U.S. patent application number 09/432229 was filed with the patent office on 2003-04-10 for ferroelectric element and process for producing the same.
Invention is credited to AIZAWA, MAMORU, SAKAMAKI, SHINICHI, TAKAHASHI, YUKIMI, TOKI, MOTOYUKI, YAMADA, YORINOBU.
Application Number | 20030067509 09/432229 |
Document ID | / |
Family ID | 27475311 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030067509 |
Kind Code |
A1 |
SAKAMAKI, SHINICHI ; et
al. |
April 10, 2003 |
FERROELECTRIC ELEMENT AND PROCESS FOR PRODUCING THE SAME
Abstract
A ferroelectric element comprising a ferroelectric material
containing at least two metals, the ferroelectric element having
been produced by a process including a sol-gel process in the
presence of a thickener and/or an association preventive from
aqueous solutions of respective salts of the metals. The
ferroelectric element is advantageous in that the handling of
starting compounds and the production of the ferroelectric element
are easy, the storage stability of the starting compound solution
is good, the cost is low, the ferroelectric element can be formed
as a thin layer, particles on the surface of the thin layer are
fine and dense, and, hence, the surface smoothness is good. The
ferroelectric element is excellent also in piezoelectric properties
and therefore can be advantageously used as a piezoelectric element
in a piezoelectric ink jet head.
Inventors: |
SAKAMAKI, SHINICHI;
(TOKOROZAWA-SHI, JP) ; TAKAHASHI, YUKIMI;
(TOKOROZAWA-SHI, JP) ; YAMADA, YORINOBU;
(TOKOROZAWA-SHI, JP) ; TOKI, MOTOYUKI; (KYOTO-SHI,
JP) ; AIZAWA, MAMORU; (KYOTO-SHI, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT &
DUNNER LLP
1300 I STREET, NW
WASHINGTON
DC
20006
US
|
Family ID: |
27475311 |
Appl. No.: |
09/432229 |
Filed: |
November 3, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09432229 |
Nov 3, 1999 |
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09117377 |
Jul 29, 1998 |
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6255762 |
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09117377 |
Jul 29, 1998 |
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PCT/JP96/03745 |
Dec 20, 1996 |
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Current U.S.
Class: |
347/68 |
Current CPC
Class: |
H01L 41/1876 20130101;
C01P 2002/34 20130101; H01L 41/318 20130101; C01G 25/006 20130101;
C01P 2002/72 20130101; Y10T 29/49002 20150115; C01P 2002/77
20130101; C01P 2004/02 20130101; Y10T 29/42 20150115 |
Class at
Publication: |
347/68 |
International
Class: |
B41J 002/045 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 1996 |
JP |
8-187117 |
Sep 3, 1996 |
JP |
8-232666 |
Sep 10, 1996 |
JP |
8-238732 |
Oct 3, 1996 |
JP |
8-263105 |
Claims
What is claimed is:
1. A ferroelectric element comprising a ferroelectric material
containing at least two metals, said ferroelectric element having
been produced by a process including a sol-gel process in the
presence of a thickener and/or an association preventive from
aqueous solutions of respective salts of the metals.
2. The ferroelectric element according to claim 1, wherein the
thickener comprises a water-soluble polymeric material which, when
heated to a temperature above a predetermined temperature at the
time of the formation of the ferroelectric element, can be
heat-decomposed.
3. The ferroelectric element according to claim 2, wherein the
thickener comprises at least one compound selected from the group
consisting of hydroxyalkyl cellulose, polyethylene oxide, and
polyvinyl alcohol.
4. The ferroelectric element according to claim 1, wherein the
association preventive comprises a water-soluble polyhydric
alcohol.
5. The ferroelectric element according to claim 4, wherein the
polyhydric alcohol comprises at least one compound selected from
the group consisting of diethylene glycol, polyethylene glycol, and
glycerin.
6. The ferroelectric element according to any one of claims 1 to 5,
wherein a powder of another ferroelectric material having a crystal
structure identical or similar to the ferroelectric material is
present in addition to the thickener and/or the association
preventive.
7. The ferroelectric element according to any one of claims 1 to 6,
wherein the ferroelectric material is a ceramic having a perovskite
structure and one of the metals is lead.
8. The ferroelectric element according to claim 7, wherein the salt
of lead is lead nitrate or lead acetate.
9. The ferroelectric element according to claim 7, wherein the
ceramic is lead zirconate titanate.
10. The ferroelectric element according to any one of claims 1 to
9, which is in the form of a thin layer.
11. The ferroelectric element according to any one of claims 1 to
10, which further comprises a ferroelectric substrate layer having
a crystal structure identical or similar to the ferroelectric
material and has been formed by hydrothermal synthesis from aqueous
solutions of metals necessary for the formation of the substrate
layer.
12. The ferroelectric element according to claim 11, wherein the
particle diameter of the ferroelectric material constituting the
substrate layer is larger than that of the ferroelectric material
constituting the overlying layer.
13. A process for producing a ferroelectric element comprising a
ferroelectric material containing at least two metals, said process
comprising the steps of: mixing aqueous solutions of respective
salts of the metals together to prepare an aqueous ferroelectric
precursor solution; adding a thickener and/or an association
preventive to the aqueous ferroelectric precursor solution and
coating the resultant-solution onto a substrate; and drying and
firing the coating to crystallize the ferroelectric material.
14. The process according to claim 13, wherein the thickener is a
water-soluble polymeric material and can be heat-decomposed in the
step of crystallizing the ferroelectric material.
15. The process according to claim 13, wherein the association
preventive comprises a water-soluble polyhydric alcohol.
16. The process according to any one of claims 13 to 15, wherein a
powder of another ferroelectric material having a crystal structure
identical or similar to the ferroelectric material is further added
in the step of adding the thickener and/or the association
preventive.
17. The process according to any one of claims 13 to 16, which
further comprises the step of adding the ferroelectric precursor in
the form of a paste derived from the aqueous ferroelectric
precursor solution.
18. The process according to any one of claims 13 to 17, which
further comprises the step of forming on the substrate a substrate
layer, having a crystal structure identical or similar to the
ferroelectric material, from aqueous solutions of metals necessary
for the formation of the substrate layer by hydrothermal
synthesis.
19. The process according to any one of claims 13 to 18, wherein
the ferroelectric material is a ceramic having a perovskite
structure and one of the metals is lead.
20. The process according to claim 19, wherein the ceramic is lead
zirconate titanate.
21. A ferroelectric precursor for use as a starting material in the
production of a ferroelectric material comprising at least two
metals by a process including a sol-gel process, said ferroelectric
precursor comprising aqueous solutions of respective salts of the
metals and containing a thickener and/or an association
preventive.
22. The ferroelectric precursor according to claim 21, which
further comprises a powder of another ferroelectric material having
a crystal structure identical or similar to the ferroelectric
material.
23. An ink jet head comprising a plurality of nozzles for ejecting
an ink, ink chambers, for passage and pressurization of the ink,
communicating with the nozzles, and pressing means for creating a
change in volume of the ink in the ink chamber to eject the ink
through the nozzles, the pressing means comprising a ferroelectric
element as a piezoelectric element, said ferroelectric element
comprising a ferroelectric material containing at least two metals
and having been produced by a process including a sol-gel process
in the presence of a thickener and/or an association preventive
from a aqueous solutions of respective salts of the metals.
24. The ink jet head according to claim 23, wherein the
ferroelectric material is a ceramic having a perovskite structure
and one of the metals is lead.
25. The ink jet head according to claim 24, wherein the ceramic is
lead zirconate titanate.
Description
TECHNICAL FIELD
[0001] The present invention relates to a ferroelectric element and
more particularly to a ferroelectric element particularly in the
form of a thin layer, which is advantageously usable as a
piezoelectric element in ink jet printers and other devices. The
present invention also relates to a process for producing the
ferroelectric element and a ferroelectric precursor which can be
advantageously used in the production of the ferroelectric element.
Further, the present invention relates to a piezoelectric ink jet
head using the above ferroelectric element as a piezoelectric
element. The term "piezoelectric" and the term "ferroelectric" used
herein are defined as follows. Materials, which, when an external
force (a stress from the outside) is applied to a crystal thereof,
develop polarization, are called piezoelectrics, and, among the
piezoelectrics, those wherein the polarization can be reversed by
an external electric field are expressly called ferroelectrics.
BACKGROUND ART
[0002] In recent years, in office automation equipment, such as
word processors, personal computers, facsimile machines, various
measuring instruments, such as medical measuring instruments, and
other devices, ink jet printers have been extensively used for
printing information from these devices at high density. As is well
known in the art, in the ink jet printer, an ink droplet is ejected
from a head section of the printer and deposited directly onto a
recording medium, such as recording paper, to perform monochrome or
color printing. The ink jet printer has many advantages including
that printing can be performed on even a three-dimensional
recording medium, running cost is low since plain paper can be used
as the recording medium, the head can be easily mounted in the
printer, the need to provide the step of transfer, fixation and the
like can be eliminated, color printing is easily performed, and a
sharp color printed image can be provided. The head section of the
ink jet printer can be classified into several types according to
the drive system for ejecting ink droplets from the head section.
Among them, a typically and advantageously used one is a
piezoelectric ink jet head.
[0003] The piezoelectric ink jet head generally comprises: a
plurality of ink chambers which are disposed at equidistant spaces
and function as an ink flow passage and a pressurizing chamber for
ejecting an ink; and a nozzle plate mounted on the front end of the
ink chambers and equipped with nozzles, for ejecting an ink,
corresponding respectively to the ink chambers; and pressing means
for pressurizing an ink within the ink chamber in response to the
demand for printing. The pressing means comprises a piezoelectric
element (known also as "piezo element"), and electrostrictive
effect attained by this piezoelectric element is utilized to create
a pressure wave within an ink chamber, filled with ink, in the head
section, permitting the ink to be ejected through the nozzle in the
head section.
