Bilayer indium gallium zinc oxide electrolyte-gated field-effect transistor for biosensor platform with high reliability

The electrolyte-gated indium gallium zinc oxide field-effect transistor (IGZO-EGFET) has advantages for use in biosensors; e.g., it is label-free and has a high sensitivity, low cost, and low power consumption. However, the reliability of IGZO-EGFET under various conditions has not been proven. In this study, we demonstrate a bilayer IGZO-EGFET with high reliability and reproducibility under various pH and buffer conditions regardless of the surface functionalization. The bilayer of IGZO developed in situ by controlling the O₂ pressure during deposition has a varying number of O vacancy-related trap sites. The top layer having less O vacancies provides a self-passivation effect, whereas the bottom layer with more O vacancies acts as the active layer of the device. The bilayer IGZO-EGFET exhibits not only high chemical stability but also very little pH-hysteresis upon cyclic variation of the pH. Moreover, it exhibits a reliable and reproducible signal in phosphate buffer solutions with different concentrations, even after surface functionalization. The biotin-functionalized bilayer IGZO-EGFET exhibits a selective sensitivity for streptavidin, with a linear relationship of 10.7 mV/dec. The proposed bilayer IGZO-EGFET structure is expected to be used as a platform for various biosensing devices.