Novel resistive-type humidity sensor based on multiwall carbon nanotube/polyimide composite films

A novel resistive-type relative humidity (RH) sensor based on plasma-treated multiwall carbon nanotube/polyimide (p-MWCNT/PI) composite films is reported. Details of the fabrication process and sensing characteristics such as linearity and sensitivity are described. The electrical resistance of the p-MWCNT/PI composite film shows typical concentration percolation behavior with increasing p-MWCNT loading. At loadings beyond the percolation threshold (0.05 wt%), this sensor exhibits very good linearity with a positive slope over the entire operational RH range. The sensor has a humidity sensitivity of about 0.0047/% RH and a linearity correlation (R2) of 0.9999. A humidity sensing mechanism for the p-MWCNT/PI composite film is proposed on the basis of charge transfer between adsorbed water molecules and the p-MWCNTs.