Exploring Low-Loss Surface Acoustic Wave Devices on Heterogeneous Substrates
Jinbo Wu, Shibin Zhang, Liping Zhang, Hongyan Zhou, Pengcheng Zheng, Hulin Yao, Zhongxu Li, Kai Huang, Tao Wu, Xin Ou
Abstract
This article presents shear horizontal surface acoustic wave (SH-SAW) devices with excellent temperature stability and low loss on ultrathin Y42-cut lithium tantalate film on sapphire substrate (LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -on-sapphire, LTOS). The demonstrated resonators exhibit scalable resonances from 1.76 to 3.17 GHz, effective electromechanical coupling coefficients between 5.1% and 7.6%, and quality factors (Bode- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) between 419 and 3019. The filter with a center frequency of 3.26 GHz features a suppressed spurious passband, a 3-dB fractional bandwidth (FBW) of 3%, and a minimum insertion loss (IL) of 2.39 dB. In addition, coplanar waveguides (CPWs) and SH-SAW resonators built on LTOS and LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -on-insulator (LTOI) substrates were compared over a temperature range of 25 °C–150 °C. Due to the extremely high resistivity of the sapphire and the excellent thermal stability of the LiTaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /sapphire interface, the IL of the CPW and the impedance ratio (in addition to Bode- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) of the SH-SAW on the LTOS are maintained well even at 150 °C, while those on the LTOI seriously deteriorate. Of these, the impedance attenuation of LTOS-SAW at the antiresonant frequency is only 3.7 dB at 150 °C, whereas that of LTOI-SAW reaches 9.6 dB, demonstrating excellent temperature stability of the LTOS substrate’s radio frequency (RF) performance. Overall, the SAW devices on LTOS substrates show great potential for temperature-sensitive and low-loss applications in RF wireless communications.