Fabrication of Nanostructured Metal Oxide Thin Film Capacitive Humidity Sensor

Abstract

Modern and daily applications such as air conditioners and humidifiers and moisture/humidity sensors are extensively used in several industrial process control, medical sciences, food manufacture, farming, home ventilation, meteorological weather forecasting, medical incubation, manufacturing of important electrical equipment’s, fabrication of semiconducting devices, organic LEDs, preservation of foods and food products, etc. This chapter describes the fabrication of two important capacitive humidity sensors such as interdigitated and parallel plate types. Range of humidity measurement is extremely wide. It extends from traces (low level) of humidity to percentage relative humidity. Parallel plate capacitor is for low-level humidity detection, and the interdigitated capacitor is for measuring relative humidity level. Both types of sensors have been fabricated by using nanostructure porous aluminum oxide (Al2O3) thin film (prepared by sol-gel method). Porous Al2O3 is one of the most suitable metal oxide sensing materials that have potential to measure humidity over wide range. Its small pore radius makes it very sensitive and attractive to low humidity. Details of fabrication of the sensors using sol-gel dip-coating method have been discussed. Also, the preparation of boehmite Al2O3 sol solution for the metal oxide film (by adopting the Yoldas method) has been explained in details.