Wideband Surface Acoustic Wave Resonator With Good Temperature Stability Using LiNbO₃ on Glass

Currently, wideband surface acoustic wave (SAW) devices are in demand. However, SAW resonators with a large coupling factor have a large negative temperature coefficient of frequency (TCF). In this work, we developed a new hetero acoustic layer (HAL) structure combining LiNbO3 (LN) and a glass with a low coefficient of thermal expansion (CTE), called ABC-G glass, to obtain the resonator with both large bandwidth (BW) and low TCF. The bulk and leaky SAW (LSAW) velocities of ABC-G glass were measured by ultrasonic microspectroscopy (UMS) technology, and its positive temperature coefficient of velocity (TCV) was confirmed. The (0°, 101°, 0°) and (0°, 120°, 0°) LNs are selected for experiments. The measured results show impedance ratio (Z-ratio) and BW as high as 82 dB and 12%, respectively. The measured TCFs reach -27 ppm/°C and -24 ppm/°C at resonance and antiresonance frequency, respectively, which are significantly improved compared with LN/Quartz (Qz). Ladder filters composed of three LN/ABC-G resonators are prototyped using a T-type configuration, and the insertion loss lower than 1 dB with a fractional bandwidth (FBW) of 15.0% was demonstrated. At the same time, no spurious response was observed up to 10 GHz. The results shown in this work prove the high performance of the LN/ABC-G structure in applications requiring good temperature stability, large BW, and out-of-band spurious-free characteristics.