[0004] The structure of the piezoelectric ink jet head will be
described in more detail with reference to FIG. 1. An ink jet head
10, a part of which is shown in the drawing, has an ink chamber
member 11 comprising a plurality of ink chambers 12 serving as an
ink flow passage and a pressurizing chamber for ejecting ink. A
nozzle plate (not shown) equipped with nozzles disposed so as to
correspond respectively to the ink chambers 12 is mounted on the
front end of the ink chamber 11. The ink pressurized within the ink
chamber 12 can be ejected as a droplet through the bore of the
nozzle. In the ink chamber member 11 shown in the drawing, pressing
means is mounted on the open face of the ink chamber 12. In the
example shown in the drawing, the pressing means comprises: a
diaphragm 15 for creating a change in volume of the ink chamber 12;
a piezoelectric element 17 as a driving element for distorting the
diaphragm 15; and an upper electrode 16 and a lower electrode 18
which can apply voltage according to need, the piezoelectric
element 17 being sandwiched between the upper electrode 16 and the
lower electrode 18.
[0005] Ferroelectric elements have been extensively used as the
piezoelectric element for the ink jet head or as an element, for
example, for capacitors, actuators, memories and other elements.
The ferroelectric element consists essentially of a ferroelectric
or a ferroelectric material. Typical ferroelectric materials
include an oxide ceramic represented by the general formula
ABO.sub.3 and having a simple perovskite structure as shown in FIG.
2 and an oxide ceramic having a composite perovskite structure
represented by the general formula (A.sub.1, A.sub.2, . . . )
(B.sub.1, B.sub.2, . . . )O.sub.3. The term "perovskite structure"
used herein refers to both a simple perovskite structure and a
composite perovskite structure unless otherwise specified. As shown
in the drawing, a ceramic having the above perovskite structure
contains metallic ions A and B in the structure. Examples of more
specific ferroelectric materials having the above structure include
lead zirconate titanate (PZT) represented by the general formula
Pb(Zr, Ti)O.sub.3. In particular, ferroelectrics, containing lead
(Pb) as one metal component, including PZT are generally known to
have large remanence, specific permittivity, and piezoelectric
constant and possesses excellent piezoelectricity and
ferroelectricity. In the present specification, the ferroelectric
material will be described particularly with reference to PZT.
[0006] A sol-gel process has hitherto been well known as a
technique for the production of PZT, particularly PZT in a thin
layer form. Use of the sol-gel process in the production of PZT is
advantageous in that a high-purity thin layer of PZT can be formed,
the composition of the formed thin layer of PZT can reflect the
composition of the starting material used, which facilitates the
control of the composition and can provide a thin layer of PZT
having high surface smoothness by repetition of spin coating and
firing.
[0007] The production of a thin layer of PZT by the sol-gel process
and use of the thin layer of PZT as a piezoelectric element will be
described in more detail. For example, as described in Japanese
Unexamined Patent Publication (Kokai) No. 6-112550, lead acetate is
dissolved in acetic acid, and the solution is heated under reflux
for 30 min. Zirconium tetrabutoxide and titanium tetraisopropoxide
are then dissolved in the solution, water and diethylene glycol are
added dropwise thereto, and the mixture is satisfactorily stirred
to conduct hydrolysis. To the resultant alcohol solution of a PZT
precursor is added polyethylene glycol monomethyl ether in an
amount of 10% by weight based on the PZT precursor, followed by
satisfactory stirring. Thus, a homogeneous sol is prepared. A
platinum electrode is formed on a silicon substrate, the sol is
then spin-coated onto the electrode, and the coating is heated at
about 350.degree. C. Thus, a 2.5 .mu.m-thick, thin, crack-free
porous gel layer can be formed.
[0008] Subsequently, the same starting material as the above PZT
material is hydrolyzed to form a sol. In this case, however, no
polyethylene glycol monomethyl ether is added. The sol is
spin-coated onto the above thin, porous gel layer to form a coating
which is then dried by heating at 400.degree. C. The thin layer
thus formed is fired in an oxygen atmosphere for 15 hr. The firing
temperature is generally 600 to 700.degree. C. Thus, a thin layer
of PZT having a perovskite structure can be formed through the
above series of steps. The above sol-gel reaction may be
represented by a general formula as shown in FIG. 3 wherein R
represents an alkyl group.
[0009] Further, hydrothermal synthesis has hitherto been well known
as a method for the formation of a thin layer of PZT from an
aqueous solution of a main starting compound. The formation of the
thin layer of PZT by hydrothermal synthesis will be described. For
example, as described in Japanese Unexamined Patent Publication
(Kokai) No. 6-112543, 0.2 mol of lead nitrate, 0.104 mol of
zirconium oxychloride, and 0.096 mol of titanium tetrachloride are
dissolved in a 2 N aqueous potassium hydroxide solution. A silicon
substrate with a platinum electrode provided thereon is immersed in
the solution, and the system is heated in an autoclave at
160.degree. C. for 30 hr. The substrate is taken out of the
autoclave and dried at 200.degree. C. for one hr to form a thin
layer of PZT of cubic particles having an average diameter of 5
.mu.m.
[0010] Alternatively, the hydrothermal synthesis may comprise a
seed crystal formation process and a crystal growth process. At the
outset, in order to form a seed crystal of PZT, a titanium
substrate is immersed in water containing lead hydroxide
Pb(OH).sub.2 and zirconium hydroxide Zr(OH).sub.4, and the system
is heated in an autoclave at a temperature of 140 to 200.degree. C.
This heating results in the formation of a thin layer of PZT,
capable of serving as a seed crystal for subsequent layer
formation, on the surface of the titanium substrate. After the
formation of the seed crystal, the titanium substrate is immersed
in water containing Pb(OH).sub.2, Zr(OH).sub.4, and titanium
hydroxide Ti(OH).sub.4, and the system is heated in an autoclave at
a temperature of 80 to 150.degree. C. The heating results in the
formation of a layer of PZT, in a coarse particle form, having a
larger thickness than the thin layer of PZT formed above on the
thin layer of PZT.
[0011] The formation of the thin layer of PZT using the
hydrothermal synthesis has advantages including that the layer
thickness can be increased at a low temperature of 200.degree. C.
or below and an additional step, which renders the process
complicated, is unnecessary since the piezoelectricity is developed
immediately after the layer formation, and the adhesion to the
substrate is excellent.
[0012] The above conventional methods for producing a ferroelectric
material, however, involves many problems to be solved. For
example, in the method, described in Japanese Unexamined Patent
Publication (Kokai) No. 6-112550, wherein the thin layer of PZT is
formed by the sol-gel process using a metal alkoxide as a main
starting compound, use of the alcohol as a solvent for the PZT
precursor poses a problem that the viscosity of the precursor
varies depending upon the moisture content of the air, leading to
the occurrence of uneven properties of the formed thin layer of
PZT. Further, in order to avoid the adverse effect of the moisture
in the air and, therefore, to avoid the formation of insolubilized
metal alkoxide, the starting compounds should be mixed together in
a specific atmosphere, so that the handling of the starting
compounds is not easy. Furthermore, in the sol-gel process, it is
difficult to increase the thickness of the thin layer of PZT.
[0013] This is true of the hydrothermal synthesis. For example, for
the thin layer of PZT formed by the hydrothermal synthesis
described in Japanese Unexamined Patent Publication (Kokai) No.
6-112543, the average diameter of PZT particles constituting the
thin layer is so large that the surface smoothness of the layer is
low and it is difficult to form the upper electrode thereon.
Further, the hydrothermal synthesis involves problems which include
the density of the thin layer being low due to coarse PZT particles
and that potassium (K) is left in the thin layer, adversely
affecting the properties.
[0014] The present inventors have further made extensive and
intensive studies and, as a result, have found that even use of
water instead of the alcohol according to the present invention
creates problems in some cases.
[0015] As described below in detail, according to the present
invention, preferably, three metal salts or metal alkoxides, lead
nitrate (Pb(NO.sub.3).sub.2), zirconium oxynitrate
(ZrO(NO.sub.3).sub.2), and titanium isopropoxide
(Ti(O-i-C.sub.3H.sub.7).sub.4), are used as the starting compound
to prepare an aqueous PZT precursor solution. The aqueous PZT
precursor solution is coated onto a predetermined substrate, and
the PZT coating is dried and fired to form a thin layer of PZT. In
this case, a first possible problem is association of lead in the
step of drying the PZT precursor coating. In general, when
components, which are different from each other in solubility in
water, are mixed together to prepare an aqueous solution, the
components contained in the solution associate with each other in
the course of the subsequent step of drying the solution. This
phenomenon occurs also in the step of drying the PZT precursor
coating, and the association of lead is significant. As a result,
there is a possibility that a material is significantly
precipitated in the form of crossed stripes on the surface of the
thin layer of PZT. More specifically, this is apparent from a
microphotograph (magnification: 20.times.) shown in FIG. 4. The
creation of the association of lead is considered to result in not
only the creation of undesired defects on the surface of the thin
layer but also other problems connected with the defects.
[0016] In PZT ceramics, it is known that, regarding the ratio of
components constituting the PZT ceramics, a Pb:Zr:Ti:O ratio of
1:0.53:0.47:3 offers the highest piezoelectric properties and, when
the ratio deviates from this ratio, the piezoelectric properties
are rapidly deteriorated. Therefore, in the thin layer of PZT thus
formed, even when the Pb:Zr:Ti:O ratio is the above desired value
in the stage of the precursor, the association of lead created in
the course of drying leads to an undesired variation of the ratio,
resulting in the formation of an uneven layer which provides
deteriorated piezoelectric properties. In addition, this lowers the
density of the layer.
[0017] A second possible problem is the creation of defects such as
cracks or pinholes. For example, coating of the aqueous PZT
precursor solution onto a substrate by a conventional method, such
as dip coating or spin coating, followed by drying, degreasing, and
firing to form a thin layer of PZT often creates cracks when the
thickness of the thin layer is 1 .mu.m or more. The creation of
cracks could not be avoided even though the thin layer of PZT is
formed by stacking a plurality of thinner layers on top of each
other or one another. The creation of cracks in the thin layer of
PZT results in lowered density of the layer, making it impossible
to form an element, such as an electrode, on the top of the layer.
