基于I-V特性的阻变存储器的阻变机制研究

随着器件尺寸的缩小,阻变存储器(RRAM)具有取代现有主流Flash存储器成为下一代新型存储器的潜力。但对RRAM器件电阻转变机制的研究在认识上依然存在很大的分歧,直接制约了RRAM的研发与应用。通过介绍阻变存储器的基本工作原理、不同的阻变机制以及基于阻变存储器所表现出的不同I-V特性,研究了器件的阻变特性;详细分析了阻变存储器的五种阻变物理机制,即导电细丝(filament)、空间电荷限制电流效应(SCLC)、缺陷能级的电荷俘获和释放、肖特基发射效应(Schottky emission)以及普尔-法兰克效应(Pool-Frenkel);同时,对RRAM器件的研究发展趋势以及面临的挑战进行了展望。     

阻变型非易失性存储器单元电路结构设计与Spice仿真

为进一步确定阻变型非易失性存储器的擦写速度、器件功耗和集成度等实用化的性能指标,设计RRAM存储器单元电路结构,并使用HSpice软件分别对RRAM存储器单元结构电路的延时和功耗性能进行仿真.同时,通过仿真对双极型和单极型两种电阻转变类型及器件工艺进行比较和分析,确定1T1R结构电路单元适用于双极型阻变型非易失性存储器件,并且电路仿真的结果为阻变型非易失性存储器的进一步实用化提供了参考.     

新型阻变存储器内的电压解决方案

相对于现在流行的FLASH型存储器,新型阻变存储器(resistive-RAM,RRAM)有很多优势,比如较高的存储密度和较快的读写速度。而针对RRAM的读写操作特性,提出了一种适用于新型阻变存储器的提供操作电压的电路。该方案解决了新型存储器需要外部提供高于电源电压的操作电压的问题,使得阻变存储器能应用于嵌入式设备。同时,对工艺波动和温度波动进行补偿,从而降低了阻变存储器的读写操作在较差的工艺和温度环境下的失败概率,具有很强的实际应用意义。该设计采用0.13μm标准CMOS 6层金属工艺在中芯国际(SMIC)流片实现,测试结果表明,采用此电路的RRAM能正确地进行数据编程和擦除等操作,测试结果达到设计要求。     

一种基于HfO2材料的RRAM波动性模型

基于HfO₂材料制作了一种具有良好非易失性的阻变存储器(RRAM)。根据ECM导电细丝机制,建立了动态的Verilog-A模型,该模型包含了RRAM的波动特性。对模型进行直流电压扫描验证,与实际器件的电流-电压特性曲线进行拟合。验证结果表明,该模型具备RRAM器件优良的电学特性,波动特性的加入对电路的前期设计具有指导意义。对模型进行脉冲仿真,仿真结果表明高、低阻态之间的鉴别窗口大于100倍,转变时间小于30 ns。     

基于RRAM延时单元的PUF设计

随着技术的发展，信息安全受到了很大挑战.物理不可克隆函数（Physically Unclonable Function，PUF）电路是一种新型的密钥生成电路，阻变存储器（Resistive Random Access Memory，RRAM）可以为其提供物理随机熵源，这使得PUF在物理上不可被攻击.但目前在基于RRAM的PUF设计方案中，RRAM延时单元的测试响应对（Challenge Response Pair，CRP）效率并不够高.本文提出一种基于RRAM延时单元的PUF结构，延时单元将RRAM的阻值输出到反向器中，形成脉冲的延迟，最后通过判决器判断两路脉冲达到顺序并编码为"0"和"1"，这就是PUF的输出位.基于RRAM延时单元，本文设计了8位、16位、32位、64位PUF，这些PUF在保证良好的随机性、稳定性、唯一性的前提下，大大提高了PUF的RRAM单元效率.实验结果表明：该设计能够有效的提高RRAM使用效率，使得PUF能够更好地防止外界的攻击.     

1T1R结构RRAM的故障可测性设计

阻变随机存储器(RRAM)中存在的故障严重影响产品的可靠性和良率.采用精确高效的测试方法能有效缩短工艺优化周期,降低测试成本.基于SMIC 28 nm工艺平台,完成了1T1R结构的1 Mbit RRAM模块的流片.详细分析了测试中的故障响应情况,并定义了一种故障识别表达式.在March算法的基础上,提出针对RRAM故障的有效测试算法,同时设计了可以定位故障的内建自测试(BIST)电路.仿真结果表明,该测试方案具有占用引脚较少、测试周期较短、故障定位准确、故障覆盖率高的优势.     

