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。     

Approaches for improving the performance of filament-type resistive switching memory

Resistive random access memory (RRAM) has received significant research interest because of its promising potential in terms of down-scaling,high density,high speed and low power. However,its endurance,retention and uniformity are still imperfect. In this article,the physical mechanisms of filament-type RRAM and the approaches for improving the switching performance,including doping,process optimization and interface engineering,are introduced.     

过渡性金属氧化物薄膜阻变存储材料进展概况

随着半导体技术和集成电路的进步,器件的集成度也不断提高,器件的特征尺寸不断减小,基于电荷存储的传统非易失性随机存储器面临着物理和技术上极限的挑战。阻变式存储器（RRAM）作为新一代的存储器件,因其器件具有结构简单、制备简便、存储密度高、擦写速度快、写入电流小等优势引起了人们广泛的研究。本文就目前基于过度氧化物薄膜的RRAM研究概况,从RRAM的基本工作原理、材料体系、存储机理和器件应用所面临的各种困难等方面对RRAM进行了简要评述。     

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.     

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.     

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.     

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.     

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.      

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.     

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。     

相变存储器单元皮秒测试信号完整性研究

针对相变存储器皮秒测试系统由于矩阵开关电路分布参数以及信号通道中阻抗突变所引起的反射,严重影响了皮秒脉冲信号的完整性,使施加在相变单元上的皮秒脉冲信号严重失真,为了消除失真,改善信号完整性,从2个方面提出了解决方案：一是采用性能优良的高频继电器构成矩阵开关;二是减小反射,采取了源端阻抗匹配、负载分支端阻抗补偿、菊花链双线拓扑结构等措施,使得反射的影响减小到最小.理论分析与仿真结果表明：皮秒脉冲信号波形质量良好,满足测试要求.本测试系统为研究皮秒编程脉冲作用下相变存储器的存储机理、速度、可靠性等提供了良好的平台,也可作为电阻式随机擦写存储器单元测试系统.     

高挤压比下挤压工艺对AZ31B镁合金组织与力学性能的影响

研究了高挤压比条件下挤压温度、速度对AZ31B镁合金微观组织、力学性能的影响。采用光学显微镜观察了显微组织,拉伸试验测试了力学性能,并配合扫描电镜观察了拉伸试样的断口形貌。结果表明,高挤压比条件下,动态再结晶较为充分,少量晶粒长大,混晶组织消失。低温、高速挤压有助于晶粒细化,并使晶粒尺寸分布均匀,因而可获得高的抗拉强度、屈服强度以及良好的塑性。350 ℃,2 m/min条件下挤压,试样抗拉强度与延伸率最高,为336.5 MPa与 23%。低温、高速下的挤压试样的拉伸断口韧窝较深且细密,呈现明显的韧性断裂特征,而高温、低速的断口为混合断裂。     

高温养护混凝土及衬砌结构力学特征研究现状与分析

随着深部矿井和深长隧道的建设需要,混凝土结构面临着更加复杂的高地温环境。高温养护混凝土水化动力过程和力学特征规律与常温养护存在较大差异。概述了深部矿井和深长隧洞结构面临的高地温环境,分析了高温养护条件下混凝土水化动力过程,对高温养护混凝土力学性能演化机制和改善方法进行了综述;总结了不同高地温环境对衬砌结构黏结性能、温度场分布规律和受力特性的影响规律以及支护体系优化方法。认为高温养护混凝土水化反应机制不明确、温-湿条件耦合影响的非线性、工程研究领域和性能指标的单一性是高温养护混凝土性能演化表征及优化改性研究存在的主要问题。应加强高温养护条件下混凝土水化动力学模型的研究,建立温-湿度耦合养护条件下混凝土性能预测模型,拓展高温养护混凝土应用领域和强度等级的研究,以便更好地为高地温环境深地工程混凝土结构设计和应用提供指导。     

高锰钢冲击磨料磨损特性的研究

本文对高锰钢在不同冲击载荷下的加工硬化规律和其磨料磨损特性作了系统的试验研究，并找出了加工硬化值与耐磨性间的对应关系，指出高锰钢以其加工硬化值大于ＨＲＣ５４的工况为其适宜工况。     

高频无极灯的技术现状与应用研究

基于目前绝大多数人对高频无极灯的不甚了解,甚至在一些较大的灯具城也很难找到了解它的人,而商家则无限扩大其优点来误导消费者的现状,文章通过对高频无极灯的结构、原理及其技术现状的分析,得出了目前高频无极灯的主要应用优势是在工矿照明等不方便换灯的场所。要想取代其他的电光源,其配件还须进行技术更新。     

平面型高频PCB变压器材料和结构工艺

根据电磁感应理论和多层PCB(印刷电路板)材料的特点，对平面型高频PCB变压器的结构和工艺进行了研究，得到了一种新颖的平面型高频多层PCB变压器。将该变压器用于高频开关电源DC／DC模块，使得该电源模块高度低、体积小、效率高、电磁干扰小、产品一致性好，可实现自动化生产。     

高等职业教育中教学改革的思考

培养社会适应能力强、有一定专业理论水平和较强专业技能的高级技术人才是高等职业技术教育职责所在。在高等职业技术教育快速发展的新形势下,以市场为导向,注重一个＂需＂字;以技能为核心,注重一个＂强＂字;以质量为保证,确保一个＂高＂字;以改革为手段,保持一个＂活＂字;以特色为前提,力求一个＂新＂字,加强教学改革,提高教学质量,意义尤为重大。