Transparent Resistive Random Access Memory Research Articles

Resistive switching characteristics of MnO2-based thin film for transparent non-volatile ReRAM

The present study covers the fabrication of indium tin oxide (ITO)/manganese dioxide (MnO2)/ITO capacitor-based transparent resistive random access memory (ReRAM) device. The ITO/MnO2/ITO device exhibits 80 % transparency in the visible region along with steady bipolar resistive switching characteristics. The conduction mechanism investigation reveals that the current in low resistance state (LRS) is governed by Ohmic conduction. However, the dominance of trap-controlled space charge limited conduction (SCLC) mechanism in high resistance state (HRS) was observed. The resistive switching phenomenon in ITO/MnO2/ITO device was caused due to the formation and rupture of conduction filament via electron trapping and de-trapping in oxide-related traps (oxygen vacancies). In terms of reliability, the MnO2-based device exhibits good endurance up to 104 cycles and long retention for 104 s at room-temperature as well as at 85 °C. Cumulative probability distribution shows resistance ratio of 103 between LRS and HRS, which is sufficient to read memory states. These outcomes suggest that the ITO/MnO2/ITO-based transparent ReRAM could be a futuristic see-through electronic device for artificial intelligence (AI) application.

Bipolar Switching Characteristics of Transparent WOX-Based RRAM for Synaptic Application and Neuromorphic Engineering.

In this work, we evaluate the resistive switching (RS) and synaptic characteristics of a fully transparent resistive random-access memory (T-RRAM) device based on indium-tin-oxide (ITO) electrodes. Here, we fabricated ITO/WOX/ITO capacitor structure and incorporated DC-sputtered WOX as the switching layer between the two ITO electrodes. The device shows approximately 77% (including the glass substrate) of optical transmittance in visible light and exhibits reliable bipolar switching behavior. The current-voltage (I–V) curve is divided into two types: partial and full curves affected by the magnitude of the positive voltage during the reset process. In the partial curve, we confirmed that the retention could be maintained for more than 104 s and the endurance for more than 300 cycles could be stably secured. The switching mechanism based on the formation/rupture of the filament is further explained through the extra oxygen vacancies provided by the ITO electrodes. Finally, we examined the responsive potentiation and depression to check the synaptic characteristics of the device. We believe that the transparent WOX-based RRAM could be a milestone for neuromorphic devices as well as future non-volatile transparent memory.

Low Temperature Sol-Gel Processed Zirconium Oxide Based Transparent Resistive Random Access Memory Devices

In this work, solution-processed ZrO2-based resistive random-access memory (RRAM) device with ITO (Indium Tin Oxide) as a bottom electrode (BE) was fabricated at a low thermal budget by sol-gel spin coating technique. The grown devices (ZrO2/ITO) were found to be amorphous by XRD measurements and exhibit 80% transmittance in the visible region. The resistive switching characteristics of solution-processed ZrO2 thin films were investigated. The W/ZrO2/ITO device exhibits good cyclic endurance with an on-off ratio (~10) and reliable switching and good retention at room temperature. The conduction mechanism for the low resistance state is ohmic, whereas the conduction mechanism of the high resistance state is ohmic at low applied voltages, while a space charge limited conduction (SCLC) at the high applied voltages. The combined ohmic and space charge limited conduction mechanisms together indicate that the RS behavior in the ZrO2 layer is due to the formation and rupture of conducting filaments. Results suggest that solution-processed ZrO2 has great potential to develop transparent and flexible resistive random access memory devices.

Sol-Gel Processed ZrO2 Based Forming-Free Resistive Switching Memory Devices

In this work, we fabricated ZrO2 based resistive random access memory by sol-gel spin coating technique and investigated its structural, optical and resistive switching properties. The X-ray diffraction pattern revealed that 400 °C annealed ZrO2 thin film has tetragonal structure. The optical band gap value of ZrO2 thin film obtained was 5.51 eV. The resistive switching behaviour of W/ZrO2/ITO capacitor like structure was studied. It was found that no initial electroforming process required for the device. The fabricated devices show a self-compliance bipolar resistive switching behaviour and have high on off ratio (>102). Our result suggests that solution processed ZrO2 has great potential to develop transparent and flexible resistive random access memory devices.

