Phase diagram of ferroelectric thin film with diluted surface

We study the influence of the surface of the ferroelectric films on the properties of the intrinsic ferroelectric polarization state in frame of statistical Transverse Ising Model (TIM). The quality of the surface is modelled by the dilution parameter q$q$ that reflects the relative weight of the paraelectric impurities vs. ferroelectric ions. Using the effective field approach the variation of the average value of spontaneous polarization as function of temperature for different film thicknesses has been investigated as function of dilution parameter q$q$. The phase diagram of the system and crossover from the ferroelectric to the paraelectric phase is discussed.     

铁电双层膜的反转动力学行为

基于Landau-Khalatnikov运动方程,本文研究了含有表面过渡层和铁电界面耦合的反转动力学行为(包括平均极化、反转时间、反转电流和矫顽场).研究结果表明:在铁电双层膜系统中存在一个竞争的机理,即表面过渡层与界面耦合的竞争作用.我们发现在双层膜反转过程中出现了反常行为,这些反常行为归因于表面过渡层与界面耦合之间的竞争.表面过渡层与界面耦合的共同行为对铁电双层膜的动力学特性起到了决定性的作用.     

Polarization Fizeau interferometer based on birefringent thin film

A polarization Fizeau interferometer based on birefringent thin film is presented. The interferometer adopts a birefringent thin film to obtain orthogonally polarized and strictly common-path reference and test beams. Advantages include ease of implementation on large-aperture interferometer, measuring test optics from long distance, and achieving high fringe visibility. The phase shift is obtained by combining a quarterwave plate and an analyzer. The concepts illustrated are verified experimentally.     

可调谐超导滤波器技术的研究

通过研究可调谐滤波器的基本原理,利用钛酸锶铁电薄膜介电常数随外加电场变化的特性,以铝酸镧为基片,采用多层薄膜和三次套刻两种方法设计出可调谐超导滤波器,通过外加电压实现滤波器频率的调谐。     

Polarization modulation imaging ellipsometry for thin film thickness measurement

A polarization modulation (PM) imaging ellipsometer is proposed and setup in order to measure precisely the thickness of thin film. Five images are collected sequentially by CCD camera with respect to five pre-determined azimuth angles of a quarter wave plate (QWP) during measurement. Then two-dimensional (2-D) distributions of the ellipsometric parameters ψ and Δ over the full dynamic range are obtained. Conceptually, PM imaging ellipsometer integrates the features of phase shift interferometry with conventional photometric ellipsometry by rotating the QWP sequentially to produce polarization modulation that is able to measure the thickness of a thin film in two dimensions precisely and quickly. The basic principle of PM imaging ellipsometer is derived wherein features such as common path configuration, full dynamic range of measurement, and insensitive to non-uniform response of the CCD are analyzed. The experimental results verify the ability and performance of PM imaging ellipsometer on 2-D thin film thickness, while the errors regarding the ellipsometric parameters measurements are discussed.     

YMnO_3薄膜的铁电行为及其纳米尺度铁电畴的研究

六方YMnO_3是一种特殊的多铁性材料,因其具有介电常数低、单一极化轴、无挥发性元素等特点,在磁电领域具有独特的优势,但目前关于YMnO_3薄膜的铁电性特别是畴结构的研究相对较少.本文采用溶胶-凝胶法在Si(100)基片上制备了多铁性YMnO_3薄膜,利用掠入射X-射线衍射、原子力显微镜对薄膜的结构及表面形貌进行了分析,用压力显微镜(PFM)技术研究了纳米尺度畴结构及微区电滞行为,并通过I-V,P-E曲线进一步研究了薄膜的漏电流和宏观电滞行为.结果表明,该薄膜为六方钙钛矿结构,YMnO_3晶粒大小均匀并且结晶性较好,薄膜表面粗糙度为7.209 nm.PFM图显示出清晰的电畴结构,结合典型的微区振幅蝴蝶曲线和相位电滞回线,证实该YMnO_3薄膜具有较好的铁电性.由于受内建电场的作用,振幅曲线和相位曲线都向正向偏移,表现出非对称特征.该薄膜的漏电流密度低于10~(-6)A·cm~(-2),因而其电滞回线基本能够达到饱和.     

