Use of a single multiplexed CMOS oscillator as direct frequency read-out for an array of eight AlN Contour-Mode NEMS Resonant Sensors

This paper reports on the first demonstration of a single multiplexed CMOS oscillator circuit employed as direct frequency readout for an array of 8 nanoscaled aluminum nitride Contour-Mode Resonant Sensors (CMR-S). In this first prototype 8 thin-film (250 nm) AlN CMR-S operating at 186 MHz were fabricated on the same chip and simultaneously wire bonded to a Pierce-like oscillator circuit (fabricated in the ON Semiconductor 0.5 μm CMOS process) by means of 8 CMOS transmission gates addressed via a 3 bit on-chip decoder. The 8 CMR-S were simultaneously exposed to different concentrations of methanol (0.1-1% of the saturated vapor pressure) and their response was monitored in a time-multiplexed mode. Frequency shifts of 300 Hz corresponding to changes of mass per unit area of 7 ag/μm² were experimentally detected. Values of phase noise derived Allan deviation as low as 0.9 Hz were measured. Such Allan deviation translates in an estimated limit of detection of 21 zg/μm².