure and the monoclinic structure
but different from the crystal structure of said first crystal
phase; and a boundary layer arranged between said first crystal
phase and said second crystal phase with a crystal structure
gradually changing in a width direction of layer.
5. A liquid discharge apparatus having a liquid discharge head for
discharging liquid, comprising: each of the piezoelectric elements
for generating energy of liquid discharge having a piezoelectric
substrate and a pair of electrodes; said piezoelectric substrate
being a perovskite-type oxide expressed by a general formula of
ABO.sub.3 having a laminate structure of a single crystal structure
or a uniaxial crystal structure expressed by
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W),
the laminate structure having: a layered first crystal phase having
a crystal structure selected from a tetragonal structure, a
rhombohedral structure, a pseudocubic structure and a monoclinic
structure; a layered second crystal phase having a crystal
structure selected from the tetragonal structure, the rhombohedral
structure, the pseudocubic structure and the monoclinic structure
but different from the crystal structure of said first crystal
phase; and a boundary layer arranged between said first crystal
phase and said second crystal phase with a crystal structure
gradually changing in a width direction of layer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a piezoelectric substrate,
a piezoelectric element and a liquid discharge head to be used for
a liquid discharge apparatus and also to methods of manufacturing
the same. More particularly, the present invention relates to a
high density piezoelectric element having a large area and a liquid
discharge head using such an element.
[0003] 2. Description of the Related Art
[0004] There is an increasing demand for long printing heads to be
used in ink jet printers in order to improve the resolution and the
printing speed of such printers. For this reason, there is a demand
for micronized multi-nozzle head structures. Then, piezoelectric
elements for discharging liquid are required to be downsized in
order to micronize liquid discharge heads. Then, piezoelectric
substrates showing a high piezoelectric constant are required in
order not to reduce the drive power if liquid discharge heads are
micronized. Thus, there is a demand for highly crystalline
piezoelectric films as piezoelectric substrates. Such piezoelectric
films are required to show a controlled crystallinity so as to
contain highly oriented crystals. For a piezoelectric film to be a
highly oriented crystal, it is preferable that the directly
underlying layer is highly crystalline and the piezoelectric film
and the directly underlying layer make a good combination in terms
of lattice matching at the time of manufacturing the piezoelectric
film.
[0005] Additionally, the piezoelectric film and the directly
underlying layer are apt to give rise to a phenomenon of film
exfoliation when stress is applied to the interface if the
piezoelectric film is made thin. Therefore, the directly underlying
layer is required to be highly adhesive relative to the
piezoelectric film in order to suppress such film exfoliation.
[0006] Conventionally, paste of powdery PbO, ZrO.sub.2 and
TiO.sub.2 is molded to form green sheets, which are then sintered
to produce a PZT type piezoelectric material for piezoelectric
films to be used for piezoelectric elements as described in
Japanese Patent Application Laid-open No. S62-213399.
[0007] However, it is difficult to produce PZT type oxide films
with a thickness of not greater than 10 .mu.m by means of the
method disclosed in Japanese Patent Application Laid-open No.
S62-213399. Additionally, since such green sheets are sintered at a
temperature level not lower than 1,000.degree. C., there arises a
problem that the piezoelectric films shrink to 70% of the original
size. Then, it is difficult to align a piezoelectric film and a
structure such as an ink chamber with an accuracy level of several
microns. Thus, no satisfactory micro piezoelectric elements have
been available to date.
[0008] Furthermore, the influence of the crystal grain boundaries
becomes unnegligible as ceramic piezoelectric films formed by
sintering green sheets show a reduced thickness to consequently
make it impossible to realize good piezoelectric characteristics.
As a result, there arises a problem of being unable to obtain
piezoelectric characteristics that are satisfactory for causing a
piezoelectric film to operate for discharging recording liquid if
the piezoelectric film is prepared by sintering a green sheet to a
thickness not greater than 10 .mu.m.
[0009] Known methods for preparing piezoelectric films include
sputtering methods, CVD methods, MBE methods and sol-gel methods in
addition to the above cited method. As a matter of fact, it is
possible to produce a thin oxide film with a film thickness of not
greater than 10 .mu.m by means of any of such methods. However,
since the piezoelectric film prepared by means of any of such
methods shows a high density to by turn give rise to very large
in-plane stress and make the piezoelectric film poorly adhesive to
the underlying layer, which is a lower electrode. For the
piezoelectric elements of an ink jet head to withstand the stress
produced when they are driven repeatedly, it is necessary that the
piezoelectric film is highly adhesive to the underlying layer of a
lower electrode. However, a piezoelectric film prepared by any of
the above-cited methods cannot be feasibly used as piezoelectric
element for ink jet recording.
[0010] Additionally, if the piezoelectric characteristics of a
piezoelectric material fluctuate due to temperature change, the
temperature of the operation environment needs to be held to a
constant level, although the temperature requirement may vary
depending on the type of piezoelectric material. In other words, a
piezoelectric material that is lowly temperature-dependent and
shows excellent piezoelectric characteristics when used as
piezoelectric element has not been found to date.
SUMMARY OF THE INVENTION
[0011] In view of the above identified circumstances, it is
therefore an object of the present invention to provide a
piezoelectric substrate that shows a controlled crystallinity and
an enhanced level of orientation to realize excellent piezoelectric
characteristics and produces an enhanced level of adhesiveness
between the piezoelectric substrate and an electrode to make itself
highly durable and capable of suppressing any possible film
exfoliation as well as a piezoelectric element, a liquid discharge
head and a liquid discharge apparatus realized by using such a
piezoelectric substrate.
