Bipolar resistance switching in the fully transparent BaSnO_3-based memory device

The fully transparent indium-tin-oxide/BaSnO3/F-doped SnO2 devices that show a stable bipolar resistance switching effect are successfully fabricated. In addition to the transmittance being above 87% for visible light, an initial forming process is unnecessary for the production of transparent memory. Fittings to the current-voltage curves reveal the interfacial conduction in the devices. The first-principles calculation indicates that the oxygen vacancies in cubic BaSnO3 will form the defective energy level below the bottom of conduction band. The field-induced resistance change can be explained based on the change of the interracial Schottky barrier, due to the migration of oxygen vacancies in the vicinity of the interface. This work presents a candidate material BaSnO3 for the application of resistive random access memory to transparent electronics.     

酞菁铜非共振反饱和吸收的稳态特性

酞菁铜溶液在波长532nm调Q激光作用下,实验获得反饱和吸收特性.在稳态条件下,用速率方程理论推得分别描述薄样品和厚样品的反饱和吸收特性的两个解析式,理论分析与实验结果一致.     

酞菁铜成膜特性的多重分形谱

运用多重分形理论,研究了酞菁铜颗粒的团聚生长成膜特性.研究表明薄膜生长是远离平衡态过程,在团聚生长中,颗粒分布有很大随机性,存在大范围的非均匀区域,这些区域具有多重分形特征.测试了酞菁铜对二氧化氮的气敏特性,结果表明通气前后,涂膜通道的频率有明显移动.     

酞菁铜染料的反饱和吸收动力学

本文用速率方程研究了酞菁铜染料氯仿溶液的反饱和吸收的动力学过程,并用YAG倍频调Q脉冲激光入射该样品,验证了理论.通过理论曲线与实验结果的拟合,估算出酞菁铜三重态激发态的吸收截面为2.6×10~(-17)cm~2.     

Light-induced negative differential resistance effect in a resistive switching memory device

The negative differential resistance (NDR) effect was observed in a Pt/BiFeO₃/TiO₂/BiFeO₃/Pt memory cell by using light-illumination as extra stimulation. Further, the coexistence appearances and gradually becomes obvious when the device is exposed to light-illumination, which display an excellent stability and reversibility of the coexistence of NDR and resistive switching (RS) at room temperature. Through analysis of the physical conduction mechanism, it is expected that a large number of photo-generated charge carriers are induced under light-illumination on the surface and interface of the heterojunction is responsible for the appearance of this coexistence phenomenon. Importantly, the NDR effect is strengthened by the competition transfer of charge carrier in the polarized electric field under light-illumination. This work shows that the coexistence of light-modulated NDR and RS can deeply explore the potential applications of light-controlled multifunctional devices.     

Atomic crystals resistive switching memory

Facing the growing data storage and computing demands, a high accessing speed memory with low power and non volatile character is urgently needed. Resistive access random memory with 4F~2 cell size, switching in sub-nanosecond cycling endurances of over 10~(12) cycles, and information retention exceeding 10 years, is considered as promising nex generation non-volatile memory. However, the energy per bit is still too high to compete against static random acces memory and dynamic random access memory. The sneak leakage path and metal film sheet resistance issues hinder th further scaling down. The variation of resistance between different devices and even various cycles in the same device hold resistive access random memory back from commercialization. The emerging of atomic crystals, possessing fin interface without dangling bonds in low dimension, can provide atomic level solutions for the obsessional issues. Moreove the unique properties of atomic crystals also enable new type resistive switching memories, which provide a brand-new direction for the resistive access random memory.     

CdTe量子点-铜酞菁复合体系荧光共振能量转移的研究

以波长为780 nm、重复频率为76 MHz、脉宽为130 fs的飞秒激光作为激发光源, 采用超快时间分辨光谱技术研究了CdTe量子点-铜酞菁复合体系的荧光共振能量转移. 实验结果表明, 在780 nm的双光子激发条件下, 复合体系中CdTe量子点的荧光寿命随着铜酞菁溶液浓度的增加而减少, 荧光共振能量转移效率增加. 同时也研究了激发功率对荧光共振能量转移效率的影响. 结果表明, 随着激发光功率的增加, 复合体系溶液中CdTe量子点的荧光寿命增加, 荧光共振能量转移效率减小, 其物理机理是因为高激发功率下的热效应和由双光子诱导的高阶激发态的跃迁. 当激发光功率为200 mW时, 双光子荧光共振能量转移效率为43.8%. 研究表明CdTe量子点-铜酞菁复合体系是非常有潜力的第三代光敏剂.     

