铌酸钾钠无铅压电薄膜的生长、界面调控及电性能研究

(K0.5Na0.5)NbO3 ( abbreviated as KNN) is a promising candidate for lead-free piezoelectric material owing to its high curie temperature and excellent piezoelectric properties. However, the most studies are focused on the bulk KNN. Driven by the miniaturization and integration, especially the development of MEMS, great effects have been made to fabricate high-quality KNN or KNN-based thin ?lms using different growth techniques. Many problems such as how to ensure the stoichiometric composition, improve the piezoelectricity, decrease the leakage current, improve the fatigue behavior et al. need to be resolved before its practical application. In this study, preferably oriented KNN films will be fabricated by RF magnetron sputtering. The chemical composition of KNN films will be controlled by the design of non-stoichiometric (K0.5Na0.5)NbO3 ceramic target and varying the parameter of sputtering. In order to fabricate highly oriented KNN films, the interface between substrates and ferroelectric films will be improved by introducing oxide LNO and SRO as a buffer layer, and the growth mechanism of KNN films will be revealed. The influence of composition, orientation, and buffer layers on the ferroelectricity, piezoelectricity, leakage and fatigue properties will be studied. Highly oriented, improved ferro- and piezo-properties of KNN films will be fabricated in this study, which will provide the basic of practical application of KNN films in developing lead-free piezoelectric thin film devices.

K0.5Na0.5NbO3(KNN)体系具有压电系数高、居里温度高等优点，是当前无铅压电材料的研究热点。目前，对KNN基材料的研究主要集中在块体材料上，但随着MEMS技术的快速发展，对无铅压电薄膜材料提出了迫切的需求。调控化学计量比、提高压电性能以及降低漏电流是KNN薄膜研究中的关键科学问题。本项目拟采用磁控溅射法，制备择优取向生长的KNN薄膜，通过巧妙设计非化学计量比的陶瓷靶材和优化溅射工艺，实现KNN薄膜的组分控制；引入氧化物电极LaNiO3、SrRuO3作为缓冲层，调控衬底与薄膜的界面特性，实现KNN薄膜的取向生长，揭示界面诱导KNN薄膜取向生长的机制；研究组分、取向、缓冲层等对KNN薄膜铁电、压电、漏电流及疲劳等性能的影响；制备高取向、铁电压电性能良好的KNN薄膜，为发展无铅压电薄膜器件用KNN薄膜材料提供材料基础和知识积累。

本项目以(K,Na)NbO3(KNN)无铅压电薄膜材料为主要研究对象，采用射频磁控溅射法作为薄膜材料的制备手段，探索了KNN薄膜的组分控制和性能调控这一关键科学问题，为发展无铅压电薄膜器件用KNN薄膜材料提供材料基础和知识积累。为补偿靶材制备以及薄膜溅射过程中K和Na的挥发，设计了K和Na过量的非化学计量比靶材。通过克服吸潮问题，在1000℃的低温下成功制备了溅射用K和Na过量的KNN陶瓷靶材。采用射频溅射的方式制备KNN无铅压电薄膜，研究了靶材组分和薄膜组分之间的关系。制备了KNN/LNO异质结构，研究了LNO底电极对KNN薄膜结构和电学性能的影响。LNO为底电极时，KNN薄膜具有 (001)择优取向，其表面为规则方形晶粒，断面显示为柱状生长。LNO底电极提高了KNN薄膜的介电常数和可调谐性能，在300kV/cm的电场下，其可调性为66%，损耗为0.03。KNN/LNO/Si薄膜表现出良好的铁电性和抗疲劳特性，经109次电循环而没有出现疲劳现象。在250kV/cm的外加电场下，Pt/KNN/LNO/Si的漏电流密度仅为1.66×10-4A/cm-2。制备了具有不同上电极的LNO/KNN/LNO/Si和Pt/KNN/LNO/Si电容器结构，比较了两者电学性能(介电性、铁电性、压电性)的差异。研究发现，LNO为上电极时，电容器表现出优异介电性的压电性，压电系数由26 pm/V提高至58 pm/V。其压电性的提高可能与介电性和铁电性的提高有关。另外，我们首次研究了两种电容器结构的变温压电性。随着温度的升高，LNO/KNN/LNO/Si的压电性逐渐降低，并在300~400℃的温度范围内与Pt/KNN/LNO/Si相当。而在整个温度区间，Pt/KNN/LNO/Si的压电性基本保持不变。 采用改进的磁控溅射法制备了KNN/SRO/STO薄膜，并对其结构和电学性能进行了研究。结果表明，KNN/SRO/STO薄膜具有 (001)择优取向，其表面为规则方形晶粒，平均晶粒尺寸为150nm。Pt/KNN/SRO/STO具有稳定的介电常数的频率依赖性，以及高达69.7%(@400 kV/cm)的可调谐性能。Pt/KNN/SRO/STO表现出良好的抗疲劳特性，经1010次电循环而没有出现疲劳现象。压电回线显示其压电系数为为36pm/V。