Porous SiC as an ammonia sensor

Ammonia gas (NH₃) detection is widely used, from air conditioning to searching for life on Mars, and in 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 be extremely sensitive to the presence of NH₃ gas. The exact sensing method is still not clear, but NH₃ levels lower than ∼0.5 ppm 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 1-50 mA/cm². Preliminary data is given for our devices response to NH₃ in the range 0-10 ppm NH₃ in dry N₂ carrier gas, as well as the response to relative humidity between 10% RH and 90% RH.