Flexible Resistive Switching Memory Research Articles

Flexible SnO2–MoS2 based memristive device exhibiting stable and enhanced memory phenomenon

Flexible non-volatile memory devices have been gaining interest in expanding the digital data storage world. Due to the burgeoning advancement in the healthcare industry, the Internet of Things, and wearable electronics, the demand for ultra-thin, low-power, and flexible memory is increasing. Further, the advancement of synthesis procedures for two-dimensional nanomaterials having better optical, electrical, and mechanical strength with flexibility has fuelled the flexible memory device area, as commonly used flash memory is approaching its physical limit. In this context, the present work reports the flexible resistive switching memory device based on pure molybdenum disulfide (MoS2) and tin oxide (SnO2) based nanocomposite powder synthesized using the simple hydrothermal process. The nanocomposite formation was characterized using x-ray diffraction and Raman spectroscopic techniques. The memory device was fabricated by spin-coating the pure MoS2, pure SnO2, and MoS2–SnO2 nanocomposite film over the ITO-PET flexible substrate. The device was completed by thermally evaporating the thin Al layer through a shadow mask. It was found that MoS2–SnO2 based memory devices exhibited improved switching performance having a higher I ON/I OFF ratio, and lower switching voltage in comparison to pure MoS2 and pure SnO2-based devices (I ON/I OFF ratio ∼100, V = 0.5 V). Furthermore, to check the stability and cyclic performance of the fabricated device, the retention and endurance test was also performed, and the MoS2–SnO2 device retained the HRS and LRS states up to 2 × 103s and showed stable performance up to 100 switching cycles without much degradation, respectively. It should be mentioned that the presently proposed ReRAM device based on SnO2 and MoS2 with flexible and low-power features had excellent potential for use in the wearable device industry.

Biodegradable natural chitosan coating films-based flexible resistive switching memory for transient electronics

Three flexible transparent transient memristors based on degradable natural chitosan coating films are reported. The Mg/Ag-doped chitosan/ITO sandwich structures were prepared by spin coating and drop coating, respectively. The plane structure device was also prepared. Three kinds of device exhibit different memory behaviors, namely, bipolar resistive switching behavior and butterfly resistive switching behavior accompanied by capacitance and negative resistance effect. The elucidated behavior of the bipolar resistive switching can be attributed to filament conduction. The behavior of the butterfly resistive switching is attributed to interface effects. In addition, the three devices have a large on/off ratio and long data retention time, showing promising non-volatile memory characteristics in flexible memory applications. The switching mechanism was evaluated by Schottky emission, hopping and direct tunneling. The transient memristor device prepared in this paper has excellent transient characteristics and controllable performance. This work reveals the potential of biodegradable flexible electronic devices.

Advances in flexible non-volatile resistive switching memory based on organic poly (3, 4-ethylenedioxythio phene): Poly (styrenesulfonate) film

In this work, the resistive switching memory has been investigated in conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) with aluminium (Al) and indium tin oxide (ITO) acting as electrodes. Current-voltage (I-V) characteristics of the fabricated Al/PEDOT:PSS/ITO flexible Polyethylene terephthalate substrate device reveal a non-volatile resistive switching behaviour. The memory device demonstrates resistive switching non-volatile memory with ION/IOFF current ratio between the high resistance state (HRS) and low resistance state (LRS) up to 104. Both the HRS and LRS of the memory devices are stable, showing no significant change in value of ION/IOFF current ratio, which is maintained at 104 in magnitude under continuous read-out testing for 100 cycles at 90º bending angle, and also retention time of 33 min that confirms the device durability and non-volatility. The charge transport mechanism of the fabricated non-volatile organic devices is governed by space-charge limited conduction. It is proposed that the reduction and oxidation of PEDOT:PSS film might be the switching mechanism. Interestingly, the performance of the memory device revealed no detectable degradation and remained identical even after bending the device from 70 to 160° angles, representing excellent flexibility. Besides, the lowest power and the critical compliant current for resistive switching are determined. The power density for 180° (without bending), 160°, 90° and 70° bending angles is ∼ 30 Wm−2. It demonstrates that for a small range of compliance current, our device showed more power capacity with lower voltage consumption, which makes it a potential candidate for low power consumption flexible non-volatile memory devices.

