An Extended-Gate FET-Based pH Sensor With an InZnxOy Membrane Fabricated on a Flexible Polyimide Substrate at Room Temperature

In this letter, a room-temperature synthesized amorphous indium-zinc oxide (InZn_xO_y) sensing membrane on flexible polyimide is employed as an extended-gate field-effect transistor (EGFET) pH sensor for the first time. The InZn_xO_y-based EGFET sensor exhibited a high pH sensitivity of 56.29 mV/pH with an excellent linearity of 0.999. Furthermore, it also demonstrated good stability in terms of a low hysteresis voltage of 4.6 mV and a small drift rate of 2.08 mV/h, presumably suggesting the formation of uniform, dense, small grains, and stoichiometric InZn_xO_y thin film, which facilitates high conductivity and provides a large number of surface binding sites. The InZn_xO_y-based EGFET pH sensor showed an excellent mechanical bendability after more than 500 bending cycles.