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 μm and 500 μm 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.