存储器用外延铁电薄膜的挠曲电效应研究

Ferroelectric random access memories (FeRAMs) is currently regarded as candidates of the most potential next generation memories with clear advantages such as non-volatility, low power consumption, high endurance, high speed writing, high density, irradiation hardening and compatible with integrated circuit (IC) process. Ferroelectric thin films have attracted a great deal of attention for the potential applications in FeRAM. To obtain high properties and thin epitaxial films is very important to satisfy the micromation and integration development of FeRAM. The flexoelectric effect can't be neglected in epitaxial films since strain gradient can affect the properties of the thin films to a great extent. Based on the above consideration, this item will focus on the flexoelectricity effect in epitaxial ferroelectric films though experimental investigation and theoretical simulation. Experimentally, the strain gradient in epitaxial thin films will be characterized and analyzed , the evolvement behavior of ferroelectric domain in different strain gradient will be observed and the electrical properties of epitaxial thin films will be investigated. Theoretically, the electromechanical coupling equation including flexoelectricity effect will be established and the domain switching will be simulated by phase field method. Subsequently, it is expected that the intrinsic mechanism of flexoelectricity effect is revealed and the strain gradient is understood and controlled to optimize experimental parameters by the combination of experimental results with theoretical simulation. It is desirable to obtain the high properties of ferroelectric film in favor of the performance of ferroelectric thin film and memory.

铁电薄膜存储器具有节能、非挥发、高速、高密度、低功耗、抗辐射和与CMOS工艺兼容等优点，被公认为下一代最具潜力的存储器之一。铁电薄膜因其在铁电随机存储器方面的潜在应用而受到广泛关注。铁电薄膜存储器微型化、集成化发展趋势迫切需要制备性能优异、厚度很薄的外延铁电薄膜。而外延铁电薄膜中的应变梯度将在很大程度上影响薄膜的性能，故挠曲电效应在外延铁电薄膜中不容忽视。基于此，本项目以存储器用SBT外延铁电薄膜为研究对象，从实验和理论两个方面对外延铁电薄膜中的挠曲电效应进行研究。通过外延薄膜中应变分布的表征分析，观察铁电畴在不同应变梯度下的演化行为，表征外延铁电薄膜的电学性能，结合理论相场模拟电畴的演化行为，建立挠曲电效应的铁电薄膜力-电耦合关系，分析挠曲电效应的物理机制，得到应变梯度对铁电薄膜电学性能的调控规律，进一步优化实验参数，为优化铁电薄膜及存储器的性能提供理论和技术指导。

铁电薄膜存储器具有节能、非挥发、高速、高密度、低功耗、抗辐射和与CMOS工艺兼容等优点，被公认为下一代最具潜力的存储器之一。铁电薄膜因其在铁电随机存储器方面的潜在应用而受到广泛关注。由于薄膜的膜、衬底结构及制备过程等因素的影响,使得应力不可避免地普遍存在与薄膜中。薄膜中的应力对薄膜的居里点、畴结构以及介电、铁电、漏电流和开关效应都会有很大的影响。本项目主要研究了以下内容：.（1）.为准备实验靶材，研究了一系列陶瓷的微观结构和电学性能，包括介电、铁电和阻抗等性能，并做了一些对比实验，发现氧空位的跃迁与弛豫现象有关，而导电性与二价的氧空位长程运动有关 。.（2）.研究不同的实验参数对薄膜电性能的影响，通过掺杂、选择不同的缓冲层和电极材料以及厚度的改变等方法，调节铁电薄膜的应变状态，测试分析不同应变状态下的电性能，发现这些因素对薄膜的电性能产生很大的影响，当加入不同的缓冲层时 ，漏电流可以减少几个数量级，BNM/LNO的漏电流密度低于BNM/LNM薄膜的4个数量级。研究薄膜应变对漏电流影响的内在机理，为降低铁电薄膜的漏电流提供理论和技术指导。根据电滞回线图，计算了PbZrO3薄膜的储能特性，储能密度高达25.25J/cm3，储能效率62%。对PbZrO3薄膜的储能效率之高，表明PZ薄膜在储能方面具有广阔的应用前景。.（3）.采用相场模拟方法研究了PbTiO3在平面基底和倾角为2°、4°、6°Si（100） miscut基底上的电学性能，为优化实验提供理论指导。