Unipolar resistive switching of Au+-implanted ZrO2 films

The resistive switching characteristics of Au+-implanted ZrO2 films are investigated.The Au/Cr/Au+-implanted-ZrO2/n+-Si sandwiched structure exhibits reproducible unipolar resistive switching behavior.After 200 write-read-erase-read cycles,the resistance ratio between the high and low resistance states is more than 180 at a readout bias of 0.7 V. Additionally,the Au/Cr/Au+-implanted-ZrO2/n+-Si structure shows good retention characteristics and nearly 100% device yield.The unipolar resistive switching behavior is due to changes in the film conductivity related to the formation and rupture of conducting filamentary paths,which consist of implanted Auions.     

金离子注入二氧化锆薄膜的单极电阻转变特性研究

The resistive switching characteristics of Au＋-implanted ZrO2 films are investigated. The Au/Cr/Au＋ -implanted-ZrO2/n＋-Si sandwiched structure exhibits reproducible unipolar resistive switching behavior. After 200 write-read-erase-read cycles, the resistance ratio between the high and low resistance states is more than 180 at a readout bias of 0.7 V. Additionally, the Au/Cr/Au＋-implanted-ZrO2/n＋-Si structure shows good retention characteristics and nearly 100% device yield. The unipolar resistive switching behavior is due to changes in the film conductivity related to the formation and rupture of conducting filamentary paths, which consist of implanted Au ions.     

两类阻变机理及性能改善方法的研究

在新型非易失性存储领域,结构简单、高速低耗的阻变存储器具有巨大优势和很强的竞争力.简要介绍了阻变存储器的结构及其两个电阻转变行为.总结了两类阻变机理,探讨了阻变存储器性能优化的方法,以及优化方法在阻变性能与器件的可靠性和稳定性之间如何取得平衡统一的问题,并展望了其前景.     

Evidence for compliance controlled oxygen vacancy and metal filament based resistive switching mechanisms in RRAM

We present electrical evidence on asymmetric metal-insulator-semiconductor (MIS) based test structures in support of the presence of two different independent switching mechanisms in a resistive random access memory (RRAM) device. The valid mechanism for switching depends on the compliance capping (I_gl) for forming/SET transition. Our results convincingly show that low compliance based switching only involves reversible oxygen ion drift to and from oxygen gettering gate electrodes, while high compliance switching involves formation and rupture of conductive metallic nanofilaments, as verified further by our physical analysis investigations. We have observed this unique dual mode switching mechanism only in NiSi-based gate electrodes, which have a moderate oxygen solubility as well as relatively low melting point.     

还原时间对AlOx/WOx RRAM开关速度的调制作用

基于128 kbit AlOx/WOx双层结构阻变存储器(RRAM)芯片,提出并验证了还原时间对RRAM开关速度的调制作用,同时设计了一种固定电压幅值逐步增大脉宽的算法用于RRAM阵列中速度的测试.还原处理的时间越长,AlOx层的厚度越薄,同时氧空位的含量增多,可加快导电细丝的形成、断裂和重新连接,进而提升芯片的开关速度.测试结果表明,还原时间由10 min增加至30 min,在4V和4.5V操作电压下,FORMING速度分布的均值分别由200 ns减小至120 ns和由100 ns减小至60 ns;在4V和4.5V操作电压下,RESET速度分布的均值分别由160 ns减小至120 ns和由120 ns减小至100 ns;SET速度分布的均值在4V电压下可由120 ns减小至80 ns.此外,还原时间的增长可以改善速度分布的一致性,减小速度的波动.     

