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Investigation of pH sensor based on liquid-solid dual-gated IGZO thin-film transistor

A pH sensor based on liquid-solid dual-gated IGZO thin-film transistor (LSDG TFT) has been demonstrated. Its sensitivity reaches 237 mV pH−1, which is nearly 4 times the Nernst limit at room temperature. The huge capacitance of the liquid gate with electric double layer (EDL) can contribute to the high sensitivity by capacitance coupling effect. However, the stability is a serious problem for its practical application. At pH measurement range of 4.00–9.18, the threshold voltage deviates seriously from the initial value at each pH solution after few cycling test. The study found that the IGZO thin film is susceptible to corrosion in pH 4.00 buffer solution. In contrast, the oxygen-related defects in the IGZO thin film are increased by immersing in pH 9.18 buffer solution, although no obvious corrosion is observed. These are presumably the causes of the device instability.