基于Au/TiO_2/FTO结构忆阻器的开关特性与机理研究

采用简单的一步水热法在FTO导电玻璃上外延生长了锐钛矿TiO_2纳米线,制备了具有Au/TiO_2/FTO器件结构的锐钛矿TiO_2纳米线忆阻器,系统研究了器件的阻变开关特性和开关机理.结果表明,Au/TiO_2/FTO忆阻器具有非易失的双极性阻变开关特性.同时,在103s的时间内,器件在0.1 V的电阻开关比始终保持在20以上,表明器件具有良好的非易失性.此外,器件在低阻态时遵循欧姆导电特性,而在高阻态时则满足陷阱控制的空间电荷限制电流传导机制,同时提出了基于氧空位导电细丝形成与断开机制的阻变开关模型.研究结果表明Au/TiO_2/FTO忆阻器将是一种很有发展潜力的下一代非易失性存储器.     

Ti/HfO2/Pt阻变存储单元中的氧空位聚簇分布

为了研究阻变存储器导电细丝的形成位置和分布规律, 使用X射线光电子能谱研究了Ti/HfO₂/Pt阻变存储器件单元中Hf 4f的空间分布, 得到了阻变层的微结构信息. 通过I-V测试, 得到该器件单元具有典型的阻变特性; 通过针对Hf 4f的不同深度测试, 发现处于低阻态时, 随着深度的增加, Hf⁴⁺化学组分单调地减小; 而处于高阻态和未施加电压前, 该组分呈现波动分布; 通过Hf⁴⁺在高阻态和低阻态下组分含量以及电子能损失谱分析, 得到高阻态下Hf⁴⁺组分的平均含量要高于低阻态; 另外, 高阻态和低阻态下的O 1s谱随深度的演变也验证了Hf⁴⁺的变化规律. 根据实验结果, 提出了局域分布的氧空位聚簇可能是造成这一现象的原因. 空位簇间的链接和断裂决定了导电细丝的形成和消失. 由于导电细丝容易在氧空位缺陷聚簇的地方首先形成, 这一研究为导电细丝的发生位置提供了参考.     

负反馈提高高阻恒流源驱动的LED的输出光场噪声压缩量

研究高阻恒流源驱动的ＬＥＤ所发射光场的粒子数噪声压缩与ＬＥＤ电、光量子效率，漏电流效应，光子流涨落负反馈及噪声频率的关系。指出：在高阻恒流ＬＥＤ中引入适量光子流涨落负反馈能产生粒子数压缩态光场并极大地提高粒子数噪声压缩，其理想压缩仅受限于高阻恒流源残余噪声、ＬＥＤ漏电流效应和量子效率。 关键词：     

金属1/f噪声理论

本文对已有四十多年实验观察历史的金属中的1/f噪声现象提出了新的物理机制:金属中局域电子的带有红外发散的扩散迁移引起1/f噪声。本文基于低频涨落、耗散、弛豫的普适理论建立了非马尔科夫扩散方程,由此求得的噪声谱能解释1/f噪声的四个基本特征,并在参数合理取值的情况下和实验结果符合得较好。本文还对已有理论等做了若干讨论。 关键词：     

电脉冲对多晶La0.7Ca0.3MnO3比热的影响

对电脉冲诱导的不同电阻态下La_0.7Ca_0.3MnO₃样品的比热进行了研究.实验结果表明,电脉冲导致La_0.7Ca_0.3MnO₃样品比热随电阻状态发生可逆变化.比热随电阻状态的减小而减小.低温比热拟合及不同电阻状态下的比热差与温度关系说明,声子对比热的贡献不随电阻状态变化,磁性和载流子对比热的贡献是导致La_0.7Ca_0.3MnO₃样品比热变化的原因.电脉冲诱导O离子沿一维扩展性缺陷的电化学迁移,导致材料中局部区域的O离子浓度发生变化.O离子浓度的变化导致载流子浓度的变化,同时载流子浓度的变化将使得低温下磁性耦合强度发生变化,从而导致比热发生变化. 关键词： 0.7Ca_0.3MnO₃')" href="#">La_0.7Ca_0.3MnO₃ 比热 氧离子迁移     

