Tunable Filters Using Ultrawide-Band Surface Acoustic Wave Resonator Composed of Grooved Cu Electrode on LiNbO_3

摘要

A leaky surface acoustic wave (LSAW) with a leaky component on a 0-15°YX-LiNbO_3 substrate has a large electromechanical coupling factor. In order to change the LSAW to a Love wave without a leaky component, a high-density electrode with a low velocity such as a Au or Cu electrode is composed on the substrate. A SAW resonator with a Cu-electrode/15°YX-LiNbO_3 structure has been reported to have a wide bandwidth of 12%. In this study, in order to obtain a SAW resonator with a wider bandwidth for application to tunable filters, the authors fabricated one-port resonators with a grooved Cu-electrode/4°YX-LiNbO_3 structure. This resonator had a 1.3-fold wider bandwidth of 17% and 1,3-fold higher resonant and antiresonant frequencies than a conventional resonator composed of the same thick Cu-electrode on 4°YX-LiNbO_3 fabricated for reference. Moreover, the authors proposed the application of this resonator to a tunable filter by using a circuit to modify a conventional band-pass filter composed of inductors and capacitors (LC) and a tunable filter with a ladder-type circuit. As a result, tunable filters having tunable ranges of 7 and 9% at the center frequency and 3dB bandwidths of 3 and 5%, respectively, have been realized.