Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-08-26
2001-08-07
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R
Reexamination Certificate
active
06271617
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave device having an interdigital transducer (hereinafter referred to as IDT) disposed on a surface acoustic wave substrate and, more particularly, to a surface acoustic wave device using Love waves.
2. Description of the Related Art
A variety of surface acoustic wave devices utilizing surface acoustic waves have been proposed. For example, the Technical Report of the Institute of Electronics, Information and Communication Engineers (IEICE), pp. 7-14, US 82-35, 1982 discloses a surface acoustic wave device in which a thin layer of a slow acoustic speed material is formed on a rotational Y-cut, X-propagated LiNbO
3
substrate, wherein a pseudo surface acoustic wave produced therein is a Love-wave type surface acoustic wave which is free from transmission attenuation.
The Technical Report of Institute of Electronics, Information and Communication Engineers, pp. 31-38, US 86-37, 1986 discloses a rotational Y-cut, X-propagated LiNbO
3
substrate, which has no single uniformly arranged film disposed thereon but has metal strips intermittently arranged thereon to generate Love waves.
Japanese Laid-Open Patent Publication No. 63-260213 discloses a surface acoustic wave device which uses Love waves and which comprises a rotational Y-cut, X-propagated LiNbO
3
substrate having an IDT constructed of a heavy metal such as gold, silver, or platinum.
Japanese Laid-open Patent Publication No. 8-125485 discloses a surface acoustic wave device which uses Love waves and which comprises an IDT constructed of tungsten or tantalum, provided on a surface acoustic wave substrate.
Japanese Laid-Open Patent Publication No. 8-250966 discloses a surface acoustic wave device which uses Love waves and which comprises an IDT of two layers of Ta/Al provided on a surface acoustic substrate.
Although Technical Reports US 82-35 and US 86-37, and Japanese Laid-Open Patent Publication No. 63-260213 describe that the surface acoustic wave device has an IDT constructed of gold, silver or platinum, the device which was actually tested is a gold IDT. To generate the Love wave, the use of the abovedescribed heavy metals having large mass is thought to be required, but the use of a heavy metal is very costly.
According to Japanese Laid-Open Patent Publication No. 8-125485, the IDT is constructed of Ta or W, which are less costly than gold and which provide a low Q factor and a relatively high specific resistance, and can still work in a resonator but experiences great difficulties and disadvantages when used in a filter.
According to Japanese Laid-Open Patent Publication No. 8-250966, the IDT is constructed of a two-layered structure of Ta/Al, resulting in a decreased specific resistance. Even with the IDT of the two-layered structure of Ta/Al, the specific resistance is not sufficiently low, and satisfactory performance is not achieved when such a configuration is used as a filter.
SUMMARY OF THE INVENTION
To overcome the problems described above, the preferred embodiments of the present invention provide a surface acoustic wave device including an IDT electrode and/or a reflector and which has a low-cost construction without using an expensive heavy metal, provides a high Q factor and a low specific resistance, and achieves an excellent performance when the device is constructed as a resonator or a bandpass filter.
According to a preferred embodiment of the present invention, a surface acoustic wave device includes a surface acoustic wave substrate and an interdigital transducer provided on the surface acoustic wave substrate, wherein the interdigital transducer includes a tungsten layer and an aluminum layer. In such a preferred embodiment, it is preferable that the laminated metal film has a structure in which a tungsten layer and an aluminum layer are laminated together to form an integral metal film.
The aluminum layer may be provided on the surface acoustic wave substrate and the tungsten layer is then preferably provided on the aluminum layer. Alternatively, the tungsten layer may be provided on the surface acoustic wave substrate and the aluminum layer is then preferably provided on the tungsten layer.
The surface acoustic wave device may further comprise a pair of reflectors made of a laminated metal film in which a tungsten layer and an aluminum layer are laminated, the pair of reflectors being disposed on both sides of the interdigital transducer.
In another preferred embodiment of the present invention, a surface acoustic wave device includes a surface acoustic wave substrate, an interdigital transducer provided on the surface acoustic wave substrate and reflectors disposed on both sides of the interdigital transducer, wherein the reflectors include a tungsten layer and an aluminum layer. In such a preferred embodiment, it is preferable that the laminated metal film used to form the reflectors has a structure in which a tungsten layer and an aluminum layer are laminated together to form an integral metal film. In this preferred embodiment, the interdigital transducer may be preferably formed of aluminum or other suitable material.
The surface acoustic wave substrate in preferred embodiments of the present invention is preferably a Y-cut, X-propagated LiNbO
3
substrate, and the surface acoustic wave device is constructed to use Love waves.
The surface acoustic wave device may further comprise a bonding electrode provided on the surface acoustic wave substrate and connected to the interdigital transducer. The bonding electrode may include a laminated metal film in which a tungsten layer and an aluminum layer are laminated together.
Alternatively, the bonding electrode may have a top layer made of aluminum. In this case, the bonding electrode includes a single layer made of aluminum which is therefore a top layer, or includes a top layer of aluminum disposed on top of a laminated metal film including an aluminum layer and a tungsten layer laminated together, such that the aluminum layer of the laminated metal layer is provided on the surface acoustic wave substrate and the top aluminum layer is provided on the tungsten layer of the laminated metal film.
For the purpose of illustrating the invention, there are shown in the drawings several embodiments and forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown therein.
REFERENCES:
patent: 4544857 (1985-10-01), Shimizu et al.
patent: 4942327 (1990-07-01), Watanabe et al.
patent: 5144185 (1992-09-01), Yuhara et al.
patent: 5152864 (1992-10-01), Ieki et al.
patent: 5162690 (1992-11-01), Ieki et al.
patent: 5453652 (1995-09-01), Eda et al.
patent: 5844347 (1998-12-01), Takayama et al.
patent: 5847486 (1998-12-01), Kadota et al.
patent: 5909156 (1999-06-01), Nishihara et al.
patent: 63-260213 (1988-10-01), None
patent: 8-125485 (1996-05-01), None
patent: 8-250966 (1996-09-01), None
patent: 10-247835 (1998-09-01), None
Japanese Patent Abstract of 5-63496, “Surface Acoustic Wave Device” (Mar. 1993).
Japanese Patent Abstract of 9-107268, “Ladder type Surface Acoustic Wave Filter” (Apr. 1997).
Technical Report of Institute of Electronics, Information and Communication Engineers (IEICE) US 82-35, 1982.
Technical Report of Institute of Electronics, Information and Communication Engineers, US 86-37, 1986.
Kadota Michio
Yoneda Toshimaro
Dougherty Thomas M.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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