Structural Instability in Amorphous In-Ga-Zn-O Films Investigated by Mechanical Stress Analysis

Abstract

Amorphous In-Ga-Zn-O (a-IGZO) experiences an inherent structural instability which restrict its applications in electronic devices. By utilizing an in-situ mechanical stress analysis, we characterized the phase and structural changes. The glass transition temperature, T g (423-562 • C) and fragility (18-28) in a-IGZO films were observed to ascertain quantitative criteria for the structural stability. The structural stability near T g was significantly reduced as the thickness decreased due to the effect of the unstable surface layer. The structural relaxation of glass below T g was identified as the viscous flow and densification.The use of amorphous materials as key functional materials in various electronic devices continues to increase because they exhibit superior flexibility, adequate processability and reasonable performance. However, because the amorphous phase is metastable structure compared with the crystalline phase, its properties may drift over time and cause instability when applied in devices. Therefore, an understanding of the structural stability of amorphous materials is a key step in the fabrication of stable electronic devices.Amorphous In-Ga-Zn-O (a-IGZO) has been actively employed in electronic applications due to its high electron mobility and high stability of amorphous structure. 1 However, if a-IGZO is utilized as a thin film structure in electronic applications, high structural stability of a-IGZO can be hindered by the effect of surface. As thinner the film, higher the surface-to-volume ratio in film, therefore effect of the surface instability will be more significant: unconstrained bonds in surface are reported to be in high mobility of atoms, 2 and distinct coordination distributions in surface of amorphous Al 2 O 3 films affect the structural stability. 3 Besides, surface-originated instabilities were observed for many polymeric glasses. [4][5][6] Unfortunately, the underlying principles of structural stabilities of a-IGZO films remain unclear due to the difficulties encountered in experimental quantification. Because the amorphous state experience complex phase and structural changes and the structural stabilities also changes based on temperature and deposition conditions, the identification of proper quantitative parameters is challenging.As depicted in Fig. 1, the phase and structural changes in the amorphous state during heating are categorized by three steps: the first step consists of the structural relaxation of glass, which is a selfstabilization process that accompanies structural changes; the second step consists of the glass transition, which is the phase transition toward a liquid-like structure that is referred to as a super-cooled liquid and the third step consists of crystallization, in which the phase changes to an ordered structure that is referred to as the crystalline state. 7 These changes are quantified by parameters such as the glass transition temperature (T g ), the crystallization temperature (T x ), and the fragility (the criterion for amorphous structura...

Thermally Stable Amorphous Oxide-based Schottky Diodes through Oxygen Vacancy Control at Metal/Oxide Interfaces

“…To verify the effect of Ga stoichiometry control on the SR behavior of a-IGZO, an in situ wafer curvature measurement system 22,33 was introduced. (Fig.…”

“…4a). By monitoring curvature changes with the volumetric changes of the a-IGZO films by SR and glass transition during heating, the parameters describing structural and phase changes in amorphous materials can be precisely quantified 22 . The detailed information for analysis method of curvature measurement system was provided in Fig.…”

“…At the Schottky contact, intrinsic atomic rearrangement in AOSs, which is known as structural relaxation (SR) 22–24 , can affect the rectification property of diodes under thermal circumstances, even below the glass transition temperature ( T g ), by increasing the doping concentration of the AOSs without changes in the absolute V O concentration. The origin of SR-driven doping suggests that the densification of a local structure with V O s transforms the electronic state of deep-donor- V O s to shallow-donor- V O s 25 .…”