Write-once-read-many-times Memory Research Articles

CsPbI3 Perovskite Quantum Dot-Based WORM Memory Device with Intrinsic Ternary States.

The migration of mobile ionic halide vacancies is usually considered detrimental to the performance and stability of perovskite optoelectronic devices. Taking advantage of this intrinsic feature, we fabricated a CsPbI3 perovskite quantum dot (PQD)-based write-once-read-many-times (WORM) memory device with a simple sandwich structure that demonstrates intrinsic ternary states with a high ON/OFF ratio of 103:102:1 and a long retention time of 104 s. Through electrochemical impedance spectroscopy, we proved that the resistive switching is achieved by the migration of mobile iodine vacancies (VIs) under an electric field to form conductive filaments (CFs). Using in situ conductive atomic force microscopy, we further revealed that the multilevel property arises from the different activation energies for VIs to migrate at grain boundaries and grain interiors, resulting in two distinct pathways for CFs to grow. Our work highlights the potential of CsPbI3 PQD-based WORM devices, showcasing intrinsic multilevel properties achieved in a simple device structure by rationally controlling the drift of ionic defects.

Multistate structures in a hydrogen-bonded polycatenation non-covalent organic framework with diverse resistive switching behaviors

The inherent structural flexibility and reversibility of non-covalent organic frameworks have enabled them to exhibit switchable multistate structures under external stimuli, providing great potential in the field of resistive switching (RS), but not well explored yet. Herein, we report the 0D+1D hydrogen-bonded polycatenation non-covalent organic framework (HOF-FJU-52), exhibiting diverse and reversible RS behaviors with the high performance. Triggered by the external stimulus of electrical field E at room temperature, HOF-FJU-52 has excellent resistive random-access memory (RRAM) behaviors, comparable to the state-of-the-art materials. When cooling down below 200 K, it was transferred to write-once-read-many-times memory (WORM) behaviors. The two memory behaviors exhibit reversibility on a single crystal device through the temperature changes. The RS mechanism of this non-covalent organic framework has been deciphered at the atomic level by the detailed single-crystal X-ray diffraction analyses, demonstrating that the structural dual-flexibility both in the asymmetric hydrogen bonded dimers within the 0D loops and in the infinite π–π stacking column between the loops and chains contribute to reversible structure transformations between multi-states and thus to its dual RS behaviors.

Donor-acceptor hyperbranched copolyimides contain different linear segment for electrochromic and resistive memory devices

In this work, two hyperbranched copolyimides (O-coPI and F-coPI) were synthesized which the diamine donors in the linear segment contain different substituents. To investigate the effects of substituents in donors on their memory behavior, the corresponding linear polyimides (F-LPI and O-LPI) were also discussed. The devices based on hyperbranched copolyimides exhibited non-volatile write once read many times memory (WORM) behavior, while the devices based on linear polyimides exhibited volatile memory dynamic random-access memory (DRAM) behavior. Polyimides (O-coPI and O-LPI) prepared with methoxy-substituted diamine donors have low switching voltages due to their good electron-donating properties. In addition, O-coPI and O-LPI also exhibit electrochromic properties. Hyperbranched copolyimide O-coPI have higher optical contrast and faster response time than that of linear polyimide O-LPI. This work provides a new direction for the development of multifunctional memory materials.

Write-Once-Read-Many-Times Memory Characteristics with a Large Memory Window Operating at a Low Voltage by Li-Ion Incorporation from the LiCoOx Ion-Supplying Layer into the InGaZnO Channel of a Thin-Film Transistor

Write-once-read-many-times (WORM) memory characteristics with a large memory window are demonstrated in a thin-film transistor (TFT) composed of an indium-gallium-zinc oxide (IGZO) channel and a lithium-cobalt oxide (LiCoOx) ion-supplying layer in the gate oxide. While the device with a thicker (5 nm) tunneling oxide showing a threshold voltage shift (ΔVT) of about 5 V by electron charging upon positive gate voltage (VGS) sweep to +25 V, the device with a 2 nm-thick tunneling oxide exhibits a large memory window with ΔVT > 20 V by Li-ion migration from LiCoOx to IGZO channel, which can be controlled as multilevel states with respect to the VGS amplitude. Incorporation of Li ions into the IGZO channel acting as p-type dopants reduces carrier concentration in the channel and consequently increases VT. The increased VT and the consequently reduced drain current are not instantly restored back by applying negative VGS, featuring WORM memory characteristics. Although the device undergoes partial retention loss, the retention remains up to about 90% after 100 min of retention time. These results verify WORM memory operations in the IGZO TFTs through gate voltage-driven Li-ion incorporation into the IGZO channel to modify its conductive states instead of using a typical electrical charging route.