Impacts of LaOx Doping on the Performance of ITO/Al2O3/ITO Transparent RRAM Devices

Fully transparent ITO/LaAlO3/ITO structure RRAM (resistive random access memory) devices were fabricated on glass substrate, and ITO/Al2O3/ITO structure devices were set for comparison. The electrical characteristics of the devices were analyzed by Agilent B1500A semiconductor analyzer. Compared with the ITO/Al2O3/ITO RRAM devices, the current stability, SET/RESET voltage distribution, and retention characteristic of the ITO/LaAlO3/ITO RRAM devices have been greatly improved. In the visible light range, the light transmittance of the device is about 80%, that of the LaAlO3 layer is about 95%, the on-off ratio of the device is greater than 40, and the data retention time is longer than 10,000 s. The devices have great optical and electrical properties and have huge application potential as fully transparent RRAM devices.

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.

Optical and resistive switching properties of Chitosan-aluminum-doped zinc oxide composite thin films for transparent resistive random access memory application

The preparation of chitosan-aluminum-doped zinc oxide (AZO) composite thin films for transparent resistive random access memory applications is reported. The variation in optical transmission, refractive index and optical bandgap of the composite films as a function of concentration of Al in ZnO and AZO weight percent in chitosan is investigated. Independent of composition, optical transmission is of the order of 87–89% at 550 nm. The refractive index at this wavelength is in the range of 1.71–1.86. The composite films exhibit reversible resistive switching behavior which is dependent on the Al concentration in ZnO as well as the weight percent of AZO in chitosan. There is a threshold Al concentration in ZnO, below and above which resistive switching is not observed. At the threshold concentration, resistive switching behavior is stable over several cycles. The co-existence of unipolar and bipolar switching controlled by Al concentration in ZnO is also observed. The current study establishes the potential of chitosan-AZO composite thin films for transparent resistive random access memory application.

Enhancement of data storage capability in a bilayer oxide-based memristor for wearable electronic applications

In this work, a ZnO/NiO bilayer architecture is introduced to fabricate a transparent and flexible resistive random access memory device (Cu/ZnO/NiO/ITO) on polyethylene terephthalate substrate. The device exhibits excellent resistive switching (RS) characteristics, such as forming-free characteristic, low operating voltages, outstanding uniformity, long retention time (>104 s), high ON/OFF current ratio ~103, reliable multilevel cell characteristics and excellent mechanical flexibility. The multilevel properties have been systematically evaluated by varying the compliance current and tuning the stopping voltage, which shows that the whole resistance state is distinguishable and remained stable without any considerable deprivation over 103 s. Intrinsic tailoring of RS mechanism has been well explained in the framework of electric field-induced formation and rupture of the reproducible Cu filaments in ZnO/NiO layer. Furthermore, the metallic nature of conducting filament has been confirmed by temperature-dependent variation of the high- and low-resistance states. Due to the increasing demand for flexible electronics, the mechanical robustness of the proposed device has been examined by varying the bending time and radius. The present RS device shows potential towards integration in many transparent, flexible and high-density storage devices, such as electronic skins and flexible displays.

