基于Cu_xSi_yO阻变材料的RRAM抗总剂量辐照性能

研究了基于CuxSiyO结构的阻变式随机存储器(RRAM)的抗总剂量辐照能力.存储器芯片置于钴源辐照室内,通过60 Co释放出的γ射线模拟空间辐照环境.在辐照总剂量达到3 000Gy的条件下,单元仍然可以保持原有的存储信息,高低阻态的阻值、写电压、良率等性能几乎没有任何衰减.良好的辐照特性使得RRAM有望在抗辐射领域中得到广泛应用.     

具有低功耗和多值存储性能的双层WO_X/AlON阻变存储器的研究

针对当前阻变存储器(RRAM)面临的功耗和高密度存储的问题,介绍了一种降低功耗和形成多值存储能力的器件结构.相比单层结构的AlON RRAM,双层结构的WOX/AlON RRAM具有低至10μA的复位(reset)电流,1 000次以上的转换特性(endurance),较低的操作电压,以及多值存储等性能.针对WOX/AlONRRAM,提出了WOX介质层的等效电路模型为固定电阻与二极管串联模型.在直流置位(DC set)过程中,电路中存在一个较大的过冲电流,使得无法通过控制限流来获得不同大小的低阻态.在增加WOX介质层后,在WOX层和AlON层间形成了界面肖特基势垒,因此有效地抵抗了过冲电流,提高了低阻态的可控性.     

新一代存储技术:阻变存储器

阻变存储器具有存储单元结构简单、工作速度快、功耗低、有利于提高集成密度等诸多优点,受到广泛的关注。作者论述了 RRAM 的基本结构和工作原理, 并介绍了三维集成和多值存储等 RRAM 新型技术。     

氧化钽基RRAM的循环耐受特性优化研究

阻变存储器(RRAM)因其性能优异、可高密度集成以及与CMOS工艺兼容成本较低等众多优点而被广泛研究.用于制备阻变型存储器的关键材料有很多种,其中氧化钽材料由于与标准CMOS工艺兼容而被各大研究机构广泛关注,但TaOx基RRAM存储阵列的可靠性仍存在很大问题,尤其是循环耐受特性.本文制备了4种具有优秀阻变性能的双层Ta2O5/TaOxRRAM器件,Ta2O5层厚度分别为5nm和3nm,TaOx层的x值分别为1.0和0.7.比较了这4种拥有不同器件参数的氧化钽基RRAM器件的循环耐受性能,给出了TaOx基RRAM的循环耐受性能优化方法,发现双层TaOxRRAM的富氧Ta2O5层的厚度越薄且缺氧TaOx层的缺氧程度越大,其循环耐受性能越好.     

基于带符号位的浮点数运算的多位宽3D RRAM设计

本文介绍了卷积神经网络（convolutional neutral network,CNN）系统中具有多位存储的三维阻变式存储器（three-dimensional resistive random-access memory,3D RRAM）的带符号位的浮点数运算. 与其他类型存储器相比,3D RRAM可以在存储器内部进行运算,且具有更高的读取速率和更低的能耗,为解决冯诺依曼架构的瓶颈问题提供新方案. 单个RRAM单元的最大和最小电阻分别达到10 GΩ和10 MΩ,可在多级电阻状态下稳定,以存储多比特位宽的数据. 测试结果表明,带符号位的浮点数的卷积运算系统的精度可以达到99.8%,测试中3D RRAM模型的峰值读取速度为0.529 MHz.      

