Phase Field Simulations The Electro-Mechanical Control Of Ferroelectric Topological Domain

Non-destructive reading,excellent integration,and radiation resistance are only a few benefits of ferroelectric memory（FRAM,Ferroelectric RAM）.Because the traditional method of improving storage density primarily relies on the reduction of the storage cell,increasing the storage density of nonvolatile ferroelectric memory is critical with the rapid increase of electronic data.As a result,it is becoming increasingly difficult to implement process technology.Therefore,it is necessary to find a new smaller information storage cell.The two different chirality of topology can be used as0 or 1 in digital logic code to store information.The topological domain structure is an ideal carrier for high-density information storage.As a result,this thesis provides a phase field model for ferroelectric topological domain structure simulation.It illustrates the regulation of ferroelectric topological domain structure in the presence of an electric field in a force and electricity situation.A computational model based on the electrical properties of ferroelectric topological domain transistors is established,and the effects of electric and force fields on the electrical properties of ferroelectric topological domain transistors are investigated.The results provide theoretical support for the application of reversibly switchable topological domains in high-density nano-iron devices such as non-volatile ferroelectric memories.（1）A phase field model for calculating ferroelectric topological domain structure is developed,and the topological domain structure is obtained by simulation in ferroelectric materials.The size dependence of the ferroelectric domain structure was studied.When the size of the ferroelectric material is small（≤4.8 nm）,vortex domains are formed.When the size increases to 7.2 nm,the vortex turns into flux-closure domains,which is caused by the difference in depolarization energy of ferroelectric domains of different sizes.The Effect of the aspect ratio of the ferroelectric material on the number of vortex domains is also investigated.When the aspect ratio of the ferroelectric material is 1,only one vortex domain is formed in the ferroelectric material.As the aspect ratio of the ferroelectric material increases from 2 to 3,the number of vortices increases.（2）Based on the established phase field model,the effects of stress,electric field,depolarization field,shielding factor,and elastic energy on the structure of ferroelectric topological domains are studied,and the regulation of the topological domain structure by electric field and force field is realized.The results are as follows:the topological domains will be flipped under the action of the vortex field;the vortex moment of the topological domains in ferroelectric materials becomes larger with the increase of the shielding factor;the vortex moment decreases with the increase of the elastic energy,and the corresponding hysteresis line based on the vortex moment becomes narrower;the vortex value of the topological domains will increase with the growth of the strain or stress.（3）Components on the electrical performance of ferroelectric topological domain-based transistors,a computational model of the electrical performance of ferroelectric topological domain-based transistors is developed:As the external electric field and the shielding factor increases,the off-state current(I_off)rises,the on-state current(I_on)falls,and the switching ratio falls;The ferroelectric memory window reduces as the elastic energy coefficient rises;as the elastic energy factor climbs,the I_off rises,the I_on lowers,and the switching ratio declines;Increased strain or stress reduces the ferroelectric memory fails memory window,which lowers the I_on of the output characteristic curve and raises the I_offcurrent,dropping the switching ratio.