Effect of electrodes on the properties of a thin ferroelectric film

The effect of various metal electrodes on the properties of thin ferroelectric films is considered using the phenomenological Ginzburg-Landau theory. The electric field produced by charges on electrodes is taken into account (with allowance for the screening of the charges in the metals) in the free energy functional and in the Euler-Lagrange equation for the film polarization. This equation is solved using the variational method, and the free energy functional is reduced to the conventional free energy with a renormalized coefficient of P ². This coefficient is dependent on the properties and thickness of the film and the properties of the electrode. Therefore, the physical characteristics of the size effect can be found by merely substituting the renormalized coefficient into the usual formulas from phenomenological theory. The calculations are shown to be in good agreement with the experimental data for Pt, Ir, IrO₂, and SrRuO₃.     

Phase transition behaviors of a ferroelectric thin film with long-range interactions

Within the framework of the mean-field approximation, the transverse-field Ising model is used to investigate the surface parameter modification of interaction constants and transverse fields on phase transition behaviors of a ferroelectric thin film with long-range interactions. The variation of Curie temperature as a function of the surface transverse field for different surface interaction constants or thickness is discussed. Meanwhile, the variation of Curie temperature as a function of the surface exchange interaction for different surface transverse fields is examined. In addition, the dependence of Curie temperature on the film thickness for different surface exchange interactions and surface transverse fields is obtained.     

Epitaxial growth of ferroelectric PLZT thin film and their optical properties

A series of experiments for growing epitaxial PLZT thin films has been made with rf sputtering. X-ray and electron diffraction analyses confirm that the fabricated films grow epitaxially on SrTiO₃ and MgO crystals. A good transparency in the region above 0.4 μm to infrared with good ferroelectric properties is obtained. Propagation loss of He−Ne laser light is less than 6 dB/cm, and the PLZT thin film is a promising candidate for the optical modulator and other functional elements for integrated optics.     

铁电薄膜铁电性能与温度关系的一种实时测量实验方法

介绍了一种实时测量铁电薄膜的铁电性能与温度关系的实验方法,为进一步研究铁电薄膜的特性提供了实验基础。     

Static Wiener spectrum of a thin film of polymer-encapsulated ferroelectric liquid crystals

Results of computer simulation of the shading effect in systems of opaque spherical particles scattering light in accordance with the Lambert law are presented. Two types of systems are studied: a semi-infinite medium and statistically uniform clusters of a finite number of particles. The simulation makes it possible to obtain photometric characteristics of systems with an accuracy better than 1%. The phase dependence of the shading effect is shown to become steeper as the packing density of particles in clusters decreases and their number increases. For statistically uniform media, the following relation takes place: The lower the packing density, the more pronounced the shadow decrease in brightness with an increasing phase angle.     

Polarization instability in polydomain ferroelectric epitaxial thin films and the formation of heterophase structures

A thermodynamic theory is developed for dense laminar domain structures in epitaxial ferroelectric films. It is found that, at some critical misfit strain between the film and substrate, the 90 degrees c/a/c/a domain structure becomes unstable with respect to the appearance of the polarization component parallel to domain walls, which results in the formation of a heterophase structure. For PbTiO3 and BaTiO3 films, the stability ranges of polydomain and heterophase states are determined. Dielectric anomalies accompanying misfit-strain-driven structural transformations are described.     

Simulation of flexoelectricity effect on imprint behavior of ferroelectric thin films

The impact of flexoelectricity on the imprint behavior in ferroelectric thin films has been investigated within the framework of Landau-Khalatnikov theory, by incorporating the coupling effect between the stress gradient and polarization. It is found that the imprint phenomenon can be in part induced by flexoelectricity. In the presence of flexoelectric coupling, the compressive stress shifts the hysteresis loop to the negative electric field axis, but the tensile stress shifts it to the opposite direction, which is in good agreement with experimental result. Besides, the characteristic length of stress distribution has a significant influence on the upper part of hysteresis loop. It highlights the pressing need to avoid the stress gradient in order to prevent degradation of device performance in ferroelectric thin films.     