Therefore, the formed thin layer of PZT cannot be used, for
example, as a piezoelectric element of an ink jet head. Further,
since the aqueous PZT precursor solution used in this case has a
low viscosity on the order of several centipoises, the coverage per
coating is small and, in addition, pinholes and the like are likely
to occur.
[0018] In view of the importance of the problem of the creation of
cracks or pinholes, the present inventors have made an experiment
and, as a result, have found that coating of an aqueous PZT
precursor solution having a composition with the Pb:Zr:Ti:O ratio
being 1:0.53:0.47:3 (the above described preferred ratio) onto a
substrate by dip coating followed by drying at 150.degree. C.
develops the formation of protrusions of a material in a crossed
stripe form. After the subsequent firing at 700.degree. C. for
crystallization, the protrusions were present, and no noticeable
disappearance of the protrusions was observed. EDX (energy
dispersive X-ray analysis) has revealed that the material in a
stripe form constituting the protrusions has a high lead content.
Further, when an aqueous solution of lead, an aqueous solution of
zirconium, and an aqueous solution of titanium were prepared as
described above, dropped on a substrate and allowed to stand at
room temperature, a crystal was precipitated only in the aqueous
lead solution.
[0019] The thickness of the thin layer of PZT formed from the
aqueous PZT precursor solution is 0.05 .mu.m at the largest per
coating step, and, in addition, pinholes were created. Further,
when a series of steps of coating, drying, degreasing, and firing
were repeated ten times, the thickness of the formed thin layer of
PZT was 0.5 .mu.m, and, in addition, cracks were created.
DISCLOSURE OF THE INVENTION
[0020] Accordingly, a first object of the present invention is to
provide a ferroelectric element having advantages including that
the handling of starting compounds and the production of the
ferroelectric element are easy, the storage stability of the
starting compound solution is good, the cost is low, the
ferroelectric element can be formed as a thin layer, particles on
the surface of the thin layer are fine and dense, and, hence, the
surface smoothness is good.
[0021] A second object of the present invention is to provide a
ferroelectric element which, in addition to the above properties,
when formed as a thin layer, permits the layer thickness to be
increased and has excellent adhesion to the underlying
substrate.
[0022] A third object of the present invention is to provide a
ferroelectric element which, when formed as a thin layer, does not
create any defect, such as a precipitate of a material in a stripe
form, on the surface of the thin layer, and enables the formation
of a dense and even thin layer and, in addition, possesses
excellent piezoelectric properties.
[0023] A fourth object of the present invention is to provide a
ferroelectric element which, when formed as a thin layer, does not
create any defect, such as a precipitate of a material in a stripe
form, on the surface of the thin layer, enables the formation of a
dense and even thin layer, possesses excellent piezoelectric
properties and, in addition, does not create defects, such as
cracks or pinholes.
[0024] A fifth object of the present invention is to provide a
process for producing the above excellent ferroelectric
element.
[0025] A sixth object of the present invention is to provide a
ferroelectric precursor which can be advantageously used for the
production of the above excellent ferroelectric element.
[0026] A seventh object of the present invention is to provide a
piezoelectric ink jet head comprising the ferroelectric element of
the present invention as a piezoelectric element.
[0027] Other objects of the present invention could be easily
understood from the following detailed description.
[0028] According to one aspect of the present invention, there is
provided a ferroelectric element comprising a ferroelectric
material containing at least two metals, said ferroelectric element
having been produced in the presence of a thickener and/or an
association preventive from aqueous solutions of respective salts
of the metals. Preferably, a sol-gel process is used for the
preparation of a solution in the formation of the element.
[0029] In this case, as described above, the ferroelectric material
consisting essentially of the ferroelectric element of the present
invention is preferably an oxide ceramic having a simple or a
composite perovskite structure, more preferably lead zirconate
titanate (PZT) represented by the general formula Pb(Zr,
Ti)O.sub.3. The PZT ceramic is preferably, but not limited to, one
having a Pb:Zr:Ti:O ratio of 1:0.53:0.47:3 from the viewpoint of
good piezoelectric properties and excellent other properties. In
the present specification, although the practice of the present
invention will be described particularly with reference to the PZT
ceramic, the present invention can be advantageously applied also
to other ferroelectric materials.
[0030] In the ferroelectric element according to the present
invention, the thickener added to the aqueous ferroelectric
precursor solution is preferably a water-soluble polymeric material
which can be heat-decomposed when the temperature exceeds a
predetermined temperature in the formation of the element,
particularly a water-soluble polymeric material which can be
heat-decomposed at the time of degreasing or the like. Suitable
thickeners include, but are no limited to, for example,
hydroxyalkyl celluloses with the number of carbon atoms in the
alkyl group being preferably 2 to 4, for example, hydroxyethyl
cellulose or hydroxypropyl cellulose, polyethylene oxide, and
polyvinyl alcohol. These thickener compounds may be used alone or
as a mixture of two or more.
[0031] In the ferroelectric element of the present invention, the
association preventive used, either alone or in combination with
the thickener, is preferably a water-soluble polyhydric alcohol.
Suitable polyhydric alcohols include, but are not limited to, for
example, diethylene glycol, polyethylene glycol, and glycerin.
These polyhydric alcohols may be used alone or as a mixture of two
or more.
[0032] In practicing the present invention, preferably, the
thickener and/or the association preventive are added to the
aqueous ferroelectric precursor solution to permit a powder of a
ferroelectric having a crystal structure identical or similar to
the ferroelectric to exist.
[0033] The ferroelectric element of the present invention is
preferably a thin layer which has been formed from the above
ferroelectric precursor solution through a solution preparation
process using a sol-gel process. Although the thin layer generally
has a single layer structure, it may if necessary have a laminate
structure of two or more layers.
[0034] According to one preferred embodiment of the present
invention, a substrate layer having a crystal structure identical
or similar to the ferroelectric of the element and formed by
hydrothermal synthesis from aqueous solutions of metals necessary
for the formation of the substrate layer may be provided as a layer
underlying the ferroelectric element in a thin layer form. In this
case, the underlying ferroelectric layer, as compared with the
ferroelectric provided on the ferroelectric layer, comprises
particles having a larger diameter and has a lower density.
[0035] According to another aspect of the present invention, there
is provided a process for producing a ferroelectric element
comprising a ferroelectric material containing at least two metals,
said process comprising the steps of:
[0036] mixing aqueous solutions of respective salts of the metals
together to prepare an aqueous ferroelectric precursor
solution;
[0037] adding a thickener and/or an association preventive to the
aqueous ferroelectric precursor solution and coating the resultant
solution onto a substrate; and
[0038] drying and firing the coating to crystallize the
ferroelectric material.
[0039] According to still another aspect of the present invention,
there is provided a ferroelectric precursor for use as a starting
material in the production of a ferroelectric material comprising
at least two metals by a process including a sol-gel process, said
ferroelectric precursor comprising aqueous solutions of the
respective salts of the metals and containing a thickener and/or an
association preventive.
[0040] According to a further aspect of the present invention,
there is provided an ink jet head comprising a plurality of nozzles
for ejecting an ink, ink chambers, for passage and pressurization
of the ink, communicating with the nozzles, and pressing means for
creating a change in volume of the ink in the ink chamber to eject
the ink through the nozzles,
[0041] the pressing means comprising a ferroelectric element as a
piezoelectric element, said ferroelectric element comprising a
ferroelectric material containing at least two metals and having
been produced by a process including a sol-gel process in the
presence of a thickener and/or an association preventive from
aqueous solutions of respective salts of the metals.
[0042] Basically, the ink jet head of the present invention can
have the same construction as the piezoelectric ink jet head
commonly used in the art and is not particularly limited so far as
the thin layer of the ferroelectric is used as the piezoelectric
element. Therefore, a suitable ink jet head is, for example, an ink
jet head which has been described above with reference to FIG.
1.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1 is a cross-sectional view showing a principal part of
a conventional piezoelectric ink jet head;
[0044] FIG. 2 is a schematic diagram showing the structure of an
oxide ceramic having a simple perovskite structure;
[0045] FIG. 3 is a flow sheet showing a process for producing lead
zirconate titanate (PZT) by the conventional sol-gel process;
[0046] FIG. 4 is a microphotograph showing a material in a crossed
stripe form formed on the surface of a thin layer of PZT in the
formation of the thin layer of PZT by the conventional liquid phase
process;
[0047] FIG. 5 is a flow sheet showing one preferred embodiment of
the process for producing an aqueous PZT precursor solution
according to the present invention;
[0048] FIG. 6 is a flow sheet showing one preferred embodiment of
the process for producing a thin layer of PZT using as a starting
material the aqueous PZT precursor solution prepared according to
the process as shown in FIG. 5;
[0049] FIG. 7 is a flow sheet showing the process for producing PZT
according to the present invention;
[0050] FIG. 8 is a flow sheet showing one preferred embodiment of
the process for producing a PZT paste, instead of the aqueous PZT
precursor solution, according to the present invention;
[0051] FIG. 9 is a cross-sectional view showing the steps of
forming a thin, composite PZT layer in sequence according to
another preferred embodiment of the present invention;
[0052] FIG. 10 is a graph showing an X-ray diffraction pattern of a
PZT powder prepared using hydroxypropyl cellulose as a thickener
according to the present invention;
[0053] FIG. 11 is a graph showing an X-ray diffraction pattern of a
comparative PZT powder prepared without use of any thickener;
[0054] FIG. 12 is a graph showing an X-ray diffraction pattern of a
thin layer of PZT prepared using hydroxypropyl cellulose as a
thickener according to the present invention;
[0055] FIG. 13 is a graph showing an X-ray diffraction pattern of a
thin layer of PZT prepared using polyethylene oxide as a thickener
according to the present invention;
[0056] FIG. 14 is a graph showing an X-ray diffraction pattern of a
thin layer of PZT prepared using polyvinyl alcohol as a thickener
according to the present invention.
