High-performance Memory Devices Research Articles

High-Performance LiNbO3 Domain Wall Memory Devices with Enhanced Selectivity via Optimized Metal-Semiconductor Contact.

Lithium niobate (LiNbO3) single-crystal nanodevices featuring elevated readout domain wall currents exhibit significant potential for integrated circuits in memory computing applications. Nevertheless, challenges stem from suboptimal electrode-LiNbO3 single crystal contact characteristics, which impact the stability of high currents within these devices. In this work, we concentrate on augmenting the domain wall current by refining the fabrication processes of domain wall random access memory (DWRAM). Each LiNbO3 domain wall nanodevice was fabricated using a self-aligned process. Device performance was significantly enhanced by introducing a 10 nm interlayer between the LiNbO3 and Cu electrodes. A comparative analysis of electrical properties was conducted on devices with interlayers made of chromium (Cr) and titanium (Ti), as well as devices without interlayers. After the introduction of the Ti interlayer, the device's coercive voltage demonstrated an 82% reduction, while the current density showed a remarkable 94-fold increase. A 100 nm sized device with the Ti interlayer underwent positive down-negative up pulse testing, demonstrating a writing time of 82 ns at 8 V and an erasing time of 12 μs at -9 V. These operating speeds are significantly faster than those of devices without interlayers. Moreover, the enhanced devices exhibited symmetrical domain switching hysteresis loops with retention times exceeding 106 s. Notably, the coercive voltage (Vc) dispersion remained narrow after more than 1000 switching cycles. At an elevated temperature of 400 K, the device's on/off ratio was maintained at 105. The device's embedded selector demonstrated an ultrahigh selectivity (>106) across various reading voltages. These results underscore the viability of high-density nanoscale integration of ferroelectric domain wall memory.

Dynamic Manipulation of Chiral Domain Wall Spacing for Advanced Spintronic Memory and Logic Devices.

Nanoscopic magnetic domain walls (DWs), via their absence or presence, enable highly interesting binary data bits. The current-controlled, high-speed, synchronous motion of sequences of chiral DWs in magnetic nanoconduits induced by current pulses makes possible high-performance spintronic memory and logic devices. The closer the spacing between neighboring DWs in an individual conduit or nanowire, the higher the data density of the device, but at the same time, the more difficult it is to read the bits. Here, we show how the DW spacing can be dynamically varied to facilitate reading for otherwise closely packed bits. In the first method, the current density is increased in portions of the conduit that, thereby, locally speeds up the DWs, decompressing them and making them easier to read. In the second method, a localized bias current is used to compress and decompress the DW spacing. Both of these methods are demonstrated experimentally and validated by micromagnetic simulations. DW compression and decompression rates as high as 88% are shown. These methods can increase the density with which DWs can be packed in future DW-based spintronic devices by more than an order of magnitude.

Current-Induced Magnetization Switching Behavior in Perpendicular Magnetized L10-MnAl/B2-CoGa Bilayer

Rare-earth-free Mn-based binary alloy L10-MnAl with bulk perpendicular magnetic anisotropy (PMA) holds promise for high-performance magnetic random access memory (MRAM) devices driven by spin-orbit torque (SOT). However, the lattice-mismatch issue makes it challenging to place conventional spin current sources, such as heavy metals, between L10-MnAl layers and substrates. In this work, we propose a solution by using the B2-CoGa alloy as the spin current source. The lattice-matching enables high-quality epitaxial growth of 2-nm-thick L10-MnAl on B2-CoGa, and the L10-MnAl exhibits a large PMA constant of 1.04 × 106 J/m3. Subsequently, the considerable spin Hall effect in B2-CoGa enables the achievement of SOT-induced deterministic magnetization switching. Moreover, we quantitatively determine the SOT efficiency in the bilayer. Furthermore, we design an L10-MnAl/B2-CoGa/Co2MnGa structure to achieve field-free magnetic switching. Our results provide valuable insights for achieving high-performance SOT-MRAM devices based on L10-MnAl alloy.

