Hafnium-doped zirconia ferroelectric thin films with excellent endurance at high polarization

Abstract

Using thermal atomic layer deposition and subsequent rapid thermal annealing without the need for metal clamping atop, a remanent polarization (P_r) of 25.5 μC cm⁻² was achieved in a 10 nm-thick ZrO₂ film deposited on a W bottom electrode. Hafnium doping was further explored to improve the ferroelectric properties in P_r as well as the endurance of zirconia-based thin films. A significantly enhanced P_r reaching 41 μC cm⁻² was obtained for 10 nm-thick hafnium-doped ZrO₂ with an optimal Zr : Hf ratio of 3 : 1. Importantly, owing to the greatly reduced leakage, the optimal hafnium-doped ZrO₂ thin films exhibited superior retention and outstanding endurance performances at relatively high polarizations, free of serious degradation for up to 2.3 × 10⁹–6.8 × 10⁹ field cycles at an initial P_r of 27 μC cm⁻² and were even capable of over 10⁷ cycles at a maximum P_r of 41 μC cm⁻². The superb ferroelectricities were demonstrated on big-sized capacitors as well as sub-micrometer ones, isolated or in array. This would empower zirconia-based ferroelectric thin films as a competitive front-runner for practical applications in ferroelectric-related nanoelectronics.