(Invited) Atomic Layer Deposited Amorphous Igzo Semiconductor with Vertical Composition Engineering for High Mobility Field Effect Transistor

Abstract

Amorphous oxide semiconductors have been widely studied for the potential use in flat-panel displays such as active matrix liquid crystal display (LCD) and Organic light emitting didoes (OLEDs). Since reporting amorphous InGaZnO semiconductor thin film transistor (TFT) in 2003 & 2004, many multi-component oxide semiconductors have been intensively investigated and developed by physical vapor deposition (PVD) method. Very recently, the sputtered InGaZnO TFTs are already adopted in mass-production to fabricate AMOLED TVs. Also, semiconductor industries have looked at metal oxide semiconductor thin films as an alternative Si channel layer because this semiconductor exhibited extremely low-off current level (below 10-18A/um). It is the unique property to decrease power consumption for various semiconductor devices. However, there remain several problems such as enhancing field effect mobility, composition uniformity, bias-temperature stability, and p-type oxide semiconductor in order to go further for the future device applications.In this talk, I will introduce various oxide semiconductor materials with atomic layer deposition (ALD) methods. Unlike PVD, ALD method has unique properties, including controlling atomic-level-thickness, manipulating atomic-level-composition control, and depositing impurity-free & uniform films. The key materials such In2O3, ZnO, SnO2, and Ga2O3 will be summarized and then I will show the combinatorial research works in terms of amorphous InGaZnO semiconductor thin film transistors. Generally, electrical properties of amorphous oxide semiconductors are strongly dependent on each element composition. The indium (In) rich InGaZnO exhibited a high mobility of 50cm2/V.sec. However, the In-rich InGaZnO TFTs have the demerit of negative threshold voltage owing to intrinsically high carrier density. I will present that In-rich IGZO TFTs with vertical stacked InOx, ZnOx and GaOx atomic layers show excellent performances such as saturation mobility of ~ 74cm cm2/V.sec, threshold voltage of -1.3V, on/off ratio of 8.9 × 108, subthreshold swing of 0.26V/decade, and hysteresis of 0.2V, while keeping a reasonable carrier density of ~1017 cm-3. Flexible ALD InGaZnO TFTs on polymer substrates were also discussed depending on gate insulator materials, in terms of device performances. ALD technique will be a very promising candidate to improve oxide semiconductor materials as well as various device applications (Display & Semiconductor Industry) because it has not only unique nano-growth mechanism but also ultimate uniform property.