阻变存储器研究进展

阻变存储器(Resistive Random Access Memory,RRAM)是最具应用前景的下一代非易失性存储器之一,与传统浮栅闪存相比在器件结构、速度、可微缩性、三维集成潜力等方面都具有明显的优势,本文对RRAM技术进行了综述.首先简单介绍了阻变存储器的工作原理、技术优势、发展历程和面临的基础科学问题.然后深入总结了RRAM的材料体系,包括固态电解质、多元金属氧化物、二元金属氧化物3类传统的阻变介质材料,总结了纳米线、二维材料等低维纳米材料在RRAM运用方面的近期研究进展,分析了绝缘/导电的低维材料分别用作阻变介质、平面电极层/纳米电极/侧边电极、界面插层所带来的微缩性、阻变性能和稳定性等的改善效果.总结和分析了细丝型电阻转变的3类物理机制:热化学机制(Thermochemical Mechanism,TCM)、电化学金属化(Electrochemical Metallization,ECM)机制、化合价变化机制(Valence Change Mechanism,VCM),详细分析了3种机制的SET/RESET转变原理和基本电学特性、透射电镜观测关键实验验证、对阻变机制的认识发展过程等.在阻变机制分析的基础上,接着阐述了RRAM电阻转变过程中由于纳米尺度下材料微观结构和能带结构的变化导致的一些新奇的物理现象,包括量子效应、磁电效应、光电效应等.最后针对RRAM实现应用的关键——集成技术,总结分析了存储阵列架构、二维/三维集成等关键问题及其研究进展.     

基于非易失性存储器的存储系统技术研究进展

 非易失性存储器（NVM）主要包括两类,即适用于外存的、块寻址的闪存和适用于内存的、字节寻址的持久性内存。相比于传统磁盘,闪存具有性能高、能耗低和体积小等优势;相比于DRAM（动态随机存储器）,持久性内存如PCM（相变存储器）、RRAM（阻变存储器）等,具有非易失、存储密度高以及同等面积/内存插槽下能给多核环境的CPU 提供更多的数据等优点,这些都为存储系统的高效构建带来了巨大的机遇。然而,传统存储系统的构建方式不适用于非易失性存储器,阻碍了其优势的发挥。为此,分析了基于非易失性存储器构建存储系统的挑战,从闪存、持久性内存两个层次分别综述了它们在存储体系结构、系统软件以及分布式协议方面的变革,总结了基于非易失性存储器构建存储系统的主要研究方向。     

单电子存储器存储时间的Monte Carlo模拟

建立了多隧道结单电子存储器存储时间的Monte Carlo模拟模型,重点分析了器件的工作温度、隧道结电容和隧道结数目等因素对单电子存储器存储时间的影响,给出了用Monte Carlo模拟方法模拟单电子存储器存储时间的模拟流程和方法。计算结果表明,当温度越低、隧道结电容越小、电路中隧道结的数目越多时,存储时间越长,器件工作越稳定。     

叠层薄膜基电荷陷阱存储器的存储性能研究

随着半导体器件特征尺寸的不断减小,传统的浮栅型存储器件逐渐接近其物理和技术的极限,多晶硅-氧化物-氮化物-氧化物-硅(SONOS)型电荷存储器件以其低电压、小尺寸及良好兼容性等特点成为近年来半导体行业研究的热点.但是,写入/擦除速度与数据保持性能之间的平衡问题一直制约着SONOS型存储器件的发展.为了解决这一问题,本文利用脉冲激光沉积系统制备了叠层薄膜基电荷陷阱存储器件,其中SiO_2作为隧穿层,叠层ZrO_2/Al_2O_3作为电荷存储层,Al_2O_3作为阻挡层,并对器件的电荷存储性能做了系统分析.利用透射电子显微镜(TEM)表征了器件的微观结构,采用4200半导体参数分析仪测试了器件的电学性能,包括存储窗口、写入/擦除速度及数据保持性能.研究结果表明,存储器件具有良好的电荷存储性能.当栅极扫描电压为±2V时,存储窗口仅为0.9V,随着电压增加到±6和±8V时,存储窗口分别达到3和4.4V;+8V,5×10~(-5) s的写入操作下,平带偏移量达到1V;室温,85和150℃测试温度下,经过1×10~5 s的数据保持时间,器件的存储窗口减小量分别为5%,10%和24%.优异的电学性能主要归功于ZrO_2和Al_2O_3之间的深能级界面陷阱及层间势垒.因此,采用ZrO_2/Al_2O_3叠层薄膜结构作为电荷存储层,具有良好的市场应用前景.     

