CMU MEMS Laboratory Publication Abstract


in Proceedings of the 3rd IEEE Sensors Conference (IEEE Sensors), pp. 955-958, October 24-27, 2004, Vienna, Austria.
CMOS MEMS Oscillator for Gas Chemical Detection
S. Bedair and G. Fedder
This work presents the fabrication and demonstration of a CMOS/MEMS electrostatically self-excited resonator gas detector under various gas exposures. The cantilever resonator includes a 100 µm square platform for the chemically sensitive layer, polystyrene. Polymer is deposited using a drop-on-demand inkjet. The electrostatically actuated resonator has approximately 967 pico-grams of polystyrene which was deposited in a 2 mg/mL 1 toluene: 1 xylene solution. An on-chip preamplifier converts the high impedance sensor output to a voltage usable off-chip. External feedback electronics complete a free-running oscillator at the mechanical resonant frequency of 5475 Hz with 40 dB SNR, a calculated 23.6 pg/Hz sensitivity, and a 1 Hz 3 dB width in a 1 Hz resolution measurement bandwidth. Initial tests demonstrate sensitivity to using an external bubbler with 1 L/min N2 flow. Frequency shift when the polystyrene is saturated with methanol, ethanol, 2- propanol, and acetone was 8.2, 8.0, 5.2 and 25.7 Hz, respectively.
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