| 摘要 |
A tunable filter includes a circuit configuration in which variable capacitors are connected with surface acoustic wave resonators. The surface acoustic wave resonators each include a piezoelectric substrate made of LiTaO3 or LiNbO3, an IDT electrode made of an electrode material filled in a recess in an upper surface of the piezoelectric substrate, and a SiO2 film arranged to cover the piezoelectric substrate.
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