AlN-based solid mounted resonators functionalized with WO3 films for NO detection

Abstract

This work presents the design, manufacture and characterization of nitric oxide (NO) sensors operating at high temperatures. The sensors rely on AlN-based solidly mounted resonators (SMRs) as transduction devices. WO₃ films are sputtered under different deposition conditions on the upper electrode of the devices to act as functionalization layers. We assess the topography and crystallinity of the layers before and after an annealing process of 350 °C for 12 h in air, observing a dominant monoclinic phase without significant degradation of the Q factor after such process. The characterization of the SMR sensors indicates that sub ppm detection can be achieved by all the studied configurations in the 200–300 °C range, with two of the sensors achieving high sensitivities even at 350 °C. The highest values reported are 5.32 kHz/ppm and 5.48 kHz/ppm for resonant and anti-resonant frequencies at 200 °C.