Comparative Study of SH-Mode Surface Acoustic Wave Resonators on Lithium Tantalate With Silicon and Silicon Carbide Substrates

Abstract

This study introduces shear horizontal (SH) surface acoustic wave (SAW) resonators based on a multilayered structure of lithium tantalate (LiTaO3 or LT)/silicon dioxide (SiO2)/4H-silicon carbide (4H SiC). SiC exhibits high resistivity (HR) ( $\rho \gt 10^{{10}}~\Omega \cdot $ cm), effectively suppressing the parasitic surface conduction (PSC) effect. The suppression of the PSC effect by 4H-SiC substrates is demonstrated by extracting the substrate loss of SiO2/4H-SiC and SiO2/Si substrates in a coplanar waveguide (CPW) structure. Consequently, SAW resonators based on 4H-SiC substrates demonstrate a superior quality factor (Q) compared to the conventional SH SAW resonators based on Si substrates. The fabricated resonators with 4H-SiC and Si substrates achieved Bode- ${Q} _{\max }$ of 3916 and 1836, ${Q} _{\text {p}}$ of 3402 and 590, and admittance ratios ( ${Y} _{\text {r}}$ ) of 92 and 74 dB, respectively. The ${Q} _{\text {p}}$ of the 4H-SiC-based resonator is 5.7 times higher than that of the Si-based resonator. Substituting the Si substrate with the 4H-SiC substrate increases Q without compromising the effective electromechanical coupling ( ${k} ^{{2}}_{\text {eff}}$ ) and temperature coefficient of frequency (TCF). To suppress the transverse mode of the SAW resonators, tilted interdigital transducers (IDTs) at various titled angles were fabricated. A 12° tilt angle IDT demonstrated the most effective transverse mode suppression. When the tilted IDT was employed, the ${Q} _{\text {p}}$ of the SAW resonator based on the 4H-SiC substrate surpassed that of Si substrate. Compared to the Si substrate, the 4H-SiC substrate resulted in a higher ${Q} _{\text {p}}$ , making this technique promising for application in filters, oscillators, and sensors.