[0012] Another object of the present invention is to provide a
piezoelectric substrate whose piezoelectric characteristics do not
degrade by the temperature change in the operation environment as
well as a piezoelectric element, a liquid discharge head and a
liquid discharge apparatus realized by using such a piezoelectric
substrate.
[0013] Still another object of the present invention is to provide
a method of manufacturing a piezoelectric substrate that utilizes
micro-processing techniques available in the field of semiconductor
processes and a highly reliable liquid discharge head having
densely arranged discharge ports prepared by means of such a
method.
[0014] According to the present invention, the above objects and
other objects of the invention are achieved by providing a
piezoelectric substrate of a perovskite-type oxide expressed by a
general formula of ABO.sub.3 having a laminate structure of a
single crystal structure or a uniaxial crystal structure expressed
by (Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yT.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W),
the laminate structure having a layered first crystal phase having
a crystal structure selected from the tetragonal structure, the
rhombohedral structure, the pseudocubic structure and the
monoclinic structure, a layered second crystal phase having a
crystal structure selected from the tetragonal structure, the
rhombohedral structure, the pseudocubic structure and the
monoclinic structure but different from the crystal structure of
said first crystal phase and a boundary layer arranged between said
first crystal phase and said second crystal phase with a crystal
structure gradually changing in a width direction of layer.
[0015] According to the present invention, there are also provided
a piezoelectric element comprising a piezoelectric substrate as
defined above and a pair of electrode, a liquid discharge head
comprising such a piezoelectric element and a liquid discharge
apparatus comprising such a head.
[0016] Thus, a piezoelectric substrate according to the present
invention is highly durable and capable of suppressing any possible
film exfoliation and produces an enhanced level of adhesiveness
between the piezoelectric substrate and an underlying layer,
showing a controlled crystallinity and an enhanced level of
orientation to realize excellent piezoelectric characteristics.
Additionally, a piezoelectric substrate according to the invention
shows piezoelectric characteristics that do not degrade by the
temperature change in the operation environment. Thus, a
piezoelectric substrate according to the present invention shows
excellent piezoelectric characteristics when it is used in a high
density piezoelectric element and a liquid discharge head.
[0017] A method of manufacturing a piezoelectric substrate can
manufacture a highly reliable piezoelectric substrate by utilizing
micro-processing techniques available in the field of semiconductor
processes that leads to a method of manufacturing a high density
piezoelectric element and a method of manufacturing a highly
reliable liquid discharge head.
[0018] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic illustration of an embodiment of
piezoelectric substrate according to the invention, showing the
laminate structure thereof.
[0020] FIG. 2 is a schematic illustration of another embodiment of
piezoelectric substrate according to the invention, showing the
laminate structure thereof.
[0021] FIG. 3 is a schematic cross sectional perspective view of an
embodiment of liquid discharge head according to the invention.
[0022] FIG. 4 is a schematic perspective view of an embodiment of
liquid discharge apparatus according to the invention.
[0023] FIG. 5 is a schematic illustration of the relationship
between a target and a shutter of a sputtering apparatus that can
be used for manufacturing an embodiment of piezoelectric substrate
according to the invention.
[0024] FIG. 6 is a schematic illustration of the relationship
between a target and a shutter of a sputtering apparatus that can
be used for manufacturing an embodiment of piezoelectric substrate
according to the invention.
DESCRIPTION OF THE EMBODIMENTS
[0025] A piezoelectric substrate according to the present invention
has a single crystal structure or a uniaxial crystal structure of a
perovskite-type oxide expressed by a general formula of ABO.sub.3.
The piezoelectric substrate has a laminate structure having a
plurality of layered crystal phases, each including a crystal
structure selected from the tetragonal structure, the rhombohedral
structure, the pseudocubic structure and the monoclinic structure.
The crystal phase is expressed by
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yT.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W).
A piezoelectric substrate according to the present invention is
additionally characterized in that it additionally comprises a
crystal phase (boundary layer) arranged between different crystal
phases with a crystal structure gradually changing in the direction
of elevation. Each of the crystal phases is obtained typically by
epitaxial growth and has a laminate structure, although it shows a
single crystal structure or a uniaxial crystal structure as a
whole.
[0026] FIG. 1 schematically illustrates exemplary boundary layers
211, 222 having a crystal structure that changes gradually in the
direction of elevation, each being arranged between a first crystal
phase 21 and a second crystal phase 22 having predetermined
respective crystal structures.
[0027] For example, for the purpose of the present invention, a
crystal phase (boundary layer) as described below may be arranged
between a first crystal phase 21 of the tetragonal structure having
a single crystal structure and a second crystal phase 22 of the
rhombohedral structure having a single crystal structure. In other
words, a crystal phase 211 is arranged between a first crystal
phase 21 and a second crystal phase 22 so as to gradually change
its crystal structure from the tetragonal structure to the
rhombohedral structure from the side of the crystal phase 21 toward
the crystal phase 22. Additionally, a crystal phase 221 is arranged
between a second crystal phase 22 and a first crystal phase 21 so
as to gradually change its crystal structure from the rhombohedral
structure to the tetragonal structure from the side of the crystal
phase 22 toward the crystal phase 21. Such an arrangement can
uniformly disperse and absorb strain from biased directions and
hence can suppress exfoliation of film if the film thickness of the
order of microns that is apt to give rise to exfoliation. In other
words, it is possible to obtain a piezoelectric substrate that
realizes a strong adhesion between the piezoelectric film and the
electrodes and makes itself highly durable and capable of
suppressing any possible film exfoliation. Thus, it is possible to
alleviate the stress applied to each of the crystal phase layers of
the piezoelectric substrate and hence improve the durability of the
piezoelectric substrate.
