Miniature LiNbO<sub>3</sub>/SiO<sub>2</sub>/Si SH-SAW Resonators With Near-Spurious-Free Response
Tzu-Hsuan Hsu, Chia-Hsien Tsai, Shao-Siang Tung, Ming‐Huang Li
Abstract
In this letter, we present an investigation into the design, simulation, and characterization of near-spurious-free shear horizontal surface acoustic wave (SH-SAW) resonators that utilize a short acoustic aperture (A) in a LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si functional substrate. By forming a miniature design through reducing the aperture of the interdigital transducer (IDT) from 20 wavelengths ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda {)}$ </tex-math></inline-formula> to only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\lambda $ </tex-math></inline-formula> , we observed a significant reduction in the transverse resonance of the guided SH-SAW, while still retaining the maximum Bode- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{{\textit {ma}{x}}}{)}$ </tex-math></inline-formula> . The proposed miniature resonators exhibit an excellent <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{{\textit {ma}{x}}}$ </tex-math></inline-formula> of 1,200 and an 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">$\mathbf {k}_{{\text {eff}}}^{{{2}}}{)}$ </tex-math></inline-formula> of 25% at 1 GHz with thin gold (Au) electrodes. These properties led to a high figure-of-merit (FoM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}_{{\text {eff}}}^{\mathbf {{2}}} \boldsymbol {\cdot }{Q}_{{\textit {ma}{x}}}{)}$ </tex-math></inline-formula> of 300. Using this technique, GHz SH-SAW resonators with miniaturized transducer capacitance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}_{o}$ </tex-math></inline-formula> down to 160 fF are also characterized with a high FoM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text {max}} >$ </tex-math></inline-formula> 200. The implementation of such miniature resonators holds significant promise for emerging applications that demand a near-spurious-free response and scalable capacitance, such as RF impedance transformers and low power oscillators for ultra-low-power radios.