Transparent Resistive Switching Research Articles

Two‐Inch Wafer‐Scale Exfoliation of Hexagonal Boron Nitride Films Fabricated by RF‐Sputtering

AbstractA film stripping method that allows for liquid phase exfoliation assisted by spin coating polymethyl methacrylate has been investigated, resulting in a two‐inch hexagonal boron nitride (hBN) film to be fully stripped and then transferred. A number of key factors that can influence the stripping and the transferring process of the films grown by sputtering have been systematically analyzed, including different solutions, different concentration of solution and different thickness of films. The morphology and properties of the hBN films before and after stripping have been characterized. The band edge absorption peak of the transferred film is 229 nm and the corresponding optical band gap is 5.50 eV. Such transferred hBN films have been fabricated into transparent resistive switching devices on indium‐tin‐oxide glass, demonstrating a constant resistance window of ≈102 even under different applied voltages. This work systematically studies the stripping process, characterizes the transferred films, and explores the application in the field of resistance switching, which lay a foundation for the further application of hBN materials in optoelectronic devices.

Transparent ZnO resistive switching memory fabricated by neutral oxygen beam treatment

In this work, a Cu/ZnO/ITO resistive random access memory (RRAM) structure in which ZnO films are irradiated with neutral oxygen beams was employed to investigate the effect of neutral oxygen beams as a surface treatment. It was confirmed that the treatment reduced the defect concentration in the sputtered-ZnO film and improved the resistance change characteristics of the device. These results indicate the great potential of neutral oxygen beams in the development of RRAM devices using ZnO films.

Transparent, Flexible, and Low-Operating-Voltage Resistive Switching Memory Based on Al2O3/IZO Multilayer.

In this study, a different number of indium zinc oxide (IZO) interlayers are fabricated into Al2O3‐based transparent resistive switching memory on a transparent indium tin oxide (ITO)/glass substrate at room temperature. Al2O3/IZO multilayer transparent memory has a transmittance of at least 65% in the wavelength range of 400–900 nm. In addition, the Al2O3/IZO multilayer transparent memory can achieve an electroforming voltage that is 35.7% lower than that of ITO/pure‐Al2O3/IZO transparent memory. The fabricated Al2O3/IZO multilayer transparent memory exhibits typical bipolar resistive switching behavior, regardless of the number of IZO interlayers. Also, the fabricated Al2O3/IZO multilayer transparent memory has a low operating voltage within ±1.5 V. In addition, a flexible Al2O3/IZO multilayer transparent memory is fabricated using the same process on ITO‐coated polyethylene terephthalate. The fabricated flexible transparent memory also maintains the resistive switching characteristics during the bending state.

Multi-level characteristics of TiOx transparent non-volatile resistive switching device by embedding SiO2 nanoparticles

TiOx-based resistive switching devices have recently attracted attention as a promising candidate for next-generation non-volatile memory devices. A number of studies have attempted to increase the structural density of resistive switching devices. The fabrication of a multi-level switching device is a feasible method for increasing the density of the memory cell. Herein, we attempt to obtain a non-volatile multi-level switching memory device that is highly transparent by embedding SiO2 nanoparticles (NPs) into the TiOx matrix (TiOx@SiO2 NPs). The fully transparent resistive switching device is fabricated with an ITO/TiOx@SiO2 NPs/ITO structure on glass substrate, and it shows transmittance over 95% in the visible range. The TiOx@SiO2 NPs device shows outstanding switching characteristics, such as a high on/off ratio, long retention time, good endurance, and distinguishable multi-level switching. To understand multi-level switching characteristics by adjusting the set voltages, we analyze the switching mechanism in each resistive state. This method represents a promising approach for high-performance non-volatile multi-level memory applications.

Memristive Devices: Planar and Transparent Memristive Devices Based on Titanium Oxide Coated Silver Nanowire Networks with Tunable Switching Voltage (Small 21/2021)

In article number 2007344, Daniel Bellet, David Muñoz-Rojas, and co-workers demonstrate transparent resistive switching devices entirely fabricated by open-air approaches, without a deposition chamber. The threshold voltage can be tuned by adjusting the density of AgNWs, while maintaining a high LRS/HRS ratio. The researchers show the effect of oxide thickness on the threshold-switching phenomenon, thus shedding light on the conduction mechanism of this type of switching devices.

Band tailoring by annealing and current conduction of Co-doped ZnO transparent resistive switching memory

The switching characteristics of ITO/Zn1-xCoxO/ITO transparent resistive random access memories were studied. 5 mol% cobalt doped ZnO resistive layer improves bipolar switching properties. In addition, the redshift in band energy caused by doping of cobalt (Co) was studied. The doped memory device also showed a change in band energy by 0.1 eV when subjected to annealing of 400 °C. Annealing below 400 °C temperature did not show any characteristic changes. The film morphology analysis suggested the increase in roughness with annealing temperature, which can be seen from FESEM and AFM images. In this study annealing and Co doping effect on ZnO based non-volatile memory device is presented. Moreover, transparent memory devices with 90% transmittance at 550 nm wavelength have been reported. At low field and high field region Schottky emission and ionic conduction are dominated respectively.

