Gate-to-source voltage response in high-sensitivity amorphous InGaZnO4 thin-film transistor pH sensors

In this paper, we discuss our top-gate-effect-based high-sensitivity amorphous InGaZnO4 thin-film transistor (a-InGaZnO TFT) pH sensor from the viewpoint of gate-to-source voltage (V-gs) response to small pH step variations. The a-InGaZnO TFT pH sensor, whose sensitivity is as high as 450mV/pH, shows V-gs response to a pH step change of 0.1 with negligible hysteresis and good linearity. Because the high sensitivity is based on the enhancement of parallel shift in the transfer characteristics through the top-gate effect, the V-gs range for detecting is randomly selected. (C) 2015 The Japan Society of Applied Physics