Pt/Au/n-InGaN肖特基接触的电流输运机理

基于热电子发射和热电子场发射模式,利用I-V方法研究了Pt/Au/n-InGaN肖特基接触的势垒特性和电流输运机理,结果表明,在不同背景载流子浓度下,Pt/Au/n-InGaN肖特基势垒特性差异明显.研究发现,较低生长温度制备的InGaN中存在的高密度施主态氮空位（V_N）缺陷导致背景载流子浓度增高,同时通过热电子发射模式拟合得到高背景载流子浓度的InGaN肖特基势垒高度和理想因子与热电子场发射模式下的结果差别很大,表明V_N缺陷诱发了隧穿机理并降低了肖特基势垒高度,相应的隧穿电流显著增大了肖特基势垒总的输运电流,证实热电子发射和缺陷辅助的隧穿机理共同构成了肖特基势垒的电流输运机理.低背景载流子浓度的InGaN肖特基势垒在热电子发射和热电子场发射模式下拟合的结果接近一致,表明热电子发射是其主导的电流输运机理.     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO₂晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法, 用第一性原理对含高氧空位浓度的锐钛矿TiO₂晶体进行了结构优化处理、能带分布和态密度分布计算, 表明在温度一定和高氧空位浓度的条件下, 锐钛矿TiO₂的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO₂晶体中高氧空位浓度时,发现有莫特相变的现象. 关键词： 高氧空位 2半导体')" href="#">锐钛矿TiO₂半导体 电子寿命 第一性原理     

基于HfN_x∶Zn薄膜的负微分阻变存储器

基于HfNx∶Zn薄膜材料制备了阻变式随机存储器,获得了良好的阻变可靠性,并观察到负微分电阻现象.Au/HfNx∶Zn/Pt器件表现出快速的擦写速度(150ns)、优异的循环耐受性(103)、长时间保持性(85℃时105 s)、较小的开启/关闭电压波动性(3.5%/8.5%)和较低的高阻/低阻波动性(13.5%/10.1%).Zn元素的掺入为薄膜引入了大量的N空位缺陷态,根据器件运行的I-V拟合曲线,得知器件阻变机制与N空位缺陷的存在有直接的关系.     

单层密集ZnO纳米棒阻变器件的导电机制

制备了一种具有多级存储效应的密集ZnO纳米棒阵列阻变存储器件,借助I-V曲线和荧光光谱分析了器件的电流传导机制和阻变机制,发现器件在不同的电阻态下分别属于欧姆传导和空间电荷限制电流( SCLC)传导机制。正向电场作用使纳米棒表面耗尽区的氧空位V++密度增大,完善了电子传输的导电细丝通道,器件实现了由高阻态向低阻态的转变;在反向电压作用下,导电通道断裂,器件恢复到高阻态。     

高氧空位浓度对锐钛矿TiO2莫特相变和光谱红移及电子寿命影响的第一性原理研究

基于密度泛函理论的第一性原理研究,通过对锐钛矿TiO₂高氧空位浓度、态密度图及吸收光谱图的分析,发现锐钛矿TiO₂高氧空位浓度的条件下,高氧空位浓度对禁带变窄、吸收光谱红移和电子寿命都有很大的影响,从理论上进一步解释了高氧空位浓度对禁带变窄的原因.同时,锐钛矿半导体在高氧空位浓度时发生莫特相变和锐钛矿氧空位在等离子体中吸收光谱红移实验进行比较,发现锐钛矿TiO₂应适量控制高氧空位浓度对吸收光谱红移好于前者.适量控制高氧空位浓度的锐钛矿TiO 关键词： 锐钛矿 高氧空位浓度 吸收光谱红移 第一性原理     

Characteristics of the bipolar resistive switching behavior in memory device with Au/ZnO/ITO structure

In this work, reproducible and stable bipolar resistive switching behavior without the requirement of forming process is observed in the memory device with Au/ZnO/ITO structure. It shows a high R_on/R_off ratio, where R_on and R_off are the resistance at low resistance state (LRS) and high resistance state (HRS), respectively. The dominated transport mechanisms for LRS and HRS are related to space charge limited current and Ohmic behavior, respectively. This bipolar resistive behavior is attributed to the formation and rupture of conducting filaments which are constructed with oxygen vacancies. The Au/ZnO/ITO device discussed in this work shows huge potential applications in the next generation nonvolatile memory field.     

Reversible resistance switching properties in Ti-doped polycrystalline Ta2O5 thin films

Unipolar reversible resistance switching effects were found in 5 at% Ti-doped polycrystalline Ta₂O₅ films with the device structure of Pt/Ti–Ta₂O₅/Pt. Results suggest that the recovery/rupture of the conductive filaments which are involved in the participation of oxygen vacancies and electrons leads to the resistance switching process. Ti-doped Ta₂O₅ thin films possess higher resistance whether in low-resistance state or high-resistance state and higher resistance switching ratio than Ta₂O₅ thin films, where Ti addition plays an important role in the resistance switching process by suppressing the migration of oxygen vacancies via forming an electrically inactive Ti/O–vacancy complex. Excellent retention properties of the high and low resistances under constant stress of applied voltage were obtained.     