Solution-Processed Flexible Biomemristor Based on Gold-Decorated Chitosan.

The main requirements for skin-attachable memory devices are flexibility and biocompatibility. We represent a flexible, transparent, and biocompatible resistive switching random access memory (ReRAM) based on gold-decorated chitosan for future flexible and wearable electronics. The device with an Ag/Au-chitosan/Au cross-bar structure shows nonvolatile ReRAM properties. This fabricated Au-chitosan-based biocompatible ReRAM (bioReRAM) shows reliable bipolar memory performance with mechanical flexibility. The device shows essential memory characterizations including long data retention and hundreds of switching cycles. The origin of the resistance switching properties is related to trap-assisted space-charge-limited conduction in the high-resistance state and formation/annihilation of a conductive filament in the low-resistance state. This transparent bioReRAM is a viable candidate for flexible and biodegradable nanoelectronic devices.

Point-contact enabled reliable and low-voltage memristive switching and artificial synapse from highly transparent all-oxide-integration

Mimicking brain-like functionality for enabling higher-level artificial intelligence is one of the ultimate goals in neuromorphic computing, which could be achieved by two-terminal memristors. However, conventional memristors are suffering from severe shortcomings such as temporal (cycle-to-cycle) and spatial (device-to-device) reproducibility along with high operative voltage, albeit all these are crucial for accurate and quick information processing. Here, we demonstrate point-contact enabled reproducible and reliable bipolar resistive switching from all-oxide-based highly transparent memristors with low operating voltage (<0.5 V) and long retention times. Analogous to bio-synapse, memristor mimics the functions like short-term potentiation and short-term depression under the action of applied pulses. Conductive atomic force microscopy unambiguously revealed the formation of the localized conducting channels as well as nanoscale dynamics. Further, finite element simulation confirms that the tip-enhanced electric field could generate localized conduction channels, in contrast to the uniform electrode in which edges are the preferred sites for conduction. These results represent an important milestone toward the use of point-contact to design all-oxide-based highly transparent and reproducible resistive switching devices as well as artificial synapse.

Effect of junction-to-nanowire resistance ratio on the percolation conductivity and critical exponents of nanowire networks

Using Monte Carlo simulations, we study the effect of the junction-to-nanowire resistance ratio on the percolation transport in nanowire networks. By varying the resistance ratio over a span of six orders of magnitude, we first investigate its effect on the conductivity of nanowire networks at different values of five parameters, namely, nanowire density, nanowire length, device width, nanowire alignment, and curviness. We find that the network conductivity decreases with an increase in the resistance ratio, which is most pronounced close to the percolation threshold. We also find that the network resistivity depends linearly on the resistance ratio in the junction-dominated regime, with the slope increasing as the network approaches the percolation threshold. For nanowire alignment, however, the minimum slope occurs for a partially aligned network, rather than a completely random one. Next, we study the effect of the resistance ratio on the percolation critical exponents for each of the five parameters. We find that that the critical exponents increase as the resistance ratio increases from a nanowire-dominated to a junction-dominated network; however, the amount of this increase depends on the parameter being varied. We explain these findings by physical arguments based on percolation transport. These results, which can be applied to any two-dimensional network comprised of one-dimensional nanoelements, show that Monte Carlo simulations are crucial for not only studying the physics of percolation transport in nanowire networks, but also enabling predictive modeling and optimization of nanowire networks for a wide range of device applications, such as transparent conductors and resistive switching memory.

Visible Light Detection and Memory Capabilities in MgO/HfO₂ Bilayer-Based Transparent Structure for Photograph Sensing

Photograph response in transparent devices has been a hot area of investigation, with several material systems being used to generate a response to illumination. In this study, we propose an ITO/MgO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ITO bilayer (BL) transparent resistive switching (RS) device that exhibits a photograph response through defect engineering in the switching layer, which resulted in a subsurface active RS location in the formed conductive filament, thus reducing the loss of oxygen through the polycrystalline electrode. We observe that the switching performance is enhanced in the ITO/MgO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ITO BL device as compared to the ITO/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /ITO single-layer device with the insertion of MgO layer between the ITO top electrode and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RS layer. The device shows excellent ON/ OFF ratio (~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> ), high and stable dc electrical set and optical reset endurance (>1000 cycles without degradation), excellent retention (>10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s at 85 °C), high transparency (>85% transmittance in the visible spectrum), and a response time of 30 μs for the optical reset. This study lays the foundation for future work involving oxide defect-based optical functionalization in RS devices with the possibility for being used in photograph sensing.