过渡金属氧化物自旋和电荷相关信息存储

信息技术的快速发展在某种程度上要求有高速度和大容量的非易失存储器.然而,随着晶体管尺度达到其量子极限,传统硅半导体器件的继续集成化发展遇到了瓶颈.因此,人们提出了一系列有潜力成为下一代更具功能性的存储器原型器件,并引起了广泛而持续的研究热潮.本文介绍3种基于新材料和新结构的新型存储原型器件：阻变开关器件、有机自旋阀和多铁隧道结.我们发现通过改变界面态,可将阻变式开关器件的反应速度提高数个量级,达到5ns;在实验上确认了超精细相互作用对自旋阀效应的影响;利用多铁隧道结实现了室温下的四重阻态存储.基于自旋、电荷相关信息存储的原理和实验结果,我们对这3种过渡金属氧化物器件目前还存在的问题及未来的应用前景进行了分析和讨论.     

An overview of resistive random access memory devices

With recent progress in material science, resistive random access memory (RRAM) devices have attracted interest for nonvolatile, low-power, nondestructive readout, and high-density memories. Relevant performance parameters of RRAM devices include operating voltage, operation speed, resistance ratio, endurance, retention time, device yield, and multilevel storage. Numerous resistive-switching mechanisms, such as conductive filament, space-charge-limited conduction, trap charging and discharging, Schottky Emission, and Pool-Frenkel emission, have been proposed to explain the resistive switching of RRAM devices. In addition to a discussion of these mechanisms, the effects of electrode materials, doped oxide materials, and different configuration devices on the resistive-switching characteristics in nonvolatile memory applications, are reviewed. Finally, suggestions for future research, as well as the challenges awaiting RRAM devices, are given.     

An overview of the switching parameter variation of RRAM

Resistive random access memory（RRAM） has been considered as one of the most promising candidates for next-generation nonvolatile memory, due to its advantages of simple device structure, excellent scalability, fast operation speed and low power consumption. Deeply understanding the physical mechanism and effectively controlling the statistical variation of switching parameters are the basis of fostering RRAM into commercial application. In this paper, based on the deep understanding on the mechanism of the formation and rupture of conductive filament, we summarize the methods of analyzing and modeling the statistics of switching parameters such as SET/RESET voltage, current, speed or time. Then, we analyze the distributions of switching parameters and the influencing factors. Additionally, we also sum up the analytical model of resistive switching statistics composed of the cell-based percolation model and SET/RESET switching dynamics. The results of the model can successfully explain the experimental distributions of switching parameters of the Ni O- and Hf O2-based RRAM devices. The model also provides theoretical guide on how to improve the uniformity and reliability such as disturb immunity. Finally, some experimental approaches to improve the uniformity of switching parameters are discussed.     

An overview of resistive random access memory devices

With recent progress in material science, resistive random access memory (RRAM) devices have attracted interest for nonvolatile, low-power, nondestructive readout, and high-density memories. Relevant performance parameters of RRAM devices include operating voltage, operation speed, resistance ratio, endurance, retention time, device yield, and multilevel storage. Numerous resistive-switching mechanisms, such as conductive filament, space-charge-limited conduction, trap charging and discharging, Schottky Emission, and Pool-Frenkel emission, have been proposed to explain the resistive switching of RRAM devices. In addition to a discussion of these mechanisms, the effects of electrode materials, doped oxide materials, and different configuration devices on the resistive-switching characteristics in nonvolatile memory applications, are reviewed. Finally, suggestions for future research, as well as the challenges awaiting RRAM devices, are given.     