微结构对Eu掺杂Bi4Ti3O12铁电薄膜铁电性能的影响

采用金属有机物分解法在Pt/Ti/Si(111)基底上制备了退火温度分别为600℃,650℃,700℃的Bi_3.15Eu_0.85Ti₃O₁₂(BET)铁电薄膜,并对其结构及铁电性能进行了测试,再使用扫描探针显微镜对BET薄膜的电畴翻转进行了实时观测.BET薄膜c畴发生180°畴变的最小电压为+6V,而r畴由于其高四方性,即使极化电压增至+12V也不会发生翻转.薄膜的铁电性主要源于c畴的极化,随着退火温度的升高,c畴的区域面积增加,BET薄膜的剩余极化强度随之增大.退火温度为700℃的BET薄膜剩余极化强度达到84μC/cm². 关键词： 铁电薄膜 电畴翻转 扫描探针显微镜     

重温Pb(Zrx Ti1-x)O3铁电薄膜极化疲劳问题

具有ABO3型钙钛矿结构的Pb(ZrxTi1-xO3(PZT)展示出良好的铁电极化性能,是使用最广的铁电材料.然而,在将它应用于铁电存储时,PZT薄膜遭遇到极化疲劳问题而被SrBi2Ta2O9(SBT)等铁电体所替代,这一问题至今未能得到妥善解决.文章首先通过变温极化疲劳实验充分理解PZT极化疲劳的基本过程,然后有针对性地进行材料设计,获得基本无极化疲劳的PZT铁电薄膜.     

重温Pb(ZrxTi1-x)O3铁电薄膜极化疲劳问题

具有ABO3型钙钛矿结构的Pb(ZrxTi1-x)O3 (PZT)展示出良好的铁电极化性能,是使用最广的铁电材料.然而,在将它应用于铁电存储时,PZT薄膜遭遇到极化疲劳问题而被SrBi2Ta2O9 (SBT)等铁电体所替代,这一问题至今未能得到妥善解决.文章首先通过变温极化疲劳实验充分理解PZT极化疲劳的基本过程,然后有针对性地进行材料设计,获得基本无极化疲劳的PZT铁电薄膜.     

Theoretical studies on the pyroelectric properties of two component composite ferroelectric thin film

Using a Ginzburg–Landau–Devonshire type model, the pyroelectric property and hysteresis loop are studied for a composite ferroelectric thin film that contains an insertion of a different type of ferroelectric material in parallel connection with the host ferroelectric film material. If these two types of ferroelectric materials are polarized along the same direction, there are two peaks occur in the pyroelectric coefficient vs temperature curve. If the two ferroelectric materials are polarized in opposite directions, one positive and one negative coefficient peaks occur in the temperature dependence of pyroelectric coefficient curve and the hysteresis loop appears to be a quasi-double loop. The effect of the external electric field on the pyroelectric coefficient is also investigated.     

Irradiation behavior and recovery effect of ferroelectric properties of PZT thin films

Lead zirconate titanate piezoelectric ceramics have important applications in space and aerospace technology, but the effect and physical mechanism of charged particle radiation on their performance yet to be clarified. In this study,we characterized PbZr_(0.52)Ti_(0.48)O_3(PZT) thin films, and changes in the ferroelectric properties of the films before and after electron and proton irradiation were investigated. The natural and heat treatment recoverability of the ferroelectric properties were studied, and the damages and mechanisms of different types of radiation in PZT films were also investigated.The results show that, in addition to ionization damages, electron irradiation causes certain structural damage on the PZT film, and the large structural damage caused by proton irradiation reduces drastically the ferroelectricity of the PZT film.