Fully Inkjet-Printed Flexible Temperature Sensors Based on Carbon and PEDOT:PSS1

Printed organic sensors on plastic substrates are of great interest due to their flexibility and low-cost fabrication. We here present a fully inkjet-printed flexible Wheatstone bridge used for temperature sensing. A carbon nanoparticle ink and a mixture of poly(3,4-ethylenedioxythophene):poly(4-styrene-sulfonate) (PEDOT:PSS) and dimethyl sulfoxide (DMSO) are used as positive (PTC) and negative (NTC) thermal coefficient materials, respectively. Different carbon inks and DMSO concentrations from 0.5 to 40 wt% are evaluated in order to optimize the temperature coefficient of resistance (TCR) and the reliability of the PTC and NTC materials. The single materials are printed on PEN substrates, and subsequently encapsulated. A climate chamber is used to evaluate their reliability. The Wheatstone bridge sensors show good linearity and little hysteresis within a temperature range of 20 °C to 70 °C and exhibit a sensitivity of ∼4 mV/°C at a bias current of 1 mA. We furthermore investigate the reproducibility of the temperature sensor fabrication in order to analyze the potential of industrial applicability of inkjet-printing.