Hf_(0.2)Zr_(0.8)O_2铁电薄膜的制备与电性能研究

采用脉冲激光沉积法(pulsed laser deposition,PLD),通过改变气氛氧压、衬底温度等工艺参数,在Pt/Ti/SiO2/Si衬底上制备了Hf0.2Zr0.8O2(HZO)薄膜。利用X射线衍射(XRD)表征了薄膜的结构特征;并采用Radiant RT66A进行铁电性能参数的测量,以此研究了工艺参数对薄膜结构和铁电性能的影响规律。分析结果表明,HZO铁电极化的原因主要是来自于HfO2-ZrO2(111)正交相和ZrO2(002)四方相的影响。通过上述实验结果得到,在Pt/Ti/SiO2/Si衬底上制备Hf0.2Zr0.8O2薄膜的优化条件为氧分压18 Pa、衬底温度500℃。在优化条件下制备的Hf0.2Zr0.8O2薄膜,剩余极化(2Pr)达到4μC/cm2。     

热分解气氛对溶胶-凝胶法制备BLT铁电薄膜性能的影响

研究了热分解气氛对溶胶-凝胶法制备在Pt/Ti/SiO2/Si衬底上的Bi3.25La0.75Ti3O12 (BLT)薄膜铁电性能的影响.在400℃时空气或氧气气氛下热分解20min,接着在700℃时氧气气氛下退火30min.氧气气氛下的热分解能充分分解掉薄膜中的有机成分,而空气气氛下的热分解使炭、氢有机成分部分残留在薄膜中.有机成分的不完全分解影响了退火过程中BLT薄膜晶化时晶粒的生长.表现出生长取向和晶粒尺寸对BLT薄膜铁电性能的影响.氧气和空气气氛下热分解的薄膜的剩余极化(Pr)和矫顽电场(Ec)分别为18.85μC/cm2,119.7kV/cm和12.56μC/cm2、112.5kV/cm.氧气气氛下热分解的薄膜的剩余极化值显著提高.所以热分解是控制铁电性能的重要步骤.     

(Pb0.90La0.10)Ti0.975O3/LaNiO3薄膜的射频磁控溅射制备和性能研究

采用射频磁控溅射技术,以LaNiO3(LNO)作为过渡层,在SiO2/Si(100)、Pt(111)/Ti/SiO2/Si(100)衬底上分别获得了(100)、(110)取向的(Pb0.90La0.10)Ti0.975O3(PLT)铁电薄膜.研究了LNO/Pt(111)/Ti/SiO2/Si(100)和LNO/SiO2/Si(100)基底对PLT薄膜微结构和铁电性能的影响.实验结果表明,与在LNO/Pt(111)/Ti/SiO2/Si(100)基底上沉积的(110)取向的PLT薄膜相比较,在LNO/SiO2/Si(100)基底上沉积的高度(100)取向的PLT薄膜具有更好的微结构和更高的剩余极化强度,其2Pr为40.4μC/cm2.     

电极对PZT铁电薄膜的微观结构和电性能的影响

采用溶胶—凝胶(sol—gel)工艺分别在Pt／Ti／SiO2／Si和LNO／Si电极上制备Pb(Zr0．53，Ti0．47)O3(PZT)铁电薄膜。研究了不同电极材料对PZT铁电薄膜的微结构及电性能的影响。(100)择优取向的PZT／LNO薄膜的介电性能和铁电性能较(111)／(100)取向的PZT／Pt薄膜略有下降，但在抗疲劳特性和漏电流特性方面都有了很大提高。PZT／LNO薄膜10m次极化反转后剩余极化几乎保持未变，直至10^12次反转后，剩余极化仅下降了17％。     

快速退火工艺条件下温度对Bi4Ti3O12铁电薄膜微观结构与性能的影响

采用快速退火工艺在Pt/Ti/SiO2/p-Si衬底上制备了Bi4Ti3O12铁电薄膜.研究了退火温度对薄膜微观结构、铁电特性及介电性能的影响.研究表明:退火温度对Si基Bi4Ti3O12铁电薄膜晶相结构的影响显著,对晶粒尺寸和表面形貌的影响较小,但退火温度超过800℃后会出现焦绿石等杂相;低于750℃时,薄膜的剩余极化随退火温度升高而增大,高于750℃时却有所减小,但矫顽电场随退火温度升高而逐渐降低;退火温度对薄膜的漏电流密度有一定的影响,薄膜的漏电流密度在200kV/cm极化电场作用下低于3×10-9A/cm2,750℃时的剩余极化和矫顽电场分别为11μC/cm2和77kV/cm,具有较好的铁电和介电性能.     

射频磁控溅射制备(Pb,La)TiO3薄膜的结晶性能与铁电畴初步研究

采用射频磁控溅射技术在Pt/Ti/SiO2/Si衬底制备了(Pb,La)TiO3(简记为PLT)铁电薄膜.利用XRD对PLT薄膜的结晶性能进行了研究.实验结果表明,在一定的制备工艺条件下,可以制备出完全钙钛相的PLT铁电薄膜.PLT铁电薄膜的结晶性能与溅射的工作气压、氧氩比、退火温度等关系密切;PFM表明PLT薄膜的电畴具有180°结构.     

