Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2000-11-01
2003-02-25
Vo, Anh T. N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06523943
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric element, which is used, for example, as an actuator for changing capacity of ink chamber in order to jet ink filled in the ink chamber from an ink nozzle through an ink passage in an ink-jet printer head, a process for producing the piezoelectric element, and an ink-jet printer head which is constructed using the piezoelectric element.
2. Prior Art
An ink-jet printer head is generally composed of a head base, a diaphragm, and an actuator. A part of the head is enlargedly and schematically shown in
FIG. 7. A
head base
11
is provided with a large number of ink nozzles for jetting ink, a large number of ink passages separately communicating to the respective ink nozzles, and a large number of ink chambers
12
separately communicating to the respective ink passages. (
FIG. 7
shows only one of the ink chambers
12
, and illustration of the ink passages and the ink nozzles is omitted.) A diaphragm
13
is mounted so as to cover the whole upper face of the head base
11
, and the diaphragm
13
closes upper face openings of all the ink chambers
12
of the head base
11
. On the diaphragm
13
, piezoelectric elements
15
for giving a vibration driving force to the diaphragm
13
are mounted and formed on positions separately corresponding to the respective ink chambers
12
. A power source
19
of an actuator
14
provided with a large number of piezoelectric elements
15
is controlled and voltage is applied to a desired and selected piezoelectric element
15
, whereby the piezoelectric element
15
is displaced and the part of the diaphragm
13
is vibrated. As a result, capacity of an ink chamber
12
located at the part corresponding to the vibration of the diaphragm
13
is changed, and ink is pushed out from the ink nozzle through the ink passage.
Each of the piezoelectric elements
15
is constructed by forming a piezoelectric film
17
on a surface of a lower electrode
16
, and forming an upper electrode
18
on a surface of the piezoelectric film
17
so as to sandwich the piezoelectric film
17
between the lower electrode
16
and the upper electrode
18
. The piezoelectric film
17
is generally made of lead titanate zirconate (Pb(Zr, Ti)O
3
; PZT) or made of a material mainly composed of the composite oxide. The piezoelectric film
17
having such composition is formed by sputtering method, vacuum deposition method, CVD method, laser ablation method, sol-gel method, thick film method (a method using piezoelectric paste), and so on.
For example, the Japanese Patent Publication (unexamined) No. 92897/1997, the Japanese Patent Publication (unexamined) No. 139594/1998, and the Japanese Patent Publication (unexamined) No. 290035/1998 disclose a process for forming a piezoelectric film of a piezoelectric element used in an ink-jet printer head utilizing sol-gel method by applying sol, which contains a piezoelectric material, over and over onto a lower electrode and repeating a heating process.
The Japanese Patent Publication (unexamined) No. 92897/1997 describes the piezoelectric element in which the lower electrode and the piezoelectric film are tightly fitted by arranging such that at least one of A and B may show a maximum value in concentration at the interface between the piezoelectric film having composition of PbZrO
3
/PbTiO
3
/Pb(A
x
B
y
)O
3
(x+y=1; A:Mg and so on, B:Nb and so on) and the lower electrode. The Japanese Patent Publication (unexamined) No. 139594/1998 describes an art of forming the piezoelectric film from a basic layer made of a ternary system piezoelectric member of lead-magnesium-niobate (PMN), lead zirconate and lead titanate, and a partial layer made of a binary system piezoelectric member of lead zirconate and lead titanate which is crystallized at a lower temperature as compared with the basic layer in order to prevent decrease in piezoelectric strain constant value even when the film is thick. The Japanese Patent Publication (unexamined) No. 290035/1998 describes a piezoelectric element in which a lower layer PZT film is formed on the lower electrode using sol-gel method, and thereafter, the lower layer PZT film is pre-annealed, the lower layer PZT film is crystallized so that titanium and lead may be crystallized faster than zirconium from the lower electrode side and that zirconium may easily segregate on the film surface, an upper layer PZT film is formed on the lower layer PZT film using sol-gel method, the PZT films are annealed, the upper layer PZT film is crystallized so that titanium and lead may be crystallized faster than zirconium from the lower layer PZT film side and that zirconium may easily segregate on the film surface, whereby, concentration of contained zirconium is lower on the lower electrode side and higher on the upper electrode side and concentration of contained titanium is higher on the lower electrode side and lower on the upper electrode side in each of the lower layer PZT film and the upper layer PZT film, and the dielectric constant of the piezoelectric film is lowered keeping the piezoelectric strain constant of the piezoelectric film in order to decrease capacitance and lower calorific value.
As disclosed in the Japanese Patent Publication (unexamined) No. 92897/1997, the Japanese Patent Publication (unexamined) No. 139594/1998, and the Japanese Patent Publication (unexamined) No. 290035/1998 respectively, many attempts have been proposed for improving characteristics and reliability in operation of the piezoelectric element used as an actuator in order to improve performance and durability of the ink-jet printer head. However, in the conventional piezoelectric element, composition of the piezoelectric film is uniform through the entire film. It is certain that the Japanese Patent Publication (unexamined) No. 290035/1998 discloses changing concentration of zirconium and titanium, which are contained in the piezoelectric film formed from PZT, in the thickness direction of the film. But, the piezoelectric element described in the Japanese Patent Publication (unexamined) No. 290035/1998 is merely arranged so that zirconium and titanium contained in the piezoelectric film may be distributed with concentration gradient (difference in concentration) in the thickness direction of the film in order that the dielectric constant of the piezoelectric film may be lowered, capacitance may be decreased, and calorific value may be lowered keeping the piezoelectric strain constant of the piezoelectric film. This known piezoelectric element is not arranged to improve piezoelectric characteristic thereof.
SUMMARY OF THE INVENTION
The present invention was made to resolve the above-discussed problems and has an object of providing a piezoelectric element capable of improving piezoelectric characteristics of a piezoelectric film, providing a process for suitably producing such a piezoelectric element, and providing an ink-jet printer head in which the piezoelectric element is used as an actuator.
An invention according to claim 1 provides a piezoelectric element in which an upper electrode and a lower electrode are arranged on two sides of a piezoelectric film formed of a composite oxide (PZT) expressed by a chemical formula, Pb(Zr
1
—
x
Ti
x
)O
3
(0.3≦x≦0.9) or formed of a material mainly composed of the composite oxide so as to sandwich the piezoelectric film therebetween, wherein concentration ratio of titanium to zirconium in the piezoelectric film is gradually increased or gradually decreased from the upper electrode side to the lower electrode side.
The foregoing expression, “concentration ratio of titanium to zirconium in the piezoelectric film is gradually increased or gradually decreased from the upper electrode side to the lower electrode side” includes not only a case in which the concentration ratio changes as indicated by the solid line I or broken line II in
FIG. 2 and a
case in which the concentration ratio changes stepwise as indicated by the solid line III or broken line IV in
FIG. 3
,
Kansai Research Institute, Inc.
Vo Anh T. N.
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