Npj Comput. Mater.: 双势垒结构—增强铁电隧道结的隧穿电致电阻

海归学者发起的公益学术平台

分享信息，整合资源

交流学术，偶尔风月

针对该问题，南京林业大学郑小宏教授与山西大学张磊教授研究团队，基于已有的量子输运理论提出，可以在铁电隧道结中引入双势垒结构来极大增强隧穿电致电阻效应，并且通过第一性原理计算验证了该想法。他们设计了Pt/BaTiO₃/LaAlO₃/Pt/BaTiO₃/LaAlO₃/ Pt双势垒铁电隧道结（图1a），并利用密度泛函计算对其输运性质展开了研究。结果发现，铁电左极化态和右极化态之间的反转可以在该铁电隧道结中实现2.210×10⁸%的巨大TER比率（这表明两种极化态之间透射系数存在巨大差异，如图1b），这一数值比Pt/BaTiO₃/LaAlO₃/Pt单势垒铁电隧道结的TER比率至少大3个数量级。其基本思想在于，微观尺度下，电子通过串联的两个势垒的透射函数与两个单一势垒的透射函数的乘积密切相关，以及一个大于1的数平方以后和原数相比呈指数增长。这一思想在双势垒铁电隧道结中得到了很好的体现。文中还提出了通过外加电压单独控制每一个势垒的极化方向，可以在双势垒铁电隧道结中实现极化头对头和尾对尾的两个额外的铁电极化态，从而得到多个电阻态（图2）。该研究表明在铁电隧道结设计中，可以利用双势垒结构显著增强其隧穿电致电阻特性并拓展其功能实现多态存储。

Greatly enhanced tunneling electroresistance in ferroelectric tunnel junctions with a double barrier design 

Wei Xiao, Xiaohong Zheng*, Hua Hao, Lili Kang, Lei Zhang* & Zhi Zeng

We propose that the double barrier effect is expected to enhance the tunneling electroresistance (TER) in the ferroelectric tunnel junctions (FTJs). To demonstrate the feasibility of this mechanism, we design a model structure of Pt/BaTiO3/LaAlO3/Pt/BaTiO3/ LaAlO3/Pt double barrier ferroelectric tunnel junction (DB-FTJ), which can be considered as two identical Pt/BaTiO3/LaAlO3/Pt single barrier ferroelectric tunnel junctions (SB-FTJs) connected in series. Based on density functional calculation, we obtain the giant TER ratio of 2.210 × 108% in the DB-FTJ, which is at least three orders of magnitude larger than that of the SB-FTJs of Pt/BaTiO3/LaAlO3/Pt, together with an ultra-low resistance area product (0.093 KΩμm2) in the high conductance state of the DB-FTJ. Moreover, it is possible to control the direction of polarization of the two single ferroelectric barriers separately and thus four resistance states can be achieved, making DB-FTJs promising as multi-state memory devices.