Improved performance of flexible citrus resistive memory device through air plasma

Flexible natural material-based electronics have attracted considerable attention because it can be applied in wearable applications and bio smart electronics. Natural material citrus is used as the dielectric layer in this work to develop flexible resistive switching memory devices, with plasma ITO surface as the bottom electrode (BE) to investigate the effects of air plasma on device performances. The work function difference between the top electrodes (TE) and BE can be increased with plasma treatment. After optimization, the flexible citrus resistive memory device with a large work function difference between the TE and BE exhibits a good ON/OFF ratio of larger than 103, a low set voltage of around 0.76 V, uniform distribution of set voltages, small coefficients of variation of high resistance state, and low resistance state currents, and a long retention time of more than 104 s. The air plasma can also modify the ITO surface to make the surface more hydrophilic. Thus, the citrus film is easier to attach to ITO, which improves the bending performance of the device. The device under a bending radius of 4.9 mm showed no significant ON/OFF ratio changes when compared with that of the flat state. This information on the correlation between the plasma treatment time and the work function of the ITO electrode would be very useful in obtaining stable and uniform resistive switching properties in the flexible natural material-based resistive memory.

Flexible and degradable resistive switching memory fabricated with sodium alginate* *Project supported by the Fund from the Ministry of Science and Technology of China (Grant No. 2018YFE0118300), the National Natural Science Foundation of China (Grant Nos. 11974072, 51902048, 61774031, and 61574031), the “111” Project, China (Grant No. B13013), the China Postdoctoral Science Foundation, China (Grant No. 2019M661185), the Fundamental Research

Transient electronics has attracted interest as an emerging technology to solve electronic-waste problem, due to its physically vanishing ability in solution. Here in this work, we demonstrate a flexible and degradable transient resistive switching (RS) memory device with simple structure of Cu/sodium alginate (SA)/ITO. The device presents excellent RS characteristics as well as high flexibility, including low operating voltage (< 1.5 V) and multilevel RS behavior. No performance degradation occurs after bending the device 50 times. Moreover, our device can be absolutely dissolved in deionized water. The proposed SA-based transient memory device has great potential for the development of green and security memory devices.

Flexible Resistive Switching Memory Devices Based on Graphene Oxide Polymer Nanocomposite

Flexible resistive switching memory devices based on graphene oxide (GO) polymer nanocomposite were prepared on flexible substrate to research the influence of bending on resistive switching behavior. The devices showed evident response in resistive switching memory characteristics to flexible bending. The 2000 cycles flexible bending leads to the switch of resistive switching memory characteristic from write-once-read-many time memory (WORM) to static random access memory (SRAM). Both WORM and SRAM memory properties are all repeatable, and the threshold switching voltage also showed good consistency. The resistive switching mechanism is attributed to the formation of carbon-rich conductive filaments for nonvolatile WORM characteristics. The bending-induced micro-crack may be responsible for the partial broken of the electrical channels, and may lead to the volatile SRAM characteristics.

Flexible Resistive Switching Memory with a Schottky Diode Function Based on a Zinc Oxide/Methylene Blue Heterojunction

For the commercialization of a resistive switching memory device, many researchers are designing different memory structures for a crossbar array. In the present work, we propose a flexible Schottky diode-based resistive memory device based on a zinc oxide (ZnO) and methylene blue (MB) heterojunction. The operating voltage of the proposed memory device is ±3 V, and high-resistance state (HRS) and low-resistance state (LRS) are 20.408 GΩ and 126.795 MΩ, respectively, and the Roff/Ron ratio is ∼ 160.97 at a voltage read of −0.30 V. It shows high retention and endurance performance for more than 500 cycles and 30 days, respectively, with bending capability up to 10 mm. The proposed device can be used in flexible and printed electronics for memory and storage purposes.

