Bipolar Resistance Switching Characteristics of ZnO/Nb-Doped SrTiO3 Heterojunctions

An electrical pulse induced resistance switching effect in ZnO/Nb-doped SrTiO3 heterojunctions is reported. The current-voltage curves of these junctions show hysteresis. Multi-resistance states are realized by applying voltage pulses with different amplitudes, and the resistance switching effect is more remarkable at low temperatures. The junction capacitance decreases dramatically with increasing frequency. Analysis of the results suggests that the trapping-detrapping process plays an important role in the resistance switching effect.     

Electric pulse-induced resistive switching in ceramic interfaces

We show the existence of a reversible, complementary and polarity dependant electric pulse-induced resistance (EPIR) switching effects in Au/YBa₂Cu₃O_7-δ ceramic superconductor interfaces. Non-volatile high and low resistance states and transition regions between them are obtained as a function of the amplitude and polarity of the pulsing voltage. Relaxation processes of the resistivity after applying the pulses, not associated with heating effects, are also observed. We also report on the temperature sensitivity of these resistance hysteresis switching loops, where both the difference between high and low resistance states and the voltage needed to produce the switching decrease with increasing temperature. Our results are consistent with a mechanism for the EPIR effect based on oxygen electromigration.     

Thermal Stability of Reliable Polycrystalline Zirconium Oxide for Nonvolatile Memory Application

Thermal stability of resistive switching of stoichiometric zirconium oxide thin films is investigated for high yielding nonvolatile memory application. The A1/ZrO2/AI cell fabricated in the conventional device process shows highly reliable switching behaviour between two distinct stable resistance states. The retention capabilities are also tested under various conditions and temperatures. The excellent performance of Ai/ZrO2/AI ceil can be explained by assuming that anode/ZrO2 interface exists and by conducting filament forming/rupture mechanism. The device failure is illustrated in terms of permanent conducting filaments formation.     

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.     

Resistance Switching Characteristic and Charge Carrier Self-Trapping in Epitaxial Pr0.7（Ca1-xSrx）0.3MnO3 Thin Films

Carrier injection performed in Pro.7 Cao.aMnOa junctions demonstrate resistance switching （RS） characteristic with dramatic changes in both resistances and interface barriers, which suggests a charge carrier self-trapping model in strongly correlated electronic framework. Un-stable RS behaviour without electric fields in epitaxial Pr0.7（Ca1-xSrx）0.3MnO3 （PCSMO） films shows dependences on insulator-metal transition temperature, which indicates that RS process is really related to the intrinsic property of carriers. The switched resistance of epitaxial PCSMO films also depends on the amount of current pulses, which shouM be another evidence of the carrier self-trapping model, similarly to the dependence on the amount of self-trapped charge carriers.     

Influence of Substrate on the Transportation Properties of Co/Alq3 Granular Films on a Si Wafer

A series of Co0.48 （Alq3）0.52 granular films were deposited on silicon substrates using the co-evaporating technique. A crossover of magnetoresistance （MR） from negative to positive was observed in the samples, due to conducting channel switching. The transport properties of samples are greatly influenced by hydrofluoric acid pretreatment, as a result, positive MR decreases drastically and the temperature dependence of resistance changes a lot near room temperature. The result indicates that the native oxide layer plays an important role in the transport mechanism. Moreover, different resistivities of Si substrates influence the current distribution of conducting channels, leading to different transport behaviors accordingly.     

Improved Resistive Switching Characteristics of Ag-Doped ZrO2 Films Fabricated by Sol-Gel Process

Ag-doped and pure ZrO₂ thin films are prepared on Pt/Ti/SiO₂/Si substrates by sol-gel process for resistive random access memory application. The highly reproducible resistive switching is achieved in the 10% Ag-doped ZrO₂ devices. The improved resistive switching behaviour in the Ag doped ZrO₂ devices could be attributed to Ag doping effect on the formation of the stablefilamentary conducting paths. In addition, dual-step reset processes corresponding to three stable resistance states are observed in the 10% Ag doped ZrO₂ devices, which may be implemented for the application of multi-bit storage.     

Coexistence of nonvolatile unipolar and volatile threshold resistive switching in the Pt/LaMnO3/Pt heterostructures

Coexistence of nonvolatile unipolar and volatile threshold resistive switching is observed in the Pt/LaMnO₃ (LMO)/Pt heterostructures. The nonvolatile unipolar memory is achieved by applying a negative bias, while the volatile threshold resistive switching is obtained under a positive bias. Additionally, the pristine low resistance state (LRS) could be switched to high resistance state (HRS) by the positive voltage sweeping, which is attributed to the conduction mechanism of Schottky emission. Subsequently, the insulator-to-metal transition in the LMO film due to formation of ferromagnetic metallic phase domain contributes to the volatile threshold resistive switching. However, the nonvolatile unipolar switching under the negative bias is ascribed to the formation/rupture of oxygen-vacancy conducting filaments. The simultaneously controllable transition between nonvolatile and volatile resistance switching by the polarity of the applied voltage exhibits great significance in the applications of in-memory computing technology.     

