A porous SiC ammonia sensor

When used as the dielectric in a capacitive sensing arrangement, porous SiC has been found to be extremely sensitive to the presence of ammonia (NH3) gas. The exact sensing method is still not clear, but NH3 levels as low as 0.5 ppm could be detected. We report the fabrication and preliminary characterisation of NH3 sensors based on porous SiC and Al electrodes. SiC is a very durable material and should be good for sensors in harsh environments. So far, the only NH3 sensors using SiC have been FET based, and the SiC was not porous. In our devices, SiC was deposited by PECVD on standard p-type single-crystal Si and was then made porous by electrochemical etching in 73% HF using anodisation current densities of 1–50 mA/cm2. Preliminary data is given for our devices response to NH3 in the range 0–10 ppm NH3 in dry N2 carrier gas.