Tailoring ferroelectricity in Al:HfO2 capacitors: A comprehensive approach to annealing, electrode selection, and Al dopant distribution

We systematically investigate the effects of annealing conditions, Al2O3 atomic layer deposition (ALD) cycle number and distribution, and top electrode (TE) material on the ferroelectric switching behavior of 10 nm-thick Al-doped HfO2 (Al:HfO2) films. We perform 150 ALD cycles, comprising HfO2 and Al2O3 sub-cycles, with precise control over the number and distribution of Al2O3 cycles. Post-metallization annealing (PMA) at 600 °C for 3 min induced spontaneous 2 remnant polarization (2Pr) through the combined Al-induced lattice stress and TE-induced mechanical stress, promoting orthorhombic phase formation. Optimization to three Al2O3 cycles within the HfO2 bulk balances polarization enhancement and suppression of oxygen-vacancy-induced leakage, yielding a 2Pr = 3 μC/cm2 and endurance up to 106 cycles. The W electrodes, with a low thermal expansion coefficient and smooth surfaces, enable uniform stress transfer and improved dipole alignment compared to Mo and Ru electrodes. Notably, asymmetric localization of Al2O3 sub-cycles near the lower HfO2 region, combined with TE-induced stress, maximizes uniform stress distribution across the film. As confirmed by positive-up-negative-down measurements, this mechanism activates a higher dipole density and achieves the highest 2Pr = ∼9 μC/cm2 without additional leakage. These findings demonstrate that jointly optimizing thermal treatment, dopant engineering, and electrode selection enhances phase stability and dipole activity in HfO2-based ferroelectrics.