A Mass Sensor Based on an Aluminum Nitride Mems Oscillator for Gas Sensing Applications

This research presents a mass sensor based on a piezoelectric thin-film MEMS oscillator with high mass resolution, real-time detection, and extremely linear behavior for gas sensing. A length-extension (LE) mode aluminum nitride (AlN) resonator with a designed frequency of 5.17 MHz has a quality factor (Q) of 747 in air, which is twice the LE mode lead zirconate titanate (PZT) resonator design. To achieve a miniaturized sensor module, a board-level piezoelectric oscillator consists of an AlN MEMS resonator, a commercial amplifier, an all-pass filter, a band-pass filter, and buffer circuits to fulfill the oscillation conditions. A carrier frequency of 5.17 MHz and a phase noise of-115 dBc/Hz at 1 kHz offset in air were observed. A mass resolution of 0.38 pg for the demonstrated mass sensor is implemented in this research. Finally, the gaseous acetone measurement results present the coefficient of determination (R
²
) of 0.98 between the frequency shifts and the gas volume of 0.5 ml to 5.0 ml, showing the potential to be used as a real-time monitor for gas sensing applications in ambient.