Data Retention Capability Research Articles

Enhanced Synaptic Characteristics Under Applied Magnetic Field in V2O5/NiMnIn Based Switching Device for Neuromorphic Computing

The present study reports a memory structure Al/V2O5/NiMnIn on a flexible stainless-steel (SS) substrate for neuromorphic applications. The fabricated device exhibits gradual SET and RESET switching characteristics with an OFF/ON resistance ratio of ~100, good consistency of 4500, and excellent data retention capability up to 3000 s. The current-voltage (I-V) study supports an Ohmic conduction mechanism in the low resistance state (LRS). In contrast, the trap-controlled modified space charge conduction mechanism demonstrated the high resistance state (HRS). The resistance versus temperature measurement (R-T) in the LRS and HRS of the device signifies that oxygen vacancies form the conduction filament. We further analyze the synaptic functioning by applying identical consecutive voltage pulses, and the device's conductance change has been observed. These characteristics show a good representation of the biological memory synapse in terms of the artificial memory device. Long-term potentiation (LTP) and long-term depression (LTD) show nonlinear and asymmetery behavior, which is substantial for neuromorphic applications. A considerable shift in LTP and LTD was detected by applying external temperature and magnetic field. This is explained via temperature and magnetic field strain in the functional NiMnIn bottom electrode of the fabricated device. The mechanical flexibility of the memory structure was tested by exploring the switching characteristics with various bending angles and bending cycles. Therefore, the present study offers new avenues for flexible devices with high data storage capability for futuristic neuromorphic applications.

Crystallization behavior and structural characteristics of Cr-doped Sb70Se30 thin films for phase change memory

In this study, we prepare Cr-doped Sb70Se30 (SS) thin films via the magnetron sputtering. The influence of Cr doping on the crystallization behavior and structure characteristics of the SS thin films is systematically studied using a combination of experimental analyzes and theoretical calculations. The results reveal that compared with SS thin films, Cr-doped SS thin films exhibit higher crystallization temperature, better data retention capability, larger crystallization activation energy, and reduced resistance drift coefficient. In addition, the incorporation of Cr effectively suppresses grain growth in the SS thin films and refines the grain size. The electrical transport properties of the Cr-doped SS thin films are analyzed using a Hall system. Both X-ray photoelectron spectroscopy and first-principles calculations indicate that Cr is more prone to occupy Sb atoms and form stronger Cr–Se bonds, consequently enhancing the stability of the SS thin films. Raman spectroscopy confirms that the introduction of Cr leads to a decrease in bond length and an increase in bond energy. Moreover, the Cr-doped SS thin film exhibits minimal volume fluctuations and a smoother surface morphology, resulting in enhanced interface performance and reliability. Taken together, these results indicate that the introduction of Cr is an effective strategy for optimizing the properties and modifying the structures of SS phase-change materials.

Uniform Oxide Layer Integration in Amorphous IGZO Thin Film Transistors for Enhanced Multilevel-Cell NAND Memory Performance

In this work, the implementation of HfZrO layers for the tunneling, charge trapping, and blocking mechanisms within the device offer benefits in terms of programmability and data retention. This configuration has resulted in a memory device that can achieve a significant difference in threshold voltage of around 2 V per memory level. This difference is crucial for effectively distinguishing between multiple levels of memory in MLC applications. Additionally, the device operates at low programming voltages below 14 V. Furthermore, the device showcases impressive endurance and data retention capabilities, maintaining a large memory window over extended periods and under varying temperature conditions. The advancement in the a-IGZO-based memory device, characterized by its uniform oxide stacking, presents a viable solution to the industry’s requirement for memory storage options that are efficient, dependable, and economical.

Superlow Power Consumption Memristor Based on Borphyrin-Deoxyribonucleic Acid Composite Films as Artificial Synapse for Neuromorphic Computing.

