ZnO/AlN stacked BAW resonators with double resonance

We have fabricated BAW resonators with a piezoelectric bilayer that combines ZnO and AlN films. These stacked devices show two resonances that could be used to simultaneously track temperature variations and another parameter, such as loaded mass or pressure. We have assessed the crystal quality of the stacked piezoelectric films using XRD and FT-IR. The TCF of the devices has been measured in a temperature range from 25°C to 100°C. Both resonances show different TCFs, of -15.8 (ppm/°C) and -19.9 (ppm/°C), and quality factors Q over 500, which make them suitable for measurement of two parameters.