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.     

HfO_x缓冲层对γ-Fe_2O_3纳米微粒膜电阻开关特性的影响

本文利用射频磁控溅射和滴涂法在Pt/Ti/SiO2/Si衬底上制备了HfOx/γ-Fe2O3/HfOx三明治结构,研究了HfOx缓冲层对γ-Fe2O3纳米微粒薄膜电阻开关特性的影响.微结构观测分析结果显示:γ-Fe2O3纳米微粒平均粒径约为34.3 nm,HfOx缓冲层为氧配比不足的单斜相多晶薄膜.电学性能测试表明:插入HfOx缓冲层后,γ-Fe2O3纳米微粒薄膜的电阻开关特性明显改善:在-0.8 V读取电压下,高/低电阻态阻值平均比值约为18.7,该比值可稳定维持100个循环周期.指数定律拟合实验曲线结果表明:高阻态漏电流以缺陷主导的空间电荷限制隧穿电流为主;而低阻态则以欧姆接触电导为主.Ag上电极与HfOx缓冲层界面处氧离子的定向漂移使得薄膜中氧空位缺陷形成的导电细丝通道周期性地导通与截断,从而使得薄膜呈现电阻开关效应.     

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.     

Ion transport-related resistive switching in film sandwich structures

Resistive switching memories based on ion transport and related electrochemical reactions have been extensively studied for years. To utilize the resistive switching memories for high-performance information storage applications, a thorough understanding of the key information of ion transport process, including the mobile ion species, the ion transport paths, as well as the electrochemical reaction behaviors of these ions should be provided for material and device optimization. Moreover, ion transport is usually accompanied by processes of microstructure modification, phase transition, and energy band structure variation that lead to further modulation of other physical properties, e.g., magnetism, optical emission/absorbance, etc., in the resistive switching materials. Therefore, novel resistive switching memories that are controlled through additional means of magnetic or optical stimulus, or demonstrate extra functionalities beyond information storage, can be made possible via well-defined ion transportation in various switching materials and devices. In this contribution, the mechanism of ion transport and related resistive switching phenomena in thin film sandwich structures is discussed first, followed by a glanceat the recent progress in the development of high-performance and multifunctional resistive switching memories. A brief perspective of the ion transport-based resistive switching memories is addressed at the end of this review.     

Evolution of resistive switching polarity in Au/Ar<Superscript>+</Superscript> bombarded SrTi<Subscript>0.993</Subscript>Nb<Subscript>0.007</Subscript>O<Subscript>3</Subscript>/In sandwiches

We investigated the resistive switching characteristics of Au/Ar+bombarded SrTi 0.993 Nb0.007O3/In sandwiches.The evolution of the resistive switching polarity with sweeping voltage was observed.Our experiments showed that under a macroscopic electrode the homogeneous trapping-detrapping-type conduction and filament-type conduction coexist and compete with each other.For a large sweeping voltage range,the trapping-detrapping-type conduction dominates.However,for a small range the latter dominates. If the bias voltage is too large,the filament conduction could be destroyed.These results will help deepen the understanding of the resistive switching polarity,and will aid in future device design.     

Eu-Ru共掺NiO-SnO2复合纳米粒子薄膜的阻变特性

通过低温水浴法制备了Eu-Ru共掺杂NiO-SnO2复合纳米粒子，透射电镜图像显示纳米粒子粒径均匀，选区电子衍射表明结晶性差，所测晶面间距与SnO2和NiO相应卡片数据一致，水热机理分析表明纳米粒子由NiO-SnO2微观p-n结组成.原子力显微镜测试薄膜表面平均粗糙度约025nm，由于薄膜太薄及样品结晶性差，XRD分析未见明显衍射峰.电学测试表明纳米粒子薄膜具有可重复双极阻变特性，阈值电压约1V，开关比约500.薄膜高阻态电学输运符合缺陷俘获载流子所致空间电荷限制导电机制，低阻态呈欧姆特性，故阻变机理应为电荷俘获及再释.     

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.     

Cu/SiO2结构单元在阻变效应中形成导电通道的模型分析*

通过建立一个模型,简单地讨论了Cu/SiO_2结构单元在阻变效应中形成导电通道的临界电压特性。该模型考虑了Cu离子在SiO_2薄膜的迁移扩散和Cu离子在薄膜内引起的空间电荷效应,同时考虑了电子电导机制。模型的计算表明,薄膜的结构参数(厚度、电极功函数、掺杂等)对导电通道的形成过程有很大的影响,其临界电压随薄膜厚度和电极功函数的增加而增大,而随Cu离子掺杂浓度增大而减小。这一结果对未来存储器件的性能设计和制造具有一定的指导意义。     

一种Cu_xSi_yO阻变存储器的温度特性与微观机制分析

应用有效控制温度偏置的方法对基于0.13μm CMOS工艺的Ta/TaN/CuxSiyO/Cu结构的1Mbit阻变存储芯片进行开关性能和高低阻态导电性能的测试,介于-40～125℃温度区间的统计结果表明：set成功过程所需加载电场能量随偏置温度升高而升高,reset成功过程所需加载电场能量随偏置温度升高而降低;高阻态和低阻态随不同偏置温度呈现相似变化趋势——在-40～25℃间阻值均随偏置温度升高而升高,在25～125℃间均随偏置温度升高而呈下降趋势.针对以上现象提出了电学与热学结合的基于filament的微观模型,由铜空位构成的filament局部的反复形成与断裂对应于阻变存储器从高阻态到低阻态的重复转换,分析了电学和热学各自在CuxSiyO系列的阻变存储器开关和导电微观机制中所起作用.     

