The Regulation Of Domain Wall Conductivity In PbTiO₃ Thin Films:A Phase Field Simulation

Ferroelectric domain walls(DWs)are deemed to be novel elements of the future nanoscale electronic devices.They have different properties from ferroelectric domains and can be easily produced,eliminated,and reconfigured on demand.Particularly,the strong conductivity of charged domain walls has attracted researcher's wide attention,which leads to the presence of "domain wall nanoelectronics".However,regulating the conductivity of ferroelectric domain walls is the key to apply domain walls to memory devices.Previous studies have shown that the conductivity of domain walls in ferroelectric thin films is closely related to the type,number,and length of domain walls,and the domain wall structure is greatly affected by the mismatch strain,external electric field,space charge and so on.Therefore,the conductivity of the ferroelectric domain wall can be regulated by these external factors.In this thesis,the phase field method is used to study the influence of mismatch strain,external electric field and space charge on the ferroelectric domain wall and its conductivity.The main research contents and results are showed as follows:(1)The phase field model of the domain wall conductivity in ferroelectric thin film was established,and the effects of mismatch strain on the 90° domain wall and its conductivity were studied.The results show that the mismatch strain causes the movement of the domain wall,which can change the distribution of charge carriers in the thin film.When the compressive strain increases from-0.001 to-0.004,the conductivity of the ferroelectric domain wall hardly changes.When the tensile strain increases from 0.001 to 0.004,the conductivity of the ferroelectric domain wall is about 5 times of the initial state.(2)Based on the established phase field model of ferroelectric domain wall conductivity,the effects of electric field on the 90° domain wall and its conductivity were studied.Under the longitudinal electric field,the conductivity of the domain wall can reach about 6 times higher than that of the bulk.Under the bidirectional electric field,the "head-to-tail" 90° domain walls in the ferroelectric thin film transforms into"head-to-head" and "tail-to-tail" 900°charged domain walls(CDWs),and the conductivity of domain wall varies from 103 to 106.The interface electric field leads to the change of the charged domain wall.However,due to the limited range of the interface electric field,the interface electric field has little effect on the conductivity of the "head-to-head" charged 90° charged domain wall.(3)The space charge was introduced into the phase field model of the domain wall conductivity,and the effects of space charge with different spatial distribution on the 90° charged domain wall in the ferroelectric thin film were investigated.Under the homogeneously distributed space charge,the "tail-to-tail" 90° charged domain wall in the ferroelectric thin film shortens gradually,while the "head-to-head" 90° charged domain wall and its conductivity are almost unaffected.Under the inhomogeneously distributed space charge,the "tail-to-tail" and "head-to-head" 90° charged domain walls both shorten a lot,and electrical conductivity gradually weakens.