[0057] FIG. 15 is a microphotograph showing the surface state of a
thin layer of PZT prepared using polyethylene glycol as an
association preventive according to the present invention; and
[0058] FIG. 16 is a microphotograph showing the surface state of a
comparative thin layer of PZT (as a control) prepared using
polyethylene glycol as the association preventive in a reduced
amount.
BEST MODE FOR CARRYING OUT THE INVENTION
[0059] Preferred embodiments of the present invention will be
described in more detail particularly with reference to lead
zirconate titanate (PZT). An embodiment wherein the ferroelectric
element of the present invention is used particularly as a
piezoelectric element of an ink jet head will be described.
However, it should be noted that the ferroelectric element can also
be advantageously applied to other devices.
[0060] The ferroelectric element according to the present invention
comprises a ferroelectric material containing at least two metals
and is produced by using, as starting materials, aqueous solutions
of the respective salts of metals constituting the ferroelectric.
Specifically, a thickener and/or an association preventive are
added to aqueous solutions of metal salts selected for the
ferroelectric, preferably aqueous solutions of metal oxides to
prepare an aqueous precursor solution, the aqueous precursor
solution is coated, either as such or, if necessary, after
preparation of a paste from the aqueous precursor solution, onto a
substrate, and the coating is dried and fired.
[0061] For example, a thin layer of PZT, which is a representative
example of the ferroelectric element of the present invention, may
be formed by preparing an aqueous solution of a salt of lead, an
aqueous solution of a salt of zirconium, and an aqueous solution of
a salt of titanium, mixing these aqueous solutions together to
prepare an aqueous PZT precursor solution, coating the aqueous
precursor solution onto a predetermined substrate, and then
subjecting the coating to treatment such as drying and firing.
[0062] The above series of steps for forming the thin layer of PZT
are described in more detail in FIGS. 5 and 6 (flow sheets) and
will be described below in sequence. One preferred embodiment of
each step will be described, but it will be understood that
variations and modifications can be effected within the spirit and
scope of the invention.
[0063] For the formation of a thin layer of PZT described herein,
three metal salts, lead nitrate (Pb(NO.sub.3).sub.2), zirconium
oxynitrate (ZrO(NO.sub.3).sub.2), and titanium isopropoxide
(Ti(O-i-C.sub.3H.sub.7).- sub.4), are used as the starting
compound.
[0064] Preparation of Aqueous Titanium Solution
[0065] A predetermined amount of titanium isopropoxide
(Ti(O-i-C.sub.3H.sub.7).sub.4) is dissolved in a 3 N aqueous nitric
acid solution, and the solution is stirred in a nitrogen atmosphere
to perform mixing. The reason why the mixing is performed in a
nitrogen atmosphere is that, when the mixing is performed in air,
titanium isopropoxide is insolubilized through a reaction with
moisture in air to produce TiO.sub.2. The mixing in a nitrogen
atmosphere gives a homogeneous aqueous titanium solution through
the following reaction
Ti(O-i-C.sub.3H.sub.7).sub.4+2H.sub.2O.fwdarw.Ti(OH).sub.4+4C.sub.3H.sub.7-
OH
[0066] Preparation of Aqueous Zirconium Solution
[0067] A predetermined amount of zirconium oxynitrate is dissolved
in pure water, and the solution is stirred to perform mixing. The
mixing gives a homogeneous aqueous zirconium solution through the
following reaction.
ZrO(NO.sub.3).sub.2+2H.sub.2O.fwdarw.Zr(OH).sub.4+2HNO.sub.3
[0068] Mixing
[0069] The aqueous titanium solution and the aqueous zirconium
solution prepared above are mixed together while stirring to
prepare a homogeneous solution.
[0070] Preparation of Aqueous Lead Solution
[0071] A predetermined amount of lead nitrate is dissolved in pure
water, and the solution is stirred to perform mixing. The mixing
gives a homogeneous aqueous lead solution through the following
reaction.
Pb(NO.sub.3).sub.2+2H.sub.2O.fwdarw.Pb(OH).sub.2+2HNO.sub.3
[0072] In this case, for example, another salt, such as lead
acetate, may be used instead of lead nitrate.
[0073] Preparation of Aqueous PZT Precursor Solution
[0074] The aqueous lead solution thus prepared is mixed with the
mixed aqueous solution, containing titanium and zirconium, prepared
above to prepare a homogeneous aqueous PZT precursor solution. The
concentration of the aqueous PZT precursor solution is not
particularly limited and may be widely varied by taking desired
results, film forming conditions and other various conditions, into
consideration. The present inventors have found that the
concentration of PZT in the aqueous PZT precursor solution is
preferably about 5 to 20% by weight, more preferably about 10% by
weight. The aqueous PZT precursor solution, as compared with the
conventional alcohol solution of the PZT precursor, is easy to
handle and is inexpensive. Thus, the series of steps shown in FIG.
5 are completed. Subsequently, the step of forming a thin layer of
PZT (see FIG. 6) is carried out.
[0075] Addition of Thickener and/or Association Preventive
[0076] A thickener and an association preventive are added, either
alone or in combination, to the aqueous PZT precursor solution
prepared above according to the present invention. These additives
may be added in any order. The thickener and the association
preventive will be described in more detail below.
[0077] After the addition of the necessary additive(s) has been
completed, the mixture is thoroughly stirred. Thus, a coating
solution for a thin layer of PZT is prepared. If desired, the
coating solution may be treated to prepare a paste.
[0078] Coating (Formation of Coating)
[0079] The coating solution or the paste prepared above is coated
on a predetermined substrate to form a desired pattern. The coating
may be performed by a conventional method, and examples of coating
methods usable herein include spin coating, dip coating, and screen
printing. An optimal coating method may be selected according to
the type of contemplated thin layer of PZT. Likewise, the coverage,
that is, the thickness of the coating formed, may be suitably
selected according to various factors. For example, a submicron
layer thickness after drying suffices for use of the resultant thin
layer of PZT as a memory, a capacitor and the like. On the other
hand, a layer thickness on the order of several tens of .mu.m
suffices for use of the thin layer of PZT as an actuator.
[0080] Driving
[0081] Subsequently, the coating thus formed is dried to cure the
coating and, at the same time, to remove excess water or the like
by evaporation. The drying temperature and time may be widely
varied. In general, however, the drying is performe d at about 100
to 200.degree. C. for about 5 to 30 min. For example, drying at
150.degree. C. for 10 min may be adopted. Defects, such as cracks,
are not created in the coating in the course of the step of drying.
Further, the step of degreasing and other conventional treatment
steps (not shown) may be interposed between the step of drying and
the step of firing.
[0082] Firing
[0083] Finally, the dried coating is fired. As with the step of
drying described above, the step of firing may be carried out by
any method commonly used in the art. The firing temperature is
preferably about 500 to 900.degree. C., more preferably about 700
to 800.degree. C. In general, firing at a temperature around
500.degree. C. can offer the desired results. The firing time may
be widely varied according to the relationship thereof with the
firing temperature or the like. In general, however, it is in the
range of about 1 to 60 min. A thin layer of PZT, which has high
density and is very high compact, is formed as a result of the
firing. As described above, when the firing temperature is low, a
problem of scattering of lead (Pb) during the firing can be
avoided. Therefore, a high-quality thin layer of PZT can be
obtained while maintaining the same composition (Pb:Zr:Ti:O ratio)
as that of the PZT precursor provided above.
[0084] The state in the course of the formation of the thin layer
of PZT is shown in FIG. 7. From comparison of FIG. 7 with FIG. 3
described above, it will be understood that the structure of the
gel according to the present invention is distinguished from that
of the conventional gel.
[0085] In the formation of the above thin layer of PZT, the
Pb:Zr:Ti:O ratio in the PZT precursor may be widely varied
according to the desired results. In order to provide the best
piezoelectric properties, as described above, it is recommended
that Pb:Zr:Ti:O be 1:0.53:0.47:3. In the present invention, when
the above composition ratio is adopted in the PZT precursor, the
ratio may be reproduced as it is in the thin layer of PZT, enabling
a thin layer of PZT, which is homogeneous, has high density and
possesses excellent piezoelectric properties, to be easily
provided.
[0086] Regarding the creation of defects, such as cracks or
pinholes, described above in connection with the prior art,
according to the present invention, addition of a PZT powder in
addition to the thickener and/or the association preventive in the
stage of preparing the aqueous PZT precursor solution can
effectively prevent the creation of the defects. In this case,
preferably, the PZT precursor is in the form of a paste rather than
an aqueous solution.
[0087] FIG. 8 shows a flow sheet of this preferred embodiment. The
procedure described above with reference to FIG. 5 may be repeated
up to the step at which the aqueous PZT precursor solution is
prepared. Next, as described above with reference to FIG. 6, the
thickener and/or the association preventive are added. The PZT
powder is added simultaneously with, before or after the addition
of these additives. The order of adding the above additives may be
properly varied according to the desired results and other factors.
PZT powders usable herein will be described in more detail
below.
[0088] After the addition of the necessary additives has been
completed, the mixture is placed in a milling device, for example,
a planetary ball mill, followed by milling for several minutes. If
necessary, the addition of the PZT powder may be carried out in the
step of milling. Thus, a homogeneous paste can be obtained which is
then coatable by screen printing or the like. Preferably, after
vacuum deaeration for several min by means of a rotary pump, the
paste is coated. The steps of coating, drying, and firing may be
carried out in the same manner as described above with reference to
FIG. 6.