Memristor synapses based on green and pollution-free organic materials are expected to facilitate biorealistic neuromorphic computing and to be an important step toward the next generation of green electronics. Metalloporphyrin is an organic compound that widely exists in nature with good biocompatibility and stable chemical properties, and has already been used to fabricate memristors. However, the application of metalloporphyrin-based memristors as synaptic devices still faces challenges, such as realizing a high switching ratio, low power consumption, and bidirectional conductance modulation. We developed a memristor that improves the resistive switching (RS) characteristics of Zn(II)meso-tetra(4-carboxyphenyl) porphine (ZnTCPP) by combining it with deoxyribonucleic acid (DNA) in a composite film. The as-fabricated ZnTCPP-DNA-based device showed excellent RS memory characteristics with a sufficiently high switching ratio of up to ∼104, super low power consumption of ∼39.56 nW, good cycling stability, and data retention capability. Moreover, bidirectional conductance modulation of the ZnTCPP-DNA-based device can be controlled by modulating the amplitudes, durations, and intervals of positive and negative pulses. The ZnTCPP-DNA-based device was used to successfully simulate a series of synaptic functions including long-term potentiation, long-term depression, spike time-dependent plasticity, paired-pulse facilitation, excitatory postsynaptic current, and human learning behavior, which demonstrates its potential applicability to neuromorphic devices. A two-layer artificial neural network was used to demonstrate the digit recognition ability of the ZnTCPP-DNA-based device, which reached 97.22% after 100 training iterations. These results create a new avenue for the research and development of green electronics and have major implications for green low-power neuromorphic computing in the future.

Crystallization kinetics of Sb70Se30 thin films for phase change memories under the non-isothermal conditions

We investigate the non-isothermal crystallization kinetics of Sb70Se30 thin films using differential scanning calorimetry and determine the kinetic triplet of Sb70Se30 thin films at various heating rates by combining model-free and model-fitting approaches. The results indicate that the crystallization activation energy decreases with increasing crystallization fraction α, confirming the presence of multi-step crystallization mechanism. In accordance with the local Avrami index n(α), the crystallization mechanism shifts from three-dimensional growth with an increased nucleation rate at 0.05 ≤ α ≤ 0.8 to three- and two-dimensional growth with a reduced nucleation rate at α＞0.8. Afterwards, we deduce that the Sb70Se30 thin films follow a second-order reaction model within the heating rate range of 20 to 40 K/min. Moreover, the Sb70Se30 thin film shows excellent data retention capability when predicting data processing and data storage time based on phase change memory units. These findings provide valuable insights into the crystallization kinetics of Sb70Se30 thin films, contributing to the advancement of phase change materials.

Single-Power-Supply Six-Transistor CMOS SRAM Enabling Low-Voltage Writing, Low-Voltage Reading, and Low Standby Power Consumption

We developed a self-controllable voltage level (SVL) circuit and applied this circuit to a single-power-supply, six-transistor complementary metal-oxide-semiconductor static random-access memory (SRAM) to not only improve both write and read performances but also to achieve low standby power and data retention (holding) capability. The SVL circuit comprises only three MOSFETs (i.e., pull-up, pull-down and bypass MOSFETs). The SVL circuit is able to adaptively generate both optimal memory cell voltages and word line voltages depending on which mode of operation (i.e., write, read or hold operation) was used. The write margin (VWM) and read margin (VRM) of the developed (dvlp) SRAM at a supply voltage (VDD) of 1 V were 0.470 and 0.1923 V, respectively. These values were 1.309 and 2.093 times VWM and VRM of the conventional (conv) SRAM, respectively.At a large threshold voltage (Vt) variability (=+6σ), the minimum power supply voltage (VMin) for the write operation of the conv SRAM was 0.37 V, whereas it decreased to 0.22 V for the dvlp SRAM. VMin for the read operation of the conv SRAM was 1.05 V when the Vt variability (= -6σ) was large, but the dvlp SRAM lowered it to 0.41 V. These results show that the SVL circuit expands the operating voltage range for both write and read operations to lower voltages. The dvlp SRAM reduces the standby power consumption (PST) while retaining data. The measured PST of the 2k-bit, 90-nm dvlp SRAM was only 0.957 μW at VDD = 1.0 V, which was 9.46% of PST of the conv SRAM (10.12 μW). The Si area overhead of the SVL circuits was only 1.383% of the dvlp SRAM.