一种阻变存储单元Hspice模型设计

提出一种满足新型双通道阻变存储器读写操作要求的Hspice模型.这种模型基于新的机理,即通过改变一块1 Mb阻变存储阵列的一个单元中2种可重配置的稳定电阻存储模式实现＂RESET态＂和＂SET态＂之间的转换,它可以通过一个模拟电流-电压特性的分立器件模型来验证.与传统阻变存储器模型相比,利用这种模型,可以用较少的器件准...     

Enhanced resistive switching properties of HfAlOx/ZrO2- based RRAM devices

Resistive Random-Access Memory (RRAM) devices are recognized as potential candidates for next-generation memory devices, due to their smallest cell size, high write/erase speed, and endurance. Particularly, the resistive switching (RS) characteristics in oxide materials have offered new opportunities for developing CMOS-compatible high-density RRAM devices. In this study, the RS behavior of HfAlO_x/ZrO₂ thin films sandwiched structure between TiN bottom electrode and Au top electrodes were investigated. It was found that Au/HfAlO_x/ZrO₂/TiN stacks were superior in terms of RS performance when compare to Au/HfAlO_x/TiN memory stacks. The devices demonstrated a good resistance ratio of high resistance state and low resistance state ～10³ for Au/HfAlO_x/TiN and ～10⁵ for Au/HfAlO_x/ZrO₂/TiN stacks, respectively. Both stacks showed good retention characteristics (>10⁴ ?s) and endurance (>10³ cycles). The experimental current-voltage characteristics fitted with different conducting mechanisms, the linear lower bias region is dominated by ohmic conductivity, whereas the non-linear higher bias region was dominated by space-charge limited current conduction mechanism.     

NiO_x阻变存储器性能增强方法及相关机理研究

通过精确控制在Pt衬底上制备NiOx薄膜的工艺过程,制备出阻值窗口增大5倍以上,高低阻态稳定的TiN/NiOx/Pt结构阻变存储器.研究发现,NiOx薄膜的多晶态结晶结构和化学组分,尤其是Ni元素的化学态,是影响NiOx阻变存储器阻值窗口和稳定性的主要因素.X射线光电子能谱和X射线多晶体衍射测试结果表明,当NiOx薄膜中间隙氧或Ni2+空位增多时,Ni2+会被氧化成为Ni3+以保持电中性,Ni3+离子在材料中引入空穴导致P型氧化物NiO的漏电流增大.基于此机理,提出通过提高淀积温度、降低氧气分压的方法抑制NiOx薄膜中间隙氧或Ni2+空位的产生,降低TiN/NiOx/Pt结构阻变存储器关态漏电流,增大阻值窗口.这种基于工艺的性能增强方法,在NiOx阻变存储器实际应用中有良好前景.     

Improving the electrical performance of resistive switching memory using doping technology

In this paper, improvements of resistive random access memory (RRAM) using doping technology are summarized and analyzed. Based on a Cu/ZrO2/Pt device, three doping technologies with Ti ions, Cu, and Cu nanocrystal, respectively, are adopted in the experiments. Compared to an undoped device, improvements focus on four points: eliminating the electroforming process, reducing operation voltage, improving electrical uniformity, and increasing device yield. In addition, thermal stability of the high resistance state and better retention are also achieved by the doping technology. We demonstrate that doping technology is an effective way of improving the electrical performance of RRAM.     

Investigation of the synaptic device based on the resistive switching behavior in hafnium oxide

Metal-oxide based electronics synapse is promising for future neuromorphic computation application due to its simple structure and fab-friendly materials. HfOx resistive switching memory has been demonstrated superior performance such as high speed, low voltage, robust reliability, excellent repeatability, and so on. In this work, the HfOx synaptic device was investigated based on its resistive switching phenomenon. HfOx resistive switching device with different electrodes and dopants were fabricated. TiN/Gd:HfOx/Pt stack exhibited the best synaptic performance, including controllable multilevel ability and low training energy consumption. The training schemes for memory and forgetting were developed.