A high-performance magnetoelectric non-volatile light-emitting memory device

A novel magnetoelectric light-emitting memory (LEM) device that can control the output light intensity and electrical signal based on the input magnetic and electric field strengths has been proposed and demonstrated.

A Study on Film Properties Control of Atomic Layer Deposition Amorphous Carbon for PRAM Electrode Application

As the amount of data usage increases with the development of technologies such as artificial intelligence, Internet of Things (IoT), and big data, the need for development of high-performance memory devices and improvement of density is increasing. Phase change memory is a next-generation memory device that stores and erases information by the resistance difference generated by reversibly and rapidly changing the crystal structure of the memory cell. Recently, research on the material engineering aspect to increase thermal efficiency by using various electrode materials and the structural aspect to increase the degree of integration by making a 3D structure is attracting attention. As an electrode material to increase the thermal efficiency of PRAM devices, carbon, which has various resistances (conductor (graphite, sp2 bond) – insulator (diamond, sp3 bond)) depending on the state of atomic bonding is an attractive material. Therefore, research using carbon as an electrode by using PVD and CVD processes has been conducted, but there is a problem that it is difficult to use it for devices with a complex 3D structure with the existing process. Therefore, in this study, an a-C ALD process that can be uniformly deposited in a 3D structure was developed using the CBr4 precursor. And by analyzing the bonding state and physical properties of the deposited thin film, the mechanism of how the a-C thin film grows according to the thin film deposition conditions is studied.

Controlled Synthesis of Lead-Free Double Perovskite Colloidal Nanocrystals for Nonvolatile Resistive Memory Devices.

Although lead-free double perovskites such as Cs2AgBiBr6 have been widely explored, they still remain a daunting challenge for the controlled synthesis of lead-free double perovskite nanocrystals with highly tunable morphology and band structure. Here, we report the controlled synthesis of lead-free double perovskite colloidal nanocrystals including Cs2AgBiBr6 and Cs2AgInxBi1-xBr6 via a facile wet-chemical synthesis method for the fabrication of high-performance nonvolatile resistive memory devices. Cs2AgBiBr6 colloidal nanocrystals with well-defined cuboidal, hexagonal, and triangular morphologies are synthesized through a facile wet-chemical approach by tuning the reaction temperature from 150 to 190 °C. Further incorporating indium into Cs2AgBiBr6 to synthesize alloyed Cs2AgInxBi1-xBr6 nanocrystals not only can induce the indirect-to-direct bandgap transition with enhanced photoluminescence but also can improve its structural stability. After optimizing the active layers and device structure, the fabricated Ag/polymethylene acrylate@Cs2AgIn0.25Bi0.75Br6/ITO resistive memory device exhibits a low power consumption (the operating voltage is ∼0.17 V), excellent cycling stability (>10 000 cycles), and good synaptic property. Our study would enable the facile wet-chemical synthesis of lead-free double perovskite colloidal nanocrystals in a highly controllable manner for the development of high-performance resistive memory devices.

Solution-Processed Hydrogen-Bonded Organic Framework Nanofilms for High-Performance Resistive Memory Devices.

The integration of hydrogen-bonded organic frameworks (HOFs) into electronic devices holds great promise due to their high crystallinity, intrinsic porosity, and easy regeneration. However, despite their potential, the utilization of HOFs in electronicdevices remains largely unexplored, primarily due to the challenges associated with fabricating high-quality films. Herein, a controlled synthesis of HOFnanofilms with smooth surface, good crystallinity, and high orientation is achieved using a solution-processed approach. The memristors exhibit outstanding bipolar switching performance with alow set voltage of 0.86V, excellent retention of 1.64 × 104 s, and operational endurance of 60 cycles. Additionally, these robust memristors display remarkable thermal stability, maintaining their performance even at elevated temperatures of up to 200 °C. More strikingly, scratched HOFfilms can be readily regenerated through a simple solvent rinsing process, enabling their reuse for the fabrication of new memristors, which is difficult to achieve with traditional resistive switching materials. Additionally, a switching mechanism based on the reversible formation and annihilation of conductive filaments is revealed. This work provides novel and invaluable insights that have a significant impact on advancing the widespread adoption of HOFs as active layers in electronic devices.