Experimental and theoretical investigation of vibrational spectra of copper phthalocyanine: polarized single‐crystal Raman spectra,isotope effect and DFT calculations

The IR‐ and Raman spectra of copper phthalocyanine (CuPc), as well as the isotopic wavenumber shifts upon ¹⁵N substitution in CuPc, were investigated experimentally and theoretically. The symmetry of molecular vibrations was determined using polarized Raman spectra of an oriented CuPc single crystal. Density functional theory (DFT) calculations were used for the detailed assignment of different bands in the vibrational spectra of CuPc. Theoretically predicted geometry, wavenumbers and isotopic shifts are in a very good agreement with the experimental values. A comparison of experimentally obtained isotopic shifts with theoretical predictions allowed us to reveal some characteristic features of normal vibrations of CuPc molecule. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation,magnetic and electromagnetic properties of organic magnetic prepolymer containing copper phthalocyanine ring

A novel kind of organic magnetic prepolymer containing copper phthalocyanine ring was prepared via the polymerization of ferrocenyl organic metal magnetic resin (FOMR) with cuprous chloride. The process of prepolymerization was monitored by Fourier transform infrared spectroscopy and ultraviolet–visible spectrophotometry. Magnetic behavior of the samples was studied by a vibrating sample magnetometer.     

Dielectric-breakdown-like forming process in the unipolar resistance switching of Ta2O5−x thin films

We report unipolar resistance switching (URS) in Ta₂O_5−x thin films. The current increased suddenly when we applied voltages up to 5-7 V to the pristine state of Pt/Ta₂O_5−x/Pt, Ni/Ta₂O_5−x/Pt, and Ti/Ta₂O_5−x/Pt cells. Just after this forming process, we observed a repetitive URS occurring independently of the electrodes. We found that the required voltages for the forming process did not depend on the top electrode type, but on the film thickness. These results suggest that the forming process is driven by a dielectric-breakdown-like phenomenon, and that URS occurs due to the formation and rupture of conducting channels inside the Ta₂O_5−x thin film.     

Analysis and modeling of resistive switching mechanisms oriented to resistive random-access memory

With the progress of the semiconductor industry,the resistive random-access memory(RAM) has drawn increasing attention.The discovery of the memristor has brought much attention to this study.Research has focused on the resistive switching characteristics of different materials and the analysis of resistive switching mechanisms.We discuss the resistive switching mechanisms of different materials in this paper and analyze the differences of those mechanisms from the view point of circuitry to establish their respective circuit models.Finally,simulations are presented.We give the prospect of using different materials in resistive RAM on account of their resistive switching mechanisms,which are applied to explain their resistive switchings.     

Twin—layer films of copper phthalocyanine and amorphous titanyl or vanadyl phthalocyanine

Metallophthalocyanine (MPc) twin-layer thin films on glass substrates, consisting of copper phthalocyanine (CuPc) overlayer and amorphous vanadyl phthalocyanine (VOPc) as well as titanyl phthalocyanine (TiOPc) buffers, were found to have different gas sensing characteristics. These twin-layer thin films were studied using x-ray photoemission spectroscopy. Photoelectrons of either V or Ti core levels were found to be present at the surface, indicating the existence of possible molecular migrations. The stability of the twin-layers under thermal annealing up to a maximum temperature of 250℃ and low-energy Ar ion bombardment was also examined and compared with that of CuPc directly grown on the substrates. We concluded that the twin-layer structures were thermally fairly stable. Ar ion bombardment, however, caused substantial damage to the Pc ligands and a reduction of the valence state of the central Cu atoms.     

Threshold resistance switching in silicon-rich SiO_x thin films

Si-rich SiO_x and amorphous Si clusters embedded in SiO_x films were prepared by the radio-frequency magnetron cosputtering method and high-temperature annealing treatment.The threshold resistance switching behavior was achieved from the memory mode by continuous bias sweeping in all films,which was caused by the formation of clusters due to the local overheating under a large electric field.Besides,the Ⅰ-Ⅴ characteristics of the threshold switching showed a dependence on the annealing temperature and the SiO_x thickness.In particular,formation and rupture of conduction paths is considered to be the switching mechanism for the 39 nm-SiO_x film,while for the 78 nm-SiO_x film,adjusting of the Schottky barrier height between insulator and semiconductor is more reasonable.This study demonstrates the importance of investigation of both switching modes in resistance random access memory.     

Dynamical switching and memory via incoherent pump assisted optical bistability

We analyze the dynamical behavior of all-optical switching and memory based on tunable optical bistability in a three-level Λ-type atomic system driven by a probe field circulating in an optical ring cavity, a coherent coupling field and an incoherent pump field outside cavity. Owing to the incoherent pump process, the absorption and Kerr nonlinearity near the atomic resonance change dramatically as a result of varied population distribution and atomic coherence, and then the switch-up and switch-down thresholds, as well as the width (or area) of bistable curve, can be manipulated effectively. By tuning the intensity of either coherent coupling field or incoherent pump field, we can make the system output flip between the lower and upper branches of different bistable hysteresis loops while the cavity input keeps to a constant value. Accordingly, all-optical switching and memory can be implemented via dynamical control of the bistable behavior under the assistance of incoherent pump. The proposed scheme can find potential applications in all-optical communication and computation.     

