Compositions – Piezoelectric
Reexamination Certificate
2000-03-02
2002-07-16
Koslow, C. Melissa (Department: 1755)
Compositions
Piezoelectric
C252S06290R, C427S100000, C347S068000, C310S320000, C310S325000, C029S025350
Reexamination Certificate
active
06419848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique for manufacturing a piezoelectric (electrostrictive) actuator functioning as an ink-expelling drive source for an ink-jet type recording head, and particularly to a technique for manufacturing a piezoelectric actuator obtained using an application method.
2. Description of the Related Art
Piezoelectric actuators functioning as electromechanical conversion elements comprise piezoelectric films sandwiched between upper and lower electrodes. These actuators are used for the ink-expelling drive sources of ink-jet type recording heads, as well as solid-element motors, relays, switches, filters, and the like. The piezoelectric films constituting such piezoelectric actuators are formed from lead zirconate titanate (Pb(Zr, Ti)O
3
) and other PZT-based piezoelectric materials, or from piezoelectric/electrostrictive materials obtained by adding oxides of niobium, nickel, magnesium, or other metals to these systems. Piezoelectric films demonstrate an inverse piezoelectric effect, which is induced when an electric field is applied, making it possible to create deformation in piezoelectric actuators and to perform drive control on a submicron scale.
For example, the printing method disclosed in Japanese Patent Laid-open No. H3-128681 is known as a technique for forming such piezoelectric films. This printing method is a technique for obtaining piezoelectric films by forming a film on the desired substrate using a paste or slurry containing piezoelectric (electrostrictive) ceramic particles as its principal component, and heat-treating the resulting film. Using this printing method makes it easier to employ lithographic techniques or mechanical processing techniques such as laser processing or slicing, and allows any piezoelectric film configuration to be designed. Integration density of piezoelectric actuators can also be improved due to a greater variety of design options.
When, however, a piezoelectric actuator is fabricated by the printing method in accordance with the aforementioned Japanese Patent Laid-open No. H3-128681, the following problems are encountered because of the need to keep the atmosphere at 800 to 1000° C. during the heat treatment (sintering of piezoelectric film precursors). First, residual stress acts during the formation of a piezoelectric film, facilitating crack initiation and making it more difficult to obtain thicker piezoelectric films. Second, the piezoelectric characteristics of piezoelectric actuators vary because the high-temperature heat treatment vaporizes the lead in the piezoelectric film precursors and changes the stoichiometric ratio of the piezoelectric films. In addition, the lead diffuses in, or otherwise affects, the lower electrode, bringing about a reduction in the withstand voltage of the piezoelectric actuators and creating other problems.
Thicker piezoelectric films should be used to make piezoelectric actuators more reliable. It is also desirable that the piezoelectric actuators be fabricated in a low-temperature environment in order to maintain the same piezoelectric film composition and to prevent lead from being vaporized by the heat treatment.
In addition, Japanese Patent Laid-open No. H9-157019 describes obtaining complex oxide films through the use of materials prepared by adding complex oxide powders and complex oxide sols to solvents. No reference is made in this publication, however, to the type of composition used for such complex oxide sols.
With the foregoing in view, it is an object of the present invention to fabricate a piezoelectric actuator by an application method in a low-temperature environment and to make it possible to obtain a thicker piezoelectric film. Another object is to provide a highly practical piezoelectric film by combining the advantages of a plurality of material types. Yet another object is to provide a piezoelectric actuator equipped with such a piezoelectric film, to provide an ink-jet type recording head and ink-jet printer equipped with this piezoelectric actuator, and to provide a method for manufacturing these.
SUMMARY OF THE INVENTION
The piezoelectric actuator of the present invention is a piezoelectric actuator comprising a stacked structure consisting of a top electrode, a piezoelectric film, and a bottom electrode, wherein the piezoelectric film comprises a first group at piezoelectric ceramic particles and a second group of piezoelectric ceramic particles; the particles constituting the first group of piezoelectric ceramic particles are larger than the particles constituting the second group of piezoelectric ceramic particles; and the first group of piezoelectric ceramic particles and second group of piezoelectric ceramic particles have different compositions.
The fact that the first group of piezoelectric ceramic particles and the second group of piezoelectric ceramic particles have different compositions makes it possible to obtain a piezoelectric actuator whose composition combines the advantages of both.
The first group of piezoelectric ceramic particles should preferably be composed of a material whose piezoelectric constant is higher than that of the second group of piezoelectric ceramic particles.
Adequate piezoelectric characteristics of the film as a whole can be obtained because the first group of piezoelectric ceramic particles (large particles) have a high piezoelectric constant.
The second group of piezoelectric ceramic particles should preferably be composed of a material having higher plasticity than the first group of piezoelectric ceramic particles.
A piezoelectric film having high plasticity overall can be obtained because of the high plasticity of the second group of piezoelectric ceramic particles.
The plasticity of film or bulk can be evaluated by Young's modulus as physical or mechanical characteristics. Material having low Young's modulus is soft and has a high plasticity. To measure Young's modulus of thin film having a micron scale thickness, we can use nano-indentor (n-indentor). To measure Young's modulus of thick material such as bulk, we can use a cantilever.
Young's modulus is, for example, 70-100 GPa (gigapascal) for PZT, 10-20 GPa for PMN-PZT. Material having low Young's modulus and high plasticity has advantages such as hardness to break when applying external force (stress) and easiness to make thick films. On the other hand, if the material is too soft (i.e. Young's modulus is too low), the film cannot efficiently transmit a mechanical force. In other words, the film absorbs the force due to a large elasticity.
This invention may, by combination of crystal with high Young's modulus and crystal with low Young's modulus, flexibly control the properties of the films.
The particle size of the first group of piezoelectric ceramic particles should preferably be from 0.2 &mgr;m to less than 10 &mgr;m. This is because the piezoelectric film has inadequate piezoelectric characteristics when the size is less than 0.2 &mgr;m, whereas using particles measuring 10 &mgr;m or greater makes the irregularities on the surface of the piezoelectric film more pronounced and has an adverse effect on the reliability of the piezoelectric film. In addition, the particle size of the second group of piezoelectric ceramic particles should preferably be from 10 nm to less than 100 nm. Furthermore, the thickness of the piezoelectric film should preferably be from 2 &mgr;m to 100 &mgr;m.
The composition of the piezoelectric ceramic particles constituting the first group of piezoelectric ceramic particles or the second group of piezoelectric ceramic particles may be any of the following: lead titanate (PbTiO
3
), lead zirconate titanate (Pb(Zr,Ti)O
3
), lead zirconate (Pb ZrO
3
), lead lanthanum titanate ((Pb, La), TiO
3
), lead lanthanum zirconate titanate ((Pb, La) (Zr, Ti)O
3
), lead zirconate titanate magnesium niobate (Pb(Zr, Ti) (Mg, Nb)O
3
), Pb(Ni, Nb)O
3
—Pb(Zr, Ti)O
3
(PNN-PZT), or a material obtained by adding any two elements selected. f
Nakamura Haruo
Nishiwaki Tsutomu
Qiu Hong
Sumi Koji
Seiko Epson Corporation
Sterne Kessler Goldstein & Fox P.L.L.C.
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