Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-08-20
2001-04-17
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S31300R, C310S363000
Reexamination Certificate
active
06218763
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave resonator using shear horizontal (SH) waves, and more specifically, the present invention relates to a surface acoustic wave resonator in which an interdigital transducer made of a metal containing W or Ta as its main component is provided on a piezoelectric substrate, a filter, a duplexer, and a communication apparatus.
2. Description of the Related Art
Conventionally, a synthesizer local oscillation circuit, which is used for selecting a channel in a portable wireless device having a VHF/UHF band, requires not only miniaturization but also a wider band function for handling the multi-channel system. In addition, even in a surface acoustic wave device used in a voltage-controlled oscillator, which is an essential component of the local oscillator, size reduction and band-widening are strongly demanded.
A surface acoustic wave resonator generating a surface acoustic wave such as a Rayleigh wave is known. In the surface acoustic wave resonator using the Rayleigh wave, however, no matter what type of piezoelectric substrate is used, the electromechanical coupling coefficient is small. Thus, it is difficult to achieve a wider band function.
As a result, a surface acoustic wave resonator using the SH wave has been studied in an attempt to provide a surface acoustic wave resonator having a large electromechanical coupling coefficient so as to achieve the wider band function. A Love wave which is known to be a type of the SH wave is generated by forming an interdigital transducer on the piezoelectric substrate, wherein the interdigital transducer is made of a metal film which has slower sound velocity and a higher density than that of a piezoelectric substrate.
Such a surface acoustic wave resonator, conventionally has a structure in which an interdigital transducer made of Au is formed on a LiNbO
3
substrate of Y-cut X-propagation.
However, since the surface acoustic wave resonator, which uses Au in the interdigital transducer, requires excessive material cost, the surface acoustic wave resonator is very expensive.
Thus, a surface acoustic wave resonator in which a metal containing W or Ta, which is cheaper than Au, as its main component, is used in an interdigital transducer, has been examined.
In general, a surface acoustic wave resonator and a surface wave filter are contained in a ceramic package, and have a structure in which the external terminal of the ceramic package and a bonding pad of an interdigital transducer are connected via wire bonding.
However, when a surface acoustic wave resonator using a metal containing W or Ta as its main component of the interdigital transducer is formed, since the metal having the main component of W or Ta resists being bonded to Au, ball bonding cannot be performed with respect to a wire made of Au or alloys of Au.
Additionally, in order to excite the Love wave, the thickness of an electrode film of the interdigital transducer made of a metal having the main component of W or Ta is set to about 0.02 &mgr;m to about 1.0 &mgr;m.
When the electrode film of the interdigital transducer made of a metal having the main component of W or Ta has a thickness which is greater than this range, there is a problem which occurs when forming an electrode pattern of the interdigital transducer via reactive ion etching.
In other words, when the electrode pattern is formed of a metal having a main component of W or Ta, a resist is removed before completion of etching of the electrode pattern and thereby, the electrode patterns are damaged.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave resonator and a method of making thereof, in which, when a metal having a main component of W or Ta is used to form an electrode, ball bonding to a wire made of Au or alloys of Au is performed. The resonator is arranged to use an SH wave and to have an electrode structure which does not influence an electrode pattern when the electrode pattern is formed by reactive ion etching.
According to one preferred embodiment of the present invention, a surface acoustic wave resonator includes a piezoelectric substrate and an interdigital transducer provided thereon. The surface acoustic wave resonator is adapted to operate using a shear horizontal wave, and the interdigital transducer includes an electrode film made of a metal containing W or Ta as its main component and an Al thin film provided on the electrode film.
According to preferred embodiments of the present invention, since the Al thin-film is formed on the electrode film made of a metal containing Ta or W as its main component, bonding of a wire made of Au or alloys of Au is possible. Additionally, in the case of performing reactive ion etching, it is possible to prevent damage to the electrode pattern itself and to avoid etching of the electrode of a necessary part of the electrode pattern.
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: 5773917 (1998-06-01), Satoh et al.
patent: 5844347 (1998-12-01), Takayama et al.
patent: 5847486 (1998-12-01), Kadota et al.
patent: 5854527 (1998-12-01), Shimizu et al.
patent: 5905325 (1999-05-01), Naumenko et al.
patent: 5909156 (1999-06-01), Nishihara et al.
patent: 19839247 (1999-03-01), None
patent: 0 936 734 (1999-08-01), None
patent: 54-132187 (1979-10-01), None
Fujimoto Koji
Kadota Michio
Yoneda Toshimaro
Dougherty Thomas M.
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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