Porous SiC as an ammonia sensor

Ammonia gas (NH3 detection is widely used, from air conditioning to searching for life on mars, and many situations there is an increasing demand for cheap and reliable NH3 sensors. When used as the dielectric in a capacitive sensing arrangement, porous SiC has been found to he extremely sensitive to the presence of NH3 gas. The exact sensing method is still not clear, but NH3 levels lower than ∼0.5ppm could be detected. We report the fabrication and preliminary characterisation of NH3 sensors based on porous SiC. 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 1-50mA/cm2. Preliminary data is given for our devices response to NH3 in the range 0-10ppm NH3 in dry N3 carrier gas, as well as the response to relative humidity between 10%RH and 90%RH