Fully-transparent resistance switching memristor based on indium-tin-oxide material

With the potential to act as the next generation of non-volatile memory, resistive random access memory (RRAM) not only has stable and excellent electrical characteristics, but can also be used in such versatile applications as neuron computing and logic circuit design. However, material selection for RRAM devices to accomplish the metal–insulator–metal (MIM) structure which initiates the resistance switching (RS) mechanism is incomplete because of the many different material characteristics between the metal and insulator. In this work, we demonstrate a via-hole structure, full transparent RRAM (TRRAM) with indium-tin-oxide (ITO) acting as both electrode and middle insulator in the ITO/ITOX/ITO structure. The originally conductive ITO thin film successfully acts as an insulator after a supercritical fluid (SCF) oxidation treatment. This all-ITO RRAM device exhibits superb electrical performance and excellent environmental stability to high temperature without significant degradation in its RS characteristics. In addition, the ITO-based TRRAM also displays stable performance under different light illumination conditions. Another ITO-based TRRAM constructed on soft polyimide (PI) substrate has also been demonstrated. The present all-ITO TRRAM is not only of great interest for future stable transparent electron applications, but it also provides a guideline for the simplification of material selection for transparent electron devices.

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.

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.

Point contact bipolar resistive switching observed in transparent ZnMgO/ZnO:Ga heterostructure

Transparent ZnMgO/ZnO:Ga/c-sapphire hetero-structures with an optical transmittance of 73% in the visible region were fabricated by pulsed laser deposition technique. Bipolar resistive switching is observed in this structure with a simple contact approach, (i.e. across a W pin on top of the ZnMgO surface and another connected to the ZnO:Ga which acts as the transparent electrode). Conduction mechanisms for low resistance state (LRS) was explained by Ohmic behavior, but for high resistance state (HRS) Schottky emission model was used to explain for the conduction behavior. Moreover, the memory effect, good retention and endurance characteristics of the fabricated ZnMgO/GaZnO/c-sapphire device suggest its prospective application for the transparent resistive random-access memory devices.

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 >82% in the visible region (370-700 nm) and exhibits stable and non-symmetrical bipolar switching characteristics with considerably low set and reset voltages (<±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.

Endurance improvement and resistance stabilization of transparent multilayer resistance switching devices with oxygen deficient WOx layer and heat dissipating AlN buffer layer

In this study, indium tin oxide (ITO), zinc oxide (ZnO), tungsten oxide (WOx), and aluminum nitride (AlN) were employed to fabricate and investigate four transparent resistive random access memory (ReRAMs) structures: ITO/ZnO/ITO (structure 1), ITO/WO3/ZnO/ITO (structure 2), ITO/WOx(x<3)/WO3/ZnO/ITO (structure 3), and ITO/WOx(x<3)/WO3/ZnO/AlN/ITO (structure 4). Structure 4 exhibited less variation in low-resistance states, lower operating voltages, and higher endurance compared with other structures. This phenomenon was attributed to the oxygen-deficient WOx layer in structure 4, which acted as an oxygen ion reservoir for efficient resistive changes, and the WO3 layer limited the filament rupture and formation region. Moreover, the high thermal conductivity of the AlN layer alleviated the thermally activated ion movement of the ReRAM and strengthened the high-resistance state. Structure 4 was found to be the optimal structure, with median operating voltages 1.6V for SET operations and −1.0V for RESET operations, retention of >104s at 200°C, and endurance of 104cycles with a resistance ratio of over 20. Structure 4 exhibited extremely high stability in both low- and high-resistance states during cycling. The transmittance of structure 4 was 85.49%, which is suitable for optoelectronic applications.

Transparent and Flexible Resistive Random Access Memory Based on Al2O3Film With Multilayer Electrodes

We report a transparent and flexible resistive random access memory (ReRAM) using a multi-thin-layer electrode. The transparent and flexible ReRAM includes a multi-thin-layer electrode that is transparent and flexible and an Al2O3 layer as a transparent oxide material. When the multi-thin-layer electrode is used for the top and bottom electrode for the ReRAM, the ReRAM has transparent and flexible properties. The stable memory operation uses a Ti layer and an MgO layer between the Al2O3 layer and multi-thin-layer electrodes. The transmittance of the ReRAM is over 70% at a visible wavelength on a PET substrate. We believe this transparent and flexible ReRAM will be useful for transparent and flexible electronic devices in the future.