[0089] In the practice of the present invention, the aqueous PZT
precursor solution may contain a thickener. Preferably, the
thickener may be added after the preparation of the aqueous
precursor solution. Functions of the thickener include, for
example, an improvement in crystallinity of the thin layer of PZT
and, when the PZT powder is also used, homogeneous dispersion of
the PZT powder. The thickener is often called a binder from the
viewpoint of the function. A suitable thickener is a water-soluble
polymeric material which can be heat-decomposed when the
temperature exceeds a predetermined temperature in the formation of
the element (that is, at the time of firing). Examples of
thickeners which can be advantageously used in the present
invention include, but are not limited to, hydroxyalkyl celluloses
with the number of carbon atoms in the alkyl group being preferably
2 to 4 (for example, hydroxypropyl cellulose), polyethylene oxide,
and polyvinyl alcohol. These thickener compounds may be used alone
or as a mixture of two or more. The amount of the thickener used
may be widely varied according to factors such as the desired
effects. In general, however, the amount is about 0.1 to 50% by
weight based on the total amount of the aqueous PZT precursor
solution. Preferably, when the thickener used is hydroxypropyl
cellulose, the amount thereof is generally 0.5 to 10% by weight
based on the total amount of the aqueous PZT precursor solution.
When the purpose of adding the thickener is to homogeneously
disperse the PZT powder, the amount of the thickener added may be
relatively large.
[0090] In the practice of the present invention, the association
preventive is used, either in combination with the thickener or
independently of the thickener, in the aqueous PZT precursor
solution. The association preventive, when contained in the aqueous
precursor solution, can be coordinated to a lead (Pb) element
contained in the aqueous solution to effectively prevent the
association of lead elements with each other which has been the
problem of the prior art. A suitable association preventive is a
water-soluble polyhydric alcohol, and examples of polyhydric
alcohols, which can be advantageously used in the present
invention, include, but are not limited to, diethylene glycol,
polyethylene glycol, and glycerin. These association preventives
may be used either alone or in combination. The amount of the
association preventive used may be widely varied according to
factors such as the desired effects. In general, however, the
amount is about 5 to 20% by weight based on the total amount of the
aqueous PZT precursor solution.
[0091] In the present invention, it is possible to attain not only
the effects inherent in the thickener and the association
preventive by the addition of these additives but also the effect,
described above, by the dissolution of the PZT precursor in water
instead of an alcohol. That is, the problem of the variation in
viscosity of the precursor due to the moisture in the air, which is
experienced in the use of an alcohol as the solvent, can be
avoided. Therefore, the precursor can be easily used in a very
stable state. Practice of the sol-gel process using this precursor
results in the formation of a thin layer of PZT which is dense and
possesses excellent piezoelectric properties.
[0092] In the practice of the present invention, when there is a
fear of cracks or pinholes being created due to the use of the
aqueous PZT precursor solution, or even though the above fear does
not exist, addition of another PZT powder having a crystal
structure identical or similar to the PZT, in addition to the
addition of the thickener and/or the association preventive, to the
aqueous PZT precursor solution is preferred. The PZT powder added
in this case can simultaneously exhibit various noteworthy
functions. For example, the PZT powder, when the PZT coating after
drying is fired, can reduce the shrinkage of the coating by the
volume of the powder added, leading to the prevention of cracking.
Further, addition of the PZT powder can increase the coverage of
PZT per coating step and hence can increase the thickness of the
thin layer of PZT. The amount of the PZT powder added may widely
vary according to factors such as the desired effects. In general,
however, the amount is about 5 to 20% by weight based on the total
amount of the aqueous PZT precursor solution. The above effects
have been described particularly with reference to the addition of
a PZT powder. Also in the production of ferroelectric elements
other than PZT, addition of a corresponding ferroelectric powder
can provide effects comparable favorably with the above
effects.
[0093] Further, in the practice of the present invention, as
described above, addition of the thickener in combination with the
PZT powder is preferred. Addition of the thickener enables the
viscosity of the PZT precursor paste to be controlled and hence can
control the thickness of the resultant thin layer of PZT. Addition
of the additives followed by agitating operation, such as milling,
permits the mixed PZT powder to be homogeneously dispersed.
Further, settling of the PZT powder can be effectively prevented.
Furthermore, the addition of the thickener can improve the
wettability of the substrate by the PZT paste and the adhesion of
the thin layer of PZT after firing to the substrate. When the
thickener is used in combination with the PZT powder, the amount of
the thickener used may vary widely depending upon the desired
viscosity, the desired effects and other factors in the paste. In
general, however, the amount is about 1 to 30% by weight based on
the total amount of the aqueous PZT precursor solution.
[0094] The addition of additional additives brings the PZT
precursor as the starting material in the form of a solution to a
paste. The resultant PZT paste may be coated by the above-described
methods, such as spin coating and dip coating. When the viscosity
is taken into consideration, however, coating may be advantageously
performed by screen printing and other methods commonly used in the
field of coating formation. Use of the screen printing enables the
PZT coating to be formed in a desired pattern and, at the same
time, can facilitate increasing the coating thickness.
[0095] Thus, addition of the PZT powder, in addition to the
thickener and/or the association preventive, to the aqueous PZT
precursor can provide a PZT paste which has excellent storage
stability and high PZT concentration. Use of this paste results in
the formation of a thin layer of PZT which is free from defects,
such as pinholes and cracks, and possesses excellent piezoelectric
properties.
[0096] According to another preferred embodiment of the present
invention, a ferroelectric element, such as a thin layer of PZT, is
produced by combining hydrothermal synthesis with the sol-gel
process. In this case, the hydrothermal synthesis is basically used
for the formation of a first layer (that is, a ferroelectric
substrate layer) of the ferroelectric element by the conventional
method. On the other hand, the sol-gel process is basically used
for the formation of a second layer (an upper ferroelectric layer)
of the ferroelectric element using as a starting material an
aqueous ferroelectric precursor solution containing at least a
thickener and/or an association preventive and optionally a
ferroelectric powder.
[0097] That is, the ferroelectric element according to this
preferred embodiment is characterized in that the upper
ferroelectric layer constituting the main part of the ferroelectric
element has, on the underside thereof, the ferroelectric substrate
layer which has a crystal structure identical or similar to the
ferroelectric material constituting the upper ferroelectric layer
and has been formed, from aqueous solutions of metals necessary for
the formation of the ferroelectric substrate layer, by hydrothermal
synthesis. In the above composite ferroelectric element,
preferably, the ferroelectric material for the ferroelectric
substrate layer, as compared with the ferroelectric material for
the upper ferroelectric layer, is constituted by particles having a
larger diameter and has lower density.
[0098] Preferably, the above composite ferroelectric element, for
example, a composite thin PZT layer, may be produced, for example,
by a process comprising steps shown in sequence in FIG. 9.
[0099] At the outset, as shown in the step A, a substrate 1 is
provided. For the substrate, the type, shape and the like may
widely vary depending upon the contemplated application of the
composite thin PZT layer and other factors. Suitable substrates
include, for example, conventional substrates, such as ceramic
substrates, for example, silicon substrates and titanium
substrates, and glass substrates. The substrate may have thereon a
layer, such as an insulating layer, wiring, or an electrode. In the
present embodiment, a titanium substrate is used.
[0100] Next, in the step B, a seed crystal layer 2 of PZT is formed
on the titanium substrate 1. The seed crystal layer 2 may be
formed, for example, by immersing the titanium substrate 1 in water
containing lead hydroxide (Pb(OH).sub.2) and zirconium hydroxide
(Zr(OH).sub.4) and heating the system in an autoclave at a
temperature of 140 to 200.degree. C.
[0101] After the formation of the seed crystal layer 2 has been
completed, in the step C, a first PZT layer (substrate layer) 3 is
further formed on the seed crystal layer 2. This PZT layer 3 may be
formed, for example, by immersing the titanium substrate 1, with
the seed crystal layer 2 formed thereon, in water containing
Pb(OH).sub.2, Zr(OH).sub.4, and titanium hydroxide (Ti(OH).sub.4)
and heating the system in an autoclave at a temperature of 80 to
150.degree. C. As a result, on the seed crystal layer 2 formed
above is formed a PZT layer 3, as shown in the drawing, which, as
compared with the seed crystal layer 2, is constituted by coarser
particles and has larger layer thickness. The PZT layer 3 is
advantageous in that an increase in the layer thickness is possible
at a low temperature and, in addition, the PZT layer 3 can develop
piezoelectricity immediately after the layer formation and has good
adhesion to the titanium substrate 1.
[0102] Finally, in the step D, a second PZT layer 4 is formed using
the aqueous PZT precursor solution or the paste according to the
present invention. Disposition of the PZT layer 4 on the first PZT
layer 3 can smoothen the roughened surface of the underlying PZT
layer 3. Since the surface of the composite thin PZT layer is
smooth, an electrode and the like may be easily formed thereon with
high reliability. In the case of the above two-layer structure, the
creation of defects, such as cracks or pinholes, can be prevented
in the composite thin PZT layer.
[0103] The ferroelectric element according to the present invention
can be advantageously used for constituting pressing means in a
piezoelectric ink jet head, that is, an ink jet head comprising: a
plurality of nozzles for ejecting an ink; an ink chamber,
communicating with the nozzles, for flow and pressurization of the
ink; and pressing means for creating a change in volume of the ink
in the ink chamber to eject the ink through the nozzle.
[0104] As described above, the ink jet head per se can have the
same construction as the piezoelectric ink jet head commonly used
in the art. The ink jet head of the present invention will be
described again with reference to FIG. 1.
[0105] An ink chamber 12 in an ink jet head 10 is provided in a
predetermined pattern in an ink chamber member 11. The ink chamber
member 11 may be made of various materials according to factors
such as the method for forming the ink chamber 12. One embodiment
of the ink chamber member 11 will be described. For example, glass,
a plastic material, for example, a polyester resin (such as PET),
an acrylic resin (such as PMMA), quartz, or other substrate is
provided, and a resin material may be then patterned onto the
substrate by photolithography or another method to form a groove
corresponding to the ink chamber.
[0106] In the ink chamber member 11 shown in the drawing, a
diaphragm 15 for creating a change in volume of the ink chamber 12
(one constituent element of pressing means referred to in the
present invention) is provided on the open face of the ink chamber
12. The diaphragm 15 may be integrally molded with the ink chamber
member 11 at the time of formation of the ink chamber member 11.
