A sensor should be sensitive, selective, reversible, and inexpensive. We have demonstrated, for the first time, a highly sensitive, rapidly responding, conductiometric device based upon the application of a stabilized porous silicon interface. This sensor, which operates at an extremely low bias voltage, at room temperature, is now able to detect gaseous HCl, NH3, and NO (L. Seals, et al, J. Appl. Phys., 91, 2519 (2002)] at a level between 10 and 100 ppm (calibrated). The sensor, which has not yet been optimized, is simple in design, operates with a rapid response and is reversible. It can be made selective with surface coatings and can be integrated into arrays with measurement electronics. The key to the sensor response is a low resistance contact made to the silicon through electroless metallization of a modified porous silicon surface, resulting in contact resistances of less than 100O's, rather than the 200 kO - MO resistances normally observed with porous silicon devices.
We propose to investigate the sensor response as a function of structure and interface variation and establish the sensing mechanism in order to optimize sensor design and enhance sensitivity, selectivity, and response time. As a means of increasing sensitivity, we will study the effect of surface morphology, in a combined microporour/nanoporous structure, on response. To increase selectivity, surface coatings and selective membranes will be placed in combination with the sensor. Alternatively we will couple the sensor to a micro-GC column as a detector or in a multiple array format within the column itself.
