Temperature coefficient and ageing of BAW composite materials

Thin film resonators have been made that exhibit a high degree of temperature compensation. These resonators are composed of piezoelectric aluminum nitride films, aluminum top and bottom electrodes, and are compensated with layers of silicon dioxide within the resonator. The resonators are fabricated with the solidly mounted resonator (SMR) configuration using a sequence of aluminum nitride and silicon dioxide reflector layers. Silicon dioxide has a positive temperature coefficient and can be used to offset the -25 ppm per degree C temperature coefficient of aluminum nitride. Results are reported on hermetic packaging, temperature cycle testing, temperature coefficient measurements, and preliminary ageing. This paper reports on progress made in ageing studies and temperature cycling of 644 MHz temperature compensated resonators.