Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-01-18
2004-10-12
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06803702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a piezoelectric material such as a piezoelectric ceramic, and more particularly relates to a method for manufacturing a piezoelectric material having a perovskite crystal structure using a hydrothermal processing. The present invention also relates to method for manufacturing a piezoelectric element that utilizes this piezoelectric material, and more particularly a piezoelectric element that functions as an ink discharge drive source for an on-demand type of ink jet recording head.
2. Description of the Related Art
Most piezoelectric bodies which can be expressed by the formula ABO
3
have a perovskite crystal structure. Of these piezoelectric bodies, those having a specific composition exhibit an electromechanical conversion action, and are utilized as piezoelectric elements. For instance, lead-zirconate titanate (abbreviated as PZT), in which lead (Pb) is used for A and a mixture of zirconium (Zr) and titanium (Ti) is used for B, exhibits extremely good piezoelectric characteristics, and has become an important piezoelectric material in actuators such as ink jet recording heads.
A variety of methods have been employed in the past to manufacture a piezoelectric material. A method in which oxides are mixed and sintered is known as a first example thereof. This involves mixing lead oxide (PbO), zirconium oxide (ZrO
2
), titanium dioxide (TiO
2
), and other such oxides, pre-firing the mixture, grinding this product, and then sintering the resulting powder. This method makes possible the molding of bulk materials in particular.
A sol-gel method is known as a second example. This involves coating a substrate with a metal alkoxide solution (sol) containing lead (pb), zirconium (Zr), titanium (Ti), or the like by spin-coating or another such process, gelling this coating, and sintering the amorphous thin film thus obtained.
A third example is sputtering. This involves performing sputtering using an alloy of lead (Pb), zirconium (Zr), titanium (Ti), or the like as the target, and heat treating the amorphous thin film thus obtained.
With the above methods, the composition of the metal elements which make up the piezoelectric material that is the final product can be controlled to a certain extent by determining the composition of the metal elements included in the raw material.
As another example of a method for manufacturing a piezoelectric material, the thesis “Application of Hydrothermal Mechanism for Tailor-making perovskite Titanate Films,” IEEE proc. of the 9
th
Int'l Symp. on Electrets, Shanghai, China, Sept. 25-30, pp. 617-622 (1996), Wuping Xu, Masanori Okuyama, et al., discloses a technique of crystallizing a piezoelectric film precursor by a hydrothermal method. This hydrothermal method involves coating a substrate with a sol of an organometal in an amorphous state, then subjecting it to a hydrothermal processing in an alkali aqueous solution, thereby promoting the orientation of metal atoms and crystallizing them into a perovskite crystal structure.
This hydrothermal method has numerous advantages because a piezoelectric film precursor can be crystallized at a lower temperature than when a film is formed by any of the first to third methods mentioned above. For example, because a low-temperature process allows for a reduction in the internal stress generated in the film in the course of the crystallization of the piezoelectric film precursor, cracking can be prevented and it is possible to form a thick film of a piezoelectric material. The ability to form a piezoelectric thick film enhances the reliability of the film because of the weak electric field produced in the film when a voltage is applied. A low-temperature process also makes a line printer feasible because of the low internal stress in the film.
Incidentally, it is mentioned in the above thesis that an alkali aqueous solution is used as the treatment solution in the crystallization of the piezoelectric film precursor. However, since the pressure chamber substrate of an ink jet recording head, for example, is produced by the fine working of a silicon substrate, it is undesirable to use a strongly alkaline aqueous solution of potassium hydroxide or the like as the treatment solution because the substrate or the piezoelectric material ends up being etched. In view of this, from the standpoints of making the substrate and other components resistant to etching, promoting the crystallization of the piezoelectric film precursor, and so forth, a barium hydroxide aqueous solution or a lead hydroxide aqueous solution has been used as the treatment solution.
SUMMARY OF THE INVENTION
The inventor, however, discovered that the lead content in the piezoelectric material decreases if a piezoelectric film precursor such as lead zirconate-titanate (Pb(Zr,Ti)O
3
; PZT) is crystallized using barium hydroxide as the treatment solution.
FIG. 5
is the EDX (Energy Dispersive X-ray Analysis) spectrum of a piezoelectric film (Pb(Zr
0.56
Ti
0.44
)O
3
) crystallized by a hydrothermal processing with barium hydroxide alone, and
FIG. 6
is the EDX spectrum of a piezoelectric film (Pb(Zr
0.56
Ti
0.44
)O
3
) formed by sol-gel method. In these figures, the horizontal axis is the characteristic X-ray energy, and the vertical axis is the X-ray intensity. It can be seen from these experimental results that the lead content in a piezoelectric film crystallized by hydrothermal processing with barium hydroxide is smaller than the lead content in a piezoelectric film formed by sol-gel method.
When the lead content decreases in a piezoelectric film, there is a drop in both dielectric and piezoelectric properties. Accordingly, if a piezoelectric element featuring a piezoelectric material crystallized by hydrothermal processing using barium hydroxide is used as an ink discharge drive source, the ink discharge characteristics may not be as good as in the past. Similarly, when a crystalline film of a piezoelectric material is manufactured by hydrothermal processing, a drawback is that the metal elements contained in the initial piezoelectric material are lost, and the composition of the manufactured product cannot be controlled as expected. On the other hand, SEM (Scanning Electron Microscopy) observation revealed that crystallization is hindered when a lead hydroxide aqueous solution is used as the treatment solution.
With a conventional crystallization method involving sintering, a step of sintering under high-temperature conditions is essential, which means that metal components such as lead (Pb) evaporate and scatter during heating. This causes a problem in that the component ratio of the intended piezoelectric material tends to deviate from the component ratio of the piezoelectric material actually obtained, and also requires finding some way to keep the vaporized metal components (such as lead) from being discharged into the outside environment, which drives up the cost.
In view of this, it is an object of the present invention to provide a manufacturing method with which a decrease in piezoelectric characteristics can be prevented and the proper lead content can be ensured in a piezoelectric film when the piezoelectric material is manufactured by a hydrothermal method. The present invention further provides a method for easily controlling the component ratio of the metal elements that make up the piezoelectric material. Also provided is a method for manufacturing a piezoelectric material that imposes less burden in terms of environmental concerns, such as preventing the outflow of metals.
It is a further object to provide a method for manufacturing a piezoelectric element that is an ink discharge drive source by the above manufacturing method, and for manufacturing an ink jet recording head with superior ink discharge characteristics. Another object is to provide an ink jet printer equipped with this ink jet recording head.
The inventor investigated the compositional changes of a hydrothermal processing in light of the above dr
Nishiwaki Tsutomu
Okuyama Masanori
Qiu Hong
Sumi Koji
Wei Zhiqiang
Dougherty Thomas M.
Seiko Epson Corporation
Sterne Kessler Goldstein & Fox P.L.L.C.
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