[0028] When a specific phase is damaged in a piezoelectric
substrate to give rise to fine cracks or the like, the cracks can
spread if the piezoelectric substrate has a single crystal phase
layer. However, with the arrangement of this embodiment, a
plurality of crystal phase layers having respective Young's moduli
that are different from each other are laid one on the other to
form a multilayer structure and hence the cracks produced in a
layer having a large Young's modulus can hardly spread into layers
having a large Young's modulus located beyond a layer having a
small Young's modulus. In short, cracks can hardly spread and hence
the piezoelectric substrate shows a high durability as a whole.
Additionally, with the arrangement of this embodiment, the crystal
phases having different compositions can disperse and absorb the
stresses applied to the films themselves in the phase changes that
arise as the films are cooled from the film forming temperature to
the room temperature in the film forming process. Still
additionally, a specific crystal phase absorbs strain in each
specific temperature range so that the piezoelectric substrate
shows excellent piezoelectric characteristics over a wide
temperature range as a whole.
[0029] In the laminate structure of this embodiment of
piezoelectric substrate, at least two of the layers of the crystal
phases preferably have different respective thicknesses. For
example, as shown in FIG. 2, the piezoelectric substrate may have
crystal phase 31 having film thickness T.sub.1, crystal phase 32
having film thickness T.sub.2 and crystal phase 33 having film
thickness T.sub.3, where T.sub.1, T.sub.2 and T.sub.3 differ from
each other. Boundary layers (311, 321, 331) are arranged to
separate the crystal phases from each other. The boundary layers
gradually change their respective crystal structures as described
above by referring to FIG. 1. The expression of film thickness
T.sub.1, T.sub.2 and T.sub.3 as used herein refers to the distance
from the center of a boundary layer to the center of the next
boundary layer. For the purpose of the present invention, in a
piezoelectric substrate having a laminate structure, the layer of
the crystal phase that is most suitable for the operating
conditions of the piezoelectric substrate preferably has a
sufficiently large film thickness. Then, the stress applied to the
piezoelectric substrate can be alleviated by the layers of the
other crystal phases. In a piezoelectric substrate where the layers
of the crystal phases have different film thicknesses, the
thicknesses of the crystal phases may be determined according to
the operating conditions to make the piezoelectric substrate
adapted to the operating conditions. While each of the boundary
layers preferably gradually changes its structure, it may be a
mixed phase of the crystal phases that are separated by the
boundary layer and held in contact with it.
[0030] A piezoelectric substrate having such a laminate structure
has crystal phases of two or more than two different types of
crystal structure selected from the tetragonal structure, the
rhombohedral structure, the pseudocubic structure and the
monoclinic structure. Each of the crystal phases is expressed by
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yT.sub.1-y)O.sub.3 (where M
represents an element selected from La, Ca, Ba, Sr, Bi, Sb and W).
Preferably, the above formula preferably satisfies the requirement
of 0.45.ltoreq.y<1. Still preferably, the above formula
preferably satisfies the requirements of 0.ltoreq.x.ltoreq.0.10 and
0.ltoreq.xm.ltoreq.1.3. It is advantageously possible to form
boundary layers as mixed phases when the above requirements are
satisfied.
[0031] Each of the crystal phases of the laminate structure of this
embodiment of piezoelectric boy preferably has a film thickness of
not less than 1 nm and not more than 1,000 nm. It is possible to
provide the piezoelectric substrate with satisfactory piezoelectric
characteristics when the film thickness is not less than 1 nm and
suppress the exfoliation that arises due to the applied in-plane
stress of the laminate structure when the film thickness is not
more thickness 1,000 nm.
[0032] [Piezoelectric Element]
[0033] A piezoelectric element according to the invention can be
embodied without particular limitations so long as it comprises a
piezoelectric substrate according to the invention as described
above by referring to the preferred embodiment and a pair of
electrodes arranged in contact with the piezoelectric substrate.
FIG. 3 schematically illustrates an embodiment of piezoelectric
element. Referring to FIG. 3, the piezoelectric element 51 has a
laminate structure formed by sequentially laying a base member 41,
a vibration plate 3, a buffer layer 43, a lower electrode 44, a
piezoelectric substrate 45 and an upper electrode 46.
[0034] The base member of the piezoelectric element of this
embodiment is preferably made of a crystalline material, which is
preferably Si. Specific examples of materials containing Si include
SOI having an SiO.sub.2 film formed on Si. The base member
typically has a thickness between 100 and 1,000 .mu.m.
[0035] The diaphragm is arranged to transmit the displacement of
the piezoelectric substrate. Preferably, the vibration plate shows
an enhanced degree of lattice matching relative to the base member
and a large Young's modulus so as to operate satisfactorily. When
the base member is made of silicon oxide, the vibration plate is
preferably made of stabilized zirconia. When the base member is
made of SOI, the SiO.sub.2 layer formed on Si single crystal layer
may be used as vibration plate. The vibration plate typically has a
thickness of 2 to 10 .mu.m.
[0036] The buffer layer is provided to take the role of enhancing
the lattice matching between the crystal lattice constant of the
base member and that of the piezoelectric substrate so that it may
be omitted when the lattice matching between the base member and
the piezoelectric substrate is satisfactory. The buffer layer may
have a laminate structure formed by laying a plurality of layers so
as to operate satisfactorily. The buffer layer is preferably made
of a material that shows a good crystal lattice matching
characteristic relative to the directly underlying vibration plate.
Examples of materials that can be used for the buffer layer include
stabilized zirconia YSZ (Y.sub.2O.sub.3--ZrO.sub.2) and CeO.sub.2
when the base member is made of silicon.
