Influence of CuS membrane annealing time on the sensitivity of EGFET pH sensor

In this study, CuS membranes were deposited on glass substrates using spray pyrolysis, and then annealed at 150 °C for durations of 5, 15 and 30 min. The precursor materials for the synthesis of the CuS membranes include copper chloride and sodium thiosulfate dissolved in deionized water. 0.4 M concentration of the mixed solution was subsequently sprayed on the glass substrates at 200 °C. Afterwards, the as-deposit membranes were implemented as extended gate field effect transistors (EGFET) for pH sensors. The structure, morphology, resistance, sensitivity and linearity of the membranes were determined. The structural characteristics showed that the maximum average grain size of the CuS membrane was 24.2 nm after 30 min of annealing. The sensitivity of the membranes was measured in buffer solutions of pH 2, 4, 6, 8, 10 and 12. The sensitivity increased with annealing time until maximum values of 31.5 µA/pH and 27.8 mV/pH were attained at 30 min, with minimum resistance of 400 Ω and minimum hysteresis of 11.4 mV. Thus, the ideal annealing time for optimum sensitivity, resistance and hysteresis is 30 min.