Metal working – Piezoelectric device making
Reexamination Certificate
2001-02-05
2003-07-22
Arbes, Carl J. (Department: 3729)
Metal working
Piezoelectric device making
C029S830000, C029S846000, C029S831000, C310S358000, C310S363000
Reexamination Certificate
active
06594875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive actuator and a method for fabricating the same, and more particularly to a piezoelectric/electrostrictive actuator including a vibrating plate made of metal, organic compound or ceramic, and a piezoelectric element formed by forming a piezoelectric/electrostrictive film, in the form of a thin or thick film, on the vibrating plate using specific ceramic powder, and thermally treating the piezoelectric/electrostrictive film at a relatively low temperature, thereby causing the piezoelectric/electrostrictive film to be integral with the vibrating plate, so that the fabrication of the piezoelectric element can be achieved without using a third material for bonding the piezoelectric element to the vibrating plate while minimizing a degradation in the properties of the vibrating plate and being capable of patterning the piezoelectric element during the formation of the piezoelectric element, thereby enabling a simultaneous fabrication of a plurality of piezoelectric/electrostrictive actuators without any requirement of post treatments. The present invention also relates to a method for fabricating such a piezoelectric/electrostrictive actuator.
2. Description of the Prior Art
Generally, actuators include a vibrating plate, a lower electrode formed on the vibrating plate, a piezoelectric/electrostrictive film formed on the lower electrode, and an upper electrode formed over the piezoelectric/electrostrictive film.
In such actuators having the above mentioned configuration, the piezoelectric/electrostrictive film arranged between the upper and lower electrodes deforms repeatedly as voltage is intermittently applied between the upper and low electrodes, so that it vibrates.
Conventionally, ceramic powder produced by solid state reaction method has been used to form piezoelectric/electrostrictive films for piezoelectric elements in piezoelectric/electrostrictive actuators.
The solid state reaction method, which is also called a “mixed oxide method”, is a method for producing ceramic powder using an oxide or molten salt as a raw material. In such a solid state reaction method, raw materials in the form of powder are mixed together and then subjected to a thermal treatment at a temperature of 1,000 to 1,200° C. The resulting mixture is milled and then sintered, thereby producing ceramic powder.
Typically, ceramic powder produced by the solid state reaction method has a relatively large grain size of 0.2 to 2 &mgr;m, even though depending on the grain size of raw materials used. For this reason, the solid state reaction method is unsuitable to obtain a grain size of 0.1 &mgr;m. Furthermore, the solid state reaction method has a drawback in that it involves a heat treatment at a high temperature of 1,000° C. or more.
In the fabrication of various film devices using ceramics, a method has conventionally been used in which ceramic paste is produced from ceramic powder, and then subjected to a thermal treatment in a state printed or molded on a vibrating plate.
In conventional ceramic paste preparation methods, a mixture is prepared which consists of a binder, a vehicle, a plasticizer, and a dispersant. The mixture is dissolved in a solvent, thereby producing a solution. Ceramic grains, which are prepared by a solid state reaction method to have a mean grain size of 1 &mgr;m, are then added to the solution. The resulting mixture is then stirred.
In order to fabricate a piezoelectric/electrostrictive film, the ceramic paste prepared by the above mentioned method is printed on a vibrating plate, dried at 130° C., and then subjected to a heat treatment at 1,000° C. or more. However, this method involves a problem in that an additional thermal treatment at a temperature of 500° C. or more should be carried out after the drying process in order to achieve a binder removal for completely removing the organic ingredients added prior to the thermal treatment.
The ceramic paste, which is produced by this method, cannot be formed into a desired shape at a low temperature because it contains ceramic grains of a large size. For this reason, the thermal treatment is carried out at a temperature of 1,000° C. However, this results in a limited selection of usable vibrating plates.
Conventional methods for fabricating piezoelectric/electrostrictive actuators are mainly classified into those associated with a vibrating plate made of metal or organic compound, and those associated with a vibrating plate made of ceramic.
First, conventional methods associated with a vibrating plate made of metal or organic compound will be described.
An example of a method for fabricating a piezoelectric/electrostrictive actuator, which is associated with a vibrating plate made of an insulating organic compound of resin, is disclosed in Japanese Patent Laid-open Publication No. Heisei 9-300609.
Where a vibrating plate made of metal or organic compound is used, a degradation in the properties thereof occurs inevitably due to a high temperature applied thereto. To this end, a piezoelectric plate, which is to be formed on the vibrating plate, is formed or fabricated separately from the vibrating plate. The piezoelectric plate is then bonded to the vibrating plate by means of a third material. The resulting structure is then mechanically cut into a desired size, so as to obtain a desired number of piezoelectric/electrostrictive actuators. This process is illustrated in FIG.
1
.
This method is advantageous in that there is no requirement to use any process involving difficulties because the vibrating plate is made of resin or metal.
However, there is a problem caused by the use of the third material as a binder to bond the vibrating plate and piezoelectric element together. A binder layer having a non-uniform thickness may be formed in the binding process. Air bubbles may also exist in the binder layer. As a result, it is difficult to form a reliable binder layer.
In order to obtain a desired number of piezoelectric/electrostrictive actuators, the piezoelectric plate is sliced by a mechanical machining process. However, there is a limitation in the integration degree of piezoelectric/electrostrictive actuators due to a limitation on the mechanical machining process. As a result, it is difficult to obtain products exhibiting a superior quality and a high productivity.
Where a vibrating plate made of metal is used, an electric discharge phenomenon may occur because the distance between the upper or lower electrode and the vibrating plate is very short, namely, about 30 &mgr;m.
Next, conventional methods associated with a vibrating plate made of ceramic will be described.
An example of a method for fabricating a piezoelectric/electrostrictive actuator, which is associated with a vibrating plate made of ceramic, is disclosed in U.S. Pat. No. 5,430,344. Where a thin or thick film for a piezoelectric element is directly formed over a vibrating plate, a degradation in the properties of the vibrating plate may occur during a sintering process carried out for the film at a high temperature. To this end, ceramic, which can withstand the sintering temperature for the piezoelectric element, is used to form a vibrating plate.
Where such ceramic vibrating plate is used, a lower electrode is formed on the ceramic vibrating plate using a thermal treatment at a temperature of 1,200° C. or more. A piezoelectric element is then formed over the lower electrode using a thermal treatment at a temperature of 1,000° C. or more. Finally, an upper electrode is formed over the piezoelectric element at a temperature of about 800° C. This process is illustrated in FIG.
2
.
A representative ceramic material used for the vibrating plate is a stabilized zirconia (ZrO
2
). Pure zirconia, which does not contain any addition ingredient, cannot be used for the vibrating plate because it involves a self collapse phenomenon occurring in the vicinity of 1,000° C.
Although zirconia exhibits most superior mechanical properties in that no oxidation or var
Chang Kwang Kyun
Kim Dong-Hoon
Yun Sang Kyeong
Arbes Carl J.
Ladas & Parry
Nguyen Tai V
Samsung Electro-Mechanics Co.
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