AN INTEGRATED AMPEROMETRIC MICROSENSOR

An amperometric microsensor has been fabricated using techniques adapted from conventional microelectronic technology. The device was tested with 100 ppm of NO in humidified air, and gave a response an order of magnitude greater than a commercially available sensor and two orders of magnitude greater than a previously fabricated microsensor with special electrodes which were defined 'with metal masks' (G. J. Maclay, W. J. Buttner and J. R. Stetter, IEEE Trans., 35 (1988) 793). This previous work indicated that improved signal/noise would be expected for an electrode with a larger ratio of the square of the perimeter to the area (P2/A). The sensor was fabricated on a thermally oxidized layer of silicon dioxide on a silicon wafer. A gold layer of 3000 Å thick was deposited by thermal evaporation and then patterned by photolithography and etching. In order to obtain good adhesion of the gold to the silicon dioxide it was necessary to first deposit a thin layer of chromium. The working electrode was etched to contain many windows about 50 micrometers square in order to obtain an improved sensor geometry with large P2/A. A thin film of Nafion (a Du Pont trade mark) was spin-coated over the electrodes and served as the electrolyte (G. J. Maclay and J. R. Stetter, U.S. Patent applied for (1988)). A fixture was built to expose the Nafion surface of the sensor to gases. The response of the integrated microsensor to NO per gram of gold catalyst was about 5000 times greater than in the commercial sensor. Unfortunately the presence of the chromium adhesion layer led to corrosion in the electrodes which eventually destroyed the sensor operation. © 1990.