CuxSiyO阻变存储器单粒子和总剂量辐照效应

对CuxSiyO结构的阻变存储器(RRAM)进行了总剂量(TID)以及单粒子辐照(SEE)实验.总剂量实验中,1T1R样品分别接受总剂量为1,2和3 kGy (SiO2)的60Co γ射线辐射.样品中没有出现低阻在辐照后翻转的现象.单粒子辐照实验中,16 kbit RRAM阵列样品分别接受线性能量转移(LET)值最高达75 MeV的4种离子束的辐射.样品中没有出现低阻在辐照后翻转的现象.除一组无翻转外,存储单元的高阻到低阻的翻转率皆在0.06％左右.实验结果证实了RRAM中已经形成的导电通道不会受辐照影响,因此不存在低阻翻转为高阻的现象.     

阻变存储器外围电路关键技术研究进展

阻变存储器(RRAM)是一种前景非常好的未来通用存储技术,也是当前国际学术界和工业界研究的热点。主要介绍了存储器外围电路的电路设计,并介绍了阻性存储器外围电路,包括验证电路、写电路、参考模块方案和形式、限流等关键技术的原理,重点讨论了提升复位操作速度,改善高阻值离散性,参考方案的设计和参考单元的组成,用限流实现低功耗操作的方法及其发展趋势。     

微电子所在面向应用的阻变存储器研究上取得新进展

正日前,微电子所在面向应用的阻变存储器研究上取得新进展。阻变存储器(RRAM)是非挥发性存储器的一种重要的替代方案,具有工艺及器件结构简单、微缩性好、高速、低功耗、可嵌入功能强等优点。微电子所纳米加工与新器件集成技术研究室科研人员在前期建立新材料、新结构及与大生产CMOS集成的     

铪/二氧化铪基双极阻变存储器特性研究

本文制备了纳米级Hf/HfO2阻变存储器（RRAM）。RRAM顶层电极和底部电极交叉，从而形成了金属-氧化物-金属结构。系统地研究了RRAM的电学特性，包括forming过程，SET过程和RESET过程。讨论了SET电压和RESET电压的相关性，以及高阻态和低阻态的相关性。RRAM的电学特性与SET过程中的限制电路强相关。可以基于量子点接触模型，阐述纳米级Hf/HfO2阻变存储器的导通机制。     

A journey towards reliability improvement of TiO2 based Resistive Random Access Memory: A review

A Resistive Random Access Memory (RRAM), where the memory performance principally originated from ‘resistive’ change rather than ‘capacitive’ one (the case with conventional CMOS memory devices), has attracted researchers across the globe, owing to its unique features and advantages meeting the demands of future generation high-speed, ultra low power, nano dimensional memory devices. A large family of semiconducting oxides have been investigated as insulator for Resistive Random Access Memory (RRAM), amongst which TiO₂ is one of the potential candidate, principally owing to some of its remarkable advantages e.g. wide band gap, high temperature stability and high dielectric constant with flexibility to offer both unipolar and bipolar switching, which are essential for RRAM device applications. In this review article, we tried to represent the long voyage of TiO₂ based RRAM, towards the improvement of the reliability aspects of the device performance in a comprehensive manner. Starting with the key factors like oxygen vacancies, Ti interstitials and electroforming, which are responsible for resistive switching phenomenon, various material preparation techniques for RRAM development have been discussed with emphasis on relative merits and bottlenecks of the process. The factors like electrode material and geometry, device structuring, doping, compliance current, annealing effect etc., which play the pivotal role in determining the switching performance of the device, have been reviewed critically. Finally, the article concludes with the comparison of different TiO₂ based RRAM devices followed by the prediction of possible future research trends.     

Comparison of three different architectures for active resistive memories

Resistive memory (RRAM) is one of the strong emerging technologies in modern memory field. This type of memories has the potential to be the replacement of several current memory types. As any new technology, RRAM brings new challenges concerning technology and design. This work discusses some aspects concerning the design of active resistive memories and compares three possible memory architectures.     

A long lifetime, low error rate RRAM design with self-repair module

Resistive random access memory (RRAM) is one of the promising candidates for future universal memory. However, it suffers from serious error rate and endurance problems. Therefore, exploring a technical solution is greatly demanded to enhance endurance and reduce error rate. In this paper, we propose a reliable RRAM architecture that includes two reliability modules: error correction code (ECC) and self-repair modules. The ECC module is used to detect errors and decrease error rate. The self-repair module, which is proposed for the first time for RRAM, can get the information of error bits and repair wear-out cells by a repair voltage. Simulation results show that the proposed architecture can achieve lowest error rate and longest lifetime compared to previous reliable designs.     

