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

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) (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rho \gt 10^{{10}}~\Omega \cdot $ </tex-math></inline-formula>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-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{\max }$ </tex-math></inline-formula> of 3916 and 1836, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{\text {p}}$ </tex-math></inline-formula> of 3402 and 590, and admittance ratios (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Y} _{\text {r}}$ </tex-math></inline-formula>) of 92 and 74 dB, respectively. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{\text {p}}$ </tex-math></inline-formula> 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 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k} ^{{2}}_{\text {eff}}$ </tex-math></inline-formula>) 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{\text {p}}$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q} _{\text {p}}$ </tex-math></inline-formula>, making this technique promising for application in filters, oscillators, and sensors.