Surface acoustic wave device and wave filter employing the same

Abstract

A surface acoustic wave device includes a piezoelectric substrate having a first surface on which comb-like electrodes are formed, and a second surface, and a support substrate joined to the second surface of the piezoelectric substrate. The piezoelectric substrate is made of lithium tantalite, and the support substrate is made of sapphire. The following expressions being satisfied: T / t<1 / 3 (1) T / lambda>10 (2) where T is a thickness of the piezoelectric substrate, t is a thickness of the support substrate, and lambda is a wavelength of a surface acoustic filter propagated along the first surface of the piezoelectric substrate.

Description

technical field [0001] The present invention generally relates to surface acoustic wave devices and filters equipped with the same, such as transmit filters, receive filters and duplexers. Background technique [0002] SAW devices are widely used in bandpass filters and duplexers for cellular phones. In recent years, since cellular phones have higher performance, filters using SAW devices have been required to have higher performance. One requirement for SAW devices is improved temperature stability, since changes in temperature change the passband frequency range of the filter. It is well known that lithium tantalate (LiTaO 3 , hereinafter abbreviated as LT) is a piezoelectric material with a large electromechanical coupling coefficient, which is beneficial for realizing wide filtering characteristics. However, LT has the disadvantage of poorer temperature stability than quartz crystals. Such piezoelectric materials generally have incompatible properties, that is, mater...

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Problems solved by technology

The proposal made by Yamanouchi et al. 2 There are difficulties in the thickness and quality of the film, which will cause the frequency deviation of the SAW device

In addition, the proposal requires a silicon oxide film to be placed on the comb electrodes (Interdigital Transformer: IDT), which will increase the SAW propagation loss

It can be seen that this recommendation can only be applied to a limited number of SAW devices

[0005] The proposal described in Japanese Patent No. 2516817 has the problem that the polarization inversion layer affects the performance of the SAW device and requires very precise depth control of the polarization inversion layer

This may change some of the constants of the piezoelectric substrate, and thus cause a change in velocity and thus a frequency deviation

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