Direct Observation of Conversion Between Threshold Switching and Memory Switching Induced by Conductive Filament Morphology

Volatile threshold switching (TS) and non‐volatile memory switching (MS) are two typical resistive switching (RS) phenomena in oxides, which could form the basis for memory, analog circuits, and neuromorphic applications. Interestingly, TS and MS can be coexistent and converted in a single device under the suitable external excitation. However, the origin of the transition from TS to MS is still unclear due to the lack of direct experimental evidence. Here, conversion between TS and MS induced by conductive filament (CF) morphology in Ag/SiO₂/Pt device is directly observed using scanning electron microscopy and high‐resolution transmission electron microscopy. The MS mechanism is related to the formation and dissolution of CF consisting of continuous Ag nanocrystals. The TS originates from discontinuous CF with isolated Ag nanocrystals. The results of current–voltage fitting and Kelvin probe force microscopy further indicate that the TS mechanism is related to the modulation of the tunneling barrier between Ag nanocrystals in CF. This work provides clearly experimental evidence to deepen understanding of the mechanism for RS in oxide‐electrolyte‐based resistive switching memory, contributing to better control of the two RS behaviors to establish high‐performance emerging devices.     

氧化钒薄膜的制备及电致开关特性的研究

采用反应溅射法,室温下,在Cu/Ti/SiO2/Si衬底上制备了氧化钒(VOx)薄膜,并对薄膜进行450℃、30min的真空退火处理.采用X-射线衍射(XRD)、原子力显微镜(AFM)对薄膜的结晶取向和表面形貌进行了表征,通过半导体参数分析仪对薄膜的电开关特性进行测试,并利用导电原子力显微镜(CAFM)对VOx薄膜的导...     

Resistive Random Access Memory Cells with a Bilayer TiO2/SiOX Insulating Stack for Simultaneous Filamentary and Distributed Resistive Switching

In order to fulfill the information storage needs of modern societies, the performance of electronic nonvolatile memories (NVMs) should be continuously improved. In the past few years, resistive random access memories (RRAM) have raised as one of the most promising technologies for future information storage due to their excellent performance and easy fabrication. In this work, a novel strategy is presented to further extend the performance of RRAMs. By using only cheap and industry friendly materials (Ti, TiO₂, SiO_X, and n⁺⁺Si), memory cells are developed that show both filamentary and distributed resistive switching simultaneously (i.e., in the same I–V curve). The devices exhibit unprecedented hysteretic I–V characteristics, high current on/off ratios up to ≈5 orders of magnitude, ultra low currents in high resistive state and low resistive state (100 pA and 125 nA at –0.1 V, respectively), sharp switching transitions, good cycle‐to‐cycle endurance (>1000 cycles), and low device‐to‐device variability. We are not aware of any other resistive switching memory exhibiting such characteristics, which may open the door for the development of advanced NVMs combining the advantages of filamentary and distributed resistive switching mechanisms.     

Resistive switching characteristic of electrolyte-oxide-semiconductor structures

The resistive switching characteristic of SiO₂ thin film in electrolyte-oxide-semiconductor (EOS) structures under certain bias voltage is reported. To analyze the mechanism of the resistive switching characteristic, a batch of EOS structures were fabricated under various conditions and their electrical properties were measured with a set of three-electrode systems. A theoretical model based on the formation and rupture of conductive filaments in the oxide layer is proposed to reveal the mechanism of the resistive switching characteristic, followed by an experimental investigation of Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS) to verify the proposed theoretical model. It is found that different threshold voltage, reverse leakage current and slope value features of the switching I-V characteristic can be observed in different EOS structures with different electrolyte solutions as well as different SiO₂ layers made by different fabrication processes or in different thicknesses. With a simple fabrication process and significant resistive switching characteristic, the EOS structures show great potential for chemical/biochemical applications.     

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。     

Coexistence of Grain‐Boundaries‐Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride

The use of 2D materials to improve the capabilities of electronic devices is a promising strategy that has recently gained much interest in both academia and industry. However, while the research in 2D metallic and semiconducting materials is well established, detailed knowledge and applications of 2D insulators are still scarce. In this paper, the presence of resistive switching (RS) in multilayer hexagonal boron nitride (h‐BN) is studied using different electrode materials, and a family of h‐BN‐based resistive random access memories with tunable capabilities is engineered. The devices show the coexistence of forming free bipolar and threshold‐type RS with low operation voltages down to 0.4 V, high current on/off ratio up to 10⁶, and long retention times above 10 h, as well as low variability. The RS is driven by the grain boundaries (GBs) in the polycrystalline h‐BN stack, which allow the penetration of metallic ions from adjacent electrodes. This reaction can be boosted by the generation of B vacancies, which are more abundant at the GBs. To the best of our knowledge, h‐BN is the first 2D material showing the coexistence of bipolar and threshold RS, which may open the door to additional functionalities and applications.     

