Ionic Liquid versus SiO₂Gated a-IGZO Thin Film Transistors: A Direct Comparison

Abstract

Here, ionic liquid gated field effect transistors have been extensively studied due to their low operation voltage, ease of processing and the realization of high electric fields at low bias voltages. Here, we report ionic liquid (IL) gated thin film transistors (TFTs) based on amorphous Indium Gallium Zinc Oxide (a-IGZO) active layers and directly compare the characteristics with a standard SiO<sub>2</sub> gated device. The transport measurements of the top IL gated device revealed the n-channel property of the IGZO thin film with a current ON/OFF ratio ~10<sup>5</sup>, a promising field effect mobility of 14.20 cm<sup>2</sup>V<sup>–1</sup>s<sup>–1</sup>, and a threshold voltage of 0.5 V. Comparable measurements on the bottom SiO2 gate insulator revealed a current ON/OFF ratio >108, a field effect mobility of 13.89 cm<sup>2</sup>V<sup>–1</sup>s<sup>–1</sup> and a threshold voltage of 2.5 V. Furthermore, temperature-dependent measurements revealed that the ionic liquid electric double layer can be “frozen-in” by cooling below the glass transition temperature with an applied electrical bias. Positive and negative freezing bias locks-in the IGZO TFT “ON” and “OFF” state, respectively, which could lead to new switching and possibly non-volatile memory applications.