Microstructural evolution and phase composition of In2Ga2ZnO7 ceramic targets during sintering

Abstract

The photovoltaic properties of indium–gallium–zinc oxide (IGZO) thin film utilized in electronic information applications depend on the quality and performance of the corresponding target. In this study, high-energy ball milling was combined with atmospheric sintering to achieve precise control over the phase composition and microstructure of In₂Ga₂ZnO₇ ceramic targets. This was achieved by controlling the sintering process and performing thermodynamic calculations to analyze the phase transition process. Further, the electronic structure simulation results of the relevant phases were analyzed, and crystal structure models were constructed. According to the density functional theory calculations, the enthalpy of formation of In₂Ga₂ZnO₇ was found to be the largest, followed by those of InGaZnO₄ and ZnGa₂O₄, which indicates that the In₂Ga₂ZnO₇ phase exhibits the highest thermal stability. The relationship of the enthalpy of formation corresponds to two distinct reactions of the IGZO powders. The ZnGa₂O₄ phase is initially formed and remains stable for an extended period. This is followed by the rapid formation and subsequent disappearance of the InGaZnO₄ phase within a narrow temperature range. Finally, a single In₂Ga₂ZnO₇ phase is formed. The target sintered at 1500 °C exhibits a narrow band gap and the lowest porosity, which results in the highest relative density (99.52%) and the lowest resistivity (3.4 mΩ·cm). These experimental findings can provide guidelines for controlling the phase and microstructural characteristics of In₂Ga₂ZnO₇ targets with the aim of producing IGZO targets with excellent properties, including homogeneous composition, high density, and low resistance in the field of flat displays.

Graphical abstract