Investigation on the temperature coefficient of frequency performance of LiNbO3 on quartz and glass surface acoustic wave resonators

High impedance ratio (Z-ratio), low temperature coefficient of frequency (TCF) and spurious free characteristic are three main requirements for surface acoustic wave (SAW) resonators. The reported LiTaO3/Quartz (Qz) hetero acoustic layer (HAL) resonator can satisfy them, but the bandwidth is too narrow. LiNbO3 (LN) is suitable for wideband resonators, but the TCF is too large due to its high coupling factor. In this work, we study wideband HAL SAW resonators combining LN and three kinds of substrates with positive TCF and small coefficient of thermal expansion, including Qz, ABC-G and ZERO glasses. By simulation, the Euler angles of (0 degrees, 101 degrees, 0 degrees) for LN, (0 degrees, 160 degrees, 90 degrees) for Qz, and the 0.1-0.2 lambda (lambda is the wavelength) LN thickness are used. Results show LN/Qz, LN/ABC-G and LN/ZERO exhibit Z-ratio of 82.7 dB, 76.2 dB and 76.2 dB, respectively. LN/ABC-G shows the lowest TCF of -61 ppm C-1 at resonance frequency and -62 ppm C-1 at anti-resonance frequency.