A solidly mounted, high frequency, thickness shear mode bulk acoustic wave resonator using X-LiTaO3 thin plate and SiO2/Ta multilayer acoustic films

This paper describes a bulk acoustic wave (BAW) high-frequency resonator with a solidly mounted structure using a single crystal LiTaO3 (LT) thin plate. A Bragg reflector solidly supports the LT thin plate, which is fragile if self-suspended. The BAW resonator uses a thickness shear mode in 1.5 mu m thick X-LT. The Bragg reflector is made of four pairs of SiO2 and Ta films, i.e. eight layers in total. The fabricated device works at a resonance frequency of 1.14 GHz and an antiresonance frequency of 1.23 GHz, showing a bandwidth of 7.9% and a low-temperature coefficient of frequency of -16 ppm degrees C-1 and -26 ppm degrees C-1 at the maximum and minimum admittances, respectively. The measured impedance ratio is 61 dB, although the structure and fabrication process are not optimized yet, suggesting a high potential for this device.