| Since Hf O2 was found to have ferroelectric properties in 2011,due to its compatibility with CMOS(complementary metal-oxide-semiconductor)process,strong radiation resistance and high-density integration,it quickly entered people's field of vision and was regarded as an ideal new-generation ferroelectric material.However,the"wake-up"effect and fatigue failure of Hf O2-based ferroelectric films have not yet been resolved,which is a bottleneck restricting the industrialization of functional devices.Besides,the Hf O2-based ferroelectric thin film with a fluorite structure which is a polycrystalline multi-phase state at room temperature,and the ferroelectric orthogonal phase that contributes to the ferroelectricity is a metastable phase.Based on the experimental results,this paper uses the phase field method to study the influence of the switching of the mesoscopic domain structure on the"wake-up"effect and fatigue failure of Hf O2-based ferroelectric thin films.At the same time,the domain structure is closely related to the grain size,not only the Hf O2-based ferroelectric film is multi-phase coexistence,but also the domain structure is in the nano-scale range,which means that the surface energy is particularly important at this scale.So the surface energy obtained by calculation,the effect of grain size on the macroscopic electrical properties of Hf O2-based ferroelectric thin films is discussed.The specific content is as follows:(1)Hf0.5Zr0.5O2(HZO)ferroelectric thin film was prepared by ALD(Atomic Layer Deposition).After i DPC-STEM(Integrated Differential Phase Contrast-Scanning Transmission Electron Microscopy)imaging analysis of the sample,were observed 90°charged domain walls,coexistence of ferroelectric and non-ferroelectric phases,and polarization relaxation at the Ti N/HZO/Ti N interface.(2)According to the energy equation of the charged system in the external electric field,the phase field model of the charged domain wall-built in electric field was constructed.The stable tail-to-tail 90°domain structure formed near the charged domain wall was successfully simulated.Introducing the surface energy vector Q,constructing a polycrystalline and multiphase non-constant surface energy phase field model by means of power series expansion and coupling of surface energy and polarization.Successfully simulated the change of surface energy under different grain sizes and its influence on the mesoscopic domain structure and macroscopic electrical properties.(3)The existence of tail-to-tail domain structure is explained through a quasi-one-dimensional analytical model.The influence of the content,angle and position of the charged domain walls in the film on the"wake-up"effect and fatigue failure of Hf O2-based ferroelectric films was further studied.The simulation results show that the higher the concentration of charged domain walls,the more obvious the antiferroelectric double hysteresis before the film"wake-up".Based on the horizontal direction of the film,when the charged domain wall horizontally inside the film,it corresponds to the antiferroelectric double hysteresis"wake-up"effect;when the charged domain wall vertically inside the film,it corresponds to the"wake-up"effect of spindle hysteresis.Films with vertical distribution of charged domain walls that produce spindle"wake-up"effects have worse fatigue performance than films with horizontal distribution that generate antiferroelectric"wake-up"effects.When the content of the charged domain wall remains constant and is evenly dispersed inside the film,the"wake-up"effect disappears.(4)The macroscopic electrical properties of Hf O2-based ferroelectric thin films with the same film thickness and different grain sizes,as well as different film thicknesses and the same grain size,are studied through the surface energy model.The simulation results show that the positive and negative remanent polarization values are mainly affected by the grain size.In the case of the same film thickness,5 nm grains have a single domain structure,with the worst ferroelectricity,and the smallest positive and negative remanent polarization values;10 nm grains have a stable 90°domain structure with the best ferroelectric performance;20 nm grains have an unstable vortex domain structure,and the positive and negative remanent polarization values are less than 10 nm grains,but larger than 5 nm grains.Furthermore,the phase distribution in the Hf O2-based ferroelectric thin film was predicted based on the surface energy. |
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