[0037] The lower electrode may be arranged directly on the buffer
layer 43 or between the vibration plate 42 and the buffer layer 43.
If the buffer layer is omitted, the lower electrode may also
operate as buffer layer. If such is the case, an adhesion layer may
be arranged between the lower electrode and the vibration plate in
order to improve the adhesion between them. The lower electrode is
preferably made of a metal of the platinum group or an electrically
conductive material formed by using oxide of such a metal. Specific
examples of materials that can be used for the lower electrode
include metals of the platinum group such as Ru, Rh, Pd, Os, Ir and
Pt and electrically conductive oxides of such metals such as
SrRuO.sub.3, BaPbO.sub.3 and RuO.sub.3. Examples of materials that
can be used for the adhesion layer include metals such as Ti, Cr,
Ir and oxides thereof such as TiO.sub.2 and IrO.sub.2.
[0038] Since the lower electrode 44 influences the orientated
crystal bearing of the piezoelectric substrate that is arranged
thereon, it is preferable that the priority oriented crystal
bearing of the substrate surface of the lower electrode is (010),
(101), (110) or (111). When the priority oriented crystal bearing
of the substrate surface of the lower electrode is (010), (101),
(110) or (111), the piezoelectric substrate 45 that is laid on the
lower electrode 44 is oriented with a priority oriented crystal
bearing of (100), (001), (010), (101), (110) or (111). The priority
oriented crystal bearing of the substrate surface of the lower
electrode is preferably (001) or (111) because the priority
oriented crystal bearing of (001) or (111) is particularly
advantageous for the piezoelectric characteristics of the
piezoelectric substrate 45.
[0039] The crystal orientation ratio of the metal thin film or the
thin film of the electrically conductive oxide material of the
lower electrode is preferably not less than 70%. The crystal
orientation ratio refers to the ratio relative to the peak
intensity of the film as observed by means of a .theta.-2.theta.
measurement of XRD (X-ray diffraction). The lower electrode shows
good electric characteristics when the crystal orientation ratio of
the metal electrode thin film is not less than 70% so that the
piezoelectric substrate 45 arranged thereon shows an excellent
crystallinity. Preferably, the crystal orientation ratio of the
metal thin film or the electrically conductive oxide material of
the lower electrode is not less than 85%. The film thickness of the
lower electrode is preferably between 100 nm and 1,000 nm and that
of the adhesion layer is preferably between 5 nm and 300 nm, more
preferably between 10 nm and 70 nm.
[0040] The above-described embodiment of piezoelectric substrate is
used in this embodiment of piezoelectric element. The film
thickness of the piezoelectric substrate is preferably not less
than 100 nm and not more than 10 .mu.m, more preferably not less
than 500 nm and not more than 8 .mu.m. When the piezoelectric
element is used in a liquid discharge head, it is highly durable
relative to the stress that may arise when it is driven repeatedly
if the film thickness of the piezoelectric substrate is not less
than 100 nm. The piezoelectric element can suppress the phenomenon
of film exfoliation if the film thickness of the piezoelectric
substrate is not more than 10 .mu.m.
[0041] The upper electrode 46 is arranged directly on the
piezoelectric substrate 45 and electrically charges the
piezoelectric substrate with the lower electrode. An adhesion layer
made of a material similar to that of the adhesion layer arranged
between the lower electrode and the vibration plate may also be
arranged between the upper electrode and the piezoelectric
substrate. The materials that can be used for the lower electrode
can also be used for the upper electrode 46.
[0042] This embodiment of piezoelectric element may have a layer
arrangement selected from those listed below. Each exemplary layer
arrangement includes upper electrode 46 // piezoelectric substrate
45 // lower electrode 44 // vibration plate 42 and each laminate
structure is expressed by using /.
Pt/Ti//PbZrTiO.sub.3//Pt/Ti//YSZ(Y.sub.2O.sub.3--ZrO.sub.2)/Si
Example 1:
Au//PbZrTiO.sub.3//Pt/Ti//YSZ(Y.sub.2O.sub.3--ZrO.sub.2)/Si Example
2:
Pt/Ti//PbZrTiO.sub.3/PbTiO.sub.3//Pt/Ti//Ysz(Y.sub.2O.sub.3--ZrO.sub.-
2)/Si Example 3:
Au/Cr//PbZrTiO.sub.3/PbTiO.sub.3//Pt/Ti//YSZ(Y.sub.2O.sub.3--ZrO.sub.2)/S-
i Example 4: Au/Cr//PbZrTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 5:
Au//PbZrTiO.sub.3/PbTiO.sub.3//Pt/Ti//YSZ(Y.sub.2O.sub.3--ZrO.sub.2)/Si
Example 6: Pt/Ti//PbZrTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 7:
Au//PbZrTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 8:
Pt/Ti//PbZrTiO.sub.3/PbTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 9:
Au//PbZrTiO.sub.3/PbTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 10:
Pt//PbZrTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 11:
Au//PbZrTiO.sub.3/PbTiO.sub.3//Ir/Ti//SiO.sub.2/Si Example 12:
Ir//PbZrTiO.sub.3//Ir/Ti//SiO.sub.2/Si Example 13:
Ir//PbZrTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 14:
Ir//PbZrTiO.sub.3//Ir/Ti//SiO.sub.2/Si Example 15:
Ir//PbZrTiO.sub.3//Pt/Ti//SiO.sub.2/Si Example 16:
[0043] [Liquid Discharge Head]
[0044] A liquid discharge head according to the invention can be
embodied without particular limitations so long as it comprises
discharge ports, separate liquid chambers communicating
respectively with the discharge ports, piezoelectric elements
arranged to correspond to the respective separate liquid chambers
and vibration plates arranged respectively between the separate
liquid chambers and the piezoelectric elements. FIG. 3 is a
schematic cross sectional perspective view of an embodiment of
liquid discharge head, which is an ink jet head. The ink jet head
comprises a base member 41 and a plurality of pressure chambers 61
that are separate liquid chambers arranged in parallel with the
base member. Each of the pressure chambers is provided with a
liquid discharge port (discharge port) 53 and a piezoelectric
element 51 along with a vibration plate 42 arranged between the
pressure chamber and the piezoelectric element. The liquid
discharge ports 53 of the ink jet head are disposed at
predetermined regular intervals on a nozzle plate 52 arranged under
the base member 41, although they may alternatively be disposed at
a lateral surface side.
