Relative humidity sensors using porous SiC membranes and Al electrodes

There is a need for humidity sensors that can operate in harsh chemical environments. In this respect SiC is a very promising material. Membrane humidity sensors using porous SiC as the (membrane) sensing element have been fabricated and tested. Earlier work established optimal anodisation conditions to make porous SiC (optimised for humidity sensing) to be: electrochemical etching in 73% HF, using an anodisation current density JA=1 mA/cm2. Due to the very low etch-rate of Al in 73% HF, we are able to use Al electrodes instead of Au, making the fabrication process of our sensors more cleanroom friendly. The response of porous SiC membrane devices, with sensitivities up to ∼200% will be discussed. Also, we will discuss the effects on sensor response of accelerated aging in an environmental test furnace and harsh environments such as the outlet of a car exhaust. SEM images are used to examine the membrane structures and porous SiC surfaces.