Write-once-read-many-times memory device based on Pt/BiFeO3/LaNiO3 heterostructures

Nonvolatile memory devices based on resistive switching effects are promising candidates for next generation high performance nonvolatile data storage. Here, we report the write-once-read-many-times (WORM) resistive switching behavior for the first time in Pt/BiFeO3/LaNiO3 heterostructures. BiFeO3 thin films with (100) preferred orientation have been prepared by RF magnetron sputtering combined with annealing at temperature higher than 600 ℃, and show excellent WORM resistive switching behaviors with data retention for>3600 s and reliable endurance for>1000 cycles. The devices with BiFeO3 annealed at 650 ℃ exhibit extremely high ON/OFF ratio (>3 × 104) and low switching voltage (∼3 V) due to the high quality of BiFeO3 thin films. The observed resistive switching behavior is attributed to the formation of permanent conducting filaments that composed of oxygen vacancies. These results demonstrate that BiFeO3 is promising for novel WORM memory device applications.

Two-Terminal Nonvolatile Write-Once-Read-Many-Times Memory Based on All-Inorganic Halide Perovskite.

Write-once-read-many-times (WORM) memory belonging to an important non-volatile memory type achieves the read-only state after the write operation and is used in the fields of data security storage widely. WORM memory has been developed based on a variety of materials. In recent years, halide perovskites have become the research hotspot material for this memory due to its excellent properties. Here, the all-inorganic CsPbBr3 perovskite thin film was prepared on a FTO substrate by using a two-step method. The prepared CsPbBr3 thin films have the characteristics of densely packed crystal grains and smooth surface. The device, having the FTO/CsPbBr3/Al sandwich structure by evaporating the Al electrode onto the CsPbBr3 thin film, represents the typical WORM behavior, with long data retention time (104 s), a low operation voltage (2.1 V) and a low reading voltage (0.1 V). Additionally, the resistance transition mechanism of the resulting WORM devices was analyzed.

Enhancing the Resistive Switching Behavior of WORM Memory Devices Using D-π-A Based Ester-Flanked Quinolines.

Donor-Acceptor systems are highly appreciated in the field of organic memory devices due to their efficient charge transport within the systems. In this work, we have designed and synthesized a D-π-A system constituting ester-flanked quinolines and functionalized triarylamines (TAA) through a single-step cross-coupling reaction to fabricate memory devices via Write-Once Read-Many times (WORM) non-volatile memory. Structure-property relationships are reconnoitered for these conjugated D-π-A systems through a series of UV, fluorescence, XRD, DFT, and memory characterizations. The UV and CV data show efficient charge transfer with intramolecular charge transfer occurring at 407-417 nm and a short band gap of 2.56-2.65 eV. An enhancement in the resistive switching behavior of the memory devices is observed for the compounds with simple TAA-quinoline and tert-butylphenyl substituted TAA and fluorophenyl substituted quinoline due to balanced charge distribution in the compounds. This enhanced switching induces an on/off ratio of 103 by generating a highly ordered arrangement in the thin films. The HOMO, LUMO levels, and the ESP images together estimate a charge transfer and charge trapping as the plausible mechanism for the solution-processable WORM memory devices. The longer retention time (103 s) and lower threshold voltages (-1.21--2.12 V) of the devices makes them intriguing compounds for memory applications.

Regulating the electrical resistive switching behaviors of polyimides through different steric hindrance substituents on 2,7-position of tetraphenyl fluorene diamines moieties

Three novel polyimides (PI(TPF-Br BPDA), PI(TPF-Ph BPDA), and PI(TPF-Ph-OMe BPDA)) with tetraphenyl fluorene (TPF) were synthesized and tested. The laboratorial results showed that the constructed electronic devices exhibited different memory behaviors due to the different steric hindrance substituents (bromine atom, phenyl, and 3,5-dimethoxyphenyl) in 2,7-position of TPF molecule. The memorizers based on PI(TPF-Br BPDA) and PI(TPF-Ph BPDA) presented volatile dynamic random access memory (DRAM) feature with turn-on voltages of −2.39 and +1.45 V, as same as −1.71 and +1.74 V, separately. However, the PI(TPF-Ph-OMe BPDA) based apparatus exhibited non-volatile write-once read-many-times memory (WORM) behavior with turn-on voltage of −1.13 V, due to the more charge traps of 3,5-dimethoxyphenyl moieties and higher dipole moment. The switching mechanism was verified by quantum simulation of energy level, electrostatic potential (ESP) surface and dipole moment. These results indicated that the electrical memory performance of the synthesized TPF-based PIs could be adjusted by modifying the electron donor structure.

