Low-Cost pH Sensors Based on Low-Voltage Oxide-Based Electric-Double-Layer Thin Film Transistors

Indium-tin-oxide-based electric-double-layer (EDL) thin-film transistors (TFTs) are used as pH sensors. Such EDL devices show a low operation voltage of similar to 1.5 V and a high field-effect electron mobility (mu(FE)) of similar to 20 cm(2).V-1.s(-1) when phosphorous-doped nanogranular SiO2-based electrolyte films are used as the gate dielectric. The pH sensor based on such EDL TFT exhibits a high sensitivity of 58.1 mV.pH(-1) and a good linearity in the pH range from 2 to 12. In addition, such pH sensors present a low threshold voltage drift rate of 2.2 mV.h(-1) and a hysteresis voltage of 8.3 mV after a pH loop of 7 -> 4 -> 7 -> 10 -> 7.