石墨烯增强的新型聚合物柔性阻变存储器的性能调控与存储机理研究

Flexible nonvolatile resistive random access memories (ReRAM) with high density, huge capacity, low-power consumption, fast switching attract great interest with the development of the flexible and wearable electronic devices. In this proposal, single graphene sheets will be obtained by exfoliating high oriented graphites in supercritical CO2 (scCO2) due to its strong penetrating and good solvating ability. The excellent mechanical, thermal, and electrical properties and multi-functionalities of graphene will be incorporated into the property of polymers by covalently grafted reaction with the -OH, -COOH, and -CO radical groups on the basal plane and edges of graphene and the in-situ polymerization reaction of the monomers between two intercalated graphene sheets. The ReRAM devices will be manufactured with the high quality and multifunctional grapheme-polymer nanocomposites as the active resistive materials sandwiched between top and bottom electrodes. The new devices will be expected to exhibit the resistive switching and rectifying characteristics. The influence of the temperature, pressure, processing time of scCO2 on structures and properties of the graphene and grapheme-polymers will be investigated. The dynamics, thermodynamics, and exfoliating mechanism will be discussed during the exfoliation of graphites in scCO2. The relationship of the configuration and the attached radicals of polymers with the structures and switching performances of the composites will be interpreted. The effects of the resistive films, electrodes, substrates, and annealing on the device performance and thermal stability will be studied. The mechanism of nonvolatile resistive switching in graphene-polymer films will be deduced based on theoretical model and experimental data. These achievements of the proposal will be useful in modulating the structure and functionality of graphene-polymer composites and the performance of resistive switching memory devices and will promote the advancements of the full carbon-based electronic and photoelectronic devices. It is of great both scientific significance and profound perspectives in electronic and information technological applications.

本项目拟利用超临界CO2（scCO2）的强渗透能力和高溶剂化能力剥离石墨制备高分散的石墨烯。通过与单体或聚合物以共价接枝或原位聚合反应，以石墨烯调控石墨烯/聚合物复合材料的结构和性能，得到稳定性好、多功能的纳米复合材料，以此组装不同架构的柔性阻变存储器(ReRAM)，使其兼具存储特性和整流效应。研究scCO2体系温度、压力、时间等对石墨烯及其复合材料的结构、性能的影响，探讨scCO2中石墨剥离的热力学和动力学过程及其机制；阐明聚合物分子空间结构和活性基团与复合材料结构和存储性能的关系；揭示阻变材料、电极、衬底、后处理对ReRAM性能、热稳定性的影响规律，以理论与实验相结合探讨存储机理，实现材料结构和功能可控、低成本、高性能的新型柔性ReRAM的构建，为将来全碳基材料电子、光电子器件的研究和应用提供理论和实践基础，具有重要的科学意义和广阔的应用前景。

传统硅基非易失性随机读取存储器的发展越来越受到制备工艺、物理尺寸极限等限制，而具有电双稳特性的新型阻变存储器(ReRAM)由于具有存储密度高、功耗低、读写速度快、耐受力强、非破坏性读取、更重要的是可缩小性好（非电荷存储机制）等优点成为最有希望的下一代易失性存储器。本项目首先利用超临界CO2（scCO2）的强渗透能力和高溶剂化能力研究了石墨或氧化石墨在scCO2中的剥离行为，得到高分散的石墨烯或氧化石墨烯(GO)。研究了不同石墨原料、辅助插层剂、温度、压强、时间等因素对石墨烯产率的影响，结合实验数据对石墨烯的剥离机理进行了理论分析。研究结果表明，在磁搅拌下二甲基甲酰胺(DMF)作为辅助插层剂，20 MPa，80 °C，24 h条件下石墨烯的产率最高。然后以剥离出的GO为活性层构建Al/GO/ITO阻变存储器(ReRAM)，研究了GO ReRAM的阻变特性和阻变机理，结果表明，Al/GO/ITO ReRAM器件在150 °C退火后展现了极好的双极阻变特性，置位电压1.3 V，复位电压-2 V，开关比约10^3。耐久性测试表明器件的开关比在100次循环后仍保持不变，10^4 s以上的数据保存能力。阻变机理分析表明器件的J-V特性符合SCLC关系，由电偏压下氧官能团的迁移所引起的表面势垒的变化引起。.本项目还对POMA阻变存储器进行了初步研究，当POMA在DMF中的浓度为1wt%、旋涂两次能够得到均匀的薄膜，以Al为上电极构建的Al/POMA/ITO ReRAM也表现出较好的双极阻变特性，置位电压为7 V，复位电压为-4V，开关比为10^3，详细研究还在进行中。建议进一步开展GO与POMA及其它共聚物复合技术的研究，包括共价接枝和原位聚合反应等，并研究该复合材料的阻变特性和阻变机理。该项目的研究成果可为将来全碳基材料电子、光电子器件的研究和应用提供理论和实践基础，具有重要的科学意义和广阔的应用前景。