Harsh Environmental Surface Acoustic Wave Temperature Sensor Based on Pure and Scandium doped Aluminum Nitride on Sapphire

This paper investigates the performance of surface acoustic wave (SAW) devices as low power MEMS temperature sensors using reactive sputter deposited aluminum nitride (AlN) and scandium doped aluminum nitride (AlScN) as piezoelectric layers on sapphire substrates. In detail, devices with a wavelength of 16 μm are fabricated with both AlN and AlScN films having a resonance frequency at room temperature of ~354 MHz and ~349 MHz, respectively. The samples are placed in a furnace and measured in argon atmosphere up to 800 °C. The temperature dependency on the frequency shows for both materials a linear decrease up to the maximum measured temperature level resulting in constant temperature coefficients of −27.62 kHz/°C and −27.81 kHz/°C, respectively.