Effects of post cooling on the remnant polarization and coercive field characteristics of atomic layer deposited Al-doped HfO2 thin films

Abstract

A study was conducted on how the cooling rate after the phase change heat treatment required to secure the ferroelectric (FE) properties affects the ferroelectricity of Al-doped HfO2 (Al:HfO2) thin films. When cooling the thin film to room temperature after heat treatment, the cooling rate was controlled through slow chamber cooling, which maintains and cools the sample inside the heat treatment equipment, slightly faster air cooling, and rapid cooling using deionized water. We achieved the dramatic increase of remnant polarization (Pr) and coercive electric field (Ec) using rapid quenching after phase change heat treatment. The 2Pr and 2Ec values of rapid quenched FE Al:HfO2 thin film are approximately ∼100 μC/cm2 and ∼9.5 MV/cm, respectively, which are the highest records among HfO2-based FE thin films reported so far. These significant improvements are attributed to inducing homogeneously distributed defects complexes and higher stress/confinement strain within Al:HfO2 thin film, leading to preventing pinched hysteresis loop and stabilize orthorhombic crystal structure. Furthermore, endurance up to 2 × 106 cycles and reasonable projected 10 years retention properties were achieved, stably without wake-up and fatigue in quenched FE Al:HfO2 capacitor. These results propose a beneficial method to improve the ferroelectricity of HfO2-based thin films.