Reproducible Switching Research Articles

Low-cost green recyclable biomaterial for energy-dependent electrical switching and intact biofilm with antibacterial properties

A highly cost-effective recycled biomaterial extracted from lime peel has been made biocompatible and has been coated on a commercial fluorine-doped tin oxide (FTO) substrate of glass using the spin coating method. Structural, morphologic, electronic, and antibacterial measurements were thoroughly characterized as a green biomaterial thin film using X-rays (XRD), PL, FTIR, Raman, SEM, HRTEM, AFM, I–V, and antibacterial diffusion techniques. The comprehensive analysis of structures of recyclable waste in the form of lime peel extract (LPE) as thin films showed the crystalline cellulose structure that corresponds to the lattice fringe (0.342 nm) exposed by HRTEM. The K+1 interstitial active sites or vacancies in LPE/FTO thin films are confirmed by the PL spectra that show important evidence about conduction mechanisms, and hence facilitates Ag+1 ion migration from the top to the bottom electrode. The AFM investigations revealed the minor surface roughness (169.61 nm) of the LPE/FTO film, which controls the current leakage that is associated with surface defects. The designed memory cell (Ag/LPE/FTO) exhibits stable, reproducible electrical switching under low operational voltage and is equipped with excellent retention over 5 × 103 s. Furthermore, owing to presence of flavonoids and their superior antioxidant nature, lime peel extract powder shows tremendous antimicrobial activity against gram-positive and Gram-negative bacterial strains.

Unraveling the origin of resistive switching behavior in organolead halide perovskite based memory devices

This study investigates the operation mechanisms of organolead halide perovskite based resistive memory cells and explores the device architectures that could ensure high memory endurance and high fabrication reproducibility. By introducing thin polyethyleneimine (PEI) interfacial layers to separate the direct contact of the perovskite layer with the top and bottom electrodes, thus producing a device structure of ITO/PEI/CH3NH3PbI3/PEI/metal, we achieved endurance cycles of more than 4000 times while maintaining a low operation voltage around 0.25 V. Furthermore, reproducible memory switching behavior was demonstrated among 180 devices fabricated from eight different device batches. To study the memory mechanism, we varied the top electrode (TE) metal materials and found three distinctively different resistive switching characteristics for InGa, Ag, and Al electrodes, respectively. The results suggest that the memory switching originates from a concerted effect of defect motion in the perovskite film and metal ion diffusion from the TE and that the switching mechanism is associated with the substitutionality of the metal ion in the Pb–I cage. For Ag ions with high substitutionality, the memory turn-on is dominated by interface vacancies, whereas for Al ions with low substitutionality, filament formation governs the memory switching.

Uncovering the Indium Filament Revolution in Transparent Bipolar ITO/SiOx/ITO Resistive Switching Memories

Transparent resistive switching random access memory (ReRAM) is of interest for the future integrated invisible circuitry. However, poor understanding of its working mechanism in transparent ReRAMs with the indium tin oxide (ITO) electrode is still a critical problem and will hinder its widespread applications. To reveal the actual working mechanism in transparent ReRAMs with the ITO electrode, we investigate the transparent ITO/SiOx/ITO memory devices (∼82% transmittance in the visible region) and compare it with ITO/SiOx/Au memory devices, which both can exhibit reproducible bipolar switching. The indium (In) filament evolution, which accounts for the bipolar switching behaviors in the ITO/SiOx/ITO (or Au) memories, is directly observed using transmission electron microscopy on samples with different memory states (electroformed, ON, and OFF). These studies uncover the microscopic mechanism behind the bipolar switching in SiOx-based ReRAM devices with the ITO electrode, providing a general guidance for the design of high-performance ReRAMs with large scalability and high endurance.

Ultrathin All-2D Lateral Graphene/GaS/Graphene UV Photodetectors by Direct CVD Growth.