Filament diffusion model for simulating reset and retention processes in RRAM

Resistive switching memory (RRAM) devices are attracting an increasing interest as a possible future technology for ultra-scaled, high-density nonvolatile/dynamic memory. Although the RRAM concept is promising from the integration and scaling viewpoints, the switching mechanism and its controllability are still under debate. This paper addresses the modeling of reset and retention processes in unipolar resistive-switching memory devices. Reset transition and data loss are described in terms of the dissolution of a conductive filament, which is modeled by thermally-activated diffusion of defects/dopants. Carrier transport, Joule heating and diffusion of oxygen ions/vacancies during the electrical pulse and/or the annealing are modeled within a 3D numerical solver. The model can account for the observed dependence of reset voltage on the width of the applied triangular pulse and on the initial resistance for NiO-based RRAM devices. Retention simulations as a function of annealing temperature also agree with available data. The model provides a first example of device simulation tool for the design and the exploration of scaling and performance of RRAM cells.     

Polymer-based non-volatile resistive random-access memory device fabrication with multi-level switching and negative differential resistance state

Resistive random-access memory (RRAM) has been widely considered for its prospective applicability owing to its non-volatile characteristics. In this study, a polymer-based vacuum-free RRAM device fabricated with the conductive polymer, poly(3,4-ethylene-dioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was proposed. Pristine PEDOT:PSS coated on indium tin oxide (ITO) electrode was used as the active layer, while PEDOT:PSS with 16 vol% ethylene glycol was added for the top electrode. The PEDOT:PSS-based RRAM device demonstrated controlled non-volatile bipolar switching and a good ON/OFF ratio with a negative differential resistance effect in the high-voltage range during the RESET process. Multi-level switching was also accomplished by controlling the voltage, which demonstrated reliable and non-volatile switching. The switching mechanism of this polymer RRAM device can be explained through the electrochemical filamentary formation as well as the current-induced phase segregation of PEDOT:PSS near the anode(ITO)/polymer interface.     

Low-Energy Oxygen Plasma Injection of 2D Bi2Se3 Realizes Highly Controllable Resistive Random Access Memory

Resistive random access memory (RRAM) based on ultrathin 2D materials is considered to be a very feasible solution for future data storage and neuromorphic computing technologies. However, controllability and stability are the problems that need to be solved for practical applications. Here, by introducing a damage-less ion implantation technology using ultralow-energy plasma, the transport mechanisms of space charge limited current and Schottky emission are successfully realized and controlled in RRAM based on 2D Bi₂Se₃ nanosheets. The memristors exhibit stable resistive switching behavior with a high resistive switching ratio (>10⁴), excellent cycling endurances (300 cycles), and great retention performance (>10⁴ s). The reliability and controllability of Bi₂Se₃ memory endowed by oxygen plasma injection demonstrate the great potential of this ultralow-energy ion implantation technology in the application of 2D RRAM.     

Towards engineering in memristors for emerging memory and neuromorphic computing:A review

Resistive random-access memory(RRAM),also known as memristors,having a very simple device structure with two terminals,fulfill almost all of the fundamental requirements of volatile memory,nonvolatile memory,and neuromorphic characteristics.Its memory and neuromorphic behaviors are currently being explored in relation to a range of materials,such as biological materials,perovskites,2D materials,and transition metal oxides.In this review,we discuss the different electrical behaviors exhibited by RRAM devices based on these materials by briefly explaining their corresponding switching mechanisms.We then discuss emergent memory technologies using memristors,together with its potential neuromorphic applications,by elucidating the different material engineering techniques used during device fabrication to improve the memory and neuromorphic performance of devices,in areas such as ION/IOFF ratio,endurance,spike time-dependent plasticity(STDP),and paired-pulse facilitation(PPF),among others.The emulation of essential biological synaptic functions realized in various switching materials,including inorganic metal oxides and new organic materials,as well as diverse device structures such as single-layer and multilayer hetero-structured devices,and crossbar arrays,is analyzed in detail.Finally,we discuss current challenges and future prospects for the development of inorganic and new materials-based memristors.     

Resistive random access memory and its applications in storage and nonvolatile logic

The resistive random access memory (RRAM) device has been widely studied due to its excellent memory characteristics and great application potential in different fields. In this paper, resistive switching materials, switching mechanism, and memory characteristics of RRAM are discussed. Recent research progress of RRAM in high-density storage and nonvolatile logic application are addressed. Technological trends are also discussed.     

适用于射频识别标签的64-kbit嵌入式阻变存储器

设计并实现了一颗适用于射频识别(RFID)标签的低功耗嵌入式64-kbit阻变存储器芯片.提出了新型的带尖峰电流控制功能的高压稳压电路,在提供稳定编程电压的同时降低了芯片电源上的瞬态大电流,改善了存储器电路的可靠性;设计了适用于2T2R(2 Transistors and 2 Resistive cells)单元的敏感...