Optical and electrical properties of 2 wt.% Al2O3-doped ZnO films and characteristics of Al-doped ZnO thin-film transistors with ultra-thin gate insulators

Al-doped ZnO (AZO) thin films have been prepared on the c-Si oriented direction of (100) and glass substrates, by radio frequency magnetron sputtering from ZnO-2 wt.% Al2O3 ceramic targets. The effects of the working pressure on the optical and electrical properties of the films have been studied. The optical properties, measured by the ultraviolet-visible system, show that the transmittance and optical bandgap energy are influenced by the working pressure. The Hall resistivity, mobility, and carrier concentration were obtained by a Hall measurement system and these parameters were also influenced by the working pressure. The AZO thin-film transistors (TFTs) were fabricated on highly doped c-Si substrates. The TFT structures were made up AZO as the active layer and SiOxNy/SiNx/SiOx as the gate layer with 20 nm and 35 nm thickness, respectively. The ultra-thin TFTs had an on/off current ratio of 10(4) and a field-effect mobility of 0.17 cm(2)/V.s. These results show that it is possible to fabricate an AZO TFT that can be operated with an ultra-thin gate dielectric. (C) 2009 Elsevier B.V. All rights reserved.