Resistance-switching properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> thin films with Ag–Al alloy top electrodes

A novel Ag–Al alloy electrode has been prepared on the La_0.67Ca_0.33MnO₃ (LCMO) film grown by pulsed laser deposition, with the aim to improve its resistance-switching properties. Nonlinear, asymmetric, and hysteretic current–voltage characteristics and reversible polarity-dependent switching properties are achieved in the Ag–Al alloy/LCMO/Pt structure. Detailed current–voltage characteristics analysis indicates that the resistance-switching behavior can be well explained by the mechanism of trap-controlled space charge limited conduction at the Ag–Al alloy/LCMO interface. The LCMO film with an Ag–Al alloy top electrode exhibits much better resistance-switching properties than that with an Al top electrode, including the shorter switching time and more stable switching process, demonstrating that the Ag–Al alloy electrode is a promising electrode materials of manganite films for resistance random access memory applications.     

Reactive Ion Etching as Cleaning Method Post Chemical Mechanical Polishing for Phase Change Memory Device

In order to improve nano-scale phase change memory performance, a super-clean interface should be obtained after chemical mechanical polishing （CMP） of Ge2Sb2Te5 phase change films. We use reactive ion etching （RIE） as the cleaning method. The cleaning effect is analysed by scanning electron microscopy and an energy dispersive spectrometer. The results show that particle residue on the surface has been removed. Meanwhile, Ge2Sb2Te5 material stoichiometric content ratios are unchanged. After the top electrode is deposited, currentvoltage characteristics test demonstrates that the set threshold voltage is reduced from 13 V to 2.7V and the threshold current from 0.1 mA to 0.025 mA. Furthermore, we analyse the RIE cleaning principle and compare it with the ultrasonic method.     

Analysis of resistive switching behaviors of vanadium oxide thin film

We demonstrated the polarization of resistive switching for Cu/VO_x/Cu memory cell. Switching behaviors of Cu/VO_x/Cu cell were tested by semiconductor device analyzer (Agilent B1500A), and the relative micro-analysis of I-V characteristics of VO_x/Cu was characterized by conductive atomic force microscope (CAFM). The I-V test results indicated that both forming and the reversible resistive switching between low resistance state (LRS) and high resistance state (HRS) can be observed under either positive or negative sweep. The CAFM images for LRS and HRS directly exhibited evidences of the formation and rupture of filaments based on positive or negative voltage. Cu/VO_x/Cu sandwiched structure exhibits a reversible resistive switching behavior and shows potential applications in the next generation nonvolatile memory field.     

Performance Improvement of Bulk Heterojunction Organic Photovoltaic Cellby Addition of a Hole Transport Material

A novel photovoltaic cell with an active layer of poly（phenyleneethynylene） （PPE）/C60/N,N＇-diphenyl-N,N＇-di-（m-tolyl）-p-benzidine （TPD） is designed. In the active layer, PPE is the major component; C60 and TPD are the minor ones. Compared with a control BHJ device based on PPE/C60, the short circuit current density Jsc is increased by 1 order of magnitude, and the whole device performance is increased greatly, however the open circuit voltage Voc is largely decreased. The possible mechanism of the improved performance may be as follows： In the PPE/C60/TPD device, PPE, C60, and TPD serve as the energy harvesting material, the electron transport material, and the hole transport material, respectively. As the TPD and C60 are spatially separated by PPE, the charge recombination is effectively retarded.     

Fatigue behavior of the electric pulse induced reversible resistance change effect in AgLa0.7Ca0.3MnO3Pt sandwich

La_0.7Ca_0.3MnO₃ (LCMO) films were prepared by a chemical solution deposition method on a Pt/Si substrate. Reversible resistance switching by electric pulses is observed in Ag/LCMO/Pt sandwich structures. This R switching behavior shows fatigue with time and applied pulse number. The voltage threshold, the stability and the durability of the reversible R switching are improved by annealing the LCMO films under oxygen atmosphere. PACS 73.40.-c; 75.70.Cn; 81.15.-z     

Development and Characterization of Metal-Insulator-Metal Capacitors with SiNx Thin Films by Plasma-Enhanced Chemical Vapor Deposition

We report the fabrication of high breakdown voltage metal-insulator-metal （MIM） capacitors with 200-nm silicon nitride deposited by plasma-enhanced chemical vapor deposition with 0.957 SiH4/NH3 gas mixing rate, 0.9 Torr working pressure, and 60 W rf power at 250℃ chamber temperature. Some optimized mechanisms such as metal source wiping, pre-melting and evaporation rate adjustment are used for increasing the yield of the MIM capacitors. N2 annealing and O2/H2 plasma pre-deposition treatment is proposed to increase the reliability of the MIM capacitors in high-temperature, high-pressure, and high-humidity environments. A 97% yield and up to 148 V breakdown voltage of a 13.06pF MIM capacitor with 0.04 mm^2 die area can be fabricated.     

