钛酸铜钙薄膜的介电弛豫和介电反常微观机制研究

CaCu3Ti4O12 (CCTO) has huge dielectric constant (~10,000), which has attracted much attention in the fields of high density memory and film devices. However, its application and development were forbidden because the origin of its huge dielectric constant was still controversial. The project puts forward the viewpoint of oxygen vacancy defects and deep level traps to observe the dielectric relaxation and dielectric anomaly of CCTO films which are suitable for minimization and integration. CCTO films of tunable oxygen vacancy concentration and cubic phase would be fabricated by radio frequency magnetron sputtering and annealed in various atmospheres. The contributions of different oxygen vacancies to the dielectric property were differentiated by dielectric spectra and complex impedance spectra in broad frequency and temperature ranges. The microcosmic information of oxygen vacancy deep level traps was measured by electron paramagnetic resonance (EPR) and deep level transient spectroscopy (DLTS). On the other hand, based on density functional theory (DFT), the energy levels of oxygen vacancy defects and deep level traps were calculated and the interface band mode was presented. In the end, the dielectric relaxation and dielectric anomaly induced by the capture and release of carriers under external electric field would be properly explained. This project is significant not only to studying on new electric behaviors of CCTO, but also to improving and perfecting the huge dielectric theory.

钛酸铜钙（CaCu3Ti4O12，简称CCTO）材料一般具有很高的介电常数（~10,000），在高密度信息存储和薄膜器件等领域受到广泛关注，但目前由于巨介电性能的起因尚未定论而制约了它的应用和发展。本项目提出氧空位缺陷和深能级陷阱态的观点，研究适合小型化和集成化要求的CCTO薄膜的介电弛豫和介电反常特性。用射频磁控溅射通过不同气氛退火处理来制备立方相结构、氧空位浓度可调节的CCTO薄膜。用宽频域和宽温区的介电谱和阻抗谱来划分不同氧空位缺陷的贡献区域。用顺磁共振和深能级瞬态谱来确定氧空位深能级陷阱态的微观信息。并基于密度泛函理论，采用第一性原理计算氧空位缺陷和深能级陷阱态能级，给出CCTO薄膜的界面能带模型。从而合理解释外电场刺激下不同形态氧空位对载流子捕获和释放导致的介电弛豫和介电反常行为。该项目不仅对CCTO新颖电学行为的研究有指导意义，而且对巨介电理论的完善有推动作用。

钛酸铜钙（CaCu3Ti4O12，CCTO）由于具有异常高的介电常数和非线性系数而受到广泛关注。该类材料介电常数有较好的温度和频率稳定性，使得其在微电子和大容量存储等领域有很好的应用前景。而到目前为止，CCTO巨介电常数产生的机制尚未明确，这限制了其性能的优化和进一步应用。本项目基于前期在CCTO陶瓷研究中提出的氧空位缺陷和深能级陷阱态机制，研究更有利于小型化和集成化应用领域的CCTO薄膜的巨介电特性。. 项目主要用射频磁控溅射，在单晶Si基片上通过调节工艺参数来制备纯立方相类钙钛矿结构的CCTO薄膜，通过宽频域和宽温区的测试手段，结合相关结构表征以及第一性原理理论计算来开展其介电弛豫和反常特性与微观缺陷间关联机制的研究。研究结果表明，在单晶Pt/Ti/SiO2/Si衬底上制备了厚度为600 nm左右的纯立方相类钙钛矿CCTO薄膜，且其中氧空位可以通过预制备后的退火工艺来调节；氧空位对CCTO薄膜介电性能有重要贡献，且受到退火工艺影响；第一性原理计算表明氧空位或Cu间隙原子对CCTO的能带结构有重要影响，从而影响其介电性能。本研究的实验结果和理论分析相互印证，说明氧空位对其介电特性的重要贡献，这不仅对CCTO巨介电理论的完善有重要意义，而且为其实际应用奠定了一定理论基础。. 与此同时，我们也开展了其他两部分与项目相关的重要工作：一是共溅射制备Nb掺杂CCTO薄膜；二是高温高压极端条件制备CCTO陶瓷及其结构与性能研究。前者表明，合理控制溅射工艺参数可以制备纯立方相的掺杂CCTO薄膜，Nb掺杂对其介电性能有明显影响；后者表明，极端制备条件可以调控CCTO显微结构和微区成份，特别是对晶粒大小和晶界区域的有效调节，从而改变其介电弛豫特性。这部分研究可以更好地佐证CCTO材料介电弛豫特性取决于其外禀机制，如缺陷或非均质结构区域。从而可以通过实验手段调节此类区域而有效优化其介电性能。