In‐Depth Physical Mechanism Analysis of Polymer Artificial Optoelectronic Synapse with High Endurance and Applications of Visual System and Operant Conditioning

AbstractBeing capable of dealing with both electrical signals and light, artificial optoelectronic synapses are considered to be an important cornerstone of neuromorphic computing. Here, an artificial optoelectronic synapse is reported through a simple solution process using organic poly(3‐hexylthiophene) (P3HT) and a remarkable analog switching characteristic similar to synaptic behavior is observed. The endurance and data retention capability of the P3HT‐based optoelectronic synapse exhibit stable characteristics up to 5000 consecutive cycles and 104 s. Through in‐depth physical mechanism analysis, it is confirmed that the analog switching characteristics of the device are mainly caused by a tunneling mechanism and space charge limited conduction. Furthermore, characterizations such as X‐ray photoelectron spectroscopy and atomic layer deposition prove that the memristive properties of device can be attributed to ion migration. More importantly, the device can co‐modulate the optoelectronic signal and successfully implement a photo‐triggered multi‐signal mode response. Based on this, a 3 × 3 synapse array is developed to demonstrate the potential application of the proposed P3HT‐based optoelectronic synapse in constructing an artificial visual system. Finally, operant conditioning is successfully simulated in the synaptic device. This work provides a reference for the construction of optoelectronic synapses in the neuromorphic visual system.

Enhanced Synaptic Characteristics under Applied Magnetic Field in V2O5/NiMnIn-Based Switching Device for Neuromorphic Computing

The present study reports a memory structure Al/V2O5/NiMnIn on a flexible stainless steel (SS) substrate for neuromorphic applications. The fabricated device exhibits gradual SET and RESET switching characteristics with an OFF/ON resistance ratio of ∼100, good consistency of 4500, and excellent data retention capability up to 3000 s. The current–voltage (I–V) study supports an Ohmic conduction mechanism in the low-resistance state (LRS). In contrast, the trap-controlled modified space charge conduction mechanism demonstrated the high-resistance state (HRS). The resistance vs temperature measurement (R–T) in the LRS and HRS of the device signifies that oxygen vacancies form the conduction filament. We further analyze the synaptic functioning by applying identical consecutive voltage pulses, and the device’s conductance change has been observed. These characteristics show a good representation of the biological memory synapse in terms of the artificial memory device. Long-term potentiation (LTP) and long-term depression (LTD) show nonlinear and asymmetry behavior, which is substantial for neuromorphic applications. A considerable shift in LTP and LTD was detected by applying external temperature and magnetic field. This is explained via temperature and magnetic field strain in the functional NiMnIn bottom electrode of the fabricated device. The mechanical flexibility of the memory structure was tested by exploring the switching characteristics with various bending angles and bending cycles. Therefore, the present study offers new avenues for flexible devices with high data storage capability for futuristic neuromorphic applications.

Ultrafast phase change speed and high thermal stability of scandium doped SnSb4 thin film for PCRAM applications

To address the challenge of reconciling the trade-off between phase change speed and thermal stability in phase change materials, we synthesized Sc-doped SnSb4 thin films with a composition of Sn22Sb76Sc2 and investigated their phase change properties. Our findings demonstrate that the Sn22Sb76Sc2 thin film exhibits enhanced thermal stability and faster phase change speed than Ge2Sb2Te5. The Sc-Sn bond formed during crystallization contributes to an improved data retention capability of up to 166 °C. Notably, the phase change speed of the Sn22Sb76Sc2 thin film on the basis of device test can reach up to 20 ns. Additionally, the power consumption of the Sn22Sb76Sc2 thin film (1.1 × 10−11 J) is nearly two orders of magnitude lower than that of Ge2Sb2Te5 (9.7 × 10−10 J). These results provide compelling evidence that the Sn22Sb76Sc2 thin film can overcome the "inverted relation" between high thermal stability and fast phase change speed, achieving a balanced performance.