UV-sensitive lateral all-two-dimensional (2D) photodetecting devices are produced by growing the large band gap layered GaS between graphene electrode pairs directly using chemical vapor deposition methods. The use of prepatterned graphene electrode pairs on the Si wafer enables more than 200 devices to be fabricated simultaneously. We show that the surface chemistry of the substrate during GaS leads to selective growth in graphene gaps, forming the lateral heterostructures, rather than on the surface of graphene. The graphene/GaS/graphene lateral photodetecting devices are demonstrated to be sensitive to UV light only, with no measurable response to visible light. Furthermore, we demonstrate UV-band discrimination in photosensing, with measured photocurrents only produced for middle-UV and not for near-UV wavelength regions. The detection limit could reach down to 2.61 μW/cm2 with a photoresponsivity as high as 11.7 A/W and a photo gain of 53.7 under 270 nm excitation. Gate-dependent modulation of the photocurrent is also demonstrated. The photodetectors exhibit long-term stability and reproducible ON-OFF switching behavior, with a response time lower than 60 ms. These results provide insights into how ultrathin UV sensing devices can be created using only 2D materials by exploiting large band gap 2D semiconductors such as GaS.

Ultra-Broadband, High Speed, and High-Quantum-Efficiency Photodetectors Based on Black Phosphorus.

Black phosphorus (BP), a narrow band gap semiconductor without out-of-plane dangling bonds, has shown promise for broadband and integrable photodetector applications. Simultaneously exhibiting high speed and high-efficiency operation, however, remains a critical challenge for current BP-based photodetectors. Here, we demonstrate a photodetector based on the BP-based van der Waals heterostructures. The developed photodetector enables broadband responses in the visible to mid-infrared range with external quantum efficiency ranging from 20 to 52% at room temperature. These results together with noise measurements indicate that the photodetector can detect light in the picowatt range. Furthermore, the demonstrated BP detector has ultrafast rise (1.8 ns) and fall (1.68 ns) times, and its photoresponse exhibits reproducible switching behavior even under consecutive and rapid light intensity modulations (2100 cycles, 200 MHz), as indicated by the eye-diagram measurement. By leveraging these features, we show our BP heterostructures can be configured as a point-like detector in a scanning confocal microscopy, useful for mid-infrared imaging applications.

Diffusive Memristive Switching on the Nanoscale, from Individual Nanoparticles towards Scalable Nanocomposite Devices

Nanoscale memristive phenomena are of great interest not only to miniaturize devices and improve their performance but also to understand the details of the underlying mechanism. Herein, we utilize conductive atomic force microscopy (C-AFM) as a non-invasive method to examine the nanoscale memristive properties of individual noble metal alloy nanoparticles that are sparsely encapsulated in a thin SiO2 dielectric matrix. The measurement of current-voltage hysteresis loops at the level of individual nanoparticles, enabled by the nanoscopic contact area of the C-AFM tip, indicates reliable memristive switching for several hours of continuous operations. Alongside the electrical characterization on the nanoscale, the method of C-AFM offers the potential for in situ monitoring of long term operation induced morphological alterations and device failure, which is demonstrated at the example of nanoparticle-based devices with additional Cr wetting layer. The application of alloy nanoparticles as reservoir for mobile silver species effectively limits the formation of stable metallic filaments and results in reproducible diffusive switching characteristics. Notably, similar behaviour is encountered on macroscopic nanocomposite devices, which incorporate multiple stacks of nanoparticles and offer a high design versatility to tune switching properties and engineer scalable memristive devices with diffusive switching characteristics. No additional forming step is required for the operation of the presented alloy nanoparticle based memristive devices, which renders them very attractive for applications.

High on/off ratio black phosphorus based memristor with ultra-thin phosphorus oxide layer

The scaling down of switching media encounters high leakage current in the traditional oxide material based memristors, resulting in high power consumption of chips. Two-dimensional (2D) materials promise an ultimate device scaling down to atomic layer thickness. Herein, black phosphorus (BP) and its self-assembly phosphorous oxide (BP) memristors are constructed, which leverages the high on/off ratio operation of oxides and low leakage current of 2D materials with high performance. The memristors exhibit reproducible and reliable switching characteristics with the on/off ratio >107 and data retention >104 s. Depending on the high reproducibility, basic “AND” and “OR” gates have been constructed on flexible substrates. Moreover, on the basis of the symmetry and linearity of conductance in the devices, the neural network simulation for supervised learning presents an online learning accuracy of 91.4%. This work opens an avenue for future flexible electronics.

