High frequency resonators with wide bandwidth using SH0 mode plate wave in thin LiNbO3

Currently, an ultrawide band resonator used for a tunable filter with a wide tunable range is strongly required, because a mobile phone with multi-bands and a cognitive radio system require such a tunable filter to simplify their wirelss front-end circuits. The authors developed resonators with ultrawide bandwidths of 26% to 29% and large impedance ratios of 92 to 98 dB between resonance (fr) and anti-resonance frequencies (f
_a
) using a 0-th shear horizontal (SH
₀
) mode plate wave in a 28-30°YX-LiNbO
₃
plate. However, the resonators were of low frequency as f
_r
= 1.8 MHz and f
_a
= 2.3 MHz and suffer from ripples due to transverse mode between f
_r
and f
_a
. In this study, high frequency SH
₀
mode plate wave resonators (f
_r
= 440 ~ 560 MHz) with a wide bandwidth and a large impedance ratio and without ripples have been fabricated using an ultrathin LiNbO
₃
plate and an apodized interdigital transducer.