弯曲载荷下铁电薄膜畴结构演化行为的模拟研究

Simulation study of domain structure evolution in ferroelectric thin film under bending mechanical loads

本文建立了三维薄膜的相场模拟方法,考虑弯曲载荷、挠曲电场、温度和尺寸等因素对PbZr_(0.2)Ti_(0.8)O_3薄膜畴结构稳定和演化的影响,探究畴结构信息力学擦除的可能性.证实了力学载荷及挠曲电效应对厚度在10 nm级别的铁电纳米薄膜畴结构可以进行有效地调控.其中温度的升高与表面挠曲电场对于畴结构演化过程有明显调控作用,有利于c--畴结构的形成.在进一步对波浪形弯曲及柱面弯曲的对比中,讨论了两种载荷方式下不同的挠曲电场取向对于力学擦除行为的影响.本文的研究对于柔性铁电电子器件往纳尺度方向的发展具有指导意义.

Focusing on ferroelectric nanofilm systems, a three-dimensional model is established utilizing phase field simulation method to simulate the stability of several domain structures and their evolution behaviors under mechanical loads. It is revealed that bending loads, surface flexoelectric field, temperature and thickness of film can sufficiently control the stability and evolution path of domains structure of Pb PbZr_（0.2）Ti_（0.8）O_3 film with thickness of 10 nm level. Although films with thickness of 16 nm have more complicated domain structures than films of 8 nm, they both show regulation effect on domains under wavy bending. With the rising of temperature and presence of surface flexoelectric field, the domain evolution behaviors become more controllable and the evolution process is beneficial to the formation of the c--domain. When temperature is 600 K under conditions with surface flexelectric field, areas with the maximum strain gradient on the films can be evolved into single domain state, which makes mechanical erasure feasible. There is also a nonlinear relationship between the bending amplitude of the film and the reversal of c-domain, leading to an easier formation of c--domain as the amplitude increasing. To further explore the mechanical erasure, we give a simulation on cylindrical bending. In the comparison of the wavy and cylindrical bending, the influence of the orientation of flexoelectric field on the mechanical erasure is clarified. Cylindrical bending can achieve complete erasure of the domain information due to its only direction of flexelectric field. The research on the mechanical erasing is of significance for the development of flexible ferroelectric electronic devices in nanoscale.