Setup and properties of a fully inkjet printed humidity sensor on PET substrate

A fully ink jet printed humidity sensor on a thin PET foil is presented in this paper. Conductive silver electrodes were ink jet printed in the first step. Afterwards film forming polymer particles were printed on top as the humidity sensitive layer. Capacitance measurements were performed to investigate the sensor behavior at different humidity levels. By optimization of the electrode printing parameters the required sensor area was significantly reduced. Systematic investigations for the improvement of the humidity dependent layer led to a suitable polymer film, which combines good processability by inkjet printing with adequate humidity sensitivity and small hysteresis. The proposed sensor shows a high potential for low cost applications, which requires thin and flexible humidity sensors. For the correction of the nonlinear sensor transfer function a correction function with three calibration points is proposed.