Miniature humidity micro-sensor based on organic conductive polymer - poly(3,4-ethylenedioxythiophene)

A resistive micro-sensor for humidity sensing based on a conductive polymer material that is deposited electrochemically is presented. The resistor is formed by filling a narrow air gap (12 mum) between two conductor pads with conductive poly(3,4-ethylenedioxythiophene) (PEDOT) polymer, and the resistance of the polymer micro-resistor thus formed is measured to be 41 Omega at a temperature of 20degC. The conductor pads are prepared with a thick layer (20 mum) of nickel using a multi-user microelectromechanical systems (MEMS) process. The area of the entire sensor is around 100 times 200 mum, making it very compact. The humidity sensor has been characterised within a sealed chamber where the relative humidity is controlled by different saturated salt solutions at a constant temperature of 20degC. The resistance of the sensor varies from 37 to 62 Omega from 22 to 99.9% of relative humidity at room temperature.