Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1999-07-07
2000-12-12
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310313B, H01L 4108
Patent
active
061603392
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to two-port surface-acoustic-wave resonators (hereinafter referred to as "two-port SAW resonators"). In particular, it relates to a structural technology for suppressing spurious responses (unnecessary resonance) caused by higher-order vertical inharmonic modes in a two-port SAW resonator.
2. Description of Related Art
The basic electrode structure of a conventional two-port SAW resonator is disclosed in, e.g., U.S. Pat. No. 3,886,504, and a rotated Y-quartz plate in the case where an electrode film thickness is 1000 .ANG. or less is disclosed in Japanese Unexamined Patent Publication No. 61-251223. In addition, in Japanese Unexamined Patent Publication No. 61-230419, an example with three interdigital transducers (hereinafter referred to as "IDTs") is described.
In a two-port SAW resonator having three interdigital transducers, the central interdigital transducer is used as an input terminal, and on both sides thereof, the other interdigital transducers are disposed. Accordingly, the frequency of the two-port SAW resonator is stable for a change in the load of the output load circuit. The use of this type causes a temperature coefficient to change to zero in a so-called ST-cut two-port SAW resonator formed on an ST-cut X-transmission plate composed of single crystals of quartz. This is superior in terms of frequency stability similarly to that of a one-port type.
According to the above-described conventional art, when, in an ST-cut two-port SAW resonator having three interdigital transducers, an electrode film thickness is set at 1000 .ANG. or more so that the device size is reduced, resonance caused by a plurality of higher-order vertical inharmonic modes exists which is less than a main resonant frequency. There is a problem in that there is resonance caused by the plurality of higher-order vertical inharmonic modes, and a mode closest to the main resonant frequency causes a frequency jump to bring about inferior communication when the two-port SAW resonator is built into an oscillating circuit of a communication apparatus, because an oscillating-frequency-adjustment expansion coil allows frequencies to be close, whereby simultaneous excitation occurs.
In addition, despite the complete suppression of the higher-order vertical inharmonic modes, it is found that, when crossbus-bar conductors are disposed between the central interdigital transducer and the interdigital transducers on both sides thereof, two spurious responses having almost equivalent amplitudes are generated, depending on the crossbus-bar conductor structure.
SUMMARY OF THE INVENTION
Accordingly, the present invention is intended to solve the foregoing problems, and an object thereof is to provide to the communication market etc., a two-port SAW resonator having a superior frequency stability and no spurious responses.
The present invention is based on the premise that, in an SAW resonator, an IDT and reflectors disposed on both sides thereof are formed so as to confine the energy of surface acoustic waves. In addition, in an energy-confinement SAW resonator, in view of frequency potential, with an IDT divided into three, the central IDT activates surface acoustic waves, and the side IDTs receive the surface acoustic waves, whereby a displacement is controlled.
The present invention provides a two-port SAW resonator comprising: a first interdigital transducer for activating surface acoustic waves; one pair of second and third interdigital transducers for receiving the surface acoustic waves on both sides of the first interdigital transducer; and one pair of reflectors positioned on both sides of the second and third interdigital transducers, the first, second, and third interdigital transducers being cyclically formed on a piezoelectric plate using parallel metal conductors, wherein the distance between two parallel conductors, obtained when the reflectors are closest with respect to the second and third interdigital transducers, is a space among the li
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Suzuki, Y., et al. "Energy-Trapping Surface Acoustic Wave Resonators", Institute of Electronics, Information and Communication Engineers Technical Report IEICE, Japan, US87-36 (Sep. 1987), pp. 9-16.
Wright, P. V., et al. "A Review of Saw Resonator Filter Technology", 1992 Ultrasonics Symposium, IEEE (1992), pp. 29-39.
Takagi Michiaki
Yamazaki Takashi
Budd Mark O.
Seiko Epson Corporation
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