Reproducible Resistive Switching Characteristics Research Articles

Scalable fabrication of vertically arranged Bi2Se3 crossbar arrays for memristive device applications

Despite the unique advantages of the memristive switching devices based on two-dimensional (2D) transition metal dichalcogenides, scalable growth technologies of such 2D materials and wafer-level fabrication remain challenging. In this work, we present the gold-assisted large-area physical vapor deposition (PVD) growth of Bi2Se3 features for the scalable fabrication of 2D-material-based crossbar arrays of memristor devices. This work indicates that gold layers, prepatterned by photolithography processes, can catalyze PVD growth of few-layer Bi2Se3 with 100-folds larger crystal grain size in comparison with that grown on bare Si/SiO2 substrates. We also present a fluid-guided growth strategy to improve growth selectivity of Bi2Se3 on Au layers. Through the experimental and computational analyses, we identify two key processing parameters, i.e., the distance between Bi2Se3 powder and the target substrate and the distance between the leading edges of the substrate and the substrate holder with a hollow interior, which plays a critical role in realizing large-scale growth. By optimizing these growth parameters, we have successfully demonstrated cm-scale highly-selective Bi2Se3 growth on crossbar-arrayed structures with an in-lab yield of 86%. The whole process is etch- and plasma-free, substantially minimizing the damage to the crystal structure and also preventing the formation of rough 2D-material surfaces. Furthermore, we also preliminarily demonstrated memristive devices, which exhibit reproducible resistance switching characteristics (over 50 cycles) and a retention time of up to 106 s. This work provides a useful guideline for the scalable fabrication of vertically arranged crossbar arrays of 2D-material-based memristive devices, which is critical to the implementation of such devices for practical neuromorphic applications.

Uniform Self-rectifying Resistive Switching Behavior via Preformed Conducting Paths in a Vertical-type Ta2O5/HfO2-x Structure with a Sub-μm(2) Cell Area.

To replace or succeed the present NAND flash memory, resistive switching random access memory (ReRAM) should be implemented in the vertical-type crossbar array configuration. The ReRAM cell must have a highly reproducible resistive switching (RS) performance and an electroforming-free, self-rectifying, low-power-consumption, multilevel-switching, and easy fabrication process with a deep sub-μm(2) cell area. In this work, a Pt/Ta2O5/HfO2-x/TiN RS memory cell fabricated in the form of a vertical-type structure was presented as a feasible contender to meet the above requirements. While the fundamental RS characteristics of this material based on the electron trapping/detrapping mechanisms have been reported elsewhere, the influence of the cell scaling size to 0.34 μm(2) on the RS performance by adopting the vertical integration scheme was carefully examined in this work. The smaller cell area provided much better switching uniformity while all the other benefits of this specific material system were preserved. Using the overstressing technique, the nature of RS through the localized conducting path was further examined, which elucidated the fundamental difference between the present material system and the general ionic-motion-related bipolar RS mechanism.

Influence of 120 MeV Au+9 ions irradiation on resistive switching properties of Cr:SrZrO3/SRO junctions

Swift heavy ion (SHI) irradiation has been successfully used to modify structural and electrical properties of heterostructured Cr doped SrZrO3 thin films grown on 200nm thick SrRuO3/SiO2 by chemical solution deposition method. Samples were irradiated by 120MeV Au+9 ions with fluence value 1 × 1012 ions/cm2 in order to investigate the influence of SHI irradiation on the resistive switching (RS) phenomenon. Structural characterization with grazing angle X-ray diffraction exhibited an enhancement of crystallinity as well as crystallographic strain. Typical energy dispersive analysis of X-rays (EDAX) spectrum was carried out to study the interface mixing, if any, after the ion irradiation. The pristine sample exhibits a narrow hysteresis loop in the current voltage (I–V) curves with maximum RS ratio of 98. Highly reproducible resistive switching characteristics with pronounced loops in the I–V curves have been observed for the irradiated Ag/Cr:SZO/SRO structure with maximum RS ratio of 985. I–V curves in low resistive state (LRS) demonstrate linear Ohmic conduction mechanism for both positive as well as negative bias region. The high resistive state (HRS) is consistent with space charge limited (SCLC) mechanism. The observed electrical behavior can be attributed to the high energy density of electronic excitations resulting from the impact of swift heavy ions induced defects and strain.

