Stimuli-responsive polymer as gate dielectric for organic transistor sensors

Abstract

Temperature is a characteristic often correlated with environmental and health issues. This paper presents an organic thin film transistor (OTFT) based temperature sensor having a detection range of 30-45 degrees C, which, therefore, encompasses the human body temperature. The OTFT sensor featured thermosensitive poly(N-iso-propylacrylamide) (PNIPAM) and pentacene as the gate dielectric and semiconductor, respectively. The PNIPAM film possessed a dielectric constant of 4.2 with very low leakage current density. The OTFT exhibited high electrical performance, with a hole mobility (mu) of 0.90 +/- 0.04 cm(2) V-1 s(-1), a threshold voltage (V-th) of -15.4 +/- 1.16 V, and an on/off ratio of 10(4). Significant changes in the drain current and the values of V-th and mu occurred when the temperature of the device was varied within the range 30-45 degrees C at an interval of 0.5 degrees C. The operating principle for this temperature sensor was based on the structural transformation of the PNIPAM dielectric and the enhanced charge transport of the pentacene semiconductor upon varying the temperature. Flexible OTFTs fabricated on polyethylene terephthalate substrate displayed hole mobilities as high as 0.39 +/- 0.01 cm(2) V-1 s(-1), values of V-th of 18.6 +/- 0.45, and on/off ratios of 10(2), and were workable for over 100 bending cycles.