Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Including heating
Reexamination Certificate
1999-06-15
2001-07-24
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Including heating
C430S315000, C430S319000, C430S329000
Reexamination Certificate
active
06265139
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a method for fabricating a micro actuator using photolithography and, more particularly, to an improvement in the aspect ratio of piezoelectric/electrostrictive patterns and in their bonding properties to a substrate, along with the method.
2. Description of the Prior Art
Generally, a micro actuator has a stacked structure in which a vibrating plate underlays a piezoelectric/electrostrictive film with two electrodes attached respectively to its bottom and top. If an electric field is applied across the two electrodes, the piezoelectric/electrostrictive film which lies between the two electrodes is repetitively distorted and restored, effecting vibration.
Conventionally, a piezoelectric/electrostrictive film, serving as a piezoelectric element in a micro actuator, is prepared from a ceramic powder produced by a solid phase method. This method, called an oxide method, comprises thermally treating a mixture of raw material oxide powders or their molten salts at, for example, 800-1,200° C., pulverizing and sintering them to yield ceramic powders.
Depending on the particle size of the raw material powder, the ceramic powders produced by this conventional solid phase method have different particle sizes, which are relatively large ranging from 0.2 to 2 &mgr;m, so that the solid phase method is unsuitable to produce ceramic particles as fine in size as 0.1 &mgr;m or less. In addition, this conventional method is disadvantageous in that a thermal treatment is conducted at a high temperature of 1000° C. or above.
Micro actuators are usually fabricated using a screen printing technique in which a ceramic paste is screen-printed on an infrastructure consisting of a vibrating plate and a chamber, to form fine patterns. In detail, a ceramic paste is printed on a vibrating plate with the aid of a screen and subjected to debindering, followed by sintering the ceramic at 1,000° C. or higher to form a piezoelectric/electrostrictive film with a predetermined thickness.
The screen printing method is widely used by virtue of its ability to increase the integration degree of micro actuators, but suffers from disadvantages as follows:
First, the piezoelectric/electrostrictive film is printed to a limitative low thickness. The thickness with which the conventional screen printing method can endow the piezoelectric/electrostrictive film is 5 &mgr;m at least. That is, it is difficult to form a piezoelectric/electrostrictive film at a thickness less than 5 &mgr;m with the conventional printing method.
Second, when a thick piezoelectric/electrostrictive film is formed, it is difficult to realize a high aspect ratio of patterns as well as to align the patterns to the infrastructure. The formation of thick piezoelectric/electrostrictive films is possible by controlling the emulsion film of the screen in use to a proper thickness or repetitively printing ceramic pastes twice or more times. As the printing procedure is repeated, however, newly added ceramic pastes
16
flow down over the side of formerly formed patterns as shown in FIG.
1
.
Third, where a thick piezoelectric/electrostrictive film is formed by repetitively printing ceramic pastes, because a thermal treatment is conducted after each printing, the repetitive thermal history may cause the earlier formed ceramic layers to be thermally deteriorated.
Fourth, if the piezoelectric/electrostrictive film is formed in fine patterns, 30 &mgr;m or greater must be given to the width of the fine patterns and the distance therebetween. That is, it is quite difficult to obtain a pattern of piezoelectric/electrostrictive films which are finer in dimension than 30 &mgr;m by the screen printing method.
Finally, because the consequence of the screen printing is dependent on the screen pattern used and other various factors, such as ceramic paste viscosity, printing pressure, printing speed, etc, account must be taken of such factors.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a method for fabricating a micro actuator, whereby a piezoelectric/electrostrictive film with a desired thickness can be formed at relatively low temperatures, a high aspect ratio of piezoelectric/electrostrictive film patterns can be realized and a controlled top electrode can be obtained.
In accordance with an aspect of the present invention, there is provided a method for fabricating a micro actuator, using photolithography, which comprises the steps of: providing a metal vibrating plate; forming molds in fine patterns on the metal vibrating plate by use of a photolithographic technique in which a photoresist is coated and patterned on the metal vibrating plate; mixing a ceramic oxide powder and a ceramic sol solution, both identical or similar in composition, to prepare a ceramic paste, the ceramic oxide powder having a particle size of 5 &mgr;m or less, which is prepared from Pb and Ti-based ceramic oxide powder by a non-explosive oxidation-reduction combustion reaction at 100-500° C., the ceramic sol solution being made in water or an organic solvent; filling the ceramic paste in the molds to form a piezoelectric/electrostrictive film; conducting a thermal treatment at 100 to 300° C. to sinter the piezoelectric/electrostrictive film; and forming a top electrode on the piezoelectric/electrostrictive film.
In accordance with another aspect of the present invention, there is provided a method for fabricating a micro actuator, using photolithography, which comprises the steps of: providing a vibrating plate; forming a bottom electrode on the vibrating plate; forming molds in fine patterns on the bottom electrode by use of a photolithographic technique in which a photoresist is coated and patterned on the metal vibrating plate; mixing a ceramic oxide powder and a ceramic sol solution, both identical or similar in composition, to prepare a ceramic paste, the ceramic oxide powder having a particle size of 5 &mgr;m or less, which is prepared from Pb and Ti-based ceramic oxide powder by a non-explosive oxidation-reduction combustion reaction at 100-500° C., the ceramic sol solution being made in water or an organic solvent; filling the ceramic paste in the molds to form a piezoelectric/electrostrictive film; conducting a thermal treatment at 100 to 300° C. to sinter the piezoelectric/electrostrictive film; and forming a top electrode on the piezoelectric/electrostrictive film.
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Chakrbarti et al. “Chemical synthesis of PZT powder by auto-combustion of citrate-nitrate gel.”, Mater. Lett., vo9l 30(2,3) pp. 169-173, 1997.*
Zhuang et al., “Pyrolysis of PLZT citrate precursor”. Wuji Cailiao Xuebao, vol. 3(1) pp. 27-31, 1988 (Abstract only).*
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Jung Yeon Kyoung
Park Sung-June
Yun Sang Kyeong
Angebranndt Martin
Darby & Darby
Samsung Electro-Mechanics Co. Ltd.
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