Electroforming-Free, Flexible, and Reliable Resistive Random-Access Memory Based on an Ultrathin TaOx Film.

A flexible resistive switching (RS) memory was fabricated on a Ta/TaOx/Pt/polyimide (PI) structure with various TaOx thicknesses (5, 10, and 15 nm). The oxygen vacancy (VO) concentrations in the TaOx films were also adjusted by controlling the oxygen partial pressure during TaOx deposition to obtain different electroforming (EF) behaviors. When the devices of Ta/TaOx/Pt/PI showed the EF-free characteristic, the reliability and endurance performance were greatly improved compared to those of devices with EF behavior. The resistive crossbar array using the thinnest (5 nm) TaOx film showed high uniformity and endurance performance up to 108 switching cycles even after bending to a 2 mm radius 10 000 times. However, for the EF samples, the endurance performance was much lower and involved the reset failure, even with the 5 nm TaOx film.

Flexible resistive switching device based on the TiO2 nanorod arrays for non-volatile memory application

In this article, a flexible resistive switching memory is developed based on TiO2 nanorod arrays with interstice between the nanorods to release the bending stress/strain. The device shows a stable forming-free bipolar resistive switching behavior with low operating voltage of below 3 V, high ON/OFF ratio of above 102, good retention for more than 105 s, good endurance of 107 cycles, and good thermal stability of the high resistance and low resistance state at 85 °C during the retention and fatigue tests. Moreover, under the different bending radius from 12 mm to 5 mm, the electrical performances referring to operating voltage and ON/OFF ratio of the device show few changes, and under the bending cycles of 400 times with the bending radius of 12 mm, all of the devices show no interfacial crack or delamination as well as keep the bipolar resistive switching behavior with the low operating voltage and high ON/OFF ratio. The good performances of the devices suggest that the TiO2 nanorod arrays resistive switching device may open up new possibilities in realizing high-performance flexible memory.

One-step solution deposited all-inorganic perovskite CsPbBr3 film for flexible resistive switching memories

Halide perovskites have attracted a great deal of attention due to their remarkable performances in solar cells, photodetectors, lasers, light emitting diodes, and memories. However, the issue of low quality of the halide perovskite films still restricts their potential applications. Here, the all-inorganic perovskite CsPbBr3 films prepared by the one-step solution deposition method are adopted as the switching layer to fabricate the flexible resistive switching (RS) memory devices. The devices exhibit a typical bipolar RS behavior including long data retention, high ON/OFF ratio, and good cycling endurance under bending, indicating that the one-step solution deposited CsPbBr3 films are promising candidates for the RS memory devices. In addition, by controlling the compliance current and applied stop voltage, the flexible RS devices demonstrate the multilevel storage capability. This work opens up the opportunity for future flexible, high performance, and multibit storage capability RS devices based on all-inorganic perovskite CsPbBr3 films.

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.

Photophysical, electrochemical and flexible organic resistive switching memory device application of a small molecule: 7,7-bis(hydroxyethylpiperazino) dicyanoquinodimethane

Abstract Utilization of Hydroxyethyl piperazine in a straightforward reaction with tetracyanoquinodimethane (TCNQ) produced a unique multifunctional molecular material 7,7-bis(Hydroxyethyl piperazino)dicyanoquinodimethane (BHEPDQ) exhibiting fluorescence, electrochemical property and capability of organic resistive switching (RS) memory device application. Obtained molecular material has been characterized by various spectroscopic and single crystal X-ray diffraction techniques. Fluorescence decay study in solid revealed single excited state conformation with life time ~1.26 ns. The energy levels were derived from the cyclic voltammetry and the electrochemical band gap was found to be 2.76 eV, good agreement with the theoretical band gap (2.75 eV). Flexible Al/BHEPDQ/ITO/PET RS non-volatile memory device was fabricated and different electrical performances were tested, which demonstrated excellent switching property. The SET/RESET voltage was found to be 2.26 V/– 2.88 V and the device offered high retention without any distortion. The effect of convex (upward bend) and concave (downward bend) bending on the resistive switching behavior of the same device was also investigated. The devices on a flexible platform under the application of a strain through different bending conditions exhibit no degradation on the electrical properties and the obtained results also matched well with the device under no stress, demonstrates its high reliability and ability for practical flexible electronic applications. The memory operations were also explained employing a proposed band diagram and transport studies were explicated to have the better insight of the obtained electrical performances. This work offers a new approach towards the realization of a novel organic material and its integration for efficient flexible memory device applications.