Recent progress in diluted ferromagnetism for spintronic application

With the continuous in-depth research of spintronics, the manufacture of high-performance magnetic random access memory devices and electronic devices that are more energy-efficient and generate less heat has received extensive attention. The traditional ferromagnet TbMnO3 is basically Tc at room temperature, which seriously limits its application. Since the discovery of diluted magnetic semiconductor materials at room temperature, such as AlNTiO2, ZnO, SnO2, etc., they have received increasing attention. Although these dopants can form ferromagnetism above-room temperature, the ferromagnetic mechanism and ferromagnetic properties are different. In this regard, we reviewed the current progress in the research on above room temperature dilute magnetic semiconductor materials; discussed the ferromagnetic mechanism of dilute magnetic semiconductors; summarized the problems and challenges, and advantages and disadvantages of different kinds of dilute magnetic semiconductor materials used in new memory devices; and prospected the application potential of spintronic devices.

Improvement of memristive switching of Pb(Zr0.52Ti0.48)O3/Nb:SrTiO3 heterostructures via La doping

The ferroelectric memory with superior stability and high operating speed has broad development prospects in areas such as neural computing and information storage. An effective strategy to improve the performance of the resistive switching (RS) of the ferroelectric memory is to improve the conductivity of ferroelectric thin films while maintaining their ferroelectric properties, because there is a competition between ferroelectric properties and conductivity in the RS behavior. Herein, we prepared La-doped Pb(Zr0.52Ti0.48)O3 (PLZT) thin films on the Nb:SrTiO3 (NSTO) substrate. By controlling La concentration, a compromise between ferroelectricity and conductivity was achieved. The RS on/off ratio reached 2.6 × 104 doped with 2 mol% La. Moreover, the conduction mechanism changes from the Schottky emission controlling PZT/NSTO interface to the coexistence of Schottky emission and space charge-limited mechanism in the PLZT/NSTO heterostructures. The results reveal that the effective matching of the ferroelectricity and conductivity of ferroelectric thin films is necessary for obtaining high RS on/off ratio, which is helpful to the accurate design of high-performance ferroelectric memory devices.

Uncovering the Role of Crystal Phase in Determining Nonvolatile Flash Memory Device Performance Fabricated from MoTe2-Based 2D van der Waals Heterostructures.

Although the crystal phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) has been proven to play an essential role in fabricating high-performance electronic devices in the past decade, its effect on the performance of 2D material-based flash memory devices still remains unclear. Here, we report the exploration of the effect of MoTe2 in different phases as the charge-trapping layer on the performance of 2D van der Waals (vdW) heterostructure-based flash memory devices, where a metallic 1T'-MoTe2 or semiconducting 2H-MoTe2 nanoflake is used as the floating gate. By conducting comprehensive measurements on the two kinds of vdW heterostructure-based devices, the memory device based on MoS2/h-BN/1T'-MoTe2 presents much better performance, including a larger memory window, faster switching speed (100 ns), and higher extinction ratio (107), than that of the device based on the MoS2/h-BN/2H-MoTe2 heterostructure. Moreover, the device based on the MoS2/h-BN/1T'-MoTe2 heterostructure also shows a long cycle (>1200 cycles) and retention (>3000 s) stability. Our study clearly demonstrates that the crystal phase of 2D TMDs has a significant impact on the performance of nonvolatile flash memory devices based on 2D vdW heterostructures, which paves the way for the fabrication of future high-performance memory devices based on 2D materials.

