Write-once Read-many Memory Research Articles

Design of Triphenylamine-based D-π-A Systems for Efficient Ternary WORM Memory Devices.

The impact of various substituent moieties on the molecular framework of a conjugated D-A system in resistive switching memory property has been scrutinized through an array of novel D-π-A molecules. The synthesized molecules with triphenylamine (TPA) as the electron donor and dicyanovinylindanone (IC) as the electron acceptor demonstrated substantial non-volatile WORM (Write-Once Read-Many) memory behaviour with appreciable ON/OFF current ratios up to 105 and a lowest recorded threshold voltage of -0.80 V. The well-balanced combination of these potent electron donating and accepting units culminated in exceptional intramolecular charge transfer interactions and minimal band gap values (1.82-2.31 eV) for the molecules, as demonstrated by photophysical and electrochemical investigations. These factors, coupled with the thin-film morphological studies, corroborated the superior performance of the fabricated devices. A longer retention time of 2000s and an endurance of 100 cycles mark the substantial stability of the memory devices. Moreover, conversion from binary to ternary WORM memory was achieved by the effective tuning of the electronic properties of the D-A systems by various substituent moieties. Molecular simulation studies revealed that the resistive switching phenomenon arises from a synergistic interplay of charge transfer and charge trapping processes within these D-A systems.

A carbon electrode approach for TiO2-write-once-read-many resistive memories

Nanomaterials are a potential alternative to conventional random resistive access memory (ReRAM) in non-volatile memory (NVM) due to their unique electrical and physical properties. Nevertheless, obtaining a specific NVM characteristic [particularly Write-Once-Read-Many (WORM)] using carbon-based electrodes necessitates further assessment. This study proposed a reinvented methodology for TiO2-based devices to produce WORM memory behavior using the doctor blade method. A carbon/graphite counter electrode (Gr/Cb) was fabricated and characterized for TiO2-based resistive switching devices. Consequently, the Gr/Cb electrode device quickly transitioned from a high to low resistance state, suggesting WORM memory behavior. Approximately 66.7 % improvement (∼1.8 V–∼0.6 V) was observed in the required applied voltage when the active area was reduced, indicating lower power consumption. Overall, this study provided evidence of the approach's feasibility in practical applications, demonstrating lower costs and simplicity. The structure also highlighted the importance of understanding the WORM behavior for effectively utilizing carbon-based electrodes in non-volatile memories.

Inherent D-A Architecture in Indoloquinoxalines with an Array of Substituents for Non-Volatile Memory Device Applications.

Donor-acceptor (D-A)-based architecture has been the key to increase storage capability efficiency through the enhanced charge transportation in the fabricated device. We have designed and synthesized a series of functionalized indoloquinoxalines (IQ) for non-volatile organic memory devices. The investigation on UV-visible spectra reveals the absorption maxima of the compounds around 420 nm, attributed to the intramolecular charge transfer between indole and quinoxaline moiety. The irreversible anodic peak in the 1.0 to 1.5 V range indicates the indole moiety's oxidation ability. Besides, the cathodic peak in the range of -0.5 to -1.0 V, contributed to the stability of the reduced quinoxaline unit. All the compounds exhibited uniformly covered thin film in SEM analysis, potentially facilitating the seamless charge carrier migration between adjacent molecules. The methoxyphenyl substituted compound exhibited the binary write-once read-many (WORM) memory behavior with the lowest threshold voltage of -0.81 V. The molecular simulations displayed the efficient intramolecular charge transfer, providing the fabricated device's distinctive conductive states. Except for the tert-butylphenyl compound, which showed volatile dynamic random-access memory (DRAM) behavior, all the other compounds exhibited non-volatile WORM memory behavior, suggesting IQs potential as an intrinsic D-A molecule in organic memory devices on further structural refinement.

Solution-processed PEDOT: PSS/PVA polymer blend write-once-read-many memory devices

In this work, all-solution-processed resistive switching memory devices in a polymer blend are realised. The memory, in this work, is Write-Once-Read-Many memory (WORM). The polymer blend is the blend of Poly(3,4-ethylenedioxythiophene) Polystyrene Sulfonate (PEDOT: PSS) and Polyvinyl Alcohol (PVA). The devices can sustain 50 bending cycles at a bending radius of 0.5mm, while still able to maintain and perform memory functions. The mechanism of the switching can be attributed to electrochemical properties of the polymers. The migrations of polymers (PEDOT: PSS/PVA blend) and electrolysis of the absorbed water distort the conducting pathways and switch the state of the device from a low resistance state (LRS) to a high resistance state (HRS). The work may pave the way for future low cost flexible electronic memory devices. Flexible memory devices

Efficient ternary WORM memory devices from quinoline-based D-A systems by varying the redox behavior of ferrocene.