Non-volatile resistive switching based on zirconium dioxide: poly (4-vinylphenol) nano-composite

Recently, resistive switching devices are getting tremendous attention since they can be used for data storage in future. In this paper, we propose a non-volatile resistive switching device based on inorganic and organic nano-composite of zirconium dioxide (ZrO2) and poly (4-vinylphenol) (PVP), respectively. The nano-composite active layer ZrO2:PVP is fabricated on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrate through a spin coater technology and the top electrodes are fabricated by using silver (Ag) epoxy. The proposed device demonstrates a bipolar resistive switching at low operating voltage of ± 1.5 V with high resistance state and low resistance state of 11.438 kΩ and 262.25 Ω, respectively. To verify the non-volatility and long-term stability, the retention time is checked for more than 30 days and Roff/Ron resistance ratio is ~ 44. The proposed device is analyzed electrically and mechanically to analyze the effect of PVP in ZrO2 for better memory application and FESEM is used for the morphological characteristics of the device. These results ensure that the ZrO2:PVP nano-composite-based resistive switching device can be a possible candidate for the forthcoming flexible and low-power non-volatile resistive switching memory device.

Fabrication of carboxymethyl cellulose and graphene oxide bio-nanocomposites for flexible nonvolatile resistive switching memory devices

Nowadays the development of natural biomaterials as promising building polymers for flexible, biodegradable, biocompatible and environmentally friendly electronic devices is of great interest. As the most common natural polymers, cellulose and its derivatives have the potential to be applied in the devices owing to the easy processing, nontoxicity and biodegradability. Here, write-once-read-many-times resistive switching devices based on biodegradable carboxymethyl cellulose-graphene oxide (CMC-GO) nanocomposite are demonstrated for the first time. The hybridization sites formed by the gelation of CMC and GO molecules contribute to the excellent memory behaviors. When compared with devices base on pure GO and CMC, the device with the Al/CMC-GO/Al/SiO2 structure exhibits brilliant write-once-read-many-times (WORM) switching characteristics such as high ON/OFF current ratio of ˜105, low switching voltage of 2.22 V, excellent stability and durability. What's more, the device shows high flexibility and good resistive switching behaviors even with soft PET substrate (Al/CMC-GO/Al/PET structure). This newly designed cellulose-graphene oxide-based polymer nanocomposites are quite cheap and easy processed for large scale manufacturing of memory devices and can further contribute to future biodegradable data storage applications such as portable stretchable displays, wearable electronics and electronic skins in the coming age of artificial intelligence.

Flexible nonvolatile resistive switching memory devices based on Bi2Te3 nanosheets films

Flexible nonvolatile resistive switching memory is a promising candidate for next generation storage technologies. Exploring new materials is of crucial importance to achieve further performances of flexible nonvolatile resistive switching memory. In this work, topological insulator bismuth telluride (Bi2Te3) nanosheets films were introduced into resistive switching memory devices firstly, a typical sandwich construction of Ag/Bi2Te3/indium tin oxide/polyethylene terephthalate with good flexibility, which exhibits nonvolatile bipolar resistive switching characteristics of operation voltage, good mechanical flexibility, and good storage stability. Furthermore, trap-controlled space charge limited current, thermionic emission are the dominant conduction mechanisms in the carrier transport. This work will provide an opportunity for Bi2Te3 nanosheets to be used in flexible electronics application.