Disturbance Characteristics of 1T DRAM Arrays Consisting of Feedback Field-Effect Transistors.

Challenges in scaling dynamic random-access memory (DRAM) have become a crucial problem for implementing high-density and high-performance memory devices. Feedback field-effect transistors (FBFETs) have great potential to overcome the scaling challenges because of their one-transistor (1T) memory behaviors with a capacitorless structure. Although FBFETs have been studied as 1T memory devices, the reliability in an array must be evaluated. Cell reliability is closely related to device malfunction. Hence, in this study, we propose a 1T DRAM consisting of an FBFET with a p+-n-p-n+ silicon nanowire and investigate the memory operation and disturbance in a 3 × 3 array structure through mixed-mode simulations. The 1T DRAM exhibits a write speed of 2.5 ns, a sense margin of 90 μA/μm, and a retention time of approximately 1 s. Moreover, the energy consumption is 5.0 × 10-15 J/bit for the write '1' operation and 0 J/bit for the hold operation. Furthermore, the 1T DRAM shows nondestructive read characteristics, reliable 3 × 3 array operation without any write disturbance, and feasibility in a massive array with an access time of a few nanoseconds.

A flexible floating-gate based organic field-effect transistor non-volatile memory based on F8BT/PMMA integrated floating-gate/tunneling layer

The solution mixing method was adopted to build polymer semiconductor poly(9,9-dioctylflfluorene-co-benzothiadiazole) (F8BT) nanoparticles (NPs), which were mixed with poly (methyl methacrylate) (PMMA) in a solution to prepare an integrated floating-gate/tunneling layer. On this basis, flexible floating-gate based organic field-effect transistor non-volatile memories (F-OFET-NVMs) were prepared. The intrinsic correlations of the microstructures in the integrated floating-gate/tunneling layer of the memory devices with the device performance were explored. Moreover, correlations of the charge injection and discharge, physical mechanism of memory, and charge trapping capacity of the floating-gate/tunneling layer with different F8BT/PMMA mass ratios with the key parameters of memory devices were investigated. Relevant results indicate that the memory devices are able to well trap charges inside the F8BT NPs during operation at a programming voltage of +40 V, an erasing voltage of −40 V, and a pulse width of 1 s. The floating gate acquires the injected and trapped bipolar charges (electrons and holes). The optimized high-performance memory device is found to have an average memory window of 9.5 V, remain stable for more than three years, and have reliable stability in more than 100 erase/write cycles. Furthermore, the memory device also exhibits outstanding durability under mechanical bending and still has high storage stability after 6,000 times of bending with a bending radius of 3 mm. The research results powerfully promote the research progress of applying semiconductor polymers to memory devices.

High-performance non-volatile memory devices from metallomacrocyclic organic micro/nanostructure: Control via molecular manipulation

Here, we report the synthesis of micro/nanostructures of a metal-macrocyclic organic compound, viz, Iron phthalocyanine (FePc) via cost-effective solvothermal method and consequent fabrication of high-performance resistive memory devices from FePc micro/nanorod embedded in poly(methyl methacrylate) (PMMA) matrix. The devices exhibited bipolar and non-volatile resistive switching characteristics. Interestingly, the performances of the devices (On/Off current ratio) improved by several orders of magnitude when an additional buffer layer of PMMA was deposited prior to the deposition of the active film (FePc embedded in PMMA). The variation in thickness of the PMMA buffer layer indicated that at an optimum thickness ca. 15 nm, the best performances were obtained with switching (Set) voltage ca. 1.6 V, On/Off current ratio ∼ 106 and retention ability of more than 10 h. The conduction mechanism has been discussed by linear fitting of the characteristics curves in both low and high resistance states of the device. The analysis lead to the conclusion that trapping/detrapping of charge carriers at the redox and defect sites within the active film (FePc embedded in PMMA) and at the PMMA-FePc/PMMA interface resulted in the resistive switching of the device and a trap induced space charge limited current was found to dominate in the Off- and On-state of the device.

