范智勇Sci. Adv.基于三维钙钛矿纳米线阵列超快阻变随机存储器
类神经形态计算、现代健康监测系统和大数据分析的高速发展给高性能的非易失性存储器带来了重大机遇。阻变随机存储器(Re-RAMs)具有多级数据存储能力，超快的写入/擦除速度，优秀的数据保持能力(>10年)，被认为是最具前景的非易失性存储器之一。目前用于制备Re-RAMs器件阻变层的材料主要为传统的金属氧化物，如NiOx, SiO2, Ta2O5, HfO2, CuOx，与此同时新型材料如二维材料，有机-无机杂化钙钛矿材料近年来也被广泛研究。其中有机-无机杂化钙钛矿材料除了具有优异光伏特性以外，其固有的迟滞效应和丰富的载流子传输通道使其在Re-RAMs领域具有广阔研究前景。同时，钙钛矿材料还具有制备工艺简单，柔性扩展性好，价格成本低等优势，也给嵌入存储器在可穿戴设备和大规模工业应用提供了机会。迄今为止报道的大多数钙钛矿阻变层都是基于薄膜形式。基于薄膜的Re-RAMs的一个典型缺点是对环境敏感的阻变介质缺乏保护。由于易遭受水分侵蚀快速降解，这个问题在有机-无机杂化钙钛矿Re-RAMs领域变得更加严重。此外基于薄膜的阻变介质在水平路径上存在更大的漏电和串扰风险，因此在单个芯片中有效提高Re-RAM单元集成度仍然存在极大困难。对此，采用氧化铝模包覆隔离的纳米线阵列作为阻变层能有效解决上述问题，在提高器件集成度的同时有效隔绝环境中的空气和水提高阻变层稳定性。
近日，香港科技大学范智勇教授课题组在Sci. Adv.上发表文章，题为“Three-dimensional perovskite nanowire array–based ultrafast resistive RAM with ultralong data retention”（第一作者张雨婷，Swapnadeep Poddar）。在此之前，该研究组多次报道了多孔氧化铝膜(PAM)对于大幅提高钙钛矿纳米线的稳定性有重要作用。在这项工作中，作者报道了基于高密度三维卤化物钙钛矿纳米线阵列的Re-RAMs。并且探索了三种卤化钙钛矿(MAPbX3;X = Cl, Br, I)材料作为阻变层对Re-RAMs器件性能的影响。重点研究了器件阻变速度和数据保持时间之间的平衡关系。其中，MAPbI3具有超快阻变速度(200 ps)，MAPbCl3器件具有超长保持时间(~7×109 s)。此外，结合第一性原理计算表明，当晶格尺寸从MAPbI3缩小到MAPbCl3时，Ag扩散能垒增加，从而影响器件从具备更快响应速度向更长保持时间转换。
(F) MAPbCl3多晶纳米线和单晶纳米线器件的低阻态保持时间比较。
文献链接：
Three-dimensional perovskite nanowire array–based ultrafast resistive RAM with ultralong data retention. Sci. Adv. 2021, doi: 10.1126/sciadv.abg3788.
范智勇教授为香港科技大学电子与计算机工程系正教授博导，香港科大智能传感器与环境技术中心主任，材料表征中心副主任，粤港澳智能微纳光电技术联合实验室副主任，科技部先进显示与光电子技术国家重点实验室核心成员。
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