High-Mobility ZnO Thin Film Transistors Based on Solution-processed Hafnium Oxide Gate Dielectrics

The properties of metal oxides with high dielectric constant (k) are being extensively studied for use as gate dielectric alternatives to silicon dioxide (SiO2). Despite their attractive properties, these high-k dielectrics are usually manufactured using costly vacuum-based techniques. In that respect, recent research has been focused on the development of alternative deposition methods based on solution-processable metal oxides. Here, the application of the spray pyrolysis (SP) technique for processing high-quality hafnium oxide (HfO2) gate dielectrics and their implementation in thin film transistors employing spray-coated zinc oxide (ZnO) semiconducting channels are reported. The films are studied by means of admittance spectroscopy, atomic force microscopy, X-ray diffraction, UV-Visible absorption spectroscopy, FTIR, spectroscopic ellipsometry, and field-effect measurements. Analyses reveal polycrystalline HfO2 layers of monoclinic structure that exhibit wide band gap (approximate to 5.7 eV), low roughness (approximate to 0.8 nm), high dielectric constant (k approximate to 18.8), and high breakdown voltage (approximate to 2.7 MV/cm). Thin film transistors based on HfO2/ZnO stacks exhibit excellent electron transport characteristics with low operating voltages (approximate to 6 V), high on/off current modulation ratio (similar to 10(7)) and electron mobility in excess of 40 cm(2) V-1 s(-1).