ZnO-based Thin Film Transistors Employing Aluminum Titanate Gate Dielectrics Deposited by Spray Pyrolysis at Ambient Air

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 center dot TixOy dielectrics as a function of the [Ti4+]/[Ti4++2 center dot Al3+] 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 center dot TixOy dielectrics that exhibit a wide band gap (similar to 4.5 eV), low roughness (similar to 0.9 nm), high dielectric constant (k similar to 13), Schottky pinning factor S of similar to 0.44 and very low leakage currents (<5 nA/cm(2)). TFTs employing stoichiometric Al2O3 center dot TiO2 gate dielectrics and ZnO semiconducting channels exhibit excellent electron transport characteristics with low operating voltages (similar to 10 V), negligible hysteresis, high on/off current modulation ratio of similar to 10(6), subthreshold swing (SS) of similar to 550 mV/dec and electron mobility of similar to 10 cm(2) V-1 s(-1).