Patterning of porous alumina for integrated humidity sensors

In this paper we would like to introduce our experimental results on the patterning of the thin film porous alumina sensing layer. We used three different approaches for the patterning of the alumina we would like to use in integrated humidity sensors in the future. The first was the wet etching of the completed alumina covering the entire wafer surface with conventional photolithography. The second method was based on selective anodization using photoresist as barrier layer to prevent the formation of alumina from aluminum where it is not necessary. In the third case we used a chemically resistant and conductive layer below the pre-patterned Al ldquoislandsrdquo for proper electrical connection needed during anodization. The results of the different methods were compared and optimal parameters were given where it was possible.