Low-cost bidirectional selector based on Ti/TiO2/HfO2/TiO2/Ti stack for bipolar RRAM arrays

In this paper, a low-cost Ti/TiO2/HfO2/TiO2/Ti stack structure is proposed as a selector for bipolar resistive random access memory (RRAM) cross-bar array applications. We demonstrate reproducible resistive switching characteristics with significant nonlinearity and good uniformity in the one selector and one resistor (1S1R) structure device that integrate the bidirectional selector with a bipolar Pt/Ti/HfO2/Pt RRAM device. These results provide a good point of reference for evaluating the potential low-cost applications in bipolar RRAM cross-bar array.

Resistive switching in lateral junctions with nanometer separated electrodes

Resistive switching in lateral tunnel junctions is reported. Nanogap tunnel junctions made of Au/SiO2/Au and Au/TiO2/Au were patterned by electrical-beam-lithography (EBL) and a controlled electromigration process. Depending on the substrate material, different reproducible resistive switching characteristics were observed under vacuum conditions. While for TiO2 substrates bipolar resistive switching was observed, nanogap junctions on SiO2 substrates showed resistive switching characteristics with a negative differential resistance. The role of the substrate material with respect to the resistive switching behavior is discussed in the framework of the electrical breakdown. All experiments were performed under vacuum to suppress parasitic effects due to charged particles in ambient air. Nanogap resistive switching devices are promising candidates for densely integrated memresistive systems such as non-volatile resistive random memories (RRAMs), field programmable arrays (FPGAs), or artificial neural networks (ANNs).

Cu-Embedded AlN-Based Nonpolar Nonvolatile Resistive Switching Memory

This letter covers the fabrication of a nonpolar resistive switching (RS) random access memory device using Cu-embedded AlN and its reproducible RS characteristics. The AlN-based memory device shows endurance of >; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , reliable retention time (ten years extrapolation at both room temperature and 85°C), and fast programming speed under 100-ns pulses in unipolar operation mode. The switching mechanism is believed to be mediated by the formation and rupture of conductive Cu filaments.

Study of the Resistive Switching Characteristics and Mechanisms of Pt/CeOx/TiN Structure for RRAM Applications

Pt (top)/CeOx/ TiN (bottom) sandwich structures with nonstoichiometric CeOx (1.3 < x < 2) films were fabricated by radio-frequency magnetron sputtering system. Their reproducible resistive switching characteristics were study systematically for resistive random access memory (RRAM) applications. The X-ray photoelectron spectroscopy was performed to analyze the mechanisms of resistive switching (RS) of CeOx-based films. The results show that both the oxygen vacancies in the CeOx film and the interfacial TiON layer formed between the dielectric CeOx film and the TiN bottom electrode play important roles in the observed RS behaviors.

Low-Power and Highly Reliable Multilevel Operation in $ \hbox{ZrO}_{2}$ 1T1R RRAM

The Ti/ZrO2/Pt resistive memory devices with one transistor and one resistor (1T1R) architecture are successfully fabricated in this letter. The tested devices show low operation current (20 μA), low switching voltage (set/reset, 0.8/-1 V), and reliable data retention for low-resistance state (LRS) with a 20-μA set current at 80°C (over ten years) via an excellent current limiter, namely, a metal-oxide-semiconductor field-effect transistor (MOSFET). In addition, multilevel storage characteristics are also demonstrated by modulating the amplitude of the MOSFET gate voltage. The various LRS levels obtained are possibly attributed to the formation of different numbers and sizes of conducting filaments consisting of oxygen vacancies caused by an external electric field. Moreover, reproducible resistive switching characteristics up to 2000 switching cycles are achieved in the same device. Our 1T1R ZrO2-based resistive switching access memory with low-power and highly reliable multilevel operation has high potential for practical applications.

