Evaluation of the effects of thermal annealing temperature and high-k dielectrics on amorphous InGaZnO thin films by using pseudo-MOS transistors

Abstract

The effects of annealing temperatures and high-k gate dielectric materials on the amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) were investigated using pseudo-metal-oxide-semiconductor transistors (Ψ-MOSFETs), a method without conventional source/drain (S/D) layer deposition. Annealing of the a-IGZO film was carried out at 150–900 °C in a N2 ambient for 30 min. As the annealing temperature was increased, the electrical characteristics of Ψ-MOSFETs on a-IGZO were drastically improved. However, when the annealing temperature exceeded 700 °C, a deterioration of the MOS parameters was observed, including a shift of the threshold voltage (Vth) in a negative direction, an increase in the subthreshold slope (SS) and hysteresis, a decrease in the field effect mobility (µFE), an increase in the trap density (Nt), and a decrease in the on/off ratio. Meanwhile, the high-k gate dielectrics enhanced the performance of a-IGZO Ψ-MOSFETs. The ZrO2 gate dielectrics particularly exhibited excellent characteristics in terms of SS (128 mV/dec), µFE (10.2 cm−2/V·s), Nt (1.1 × 1012 cm−2), and on/off ratio (5.3 × 106). Accordingly, the Ψ-MOSFET structure is a useful method for rapid evaluation of the effects of the process and the material on a-IGZO TFTs without a conventional S/D layer deposition.