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 (R2) 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.