Liquid-Based Memory Devices for Next-Generation Computing

Liquid-based devices have emerged as bioinspired neuromorphic applications owing to their high ion-diffusion coefficients, diverse structures, and controllable ion-exchange reactions. By engineering and modifying liquid materials, multifunctional liquid-based computing devices have been developed for next-generation memory and neuromorphic devices. The unique properties of liquids make them feasible for memory functions and various synaptic applications, such as emulating synaptic plasticity, homeostasis, and action potentials. Utilizing liquids in computing devices provides a promising and versatile platform for high-performance memory devices and enables the emulation of bioinspired computing functions. In this Spotlight, we highlight recent advances in liquid-based memory devices and focus on synaptic applications. We then discuss possible array structures and scaling-down technologies for liquid-based devices. Finally, the challenges and future prospects of liquid-based devices are discussed.

Tunnel electroresistance effect in a two-dimensional organic ferroelectric tunnel junction.

Two-dimensional (2D) ferroelectric materials have important application potential in device miniaturization due to their characteristics of only being a few atomic layers thick and non-volatility. How to design high-performance ferroelectric memory devices based on 2D ferroelectric materials has attracted extensive attention. In this work, based on the 2D organic ferroelectric material semi-hydroxylized graphane (SHLGA), which has in-plane ferroelectric polarization along three different directions, we construct a 2D organic ferroelectric tunnel junction (FTJ). By means of density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method, we calculate the transport properties of the FTJ under different polarizations and obtain a giant tunnel electroresistance (TER) ratio of 7.55 × 104%. We find that the mechanism behind the TER effect in the organic SHLGA is based on the unique built-in electric field. That is, among the three ferroelectric polarization directions, any two directions have an angle of 120°. As a result, the built-in electric fields along the transport direction of the FTJ under different ferroelectric polarization directions are different. Moreover, our study shows that the giant TER effect can also be achieved by utilizing the asymmetry of the polarization along the transport direction of the ferroelectric material itself, which provides another route for the design of 2D FTJs.

Electrochemical-tunable and mesostructure-dependent abrupt-to-progressive conversion in fibroin-based transient memristor

The unique degradability and excellent biocompatibility make silk fibroin an attractive material for flexible transient memristors. Materials functionalization from the mesoscopic reconstruction view is a promising route to expand functions and create new types of electronic devices. Here, the transformation of the abrupt-to-progressive switching behavior in fibroin-based memristors is achieved via annealing to adjust the mesoscopic structure. Through electrical test and scanning electron microscope analysis, we study the electrochemical dynamics of metal nanoparticles in switching medium with different mesoscopic structures and directly reveal the microscopic origin of the abrupt-to-progressive transformation in fibroin-based transient memristors. The device exhibits abrupt resistive switching behaviors when the mobility and redox rate are high and displays progressive resistive switching behaviors under the low mobility and low redox rate condition. These findings reveal the microscopic origins of abrupt-to-progressive conversion and provide general guidance for designing high-performance memory devices and artificial synapses.

Highly improved performance in Ta/MoO3/Pt structure by optimizing molybdenum oxide sputtering process for resistive switching memory

The excellent resistive switching (RS) performances based on Ta/MoOx/Pt device were achieved by controlling the deposition temperature and the thickness of MoOx. The results of X-ray diffraction (XRD) and X-ray photoelectron (XPS) spectroscopy confirmed that the deposition temperature has a significant influence on the MoOx crystalline form and oxygen vacancy content. Compared with the samples deposited at other temperatures (room temperature, 300 °C and 500 °C), MoO3 sputtered at 400 °C obtained nanocrystals with appropriate oxygen vacancies, resulted in improved RS performance. When the 50 nm MoO3 was sputtered at 400 °C, the device showed an ultra-low RS current (10 μA), large HRS/LRS ratio (>104), high endurance (108 cycles) and stable data storage capacity at 85 °C (10 years). This research provides a simple method to design high-performance memory devices.

