High Frequency, Low Loss and Low TCF Acoustic Devices on LiTaO3-on-SiC Substrate

In this work, a novel heterogeneous substrate of lithium tantalate thin film on silicon carbide (LiTaO
3
-on-SiC, LTOSiC) was proposed and prepared. Since the SiC features an extremely-high phase velocity, a low acoustic loss and a small thermal expansion coefficient (CTE), surface acoustic wave devices with high frequency, low loss and low TCF were achieved on the LTOSiC substrate. The fabricated shear horizontal surface acoustic wave (SH-SAW) resonator shows a maximum Bode-Q (Bode-Qmax) of 2235 and a low TCF of -9.4 ppm/K at 1.90 GHz, while the longitudinal leaky surface acoustic wave (LLSAW) resonator shows a high Bode-Qmax of 1180 and an improved TCF of -24.7 ppm/K at 4.40 GHz. The ladder-type filter composed of SH-SAW resonators was also demonstrated, showing a center frequency (fc) of 3.03 GHz, an insertion loss (IL) of 0.9 dB and a 3-dB bandwidth of 101 MHz. The TCFs at - 3 dB attenuation of the lower and higher frequency side of passband are -13.8 and -15.8 ppm/K, respectively. The acoustic devices on LTOSiC substrate possess the prospect of commercial applications in 5G era.