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Oxygen vacancies play a crucial role in stabilizing the ferroelectric phase in hafnium (Hf) oxide-based thin films and in shaping the evolution of their ferroelectric properties. In this study, we directly manipulated the oxygen vacancy concentration in Hf0.5Zr0.5O2−x (HZO) ferroelectric thin films in situ using oxygen plasma treatment. We scrutinized the variations in the ferroelectric properties of HZO films across different oxygen vacancy concentrations by integrating the findings from ferroelectric performance tests. Additionally, we elucidated the mechanism underlying the influence of oxygen vacancies on the coercive field and polarization properties of HZO ferroelectric films through the first-principles density functional theory (DFT) calculations. Finally, to study the impact of oxygen vacancies on the practical application of HZO ferroelectric synaptic devices, leveraging the plasticity of the ferroelectric polarization, we constructed a multilayer perceptron (MLP) network. We simulated its recognition accuracy and convergence speed under different oxygen vacancy concentrations in the MNIST recognition task. [ABSTRACT FROM AUTHOR]

Doping with various cations is considered to be a key method for inducing ferroelectricity in HfO2. However, previous studies often neglected the role of carriers introduced by heterovalent dopants. Here, using first-principles calculations, we show that carriers profoundly affect the stability of polar phases and advocate that carriers should be considered as a fundamental framework for understanding the origin of ferroelectricity in doped HfO2. Although doping with p-type elements that introduce holes can stabilize the polar phase, it is not sufficient to make them the ground state phase. However, when they are co-doped with an n-type V element, they not only stabilize the polar phase to the ground state, but also achieve charge neutrality through electron compensation. This is due to the formation of deep energy levels (electron–hole recombination centers) by V doping, similar to oxygen vacancies. Unlike oxygen vacancy compensation, which favors the formation of tetragonal phases, co-doping is more favorable for the formation of polar phases and the absence of structural defects. Our results contribute to the understanding of the origin of HfO2 ferroelectricity and provide a potential method for the preparation of HfO2-based films with excellent ferroelectric properties. [ABSTRACT FROM AUTHOR]