Hydrogen barrier performance of sputtered La2O3 films for InGaZnO thin-film transistor

Abstract

We report the hydrogen barrier performance of sputtered La2O3 thin films for the device stability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). Hydrogen acts as a shallow donor in a-IGZO films, which makes TFTs conductive, resulting in degradation of their on/off properties. Since hydrogen can be easily incorporated by external environments or post-processing, an appropriate hydrogen barrier is essential for enhancing device stability. La2O3, with its extreme electronegativity, can provide excellent hygroscopic characteristics. Because hydrogen exists in the form of -OH groups inside a-IGZO films, La2O3 is expected to be a promising barrier material for preventing hydrogen incorporation. Therefore, we investigate the growth characteristics of sputtered La2O3 thin films as hydrogen barrier layers, focusing on variations in growth rate, refractive index, and film stress, which depend on various process parameters, such as radio-frequency (RF) power, O-2 partial pressure, and substrate temperature during reactive magnetron sputtering. The effects of these parameters on hydrogen barrier properties are systematically investigated and correlated with the microstructures of La2O3 films. The results demonstrate that La2O3 films grown with low RF power and low O-2 partial pressure have an amorphous phase and provide excellent hydrogen barrier performance. We anticipate that these experimental results will help improve the environmental stability of a-IGZO TFTs.