氧化钽/氧化铝薄膜的阻变特性和突触特性

通过微电子加工工艺,制备出具有ITO/TaO_x/AlO_x/Ti结构的双介质层阻变存储器.器件中引入的氧化铝介质层有效地减小了器件的运行电流,降低了高/低阻态间切换所需的功耗,并增大了高/低阻态电阻比值.研究表明,器件的高低态电阻与其切换电压均有良好的稳定性和均匀性,且器件表现出可靠的擦写性能与保持性能.进一步研究表明,器件高阻态导电受肖特基发射机制主导,低阻态导电受空间电荷限制机制主导.器件还具有连续可调的电阻渐变行为,利用反复电脉冲刺激下的器件电阻变化来表征突触的权值,可以模拟突触行为.     

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。     

谐波起动电动机起动切换瞬变电流的研究

本文研究了谐波起动电动机起动切换瞬变电流的规律.运用四阶尤格-库塔法,对Y-△起动和谐波起动过程的切换瞬变电流进行仿真计算,给出了计算结果,与实测值相比,获得了较为一致的结果,分析计算与实测结果表明,A型谐波起动的断电切换过程中存在着瞬变电流冲击,就其冲击幅度和持续时间看,不会对电网和电源变压器造成不良的影响.     

Advancements in organic nonvolatile memory devices

As one of the most promising candidates for next generation storage media, organic memory devices have aroused worldwide research interest in both academia and industry. In recent years, organic memories have experienced rapid progress. We review the development of organic resistive switching memories in terms of structure, characteristics, materials used, and integration. Some basic concepts are discussed, as well as the obstacles hindering the development and possible commercialization of organic memory d...     

影响STATCOM核心开关器件的关键问题

功率开关器件的有效控制是影响STATCOM运行性能的关键因素,因此,对大功率开关器件的本身特性的研究至关重要.通过对IGBT的试验及仿真和计算,讨论了STATCOM的核心器件IGBT的不同开关频率对设备电流波形正弦性、谐波、功率器件损耗,以及硬件电路产生影响;IGBT驱动取能对直流侧电容电压平衡产生影响,驱动电路单管反激式开关电源存在单管反击变换器易被击穿的问题;驱动电路的设计除采用栅压保护,还需采用软硬件防止CPLD在强的电磁干扰下产生误动作.     

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...     

砷化镓光导开关中电流丝的自发辐射效应

应用统计物理方法研究了高增益砷化镓光导开关中电流丝的自发辐射效应.导出了高增益砷化镓光导开关中电流丝的自发辐射规律,在砷化镓样品中引入复合辐射强度与辐射的波长分布函数的概念,近似确定了高增益砷化镓光导开关中电流丝的平均辐射复合系数为(883 nm)≈0.1125,导出了各辐射波长的辐射复合系数与平均辐射复合系数之间的关系,验证了峰值波长为890 nm的光输出能量与实验观察结果吻合,在理论上揭示了电流丝顶部的光生载流子密度的分布规律.结果表明:电流丝的体积面积比值和电流丝内平均载流子密度是影响电流丝辐射效应的两个主要因素,波长876 nm的辐射在紧邻电流丝顶部产生的最大载流子密度具有主导作用,最大光生载流子密度比电流丝内平均载流子密度小1–2个数量级.     

基于嵌入式系统触摸屏接口电路的实现

介绍了四线电阻触摸屏和触摸屏的驱动控制芯片ADS7843的工作原理,给出触摸屏与ARM7微处理器S3C44B0X芯片接口电路的连接方法及软件编程的实现方法.     

铁路信号点灯智能监测系统设计

铁路信号灯是铁路安全运行的可靠保证,信号灯的安全监测、控制和维护是铁路部门的一项重要工作.为了实现铁路信号灯的自检、控制,并能及时报告信号灯的故障,把安全隐患降到最低,设计了铁路信号灯智能点灯及监测系统[1].1系统硬件设计系统硬件分为两大部分:信号灯智能点灯检测单     

砷化镓光导开关中流注自发辐射实验的理论分析

分析了高增益砷化镓光导开关中流注（即电流丝）一端不同辐射波长的自发辐射实验现象,导出了不同辐射波长的辐射复合系数之间的关系,拓展了电流丝的自发辐射随电流丝电流变化的数学模型．计算结果表明,丝电流相同时流注自发辐射的其他峰值强度略小于890nm自发辐射强度．     

电流滞环法控制BOOST PFC 电路的设计与分析

讨论了滞环电流控制模式中的电感电流，开关电流的有效值和MOSFET开关损耗与效率之间的关系，促进了计算机辅助设计程序的优化，从而能有效地选择电路元件以满足各种指标设计要求。