Solution-processed flexible non-volatile resistive switching device based on poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4, 8-diyl)]: polyvinylpyrrolidone composite and its conduction mechanism

Recently, solution-processed resistive switches for wearable electronics have got tremendous attention and are required for different applications due to their easy process and fabrication. Hence, this paper proposes the solution-processed resistive switching memory device based on two polymers, poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4, 8-diyl)] (F8BT) and polyvinylpyrrolidone (PVP) composite, which is fabricated on a flexible indium–tin–oxide (ITO)-coated polyethylene terephthalate (PET) substrate through spin coating technology. The fabricated device demonstrates a perfect non-volatile bipolar resistive switching through small operating voltage sweeping of ± 1.5 V, and its high-resistance state (HRS) and low-resistance state (LRS) are 92678.89 Ω and 337.85 Ω, respectively. To verify the non-volatility and long-term stability, the device is checked for more than 700 endurance cycles. During these cycles, the variations of HRS and LRS are 48 Ω and 37.35 Ω, respectively. The retention time is checked for more than 60 days, and the ROFF/RON ratio is 274.31. The bendability is carried out up to bending diameters < 10 mm, and FESEM is used for the morphological characteristics of the device. Conduction mechanism of the proposed device is supported by space charge-limited conduction (SCLC) which is explained by the log–log I–V slope-fitting curve. The results insure that the F8BT:PVP composite-based resistive switching device is to be a potential candidate for the future flexible and low-power non-volatile resistive switching memory device.

Biodegradable Natural Pectin-Based Flexible Multilevel Resistive Switching Memory for Transient Electronics.

Transient electronics that can physically vanish in solution can offer opportunities to address the ecological challenges for dealing with the rapidly growing electronic waste. As one important component, it is desirable that memory devices combined with the transient feature can also be developed as secrecy information storage systems besides the above advantage. Resistive switching (RS) memory is one of the most promising technologies for next-generation memory. Herein, the biocompatible pectin extracted from natural orange peel is introduced to fabricate RS memory devices (Ag/pectin/indium tin oxides (ITO)), which exhibit excellent RS characteristics, such as forming free characteristic, low operating voltages (≈1.1 V), fast switching speed (<70 ns), long retention time (>104 s), and multilevel RS behaviors. The device performance is not degraded after 104 bending cycles, which will be beneficial for flexible memory applications. Additionally, instead of using acid solution, the Ag/pectin/ITO memory device can be dissolved rapidly in deionized water within 10 min thanks to the good solubility arising from ionization of its carboxylic groups, which shows promising application for green electronics. The present biocompatible memory devices based on natural pectin suggest promising material candidates toward enabling high-density secure information storage systems applications, flexible electronics, and green electronics.

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.

Solution processed flexible resistive switching memory based on Al-In-O self-mixing layer

In this work, a solution processed Al-In-O/InOx bilayer resistive switching random access memory (RRAM) is demonstrated at temperature as low as 180 °C. The memory cell exhibits remarkable forming free resistive switching characteristics with stable data retention and low set/reset voltages. More importantly, this solution processed bilayer shows stable memory properties under different bending angles on a flexible substrate. The resistive switching mechanism was systematically investigated. Compared to single layer devices, an Al-In-O mixing layer is induced by the solution process in the bilayer RRAM. The first principle calculation confirms that in the Al-In-O mixing layer, the formation energy of oxygen vacancies is significantly reduced compared with the AlOx layer. As a result, the formation of the oxygen vacancy based conductive filament is realized without the electroforming process. The RRAM fabricated by the printable solution process at low temperature shows great application potential in next generation wearable electronics.

A flexible nonvolatile resistive switching memory device based on ZnO film fabricated on a foldable PET substrate

In this work, a flexible resistive switching memory device based on ZnO film was fabricated using a foldable Polyethylene terephthalate (PET) film as substrate while Ag and Ti acts top and bottom electrode. Our as-prepared device represents an outstanding nonvolatile memory behavior with good “write–read–erase–read” stability at room temperature. Finally, a physical model of Ag conductive filament is constructed to understanding the observed memory characteristics. The work provides a new way for the preparation of flexible memory devices based on ZnO films, and especially provides an experimental basis for the exploration of high-performance and portable nonvolatile resistance random memory (RRAM).