Phase transformation of sputtered hafnium oxide by post annealing treatment and its effect on the amorphous Si-In-Zn-O thin film transistor

Abstract

The effect of post annealing treatment on the phase transformation and the electrical properties of the sputtered hafnium oxide (HfO2) is investigated. As-deposited HfO2 films were annealed at 200 and 400 ? in ambient conditions. Film annealed at 200 ?& nbsp;is amorphous, but further annealing at 400 ?& nbsp;crystallizes it into the monoclinic structure. Amorphous films exhibit a higher bandgap (>=& nbsp;5.8 eV) than the monoclinic film (asymptotic to 5.65 eV). The electrical characteristics of the Metal-Insulator-Metal devices reveal a nonlinear capacitance with respect to the voltage. The nonlinearity is predominant in the as-deposited film due to the oxygen vacancy related defects formed during the deposition. However, excess Hf-O bond formation occurs with annealing at higher temperatures, reducing the capacitance-voltage curve's nonlinearity. The dielectric constant of the as-deposited, 200, and 400 ?& nbsp;annealed films are estimated as 22.35, 22.64, and 20.57, respectively. The increment in the dielectric constant at 200 ?& nbsp;is due to its amorphous phase and reduced defects. Amorphous Si-In-Zn-O thin film transistors fabricated using the as-deposited and annealed hafnium oxide as gate insulator show almost similar threshold voltage of asymptotic to & nbsp;-1 V. The transistor with hafnium oxide annealed at 200 ?& nbsp;shows the highest on current (1.04 x 10(-6) A) followed by as-deposited (6.82 x 10(-7) A) and 400 ?& nbsp;annealed device (5.86 x 10(-7) A), respectively. Moreover, the interface state density increases monotonically from 3.98 x 10(12) to 1.11 x 10(13) cm(-2) for as-deposited and 400 ?, respectively. The increment in the interface state density is due to the grain boundary formation due to the crystallization of HfO2. (C)& nbsp;2022 Elsevier B.V. All rights reserved.