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.     

Random and localized resistive switching observation in Pt/NiO/Pt

Resistive memory switching devices based on transition metal oxides are now emerging as a candidate for nonvolatile memories. To visualize nano‐sized (10 nm to 30 nm in diameter) conducting filamentary paths in the surface of NiO thin films during repetitive switching, current sensing–atomic force microscopy and ultra‐thin (<5 nm) Pt films as top electrodes were used. Some areas (or spots), which were assumed to be the beginning of the conducting filaments, appeared (formation) and disappeared (rupture) in a localized and random fashion during the switching and are thought to contribute to resistive memory switching. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Coexistence of unipolar and bipolar modes in Ag/ZnO/Pt resistive switching memory with oxygen-vacancy and metal-Ag filaments

In this study, the unipolar resistive switching(URS) and bipolar resistive switching(BRS) are demonstrated to be coexistent in the Ag/Zn O/Pt memory device, and both modes are observed to strongly depend on the polarity of forming voltage. The mechanisms of the URS and BRS behaviors could be attributed to the electric-field-induced migration of oxygen vacancies(VO) and metal-Ag conducting filaments(CFs) respectively, which are confirmed by investigating the temperature dependences of low resistance states in both modes. Furthermore, we compare the resistive switching(RS)characteristics(e.g., forming and switching voltages, reset current and resistance states) between these two modes based on VO- and Ag-CFs. The BRS mode shows better switching uniformity and lower power than the URS mode. Both of these modes exhibit good RS performances, including good retention, reliable cycling and high-speed switching. The result indicates that the coexistence of URS and BRS behaviors in a single device has great potential applications in future nonvolatile multi-level memory.     

Charge transport and bipolar switching mechanism in a Cu/HfO_2/Pt resistive switching cell

Bipolar resistance switching characteristics are investigated in Cu/sputtered-HfO_2/Pt structure in the application of resistive random access memory(RRAM).The conduction mechanism of the structure is characterized to be SCLC conduction.The dependence of resistances in both high resistance state(HRS) and low resistance state(LRS) on the temperature and device area are studied.Then,the composition and chemical bonding state of Cu and Hf at Cu/HfO_2 interface region are analyzed by x-ray photoelectron spectroscopy(XPS).Combining the electrical characteristics and the chemical structure at the interface,a model for the resistive switching effect in Cu/HfO_2/Pt stack is proposed.According to this model,the generation and recovery of oxygen vacancies in the HfO_2 film are responsible for the resistance change.     

The effect of size on the resistive switching characteristics of NiO nanodots

NiO nanodots were fabricated via a shattering process using an AFM tip, where an NiO nanodot with a diameter of approximately 90 nm was broken into very small pieces. The pieces showed diverse diameters, including three diameters of approximately 10, 20, and 30 nm. The NiO nanodots exhibited unipolar switching characteristics including bistable resistivity during 200 repeated switching cycles. Significantly, the magnitude of the “ON currents” was observed to depend on the formation of conducting filaments in the NiO nanodots. We suggest that the critical diameter of the RRAM NiO nanodots is approximately 30 nm.     

Modeling of conducting bridge evolution in bipolar vanadium oxide-based resistive switching memory

We investigate the resistive switching characteristics of a Cu/VOx/W structure. The VOx film is deposited by radio- frequency magnetron sputtering on the Cu electrode as a dielectric layer. The prepared VOx sample structure shows reproducible bipolar resistive switching characteristics with ultra-low switching voltage and good cycling endurance. A modified physical model is proposed to elucidate the typical switching behavior of the vanadium oxide-based resistive switching memory with a sudden resistance transition, and the self-saturation of reset current as a function of compliance current is observed in the test, which is attributed to the conducting mechanism is discussed in detail. growth pattern of the conducting filaments. Additionally, the related     

Low power consumption bipolar resistive switching characteristics of ZnO-based memory devices