Tuning memory behavior from volatile to nonvolatile by increasing the linear segment length of hyperbranched copolyimides

In this work, three donor-acceptor contained hyperbranched copolyimides (O30-coPI, O50-coPI and O70-coPI) with different linear segment length were synthesized by varying the feed ratio of monomers. The memory device based on O30-coPI showed an unstable volatile static random access memory (SRAM) behavior, while the devices based on O50-coPI and O70-coPI with longer linear segment exhibited stable non-volatile write once read many times memory (WORM) behavior. Theoretical simulations based on density functional theory (DFT) showed that the linear segment induce a twisted conformation, which helps to stabilize the charge-separation state. As the linear segment grows, the conformation becomes more distorted, resulting in a more stable charge-separated state. Compared to O30-coPI, O50-coPI and O70-coPI have longer linear segment and more twisted conformations, thus they exhibit non-volatile memory behavior. This work demonstrates that the memory behavior can be controlled by changing the linear segment length of HB-coPI, providing a practicable strategy for the design of polymer memory materials.

Memory effect of vertically stacked hBN/QDs/hBN structures based on quantum-dot monolayers sandwiched between hexagonal boron nitride layer

The characteristics of a flexible write-once-read-many-times (WORM) memory fabricated with monolayered 0-dimensional (0D) CdSe–ZnS quantum dots (QDs) layers sandwiched between two insulating 2-dimensional (2D) hexagonal boron nitride (hBN) multilayers were investigated by electrical measurement method. The hBN/QDs monolayer/hBN structure was fabricated in a vertical stacked structure using a technique which control the formation of the QDs monolayer. QDs monolayer was formed by electrostatic interaction between the negative charge group on the CdSe–ZnS QDs surface and the positive charge group on the hBN surface. The device has a WORM characteristic due to the presence of QDs in the current-voltage (I–V) measurement. When a bias is applied, carriers were initially trapped by tunneling due to the QDs and then a conductive filament was formed in the hBN, which were not detrapped and exhibit characteristics of write-once-read-many-times memory. The maximum ON/OFF ratio of the current for the devices was as large as 4 × 10, and the endurance was 5 × 10 4 cycles, and a retention time was larger than 1 × 10 5 s. In order to explain the carrier transport mechanism and conductive filament of the WORM memory device caused by QDs, it through various methods such as I–V fitting data, simulation, and conductive AFM. Unlike the conventional conductive filament mechanism, through random diffusion such as Ag filament, the Au/hBN/QD/hBN/ITO/PET structures implemented a consistent conductive filament using Au metal and QDs active layer.

Write-once-read-many-times characteristics of CuO layer with Ag conductive bridges

This paper demonstrates write-once-read-many-times (WORM) behavior of an Ag/CuO/n+-Si memory device. The CuO resistive switching layer with a thickness of 9.7 nm was prepared using a sol–gel process. The device shows a low conduction current of 10−10 A at a read voltage of 1 V. A sudden current increase is observed when the voltage increases to ∼3 V, corresponding to a resistance switching from a high-resistance state (HRS) to a low-resistance state (LRS). After that, the device remains in the LRS. Degradation of the HRS and the LRS is not observed for 104 read cycles. The HRS/LRS resistance ratio is 106, and the data retention time is over 105 s. The abrupt current increase cannot be triggered by a negative bias. The formation of Ag conductive bridges in the CuO layer is responsible for the resistance switching. Statistical analyses are performed to study the distributions of the set voltages and the resistances in the HRS and LRS. The effect of the compliance current on the operating current of the Ag/CuO/n+-Si WORM memory is also investigated. The carrier transport mechanisms are found to be dominated by Schottky emission, Ohmic, and SCLC conductions. The energy barrier is 1.066 eV, which is extracted by Schottky emission analysis.

