Fabrication of an anodized porous alumina relative humidity sensor with improved sensitivity

Abstract

Sensitivity is an important parameter of any humidity sensor. In recent times, nanostructure materials have been used to fabricate the capacitive-type humidity sensors to improve the sensitivity. However, for the nanostructure sensors, in most cases, the sensitivity improvement is not guaranteed although extra efforts are made in terms of time and cost. Our aim is to improve the sensitivity of an anodized porous alumina capacitive humidity sensor by a simple method. A nanostructure porous film has been formed on each side of a pure aluminum substrate (99% purity) by an electrochemical anodization method. Two parallel plate capacitors are formed by depositing metal plate on each side of the metal oxide film with bulk aluminum as the common electrode. The sensitivity has been increased by connecting the two parallel plate capacitive sensors in parallel. Thus, two capacitive sensors on single substrate are fabricated and connected in parallel to form the third capacitor, which is used as the humidity sensor. The sensitivity, response time, recovery time, and hysteresis of the sensors are determined with variation in the range from 10% to 99% relative humidity (RH). The sensitivity of the sensor obtained by connecting two capacitors in parallel has been increased by almost two times compared to the sensitivity of an individual sensor fabricated on each side.