The design and synthesis of ferrocene-functionalized organic small molecules using quinoline cores are rendered to achieve a ternary write-once-read-many (WORM) memory device. Introducing an electron-withdrawing group into the ferrocene system changes the compounds' photophysical, electrochemical, and memory behavior. The compounds were synthesized with and without an acetylene bridge between the ferrocene unit and quinoline. The electrochemical studies proved the oxidation behavior with a slightly less intense reduction peak of the ferrocene unit, demonstrating that quinolines have more reducing properties than ferrocene with bandgaps ranging from 2.67-2.75 eV. The single crystal analysis of the compounds also revealed good interactive interactions, ensuring good molecular packing. This further leads to a ternary WORM memory with oxidation of the ferrocene units and charge transfer in the compounds. The devices exhibit on/off ratios of 104 and very low threshold voltages of -0.58/-1.02 V with stabilities of 103 s and 100 cycles of all the states through retention and endurance tests.

Improved Resistive Switching WORM Memory Behavior in D-π-A Architectures by Modifying the Terminal Donor Units

A series of D-π-A, D-π-D, and A-π-A based push–pull compounds with triarylamine and benzophenone were designed and synthesized for nonvolatile memory applications. All of the compounds showed good solubility in common organic solvents, which permits solution processability. D-π-A based compounds exhibited write-once-read-many (WORM) memory applications, and the compound with a methoxyphenyl substituent exhibited switching with a low threshold voltage of −0.82 V, an ON/OFF current ratio of 102, and a long-lasting retention time of 103 s. The effect of differently functionalized triarylamines on memory behavior was explored by optical, electrochemical, and computational studies. The highest HOMO levels of around ∼5.0 eV and irreversible anodic peaks (0.7–1.3 V) obtained for the compounds facilitate charge injection and switching behavior. Besides, electrochemical and density functional theory studies disclose the charge-transfer mechanism of the D-π-A systems, which is related to the bistability of the devices.

ReWORM Memory Effect in PET-Metal Fiber-Based Electroconductive Yarn

Write-once-read-many (WORM) memory effect is reported in the 19.68 Tex, 80:20 ratio polyethylene terephthalate (PET)-metal fiber spun electroconductive yarn. The yarn sample displayed a typical WORM memory behavior having electrical bistability with an OFF/ ON resistance ratio up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{9}}$ </tex-math></inline-formula> and a long retention period. As the polyester fibers transform from amorphous (resistive state) to semicrystalline (conductive state) upon the application of bias voltage, the charge conduction changes from electronic to ionic, above the glass transition temperature. Furthermore, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}-{V}$ </tex-math></inline-formula> curves were fit to explain the charge carrier transport mechanisms in the WORM behavior. Additionally, upon intentional mechanical perturbation, the sample could reset to its native high-resistive state (the phenomenon is termed as Reset WORM or ReWORM), ready for another WORM storage cycle.

RRAM and WORM memory devices using Protamine Sulfate and Graphene Oxide

Biomaterials are extensively exploited as the resistive switching materials since last decade. Biomaterials such as proteins, DNA, enzymes, polysaccharides, starch, natural materials are being used as the active layer for the resistive switching memory devices. In this report we have investigated the Resistive Switching (RS) Memory behavior of a biomolecule Protamine Sulfate (PS), Graphene Oxide (GO) and their mixture. It has been observed that RS device having pure PS or GO as the active layer showed non-volatile memory behavior suitable for Write Once Read Many (WORM) memory applications. Dynamic transition of switching behavior from WORM to bipolar switching observed in the device designed with PS + GO mixed system. In case of the mixed film the set and reset power is found to be less than the individuals which is advantageous with respect to the power consumption. The memory window is also found to be increased multiple times.

An electrospun polymer composite with fullerene-multiwalled carbon nanotube exohedral complexes can act as memory device

Functional polymer nanocomposites with distinctive electrical properties made of nanocarbon structures and biodegradable polymers are promising materials for the development of flexible and eco-friendly smart systems. In this work, a novel electrospun conductive polymer nanocomposite made of polycaprolactone with an exohedral complex made of multiwalled carbon nanotubes and fullerene C60 was prepared and characterized. The preparation was straightforward and the complexes self-assembled within the nanocomposite fibers. The nanocomposite showed electrical switching behavior due to charge accumulation of fullerene C60 upon electrical stimulation. Write-once read-many memory devices were fabricated by electrospinning a nanocomposite with 0.8%wt. fullerene C60 onto interdigitated coplanar electrodes. The device retained the ON state for more than 60 days and could be thermally reset, reprogrammed and erased with subsequent electrical and thermal cycling. Moreover, the electrical resistance of the device could be modulated by applying different programming voltage amplitudes and programming times, which revealed its adaptive behavior and potential application to neuromorphic systems.