Electron configurations at 3d orbital of metal ion determining charge transition process in memory devices

Functional polymeric materials with electrical bi-stable states possess significant potential for high-density data storage due to their nanoscale memory site, three-dimensional-stacking ability and intrinsic flexibility. Aromatic polyimides bearing donor-acceptor (D-A) skeleton could form charge transfer complex (CTC) under electrical field, leading to their feasibility as memory materials. Three novel porphyrinated polyimides DATPP-DSDA, Zn-DATPP-DSDA and Mn-DATPP-DSDA were designed and synthesized for information memory applications. Metal ions with different electron configurations at 3d orbital have a determining influence on memory behaviors of polyimides: nonvolatile write-once-read-many-times memory (WORM) for DATPP-DSDA, volatile static random access memory (SRAM) for Zn-DATPP-DSDA, but no memory performance for Mn-DATPP-DSDA. By comparing the contribution of orbital transition and hole-electron distribution of charge-transfer excited states, roles of metal ions in regulating memory types were discussed. Molecular simulation results indicate that the Zn ion could play a bridge role in paving the route for excited electrons from a D to an A, while a trap role for the Mn ion in hindering this process. This study proves the feasibility of the strategy for modulating the memory behaviors of porphyrinated polyimides by varying the central metal ion and provides the exact effects of various metal ions on regulating charge transfer processes.

TiO x -based self-rectifying memory device for crossbar WORM memory array applications* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61774079 and 61664001), the Science and Technology Plan of Gansu Province, China (Grant No. 20JR5RA307), and the Key Research and Development Program of Gansu Province, China (Grant No. 18YF1GA088).

Resistive switching with a self-rectifying feature is one of the most effective solutions to overcome the crosstalk issue in a crossbar array. In this paper, a memory device based on Pt/TiO x /W structure with self-rectifying property is demonstrated for write-once-read-many-times (WORM) memory application. After programming, the devices exhibit excellent uniformity and keep in the low resistance state (LRS) permanently with a rectification ratio as high as 104 at ± 1 V. The self-rectifying resistive switching behavior can be attributed to the Ohmic contact at TiO x /W interface and the Schottky contact at Pt/TiO x interface. The results in this paper demonstrate the potential application of TiO x -based WORM memory device in crossbar arrays.

Flexible and fully transparent WORM memory devices based on Ag nanoparticles blended with poly(ethylene-co-vinyl acetate)

Silver nanoparticles (Ag NPs) blended with poly(ethylene-co-vinyl acetate) (EVA) were used as an active layer to fabricate flexible and fully transparent memory devices by using the spin-coating method followed by the thermal roll lamination technique with the structure of ITO/EVA:Ag NPs/ITO. The devices exhibited a non-volatile write-once-read-many-times (WORM) memory type and possessed current bi-stability with ON/OFF current ratio within the range of 104-105 at a reading voltage of +1 V. The data continuous read operations reached more than 10 h, which revealed the stability of the memory devices over a long period of time. The conduction mechanisms of the memory device could be explained by theoretical models and proposed by electron trapping at the trapping center of Ag NPs inside the EVA matrix. In addition, the memory device showed a fast response of 231 ns and was fully transparent with maximum transmittance of the device at 83.2%. Further, the devices could be operated under the bending condition of more than 0.83% strain.

Study on synthesis, characterization, and nonvolatile memory behavior of ferrocene-containing metallopolymers

In this work, two metallopolymers (P1 and P2) were designed and synthesized through coupling of ferrocene-anchored fluorene derivatives with porphyrin and benzene based diethynyl ligand, respectively. The chemical structure and physical properties of these two metallpolymers were fully characterized, which indicate that these two metallopolymers are thermally stable and semiconducting. Then, sandwich-like organic resistive memory based on P1 and P2 for data storage were explored. The memory device testing results manifest that both P1 and P2 are of the stable electric bistability and show write once read many times memory (WORM) characteristics.