Otherwise, it may be bonded to the ink chamber member 11 with the
aid of an adhesive. Suitable materials for the diaphragm 15
include, for example, ceramics having high rigidity, for example,
ZrO.sub.2. The remaining elements of the pressing means are
attached so as to abut against the diaphragm 15.
[0107] In the case of the embodiment shown in the drawing, the
remaining elements of the pressing means are a piezoelectric
element 17 as a drive for distorting the diaphragm 15 and an upper
electrode 16 and a lower electrode 18 which sandwich the
piezoelectric element 17 therebetween and, when necessary, can
apply a voltage. The piezoelectric element 17 may be formed by the
above process according to the present invention. The electrodes 16
and 18 each may be formed in a desired pattern by a conventional
method, for example, sputtering, screen printing, or vapor
deposition.
[0108] The ink jet head shown in the drawing may be operated as
follows. An ink is fed into the ink chamber 12 through an ink feed
port (not shown) of the head 10 to fill the ink chamber 12 with the
ink. In this state, application of a voltage across the electrodes
16 and 18 creates a displacement of the piezoelectric element 17
sandwiched between these electrodes due to the piezoelectric
properties, permitting the diaphragm 15 disposed so as to abut
against the piezoelectric element 17 to be pushed out towards the
ink chamber 12. This reduces the volume of the ink filled into the
ink chamber 12, leading to ejection of the ink in a dot form in an
amount corresponding to the reduction of the volume through a
nozzle (not shown) communicating with the ink chamber 12.
EXAMPLES
[0109] The present invention will be described in more detail with
reference to the following examples. It should be understood that
the present invention is not limited to these examples only.
Example 1
[0110] 0.014 mol of titanium tetraisopropoxide was dissolved in 30
g of a 3 N aqueous nitric acid solution to prepare an aqueous
titanium solution. Separately, 0.016 mol of zirconium oxynitrate
was dissolved in 20 g of pure water to prepare an aqueous zirconium
solution. Further, 0.03 mol of lead nitrate was dissolved in 20 g
of pure water to prepare an aqueous lead solution.
[0111] The three aqueous solutions thus prepared were mixed
together to prepare an aqueous PZT precursor solution. In this
connection, it should be noted that the ratio of Zr to Ti in PZT is
closely related to the ferroelectricity. Therefore, in the
preparation of the aqueous solutions followed by mixing of these
aqueous solutions, this has been taken into consideration, and the
preparation and mixing were performed so that the finally formed
thin layer of PZT had a desired composition ratio
(Pb:Zr:Ti:O=1:0.53:0.47:3).
[0112] At the outset, the aqueous titanium solution and the aqueous
zirconium solution were thoroughly mixed together at room
temperature while stirring. After the completion of the stirring,
the mixture was mixed with the aqueous lead solution. The resultant
mixture was thoroughly stirred at room temperature and then heated
under reflux at a temperature of 100.degree. C. or above to conduct
hydrolysis. Metal ions contained in each aqueous solution, when the
aqueous solutions were mixed together at room temperature, merely
formed corresponding metal hydroxides, and the degree of bonding
among the metal ions was small. Subsequent reflux and hydrolysis,
however, permit the metal ions, that is, titanium, zirconium, and
lead ions, to be bonded to one another through oxygen. In this
case, a Pb--O--Ti--O--Zr bond is formed to bring the system to a
sol. In the present invention, the aqueous solution in this sol
state is expressly called an "aqueous PZT precursor solution."
[0113] After the temperature of the aqueous PZT precursor solution
was returned to room temperature, water and a small amount (about
0.5% by weight) of hydroxypropyl cellulose were added thereto,
followed by thorough mixing with stirring at room temperature for
about one hour. As a result, a transparent, homogeneous solution
was obtained which was neither cloudy nor contained any
precipitate.
[0114] In this connection, it was confirmed that hydroxypropyl
cellulose added to the aqueous PZT precursor solution has various
effects. Specifically, hydroxypropyl cellulose increases the
viscosity of the aqueous PZT precursor solution having relatively
low viscosity and, when the aqueous PZT precursor solution is
coated on the substrate in the step of coating, enables the
formation of a coating having large thickness. Not only has
hydroxypropyl cellulose the effect of increasing the viscosity, but
also the effect of strengthening the Pb--O--Ti--O--Zr bond and the
effect of reducing the distance among the metal ions. Although the
reason why these effects can be attained has not been fully
elucidated yet, according to studies conducted by the present
inventors, it is believed that the metal ions and oxygen are
intertwined with hydroxypropyl cellulose as the backbone, leading
to the above effects. As a result, the firing temperature in the
layer formation can be lowered, resulting in improved crystallinity
of the thin layer.
[0115] The results of an experiment conducted by the present
inventors to confirming the above excellent effects of
hydroxypropyl cellulose will be described.
[0116] The aqueous PZT precursor solution prepared as described
above was placed in a crucible and fired at a predetermined
temperature for a given period of time. As a result, a light-yellow
PZT powder (sample 1) was obtained. For comparison, a light-yellow
PZT powder (sample 2) was prepared in the same manner as described
above, except that hydroxypropyl cellulose (thickener) was not
used. For the samples, the X-ray diffraction pattern was measured.
The results were as shown in FIG. 10 (sample 1) and FIG. 11 (sample
2).
[0117] In the X-ray diffraction patterns shown in FIGS. 10 and 11,
a peak around an X-ray diffraction angle 2.theta.=29.degree. is
one, derived from a pyrochlore layer which appears when the
crystallization of PZT is unsatisfactory. The crystallinity of PZT
can be quantitatively determined by comparing the intensity of this
peak with the peak intensity of the (101) face having the highest
diffraction intensity among the PZT diffraction peaks. For sample 1
(FIG. 10) which is an example of the present invention, the
proportion of the pyrochlore layer was 1.3%, whereas for sample 2
(FIG. 11) which is a comparative example, the proportion of the
pyrochlore layer was 11.6%. This indicates that addition of
hydroxypropyl cellulose as the thickener can provide a more
complete PZT crystal.
Example 2
[0118] A thin layer of PZT was formed from the aqueous PZT
precursor solution prepared in Example 1, and the thin layer of PZT
was incorporated as a piezoelectric element into a piezoelectric
ink jet head having a structure shown in FIG. 1.
[0119] A diaphragm of a thin ceramic sheet was prepared, and a
platinum electrode was formed in a predetermined area by
sputtering. Further, the aqueous PZT precursor solution prepared in
Example 1 was spin-coated at 2000 rpm onto the platinum electrode.
The PZT coating on the platinum electrode was dried at 150.degree.
C. for 10 min and further pre-fired at 550.degree. C. for one hr.
As a result of the pre-firing, hydroxypropyl cellulose contained in
the PZT coating was decomposed and scattered.
[0120] The PZT coating on the platinum electrode was then fired at
700.degree. C. for one min. This allowed the crystallization of PZT
to proceed and a thin layer of PZT having a perovskite structure
was obtained. This thin layer of PZT had good adhesion to the
platinum electrode and the diaphragm and further exhibited
satisfactory adhesion in the sputtering of an additional platinum
electrode on the thin layer of PZT. Further, since a relatively low
temperature can be applied to the firing of the thin film of PZT,
the range of selection of the underlying diaphragm can be
broadened.
[0121] FIG. 12 shows an X-ray diffraction pattern of the thin layer
of PZT thus formed. In the X-ray diffraction pattern, no
diffraction peak other than peaks derived from PZT is observed,
indicating that the layer formed on the platinum electrode is a
thin layer of PZT.
Example 3
[0122] The procedure of Example 2 was repeated, except that, in the
preparation of the aqueous PZT precursor solution in the same
manner as in Example 1, polyethylene oxide (sample 3) and polyvinyl
alcohol (sample 4) were used as a thickener instead of
hydroxypropyl cellulose. As a result, satisfactory thin layers of
PZT comparable with the thin layer of PZT formed in Example 2 could
be formed.
[0123] The X-ray diffraction patterns of the thin layers of PZT
thus formed were as shown in FIG. 13 (sample 3) and FIG. 14 (sample
4). The thickness of the thin layers of PZT was so small that, in
these X-ray diffraction patterns, peaks derived from the platinum
electrode could be observed around diffraction angles, 2.theta., of
40.degree., 47.degree., and 67.degree.. Peaks other than the peaks
derived from platinum were only those derived from PZT, indicating
that the formed layer was a thin layer of PZT.
Example 4
[0124] 0.014 mol of titanium tetrachloride was dissolved in aqueous
ammonia, and the resultant titanium hydroxide was collected by
filtration and washed. The titanium hydroxide was dissolved in a 3
N aqueous nitric acid solution to prepare an aqueous titanium
solution. Separately, 0.016 mol of zirconium oxynitrate was
dissolved in 20 g of pure water to prepare an aqueous zirconium
solution. Further, 0.03 mol of lead nitrate was dissolved in 20 g
of pure water to prepare an aqueous lead solution.
[0125] The three aqueous solutions thus prepared were mixed
together to prepare an aqueous PZT precursor solution. At the
outset, the aqueous titanium solution and the aqueous zirconium
solution were thoroughly mixed together at room temperature while
stirring. After the completion of the stirring, the mixture was
mixed with the aqueous lead solution. The resultant mixture was
thoroughly stirred at room temperature and then heated under reflux
at a temperature of 100.degree. C. or above to conduct hydrolysis.
After the temperature of the resultant aqueous PZT precursor
solution was returned to room temperature, water and a small amount
(about 0.5% by weight) of hydroxypropyl cellulose were added
thereto, followed by thorough mixing with stirring at room
temperature for about one hr. As a result, a transparent,
homogeneous solution was obtained which was neither cloudy nor
contained any precipitate.