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.

Self-rectifying resistive switching behavior observed in sodium copper chlorophyllin-polyvinyl alcohol composites on a flexible and transparent substrate

Sodium copper chlorophyllin (SCC)- polyvinyl alcohol (PVA) composites thin films have been prepared on flexible and transparent ITO/PET substrates using Ag as the top electrode. FE-SEM shows that the prepared SCC-PVA thin films are smooth and dense, SCC particles have embedded in PVA and formed nano-islands, which are distributed irregularly in the thin film. The optical transmittance spectrum demonstrates that Ag/SCC-PVA/ITO/PET can be used as a transparent electronic device. I–V characteristics of the Ag/SCC-PVA/ITO/PET show that the device exhibits self-rectifying resistive switching performance, which could be related to the forming/rapture of Ag conductive filaments induced by the migration of Ag ions. This study demonstrates the potential uses of SCC-PVA in low-cost, flexible and transparent resistive switching memory.

The observation of resistive switching characteristics using transparent and biocompatible Cu2+-doped salmon DNA composite thin film

For the potential switching bio-memory device application using DNA composite thin film, we fabricated and characterized the transparent and biocompatible resistive switching random access memory (RRAM) device within the structure stacking of Pt/Cu2+ doped salmon DNA/FTO, where Cu2+ doping into salmon DNA was solution-processed. The device shows good bipolar switching characteristics with SET and RESET processes at negative and positive sweeps, respectively, with switching memory window greater than 103 ratios. The device was observed to be in low resistance state as its pristine state and an initial RESET state was necessary to achieve programmable SET and RESET cycles. Based on the electrical characteristics of the Cu2+-doped salmon DNA-based RRAM device we propose a switching mechanism with the formation and rupture of conductive filaments due to the migration of Cu2+ during the electrical stress. Our understanding could contribute to the engineering of biomaterial memory switching medium for the environmentally benign, biocompatible and biodegradable memory storage devices.

Characteristics of flexible and transparent Eu2O3 resistive switching memory at high bending condition

The characteristics of ITO/Eu2O3/ITO/PET transparent and flexible resistive switching memory are studied. The device exhibits superior characteristics such as device area-independent and forming-free resistive switching behavior with a resistance on/off ratio of 104, good retention of >104 s and high AC endurance of >107 cycles. The conduction mechanism of the high-resistance state is the Poole–Frenkel mechanism, while that of the low-resistance state is ohmic conduction. The electrical characteristics of the flexible device have shown excellent results up to 5 mm bending radius, at which a degradation in the on/off ratio of the memory window is observed, due to the change in the dielectric layer resistance. The resistive switching characteristics can be improved during bending up to the radius of 2 mm by the incorporation of an aluminum-doped zinc oxide layer in the device as the bottom electrode, proving its application in future flexible and transparent memory devices.

Flexible, transparent resistive switching device based on topological insulator Bi2Se3-organic composite

Two-dimensional topological insulator bismuth selenide (Bi2Se3) nanosheets (NSs) embedded in poly-methyl methacrylate (PMMA) are employed for the first time for the resistive switching (RS) application. Hexagonal 2D Bi2Se3 NSs are synthesized by a simple solvothermal method and combine with PMMA at different weight percentages of 2D Bi2Se3. Field emission scanning electron microscopy and transmission electron microscopy along with other characterizations such as X-ray photoelectron spectroscopy and Raman spectroscopy were performed for the characterization of Bi2Se3@PMMA hybrid system. The composite was deposited on a transparent, flexible polyethylene terephthalate substrate to form Ag/Bi2Se3@PMMA/indium doped tin oxide memory cell. I-V characteristics of the device revealed a stable and non-volatile memory effect. The device shows a significantly high resistance (RHRS/RLRS) ratio, more than 103, high retention time (more than 9000 s) with high reproducibility over a large number of (105) ac cycles. From the experimental data, RS performances are explained by using a charge trapping–detrapping mechanism. Owing to the increasing interest in flexible electronics, bending tests are carried out at various bending diameters (10–30 mm) to show the mechanical robustness of the proposed device.

Forming-Free One-Selector/One-Resistor Characteristics of Oxygen-Rich ITO Based Transparent Resistive Switching Memory via Defect Engineering Using the Reactive Sputtering Process.