Triggering WORM/SRAM Memory Conversion by Composite Oxadiazole in Polymer Resistive Switching Device

Electrical characterization indicates that the nonvolatile write once read many (WORM) times/volatile static random access memory (SRAM) conversion was triggered by the composite of the oxadiazole small molecule. FTO/PMMA/Ag device possesses nonvolatile WORM memory behavior, while the FTO/PMMA+oxadiazole/Ag device shows vastly different volatile SRAM feature. The FTO/PMMA/Ag and FTO/PMMA+oxadiazole/Ag memory devices both exhibit high ON/OFF ratio nearly 104. The additive oxadiazole small molecule in the polymethyl methacrylate was suggested to form an internal electrode and serve as a channel during the charge transfer process, which is easy to both the charge transfer and back charge transfer, as a consequence, the WORM/SRAM conversion upon oxadiazole small molecule complexation was triggered. The results observed in this work manifest the significance of oxadiazole small molecule to the memory effects and will arouse the research interest about small molecule composite applied in memory devices.

Nonvolatile WORM and rewritable multifunctional resistive switching memory devices from poly(4-vinyl phenol) and 2-amino-5-methyl-1,3,4-thiadiazole composite

A multifunctional resistive switching memory devices with the typical sandwich structure of Al/Poly(4-vinylphenol) (PVP)+2-Amino-5-methyl-1,3,4-thiadiazole/Al is fabricated. Al as the bottom and top electrodes is easy to realize by simple thermal evaporation process, and a PVP and 2-Amino-5-methyl-1,3,4-thiadiazole composite film as the active layer is prepared by sol-gel method and spin coating process. The as-fabricated resistive switching memory device shows write-once-read-many (WORM) and rewritable multifunctional memory behaviors, for the rewritable and WORM memory modes, the ON/OFF ratio is 104 and 80, respectively. The as-fabricated device shows tristable conductivity states which equivalent to “0”, “1” and “2”, and these three conductance states are steady under the constant voltage retention test, as well as during the endurance test, indicating advantageous features of stable operation and dependable endurance. It is noteworthy that the simple preparation process is expected to promisingly hold the post of industrialization low-cost preparation in future electronic devices for ternary data storage utilities.

Write once read many times resistance switching memory based on all-inorganic perovskite CsPbBr3 quantum dot

Write Once Read Many (WORM) Memory, as one of the most important nonvolatile memory type, has widespread used in a variety of permanent storage applications in the Big Data age. As an excellent material, CsPbBr3 quantum dots have widely used in a lot of photoelectric devices, but CsPbBr3 quantum dots based memory device remain to be studied. In this work a WORM memory device based on CsPbBr3 quantum dots is demonstrated. The CsPbBr3 QDs based WORM shows great reproducibility, good data retention ability, irreversible electrical transition from the high resistance state (HRS) or OFF state to the low resistance state (LRS) or ON state and the resistance ratio (ON/OFF) can reach almost 104. Additionally, the device exhibits high performances under low power consumption — low reading voltage (−0.5 V) and writing voltage (−1.1V). To study the CsPbBr3 QDs based WORM provides an opportunity to develop the next generation high-performance and stable WORM devices.

Coexistence of Write Once Read Many Memory and Memristor in blend of Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate and Polyvinyl Alcohol.

In this work, the coexistence of Write Once Read Many Memory (WORM) and memristor can be achieved in a single device of Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) and Polyvinyl Alcohol (PVA) blend organic memory system. In memristor mode, the bistable resistance states of the device can be cycled for more than 1000 times. Once a large negative bias of −8V was applied to the device, it was switched to permanent high resistance state that cannot be restored back to lower resistance states. The mechanism of the memristor effect can be attributed to the charge trapping behaviour in PVA while the WORM effect can be explained as the electrochemical characteristic of PEDOT: PSS which harnesses the percolative conduction pathways. The results may facilitate multipurpose memory device with active tunability.

Resistive Switching Memory Phenomena in PEDOT PSS: Coexistence of Switchable Diode Effect and Write Once Read Many Memory.

We study resistive switching memory phenomena in conducting polymer PEDOT PSS. In the same film, there are two types of memory behavior coexisting; namely, the switchable diode effect and write once read many memory. This is the first report on switchable diode phenomenon based on conducting organic materials. The effect was explained as charge trapping of PEDOT PSS film and movement of proton. The same PEDOT PSS device also exhibits write once read many memory (WORM) phenomenon which arises due to redox reaction that reduces PEDOT PSS and renders it non-conducting. The revelation of these two types of memory phenomena in PEDOT PSS highlights the remarkable versatility of this conducting conjugated polymer.