Effects of oxygen partial pressure on resistive switching characteristics of ZnO thin films by DC reactive magnetron sputtering

Cu/ZnO/n +-Si structures were prepared by magnetron sputtering of a layer of ZnO thin film onto heavily doped silicon substrate, followed by thermal evaporation of a thin layer of metallic Cu. The resistive switching characteristics of Cu/ZnO/n +-Si structures were investigated as a function of oxygen partial pressure during ZnO deposition. Reproducible resistive switching characteristics were observed in ZnO thin films deposited at 20%, 33% and 50% oxygen partial pressure ratios while ZnO thin film deposited at 10% oxygen partial pressure ratio did not show resistive switching behavior. The conduction mechanisms in high and low resistance states are dominated by space-charge-limited conduction and ohmic behavior respectively, which suggests that resistive switching behaviors in such structures are related to filament formation and rupture. It is also found that the reset current decreases as oxygen partial pressure increases, due to the variation of oxygen vacancy concentration in the ZnO thin films.

Mass fabrication of resistive random access crossbar arrays by step and flash imprintlithography

Step and flash imprint lithography (SFIL) is a promising method recently used for nextgeneration lithographic technology because it is a high-speed process that canbe carried out at room temperature and low pressures. Improvements made toSFIL enable the replication of crossbar patterns with a high resolution and thedevelopment of suitable materials and techniques to achieve high resolution capability. Inthis study, SFIL is used to fabricate high-density random access crossbar arraysbased on a NiO resistive switching system. The bottom and top electrodes aretransferred onto silicon wafers perpendicular to each electrode using the inductivelycoupled plasma reactive ion etching (ICP-RIE) technique. Direct metal etchingwithout a wet-based process minimizes damage to the electrode surface. TheI–V curves of individualactive cells (70 × 70 nm2) for crossbar arrays reveal the unipolar resistive switching (RS) behaviour of the fabricated device. A highoff/on resistanceratio (>104) and reproducible resistance switching characteristics for each active cell were found indifferent fields and for different wafers. The experimental data indicate that high-densitycrossbar arrays can be well replicated and that the electrical performance of these arrays isreliable.

Study on Resistance Switching Properties of Na0.5Bi0.5TiO3Thin Films Using Impedance Spectroscopy

The Na0.5Bi0.5TiO3(NBT) thin films sandwiched between Au electrodes and fluorine-doped tin oxide (FTO) conducting glass were deposited using a sol–gel method. Based on electrochemical workstation measurements, reproducible resistance switching characteristics and negative differential resistances were obtained at room temperature. A local impedance spectroscopy measurement of Au/NBT was performed to reveal the interface-related electrical characteristics. The DC-bias-dependent impedance spectra suggested the occurrence of charge and mass transfer at the interface of the Au/NBT/FTO device. It was proposed that the first and the second ionization of oxygen vacancies are responsible for the conduction in the low- and high-resistance states, respectively. The experimental results showed high potential for nonvolatile memory applications in NBT thin films.

Reproducible resistance switching characteristics of hafnium oxide-based nonvolatile memory devices

The resistance switching characteristics of HfO2 thin films deposited by reactive sputtering were examined as a function of the annealing temperature. The results showed that the Pt/HfO2/Pt devices exhibited reversible and steady bistable resistance states [high-resistance state (HRS) and low-resistance state (LRS)]. Reproducible resistance switching from one state to another state or vice versa could be achieved by applying the appropriate voltage bias. The memory performances were related to the crystal structures of the HfO2 films, as confirmed by x-ray diffraction. From current-applied voltage analysis of the devices, LRS in the low electric field regime exhibited Ohmic conduction behavior, while HRS in the high electric field was followed by Poole–Frenkel conduction behavior. The resistance ratios of the two states were maintained in the range of around two orders of magnitude during the endurance test. In addition, it was confirmed that the resistance of the on and off states can be well maintained according to the time elapsed.