Controllable coexistence of threshold and non-volatile crosspoint memory for highly linear synaptic device applications

A highly reliable and versatile resistive memory device that demonstrates threshold and non-volatile memory (NVM) switching behaviour depending on the compliance current (CC) modulation was utilised by doping a semiconducting (Si) material into a high-k (HfO x ) film with highly linear synaptic behaviour. The device shifted towards volatile switching at a CC less than 1 µA and exhibited NVM behaviour at a CC limit above 10 µA. A 3-bit/cell data storage capability on RESET voltage modulation was implemented for high-density memory application. The device exhibited excellent programming linearity of potentiation/depression responses up to 10 000 pulses compatible with fast pulse (100 ns) with good I ON/I OFF ratio (>103), stable data retention capability (105 s) at 85 °C and high WRITE endurance (∼107 cycles) with a pulse width of 200 ns. The neuromorphic applications were successfully emulated through neural network simulations using the experimentally calibrated data of the Si-doped HfO x resistive cross-point devices. Simulation results revealed a low nonlinearity of 0.03 with 98.08% pattern recognition accuracy. The estimated results revealed the potential of the device as a low-power selector and high-density NVM storage in large-scale crossbar array in future neuromorphic computing applications.

Bit upset and performance degradation of NAND flash memory induced by total ionizing dose effects

In order to develop the shift model of threshold voltage distribution of the memory array in a radiation environment based on the bit upset test results of NAND Flash and study the coupling effect caused by the simultaneous performance degradation of NAND Flash fundamental modules, the experimental research on the total dose effect of two types of SLC NAND Flash memories, with a feature size of 25 nm and storage capacities of 8 and 32 Gb, respectively, was carried out. When irradiated, the partial memory array and peripheral circuit were shielded. An analytical shift model of threshold voltage distribution was developed. The model parameters are extracted from the experimental data of the 32 Gb devices, and the model and the data were in good agreement. The normalized threshold voltage distributions of the memory array at different total doses were obtained through this model, which showed the changing process of the threshold voltage distribution of the memory array more intuitively and quantitatively. The experimental results also show that the reduced voltage applied to the word line of the memory array generated by the charge pump is the cause of the performance degradation of NAND Flash. The factors that reduce the output voltage of the charge pump are the leakage current of the charge pump itself, the global leakage, the local leakage, and their coupling. Reducing the leakage of NAND Flash peripheral circuits, improving the driver of the charge pumps, and designing a data refresh strategy according to the estimation of the bit upset ratio will help improve the data retention capability in the radiation environment.

Improvement of memory performance of 3-D NAND flash memory with retrograde channel doping

The examination of the effect of retrograde channel doping on reliability and performance of 3-D junction-free NAND based flash memory is done for this paper. Specifically, we study the program characteristics, data retention capability junction-free NAND flash memory with half pitch range from 35 nm to 12 nm. Based on our analysis, we highlight that the retrograde channel doping approach can improve not only the SCEs but also the program speed and data control time for 3-D junction-free NAND flash memory, without varying the oxide stack in charge trap-based flash memory.

Ligand-Triggered Self-Assembly of Flexible Carbon Dot Nanoribbons for Optoelectronic Memristor Devices and Neuromorphic Computing.

Carbon dots (CDs) are widely utilized in sensing, energy storage, and catalysis due to their excellent optical, electrical and semiconducting properties. However, attempts to optimize their optoelectronic performance through high-order manipulation have met with little success to date. In this study, through efficient packing of individual CDs in two-dimensions, the synthesis of flexible CDs ribbons is demonstrated technically. Electron microscopies and molecular dynamics simulations, show the assembly of CDs into ribbons results from the tripartite balance of π-π attractions, hydrogen bonding, and halogen bonding forces provided by thesuperficialligands. The obtained ribbons are flexible and show excellent stability against UV irradiation and heating. CDs ribbons offeroutstanding performance as active layer material in transparent flexible memristors, with the developed devices providing excellent data storage, retention capabilities, and fast optoelectronic responses. A memristor device with a thickness of 8µm showsgood data retention capability even after 104 cycles of bending. Furthermore, the device functionseffectively as a neuromorphic computing system with integrated storage and computation capabilities, with the response speed of the device being less than 5.5ns. These properties createan optoelectronic memristor with rapid Chinese character learning capability. This work lays the foundation for wearable artificial intelligence.