Example 5
[0126] A thin layer of PZT was formed from the aqueous PZT
precursor solution prepared in Example 4, and the thin layer of PZT
was incorporated as a piezoelectric element into a piezoelectric
ink jet head having a structure shown in FIG. 1.
[0127] A diaphragm of a thin ceramic sheet was prepared, and a
platinum electrode was formed in a predetermined area by
sputtering. Further, the aqueous PZT precursor solution prepared in
Example 4 was spin-coated at 2000 rpm onto the platinum electrode.
The PZT coating on the platinum electrode was dried at 150.degree.
C. for 10 min and further pre-fired at 500.degree. C. for one hr.
As a result of the pre-firing, hydroxypropyl cellulose contained in
the PZT coating was decomposed and scattered.
[0128] The PZT coating on the platinum electrode was then fired at
650.degree. C. for one hr. This allowed the crystallization of PZT
to proceed and a thin layer of PZT having a perovskite structure
was obtained. This thin layer of PZT had good adhesion to the
platinum electrode and the diaphragm and further exhibited
satisfactory adhesion in the sputtering of an additional platinum
electrode on the thin layer of PZT.
Example 6
[0129] In this example, lead nitrate (Pb(NO.sub.3).sub.2),
zirconium oxynitrate (ZrO(NO.sub.3).sub.2), and titanium
isopropoxide (Ti(O-i-C.sub.3H.sub.7).sub.4) were used as starting
compounds.
[0130] At the outset, 4.03 g of titanium isopropoxide was dissolved
in and mixed with 23.3 g of a 2.8 N aqueous nitric acid solution
while stirring in a nitrogen atmosphere to give an aqueous titanium
solution. Separately, 4.27 g of zirconium oxynitrate was dissolved
in and mixed with 18 g of pure water while stirring to give an
aqueous zirconium solution. After the preparation of the aqueous
titanium solution and the aqueous zirconium solution, these aqueous
solutions were mixed together while stirring to prepare a
homogeneous solution. Separately, 10 g of lead nitrate was
dissolved in and mixed with 32 g of pure water while stirring. The
resultant aqueous lead solution was then mixed with the mixed
aqueous solution containing titanium and zirconium while stirring.
Finally, 10% by weight, based on the resultant mixture, of
polyethylene glycol (weight average molecular weight=200) was added
to the mixture. Thus, a homogeneous aqueous PZT precursor solution
was prepared.
[0131] In the aqueous PZT precursor solution prepared above, the
PZT concentration was 9% by weight, and the composition (molar
ratio of metal elements contained) was Pb:Zr:Ti=1:0.53:0.47. Among
a number of PZTs, the PZT having this molar ratio offered the
maximum values respectively for the permittivity, the piezoelectric
constant and the like.
[0132] The aqueous PZT precursor solution prepared above was then
spin-coated on a Pt/Ti/Si substrate, and the coating was dried at
150.degree. C. for 10 min, pre-fired at 500.degree. C. for 60 min,
and fired at 800.degree. C. for 60 min. As a result, a dense thin
layer of PZT having a thickness of 100 nm was formed. The thin
layer of PZT was examined, and, as a result, precipitation of a
material in a stripe form on the surface of the thin layer was not
observed.
[0133] Further, in order to evaluate a change in the aqueous PZT
precursor solution with the elapse of time, the aqueous PZT
precursor solution was allowed to stand in air at room temperature
for one month. As a result, no change occurred. Since polyethylene
glycol used as the association preventive in this example has
already been found, by TG-DTA (thermogravimetry-differential
thermal analysis), to be a material which could be degreased at
300.degree. C., it is considered that degreasing could be fully
achieved in the step of pre-firing.
Example 7
[0134] The procedure of Example 6 was repeated, except that, in the
preparation of the aqueous lead solution, lead acetate, instead of
lead nitrate, was used in the same amount. As a result, a
satisfactory thin layer of PZT comparable with the thin layer of
PZT formed in Example 6 was formed.
Example 8
[0135] In order to evaluate the influence of an association
preventive on lead (Pb) in an aqueous PZT precursor solution, the
procedure of Example 6 was repeated, except that the amount of
polyethylene glycol used as the association preventive was reduced
from 10% by weight to 5% by weight. As a result, unlike Example 6
(amount of association preventive used: 10% by weight) wherein no
association of lead was observed, in this example (amount of
association preventive used: 5% by weight), the association of lead
was significant.
[0136] The above results indicate that, since polyethylene glycol
used here has an average molecular weight of 200 and a
monomolecular weight of 63, a large amount of tetramer exists. In
this case, regarding the length of the molecule, Pb.sup.2+ is 1.2
.ANG., while polyethylene glycol in a tetramer form is several tens
of .ANG.. That is, the polyethylene glycol molecule is considerably
longer than Pb.sup.2+. It is considered that several molecules of
Pb.sup.2+ are coordinated to one molecule of polyethylene glycol,
preventing the association of Pb.
Example 9
[0137] The procedure of Example 6 was repeated, except that
glycerin was used instead of polyethylene glycol as the association
preventive. As a result, a 100 nm-thick, dense, thin layer of PZT
free from precipitation of a material in a stripe form was
formed.
[0138] Further, the procedure of Example 8 was repeated. The
results of evaluation indicate that, although there is a slight
difference, as with Example 6, the association of lead could be
effectively prevented.
Example 10
[0139] The procedure of Example 6 was repeated, except that
diethylene glycol was used instead of polyethylene glycol as the
association preventive. As a result, a 100 nm-thick, dense, thin
layer of PZT free from precipitation of a material in a stripe form
was formed.
[0140] Further, the procedure of Example 8 was repeated. The
results of evaluation indicate that, although there is a slight
difference, as with Example 6, the association of lead could be
effectively prevented.
Example 11
[0141] In this example, lead nitrate (Pb(NO.sub.3).sub.2),
zirconium oxynitrate (ZrO(NO.sub.3).sub.2), and titanium
isopropoxide (Ti(O-i-C.sub.3H.sub.7).sub.4), were used as starting
compounds.
[0142] At the outset, 4.03 g of titanium isopropoxide was dissolved
in and mixed with 23.3 g of a 2.8 N aqueous nitric acid solution
while stirring in a nitrogen atmosphere to give an aqueous titanium
solution. Separately, 4.27 g of zirconium oxynitrate was dissolved
in and mixed with 18 g of pure water while stirring to give an
aqueous zirconium solution. After the preparation of the aqueous
titanium solution and the aqueous zirconium solution, these aqueous
solutions were mixed together while stirring to prepare a
homogeneous solution. Separately, 10 g of lead nitrate was
dissolved in and mixed with 32 g of pure water while stirring. The
resultant aqueous lead solution was then mixed with the mixed
aqueous solution containing titanium and zirconium while stirring.
Finally, 10% by weight, based on the resultant mixture, of
polyethylene glycol (weight average molecular weight=200) was added
to the mixture. Thus, a homogeneous aqueous PZT precursor solution
was prepared.
[0143] In the aqueous PZT precursor solution prepared above, the
PZT concentration was 9% by weight, and the composition (molar
ratio of metal elements contained) was Pb:Zr:Ti=1:0.53:0.47. Among
a number of PZTs, the PZT having this molar ratio offered the
maximum values respectively for the permittivity, the piezoelectric
constant and the like.
[0144] To the aqueous PZT precursor solution were added a PZT
powder having the same composition as the PZT and hydroxypropyl
cellulose (as a binder) each in an amount of 10% by weight based on
the aqueous PZT precursor solution. The mixture was milled by means
of a planetary ball mill for 3 min to prepare a PZT precursor
paste.
[0145] The PZT precursor paste thus prepared was coated on a
Pt/Ti/Si substrate by using a metal mask and a doctor blade, and
the coating was dried at 150.degree. C. for 10 min, degreased at
500.degree. C. for 60 min, and fired at 800.degree. C. for 60 min.
As a result, a 3 .mu.m-thick, dense, thin layer of PZT was formed.
The thin layer of PZT was examined and found to be free from
cracking.
[0146] Thin layers of PZT having varied thicknesses (2 to 4 .mu.m)
were formed in the same manner as described above, except that the
amount of polyethylene glycol (used in an amount of 10% by weight
in the above case) and the amount of the PZT powder (used in an
amount of 10% by weight in the above case) were varied. As a
result, as with the above case, crack-free, dense, thin layers of
PZT could be formed.
[0147] FIG. 15 is a microphotograph (magnification: 20.times.)
showing the surface appearance of the thin layer of PZT (thickness
3 .mu.m) thus formed. From this microphotograph, it is apparent
that the surface of the thin layer of PZT is free from cracks,
pinholes, and material in a stripe form.
[0148] Further, in order to evaluate a change in the aqueous PZT
precursor solution with the elapse of time, the aqueous PZT
precursor solution was allowed to stand in the air at room
temperature for one month. As a result, no change occurred. Since
polyethylene glycol used as the association preventive in this
example has already been found, by TG-DTA, to be a material which
could be degreased at 300.degree. C., it is considered that
degreasing could be fully achieved in the step of degreasing.
Example 12
[0149] In order to evaluate the influence of an association
preventive on lead (Pb) in an aqueous PZT precursor solution, the
procedure of Example 11 was repeated, except that the amount of
polyethylene glycol used as the association preventive was reduced
from 10% by weight to 5% by weight. As a result, unlike Example 11
(amount of association preventive used: 10% by weight) wherein no
association of lead was observed, in this example (amount of
association preventive used: 5% by weight), the association of lead
was significant. The large number of defects in a stripe form
appearing on the microphotograph (magnification: 20.times.) of the
thin layer of PZT shown in FIG. 16 demonstrates the association of
lead. Regarding the prevention of the association of Pb, the
description in Example 8 is true of this example.
Example 13
[0150] The procedure of Example 11 was repeated, except that the
PZT precursor paste was coated using a spatula instead of the
doctor blade. As a result, as with Example 11, a crack-free, dense,
thin layer of PZT (layer thickness 3 .mu.m) was formed. The crystal
structure of the thin layer of PZT was examined by X-ray
diffractometry and found to be constituted by a single phase of
PZT.
