Selectivity Improvements and Response Time Scale of Porous Silicon Conductometric Gas Sensors

Abstract

Nanopore covered microporous silicon conductometric gas sensors have been fabricated using electrochemical etching in an HF and acetonitrile solution and standard cleanroom microfabrication techniques. Sensing of NH3, NOx, PH3, and SO2 at or below the ppm level has been accomplished. A porous silicon (PS) surface has been modified using selective depositions formed from electroless tin, gold, nickel, and copper solutions to increase the response to several gases including PH3. The diffusion of the PH3 analyte has been investigated in the nanopore and micropore regimes by numerical analysis. By comparing the response time of the hybrid porous sensor surface with numerical diffusion calculations based on a realistic model of the pores, it is demonstrated that Knudsen diffusion time scales dominate the sensor response.