Improvement of sensitivity and response speed of capacitive type humidity sensor using partially fluorinated polyimide thin film

We investigated the relationship between the relative humidity and the electrical capacitance of partially fluorinated polyimide thin films with the parameter of the thickness of polyimide, deposition angle of top Au electrode, and the fluorine content (in wt%) in polyimide. The electrical capacitance changed almost linearly over the humidity range of 0-80% RH. High sensitive polyimide humidity sensors were successfully prepared by adopting the double layered structure consisting of ultra thin anodic Ta2O5(ca. 50 nm) and polyimide (50 nm). The response speed of the sensors was also improved to less than 1s by oblique deposition of semi-transparent Au top electrode and the adsorption and desorption of water molecules proceeds more quickly by increasing the fluorine content of polyimide.