A new ammonia sensor based on a porous SiC membrane

Porous SiC has been found to be extremely sensitive to the presence of ammonia (NH/sub 3/) gas. We report the fabrication and preliminary characterisation of NH/sub 3/ sensors based on porous SiC and Al electrodes. The idea of the SiC is that it is a very durable material and that it should be good for sensors in harsh environments. Until now the only NH/sub 3/ sensors using SiC have been FET based, and the SiC was not porous. The SiC was deposited by PECVD on standard p-type single-crystal Si and was made porous by electrochemical etching in 73% HF and anodisation current-densities of 1-50 mA/cm/sup 2/. Because the etch-rate of Al in 73% HF is very low, we can use Al electrodes instead of Au. This also facilitates our sensor fabrication, as Al is more cleanroom friendly than Au. Preliminary data is given for our devices response to NH/sub 3/ in the range 0-10 ppm NH/sub 3/ in dry N/sub 2/ carrier gas.