Title :
CMOS MEMS oscillator for gas chemical detection
Author :
Bedair, Sarah S. ; Fedder, Gary K.
Author_Institution :
Dept. of Electr. & Comput. Eng., Carnegie Mellon Univ., Pittsburgh, PA, USA
Abstract :
The paper 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.
Keywords :
CMOS integrated circuits; feedback oscillators; gas sensors; micromachining; micromechanical resonators; microsensors; polymers; preamplifiers; sensitivity; 100 micron; 2-propanol; 5475 Hz; CMOS MEMS oscillator; SNR; acetone; cantilever resonator; drop-on-demand inkjet; electrostatically self-excited resonator; ethanol; external bubbler; feedback electronics; free-running oscillator; gas chemical detection; gas detector; mechanical resonant frequency; methanol; on-chip preamplifier; polymer; polystyrene; toluene-xylene solution; Chemical sensors; Fabrication; Gas detectors; Impedance; Mechanical sensors; Micromechanical devices; Oscillators; Polymers; Preamplifiers; Voltage;
Conference_Titel :
Sensors, 2004. Proceedings of IEEE
Print_ISBN :
0-7803-8692-2
DOI :
10.1109/ICSENS.2004.1426330