Effects of Interfacial Polarization on Voltage Tunability of Pb(Fe1/2Nb1/2)1-xTixO3 Single Crystals

The voltage tunability of Pb(Fe_1/2Nb_1/2)_1-xTi_xO₃ single crystals is investigated at a low electric field (<130 V/cm) in a low frequency range (<1 MHz). The results show that the capacitance is strongly suppressed by the applied dc biases for both the rhombohedral sample and the tetragonal sample. A negative voltage tunability is only detected in the tetragonal sample. The origin of the giant tunability and the negative tunability is discussed based on the multipolarization-mechanism model and the equivalent circuit model, respectively. It is ascribed to the interfacial polarization at the interface of electrode/sample.     

The influence of polarity on trigatron switching performance

This paper reports on a study into the effect of trigger voltage polarity and main gap voltage polarity on the switching performance of a pulse charged trigatron. The four polarity combinations possible, two homopolarity (trigger voltage and main gap voltage of the same polarity) and two heteropolarity (trigger voltage and main gap voltage of opposite polarity), were studied and compared in terms of their effect upon the switching range, delay time to breakdown, jitter, and voltage collapse time. It was found that the two heteropolarity configurations were superior to the homopolarity configurations in terms of the above switching characteristics, with the positive trigger/negative main gap heteropolarity configuration performing the best. The results are discussed, and an explanation of the influence of the polarity configuration on switching is suggested in terms of the discharge initiation mechanisms and subsequent development     

Colossal resistance switching in Pt/BiFeO3/Nb:SrTiO3 memristor

We report reversible resistance switching behaviors in Pt/BiFeO₃/Nb:SrTiO₃ memristor. The resistance of the junctions can be tuned up to about five orders of magnitude by applying voltage pulses at room temperature, which exhibits excellent retention and anti-fatigue characteristics. The high performances are promising for employing ferroelectric junctions in nonvolatile memory and logic devices. The nonvolatile resistance switching behaviors could be attributed to the formation and annihilation of trap centers in the BFO films, resulting in Poole–Frenkel emission for low resistance state and the thermionic emission for high resistance state, respectively.     

Pulsed-laser deposition of Ta-doped PZT ferroelectric films for memory applications using conductive oxide La0.25Sr0.75CoO3 and SrRuO3 electrodes

New methods for fabricating highly 𘚡¢-oriented and complete 𘜏¢-textured Pb(Ta_0.05Zr_0.48Ti_0.47)O₃ (PTZT) films on Pt/TiO₂/SiO₂/Si(001) substrates by pulsed-laser deposition have been developed using conductive oxide La_0.25Sr_0.75CoO₃ and SrRuO₃ electrodes. The 𘚡¢-preferred orientated PTZT ferroelectric capacitor was not subjected to loss of its polarization after 1᎒¹⁰ switching cycles at an applied voltage of 5 V and a frequency of 1 MHz, and the 𘜏¢-textured PTZT film capacitor retains 94.7% of its polarization after 1.5᎒¹⁰ switching cycles at 5 V and 50 kHz. The PTZT capacitors using these conductive oxide electrodes have low leakage current dominated by Schottky field emission mechanism.     

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.     

Analysis of the resistive switching behaviors of vanadium oxide thin film

We demonstrate the polarization of resistive switching for a Cu/VOx/Cu memory cell.The switching behaviors of Cu/VOx/Cu cell are tested by using a semiconductor device analyzer(Agilent B1500A),and the relative micro-analysis of I-V characteristics of VOx/Cu is characterized by using a conductive atomic force microscope(CAFM).The I-V test results indicate that both the forming and the reversible resistive switching between low resistance state(LRS) and high resistance state(HRS) can be observed under either positive or negative sweep.The CAFM images for LRS and HRS directly exhibit evidence for the formation and rupture of filaments based on positive or negative voltage.The Cu/VOx/Cu sandwiched structure exhibits reversible resistive switching behavior and shows potential applications in the next generation of nonvolatile memory.