导　　师： 于军

学科专业： H0903

授予学位： 博士

作　　者： ;

机构地区： 华中科技大学

摘　　要： 铁电存储器是一种具有快速读写操作、低功耗、抗辐射等优异特性的非易失性存储器，有广阔的应用前景。掺LA钛酸铋（BLT，BI3.25LA0.75TI3O12）铁电薄膜是用于铁电存储器最具潜力的材料之一。本论文研究了提高BLT系列铁电薄膜性能的优化工艺及薄膜生长的模拟。
　　 采用溶胶－凝胶法在PT/TIO2/SIO2/P-SI(100)衬底上制备了BLT铁电薄膜。研究了退火工艺对薄膜性能的影响。退火温度对薄膜的微观结构和铁电性能有强烈的影响。同时，温度和气氛对薄膜铁电性能的影响存在着竞争关系，综合考虑，750℃下氧气含量为20%的氮氧混合气氛退火的薄膜具有最佳的铁电性能。退火氧气压对薄膜的晶化度、微观形貌、铁电性能都有影响，10-1 ATM氧气压下退火的薄膜具有A轴择优取向和良好的铁电性能。
　　 对BLT薄膜进行B位V5+掺杂改性研究。分别制备了BI4TI3O12（BIT）、BLT、BI3.99TI2.97V0.03O12（BTV）和BI3.24LA0.75TI2.97V0.03O12（BLTV）薄膜。BLTV薄膜表现出随机取向，并由倾斜于薄膜表面的柱状晶粒构成。同时，拉曼光谱表明，A位的LA掺杂对B位的TI有一定的影响，V的掺杂对TIO6（或VO6）八面体的对称性有所降低，并增强了TI-O键（或V-O键）的杂化。此外，V掺杂能起到电荷中和的作用，从而抑制和减少氧空位的产生。对比BLT薄膜，BLTV薄膜在V掺杂的作用下提高了铁电性能、抗疲劳特性并改善了漏电流特性。
　　 为确定最佳V掺杂量，制备了不同V掺杂量的BI3.25-X/3LA0.75TI3-XVXO12（X: 0～8%）薄膜。随着V掺杂量的增加，薄膜的剩余极化和抗疲劳特性都表现出先提高后降低的变化规律，当V掺杂量为3%时，BLTVX薄膜获得最大的剩余极化值（25.4 μC/CM2）和最好的抗疲劳性能（经1010极化翻转后，剩余极化保持为初始值的90%）。当V掺杂量达到5%时，这种性能的提高达到饱和。而当V掺杂量达到8%时，BLTVX薄膜将出现较大的晶格畸变，且过量的V将产生电荷缺陷，因此过量的V掺杂又将降低薄膜的铁电性能。
　　 在研究V掺杂提高BLT薄膜性能的基础上，为了降低晶化温度，采用紫外光辅助溶胶－凝胶法制备BLTV铁电薄膜。紫外光辐照促进了凝胶薄膜中相关C、H、O有机成分的分解，有利于薄膜在后期退火处理过程中的晶化。经紫外光辐照的BLTV薄膜样品在650℃退火处理后表现出良好的铁电性能（2PR为38.7 μC/CM2，2EC为202.4 KV/CM）。
　　 以形核理论为基础，研究了随着晶化温度的升高，晶粒尺寸增加，同时形核势垒增加，形核主要由界面形核决定，并从实验中观测到800℃晶化得到的BLT薄膜表现出与界面形核相对应的C轴取向的柱状晶粒。结合扩散限制簇团聚模型和反应限制聚集模型模拟了随着粒子数量增加对薄膜生长过程的影响。粒子数量较少时，粒子聚集具有一定取向；随着粒子数量的增加，粒子聚集分布逐渐均匀。同时，通过设计相关实验得到了模型的验证，粒子数量较少的薄膜的晶粒分布有一定的取向，且晶粒尺寸较大，反映了粒子的集中聚集、长大；随着粒子数量的增加，晶粒尺寸逐渐减少并逐渐分布均匀。 Ferroelectric nonvolatile memories have attracted much attention since last decades due to their potential advantages of high speed,low power consumption,nonvolatility and anti-radialization.Bi/_/(3.25/)La/_/(0.75/)Ti/_3O/_/(12/)/(BLT/) thin film is one of the most promising materials for application in ferroelectric memories.In this thesis,properties and growth of BLT thin films were studied. The BLT thin films were deposited on Pt//TiO/_2//SiO/_2//p-Si/(100/)substrates by Sol-Gel method and the effect of annealing paraments on their properties were investigated.The microstructure and ferroelectric properties are influenced greatly by annealing temperature. The co-effect of annealing temperature and ambient results in optimal ferroelectric properties of BLT thin films in 20/%O/_2 in mixed gas of oxygen and nitrogen at 750℃.The structure,crystallization degree and morphology are also influenced by annealing pressure. The thin films annealed under oxygen pressure of 0.1 atm are a-axis preferred oriented and acquire excellent ferroelectric properties. Bi/_4Ti/_3O/_/(12/)/(BIT/),BLT,Bi/_/(3.99/)Ti/_/(2.97/)V/_/(0.03/)O/_/(12/)/(BTV/) and Bi/_/(3.24/)La/_/(0.75/)Ti/_/(2.97/)V/_/(0.03/)O/_/(12/)/(BLTV/) were