共振隧穿铁电隧道结巨TER效应与存储特性研究

Ferroelectric tunnel junctions have a broad applied prospect in the area of memory due to the tunneling electroresistance (TER) effect. However, the applications of ferroelectric tunnel junctions are limited because the current TER effect can be hardly enhanced to a large extent. In this proposal, the concept of resonant-tunneling ferroelectric tunnel junctions (RTFTJs) is proposed, in which the giant TER effect will be achieved by adjusting the resonant tunneling effect to enlarge the difference between the high and low resistance states. We will study the effect of the fabrication process on the microstructure, phase structure,surface and interface structure of the ferroelectric tunnel junctions, and the optimal fabrication process and geometry structure parameters will be expected in the RTFTJs with giant TER effect. A physical model associated with resonant tunneling effect will be built to reveal the influence of the geometry structure parameters and electric feature parameters of the RTFTJs on resonant tunneling. We will investigate the electron transport of the RTFTJs under high-low temperature environment, establish the model of electron transport, and set up the relationship among the feature parameters, resonant tunneling effect and TER effect, then demonstrate the physical mechanism of the giant TER effect. The storage features of the RTFTJs will be studied and the method of controlling the storage feature will be explored. The research results of this proposal will afford a deep insight into the band engineering, interface control technique and mechanisms of electron transport, and will be of great scientific importance and practical guiding value to develop new types of storage devices and put them into practice.

铁电隧道结由于具有TER效应而在存储器领域有着广阔的应用前景，但目前TER效应提升的潜力十分有限，限制了铁电隧道结的实际应用。本项目提出共振隧穿铁电隧道结(RTFTJs)的概念，通过调控共振隧穿效应扩大高、低阻态差别从而获得巨TER效应。研究铁电隧道结的制备工艺对微结构、表面与界面结构及相结构的影响，探求具有巨TER效应的共振隧穿铁电隧道结优化制备工艺与几何结构参数；建立共振隧穿效应模型，揭示几何结构特征参数和电学特征参数对共振隧穿效应的影响规律；研究共振隧穿铁电隧道结高、低温电输运特性，建立电子输运的物理模型，揭示共振隧穿铁电隧道结特征参数、共振隧穿效应和TER效应之间的关联，阐明巨TER效应的物理机制；研究共振隧穿铁电隧道结的存储特性，探索存储功能的调控方法。本项目的研究成果有助于深刻认识能带工程、界面调控技术及电子输运机制，对推动新型存储器的开发应用具有重要的科学意义和实践指导价值。

1. 共振隧穿铁电隧道结的隧穿电阻效应研究。.（1）制备了Pt/BaTiO3(5 nm)/SrRuO3/BaTiO3(5 nm)/Nb: SrTiO3量子阱结构铁电隧道结，观察到了共振隧穿现象。.（2）研究了阱宽和极化电压对共振隧穿效应及隧穿电阻效应的调制作用。随阱宽增加，共振峰位向低压方向偏移。在极化电压较小时，共振峰随极化电压的增加向高电压方向移动。.（3）获得了TER值达到23000的巨隧穿电阻效应。.2. 铁电隧道结隧穿电阻效用研究。.(1) 制备了单势垒层及复合势垒层铁电隧道结。.(2) Pt/Pb0.2Zr0.8TiO3 (5 nm)/SrRuO3铁电隧道结的TER≈450%。.(3) Pt/Pb0.2Zr0.8TiO3/Nb:SrTiO3铁电隧道结的隧穿电阻值随铁电厚度的增加而增大，随环境温度的升高而降低。.(4) Pt/MgO(2 nm)/Pb0.2Zr0.8TiO3 (5 nm)/SrRuO3复合铁电隧道结的TER值为~2000%。交换MgO与Pb0.2Zr0.8TiO3 的位置后TER值为~2600%。.3. 铁电隧道结I-V特性及复合铁电隧道结优化结构的理论研究。.(1) SrRuO3/BaTiO3/Pt铁电隧道结在BaTiO3厚度为2.4 和4.8 nm 时TER分别为7和80。.(2) Pt/BaTiO3/SrTiO3/SrRuO3/SrTiO3在交换BaTiO3与SrTiO3沉积次序后TER值增大，这可以用提高的非对称因子来解释。.(3) 研究了SrRuO3/SrTiO3 (2 nm)/BaTiO3 (1.6 nm)/SrRuO3 与SrRuO3/SrTiO3 (2 nm)/BaTiO3 (1.6 nm)/Pt铁电隧道结的隧穿电阻效应。前者具有较高的TER值, 也可以用前者具有较高的非对称因子来解释。.4. 铁电隧道结忆阻行为研究。.(1) 观察到了Pt/BaTiO3/Nb:SrTiO3铁电隧道结中的忆阻行为。.(2) 发现Pt/BaTiO3/Nb:SrTiO3铁电隧道结中的电子输运机制与写电压有关。ON态时直接隧穿占主导；OFF态当写电压较小时直接隧穿占主导，写电压较大时肖特基热发射占主导。.(3) Pt/BaTiO3/Nb:SrTiO3铁电隧道结的忆阻行为与输运机制可以用极化调制的铁电/半导体界面肖特基势垒的高度/宽度变化来解释。