A 36% Scandium Aluminum Nitride pMUT - FBAR Dual Mode Pressure Sensor for IoT Applications

This work presents a novel dual-mode frequency-based pressure sensor, which implements a Piezoelectric Mi-cromachined Ultrasonic Transducer (pMUT) operating in the fundamental flexural mode around 1.4 MHz and in the S
1
bulk mode around 4.2 GHz. The sensor's active layer is fabricated with Scandium-doped Aluminum Nitride (ScAIN) thin film, with a doping level of 36%. The device's behavior is monitored under different temperature and pressure conditions by observing the resonance positions when excited at the respective modes. The sensor displays a change in the resonance frequency of the flexural mode and in the anti-resonance of the S
1
bulk mode, with a shift of 3.5 kHz at 1.4 MHz (0.25%) and 8 MHz at 3.6 GHz (0.22%), respectively. This shift is observed over a pressure range spanning from 1 mbar to 1 bar. Furthermore, when the temperature range is varied from 20°C to 200°C, the anti-resonance of the S1 bulk mode is monitored, resulting in the estimation of the first and second order temperature coefficients of frequency (TCFs) as -40 ppm/K and -110 ppb/K
²
, respectively.