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 ~ 1.5 V and a high field-effect electron mobility (μFE) of ~ 20 cm<sup>2</sup>·V<sup>-1</sup>·s<sup>-1</sup> 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<sup>-1</sup> 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<sup>-1</sup> and a hysteresis voltage of 8.3 mV after a pH loop of 7→ 4→ 7→ 10→7.

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