Ferroelectric properties of lightly doped La:HfO2 thin films grown by plasma-assisted atomic layer deposition

The structural and ferroelectric properties of lightly La-doped (1 mol. %) HfO2 thin films grown by plasma-assisted atomic layer deposition were examined. An annealing temperature as low as 400 °C crystallized the film into the desired orthorhombic phase, which resulted in it displaying promising ferroelectric performance. The remanent polarization (Pr) increased with annealing temperature, but the performance enhancement seemed to saturate at 500 °C. A slight decrease in the dielectric constant, which was associated with the preferential formation of a polar orthorhombic phase at higher temperatures, was also observed. The long-term wake-up effect, i.e., a marked rise in the 2Pr value during field cycling, was demonstrated for films processed at all annealing temperatures. The presence of domain groups with opposite internal electric biases was found in the pristine state, while the internal bias distribution became more uniform during wake-up. The endurance of up to 4 × 108 switching cycles without marked fatigue using bipolar pulses with a duration of 600 ns, and an amplitude of ±3 MV/cm was demonstrated.