A locally cured polyimide-based humidity sensor with high sensitivity and high speed

A novel capacitive-type humidity sensor based on polyimide thin films locally cured using MEMS microhotplate was developed. The locally cured polyimide films have been characterized using infrared spectroscopy and compared to those of films cured using a conventional thermal process. The polyimide locally cured at temperature over 350degC for 1 hour was fully cured. There were no significant differences in the polyimide thin films between locally cured on microhotplate and cured in convection ovens. The measured sensitivity for a sensor with a 1400 aring-thick polyimide film is 0.78 pF/%RH. Measurements show an offset drift of less than 1% RH at 50% RH and 37degC, and a hysteresis of <0.6%RH over a range of 25-85% RH, and a time response of 2.5 s. These results can be attributed to both locally-cured polyimide and sensor design and show the possibility of locally-cured polyimide films as high-speed, high-sensitivity humidity sensors.