Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1996-05-29
1999-04-20
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
310313A, 310361, 310316, H01L 4108
Patent
active
058959963
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device utilizing elastic surface waves (referred to as SAW (Surface Acoustic Waves) hereinafter), and it particularly relates to a SAW resonator which can generate a high-frequency range in a stable manner.
BACKGROUND ART
As for construction of a SAW resonator where there is provided a fingers-interleaved electrode (referred to as IDT (Interdigital transducer)) on the surface of a piezoelectric plate such as a quartz piece and a reflector disposed at both ends of this IDT, for example, U.S. Pat. No. 471,616 Official Gazette and U.S. Pat. No. 3,886,504 Official Gazette disclose such construction.
As the piezoelectric plate constituting the SAW resonator, a so-called ST-cut SAW resonator is known which utilizes a crystal ST cut and an X axis thereof serves as the propagating direction of the elastic wave. In this ST cut SAW resonator the zero temperature coefficient that is a primary coefficient .alpha. for the frequency temperature characteristic becomes 0, thus being excellent in frequency stability.
Conventionally, the SAW device has been used as a SAW filter, which is a filter for use with high frequency, so that not so high a Q-value is required. However, in recent years, in a SAW resonator constituting an oscillator for the use, it is important that a further stable resonance frequency be obtained and it is required to provide the resonator with a favorable temperature characteristics and high Q value. Moreover, the primary temperature coefficient .alpha. for the ST cut SAW resonator is almost 0, while the secondary temperature coefficient .beta. is relatively large i.e. -3.4.times.10 .sup.-8 /.degree.C.sup.2. Thus, the frequency change of approximately 110 ppm will be generated in the temperature range of -20.degree. C. through 80.degree. C. which is an operating temperature range of the SAW resonator. Therefore, under usage with the mobile communication, etc., it is necessary to provide a SAW resonator having further stable temperature characteristics in order to generate the high frequency precisely.
SUMMARY OF THE INVENTION
In the ST cut SAW resonators and the like, it is an object of the present invention to provide a SAW resonator having a high Q value without deteriorating the excellent frequency temperature characteristics. In order to achieve this object, the SAW resonator of the present invention is configured such that an IDT and a reflector disposed at both sides thereof confine the energy of elastic surface waves. Moreover, the IDT and reflector are disposed so that they cover also the progressing direction of the energy together with the progressing direction of the phase of the elastic surface waves on the piezoelectric material, whereby the energy of the elastic surface waves are further efficiently confined.
Moreover, it is another object of the present invention to further improve the frequency temperature characteristics together with the improvement of the Q value. In order to achieve another object, a cutting orientation is found such that a secondary coefficient .beta. can be reduced while a primary coefficient .alpha. becomes zero, and the energy of the elastic surface waves is efficiently confined by utilizing the crystal piece having this cutting orientation, whereby there can be provided a SAW resonator in which the Q value is high and the frequency deviation is small in the range of the operating temperatures.
Moreover, in recent years, Ouhara et al. announced a crystal K cut which excels the ST cut in the short-term frequency stability by a factor of 1-2 digit(s) in the U.S. FCS (Frequency Control Symposium, June 1994) and Japanese Electric Academic Society Electronics Circuit Research Session (The Institute of Electrical Engineers of Japan, Sep. 8, 1994). As the crystal K cut, an angle in the vicinity of (.phi., .mu., .nu.)=(0., 96.51, 33.79) (degree) expressed by the Euler angle in the orthogonal coordinate system, is suggested. However, though this cut angle is said to present superior heat resistant shock characte
REFERENCES:
patent: 4398115 (1983-08-01), Gagnepain et al.
patent: 4542356 (1985-09-01), Nakazawa et al.
Ikusaka Yoshinori
Momosaki Eishi
Takagi Michiaki
Budd Mark O.
Seiko Epson Corporation
Williams Timothy A.
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