Realistic Nanostructure Modeling of Indium Gallium Zinc Oxide

Abstract

Indium-Gallium-Zinc-Oxide (IGZO) has been recently proposed as a substitute for amorphous silicon due to its low leakage current, high carrier mobility, and favorable low-temperature process conditions. However, the quaternary compounds give possibilities for various phases which results in a dramatic change in their electrical performance. For the application to high-performance devices, analysis of the realistic structures must be made with the Molecular Dynamics simulations utilizing a bond order potential that can provide the realistic arrangements of tens of thousands of atoms in a crystal. Several potential functions for the IGZO were made but were in the form of two-body interactions which are limited in representing the covalent bonds of the IGZO. Therefore, in this work, a Tersoff-style three-body potential function with a local bond order dependence was parameterized for the IGZO system by reproducing the calculated results from the first principles which were scaled to follow the experimental observation values. The newly developed potential not only shows stability at ambient room temperature conditions but also was able to generate the phase transition from the crystalline phase to an amorphous phase by melt-quenching method, showing an increase in bond lengths between Indium and the metal components around 3.2 Å and decrease in density from 5.91 g/cm3 to 5.69 g/cm3 consistent with the experimental results. In further investigation, the proposed potential was used for the simulation of the sputtering process, and the potential function not only showed the formation of the amorphous phase at room temperature conditions but successfully reproduced the atomic ratio of the sputtered film of In : Ga : Zn = 1 : 0.93 : 0.58 which is in reasonable agreements to the reported results. The sputtered IGZO film showed a low oxygen ratio, which shows that the film has many oxygen vacancies that induce a negative bias stress which degrades device performances and raises stability issues. For the increase of oxygen ratio, the simulation result suggests that the sputtering targets must contain a high ratio of oxygens up to six times of the ratio of the metal components. This widely transferable potential will save time and cost on the study of the realistic crystal structures of the IGZO and will promote the development of applications of the IGZO on nanoscale devices.