Transparent write-once-read-many-times memory devices based on an ITO/EVA:rGO/ITO structure

Fully transparent electronic devices play an important role in electronic applications. Well-known examples are the wearable devices and transparent displays; their applications are transparent memory devices of interest. The transparent write-once-read-many-times (WORM) memory devices based on synthesized graphene oxide (GO) blended in poly (ethylene-co-vinyl acetate) (EVA) had been fabricated by a thermal roll lamination technique in which the synthesized GO inside the EVA matrix was reduced into reduced graphene oxide (rGO) during the lamination process. The memory devices exhibited an optical transmittance of more than 60% in the visible light region. The conduction mechanisms of the memory devices were identified using theoretical models based on the current–voltage (I–V) curves. The fitted I–V results were described by the conductive filaments in which electrons were transported through the rGO direct contacts. In addition, the maximum ON/OFF current ratio of the transparent WORM memory device was approximately 5 × 105, and the retention time tests showed two current states with good data retention properties under different temperatures.

Highly-stable write-once-read-many-times switching behaviors of 1D\u20131R memristive devices based on graphene quantum dot nanocomposites

One diode and one resistor (1D–1R) memristive devices based on inorganic Schottky diodes and poly(methylsilsesquioxane) (PMSSQ):graphene quantum dot (GQD) hybrid nanocomposites were fabricated to achieve stable memory characteristics. Current-voltage (I-V) curves for the Al/PMSSQ:GQDs/Al/p-Si/Al devices at room temperature exhibited write-once, read-many-times memory (WORM) characteristics with an ON/OFF ratio of as large as 104 resulting from the formation of a 1D–1R structure. I-V characteristics of the WORM 1D–1R device demonstrated that the memory and the diode behaviors of the 1D–1R device functioned simultaneously. The retention time of the WORM 1D–1R devices could be maintained at a value larger than 104 s under ambient conditions. The operating mechanisms of the devices were analyzed on the basis of the I–V results and with the aid of the energy band diagram.

Biodegradable skin-inspired nonvolatile resistive switching memory based on gold nanoparticles embedded alkali lignin

Natural biomaterials are capable of producing biodegradable and/or biocompatible electronic devices for vast applications such as next-generation green data storage. Here, we demonstrate an environment-friendly alkali lignin as a favourable candidate for resistive switching memory storage applications. The resistive memory devices based on gold nanoparticles embedded alkali lignin (Au NPs:lignin) exhibits a typical write-once-read-many-times memory (WORM) resistive switching behaviour with a large on-off ratio (>104), and long data retention characteristics (>103 s) under low power operation (4.7 V). Au NPs acting as trapping sites in the active layer are responsible for the resistive switching mechanism. The active layer is fabricated on organic substrates through facile solution-processed methods under normal ambient conditions. The skin-inspired polylactide (PLA) film is utilized as an ultrathin substrate endowing the memory devices with good mechanical support and biodegradability. This work opens up new avenues towards renewable and environmentally benign lignin-based materials for biodegradable electronic devices.

Thickness effect of nickel oxide thin films on associated solution-processed write-once-read-many-times memory devices

With self-prepared nickel acetate based solution, NiO thin films with different thicknesses have been fabricated by spin coating followed by thermal annealing. By forming a two-terminal Ag/NiO/ITO structure on glass, write-once-read-many-times (WORM) memory devices are realized. The WORM memory behavior is based on a permanent switching from an initial high-resistance state (HRS) to an irreversible low-resistance state (LRS) under the application of a writing voltage, due to the formation of a solid bridge across Ag and ITO electrodes by conductive filaments (CFs). The memory performance is investigated as a function of the NiO film thickness, which is determined by the number of spin-coated NiO layers. For devices with 4 and 6 NiO layers, data retention up to 104 s and endurance of 103 reading operations in the measurement range have been obtained with memory window maintained above four orders for both HRS and LRS. Before and after writing, the devices show the hopping and ohmic conduction behaviors, respectively, confirming that the CF formation could be the mechanism responsible for writing in the WORM memory devices.

Write-Once-Read-Many-Times Characteristic of InZnO Oxide Semiconductor

Write-once-read-many-times (WORM) characteristics of sol-gel InZnO (IZO) thin films are investigated in this paper. The Ag/IZO/n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si WORM memory exhibits a poor read disturb immunity. Although a postannealing process is capable of improving the performance due to formation of a thin interfacial AgxO layer, the memory window is only 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the resistance in high resistance state degrades dramatically during read disturb testing. By replacing the Ag electrode with an Al electrode, without the postannealing process, the Al/IZO/n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si WORM memory shows a superior read disturb immunity and a large memory window of 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The read endurance is over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> cycles. X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and energy dispersive spectroscopy were utilized to investigate the physical mechanisms of the WORM characteristics. The carrier conduction mechanisms were also explored.