CMU MEMS Laboratory Publication Abstract


in M.S. Thesis, December 2004, Carnegie Mellon University, Pittsburgh, PA.
CMOS MEMS Oscillator for Gas Chemical Detection
S. Bedair
This work describes the fabrication and testing of a CMOS/MEMS electrostatically self-excited cantilever based resonator gas detector under various gas exposures. CMOS/MEMS fabrication of a mass sensitive gas detector allows for integration with CMOS circuitry potentially leading to fully integrated sensor arrays of different physical modalities for organic vapors and biological agents. Such an environmental sensor will be portable, cheap, and small compared to other non-integrated gas detection methods. The cantilever resonator includes a 100 ┬Ám square platform for the chemically sensitive receiver layer used in this work, polystyrene. The polymer is deposited using a drop-on-demand inkjet, an attractive technique due to its low cost and ease of processing. The ability of casting precise amounts of different sensitive materials combined with fully integrated mass sensitive oscillator electronics is a potential technology for single chip electronic noses and "lab on chip" applications. The device was tested with and without 2.3 pL of polystyrene. Nitrogen gas saturated with methanol, ethanol, 2-propanol, and acetone gases was flowed over the device and gas concentration sensitivities of -4.56, -9.14, - 10.21, and -8.54 x 10-5 Hz/ppm, respectively, were found. Theoretically, a higher limit of ethanol gas sensitivity of - 0.03 Hz/ppm was estimated for the current device with a maximum achievable polystyrene volume, 54 pL, that can deposited onto the device. Further improvements for future designs are proposed with an estimated sensitivity of -0.37 Hz/ ppm, which is a three order of magnitude improvement over the current device.
© 2004 Carnegie Mellon University, Department of Electrical and Computer Engineering.
Full paper (PDF) (opens in new window).

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