prepared for the study of the effect of the B-site V substitution on the BLT thin films. The BLTV thin film shows randomly oriented with fine rod-like grains.Raman spectra show the A-site La substitution exerts influence on Ti ions in B sites of the BIT thin film, TiO/_6/(or VO/_6/) symmetry decreases and Ti-O/(or V-O/) hybridization increases for V substitution.On the other hand,the oxygen vacancies are suppressed by the higher-valentcation substitution due to the charge neutrality restriction.Compared with the BLT thin films,the ferroelectric,fatigue and leakage current properties of the BLTV thin films with V substitutition are improved greatly. To acquire the optimal concentration of V substitutition,Bi/_/(3.25-x//3/)La/_/(0.75/)Ti/_/(3-x/)V/_xO/_/(12/) were prepared with different concentration of V substitutition/(x:0～8/%/).The remanent polarization and fatigue properties first increase then decrease with increasing of dopant concentration.When x=3/%,the thin film exhibits excellent ferroelectric property/(P/_r:25.4μc//cm~2/) and the strongest fatigue endurance up to 10~/(10/) cycles.When x increases to 8/%, the properties decrease due to slightly large distortion of crystal lattice and charge defects caused by excessive V substitution. To lower crystallization temperature,the BLTV thin films were deposited by UV-assisted Sol-Gel method.The UV irradiation during pyrolysis promotes the decomposition of C,H,O organic species,which results in good crystallization for the films in the following annealing process.The UV-irradiated BLTV thin films show good ferroelectric property/(2P/_r:38.7μc//cm~2,2E/_c:202.4 kV//cm/) after annealing at 650℃. Based on the theory of nucleation,both grain size and the barrier height increase with crystallization temperature increasing.The BLT thin films annealed at 800℃display c-axis-oriented columnar grains where the interface nucleation dominates microstructure. The effect of the number of particles on the growth of thin films was simulated by Diffusion Limited Cluster Aggregation/(DLCA/) and Reaction Limited Aggregation/(RLA/) models.Thin films exhibit oriented distribution when the number of particles is small, while uniform distribution when the number increasing.And the simulation is consistent with the experimental results.When the number of particles is small,the grains distribute orientedly and their size is large,which reflects the concentrated growth of particles. When the number of particles is increasing,the grains distribute uniformly and their size decreases.

关 键 词： 铁电存储器 薄膜生长 非易失性存储器 钛酸铋 晶化度

分 类 号： [TM223 TB383]

领　　域： [电气工程] [一般工业技术] [一般工业技术]