Theoretical investigation of acoustic wave devices based on different piezoelectric films deposited on silicon carbide

摘要

Performances of acoustic wave (AW) devices based on silicon carbide (SiC) substrates are theoretically studied, in which two types of piezoelectric films of ZnO and A1N deposited on 4H-SiC and 3C-SiC substrates are adopted. The phase velocities (PV), electromechanical coupling coefficients (ECC), and temperature coefficients of frequency (TCF) for three AW modes (Rayleigh wave, A_0 and S_0 modes of Lamb wave) often used in AW devices are calculated based on four types of configurations of interdigital transducers (IDTs). It is found that that the ZnO piezoelectric film is proper for the AW device operating in the low-frequency range because a high ECC can be realized using a thin ZnO film. The A1N piezoelectric film is proper for the device operating in the high-frequency range in virtue of the high PV of A1N, which can increase the finger width of the IDT. Generally, in the low-frequency Lamb wave devices using ZnO piezoelectric films with small normalized thicknesses of films to wavelengths h_f/λ, thin SiC substrates can increase ECCs but induce high TCFs simultaneously. In the high-frequency device with a large h_f/λ, the S_0 mode of Lamb wave based on the A1N piezoelectric film deposited on a thick SiC substrate exhibits high performances by simultaneously considering the PV, ECC, and TCF.