Advanced Surface Acoustic Wave Resonators on LiTaO₃/SiO₂/Sapphire Substrate

The shear horizontal surface acoustic wave (SH-SAW) resonators with excellent quality factor and temperature stability were fabricated on 42°YX-LiTaO3/SiO2/sapphire substrate. For comparison, the 4-inch LiTaO3/SiO2/sapphire (fully insulating LiTaO3-on-insulator, FI-LTOI) and LiTaO3/SiO2/poly-Si/Si (trap-rich layer assisted LiTaO3-on-insulator, TR-LTOI) substrates are prepared by ion-cutting process. The GHz acoustic delay lines (ADLs) built on FI-LTOI exhibit a propagation loss of only 2.95 dB/mm, which is 37.5% smaller than the 4.72 dB/mm of the ADLs on TR-LTOI. The demonstrated SH-SAW resonators on FI-LTOI exhibit higher
${Q}$
-values than those on TR-LTOI. Among them, a FI-LTOI based resonator with the resonant frequency of 1.76 GHz exhibits a maximum Bode-
${Q}$
(
${Q} _{{\mathrm {max}}}$
) of 4,421, an effective electromechanical coupling coefficient of 13.34%, an excellent figure of merit of 589.8, and a well-compensated temperature coefficient of frequency of −9.1 ppm/°C. More importantly, the
${Q} _{{\mathrm {max}}}$
of the FI-LTOI based resonator is maintained well (2,791) even at 200 °C whereas that of the TR-LTOI based resonator decreased to 674. Overall, the FI-LTOI substrate may serve as an advanced material platform of SAW devices for 5G-FR1 bands.