O2 plasma treated polyimide-based humidity sensors

Abstract

The effect of non-plasma and plasma treated polyimide-based humidity sensors is presented. Pure oxygen was used to etch polyimide in a plasma etcher. The sensor treated in a plasma exhibited higher sensitivity and faster response speed against moisture. The plasma treated sensor had 3.4 times the sensitivity and responded almost twice as fast as the non-plasma treated sensor. A further comparison of sensor outputs, sensitivity and response speed are presented. Chemical analysis of the polyimide surface was carried out by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (ATR-FTIR). XPS and ATR-FTIR showed the increase in carbonyl carbon bonds, CO, after the plasma treatment. Geometrical modification was observed by atomic force microscopy (AFM). It showed considerable surface roughness after the plasma treatment. O₂ plasma treatment improved the sensitivity, and reduced the hysteresis of the sensor due to the increase in CO bonds in the polyimide.