Fully Printed Flexible Humidity Sensor

A humidity sensor that employs interdigitated capacitors (IDC) printed with silver (Ag) nanoparticle based ink on a flexible poly ethylene terephthalate (PET) substrate was successfully fabricated using gravure printing process. Thicknesses of 1 mu m and 500 mu m of a humidity sensitive polymer poly (2-hydroxyethyl methacrylate) (pHEMA) was deposited on the IDCs by means of gravure printing. The capacitive response of the sensor towards relative humidity (RH) was measured in the range of 30% RH to 80% RH; the maximum percentage change in capacitance was 172 % at 80% RH when compared to base capacitance at 30% RH. The humidity response of the printed sensor revealed a very high stability with a maximum error of 0.6 % and 0.8 % from the average value at 40% RH and 60% RH, respectively. (C) 2011 Published by Elsevier Ltd.