Chemical vapor deposition synthesis of sp2-BN film on 2-inch Si substrates for bipolar resistive random access memory device

Resistive random access memory (RRAM) devices with Au/sp2-BN/p-Si sandwich structure have been successfully fabricated. Single precursor ammonia borane (NH3BH3) chemical vapor deposition (CVD) was used to directly grow amorphous sp2-BN film on a 2-inch commercial p-type Si substrate without any extra catalyst. The sp2-BN-based RRAM device exhibit reproducible switching endurance (>1000 cycles), long retention time (>1 × 104 s), capability to operate under appropriate voltages (between 2.225 V and 1.475 V for SET process) as well as large area uniformity (2 inch). The resistance value of low resistance state (LRS) is as high as 3 × 103 Ω and the typical VSET/ISET and VRESET/IRESET are 4.292 × 10−4 A @ 1.925 V and 6.143 × 10−4 A @ −0.862 V, respectively. A boron vacancies (VB) induced mechanism similar to valence change memory (VCM) has been used to explain the parameters of noble Au/sp2-BN/Si RRAM device such as, RESET stop voltage, temperature and device area dependence of resistances (both low & high states). This work will propel the combination of low power consumption in sp2-BN based RRAM with Si based electronics devices.

Silver Iodide Induced Resistive Switching in CsPbI3 Perovskite‐Based Memory Device

AbstractLead halide perovskites‐based memory devices have attracted considerable interest due to their unique current–voltage (I–V) hysteresis. Herein, all‐inorganic CsPbI3 perovskite film surviving 30 d of air storage is prepared by using a poly‐vinylpyrrolidone‐assisted passivation method under fully open‐air condition. Afterwards, a memory device with a sandwich structure of Ag/CsPbI3/indium tin oxide is manufactured. From I–V characteristics of pristine device, a spontaneous reaction between the active Ag electrode and I− ions under air exposure is suggested. Furthermore, complete degradation of Ag electrode and formation of AgIx are verified, which also accompanies with generation of more iodine vacancies (VI) in perovskite film. The memory device with AgIx layer shows a bipolar resistive switching behavior, ultrahigh ON/OFF ratio (above 106), nonvolatile, reliable, and reproducible switching performance. Cell area and temperature dependent characteristics propose that the resistive switching is dominated by VI filament in low‐resistance state and thermally assisted hopping in high‐resistance state. This study provides a new insight to understand switching behavior from the way of electrode degradation and metal iodide formation in lead iodide perovskites‐based memory devices and also suggests a potential application for AgIx‐induced resistive switching in CsPbI3‐based memory device.

Ultrafast Multilevel Switching in Au/YIG/n‐Si RRAM

AbstractResistive random access memory (RRAM) with ultrafast and multilevel switching is extremely promising for next‐generation nonvolatile memory. Here, ultrafast unipolar resistive switchings (≈540 ps) with high off/on resistance ratio (≈104) are obtained in yttrium iron garnet Y3Fe5O12 (YIG)‐based resistive memory on n‐Si substrate. The sub‐nanosecond operation is also successfully performed up to 85 °C with an off/on resistance ratio of ≈103. In addition, by using different compliance currents for the set process, five discrete resistance levels with ultrafast switchings among them are achieved and the multilevel states show reliable retention (>104 s). The large, stable, reproducible, and reliable switching behaviors of the Au/YIG/n‐Si RRAM cell shows its great potential for ultrafast multilevel memory applications.

A flexible organic memory device with a clearly disclosed resistive switching mechanism

Flexible electronics is one of the main challenges for future hi-tech electronics. Since information storage elements are essential in any electronic system, the development of high-performance and flexible organic memories is a key requirement. Organic resistive switching memories represent a viable and promising technology ensuring scalability, flexibility, low cost and easy processing. However, despite of the remarkable progress, organic memory reliability, long term stability, ambient operation and large-area processing still need to be improved. Moreover, the rational device implementation lacks of a clear understanding of resistive switching mechanisms. In this work, high-performance cross-bar resistive memories based on a Parylene-C resistive layer sandwiched between silver electrodes are fabricated by means of large-area and high-throughput procedure. Parylene-C is a biocompatible, thermoplastic polymer, which can be deposited at room temperature. Memory elements show a reliable and reproducible switching behavior with low operating voltages, high ION/IOFF current ratio and record retention time in ambient conditions as well as high mechanical stability under bending conditions. The 3D molecular distribution of pristine and programmed devices is determined by state-of-the-art time-of-flight secondary ion mass spectrometer combined with an in-situ scanning probe microscopy (TOF-SIMS/SPM). The depth profile analysis indicates that resistive switching is driven by the formation of few localized nanometer scale conductive filaments formed by the diffusion of silver and oxygen across the organic layer which are activated, locally interrupted and re-activated during the memory cycling. The SPM images allow separating surface morphology related effects from the 3D molecular analysis and to identify some typical artefacts in TOF-SIMS image reconstructions due to preferential sputtering.