Example 14
[0151] The procedure of Example 11 was repeated, except that
diethylene glycol was used instead of polyethylene glycol as the
association preventive. As a result, as with Example 11, a dense,
thin layer of PZT (layer thickness 3 .mu.m) free from precipitation
of a material in a stripe form and a crack was formed. This
demonstrates that, as with use of polyethylene glycol (Example 11),
use of diethylene glycol as the association preventive results in
the preparation of a highly stable ferroelectric precursor and, in
addition, coating of the precursor onto a substrate followed by
firing can provide a ferroelectric element which is dense and
possesses excellent piezoelectric properties.
Example 15
[0152] The procedure of Example 11 was repeated, except that
glycerin was used instead of polyethylene glycol as the association
preventive. As a result, as with Example 11, a crack-free, dense,
thin layer of PZT (layer thickness 3 .mu.m) free from precipitation
of a material in a stripe form was formed. This demonstrates that,
as with use of polyethylene glycol (Example 11), use of glycerin as
the association preventive results in the preparation of a highly
stable ferroelectric precursor and, in addition, coating of the
precursor onto a substrate followed by firing can provide a
ferroelectric element which is dense and possesses excellent
piezoelectric properties.
Example 16
[0153] This example demonstrates the formation of a composite thin
layer of PZT.
[0154] A first thin layer of PZT (substrate layer) was first
prepared according to the following procedure. A solution of
0.00682 mol of lead nitrate in water, a solution of 0.00273 mol of
zirconium oxychloride in water, and a solution of 0.05 mol of
potassium hydroxide in water were mixed together. A titanium
substrate was immersed in the mixed solution, followed by
hydrothermal treatment at 150.degree. C. for 24 hr. As a result, a
crystal nucleus of PZT was produced on the surface of the titanium
substrate. Separately, a solution of 0.00682 mol of lead nitrate in
water, a solution of 0.00273 mol of zirconium oxychloride in water,
a solution of 0.00252 mol of titanium tetrachloride in water, and a
solution of 0.05 mol of potassium hydroxide in water were mixed
together, and the titanium substrate with a PZT crystal nucleus
prepared in the above step was then immersed in the resultant mixed
solution, followed by hydrothermal treatment at 120.degree. C. for
48 hr. Thus, a first thin layer of PZT having an average particle
diameter of 5 .mu.m and a very poor surface smoothness was
obtained.
[0155] Subsequently, on the first thin layer of PZT, formed on the
titanium substrate, was formed a second thin layer of PZT from an
aqueous PZT precursor solution by the sol-gel process according to
the following procedure.
[0156] At the outset, 0.014 mol of titanium tetraisopropoxide was
dissolved in 30 g of a 3 N aqueous nitric acid solution to prepare
an aqueous titanium solution. Separately, 0.016 mol of zirconium
oxynitrate was dissolved in 20 g of pure water to prepare an
aqueous zirconium solution. Further, 0.03 mol of lead nitrate was
dissolved in 20 g of pure water to prepare an aqueous lead
solution. In this connection, it should be noted that the ratio of
Zr to Ti in PZT is closely related to the ferroelectricity and this
ratio is determined by the molar ratio of the corresponding metal
salts. Therefore, the aqueous solutions of respective metal salts
were prepared so that mixing was performed in a desired molar
ratio.
[0157] The aqueous titanium solution and the aqueous zirconium
solution were thoroughly mixed together at room temperature while
stirring, and the aqueous lead solution was then added to and mixed
with the mixture. The present inventors have found that in
practicing the present invention, the addition of aqueous metal
salt solutions in the above order is preferred. The resultant
mixture was thoroughly stirred at room temperature and then heated
under reflux at a temperature of 100.degree. C. or above to conduct
hydrolysis. Metal ions contained in each aqueous metal salt
solution, when the aqueous solutions were mixed together at room
temperature, merely formed metal hydroxides corresponding to
respective metal ions, and the degree of bonding among the metal
ions was small. Subsequent reflux and hydrolysis, however,
permitted the metal ions, that is, titanium, zirconium, and lead
ions, to be bonded to one another through oxygen. In this case, a
Pb--O--Ti--O--Zr bond was formed to bring the system to a sol. In
the present invention, the aqueous solution in this sol stage is an
aqueous PZT precursor solution referred to in the present
invention.
[0158] The temperature of the aqueous precursor solution was
returned to room temperature, water and a small amount of
hydroxypropyl cellulose were added dropwise thereto, followed by
thorough mixing with stirring. In this case, the purpose of adding
hydroxypropyl cellulose is to increase the viscosity of the aqueous
PZT precursor solution having relatively low viscosity and to
enable the formation of a coating having large thickness in the
coating of the aqueous PZT precursor solution on the substrate. Not
only has hydroxypropyl cellulose the effect of increasing the
viscosity, but also the effect of strengthening the
Pb--O--Ti--O--Zr bond and the effect of reducing the distance among
the ions. This can lower the firing temperature in the layer
formation and in addition can improve the crystallinity of the
layer. The aqueous PZT precursor solution after the addition of
hydroxypropyl cellulose was a transparent, homogeneous solution
which was neither cloudy nor contained any precipitate.
[0159] The aqueous PZT precursor solution thus prepared was
spin-coated onto the substrate with the first thin layer of PZT
formed above. In this case, the aqueous PZT precursor solution
coated on the substrate with the first thin layer of PZT is in the
uncrystallized state. Therefore, the coating was dried at
150.degree. C. for 10 min and once fired at a temperature of
500.degree. C. or above to decompose hydroxypropyl cellulose as the
additive.
[0160] After the completion of the firing for the decomposition of
hydroxypropyl cellulose, the substrate was fired at 650.degree. C.
for one hr, thereby forming a second PZT structure having
significantly enhanced surface smoothness. Thus, a more dense,
composite thin layer of PZT was obtained which had no boundary
between the first thin layer and the second thin layer.
[0161] In the production of an ink jet head, the thin layer of PZT,
which has been formed through the above series of steps, has good
adhesion to a diaphragm and an electrode to be jointed to a
piezoelectric element comprising the thin layer of PZT, so that
they can be integrally bonded without the aid of any adhesive. Use
of the hydrothermal synthesis with the sol-gel process can bring
the firing temperature to a relatively lower value than that in the
case of the conventional solid phase process. Therefore, the range
of selection of the diaphragm as the substrate can be
broadened.
Example 17
[0162] The procedure of Example 16 was repeated, except that the
second thin layer of PZT was formed according to the following
procedure.
[0163] 0.014 mol of titanium tetrachloride was dissolved in aqueous
ammonia, and the resultant titanium hydroxide was collected by
filtration and washed. The collected titanium hydroxide was
dissolved in a 3 N aqueous nitric acid solution to prepare an
aqueous titanium solution. Separately, 0.016 mol of zirconium
oxynitrate was dissolved in 20 g of pure water to prepare an
aqueous zirconium solution. Further, 0.03 mol of lead nitrate was
dissolved in 20 g of pure water to prepare an aqueous lead
solution.
[0164] The aqueous titanium solution and the aqueous zirconium
solution were thoroughly mixed together at room temperature while
stirring. The aqueous lead solution was added to and mixed with the
mixture. The mixed solution was thoroughly stirred at room
temperature and heated under reflux at a temperature of 100.degree.
C. or above to conduct hydrolysis. The temperature of the resultant
mixed solution after the hydrolysis was returned to room
temperature, water and a minor amount of hydroxypropyl cellulose
were added dropwise thereto, followed by thorough mixing with
stirring. As a result, a homogeneous PZT solution was obtained.
[0165] The PZT solution thus prepared was spin-coated onto the
titanium substrate with the first thin layer of PZT formed above.
The coating was dried at 150.degree. C. for 10 min and once fired
at a temperature of 500.degree. C. or above to decompose
hydroxypropyl cellulose as the additive. Finally, firing was
performed at 650.degree. C. for one hr, thus completing the
formation of a second thin layer of PZT.
[0166] As with the composite thin layer of PZT prepared in Example
16, the composite thin layer of PZT prepared in this example was
satisfactory.
Industrial Applicability
[0167] According to the present invention, aqueous solutions of
respective metal oxides constituting a ferroelectric material are
prepared and mixed together to prepare a mixed solution as a
ferroelectric precursor, and additives characteristic of the
present invention, such as a thickener and an association
preventive, are added. This constitution can offer many advantages
unexpected from the prior art. For example, according to the
present invention, the use of the aqueous metal oxide solution as
the ferroelectric precursor is advantageous in that handling and
preparation are easy and, in addition, the storage stability of the
starting compound solution is excellent, addition of an association
preventive can enhance the stability of the precursor, a
ferroelectric element can be easily produced at low cost and can be
formed as a thin layer, and, since particles on the surface of the
thin layer are fine and dense, excellent surface smoothness can be
realized.
[0168] Further, according to the present invention, addition of a
ferroelectric powder, an organic binder and the like to prepare a
precursor paste followed by the formation of a thin layer of a
ferroelectric can prevent the creation of defects, such as
precipitation of a material in a stripe form, on the surface of the
thin layer of a ferroelectric, can provide a dense, homogeneous,
thin layer of a ferroelectric, ensuring excellent piezoelectric
properties. In addition, this can prevent the creation of cracking
on the surface of the thin layer.
[0169] Furthermore, according to the present invention, stacking of
a second thin layer of a ferroelectric prepared by the sol-gel
process on a first thin layer of a ferroelectric prepared by
hydrothermal synthesis enables the thickness of the ferroelectric
element to be increased while maintaining the features of the
ferroelectric element of the present invention and, in addition,
can offer good adhesion to the underlying substrate.
[0170] In addition, application of the ferroelectric element of the
present invention as a piezoelectric element to a piezoelectric ink
jet head can, of course, offer excellent piezoelectric properties
and, further, permits an electrode to be easily formed on the
piezoelectric element without creating any defect.
* * * * *