取向对PLD法制备BiFeO3薄膜性能的影响

以快速等离子烧结法(SPS)制备的BiFeO3块体为靶材,用激光脉冲沉积(PLD)法在不同衬底上制备了BiFeO3(100)/LaNiO3(100)/Si(100)、BiFeO3(111)/LaNiO3(111)/SrTiO3(111)、BiFeO3(110)/Pt/TiO2/SiO2/Si、BiFeO3(110)LaNiO3(110)/Pt/TiO2/SiO2/Si不同择优取向的薄膜,并对薄膜进行了XRD和SEM分析。X射线衍射结果表明,BiFeO3薄膜外延沉积在导电层衬底上,并且它们具有相同的高度取向。SEM分析表明,薄膜上的晶粒是柱状形态,表面光滑致密且颗粒分布非常均匀,晶粒的边界和尺寸也能被清晰地观察到。通过铁电铁磁性能研究,BiFeO3(111)择优取向性能最佳。SrTiO3衬底上(111)取向的BiFeO3薄膜铁电剩余极化值达到了30.3μC/cm2,漏电流为1.0×10-3 A/cm2,饱和磁化强度为20.0kA/m。     

不同衬底上LaNiO3导电氧化物薄膜的制备和研究

通过MOD法和快速热处理过程,在Si(100)和Pt(111)/Ti/SiO2/Si衬底上制备了LaNiO3(LNO)导电氧化物薄膜.经XRD结构分析表明,所制备的LNO薄膜具有纯的钙钛矿结构,并且以(100)方向择优取向.经SEM和AFM分析表明,LNO薄膜具有表面均匀、无裂纹.经标准四探针法测试表明,LNO薄膜具有好的金属特性,其室温电阻率为7.6×10-4Ω·cm.铁电性能测试表明,LNO薄膜可以提高PZT铁电薄膜的剩余极化强度.     

Sol-gel法制备Pb(Zr0.53Ti0.47)O3铁电薄膜

利用Sol-gel工艺在Pt/Ti/SiO2/Si衬底上制备了Pb(Zr0.53Ti0.47)O3(PZT)薄膜,研究了退火温度、保温时间和薄膜厚度对其晶相、微观结构和铁电性能的影响.在500℃退火处理的PZT薄膜开始形成钙钛矿相;在550℃退火处理的PZT薄膜基本形成钙钛矿相结构;升高退火温度(500～850℃)、延长保温时间(30～150min)、增加薄膜厚度(120～630nm)都有利于PZT晶粒的长大.在650～750℃退火的PZT薄膜具有较好的铁电性能,保温时间对PZT薄膜的铁电性能影响不大,PZT薄膜的厚度为200～300nm时可以得到比较好的铁电性能.在退火温度750℃、保温时间30min条件下退火处理厚310nm的PZT薄膜,其剩余极化值(2Pr)和矫顽电场(2Ec)分别是72μC/cm2、158kV/cm.     

溶胶-凝胶法制备(Na0.85K0.15)0.5Bi0.5TiO3铁电薄膜晶化行为研究

利用溶胶-凝胶法在(111)Pt/Ti/SiO2/Si衬底上成功制备了无铅(Na0.85K0.15)0.5Bi0.5TiO3(NKBT)铁电薄膜。利用XRD和原子力显微镜(AFM)分别对薄膜的晶化行为和表面形貌进行了表征。结果表明,在一定温度范围内,随着热分解温度和退火温度的升高,薄膜的晶化程度变得越来越完全,晶粒变得更加均匀致密。当热分解温度为450℃、退火温度为700℃时,薄膜表现出最优的晶化行为,其铁电性能良好,剩余极化强度(Pr)和矫顽场强(Ec)分别为10.37μC/cm2和78.2kV/cm。     

应力对铁电薄膜电滞回线及蝶形曲线的影响

应用与时间有关的Ginzburg- Landau方程(time dependent Ginzburg-Landau,简称TDGL方程),在考虑表面效应的条件下分析了应力对外延铁电薄膜铁电性能的影响.计算结果显示剩余极化强度值随着压应力的增加而增加,随着张应力的增加而减小.场致应变值随着压应力的增加而增加,随着张应力的增加而减小.这种变化趋势与实验结果是一致的.考虑表面效应计算得到的剩余极化强度值小于不考虑表面效应时计算得到的数值(当外推长度＞0时).     

Magnetic ferroelectric materials

In the form of a succinct overview the structure and symmetry requirements of magnetic ferroelectrics are discussed. Boracites are the best-studied examples and have phases being simultaneously ferroelectric, ferromagnetic and ferroelastic. One of the salient features of such materials is the obligatory occurrence of the linear and bilinear magnetoelectric effects. They represent an invaluable auxiliary information for magnetic symmetry determination by neutron diffraction. Owing to the complexity of property combinations, work with single crystals and polarized light microscopy is obligatory. Key references of the field are given.     