Oxygen-deficient strontium titanate based stretchable resistive memories

A stretchable non-volatile resistive memory is a fundamental element in realizing complex neuromorphic computing and compact logic application adaptable to wearable electronics. A room temperature deposited SrTiO3−x (STO) based resistive memory on stretchable polydimethylsiloxane (PDMS) substrate has been developed. The STO-based resistive memory does not require energy-intensive electroforming, exhibits stable complementary switching, long retention time, and reproducible endurance switching. The devices demonstrate the ability to operate under uniaxial tensile strain and extreme bending conditions. This work is an important step realizing metal oxide based stretchable non-volatile memories, critical to integrated devices for skin-mounted electronics.

Al2O3 thin film multilayer structure for application in RRAM devices

This study investigated the effect of resistive switching on Pt/Al2O3/Cu/Al2O3/ITO multilayer structures grown by RF/DC magnetron sputtering. A reproducible unipolar switching free forming was found only for the negative voltage. The SET and RESET processes occurred at very low voltage values, which may be advantageous for practical applications. The ON/OFF ratio was approximately five orders of magnitude for more than 103 s, which is desirable for nonvolatile memories such as resistive random-access memories (RRAMs). We explain the unipolar behavior of the characteristic (I–V) curves in terms of the formation and rupture of conductive filaments, connected via a Cu metal layer.

Reset Voltage-Dependent Multilevel Resistive Switching Behavior in CsPb1–xBixI3 Perovskite-Based Memory Device

All-inorganic CsPb1- xBi xI3 perovskite film was successfully fabricated by incorporating Bi3+ in CsPbI3 to stabilize the cubic lattice. Furthermore, the perovskite film was applied to manufacture a simple Ag/CsPb1- xBi xI3/indium tin oxide (ITO) memory device with a bipolar resistive switching behavior. Nonvolatile, reliable, and reproducible switching properties are demonstrated through retention and endurance test under fully open-air conditions. The memory device also presents highly uniform and long-term stable characteristics. Importantly, by modulating the reset stop voltages, multilevel high-resistance states are observed for the first time in lead halide perovskite memory device. The resistive switching behavior is proposed to explain the formation and partial rupture of conductive multifilament that are dominated by the migration of iodine ions and their corresponding vacancies in perovskite film. This study suggests Ag/CsPb1- xBi xI3/ITO device potential application for multilevel data storage in a nonvolatile memory device.

A reversible fluorescent chemosensor for the rapid detection of Hg2+ in an aqueous solution: Its logic gates behavior

A new easily available “off-on-off” colorimetric and fluorescent probe (L) was synthesized and it displayed the selective detection towards Hg2+ in aqueous solution over other competing metal ions. In presence of Hg2+, L showed the incredible color and fluorescent response. More interestingly, the color and fluorescence could be recovered upon the addition of EDTA into the L-Hg2+ solution. Moreover, this compound can be efficiently applied to molecular logic functions of OR, AND, NOR and NOT gates through the procured spectral results. Based on the reversible and reproducible switching process, we designed a molecular-scale sequential memory unit exhibits the “Writing-Reading-Erasing-Reading” and “Multi-write” activities in the form of binary logic. Density Functional Theory (DFT) calculations were theoretically supported the photo physical changes. Furthermore, the probe efficacy was studied by monitoring changes in intracellular Hg2+ ions in HeLa cells.

Multistate storage nonvolatile memory device based on ferroelectricity and resistive switching effects of SrBi2Ta2O9 films

A memory device with a Pt/SrBi2Ta2O9(SBT)/Pt(111) structure was shown to have excellent combined ferroelectricity and resistive switching properties, leading to higher multistate storage memory capacity in contrast to ferroelectric memory devices. In this device, SBT polycrystalline thin films with significant (115) orientation were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates using CVD (chemical vapor deposition) method. Measurement results of the electric properties exhibit reproducible and reliable ferroelectricity switching behavior and bipolar resistive switching effects (BRS) without an electroforming process. The ON/OFF ratio of the resistive switching was found to be about 103. Switching mechanisms for the low resistance state (LRS) and high resistance state (HRS) currents are likely attributed to the Ohmic and space charge-limited current (SCLC) behavior, respectively. Moreover, the ferroelectricity and resistive switching effects were found to be mutually independent, and the four logic states were obtained by controlling the periodic sweeping voltage. This work holds great promise for nonvolatile multistate memory devices with high capacity and low cost.

