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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 µm 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.
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