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
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.