High-speed porous thin film humidity sensors

We evaluate two thin-film microstructures in high-speed humidity sensor applications. The first sensing structure consists of high aspect ratio SiO posts between metal electrodes. Examples of this microstructure were found to respond to steplike changes in humidity with speeds as low as 35 ms as moisture diffuses inward and 25 ms as dry air is added. The second sensor is the negative image of the first, a polymer matrix perforated by networks of high aspect ratio pores. In this case, response times on the order of 75 ms were measured as moisture was added to the system and 175 ms when dry air was added. (C) 2002 The Electrochemical Society.