Effect of stoichiometry on the resistive switching characteristics of STO resistive memory

Herein, we modify the stoichiometry of an SrTiOx resistive switching layer to fabricate a memristor with a high ON/OFF current ratio and high data retention capability.

Remotely tuned multistate resistive switching in MoS2/NiMnIn thin film heterostructure for highly flexible ReRAM application

In this article, the Cu/MoS2/NiMnIn memory structure was fabricated over stainless steel substrate for flexible electronics applications. The bipolar resistive switching characteristics were observed in two different fabricated devices (i) without sulfur vacancies (D1) and (ii) with sulfur vacancies (D2) in MoS2 thin film. Three different resistance states such as the high resistance state (HRS), intermediate resistance state (IRS) and low resistance state (LRS) have been detected for the D2 memory device. It could be ascribed to the two filamentary models based on the movement of sulfur vacancies and the formation of Cu metallic filament with applied bias voltage. Moreover, the Ohmic and modified space charge limited conduction mechanisms clearly explain the current conduction in different resistance states of device D2. The fabricated MoS2 thin film-based memory structure exhibits stable resistive switching behavior with a high OFF/ON ratio of ∼3.6 × 103, good consistency of ∼3600 endurance cycles and excellent data retention capability up to 3000 s. Moreover, the remote tuning of device D2 was thoroughly investigated and an appreciable change in SET voltage was detected with external temperature and magnetic field. Additionally, the external magnetic field altered the switching states and enhanced the multi-bit data storage capability of the memory device. This can be ascribed to the effect of the Lorentz force on ionic movement in the presence of the external magnetic field. The mechanical flexibility of the memory structure was tested for 1000 bending cycles at various bending angles in both the tensile and compressive bending modes. Hence, the present study opens up new ways for the futuristic flexible device for high data storage and neuromorphic computing applications.

Demonstration of a 2-D SnS/MXene Nanohybrid Asymmetric Memristor

This article demonstrates the fabrication and characterization of a low-cost, energy-efficient, easy-to-fabricate SnS/MXene memristor in which an SnS/Ti3C2Tx active layer is sandwiched in between two copper electrodes. The device has been showing substantial merits with an experimental <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{off}}$ </tex-math></inline-formula> : <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{\text{on}}$ </tex-math></inline-formula> ratio of ~22 with good cyclic stability, exceptional reproducibility, and data retention capability up to 1000 cycles. This article explains the detailed physics governing the various regions of the proposed memristor characteristics in terms of the dual ionic conduction mechanism. Furthermore, the article explains the memristor’s asymmetric behavior using the concept of the trapping and de-trapping of charge carriers. Real-time band structures extracted using sophisticated ultraviolet photoelectron spectroscopy (UPS) strongly support the claims reported in this article. Finally, this article concludes with a practical application of the fabricated device as a low-cost, tunable asymmetric clock generator circuit.

공공영역에서의 개인정보 수집과 활용을 위한 제도적 개선방안

In recent years, artificial intelligence technology, which enables new technologies to be deployed, has expanded the scope and methods of data collection and utilization of government agencies. Data analysis and AI technology are deployed to enhance the intelligent and accurate use of Closed-circuit television (CCTV) surveillance cameras for crime prevention, security, and public safety purposes. The use of facial recognition technology enables an individual to be identified by processing images captured on CCTV, the suspects to be tracked on the CCTV footage, and crime scenes to be monitored in real time. Amidst this expansion, there is an increasing need for discussions to protect privacy. The need for privacy control is emphasized as data collection, retention, and utilization capabilities resulting in losing control over individual’s own information. The value and importance of personal data have been changed from the previous, and government surveillance issues arises as vast quantities of personal data being stored and easily shared. The need for government data access for various purposes and storage of data on a large scale may lead to the privacy right and the infringement of informational self-determination. In a situation where the use of CCTV information is allowed and gradually expanding, it is difficult to evaluate that legal grounds for controlling the actions of government agencies or guaranteeing the rights of individual subjects are sufficient. This paper aims to examine the current status of data collection by government institutions, especially the institutional basis for the use of CCTV and video information collection by government agencies, and problems with the system regarding personal data protection.