In recent research of resistive random access memory (RRAM), solving the degradation phenomenon induced by both a high forming voltage to form the conducting filaments (CFs) and a high reset current is one of the main issues encountered. In this study, to overcome these problems, we propose forming-free bipolar resistive switching (BRS) behaviors by employing an ITO film with abundant oxygen vacancies, instead of conventional CF based RRAM requiring a forming process, and systematically investigate the feasibility of forming free BRS behaviors and a possible switching mechanism. Compared to conventional CF based RRAM devices, it is possible for the proposed devices to achieve stable BRS properties (i.e., narrow variations of operating current and voltage, and retention) without the forming process, under an operating current of sub-nano ampere. In addition, the proposed cell shows a stable hysteresis of current-voltage curves, which is well matched with the Poole-Frenkel emission, and currents at a low voltage are limited due to a formed barrier height like Schottky diode between the active layer and electrodes.

Bipolar resistance switching properties of pulse laser deposited a-ZrO2/a-IGZO transparent heterojunction

Transparent resistive switching characteristics of amorphous ZrO2 (a-ZrO2) based memory film with amorphous In and Ga co-doped ZnO (a-IGZO) conducting electrode were investigated. a-ZrO2/a-IGZO heterojunction was fabricating using pulse laser deposition techniques on quartz substrate. Structural, surface, electrical, and optical properties of a-ZrO2/a-IGZO heterojunction were investigated at room temperature. Smooth surface morphology and amorphous nature of the structure has been confirmed from the atomic force microscopy (AFM) and grazing incident X-ray diffraction (GIXRD) analysis. a-ZrO2/a-IGZO heterojunction has optical transmission exceeding 80% in visible light of electromagnetic spectrum. I–V characteristics show a forming free, bipolar resistance switching type behavior. Migration of oxygen ions from IGZO layer through ZrO2 layer creating the oxygen vacancy filament play an important role in the forming free resistive switching.

A graphene integrated highly transparent resistive switching memory device

We demonstrate the hybrid fabrication process of a graphene integrated highly transparent resistive random-access memory (TRRAM) device. The indium tin oxide (ITO)/Al2O3/graphene nonvolatile memory device possesses a high transmittance of &amp;gt;82% in the visible region (370-700 nm) and exhibits stable and non-symmetrical bipolar switching characteristics with considerably low set and reset voltages (&amp;lt;±1 V). The vertical two-terminal device shows an excellent resistive switching behavior with a high on-off ratio of ∼5 × 103. We also fabricated a ITO/Al2O3/Pt device and studied its switching characteristics for comparison and a better understanding of the ITO/Al2O3/graphene device characteristics. The conduction mechanisms in high and low resistance states were analyzed, and the observed polarity dependent resistive switching is explained based on electro-migration of oxygen ions.

Conductive bridge random access memory characteristics of SiCN based transparent device due to indium diffusion

In this work, the transparent bipolar resistive switching characteristics of a SiCN-based ITO/SiCN/AZO structure due to In diffusion from ITO is studied. The SiCN based device is found to be 80% transparent in the visible wavelength region. This device, with AZO as both top and bottom electrodes, does not show any RRAM property due to deposition of the high quality O2-free SiCN film. Replacing the AZO top electrode with ITO in this device results in good resistive switching (RS) characteristics with a high on/off ratio and long retention. Replacing the SiCN film with ZrO2 also results in excellent RS characteristics due to the formation of an oxygen vacancies filament inside the ZrO2 film. A resistance ratio of on/off is found to be higher in the SiCN based device compared to that of the ZrO2 device. Diffusion of In from ITO into the SiCN film on application of high positive voltage during forming can be attributed to the occurrence of RS in the device, which is confirmed by the analyses of energy dispersive spectroscopy and secondary-ion mass spectrometry. This study shows a pathway for the fabrication of CBRAM based transparent devices for non-volatile memory application.

Hydrogen-peroxide-modified egg albumen for transparent and flexible resistive switching memory

Egg albumen is modified by hydrogen peroxide with concentrations of 5%, 10%, 15% and 30% at room temperature. Compared with devices without modification, a memory cell of Ag/10% H2O2-egg albumen/indium tin oxide exhibits obviously enhanced resistive switching memory behavior with a resistance ratio of 104, self-healing switching endurance for 900 cycles and a prolonged retention time for a 104 s @ 200 mV reading voltage after being bent 103 times. The breakage of massive protein chains occurs followed by the recombination of new protein chain networks due to the oxidation of amidogen and the synthesis of disulfide during the hydrogen peroxide modifying egg albumen. Ions such as Fe3+, Na+, K+, which are surrounded by protein chains, are exposed to the outside of protein chains to generate a series of traps during the egg albumen degeneration process. According to the fitting results of the double logarithm I–V curves and the current-sensing atomic force microscopy (CS-AFM) images of the ON and OFF states, the charge transfer from one trap center to its neighboring trap center is responsible for the resistive switching memory phenomena. The results of our work indicate that hydrogen- peroxide-modified egg albumen could open up a new avenue of biomaterial application in nanoelectronic systems.