Solution processed hafnium oxide as a gate insulator for low-voltage oxide thin-film transistors

Abstract

We report a solution processed high-k hafnium oxide (HfO_x) dielectric used for a solution processed zinc-tin-oxide (ZTO) thin-film transistor (TFT) at the maximum process temperature of 300 °C. The HfO_x is close to stoichiometric composition (35% hafnium and 65% oxygen), has no impurity related to the solvent or precursor used, and exhibits an amorphous structure. The HfO_x is smooth enough, with a rms roughness of 0.33 nm, to be used as a gate insulator for TFT. The ZTO TFT with HfO_x exhibits a threshold voltage of 1.18 V, a gate voltage swing of 105 mV per decade, and a field-effect mobility in the saturation region of 1.05 cm² V⁻¹ s⁻¹. The resulting TFT properties are impacted by the formation of nanopores at the HfO_x/ZTO interface and nanocrystals at the HfO_x/IZO (source/drain) interface.