Gas sensor fabricated in commercial CMOS technology

Reports the design of a bulk-micromachined gas sensor fabricated in commercial 2 /spl mu/m n-well CMOS technology using a high level computer aided design tool. The gas sensor is a palladium-oxide-polysilicon micromachined MOS structure. The design includes an additional layer in CMOS called 'open' which enables the formation of a 'cavity' in the silicon substrate. After the fabrication of CMOS chips single maskless etch in an aqueous solution of ethylenediamine-pyrocatechol (EDP) or xenon difluoride (XeF/sub 2/) is done to create a cavity. This results in a micromachined structure with the polysilicon and the oxide on it, suspended over the 'cavity' formed. Finally palladium is deposited over the micromachined structure in a high vacuum evaporator. The adsorption of the hydrogen gas in palladium changes C-V characteristics of the MOS structure. In the present work we report part of the studies on gas sensor development.