BiFeO3外延薄膜受铁电极化调控阻变效应的研究

Due to the advantages of high-density, fast write and read access, low energy operation, ferroelectric resistive random access memory (FeRRAM) has been regarded as one of the potential candidates for the next generation nonvolatile random access memory. However, FeRRAM are facing low On/Off ratio and the difficulty of characterizing ferroelectric polarization during resistance switching. To solve the problems, this project will focus on the design and fabrication of electrode/BiFeO3(BFO)/electrode devices which exhibit resistance switch dominated by ferroelectric polarization. Both defect-related and polarization-controlled resistance switch are expected to be observed in electrode/ BiFeO3(BFO)/electrode devices. To explore the key factors for preparing the devices, which exhibit intrinsic ferroelectric resistance switch, the effect of the electrode (work function and electro negativity etc.), the preparation of BFO thin film (phase and component etc.) and the electric characteristics of BFO thin film (resistivity etc.) on the resistance switch will be investigated. To understand the physical mechanism of ferroelectric resistance switch, piezoelectric and pyroelectric etc. properties of BFO thin film are investigated. This research will shed some new light on the development of high-performance FeRRAM.

由于铁电阻变存储器（FeRRAM）兼备铁电存储器（FeRAM）读写速度快、阻变存储器（RRAM）小电压非破坏性读取等优点，FeRRAM的开发具有重要的物理意义和实际应用价值。本项目以基于BiFeO3（BFO）薄膜的铁电阻变存储器为研究对象，针对铁电阻变存储器开关比不高、阻变效应中铁电极化表征难度大等问题，拟制备铁电极化调控阻变效应的原型器件。通过研究电极材料的功函数、电负性，BFO薄膜的晶相、组分、电阻率等，分析缺陷和极化调控的阻变效应的共存性，探索制备具有铁电阻变效应FeRRAM的关键条件。结合测试铁电极化相关性能（如压电性、热释电性和铁电畴反转特性等）解决阻变效应中铁电极化表征困难的问题。深入理解极化反转对铁电阻变效应的影响，阐释极化调控铁电阻变的物理机制，为开发高稳定的FeRRAM提供理论和实验依据。

阻变存储器(RRAM)由于具有结构简单、擦写速度快和半导体工艺兼容性好等优点，具有广泛的应用价值。然而大多数RRAM都是基于缺陷机制调制的阻变效应，这导致RRAM器件的均匀性和可靠性差，从而成为阻碍RRAM器件大规模应用的主要原因之一。因此，探索基于非缺陷调制机制的新型RRAM器件具有重要的科学意义和应用价值。.本项目以基于BiFeO3(BFO)的铁电阻变存储器(FeRRAM)为研究对象。FeRRAM的阻变效应已被证明受控于非缺陷调控的铁电极化反转，结合BFO的高铁电极化特性，所以这一类FeRRAM被认为将具有更好的稳定性，更大的开关比。然而，当BFO层及BFO/电极界面区域存在较多的缺陷时，器件中极有可能共存铁电极化和缺陷调控的两种阻变效应，因此减少器件结构中缺陷的引入成为关键问题，这也一直是材料科学和半导体工艺中难点。.在本项目的研究中，我们通过高质量外延复合薄膜的制备从而达到减少器件中缺陷的目的。利用脉冲激光沉积法(PLD)，通过系统研究SRO及BFO薄膜的生长特性，确定了影响SrRuO3(SRO)/BFO薄膜的外延性、结晶度、电学特性和铁电特性的关键参数，绘制了原子级平整的BFO薄膜的生长相图。实验发现，高氧压(大于10Pa)是制备具有优异金属特性的SRO薄膜的重要工艺参数。高质量外延的BFO薄膜的生长窗口则非常小，避免杂相的出现和薄膜的3D生长是制备原子级BFO薄膜的关键因素。通过全外延SRO/BFO复合薄膜的生长，减少了器件结构中缺陷的引入，从而成功制备出铁电极化调制的FeRRAM器件，其开关比达到10000。此外，针对阻变效应中铁电极化表征困难的问题，提出结合压电原子力显微镜和导电原子力显微镜，深入研究铁电极化反转与微区电阻状态的研究方法。这些结果为开发高稳定的FeRRAM提供了实验依据。