[0045] The piezoelectric elements 51 are typically arranged on the
top surface of the base member 41 at respective positions that
correspond to the pressure chambers 61. Each of the piezoelectric
elements 51 is typically a laminate comprising a buffer layer 43, a
lower electrode 44, a piezoelectric substrate 45 which is a
piezoelectric thin film, and an upper electrode 46 that are laid
sequentially one on the other in the above described order.
[0046] The embodiment of liquid discharge head of FIG. 3 is adapted
to discharge liquid in the form of liquid droplets from each of the
separate liquid chambers by means of the volume change produced in
the liquid chamber by the vibration plate to which the displacement
of the corresponding piezoelectric substrate is transmitted.
[0047] This embodiment of liquid discharge head can find
applications not only in ink jet heads but also in liquid discharge
sections of apparatus that are adapted to discharge liquid of
various types.
[0048] In the liquid discharge head of the above described
embodiment, the performances of the piezoelectric elements do not
show remarkable variances because each of the piezoelectric
elements comprises a vibration plate, a buffer layer, a lower
electrode, a piezoelectric substrate and an upper electrode with
their respective crystal orientation bearings aligned with each
other. Thus, it is possible to realize a high adhesion device.
Additionally, it is possible to achieve satisfactory piezoelectric
characteristics and mechanical characteristics if the liquid
discharge head is downsized. Additionally, the durability of the
piezoelectric elements is improved to provide the liquid discharge
head with excellent durability when the piezoelectric substrates
are formed by using highly oriented crystal.
[0049] [Liquid Discharge Apparatus]
[0050] An embodiment of liquid discharge apparatus comprises the
above-described embodiment of liquid discharge head.
[0051] This embodiment of liquid discharge apparatus may be used as
an ink jet recording apparatus. FIG. 4 is a schematic perspective
view of an embodiment of liquid discharge apparatus according to
the invention, which is an ink jet recording apparatus 81 having an
operation mechanism section. Referring to FIG. 4, the ink jet
recording apparatus comprises an automatic feed section 97 for
automatically feeding sheets of recording paper, or recording
mediums, into the apparatus main substrate 96 along with a transfer
section 99 for leading each sheet of recording paper fed from the
automatic feed section 97 to a predetermined recording position and
then from the recording position further to a delivery port 98, a
recording section 91 for recording data on the sheet of recording
paper transferred to the recording position and a recovery section
90 for executing a recovery process on the recording section 91.
The recording section 91 is equipped with a carriage 92 that
contains a liquid discharge head of this embodiment and drives it
to move back and forth on a rail.
[0052] In the ink jet recording apparatus having the
above-described configuration, the carriage 92 is driven to move on
the rail according to electric signals transmitted from a computer
and any of the piezoelectric substrates is displaced as a drive
voltage is applied to the electrodes between which the
piezoelectric substrate is sandwiched. Then, the corresponding
pressure chamber is pressurized by the displacement of the
piezoelectric substrate by way of the corresponding vibration plate
so as to discharge ink from the discharge port for printing.
[0053] This embodiment of liquid discharge apparatus can uniformly
discharge liquid droplets at high speed. Additionally, it is
possible to downsize the apparatus.
[0054] While the embodiment is described above as a printer, the
above-described embodiment of liquid discharge apparatus finds
applications as ink jet recording apparatus of a fax machine, a
composite machine or a copying machine and also as industrial
liquid discharge apparatus.
[0055] [Method of Manufacturing Piezoelectric Substrate]
[0056] A piezoelectric substrate as shown in FIG. 1 can be
manufactured by means of a film forming method of laying crystal
phases having respective crystal structures that are different from
each other one on the other and selecting piezoelectric materials
that make each of the crystal phase show the tetragonal structure,
the rhombohedral structure, the pseudocubic structure or the
monoclinic structure. Preferably, each of the crystal phases is
made to grow by sputtering. The crystal phases can be made to grow
sputtering by way of a step of arranging a target on which a
plurality of different piezoelectric materials are arranged in
different regions and a step of sputtering, shifting the sputtering
area on said target. A technique of using a chamber where a base
member for a piezoelectric substrate and a target of oxides
expressed by the above formula of
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yT.sub.1-y)O.sub.3 that are to be
used as piezoelectric materials for forming the crystal phases are
arranged vis-a-vis may be employed for the sputtering. After
producing a high degree of vacuum in the chamber, a voltage is
applied between the base member and the target to produce a glow
discharge and ionizes gas such as argon gas introduced into the
chamber. Then, ions are accelerated in a strong electric field to
hit the target and the crystal phases are made to grow on the base
member by means of the elements jumping out from the target.
Particularly, when manufacturing a piezoelectric substrate by
periodically repeating the process of laying different crystal
phases, a target where two different piezoelectric materials of
compositions 1 and 2 (targets 57,39) for forming different crystal
phases are arranged as shown in FIG. 5 may advantageously be used.