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.     

基于RRAM双交叉阵列结构的三值存内逻辑电路设计

在RRAM交叉阵列结构中实现逻辑运算可以较好地解决传统冯诺依曼架构中的存储墙问题.三值逻辑相比于传统的二值逻辑,具有更少的逻辑操作数目和更快的运算速度.文中提出了一种基于RRAM双交叉阵列结构的三值存内逻辑电路设计,其中三值逻辑电路的输入与输出均通过多值RRAM的阻值表示.该结构支持两种三值逻辑门和一种二值逻辑门以提升...     

Effect of the top electrode material on the resistive switching of TiO2 thin film

Effect of the top electrode (TE) metal on the resistive switching of (TE)/TiO₂/Pt structure was investigated. It was confirmed that the potential barrier height between the metal and TiO₂ is an important factor on the resistive switching characteristics. When high Schottky barrier was formed with the TiO₂ film, using Pt or Au as a top electrode, both stable URS (unipolar) and BRS (bipolar resistive switching) characteristics were observed depending on the current compliance level. In the case of Ag, which forms a relatively low Schottky barrier, only BRS characteristics were observed, regardless of the current compliance level. In the case of Ni and Al, which have similar work function as Ag, unstable URS and BRS at very low current compliance levels were observed due to a chemical reaction at the interface. For the Ti electrode, resistive switching was not observed, because the work function of Ti is lower than that of TiO₂ and TiO phase was formed at the interface (Ti/TiO_x contact is ohmic).     

The conductive path in HfO2:first principles study

正The conductive path formed by the interstitial Ag or substitutional Ag in HfO_2 was investigated by using the Vienna ab initio simulation package based on the DFT theory.The calculated results indicated that the ordering of interstitial Ag ions at special positions can form a conductive path,and it cannot form at other positions. The orientation dependence of this conductive path was then investigated.Various types of super cells are also built to study the rupture of the path,which corresponds to some possible "off" states.     

Organic nonpolar nonvolatile resistive switching in poly(3,4-ethylene-dioxythiophene): Polystyrenesulfonate thin film

In this paper, the reproducible nonpolar resistive switching is demonstrated in devices with the sandwiched structure of Au/poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate/Au for nonvolatile memory application. The switching between high resistance state (OFF-state) and low resistance state (ON-state) does not depend on the polarity of the applied voltage bias, which is different from both the WORM characteristics and the bipolar switching characteristics reported before. The resistive ratio between the ON- and OFF-state is on the order of 10³ and increases with the device area decreasing. Both the ON- and OFF-state of the memory devices are stable, showing no significant degradation over 10⁴ s under continuous readout testing. It is proposed that the reduction and oxidation of PEDOT: PSS film might be the switching mechanism.     

铅基卤素钙钛矿阻变式存储器研究进展

随着数字通信在大数据以及物联网等领域的应用,推动了下一代存储设备的发展.阻变式存储器因其功耗低、尺寸可调、操作速度快等优点被认为是最有前景的信息存储器件之一.近年来,兼具成本低、带隙可调、载流子扩散长度长、离子迁移速率快、载流子迁移率高等优点的铅基卤素钙钛矿,在阻变式存储器领域引起了广泛关注.主要对铅基卤素钙钛矿阻变式...     

Reducing average delay after link failure in single-link recovery trees using distributed switching mechanism

Based on the modified MFBG algorithm, the distributed switching mechanism (DSM) is proposed to reduce the average delay after link failure in the preplanned single-link recovery trees. The main principle of the DSM is to use as many links in the blue tree as possible to keep connected, and the key feature is that all the active links comprise a new spanning tree after distributed switching. Simulation results demonstrate the effectiveness of the DSM in reducing the average delay.