High Performance SAW Resonators Using LiTaO3/SiO2/4H-SiC Multilayer Substrate

The Radiofrequency (RF) industry needs surface acoustic wave (SAW) resonators with high-quality factors (
${Q}$
) and spurious-free response characteristics to also have steep roll-off and a flat passband. In this work, SAW resonators based on 36°YX-LiTaO
$_{{3}} /$
SiO
$_{{2}} /4\text{H}$
-SiC multilayer substrates are fabricated that can effectively suppress acoustic energy leakage. Finite element method (FEM) simulations show that the effective electromechanical coupling coefficient (
${k}^{{2}}_{\text {eff}}$
) of the multilayer structure SAW resonators can be improved by choosing SiO2 and 36°YX-LT layers of appropriate thickness, and it is the high acoustic velocity of the slow shear bulk wave in 4H-SiC that leads to the multilayer structure SAW resonators showing excellent performance in confining acoustic energy. However, from the slowness curve, we measure the power flow angle (PFA) to be 10°, which, if uncorrected, would lead to serious transverse modes between the resonant frequency (
${f}_{\text {r}}$
) and the antiresonant frequency
$({f}_{\text {a}})$
. To counter this, a multilayer structure SAW resonator with transverse mode suppression is fabricated using interdigital transducers (IDT) with a tilted angle of 10°. The multilayer resonator displays an extremely high Bode-
${Q}$
of over 3500 and a high impedance ratio of 85 dB. As predicted by the simulation results,
${k}^{{2}}_{\text {eff}}$
is up to 12%, and an extremely high figure of merit (FOM) of 423 is achieved. The enhanced performance of SAW resonators demonstrated in this work can open a door for constructing high-performance SAW filters with low insertion loss and high stability characteristics.