ZnO-based thin film transistors employing aluminum titanate gate dielectrics deposited by spray pyrolysis at ambient air

Afouxenidis, Dimitrios and Mazzocco, Riccardo and Vourlias, G. and Livesley, Peter and Krier, Anthony and Milne, W.I. and Kolosov, Oleg and Adamopoulos, George (2015) ZnO-based thin film transistors employing aluminum titanate gate dielectrics deposited by spray pyrolysis at ambient air. ACS Applied Materials and Interfaces, 7 (13). pp. 7334-7341. ISSN 1944-8244

Abstract

The replacement of SiO2 gate dielectrics with metal oxides of higher dielectric constant has led to the investigation of a wide range of materials with superior properties compared with SiO2. Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. To overcome this bottleneck, research has focused on the development of alternative deposition methods based on solution-processable metal oxides. Here we report the application of spray pyrolysis for the deposition and investigation of Al2x-1•TixOy dielectrics as a function of the [Ti+4]/[Ti+4+2•Al+3] ratio and their implementation in thin film transistors (TFTs) employing spray-coated ZnO as the active semiconducting channels. The films are studied by UV-visible absorption spectroscopy, spectroscopic ellipsometry, impedance spectroscopy, atomic force microscopy, x-ray diffraction and field-effect measurements. Analyses reveal amorphous Al2x-1•TixOy dielectrics that exhibit a wide band gap (~4.5 eV), low roughness (~0.9 nm), high dielectric constant (k~13), Schottky pinning factor S of ~0.44 and very low leakage currents (<5 nA/cm2). TFTs employing stoichiometric Al2O3•TiO2 gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with low operating voltages (~10 V), negligible hysteresis, high on/off current modulation ratio of ~106, subthreshold swing (SS) of ~550 mV/dec and electron mobility of ~10 cm2 V-1 s-1.