Solution processed ZnInxOy sensing membranes on flexible PEN for extended-gate field-effect transistor pH sensors

Abstract

This work describes the impact of indium content of the structural properties and sensing characteristics of ZnInxOy sensing films for extended-gate field-effect transistor (EGFET) sensors. The synthesis of the ZnInxOy sensing films was made by a solution processing technique directly deposited on flexible polyethylene naphthalate (PEN) through a simple spin-coating method. The synthesized ZnInxOy films at three different indium concentrations (10%, 20% and 30% moles) were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy to examine their chemical features, film structures and surface morphologies, respectively. Experiments were performed to explore the pH sensitivity, drift rate, and hysteresis voltage in the ZnInxOy EGFET sensors. Compare with these conditions, a higher pH sensitivity of 61.76 mV/pH, a lower drift rate of 1.08 mV/h, and a smaller hysteresis voltage of ∼1 mV were obtained in the ZnInxOy EGFET sensor fabricated at the 20% condition. Moreover, after 500 bending cycles, the ZnInxOy EGFET sensor fabricated at the 20% condition showed good mechanical flexibility. The ZnInxOy EGFET sensor also demonstrated a high selective response towards H+. This result indicates that the ZnInxOy sensing film with a rougher surface and a higher Zn–O–In content to generate lower crystal deformities, imperfections and oxygen vacancies.