挠曲电耦合效应对铁电薄膜漏电流的影响

发布时间：2018-04-04 02:58

本文选题：铁电薄膜　切入点：漏电流　出处：《湘潭大学》2015年硕士论文

【摘要】：非易失性铁电存储器因其抗辐射、高读写速度和非易失性等优良特性有着广泛的应用潜力,被公认为下一代存储器之一。引起了广大科学家与研究人员的关注。然而目前已商业化基于铁电电容的铁电随机存储器FeRAM有着存储密度低的缺点。为提高存储密度,一般采用减小铁电薄膜尺寸的办法,而铁电薄膜尺寸减小后会存在一系列的失效问题,如保持性能损失,印记、疲劳等。虽然疲劳和印记问题可以通过改变铁电材料、电极材料等方式解决,但是铁电薄膜保持性能损失的问题一直没能得到有效解决。而纳米尺度的铁电薄膜漏电流是铁电保持性能损失的原因之一。由于铁电存储器为多层结构,铁电薄膜漏电流产生机制复杂。最近研究表明纳米化的铁电薄膜中存在很大的应变梯度,应变梯度与极化之间的耦合对铁电薄膜性能有很大的影响。不均匀应变会影响极化的大小,如此在铁电薄膜内也会产生内电场,内电场势必影响铁电薄膜内带电粒子的分布和输运,进而影响铁电薄膜漏电流。因此本文采用考虑挠曲电效应及带电粒子漂移扩散的相场模拟的方法,研究了挠曲电耦合效应对铁电薄膜载流子分布及漏电流的影响。本论文的主要工作包括以下几个方面:(1)建立了考虑挠曲电效应及带电粒子漂移扩散的相场模型。验证了单畴纳米线BaTiO3中束缚电荷对其电子输运有一个整流二极管的作用,而这种作用随着束缚电荷的增加而增强,开关比越来越大。(2)以Pb(Zr0.1Ti0.9)O3为研究对象,在考虑了挠曲电效应情况下,研究了外延应变下及在局部力作用下的只有单畴结构铁电薄膜的漏电流。发现挠曲电耦合效应对外延应变下单畴铁电薄膜漏电流影响不显著,应变梯度还是较小,而在局部力作用下,且单畴方向与力方向相反时,铁电薄膜漏电流较大的变化,这是因为局部力作用下产生了很大的应变梯度,导致力作用下铁电薄膜电势降低空穴载流子大量聚集,在作用力低于铁电薄膜临界翻转应力情况下,铁电薄膜漏电流随压应力增大而增大。(3)分别研究了挠曲电系数11f及12f对只有多畴Pb(Zr0.1Ti0.9)O3结构铁电薄膜漏电流的影响。11f所描述的是极化与纵向应变梯度的之间耦合,会导致铁电薄膜内电势的降低,增加载流子空穴在铁电薄膜内的浓度,进而提高了铁电薄膜漏电流,12f所描述的是极化与纵向应变梯度的之间耦合,会导致铁电薄膜内电势的升高,减小载流子空穴在铁电薄膜内的浓度,进而减小铁电薄膜漏电流。
[Abstract]:Non-volatile ferroelectric memory has been recognized as one of the next generation memory because of its excellent characteristics such as radiation resistance, high reading and writing speed, non-volatile and so on.It has attracted the attention of scientists and researchers.However, the current commercialized ferroelectric random access memory (FeRAM) based on ferroelectric capacitance has the disadvantage of low storage density.In order to improve the storage density, the method of reducing the size of ferroelectric thin films is generally adopted. However, there are a series of failure problems when the size of ferroelectric thin films is reduced, such as loss of retention performance, imprint, fatigue, and so on.Although the problems of fatigue and imprinting can be solved by changing ferroelectric materials and electrode materials, the problem of loss of performance of ferroelectric thin films has not been effectively solved.The leakage current of nanoscale ferroelectric thin films is one of the reasons for the loss of ferroelectric retention performance.Due to the multilayer structure of ferroelectric memory, the mechanism of leakage current generation in ferroelectric thin films is complicated.Recent studies have shown that there is a large strain gradient in nanocrystalline ferroelectric thin films, and the coupling between strain gradient and polarization has great influence on the properties of ferroelectric thin films.The inhomogeneous strain will affect the size of polarization, so there will be an internal electric field in the ferroelectric thin film. The internal electric field will affect the distribution and transport of charged particles in the ferroelectric thin film, and then affect the leakage current of the ferroelectric film.In this paper, the effect of the flexural coupling effect on the carrier distribution and leakage current of ferroelectric thin films is studied by using the method of phase field simulation considering the flexural effect and charged particle drift diffusion.The main work of this thesis includes the following aspects: 1) A phase field model considering the flexural effect and charged particle drift diffusion is established.It is verified that the binding charge in single-domain nanowire BaTiO3 has a rectifier diode effect on electron transport, and this effect increases with the increase of bound charge, and the switching ratio is larger and larger.The leakage current of ferroelectric thin films with single domain structure under the condition of epitaxial strain and local force is studied by taking into account the flexural effect.It is found that the flexoelectric coupling effect has no significant effect on the leakage current of the epitaxial strain issuing order domain ferroelectric thin film, and the strain gradient is still small. However, the leakage current of the ferroelectric thin film changes greatly under the action of local force and when the direction of single domain is opposite to the direction of force.This is because a large strain gradient is produced under the action of local forces, which results in the reduction of a large number of hole carriers in the ferroelectric thin film under the action of the force, when the force is lower than the critical inversion stress of the ferroelectric film.The effect of flexural coefficient 11f and 12f on leakage current of ferroelectric thin film with multi-domain Pb(Zr0.1Ti0.9)O3 structure. 11f describes the coupling between polarization and longitudinal strain gradient.It will lead to the decrease of the electric potential in the ferroelectric film, increase the concentration of the carrier hole in the ferroelectric film, and thus increase the leakage current of the ferroelectric film 12f, which describes the coupling between polarization and longitudinal strain gradient.It will lead to the increase of the electric potential in the ferroelectric film and decrease the concentration of the carrier hole in the ferroelectric film and thus reduce the leakage current of the ferroelectric film.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.2

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