A Capacitive Type Humidity Sensor with Potassium Ion Doped TiO2 Thin Film as Humidity Sensing Material

A novel capacitive type relative humidity sensor has been fabricated and studied using micro-electromechanical system (MEMS) technology. The sensor is composed of three parallel plate capacitors on a silicon substrate. Titanium dioxide doped with 10 wt.% doped potassium served as dielectric and humidity sensing material between two capacitor plates made up of aluminum metal. The humidity sensing principle of the sensor was based on the permittivity change of doped coated film upon adsorption/desorption of water vapor molecules. Capacitance values measured at different relative humidity levels showed that the device is very sensitive to it, due to nanometer-sized grains and porous structure of the annealed film, and coated with an appropriate solution made from sol-gel method. Increased surface area and roughness have been confirmed by performing XRD, Raman spectroscopy, and SEM analysis. Experimental results obtained at different environments exhibited that device stability, repeatability, robustness, reliability is fairly impressive. The sensor can measure relative humidity in the range of 20%-97% RH with sensitivity in nF/RH%.