【作者】 郭鸣；

【导师】 杨平雄；

【作者基本信息】 华东师范大学 ， 微电子学与固体电子学， 2010， 博士

【摘要】 近年来,铋基类钙钛矿铁电材料是铁电和固态电解质材料应用领域备受关注的功能材料之一,其应用研究已成为固态电子学领域的研究热点。它的高居里温度、低介电常数、良好的抗疲劳性、高氧离子导电率和环境友好,在铁电存储器和中低温固态氧化物燃料电池（SOFC）等应用上具有潜在的发展前景。但是,满足器件用的铋基类钙钛矿材料还面临若干问题,例如,铋基铁电薄膜的各向异性和结构稳定性问题,电解质材料满足器件集成的制备工艺和热稳定问题等。本论文以钒酸铋(Bi₂VO_5.5,BVO)及其金属掺杂材料为研究对象,针对以上问题研究了BVO体系铁电薄膜和Bi₂ME_0.1V_0.9O_5.5-δ（BIMEVOX.10）电解质材料的制备及性能。主要研究结果如下:（1）采用化学溶液沉积（CSD）法,分别在LaNiO₃（LNO）/Si（100）、Pt/TiO₂/SiO₂/Si（100）衬底上制备了c轴取向的高质量BVO薄膜。并对CSD工艺做了改进,用钒无机盐替代最初采用的乙酰丙酮氧钒,成功解决了金属醇盐价格昂贵且不易保存的问题。深入研究了不同退火温度对BVO薄膜性能的影响。700℃退火后的BVO薄膜显示出最优的性能,具有高度c轴取向,剩余极化和漏电流密度提高到10.62μC/cm²和1.92×10^-8 A/cm²。分析了260-480 K温度范围的介电特性,发现BVO薄膜中存在的多分散弛豫由氧空位等缺陷引起,传导机制主要为氧空位传导。（2）研究了BVO薄膜与p-Si（100）衬底集成所形成MFIS（Metal-Ferroelectrics-Insulator-Semiconductor）结构的C-V特性,记忆窗大小约0.5 V,这为BVO薄膜在场效应型铁电存储器的应用提供了优化的工艺条件。采用椭偏光谱获得了BVO薄膜的光学常数,有助于开发其光学特性上的应用。（3）首次用CSD法合成了具有良好铁电特性的混合铋基类钙钛矿铁电薄膜Bi₂VO_5.5-Bi₄Ti₃O₁₂,薄膜剩余极化2P_r提高到12.46μC/cm²,漏电流密度为1.17×10^-8A/cm²。为提高BVO材料的铁电特性提供了新技术途径。（4）首次系统研究了不同比例La掺杂对BVO薄膜介电特性的影响。La掺杂使BVO薄膜的介电常数、介电损耗增加,在少量掺杂（0.025摩尔比）时表现最明显。其机理在于低浓度的La会先进行V位替换,La³⁺和V⁵⁺间的非等价替代及原子半径间的巨大相差,引起晶格体积膨胀和晶格扭曲的结构重排,引发氧空位V_o^¨等缺陷,造成介电常数、介电损耗的增加和弛豫程度的显著增强。（5）用CSD法成功制备了BIMEVOX.10（ME=Ti,Co,Fe,Ni,Mn）薄膜,研究了其结构和电学特性。重点讨论了BIMNVOX.10薄膜在300-485 K温度范围的电特性,研究表明BIMNVOX.10薄膜的介电弛豫可能是由氧空位的短程扩散传导引起,属于多分散性弛豫。发现BIMNVOX.10薄膜具有室温弱铁磁特性。（6）深入研究了BIMEVOX体系电解质材料中具有最高电导率的Bi₂Cu_0.1V_0.9O_5.35（BICUVOX.10）粉体和薄膜材料的制备和特性。采用化学溶液法制备了BICUVOX.10纳米粉末,比常规固相法的合成温度降低了～300℃。研究了PEG4000表面活性剂、制备方法和粉末分散性间的联系。发现PEG4000能有效改变纳米颗粒的团聚现象,其添加量和制备方法有关。利用反向滴定沉淀法获得了平均粒径为20 nm的产物,PEG4000的添加量约5 wt%。这一结果为获得分散性良好的BIMEVOX纳米粉末提供了工艺途径。在LNO/Si（100）上生长了高质量的c轴择优取向BICUVOX.10薄膜,300-620 K的中低温范围样品具有高氧离子导电性和良好的热稳定性,氧空位激活能为0.3 eV,600 K下的氧离子电导率为5×10^-2S·cm^-1。（7）首次研究了BVO和BIMEVOX.10（ME=Mn,Fe,Co）粉体的磁性,发现该系列材料均表现出室温铁磁特性。经过渡金属离子掺杂后,BVO铁磁性变强,其中Mn掺杂表现最明显。BVO和BIMNVOX.10的剩余磁化,饱和磁化和矫顽场分别为2.11,4.67 memu/g;3.33,11.02 memu/g和0.02,0.04 kOe;BIMNVOX.10的居里温度为279℃。另外,从理论上分析得出室温铁磁特性主要是由氧空位所引起;掺杂离子d态电子自旋引起不成对电子对自旋态重新分布,是造成磁性大小改变的主要因素。更多还原

