High-frequency edge reflection type resonators with excellent temperature characteristics

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 SiO ₂ 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.