氧分压对Ni/HfO_x/TiN阻变存储单元阻变特性的影响

采用射频磁控溅射的方法,基于不同氧分压制备的氧化铪构建了Ni/HfO_x/TiN结构阻变存储单元.研究发现,随着氧分压的增加,薄膜表面粗糙度略有降低;另一方面,阻变单元功耗降低,循环耐受性能可达10~3次,且转变电压分布的一致性得到改善.结合电流-电压曲线线性拟合结果及外加温度测试探究了器件的转变机理,得出在低阻态的传导机理为欧姆传导机理,在高阻态的传导机理为肖特基发射机理,并根据氧空位导电细丝理论,对高低阻态的阻变机理进行了详细的理论分析.     

Resistive switching in ceramic multiferroic Bi0.9Ca0.1FeO3

We report resistive switching effects in polycrystalline samples of the multiferroic Bi_0.9Ca_0.1FeO₃ with silver electrodes. Mössbauer spectroscopy shows that upon Ca-doping the Fe remains in a 3+ valence state, suggesting charge compensation through the creation of large amounts of oxygen vacancies. Electrical characterization shows that the oxide/metal resistance can be switched between high and low resistance states by applying voltage pulses. This process was shown to be forming free and a strong relaxation after switching was found. We rationalize our results by considering oxygen vacancies migration to and from the metal–oxide interface, resulting in variations of the Schottky potential barrier height that modulate the interface resistance.     

Evidence for an oxygen diffusion model for the electric pulse induced resistance change effect in transition-metal oxides

Electric-pulse induced resistance hysteresis switching loops for Pr0.7Ca0.3MnO3 perovskite oxide films were found to exhibit an additional sharp "shuttle tail" peak around the negative pulse maximum for films deposited in an oxygen-deficient ambient. The resistance relaxation in time of this "shuttle tail" peak as well as resistance relaxation in the transition regions of the resistance hysteresis loop show evidence of oxygen diffusion under electric pulsing, and support a proposed oxygen diffusion model with oxygen vacancy pileup at the metal electrode interface region as the active process for the nonvolatile resistance switching effect in transition-metal oxides.     

Nonvolatile Resistive Switching and Physical Mechanism in LaCrO_3 Thin Films

Polycrystalline LaCrO_3(LCO) thin films are deposited on Pt/Ti/SiO_2/Si substrates by pulsed laser deposition and used as the switching material to construct resistive random access memory devices. The unipolar resistive switching(RS) behavior in the Au/LCO/Pt devices exhibits a high resistance ratio of ~104 between the high resistance state(HRS) and low resistance state(LRS) and exhibits excellent endurance/retention characteristics.The conduction mechanism of the HRS in the high voltage range is dominated by the Schottky emission, while the Ohmic conduction dictates the LRS and the low voltage range of HRS. The RS behavior in the Au/LCO/Pt devices can be understood by the formation and rupture of conducting filaments consisting of oxygen vacancies,which is validated by the temperature dependence of resistance and x-ray photoelectron spectroscopy results.Further analysis shows that the reset current I_R and reset power P_R in the reset processes exhibit a scaling law with the resistance in LRS(R_0), which indicates that the Joule heating effect plays an essential role in the RS behavior of the Au/LCO/Pt devices.     

过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器性能的影响

实验表明掺杂是一种改善阻变存储器性能的有效手段,但其物理机理鲜有研究.本文采用第一性原理方法系统研究了过渡金属元素X(X=Mn,Fe,Co,Ni)掺杂对ZnO基阻变存储器中氧空位迁移势垒和形成能的影响.计算结果表明Ni掺杂可同时有效降低+1和+2价氧空位在掺杂原子附近的迁移势垒,X掺杂均减小了氧空位的形成能,特别是掺杂Ni时氧空位的形成能减小最为显著(比未掺杂时减少了64%).基于该结果制备了未掺杂和Ni掺杂ZnO阻变存储器,研究表明通过掺杂控制体系中氧空位的迁移势垒和形成能,可以有效改善器件的初始化过程、操作电压、保持性等阻变性能.研究结果有助于理解探究影响阻变的微观机制,并可为掺杂提高阻变存储器性能提供一定的理论指导.     

Fabrication and photoluminescence characteristics of In2O3 nanohillocks

Uniformly distributed polycrystalline indium nanohillocks are synthesized on silicon substrates with Au catalyst by using the radio frequency magnetic sputtering technique. The results show that the Au catalyst plays a key role in the formation of indium nanohillocks. After thermally oxidizing the indium nanohillocks at 500 ℃ in air for 5 h, the indium nanohillocks totally transform into In₂O₃ nanohillocks. The energy-dispersive X-ray spectroscopy result indicates that many oxygen vacancies and oxygen-indium vacancy pairs exist in the In₂O₃ nanohillocks. Photoluminescence spectra under an Ne laser excitation at 280 nm show broad emissions at 420 nm and 470 nm with a shoulder at 450 nm related to oxygen vacancies and oxygen-indium vacancies at room temperature.