Abstract
Currently, some duplexers are required to have a good temperature coefficient of frequency (TCF). An Al electrodes/36–48° YX-LiTaO3 substrate, which is used for most surface acoustic wave (SAW) duplexers, does not have a good TCF. Its TCF can be improved by depositing a SiO2 film with a positive TCF on a transversal SAW filter consisting of a substrate with a negative TCF such as LiTaO3 and LiNbO3. However, resonator-type SAW devices combining a SiO2 film, Al electrodes, and a LiTaO3 substrate do not show good frequency characteristics because of their small reflection coefficient and so on. It is considered as a countermeasure that a resonator using the reflection of a shear horizontal (SH) wave at substrate edges will show good frequency characteristics because its reflection coefficient is very large regardless of the Al electrode and SiO2 films thicknesses. It has been difficult to obtain a high-frequency edge reflection resonator using ordinary machining techniques because it requires extremely fine substrate edges. However, a high-frequency edge reflection resonator with a good TCF and excellent frequency characteristics has been realized using our newly developed method of obtaining fine edges.
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