Novel Porphyrin–Perylene diimide for ultrafast high-performance resistive memory devices

The novel solution-processable porphyrin–perylene diimide (TPP–6FDI–TPP) was synthesized via condensation of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (ATPP) (electron donor) and 4,4’-(hexafluoroisoprpoylidine)diphthalic anhydride (6FDA) (electron acceptor), and the structure of TPP–6FDI–TPP was confirmed by FTIR and NMR spectroscopy. Its optical and electrochemical properties were evaluated via ultraviolet visible spectroscopy and cyclic voltammetry, respectively. Furthermore, this dyad showed good solubility in organic solvent, which is desirable for smooth thin-film formation and application in electronic devices. The current–voltage (I–V) results of the sandwich memory device (ITO/thin layer of TPP–6FDI–TPP/Al) indicated that it exhibits a volatile nature with static random-access memory (SRAM) behavior. Moreover, the sandwich device showed a high ON/OFF current ratio up to 10 5 , as well as excellent long-term operation stability over 10 8 read cycles with no current degradation up to 4000 s of retention time. The electrical function of the donor/acceptor moiety and the charge transfer (CT) in the dyad were related to the electrical switching effect, which was further investigated on the basis of electrochemical and optical measurements, as well as quantum simulation results. More importantly, the different work functions of various noble metals inserted into the porphyrin ring may lead to promising memory behaviors. The present study opens a new direction for researchers to utilize the 18 π-electron system of porphyrin, which can be easily modified via complexation with different transition metals, and which is expected to be employed for future memory applications. • Synthesis of novel small porphyrin-perylene diimide though simple imidization reactions. • Investigation the correlation of the structure to the Memory performance of porphyrin-perylene dyad (SRAM). • Future Idea of metal chelation for the desirable memory performance. • Ultrafast high-performance resistive memory devices from the solutions processible small molecules.

WSe2/WS2 Heterobilayer Nonvolatile Memory Device with Boosted Charge Retention.

A two-dimensional (2D) nonvolatile memory device architecture to improve the long-term charge retention with the minimum charge loss without compromising storage capacity and the extinction ratio for practical applications has been an imminent demand. To address the current issue, we adopted a novel type-II band-aligned heterobilayer channel comprising vertically stacked monolayer WSe2 nanodots on monolayer WS2. The band offset modulation leads to electron doping from WSe2 nanodots into the WS2 channel without any external driving electric field. As a result, the tested device outperformed with a memory window as high as 34 V and a negligible charge loss of 7% in a retention period of 10 years while maintaining a high extinction ratio of 106. The doping technique presented in this work provides a feasible route to modulate the electrical properties of 2D channel materials without hampering charge transport, paving the way for high-performance 2D memory devices.

Flexible and recyclable bio-based transient resistive memory enabled by self-healing polyimine membrane

The recyclable, self-healing and easily-degradable transient electronic technology has aroused tremendous attention in flexible electronic products. However, integrating the above advantages into one single flexible electronic device is still a huge challenge. Herein, we demonstrate a flexible and recyclable bio-based memory device using fish colloid as the resistive switching layer on a polyimine substrate, which affords reliable mechanical and electrical properties under repetitive conformal deformation operation. This flexible bio-based memory device presents potential analog behaviors including memory characteristics and excitatory current response, which undergoes incremental potentiation in conductance under successive electrical pulses. Moreover, this device is expected to greatly alleviate the environmental problems caused by electronic waste. It can be decomposed rapidly in water and well recycled, which is a promising candidate for transient memories and information security. We believe that this study can provide new possibilities to the field of high-performance transient electronics and flexible resistive memory devices.