Metal working – Piezoelectric device making
Reexamination Certificate
1998-11-16
2001-02-13
Hall, Carl E. (Department: 3729)
Metal working
Piezoelectric device making
C310S31300R, C310S31300R, C310S312000
Reexamination Certificate
active
06185801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a surface acoustic wave device such as a surface acoustic wave filter, a surface acoustic wave resonator, or the like, and more particularly, to a method of manufacturing a surface acoustic wave device in which a step of adjusting the frequency thereof is improved.
2. Description of the Related Art
A surface acoustic wave device is used to define various components such as a filter, a resonator, and the like. In manufacturing such a surface acoustic wave device, at least one interdigital transducer (referred to as “IDT” hereinafter) is formed on a piezoelectric substrate. In surface acoustic wave devices, the number of IDTs, and the shape and number of other electrodes are appropriately selected according to the desired component.
When used as a filter or a resonator, the surface acoustic wave device must be manufactured to achieve necessary frequency characteristics. However, there is a problem that frequency characteristics of surface acoustic wave devices deviate from the designed characteristics due to variations of physical properties between various piezoelectric substrates and poor manufacturing precision in forming IDTs.
Therefore, a method of manufacturing a surface acoustic wave device has been proposed in which a frequency can be adjusted by controlling the thickness of a polyimide resin coating layer formed on the surface acoustic wave device (for example, see Japanese Laid-Open Patent Publication Nos. 61-208916 and 8-32392).
More specifically, Japanese Laid-Open Patent Publication No. 61-208916 discloses that an operation frequency of a surface acoustic wave device can be adjusted by depositing a polyimide resin coating layer on a surface acoustic wave substrate so as to have a predetermined thickness.
Japanese Laid-Open Patent Publication No. 8-32392 discloses a method in which a fluorinated polyimide resin coating is formed, by a spin coating method to have a thickness corresponding to an amount of required frequency adjustment, on the substrate surface where a surface acoustic wave propagates. Japanese Laid-Open Patent Publication No. 8-32392 further discloses that the fluorinated polyimide resin coating may be etched by a plasma containing oxygen gas for further adjustment of the frequency.
However, the above-explained conventional methods using a polyimide resin coating can only decrease the operation frequency of the surface acoustic wave device. That is, it has been impossible to adjust an operation frequency of a surface acoustic wave device so that the operation frequency is increased.
In addition, when the fluorinated polyimide resin coating is etched by using a plasma containing oxygen gas, it is necessary to use a vacuum apparatus. Thus, each surface acoustic wave device requiring frequency adjustment must be loaded into a vacuum chamber and the vacuum chamber must be evacuated thereafter. As a result, it takes considerable time to adjust the frequency of a large number of surface acoustic wave devices, which makes the frequency adjustment process have a low through-put.
SUMMARY OF THE INVENTION
To overcome the problems described above, the preferred embodiments of the present invention provide a method of manufacturing a surface acoustic wave device, which is capable of adjusting an operation frequency of the surface acoustic wave device by shifting the operation frequency to both lower and higher frequency sides and which performs the adjustment of the operation frequencies of the surface acoustic wave devices with high through-put.
According to a preferred embodiment of the present invention, a method of manufacturing a surface acoustic wave device having a piezoelectric substrate and an interdigital transducer provided thereon, includes the steps of forming a coating layer made of an inorganic material or an organic material on the piezoelectric substrate so as to cover the interdigital transducer and etching the coating layer via a laser light to adjust an operation frequency of the surface acoustic wave device.
The method may also include the steps of determining whether the operation frequency is to be increased or decreased and selecting a particular inorganic material for the coating layer in the case where the operation frequency is to be increased and selecting a particular organic material for the coating layer in the case where the operation frequency is to be decreased. Then, the step of forming the coating layer is performed based on a result of the selecting step.
The etching step is preferably performed at an atmospheric pressure. The inorganic material is preferably at least one material selected from the group consisting of SiO
2
, SiO, ZnO, Ta
2
O
5
, TiO
2
, and WO
3
. The organic material is preferably at least one material selected from the group consisting of polyimide, parylene and silicone.
According to preferred embodiments of the present invention, the operation frequency can be easily adjusted with high precision, as compared with a conventional method of adjusting the frequency, and a surface acoustic wave device having exact desired frequency characteristics can be reliably provided at a low cost.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
REFERENCES:
patent: 4442574 (1984-04-01), Wanuga et al.
patent: 61-208916 (1986-09-01), None
patent: 8-32392 (1996-02-01), None
Japanese Patent Abstract (9-55636), Feb. 25, 1997, “Frequency Adjustment Method for Surface Acoustic Wave Element and Device Therefor”.
Fujimoto Koji
Kadota Michio
Yoneda Toshimaro
Hall Carl E.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd
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