Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-11-17
2004-08-10
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S324000
Reexamination Certificate
active
06774541
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric element for use in, for example, 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. 5. 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 nozzle, and a large number of ink chambers
12
separately communicating to the respectively ink passages. (
FIG. 5
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 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
which is located at the part corresponding to the vibration of the diaphragm
13
is changed, and ink is pushed out from the jet nozzle through the ink passage.
Each of the piezoelectric elements
15
is constructed by forming a piezoelectric film
17
on a lower electrode
16
and forming an upper electrode
18
on 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 PZT. 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. 217458/1998 discloses a process for forming a piezoelectric film made of PZT, in which an organic raw material of PZT is spin coated on a lower electrode, dried, and degreased, and after repeating the process of applying the organic raw material, drying, and degreasing several times, burning is conducted and a piezoelectric film is obtained. When a PZT film to be a piezoelectric film is prepared by the mentioned method, a low dielectric substance, which has pyrochlore structure or is amorphous, whose dielectric constant is lower than that of the PZT film consisting of crystals of perovskite structure is formed in a grain boundary exposure region of the piezoelectric film. This Japanese Patent Publication (unexamined) No. 217458/1998 describes that an excess composition produced in the process of growing crystals by burning the piezoelectric film is transferred to a grain boundary along with the growth of PZT crystal grains, and when the neighboring crystal grains finally join to close the grain boundary, the excess composition is pushed out on a surface layer face through the grain boundary, and the low dielectric substance is thus formed. This Japanese Patent Publication (unexamined) No. 217458/1998 explains that the low dielectric substance is formed in the grain boundary exposure region of the piezoelectric film, and consequently, the voltage applied on the crystal grain boundary of the piezoelectric film at the time of applying and electric field is lowered as compared with the voltage in a case where the low dielectric substance is not formed and leakage current flowing through the grain boundary of the piezoelectric film is decreased, and therefore voltage-proof characteristics of the piezoelectric element are improved.
However, in the method in which the leakage current of the piezoelectric element is restrained by forming the low dielectric substance, which has pyrochlore structure or is amorphous, in the grain boundary exposure region of the piezoelectric film as disclosed in Japanese Patent Publication (unexamined) No. 217458/1998, it is difficult to control the process so that the low dielectric substance may be constantly formed at all times in a uniform state in the grain boundary exposure region of the piezoelectric film or on substantially the whole face of the piezoelectric film, and therefore it is difficult to obtain a piezoelectric element which has uniform piezoelectric characteristics at all times.
SUMMARY OF THE INVENTION
The present invention was made to resolve the above-discussed problems and has an object of providing a piezoelectric element in which the piezoelectric element has uniform and excellent piezoelectric characteristics at all times and process control in the production of the piezoelectric element is relatively easy. Another object of the invention is to provide a process for suitably producing such a piezoelectric element. A further object of the invention is to provide an ink-jet printer head in which the mentioned piezoelectric element is used as an actuator.
An invention according to claim 1 provides a piezoelectric element in which electrodes are arranged on both sides of a piezoelectric film respectively, in which the piezoelectric film is provided with an oxide layer containing 0 or not more than 15 weight percent of Pb arranged on a face of the piezoelectric film, the face being in contact with at least one of the electrodes, and said oxide layer being formed of a composite oxide expressed by a chemical formula ABO
3
or of a solid solution of one or not less than two kinds of composite oxides respectively expressed by the chemical formula ABO
3
.
An invention according to claim 2 provides the piezoelectric element according to claim 1, wherein the oxide layer is formed of: a composite oxide a expressed by the chemical formula, ABO
3
, in which A is one or not more than two kinds of elements selected among a group of alkaline-earth metals and Pb and B is one or not more than two kinds of elements selected among a group of Ti, Zr, and Sn; a composite oxide b expressed by the chemical formula, ABO
3
, in which A is one or at least two kinds of elements of alkaline-earth metals and B is Nb and/or Ta; or a solid solution of the composite oxide a and the composite oxide b.
An invention according to claim 3 provides the piezoelectric element according to claim 1 or 2, in which an oxide forming the oxide layer is a ferroelectric material.
An invention according to claim 4 provides the piezoelectric element according to any of claims 1 to 3, in which the oxide layer contains not more than 5 weight percent of Pb.
An invention according to claim 5 provides the piezoelectric element according to any of claims 1 to 4, in which the piezoelectric film is formed of PZT expressed by a chemical formula, Pb (Zr
1-x
Ti
x
)O
3
(0.1≦x≦1) or formed of a material mainly composed of PZT.
An invention according to claim 7 provides the piezoelectric element according to claim 1, in which the oxide layer is 0.05 &mgr;m to 1 &mgr;m in thickness.
An invention according to claim 8 provides the piezoelectric element according to claim 1, in which the piezoelectric film is 1 &mgr;m to 25 &mgr;in thickness.
An invention according to claim 9 provides the piezoelectric element according to claim 1, in which the oxide layer is not more than 10% of the piezoelectric film in thickness.
In the piezoelectric element according to claim 1 or 2, the piezoelectric film is provided with an oxide layer whic
Dougherty Thomas M.
KRI, Inc.
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