Referring to FIG. 5, the aperture of shutter 5 is arranged
vis-a-vis the region of the corresponding piezoelectric material on
the target 53. Then, only the region of the piezoelectric material
to be used is sputtered by way of the aperture for a predetermined
period of time to cause the corresponding element to jump out and
form a film on the substrate. Subsequently, the shutter is moved
slowly until the aperture comes vis-a-vis the region of the other
piezoelectric material of the other composition for forming the
next crystal phase and the region is sputtered. By repeating the
above described process, it is possible to obtain a piezoelectric
substrate having a laminate structure where two different
compositions, or the crystal phases of two different types having
different crystal structures, and boundary layers separating the
crystal phases are laid one on the other. In FIG. 5, reference
numeral 55 denotes the aperture section. When manufacturing a
piezoelectric substrate having a laminate structure where crystal
phases of three different types are periodically laid one on the
other, three different piezoelectric materials of compositions 1, 2
and 3 (targets 61, 63, 65) for forming different crystal phases are
arranged in respective regions on a target that are formed by
dividing the overall target region into three. Then, it is possible
to obtain a piezoelectric substrate having a laminate structure
where three different compositions 1, 2 and 3, or the crystal
phases of three different types having different crystal
structures, and boundary layers separating the crystal phases are
laid one on the other by sequentially and periodically placing the
aperture of the shutter vis-a-vis the regions of the piezoelectric
materials and sputtering them. In FIG. 6, reference numeral 69
denotes the target and reference numeral 71 denotes the aperture
section.
[0057] The oxides expressed by the above formula of
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yT.sub.1-y)O.sub.3 that are to be
used on the target can be obtained by sintering or by means of a
powder method of using powers prepared to respectively show desired
compositions.
[0058] A layer having a crystal phase where the crystal structure
gradually changes in the direction of elevation that is to be
arranged between two layers of crystal phases having predetermined
respective crystal structures is manufactured by regulating the
moving speed of the shutter whose aperture is sequentially placed
vis-a-vis the regions where different piezoelectric materials are
arranged. It is possible to prepare a crystal phase whose crystal
structure gradually changes by regulating the moving speed of the
aperture of the shutter so as to form a film corresponding to the
crystal structure that gradually changes in the direction of
elevation of the piezoelectric substrate.
[0059] In this way, it is possible to obtain a piezoelectric
substrate showing excellent piezoelectric characteristics when the
piezoelectric substrate has a laminate structure of a plurality of
layers but shows a single crystal structure or a uniaxial structure
as a whole. Such a piezoelectric substrate can be obtained by
forming the phases by epitaxial growth by means of the
above-described technique.
[0060] [Method of Manufacturing Piezoelectric Element]
[0061] An appropriate thin film forming technique may be used for a
method of manufacturing a piezoelectric element of this embodiment.
Thin film forming techniques that can be used for forming a
vibration plate 42 in the process of manufacturing a piezoelectric
element according to the present invention include sputtering, CVD,
laser abrasion and MBE. Particularly, the use of sputtering is
advantageous because it is possible to produce an epitaxially grown
oxide thin film on a base member 41 by sufficiently heating the
film forming substrate in a heating process.
[0062] Thin film forming techniques that can be used for preparing
a lower electrode 44 and an upper electrode to be laid on a base
member 41 in the course of manufacturing a piezoelectric element
include sputtering, CVD, PLD, Sol-Gel, MBE and hydrothermal
synthesis. With any of these techniques, it is possible to form a
film of an electrode material, orienting the electrode material in
a specific direction.
[0063] Techniques that can be used for forming a film of a
piezoelectric substrate 45 and growing the crystal of the film on a
lower substrate 44 include sputtering, CVD, Sol-Gel, MBE and
hydrothermal synthesis.
[0064] Techniques that can be used for forming a thin film of an
upper electrode 46 on a piezoelectric substrate 45 include vapor
phase techniques such as sputtering and evaporation coating,
application techniques such as screen printing and liquid phase
techniques such as plating.
[0065] Techniques similar to those that can be used for preparing
an electrode may also be used for preparing a buffer layer for a
piezoelectric element according to the present invention.
[0066] [Method of Manufacturing Liquid Discharge Head]
[0067] An appropriate thin film forming technique may be used for a
method of manufacturing a liquid discharge head of this embodiment
according to the present invention. When manufacturing a liquid
discharge head of this embodiment, either a process of arranging
separate liquid chambers (pressure chambers) 61 on the base member
41 of piezoelectric elements according to the present invention or
a process of arranging separate liquid chambers that are separated
from the base member and bonding them to piezoelectric
elements.
[0068] With the former process, piezoelectric elements are formed
by the above-described method and the base member 41 is partly
removed at regular intervals to produce recesses for forming a
plurality of separate liquid chambers. The recesses can be formed
by wet etching that utilizes anisotropic etching or by dry etching
such as ICP, LIGA process or bosch process. The pressure chambers
may have an appropriate lateral profile selected from rectangular,
circular, elliptic, etc. In the case of a side shooter, the
pressure chambers may have a constricted profile having a tapered
section directed toward the liquid discharge port. Then, a nozzle
plate 52 where discharge ports 53 are bored is bonded to the base
member where recesses are formed for pressure chambers 61.
Alternatively, a nozzle plate where discharge ports 53 and recesses
are formed may be bonded to the base member to prepare a liquid
discharge head. The material of the nozzle plate may be same as or
different from that of the base member to which the nozzle plate is
to be bonded. Materials that can be used for the nozzle plate
include SUS and Ni. Preferably, the material of the nozzle plate
shows a thermal expansion coefficient that differs from the thermal
expansion coefficient of the base member to which the nozzle plate
is to be bonded by 1E.sup.-6/C.degree. to 1E.sup.-8/C.degree.. The
discharge ports may be bored through the nozzle plate by means of
etching, machining, and laser processing.