Time and spatial evolution of spin–orbit torque-induced magnetization switching in W/CoFeB/MgO structures with various sizes

We study spin–orbit torque (SOT) switching in W/CoFeB/MgO structures with various dot sizes (120–3500 nm) using pulsed current of various widths τ (800 ps–100 ms) to examine the time and spatial evolution of magnetization switching. We show that the switching behavior and the resultant threshold switching current density Jth strongly depend on device size and pulse width. The switching mode in a 3500 nm dot device changes from probabilistic switching to reproducible partial switching as τ decreases. At τ = 800 ps, Jth becomes more than 3 times larger than that in the long-pulse regime. A decrease in dot size to 700 nm does not significantly change the switching characteristics, suggesting that domain-wall propagation among the nucleated multiple domains governs switching. In contrast, devices with further reduced size (120 nm) show normal full switching with increasing probability with current and insignificant dependence of Jth on τ, indicating that nucleation governs switching.

Writing and reading antiferromagnetic Mn2Au by N\xe9el spin-orbit torques and large anisotropic magnetoresistance

Using antiferromagnets as active elements in spintronics requires the ability to manipulate and read-out the Néel vector orientation. Here we demonstrate for Mn2Au, a good conductor with a high ordering temperature suitable for applications, reproducible switching using current pulse generated bulk spin-orbit torques and read-out by magnetoresistance measurements. Reversible and consistent changes of the longitudinal resistance and planar Hall voltage of star-patterned epitaxial Mn2Au(001) thin films were generated by pulse current densities of ≃107 A/cm2. The symmetry of the torques agrees with theoretical predictions and a large read-out magnetoresistance effect of more than ≃6% is reproduced by ab initio transport calculations.

Stable switching among high-order modes in polariton condensates

We report multistate optical switching among high-order bouncing-ball modes ("ripples") and whispering-gallerying modes ("petals") of exciton-polariton condensates in a laser-generated annular trap. By tailoring the diameter and power of the annular trap, the polariton condensate can be switched among different trapped modes, accompanied by redistribution of spatial densities and superlinear increase in the emission intensities, implying that polariton condensates in this geometry could be exploited for a multistate switch. A model based on non-Hermitian modes of the generalized Gross-Pitaevskii equation reveals that this mode switching arises from competition between pump-induced gain and in-plane polariton loss. The parameters for reproducible switching among trapped modes have been measured experimentally, giving us a phase diagram for mode switching. Taken together, the experimental result and theoretical modeling advances our fundamental understanding of the spontaneous emergence of coherence and move us toward its practical exploitation.

Air‐Stable Cesium Lead Iodide Perovskite for Ultra‐Low Operating Voltage Resistive Switching

AbstractCsPbX3 (X = halide, Cl, Br, or I) all‐inorganic halide perovskites (IHPs) are regarded as promising functional materials because of their tunable optoelectronic characteristics and superior stability to organic–inorganic hybrid halide perovskites. Herein, nonvolatile resistive switching (RS) memory devices based on all‐inorganic CsPbI3 perovskite are reported. An air‐stable CsPbI3 perovskite film with a thickness of only 200 nm is successfully synthesized on a platinum‐coated silicon substrate using low temperature all‐solution process. The RS memory devices of Ag/polymethylmethacrylate (PMMA)/CsPbI3/Pt/Ti/SiO2/Si structure exhibit reproducible and reliable bipolar switching characteristics with an ultralow operating voltage (<+0.2 V), high on/off ratio (>106), reversible RS by pulse voltage operation (pulse duration < 1 ms), and multilevel data storage. The mechanical flexibility of the CsPbI3 perovskite RS memory device on a flexible substrate is also successfully confirmed. With analyzing the influence of phase transition in CsPbI3 on RS characteristics, a mechanism involving conducting filaments formed by metal cation migration is proposed to explain the RS behavior of the memory device. This study will contribute to the understanding of the intrinsic characteristics of IHPs for low‐voltage resistive switching and demonstrate the huge potential of them for use in low‐power consumption nonvolatile memory devices on next‐generation computing systems.