Unraveling the Effect of the Water Content in the Electrolyte on the Resistive Switching Properties of Self-Assembled One-Dimensional Anodized TiO2 Nanotubes.

The applied potential, time, and water content are crucial factors in the electrochemical anodization process because the growth of one-dimensional nanotubes can be accelerated by enhancing the corrosive effect. We investigated the effect of the water content on the resistive switching (RS) properties of Ti foils by anodizing the foils and varying the water content in an electrolyte (1-10 vol %). By increasing the water content, we facilitated a slow transition from nanopores to nanotubes and realized an increase in the tube wall diameter and tube length. All of the fabricated memristive devices exhibited a reliable and reproducible bipolar resistive switching effect. The optimized device exhibited bipolar RS properties with good dc endurance (104 cycles) and data retention capability (105 s). Our results suggest that as the water content increases to 5 vol %, the RS process improves; further increases in the water content impair the RS process.

Multifunctionality in ferromagnetic shape memory alloy-based resistive switching memory for flexible ReRAM application

Multifunctional flexible electronics is the ongoing demand for fabricating wearable data storage and communication devices. The magnetoelectric (ME) heterostructure consisting of piezoelectric (AlN) and ferromagnetic magnetic shape memory alloy [FSMA (Ni–Mn–In)] was fabricated over stainless steel (SS) substrate for resistive random access memory application. The Cu/AlN/FSMA/SS metal–insulator–metal based memory cell displays bipolar resistive switching (RS) behavior. The formation of Cu metallic filament at a particular SET voltage leads the memory cell in a low resistance state (LRS) from its pristine high resistance state (HRS). The LRS and HRS are explained well by Ohmic and space charge limited conduction mechanisms, respectively. The fabricated memory cell displays excellent endurance and data retention capability with a high OFF/ON ratio of ∼1.2 × 103. Furthermore, the multifunctionality of the ME heterostructure-based RAM was investigated by tuning the SET voltage with ambiance temperature and external magnetic field remotely. A significant change in the SET voltage could be ascribed to the temperature and magnetic field-induced strain transferred to the AlN piezoelectric layer from the magnetostrictive FSMA (Ni–Mn–In) bottom electrode. The residual Lorentz force explains the remotely tuned LRS and HRS in the transverse magnetic field for multi-bit data storage applications. Moreover, the RS characteristics remain stable even after 800 bending cycles as well as with bending angle (0°–180°). Hence, the present ME heterostructure integrated with flexible SS substrate can be a better choice for highly flexible, low-cost, and multifunctional futuristic RAM applications.

Data inversion and erroneous annealing of floating gate cell under proton radiation

In this paper, the 60-MeV proton beam is used to carry out the proton irradiation experiment on NAND (not and) flash memory, the single-event-upset cross section data of the floating gate cell are obtained, the annealing rule of the floating gate cell errors is analyzed, and the effect of proton irradiation on the data retention capability of floating gate cells is studied. The obtained results are as follows. The single-event-upset cross section of the floating gate cell increases with the increase of proton energy, and decreases with the increase of proton fluence. The floating gate cell errors continue to increase over time, and this effect is more pronounced when low energy protons are incident. After proton irradiation, the data retention capability of the floating gate cell is significantly degraded. The analysis suggests that the high energy protons are indirectly ionized through the nuclear reaction with the target atom, causing single-event-upset of the floating gate cell. The correlation between the upset cross section and the proton fluence is due to the difference in single-event-effect sensitivity of the floating gate cell. The proton-induced non-ionizing damage can form partially permanent defect damage in the tunnel oxide layer, creating multiple auxiliary trap channels that can leak floating gate electrons, resulting in the increase of floating gate cell errors and the degradation of data retention capability.