【Abstract】 In recent years,bismuth-based perovskite-like ferroelectric materials have attracted great interest in ferroelectrics and solid electrolyte fields.Their applications have become popular in the solid-state electronics.They are promising candidates for applications of integrated non-volatile memories and intermediate-low temperature solid oxide rule cells,due to their high Cutie temperature,low dielectric constant, high ionic conductivity,fatigue-flee and environment-friendly properties.However, the development of practical devices are still hindered by some problems,such as the anisotropy and structure stability for bismuth-based ferroelectric films,the deposition process and thermal stability for solid electrolyte films.In this work,Bi₂VO_5.5（BVO） and metal doped BVO materials were synthesized. The characteristics of BVO system films and Bi₂ME_0.1V_0.9O_5.5-δ（BIMEVOX.10） solid electrolyte materials were investigated.The main results are as follow:（1） High quality BVO thin films with c-preferred orientation were successfully fabricated on LaNiO₃（LNO）/Si（100） and Pt/TiO₂/SiO₂/Si（100） substrates via chemical solution deposition（CSD）.The CSD process was improved by using vanadium inorganic salt instead of the original vanadyl acetylacetonate.It has successfully solved the problem that the metal alkoxides are pricey and difficult to keep.It was intensively investigated the influence of annealing temperatures on the characteristics of BVO thin films.The films annealed at 700℃showed the highest c-preferred orientation and the best ferroelectric properties.The values of remnant polarization and leakage current were improved to 10.62μC/cm² and 1.92x10^-8 A/cm².The dielectric properties were studied in 260-480 K temperatures.It was found that a poly-dispersive dielectric relaxation in the films originated from localized charge carrier like oxygen vacancy diffusion.The conductivity mechanism was mainly due to oxygen ion conductivity.（2） The C-V characteristics of BVO/p-Si（100） films with a MFIS （Metal-Ferroelectrics-Insulator-Semiconductor） structure were studied.Its memory window was about 0.5 V.The research provides a better process for the ferroelectric field effect memory applications of BVO films.The optical constants were obtained by ellipsometry spectra,which were beneficial to developing the applications of optical characteristics.（3） It was the first time to synthesize the Bi₂VO_5.5-Bi₄Ti₃O₁₂ films with mixed bismuth-based perovskite-like structure.It showed good ferroelectric properties.The values of remnant polarization and leakage current were improved to 12.62μC/cm² and 1.17×10^-8 A/cm².The results provide a new technological approach to optimize the ferroelectric properties for BVO films.（4） La-doping BVO films were studied extensively for the first time.The dielectric permittivity and dispersion increased by La doping,especailly with 0.025 mole ratio of La doping.The mechanism can be explained as follow:When La ions go into BVO structure,some of them possibly preferentially enter V sites.A readjustment of lattice structure toward a defective structure will happen,which is due to volume increase and distortion caused by the nonequivalent substitution and large radii difference.It results in defects such as oxygen vacancies,giving rise to a deterioration of dielectric properties and dispersion increase.（5） BIMEVOX.10（ME=Ti,Co,Fe,Ni,Mn） thin films were successfully prepared by CSD.The structure and electrical properties were studied and the electrical properties of BIMNVOX.10 films were selectively analyzed in 300-485 K temperatures.The results indicated that the dielectric relaxation in the films was a poly-dispersive dielectric dispersion which originated from oxygen ion conductivity. Furthermore,a weak room temperature ferromagnetism was observed in the BIMNVOX.10 thin films.（6） It was intensively investigated the preparation and characteristics of Bi₂Cu_0.1V_0.9O_5.35（BICUVOX.10） powders and thin films.BICUVOX.10 nano-powders were obtained through chemical solution methods,which synthesis temperature was lower about 300℃compared with that of conventional solid-state process.The relationships of dispersivity,synthesis methods and the PEG4000 surfactant additive capacity were studied.It was found that PEG4000 had a great effect on disagglomeration of nano powders and its additive content was associated with the synthesis process.In the reversing titration co-precipitation process,the average grain size of the sample was about 20 nm when with 5 wt%PEG4000.The results provide a way to get BIMEVOX nano-powders with good dispersivity. Furthermore,high quality BICUVOX.10 thin films were deposited on LNO/Si（100） substrates with a tendency of c-preferred orientation.The films showed good oxide ion conductivity and thermal stability in the intermediate-low temperatures from 300 to 620 K.The activity energy of oxide vacancy was about 0.3 eV and the oxygen conductivityσ_{600 K} was 5×10^-2 S·cm^-1.（7） It was the first time to probe the magnetism of BVO and BIMEVOX.10 （ME=Mn,Fe,Co） powders.It was found room temperature ferromagnetism in these samples.The ferromagnetism became stronger when doped with transition metal ions, especially by Mn doping.The remnant magnetization,saturation magnetization,and coerced field of BVO and BIMNVOX.10 were 2.11 and 4.67 memu/g,3.33 and 11.02 memu/g,0.02 and 0.04 kOe,respectively.The Curie temperature of 279℃was observed for BIMNVOX.10 powders.Theoretically,the presence of oxygen vacancies was used to explain the room temperature ferromagnetism behaviors.The variety of magnetization was mainly caused by the redistribution of unpaired electron spin state,which resulted from the d-electron spinning of doped ions.更多还原