Ag/ZnO/Pt structure resistive switching devices are fabricated by radio frequency (RF) magnetron sputtering at room temperature. The memory devices exhibit stable and reversible resistive switching behavior. The ratio of high resistance state to low resistance state can reach as high as 10 2 . The retention measurement indicates that the memory property of these devices can be maintained for a long time (over 10 4 s under 0.1-V durable stress). Moreover, the operation voltages are very low, -0.4 V (OFF state) and 0.8 V (ON state). A high-voltage forming process is not required in the initial state, and multi-step reset process is demonstrated. Resistive switching device with the Ag/ZnO/ITO structure is constructed for comparison with the Ag/ZnO/Pt device.     

Enhanced bipolar resistive switching of HfO2 with a Ti interlayer

The characteristics of resistive switching of TiN/HfO₂/Ti/HfO₂/Pt/Ti stacks on SiO₂/Si substrates were investigated and compared to TiN/HfO₂/Pt/Ti stacks in order to study Ti interlayer effects on resistive switching. The Ti interlayers were deposited in situ during the reactive sputtering of HfO₂ films. The current–voltage measurements showed that the Ti interlayers enhanced the memory window but reduced the endurance of SET/RESET operations. The energy filtered images by TEM showed asymmetric oxygen accumulation at the Ti/HfO _x interfaces. Subsequent heat treatment improved the endurance of SET/RESET operation of TiN/HfO₂/Ti/HfO₂/Pt/Ti stacks.     

Effect of fatigue fracture on the resistive switching of TiO2-CuO film/ITO flexible memory device

We fabricated the GaIn/TiO₂-CuO/ITO resistive memory and studied the effect of fatigue fracture on the switching performance. The device shows the stable bipolar resistive switching over 10⁸ s under ambient condition. The ON/OFF ratio decreases seriously with increase of bending cycles. The main fatigue fracture caused by dynamic strain includes micro defect between nanoparticles, vertical crack along the film thickness and interfacial delamination between layers. Finite element analysis indicates that channel crack plays a key role to cause the interfacial delamination between function layer and ITO electrode. The channel crack and interfacial delamination can hinder the formation of tree−like conduction filaments. Moreover, oxygen via the cracks can be easily transformed to ions and reduce the density of oxygen vacancies under the catalytic assistance of CuO. Our studies may provide some useful information for inorganic materials applied in flexible nonvolatile memory.     

Au/SrTiO3/Au界面电阻翻转效应的低频噪声分析

本文研究了Au/SrTiO₃/Au三明治结构中的双极电阻翻转效应, 观察到高、低阻态的电阻弛豫现象. 低频噪声测量表明高、低阻态的电阻涨落表现出1/f行为. 对比试验表明, 高阻态的低频噪声来源于反向偏置肖特基势垒和氧空位的迁移, 强度较大, 低阻态的噪声则源于类欧姆接触底电极区域的氧空位迁移导致的载流子涨落, 强度较低. 同时, 界面上氧空位浓度的弛豫导致了高、低阻态的弛豫过程. 关键词： 电阻翻转效应 低频噪声 氧空位     

Reversible alternation between bipolar and unipolar resistive switching in La-SrTiO_3 thin films

The alternation from bipolar to unipolar resistive switching is observed in perovskite La0.01Sr0.99TiO3thin films.These two switching modes can be activated separately depending on the compliance current(Icomp)during the electroforming process:with a higher Icomp(5 mA)the unipolar resistance switching behavior is measured,while the bipolar resistance switching behavior is observed with a lower Icomp(1 mA).On the basis of I–V characteristics,the switching mechanisms for the URS and BRS modes are considered as being a change in the Schottky-like barrier height and/or width at the Pt/La-SrTiO3interface and the formation and disruption of conduction filaments,respectively.     

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.     

