A Simple MOX Vapor Sensor on Polyimide Substrate for Measuring Humidity in ppm Level

This paper deals with the development of a novel metal-oxide-based sensor for measuring moisture in ppm level. The device consists of parallel plate capacitive structure having γ-Al
₂
O
₃
nanostructured sensing film deposited on the polyimide by sol-gel method. The pore morphology of the thin film has been studied by Brunauer-Emmett-Teller, atomic force microscopy, and field emission scanning electron microscopy. The sensor has been designed to make it suitable for integrated type of application. The electrical characteristics of the sensor have been measured using Agilent 4294A impedance analyzer over the frequency from 1 to 50 kHz. The sensitivity of the sensor for 3.5-800-ppm humidity range is 0.13 pF/ppm. The response and recovery time are 158 and 216 s, respectively. The experimental results show that the output is linear (4.2%), reproducible, and stable. Proposed work is aimed to develop a low power consumption sensor on fully flexible and plastic substrate commercially used in printed circuit board for mobile application.