Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-10-20
2001-09-04
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S311000, C430S315000, C430S330000
Reexamination Certificate
active
06284434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a piezoelectric thin film element, and more particularly concerns the manufacture of ink jet recording heads used in ink jet recording apparatuses.
2. Related Art
In forming piezoelectric thin film typified by plumbum (lead) zirconate titanate (PZT), a piezoelectric thin film is first formed on a substrate by a sputtering method such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or a sol-gel method such as spin coating, and this is subjected to a heat treatment at a high temperature of from 700° to 1000° C.
In seeking to increase the film thickness of piezoelectric thin film, methods attempted have included increasing the accumulation time for film growing and repeating the film growing operation a number of times.
Another method of increasing the film thickness of piezoelectric thin films that is being studied is that of hydrothermal synthesis (known also as “hydrothermal processing”), wherein a reaction for growing the piezoelectric thin film is promoted in a low-temperature environment at 200° C. or lower.
This hydrothermal processing method comprises a seed crystal formation process wherein PZT seed crystals are deposited on the surface of a titanium metal substrate, and a crystal growth process wherein additional PZT crystals are deposited and grown above the PZT seed crystal. This method is set forth, for example, in “Suinetsu goseiho ni yoru PZT kesshomaku no sakusei to sono denki tokusei (Preparation of PZT crystal films by hydrothermal synthesis, and electrical properties thereof),” a research paper recently published in the collected papers presented at the 15th Electronic Materials Research Forum of The Ceramic Society of Japan.
Manufacturing piezoelectric thin films by a sputtering method or sol-gel method requires heat treatment at high temperature, making such methods unsuitable for the fabrication of films of 1&mgr; or greater thickness, requiring, as they do, considerably long times for film formation, and, even when thicker films are realized, resulting in problems such as the development of cracks. When a piezoelectric thin film is used as an element employed in an ink jet recording apparatus, film thickness of from 0.5&mgr; to 10&mgr; or so are preferred. Thus it is needful to prevent the problems noted from occurring. Accordingly, it is possible to employ the hydrothermal processing method wherewith thick films can be made at low temperature, but when this method is used it is very difficult to control the composition of the piezoelectric thin film within an optimal range.
With the hydrothermal method alone, moreover, the crystals in the piezoelectric thin film layer become several &mgr; in diameter, whereupon fine, smooth films cannot be obtained, and fine patterning cannot be done, for which reasons deficiencies and other problems arise in the piezoelectric thin films.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a piezoelectric thin film element that functions well as an actuator, and wherewith the desired composition is obtained, good piezoelectric body distortion characteristics are exhibited, and the problems noted above are resolved.
Another object of the present invention is to provide a piezoelectric thin film element exhibiting the desired film thickness, wherein cracks do not develop in the piezoelectric thin film layer.
Another object of the present invention is to provide a piezoelectric thin film element wherewith there is no danger of deficiencies developing in the piezoelectric film.
Another object of the present invention is to provide an ink jet recording head that uses the piezoelectric thin film element of the present invention, and an ink jet printer that uses that head.
The Applicant has already, in Patent Application H8-77668/1996 (European Laid-Open Patent Application 794579A), proposed that, following the use of a sol-gel method to form a seed crystal layer for obtaining a piezoelectric thin film, a piezoelectric thin film layer be formed by hydrothermal processing.
The Inventors perfected the present invention after discovering that the objects stated above can be realized by using a sol-gel method to form a thin film layer consisting of a piezoelectric precursor, and then crystallizing the precursor thin film layer using hydrothermal processing. In doing so, the Inventors made reference to a recently published paper entitled “Application of Hydrothermal Mechanism for Tailor-making Perovskite Titanate Films,” IEEE Proc. of the 9th Int'l Symp. On Electrets Shanghai China, Sep. 25-30 (1996), pp 617-622, W-ping Ku, Masanori Okuyama, et al.
In other words, the present invention is a method of manufacturing a piezoelectric thin film element by forming, on a substrate, a lower electrode layer, a piezoelectric thin film layer, and then an upper electrode layer, wherein a piezoelectric body precursor thin film layer is formed by a sol-gel method, MOD method, sputtering method, or CVD method on the lower electrode, after which the hydrothermal processing method is implemented, that is, the substrate on which the precursor thin film is formed is immersed into a heating solution to implement hydrothermal processing and the precursor thin film is crystallized.
The main aspect of the present invention involves patterning the precursor noted earlier, by photolithography or the like, and crystallizing it. In other words, it involves forming a mask pattern on the precursor thin film layer, removing the unnecessary portions of the precursor layer, and then processing this substrate in the heating solution noted earlier.
In one aspect of the present invention, a mask pattern is formed on the precursor thin film layer to pattern the thin film layer, after which the hydrothermal process noted earlier is applied, thereby crystallizing the areas of the thin film layer whereon no mask pattern has been formed.
Another aspect of the present invention is characterized in that a sol is used for forming a precursor exhibiting photosensitivity. More specifically, the sol is applied to a substrate to form the precursor thin film, which thin film is selectively exposed to light, thereby patterning the precursor. The patterned precursor is then crystallized in a heating solution. This precursor sol may comprise, for example, a mixture of a liquid-form photosensitive resist and the sol for forming the piezoelectric body precursor thin film.
In another aspect of the present invention, after forming a lower electrode layer on a substrate, a crystal layer comprising seeds or a layer of seeds for promoting the crystallization of the precursor is formed on the lower electrode, after which a precursor thin film layer is formed on the seed crystal layer. Then the precursor thin film is crystallized in a heating solution.
In a variation of this aspect, a precursor thin film is formed on the substrate by a sol-gel method, on top of which the seeds or seed layer noted above is formed, after which the precursor pattern is crystallized in a heating solution. In yet another variation, in the process of forming multiple layers of the precursor thin film, seeds or a layer of seeds is formed between the precursor thin films.
In yet another aspect of the present invention, the seeds noted above are mixed into the piezoelectric precursor thin film. The piezoelectric precursor thin film layer may be formed, for example, with a sol-gel method using a sol into which the seeds have been mixed as the sol for forming the precursor.
In yet another aspect of the present invention, the element constituting the seeds is mixed into a heating solution for hydrothermal processing. This heating solution is an alkaline aqueous solution, or the like, used in hydrothermal synthesis.
In yet another aspect of the present invention, the piezoelectric thin film element pertains to an ink jet recording head that is an actuator for the purpose of discharging ink inside an ink cavity provided in the substrate. Yet another aspect of the present invention is an ink jet prin
Kamei Hiroyuki
Matsuzaki Makoto
Matsuzawa Akira
Nishiwaki Tsutomu
Shimada Masato
Barreca Nicole
Huff Mark F.
Seiko Epson Corporation
Sterne Kessler Goldstein & Fox P.L.L.C.
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