[0069] The base member 41 and the nozzle plate 52 may be bonded by
means of an organic adhesive agent, although they are preferably
bonded by metallic bonding, using an inorganic material. Materials
that can be used for metallic bonding include In, Au, Cu, Ni, Pb,
Ti and Cr. Any of these metals can bond the base member and the
nozzle plate at low temperature not higher than 250.degree. C. and
the thermal expansion coefficient thereof shows a small difference
from the thermal expansion coefficient of the base member so that
it can avoid the problem of warping if the liquid discharge head is
made long and hence suppress damages to the piezoelectric
substrates if such damages arises.
[0070] A liquid discharge head comprising piezoelectric elements
and hence piezoelectric substrates according to the present
invention will be described further below by way of examples. The
technical scope of the piezoelectric substrates, piezoelectric
elements and liquid discharge head using the piezoelectric elements
is by no means limited to the examples described below.
[0071] Specimens of liquid discharge head according to the present
invention were prepared as described below.
EXAMPLE 1
[0072] Firstly, a vibration plate was prepared by forming a film of
stabilized zirconia YSZ (Y.sub.2O.sub.3--ZrO.sub.2) on an open
section of an Si substrate by means of a sputtering system
(L-210-FH (available from ANELVA)). In this process, the Si
substrate was heated to 800.degree. C. and Ar and O.sub.2 were used
as gas to be ionized. Electric power of 100 W was applied between
the Si substrate and the target and the internal pressure of the
system was held to 1.0 Pa. As a result, a 200 nm thick uniaxial
vibration plate was obtained.
[0073] Then, a process same as that of preparing the vibration
plate was used to prepare a lower electrode. In this process, Pt
was used as target and the substrate was heated to 600.degree. C.,
while Ar was used as gas to be ionized. Electric power of 100 W was
applied between the vibration plate and the target and the internal
pressure of the system was held to 0.5 Pa. As a result, a 400 nm
thick highly uniaxial Pt film was obtained.
[0074] Subsequently, films of two different oxides having
respective target compositions (1) and (2) as listed below were
formed on the substrate by means of the above described sputtering
system, placing the aperture of the shutter vis-a-vis one of the
composition regions of the target, holding it for a predetermined
time period, then sliding the aperture of the shutter to place it
vis-a-vis the other composition region of the target and holding it
for a predetermined time period. This process was repeated to form
20 layers of each of the two different compositions, or the crystal
phases, in an alternate manner, the crystal phases being separated
by boundary layers having a crystal structure that changes
gradually. A piezoelectric substrate was obtained as a result. In
this process, the substrate was heated to 650.degree. C., while Ar
and O.sub.2 were used as gas to be ionized. Electric power of 100 W
was applied between the electrode and the target and the internal
pressure of the system was held to 0.5 Pa. The sputtering time was
8 minutes for both the target composition (1) and the target
composition (2) and 2 minutes were spent to form a boundary layer,
while moving the aperture of the shutter from one of the
compositions to the other. As a result, a piezoelectric substrate
having a film thickness of 300 nm and comprising layers of the
tetragonal structure and the rhombohedral structure and boundary
layers that were mixed layers of the two structures was obtained,
as shown in FIG. 1.
[0075] Target Compositions
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where x=0,
y=0.45 (1) (Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3,
where x=0, y=0.55 (2)
[0076] Subsequently, an upper electrode was prepared by way of a
process similar to that of preparing the lower electrode.
[0077] Then, the Si substrate was subjected to a dry etching
process by means of ICP from the surface opposite to the surface
where the vibration plate 42 was arranged to remove a central part
and produce a recess. At this time, the temperature of the
substrate was held to 20.degree. C. and gases of SF.sub.6 and
C.sub.4F.sub.8 were used, while the high frequency coil was
operated by RF induction with 1,800 W and the internal pressure of
the system was held to 4.0 Pa. A nozzle plate made of Si and
provided with a liquid discharge port 53 was bonded to the Si
substrate where a recess had been formed by means of an Si-Si
bonding process. In this way, a liquid discharge head comprising a
piezoelectric element with a 5,000 .mu.m long and 100 .mu.m wide
vibration plate was prepared.
[0078] The piezoelectric element and the liquid discharge head that
were obtained in Example 1 were tested to observe the displacement
of the piezoelectric element, the quantity of discharged liquid
droplets and the speed of discharge of liquid droplets when the
applied voltage was 20 V and the frequency was 10 kHz. Tables 1 and
2 summarily show the obtained results.
EXAMPLE 2
[0079] A liquid discharge head was prepared by following the
process of Examples 1 and 2 except that the target compositions as
listed below were used for preparing the piezoelectric substrate
and a target as illustrated in FIG. 6 was used. As shown in FIG. 6,
the target compositions (1) through (3) were arranged in the
respective target regions formed by dividing the target by three as
materials of the piezoelectric substrate. The sputtering time was
15 minutes, 13 minutes and 11 minutes for the three regions of the
different compositions and 4 minutes were spent to form a boundary
layer, while moving the aperture of the shutter from one of the
compositions to the other. As a result, a piezoelectric substrate
comprising 20 layers of the tetragonal structure and 20 layers of
the rhombohedral structure and 20 MPB layers that were mixed layers
of the two structures was obtained. Thus, it is possible to form a
piezoelectric boy having different film thicknesses for layers of
different crystal phases as shown in FIG. 2 by differentiating the
film forming time for the crystal phases.