Numerical analysis of ferroelectric/ferroelastic domain switching in ferroelectric ceramics

A numerical approach predicting the behavior of ferroelectric ceramics under electric field and mechanical loading is proposed in this paper. In the model, macroscopic properties of ferroelectric ceramics are determined by microscopic structures. Ferroelectric ceramics are seen to be composed of many domains with different orientations, and domain switching is the source of the nonlinear constitutive behavior of the ferroelectric ceramics. Numerical calculations based on the model were carried out, and the computational results are compared with the experimental results, which shows the two sets of results consist with each other. The calculation approach can provide a guidance for the ceramics component design.     

From normal ferroelectric transition to relaxor behavior in Aurivillius ferroelectric ceramics

The influence of the barium concentration on the dielectric response of Sr_1?x Ba _x Bi₂Nb₂O₉ system, with x = 0, 15, 30, 50, 70, 85, 100 at.%, has been studied. The barium concentration dependence of T _m, as well as the temperature of the corresponding maximum for the real part of the dielectric permittivity, has suggested a cation site mixing among atomic positions, which has been supported by the structural analysis. A transition from normal ferroelectric–paraelectric phase transition to a relaxor behavior has been observed in the studied samples, when the barium concentration has increased. The relaxor behavior has been discussed.     

Science and technology of ferroelectric films and heterostructures for non-volatile ferroelectric memories

We present in this article a review of the status of thin film ferroelectric materials for nonvolatile memories. Key materials issues relevant to the integration of these materials on Si wafers are discussed. The effect of film microstructure and electrode defect chemistry on the ferroelectric properties relevant to a high density nonvolatile memory technology are discussed. The second part of this review focuses on approaches to integrate these capacitor structures on a filled poly-Si plug which is a critical requirement for a high density memory technology. Finally, the use of novel surface probes to study and understand broadband polarization dynamics in ferroelectric thin films is also presented.     

Normal ferroelectric to ferroelectric relaxor conversion in fluorinated polymers and the relaxor dynamics

To elucidate the molecular origin of the polarization dynamics in the ferroelectric relaxor poly(vinylidene fluoride—trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer, a broadband dielectric study was carried out in the frequency range from 0.01 Hz to 10 MHz and temperatures from −150°C to 120°C for the terpolymer and a normal ferroelectric P(VDF-TrFE) copolymer. The relaxation processes were also studied using dynamic mechanical analysis. It was shown that in the terpolymer, which was completely converted to a ferroelectric relaxor, there is no sign of the relaxation process associated with the ferroelectric-paraelectric transition which occurs in the P(VDF-TrFE) copolymer. In the copolymer, three additional relaxation processes have been observed. It was found that the relaxation process β_a, which was commonly believed to be associated with the glass transition in the amorphous phase, in fact, contains significant contribution from chain segment motions such as domain boundary motions in the crystalline region. In the temperature range studied, the terpolymer exhibits the latter three relaxation processes with the one (termed β_r) near the temperature range of β_a significantly enhanced. This is consistent with the observation that in conversion from the normal ferroelectric to a ferroelectric relaxor, the macro-polar domains are replaced by nano-polar-clusters and the boundary motions as well as the reorientation of these nano-clusters generate the high dielectric response. The experimental data also reveal a broad relaxation time distribution related for the β_r process whose distribution width increases with reduced temperature, reflecting the molecular level heterogeneity in the crystalline phase due to the random introduction of the CFE monomer in the otherwise ordered macro-polar domains. The random interaction among the nano-clusters as well as the presence of the random fields produces ferroelectric relaxor behavior in the terpolymer.     

One-dimensional nanostructures of ferroelectric perovskites

Nanorods, nanowires, and nanotubes of ferroelectric perovskites have recently been studied with increasing intensity due to their potential use in non-volatile ferroelectric random access memory, nano-electromechanical systems, energy-harvesting devices, advanced sensors, and in photocatalysis. This Review summarizes the current status of these 1D nanostructures and gives a critical overview of synthesis routes with emphasis on chemical methods. The ferroelectric and piezoelectric properties of the 1D nanostructures are discussed and possible applications are highlighted. Finally, prospects for future research within this field are outlined.     

O.92PZN-0.08PT晶体的缺陷与畴结构研究

应用环境扫描电子显微术(ESEM)、原子力扫描显微术(AFM)、同步辐射白光形貌术(SRWBT)等形貌成像技术研究了0.92PZN-0.08PT晶体的表面缺陷形态与铁电畴结构.通过对畴结构动态演化的同步辐射形貌观察,可揭示出该晶体的结构相变过程.     

Acoustic microscopy of ferroelectric ceramics

Ferroelectric ceramics have been observed in an acoustic microscope. The images demonstrate the ability of the microscope to image elastic properties and to penetrate opaque layers.