Phase Field Theory Study Of Si:HfO₂ Thin Film Ferroelectric Phase Transition And Domain Evolution

The discovery of the ferroelectric properties of Si-doped hafnium oxide-based films has brought a great opportunity to the development of ferroelectric materials.This is because the hafnium oxide-based film not only has ferroelectric properties even down to a thickness of 10 nm but is also compatible with Complementary Metal Oxide Semiconductor（CMOS）processes.However,the ferroelectric phase of the hafnium oxide-based film is not stable.Therefore,stabilizing the ferroelectric phase and improving the ferroelectric properties of hafnium oxide-based films has become the focus of recent research.Si doping is considered to be one of the important means for stabilizing the ferroelectric phase of hafnium oxide-based thin films and has been extensively reported.However,the regulation mechanism of Si dopant in the ferroelectric phase is complex and the effect may also be affected by other factors.Therefore,in order to better manipulate the Si-doping to stabilize the ferroelectric phase,and greatly optimize the ferroelectric properties of the film,a phase-field dynamics model of Si-doped hafnium oxide-based ferroelectric thin film is established to analyze the effect of Si dopants on the ferroelectric properties of the films.The specific research contents are as follows:（1）A phase-field model of Si-doped hafnium oxide-based ferroelectric thin films is established.The result shows that when Si is uniformly distributed in the film,the effect of concentration on the ferroelectric properties of the film is not monotonous,it has two sides.The remanent polarization value of the film increases first and then decreases with the increase of Si concentration,the highest remanent polarization value that the film can obtain via Si concentration modulation is 29.4μC/cm²,and the corresponding Si concentration is 3.8 cat%,which is consistent with the experimental results and prove the correctness of our model.（2）Using the model,the synergistic effect of Si concentration and distribution on ferroelectric properties optimization of Si:HfO₂ ferroelectric thin films is studied.When the concentration of Si is constant,the residual polarization value of the film increases first and then decreases with the increase of concentration difference between the Si-rich and Si-poor layers.When the concentration difference between the Si-rich and Si-poor layer is 7.6%,in the Si concentration range of 3.6 cat%-3.8 cat%,the residual polarization value of the film reaches the maximum 36.05μC/cm²-36.4μC/cm²,which is 21%higher than that when Si dopants are evenly distributed in the film.The result shows that controlling the concentration difference between Si-rich and Si-poor layers in an appropriate range can not only greatly improve the ferroelectric properties of the films,but also broaden the Si concentration optimization range of the ferroelectric properties of the films.（3）Then the synergistic effect of Si dopant and strain on ferroelectric properties optimization of Si:HfO₂ ferroelectric thin films is studied.With the increase of compressive strain,the remanent polarization value of the films gradually decreases,conversely,the remanent polarization value of the films decreases with the increase of tensile strain.Besides,the tensile strain changes the optimal concentration of the maximum residual polarization.When no strain or compressive strain is applied,the residual polarization value of 3.8 cat%Si:HfO₂ film is the largest.However,under the action of tensile strain,the Si concentration corresponding to the maximum residual polarization value of the film is 3.6 cat%.