本文選題：鐵電薄膜　切入點：漏電流　出處：《湘潭大學(xué)》2015年碩士論文

【摘要】：非易失性鐵電存儲器因其抗輻射、高讀寫速度和非易失性等優(yōu)良特性有著廣泛的應(yīng)用潛力,被公認(rèn)為下一代存儲器之一。引起了廣大科學(xué)家與研究人員的關(guān)注。然而目前已商業(yè)化基于鐵電電容的鐵電隨機存儲器FeRAM有著存儲密度低的缺點。為提高存儲密度,一般采用減小鐵電薄膜尺寸的辦法,而鐵電薄膜尺寸減小后會存在一系列的失效問題,如保持性能損失,印記、疲勞等。雖然疲勞和印記問題可以通過改變鐵電材料、電極材料等方式解決,但是鐵電薄膜保持性能損失的問題一直沒能得到有效解決。而納米尺度的鐵電薄膜漏電流是鐵電保持性能損失的原因之一。由于鐵電存儲器為多層結(jié)構(gòu),鐵電薄膜漏電流產(chǎn)生機制復(fù)雜。最近研究表明納米化的鐵電薄膜中存在很大的應(yīng)變梯度,應(yīng)變梯度與極化之間的耦合對鐵電薄膜性能有很大的影響。不均勻應(yīng)變會影響極化的大小,如此在鐵電薄膜內(nèi)也會產(chǎn)生內(nèi)電場,內(nèi)電場勢必影響鐵電薄膜內(nèi)帶電粒子的分布和輸運,進而影響鐵電薄膜漏電流。因此本文采用考慮撓曲電效應(yīng)及帶電粒子漂移擴散的相場模擬的方法,研究了撓曲電耦合效應(yīng)對鐵電薄膜載流子分布及漏電流的影響。本論文的主要工作包括以下幾個方面:(1)建立了考慮撓曲電效應(yīng)及帶電粒子漂移擴散的相場模型。驗證了單疇納米線BaTiO3中束縛電荷對其電子輸運有一個整流二極管的作用,而這種作用隨著束縛電荷的增加而增強,開關(guān)比越來越大。(2)以Pb(Zr0.1Ti0.9)O3為研究對象,在考慮了撓曲電效應(yīng)情況下,研究了外延應(yīng)變下及在局部力作用下的只有單疇結(jié)構(gòu)鐵電薄膜的漏電流。發(fā)現(xiàn)撓曲電耦合效應(yīng)對外延應(yīng)變下單疇鐵電薄膜漏電流影響不顯著,應(yīng)變梯度還是較小,而在局部力作用下,且單疇方向與力方向相反時,鐵電薄膜漏電流較大的變化,這是因為局部力作用下產(chǎn)生了很大的應(yīng)變梯度,導(dǎo)致力作用下鐵電薄膜電勢降低空穴載流子大量聚集,在作用力低于鐵電薄膜臨界翻轉(zhuǎn)應(yīng)力情況下,鐵電薄膜漏電流隨壓應(yīng)力增大而增大。(3)分別研究了撓曲電系數(shù)11f及12f對只有多疇Pb(Zr0.1Ti0.9)O3結(jié)構(gòu)鐵電薄膜漏電流的影響。11f所描述的是極化與縱向應(yīng)變梯度的之間耦合,會導(dǎo)致鐵電薄膜內(nèi)電勢的降低,增加載流子空穴在鐵電薄膜內(nèi)的濃度,進而提高了鐵電薄膜漏電流,12f所描述的是極化與縱向應(yīng)變梯度的之間耦合,會導(dǎo)致鐵電薄膜內(nèi)電勢的升高,減小載流子空穴在鐵電薄膜內(nèi)的濃度,進而減小鐵電薄膜漏電流。
[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.
【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB383.2

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