Fig. 3
Electrochemical impedance spectroscopy (EIS) analysis using solutions with various pH levels. (A) Schematic of the experimental setup of EIS and electrical connections of the working reference and counter electrodes. The Ag/AgCl RE was utilized as the RE to inhibit the creation of an EDL at the interface between the Ag/AgCl RE and the electrolyte. (B) Bode phase showing the effect of pH on the electrochemical and semiconducting properties of the interface between IGZO and electrolyte. In the inset, an equivalent electrochemical circuit is depicted. (C) Nyquist plot displaying the real (Ζ′) and imaginary (Ζ′′) components of impedance for the IGZO-electrolyte-Ag/AgCl RE configuration. The points indicate the experimental data, while the solid lines of matching colors represent the fitting outcomes. (D) Extracting resistance and capacitance parameters with different pH solutions. Schematic of the pH sensing mechanism at the IGZO-electrolyte interface according to pH solution with (E) top gate biasing and (F) top and back-gate biasing.