[0080] Target Compositions
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=La,
x=0.07, y=0.40, xm=1.10 (1)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=Ca,
x=0.02, y=0.52, xm=1.10 (2)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=Ba,
x=0.03, y=0.55, xm=1.10 (3)
[0081] The piezoelectric element and the liquid discharge head that
were obtained in Example 2 were tested to observe the displacement
of the piezoelectric element, the quantity of discharged liquid
droplets and the speed of discharge of liquid droplets as in
Example 1. Tables 1 and 2 summarily show the obtained results.
EXAMPLE 3
[0082] A liquid discharge head was prepared by following the
process of Examples 1 and 2 except that the target compositions (1)
through (4) as listed below were used for preparing the
piezoelectric substrate and a target where the materials of the
piezoelectric substrate were arranged in the respective target
regions formed by dividing the target by four. The sputtering time
was 24 minutes, 24 minutes, 24 minutes, 30 minutes, 24 minutes and
36 minutes for the regions of the different compositions and 6
minutes were spent to form a boundary layer, while moving the
aperture of the shutter from one of the compositions to the other.
As a result, a piezoelectric substrate comprising 10 layers of each
of the six structures including the tetragonal structure, the
rhombohedral structure, the tetragonal structure, the pseudocubic
structure, the tetragonal structure and the monoclinic structure
was obtained. Thus, it is possible to form a piezoelectric
substrate having desired film thicknesses for respective layers of
a plurality of crystal phases by differentiating the quota regions
on the target and the sputtering time.
[0083] Target Compositions
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=La,
x=0.07, y=0.40, xm=1.15 (1)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=Sr,
x=0.02, y=0.52, xm=1.15 (2)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=Bi,
x=0.03, y=0.40, xm=1.15 (3)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=Sb,
x=0.02, y=0.52, xm=1.15 (4)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=W,
x=0.02, y=0.40, xm=1.15 (5)
(Pb.sub.1-xM.sub.x).sub.xm(Zr.sub.yTi.sub.1-y)O.sub.3, where M=La,
x=0.03, y=0.52, xm=1.15 (6)
[0084] It may be safe to assume that (2), (4) and (6) respectively
took the form of the rhombohedral structure, that of pseudocubic
structure and that of the monoclinic structure because the film
forming time was 8 minutes, 10 minutes and 12 minutes for (2), (4)
and (6) where the quantity of Zr was 0.52 and the stress applied to
the film was differentiated.
[0085] The piezoelectric element and the liquid discharge head that
were obtained in Example 3 were tested to observe the displacement
of the piezoelectric element, the quantity of discharged liquid
droplets and the speed of discharge of liquid droplets as in
Examples 1 and 2. Tables 1 and 2 summarily show the obtained
results.
COMPARATIVE EXAMPLE 1
[0086] A liquid discharge head was prepared by following the
process of Examples 1, 2 and 3 except that the values of x=0 and
y=0.50 and a sintered substrate were used for the target
composition of (Pb.sub.1-xM.sub.x)(Z.sub.ryTi.sub.1-y)O.sub.3M for
preparing the piezoelectric substrate of the example and the
substrate was heated to 600.degree. C. As a result, a
polycrystalline piezoelectric substrate where the crystal phases of
the tetragonal structure and the rhombohedral structure coexist as
mixture was obtained.
[0087] The piezoelectric element and the liquid discharge head that
were obtained in Comparative Example 1 were tested to observe the
displacement of the piezoelectric element, the quantity of
discharged liquid droplets and the speed of discharge of liquid
droplets as in Examples 1, 2 and 3.
[0088] The displacement of the piezoelectric element of Example 1
was 0.40 nm, that of the piezoelectric element of Example 2 was
0.55 nm and that of the piezoelectric element of Example 3 was 0.54
nm, whereas the displacement of the piezoelectric element of
Comparative Example 1 that comprised only a mixed layer of the
tetragonal structure and the rhombohedral structure was 0.35
nm.
[0089] The quantity of discharged liquid droplets of the liquid
discharge head was 17 pl and the discharge speed was 14 m/sec in
Example 1 when a voltage of 20 V was applied to the liquid
discharge head (10 kHz). The quantity of discharged liquid droplets
of the liquid discharge head was 19 pl and the discharge speed was
16 m/sec in Example 2 when a voltage of 20 V was applied to the
liquid discharge head (10 kHz). The quantity of discharged liquid
droplets of the liquid discharge head was 19 pl and the discharge
speed was 15 m/sec in Example 3 when a voltage of 20 V was applied
to the liquid discharge head (10 kHz). On the other hand, the
quantity of discharged liquid droplets of the liquid discharge head
was 16 pl and the discharge speed was 13 m/sec in Comparative
Example 1. Apparently, both the quantity of discharged liquid
droplets and the discharge speed of the liquid discharge head of
Comparative Example 1 were inferior relative to those of Examples 1
through 3.
[0090] The liquid discharge heads were subjected to a durability
test. The liquid discharge heads of Examples 1 through 3 did not
give rise to any nozzle incapable of discharging liquid after
10.sup.9 operations. On the other hand, the liquid discharge head
of Comparative Example 1 produced film exfoliation and a nozzle
incapable of discharging liquid any more after 10.sup.6 to 10.sup.7
operations. Thus, according to the present invention, it is
possible to provide a piezoelectric element that is highly durable
and practically free from film exfoliation.
[0091] 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 such modifications and
equivalent structures and functions.
[0092] This application claims the benefit of Japanese Patent
Application No. 2005-241378, filed Aug. 23, 2005, which is hereby
incorporated by reference herein in its entirety.
* * * * *