Exploring Low-Loss Surface Acoustic Wave Devices on Heterogeneous Substrates

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2022-08, Vol.69 (8), p.2579-2584
• Main Authors: Wu, Jinbo, Zhang, Shibin, Zhang, Liping, Zhou, Hongyan, Zheng, Pengcheng, Yao, Hulin, Li, Zhongxu, Huang, Kai, Wu, Tao, Ou, Xin
• Format: Article
• Language: English
• Subjects: Coplanar waveguides; Coupling coefficients; Impedance; Insertion loss; Interface stability; LiTaO₃-on-sapphire (LTOS); Lithium tantalates; piezoelectric filter; Radio frequency; radio frequency (RF) loss; Resonant frequency; Resonators; Sapphire; shear horizontal (SH)mode; Silicon; Substrates; surface acoustic wave (SAW) resonator; Surface acoustic wave devices; Surface acoustic waves; Temperature measurement; Thermal stability; Wireless communications
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2022.3179699

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 3 -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- Q ) 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 3 -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 3 /sapphire interface, the IL of the CPW and the impedance ratio (in addition to Bode- Q ) 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.