Currently, an ultra-wideband resonator is greatly needed to realize a tunable filter with a wide tunable range, because mobile phones with multiple bands and cognitive radio systems require such tunable filters to simplify their circuits. Although tunable filters have been studied using SAW resonators, their tunable range was insufficient for the filters even when wideband SAW resonators with a bandwidth of 17% were used. Therefore, the fabrication of wider-bandwidth resonators has been attempted with the goal of realizing tunable filters with wide tunable ranges. In this study, an SH0- mode plate wave resonator in a 27.5°YX-LiNbO3 plate with an ultra-wide bandwidth of 29.1%, a high impedance ratio of 98 dB, and a high Q (Q(r) = 700 and Q(a) = 720) was realized. Two types of tunable filters were constructed using such SH0-mode resonators and capacitors. As a result, tunable ranges (bands) of 13% to 19% were obtained. The possibility of applying the SH0-mode resonator in the high-frequency gigahertz range is discussed.

Lamb wave modes can be classified as a fundamental anti-symmetric mode (A 0 ), a symmetric mode (S 0 ), and their higher order modes. Membrane-type A 1 mode Lamb wave resonators have been reported by the authors for future mobile communication systems. Although the reports show promising results, it is difficult to fabricate the resonators because they have a large dispersion of phase velocity and electromechanical coupling factor, and also are fragile. In this study, the authors suggest a solidly mounted resonator (SMR)-type S 0 mode Lamb wave resonator, which can solve the above-mentioned difficulty. An SMR-type S 0 mode Lamb wave resonator was successfully realized for the first time. The resonator exhibits a 1.5 times faster phase velocity and a 1/3 smaller temperature coefficient of frequency than the commonly used surface acoustic wave (SAW) devices composed of an Al electrode and a 36-48 YX-LiTaO 3 substrate.