Conversion of two types of bipolar switching induced by the electroforming polarity in Au/NiO/SrTiO3/Pt memory cells

The resistive switching characteristics of Au/p-NiO/n-SrTiO₃(STO)/Pt memory cells are investigated. Two types of bipolar switching with opposite polarity coexist in the cell and can be repeatedly adjusted by the electroforming polarity. The conduction mechanisms of low resistance and high resistance states are dominated by electron tunneling and interface barrier effect, respectively. The impact of electroforming polarity on the switching mechanism and the distribution of defects are discussed. The results indicate that these two types of switching originate from a variation of interface barrier respectively at the NiO/STO p–n junction and STO/Pt Schottky contact.     

Study of the multiple-negative-differential-resistance (MNDR) switching behaviors based on heterojunction bipolar transistor (HBT) structures

In this paper, we demonstrate multiple-negative-differential-resistance (MNDR) switching behaviors based on the InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) and InGaAlAs/InP heterojunction bipolar transistor (HBT) structures. The devices act like conventional HBTs under forward operation mode. The proposed HEBTs show lower offset voltage due to the correct design of the emitter thickness. On the other hand, MNDR phenomena resulting from avalanche multiplication, confinement effects and the potential redistribution process are observed under inverted operation mode for both devices. In addition, three-terminal NDR characteristics are investigated under the applied base currentI_B . Moreover, for the InGaAlAs/InP HBT, anomalous multiple-route and multiple-step current–voltage (I–V) characteristics at 77 K are observed due to the insertion of a InGaAs quantum well (QW) between the base and collector layers.     

Transparent conductive ITO/Ag/ITO multilayer electrodes deposited by sputtering at room temperature

ITO/Ag/ITO multilayers have been prepared onto conventional soda lime glass substrates by sputtering at room temperature. The optical and electrical characteristics of single layer and multilayer structures have been investigated as a function of the Ag and ITO film thicknesses. Transmittance and sheet resistance values are found mainly dependent on the Ag film thickness; whereas the wavelength range at which the maximum transmittance is achieved can be changed by adjusting the ITO films thickness. ITO/Ag/ITO electrodes with sheet resistance below 6 Ω/sq have been obtained for Ag film thickness above 10 nm and ITO layers thickness in the 30-50 nm range. These multilayers also show high transmittance in the visible spectral region, above 90% by discounting the glass substrate, with a maximum that is located at higher wavelengths for thicker ITO.     

Photonic-sensitive InAlGaAs/InP negative-differential-resistance heterojunction bipolar transistor

A novel photonic-sensitive InAlGaAs/InP negative-differential-resistance heterojunction bipolar transistor (NDR-HBT) is fabricated and demonstrated. Due to the appropriately designed narrow base width and the employment of a δ -doped sheet at the emitter–base (E–B ) heterojunction, the base resistance effect results in the significant NDR phenomenon. In addition, the experimental results show that the device studied is very sensitive to the applied light source. The N-shaped NDR phenomena are clearly observed under illumination. This phenomenon is attributed to the base resistance and barrier lowering effect resulting from holes induced by the applied light source.     

Interface-engineered resistive switching in Ag/SrTiO3/Nd0.7Ca0.3MnO3/YBa2Cu3O7 heterostructures

For Ag/Nd_0.7Ca_0.3MnO₃/YBa₂Cu₃O₇ (Ag/NCMO/YBCO) heterostructures, we investigate effects of an SrTiO₃ (STO) buffer layer inserted into the Ag/NCMO interface upon the room-temperature resistive switching. In comparison with the non-buffered (Ag/NCMO/YBCO) structure, the insertion of the STO buffer layer can greatly enhance the electric-field-induced-resistance (EPIR) effect. The STO-buffered (Ag/STO/NCMO/ YBCO) device can be switched on-and-off between the higher to lower resistance states at an EPIR ratio of 253% with pulsed voltage ±1.5 V and 405% with pulsed voltage ±3.0 V. The enhanced EPIR ratio is attributed to a combined effect of the migration of oxygen vacancies near the interface and ferroelectric polarization of the STO buffer.