Resistive switching memory for high density storage and computing

The resistive random access memory (RRAM) has stimulated a variety of promising applications including programmable analog circuit, massive data storage, neuromorphic computing, etc. These new emerging applications have huge demands on high integration density and low power consumption. The cross-point configuration or passive array, which offers the smallest footprint of cell size and feasible capability of multi-layer stacking, has received broad attention from the research community. In such array, correct operation of reading and writing on a cell relies on effective elimination of the sneaking current coming from the neighboring cells. This target requires nonlinear I-V characteristics of the memory cell, which can be realized by either adding separate selector or developing implicit build-in nonlinear cells. The performance of a passive array largely depends on the cell nonlinearity, reliability, on/off ratio, line resistance, thermal coupling, etc. This article provides a comprehensive review on the progress achieved concerning 3D RRAM integration. First, the authors start with a brief overview of the associative problems in passive array and the category of 3D architectures. Next, the state of the arts on the development of various selector devices and self-selective cells are presented. Key parameters that influence the device nonlinearity and current density are outlined according to the corresponding working principles. Then, the reliability issues in 3D array are summarized in terms of uniformity, endurance, retention, and disturbance. Subsequently, scaling issue and thermal crosstalk in 3D memory array are thoroughly discussed, and applications of 3D RRAM beyond storage, such as neuromorphic computing and CMOL circuit are discussed later. Summary and outlooks are given in the final.     

Enhanced resistance switching stability of transparent ITO/TiO2/ITO sandwiches

We report that fully transparent resistive random access memory(TRRAM) devices based on ITO/TiO2/ITO sandwich structure,which are prepared by the method of RF magnetron sputtering,exhibit excellent switching stability.In the visible region(400-800 nm in wavelength) the TRRAM device has a transmittance of more than 80%.The fabricated TRRAM device shows a bipolar resistance switching behaviour at low voltage,while the retention test and rewrite cycles of more than 300,000 indicate the enhancement of switching capability.The mechanism of resistance switching is further explained by the forming and rupture processes of the filament in the TiO 2 layer with the help of more oxygen vacancies which are provided by the transparent ITO electrodes.     

分子包埋纳米粒子薄膜阻变特性研究进展

有机分子包埋纳米粒子阻变薄膜是信息存储领域的研究热点之一,本文从器件电极、介质层结构、纳米粒子种类、阻变机理和柔性弯折等方面,综述了其近年来的研究进展.电极/分子及分子/纳米粒子界面性质对器件阻变特性影响较大,但影响规律及界面调控机理仍待探究;分子结构与纳米粒子的种类、尺度及分布可改变膜内界面性质进而影响阻变特性;器件阻变机理主要包括导电细丝、电荷俘获与释放和电荷转移三种,其中导电细丝又分金属、氧空位和碳细丝.分子包埋纳米粒子薄膜阻变研究现多停留在小规模和静态器件方面,下一步应从连续卷绕制备、纳米粒子分布精确控制和耐弯扭特性等方面深入研究,为实现大面积、低成本、高柔性阻变存储器奠定基础.     

Resistance switching memory in perovskite oxides

The resistance switching behavior has recently attracted great attentions for its application as resistive random access memories (RRAMs) due to a variety of advantages such as simple structure, high-density, high-speed and low-power. As a leading storage media, the transition metal perovskite oxide owns the strong correlation of electrons and the stable crystal structure, which brings out multifunctionality such as ferroelectric, multiferroic, superconductor, and colossal magnetoresistance/electroresistance effect, etc. The existence of rich electronic phases, metal–insulator transition and the nonstoichiometric oxygen in perovskite oxide provides good platforms to insight into the resistive switching mechanisms.     

Self-assembly growth and electron work function of copper phthalocyanine films on indium tin oxide glass

Organic semiconductor materials are becoming a promising subject of not only scientific interest but also potential applications in the field of new energy resources. In this study, the copper phthalocyanine (CuPc) films as an excellent organic semiconductor were self-assembly grown on indium tin oxide glass by electrodeposition, the structural and electronic properties were investigated using various techniques. The results demonstrated that ordered α-form crystalline CuPc films were obtained. The decrease of electron work function of CuPc films with the increase of film thickness was found, which was obviously dependent on the surface morphology. The understanding of these behaviors of CuPc films will be significant for designing related photoelectric devices.     

Nd0.7Sr0.3MnO3陶瓷中界面“陷阱态”相关电阻转变行为

通过固相烧结和高能球磨后热处理两种方法分别得到不具晶(相)界和具有明显晶(相)界的两种Nd_0.7Sr_0.3MnO₃陶瓷样品, 并用两线法和四线法分别对这两种样品的电极-块体接触界面和晶(相)界界面的I-V和电脉冲诱导电阻转变效应(EPIR)进行研究. 结果发现, 在两线法测试下, 电极-块体界面具有回滞的非线性I-V特征, 并能产生稳定的EPIR效应, EPIR的稳定性随温度的升高逐渐减弱并消失; 而对具有明显晶(相)界的陶瓷样品, 四线法测试结果表明, 虽然其I-V行为也具有非线性和回滞性特点, 但不能产生EPIR 效应. 这些奇特的界面输运行为与界面中的各种缺陷充当“陷阱”并实现对载流子的捕捉和释放过程密切相关. 而大量的晶(相)界界面及其复杂的连接方式导致较大的漏导则是晶(相)界不能出现EPIR效应的主要原因.