Optically readout write once read many memory with single active organic layer

An optically readable write once read many memory (WORM) in Ag/Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH PPV)/ITO is demonstrated in this work. Utilising characteristics of the organic light emitting diode structure of Ag/MEH PPV/ITO and electrochemical metallization of Ag, a WORM with light emitting capability can be realised. The simple fabrication process and multifunction capability of the device can be useful for future wearable optoelectronics and photomemory applications, where fast and parallel readout can be achieved by photons.

Interfacial behavior of resistive switching in ITO–PVK–Al WORM memory devices

Understanding the mechanism of resistive switching in a memory device is fundamental in order to improve device performance. The mechanism of current switching in a basic organic write-once read-many (WORM) memory device is investigated by determining the energy level alignments of indium tin oxide (ITO), poly(9-vinylcarbazole) (PVK) and aluminum (Al) using x-ray and ultraviolet photoelectron spectroscopy, current–voltage characterization and Auger depth profiling. The current switching mechanism was determined to be controlled by the interface between the ITO and the PVK. The electric field applied across the device causes the ITO from the uneven surface of the anode to form metallic filaments through the PVK, causing a shorting effect within the device leading to increased conduction. This was found to be independent of the PVK thickness, although the switch-on voltage was non-linearly dependent on the thickness. The formation of these filaments also caused the destruction of the interfacial dipole at the PVK–Al interface.

Stabilization of space charge polarization in ion-dispersed gate dielectric layer of organic transistors by ultraviolet illumination for write-once read-many memory

In this work, a new type organic field effect transistor (OFET) based write-once read-many memory (WORM) device was developed. The device uses an ultraviolet (UV) cross-linkable matrix polymer mixed with ionic compounds to form an ion-dispersed gate dielectric layer. Under an applied gate voltage bias, migration of cations and anions in opposite directions forms space charge polarization in the gate dielectric layer, resulting in change of the electrical characteristics. It is shown that, with UV illumination to cross-link the matrix polymer, the formed space charge polarization can be stabilized. Therefore, the OFET can be operated as a WORM with the applied voltage bias to define the polarization and in turn the stored data, and the UV illumination to stabilize the stored data.

Investigation of Aloe Vera as active layer for development of organic based memory devices

This work had successfully employed commercially purchased Aloe Vera gel as the active layer on indium tin oxide (ITO) glass substrate. Different heating temperatures were studied on the Aloe Vera/ITO samples. Results showed the existence of OH and C–H groups in the samples using Fourier transform infrared spectroscopy. Typical thickness (246·8 nm) of Aloe Vera was determined using field emission scanning electron microscopy cross-sectional studies. Direct band gap (Eg) energies (3·88–4·00 eV) were calculated using Tauc plot by extracting data from the UV-Vis absorption spectra while dielectric permittivity values were measured using impedance analyser. Current-gate voltage (I–V) characteristics and time dependence I–V characteristics of the Al/Aloe Vera/ITO device deduced that the device was showing a write-once-read-many (WORM) memory response and thus was potential to serve as the WORM memory device.

Chemically programmed ink-jet printed resistive WORM memory array and readout circuit

In this paper an ink-jet printed write once read many (WORM) resistive memory fabricated on paper substrate is presented. The memory elements are programmed for different resistance states by printing triethylene glycol monoethyl ether on the substrate before the actual memory element is printed using silver nano particle ink. The resistance is thus able to be set to a broad range of values without changing the geometry of the elements. A memory card consisting of 16 elements is manufactured for which the elements are each programmed to one of four defined logic levels, providing a total of 4294 967 296 unique possible combinations. Using a readout circuit, originally developed for resistive sensors to avoid crosstalk between elements, a memory card reader is manufactured that is able to read the values of the memory card and transfer the data to a PC. Such printed memory cards can be used in various applications.

Molecular memory with atomically smooth graphene contacts

We report the use of bilayer graphene as an atomically smooth contact for nanoscale devices. A two-terminal bucky-ball (C60) based molecular memory is fabricated with bilayer graphene as a contact on the polycrystalline nickel electrode. Graphene provides an atomically smooth covering over an otherwise rough metal surface. The use of graphene additionally prohibits the electromigration of nickel into the C60 layer. The devices exhibit a low-resistance state in the first sweep cycle and irreversibly switch to a high-resistance state at 0.8 to 1.2 V bias. In the subsequent cycles, the devices retain the high-resistance state, thus making it write-once read-many memory.