Transparent Memory For Harsh Electronics

As a new class of non-volatile memory, resistive random access memory (RRAM) offers not only superior electronic characteristics, but also advanced functionalities, such as transparency and radiation hardness. However, the environmental tolerance of RRAM is material-dependent, and therefore the materials used must be chosen carefully in order to avoid instabilities and performance degradation caused by the detrimental effects arising from environmental gases and ionizing radiation. In this work, we demonstrate that AlN-based RRAM displays excellent performance and environmental stability, with no significant degradation to the resistance ratio over a 100-cycle endurance test. Moreover, transparent RRAM (TRRAM) based on AlN also performs reliably under four different harsh environmental conditions and 2 MeV proton irradiation fluences, ranging from 1011 to 1015 cm−2. These findings not only provide a guideline for TRRAM design, but also demonstrate the promising applicability of AlN TRRAM for future transparent harsh electronics.

Flexible transparent memory cell: bipolar resistive switching via indium–tin oxide nanowire networks on a poly(dimethylsiloxane) substrate

This report describes the fabrication and resistive switching (RS) characteristics of a novel flexible transparent (FT) resistive random access memory (ReRAM) device with a Ag/indium–tin oxide (ITO) nanowire network/ITO capacitor deposited on a PDMS substrate. The transmittance of the device is ∼70% in the visible region, and it exhibits a stable high-resistance state (HRS) to low-resistance state (LRS) ratio (HRS/LRS ratio) in different bending states. The RS characteristics are attributed to the congregate state of oxygen vacancies at different voltages, and the difference between positive and negative bending is mainly contributed by the effect of stress on the conductive layer. The FT-ReRAM can be used as nonvolatile memory element in future flexible transparent devices.

Effect of Working Pressure During ZnO Thin-Film Layer Deposition on Transparent Resistive Random Access Memory Device Characteristics

Effect of Working Pressure During ZnO Thin-Film Layer Deposition on Transparent Resistive Random Access Memory Device Characteristics

Forming-free, bipolar resistivity switching characteristics of fully transparent resistive random access memory with IZO/α-IGZO/ITO structure

Fully transparent resistive random access memory (TRRAM) containing amorphous indium gallium zinc oxide as the resistance switching (RS) layer and transparent conducting oxides (indium zinc oxide and indium tin oxide) as the electrodes was prepared. Optical measurement indicated the transmittance of device exceeds 80% in visible-light wavelength range. TRRAM samples exhibited the forming-free feature and the best electrical performance (VSET = 0.61 V; VRESET = −0.76 V; RHRS/RLRS (i.e. the R-ratio) >103) was observed in the device subject to a post-annealing at 300 °C for 1 hr in atmospheric ambient. Such a sample also exhibited satisfactory endurance and retention properties at 85 °C as revealed by the reliability tests. Electrical measurement performed in vacuum ambient indicated that the RS mechanism correlates with the charge trapping/de-trapping process associated with oxygen defects in the RS layer.

Oxygen-doped zirconium nitride based transparent resistive random access memory devices fabricated by radio frequency sputtering method

In this work, we present a feasibility of bipolar resistive switching (RS) characteristics for Oxygen-doped zirconium nitride (O-doped ZrNx) films, produced by sputtering method, which shows a high optical transmittance of approximately 78% in the visible region as well as near ultra-violet region. In addition, in a RS test, the device has a large current ratio of 5 × 103 in positive bias region and 5 × 105 in negative bias region. Then, to evaluate an ability of data storage for the proposed memory devices, we measured a retention time for 104 s at room temperature (RT) and 85 °C as well. As a result, the set and reset states were stably maintained with a current ratio of ∼102 at 85 °C to ∼103 at RT. This result means that the transparent memory by controlling the working pressure during sputtering process to deposit the ZrNx films could be a milestone for future see-through electronic devices.