Bipolar Switching Research Articles

A BaTiO3-based flexible ferroelectric capacitor for non-volatile memories

BaTiO3 (BTO) ferroelectric films, which are renowned for their lead-free compositions, superior stability, and absence of a wake-up effect, are promising candidate materials in the field of non-volatile memories. However, the prerequisites for high-temperature conditions in the fabrication of ferroelectric thin films impose constraints on the substrate choice, which has limited the advancement in non-volatile memories based on single-crystal flexible BTO films with robust ferroelectric properties. Herein, a technique has been developed for the fabrication of flexible devices using a pulsed laser deposition system. BTO ferroelectric films have then been deposited onto a flexible mica substrate, with SrTiO3 (STO) serving as a buffer layer. The obtained flexible BTO devices exhibited excellent ferroelectricity, with a maximum polarization (2Pmax) of up to 42.58 μC/cm2 and a remnant polarization (2Pr) of up to 21.39 μC/cm2. Furthermore, even after 1000 bending cycles, the bipolar switching endurance remained high at 1012 cycles. After 104 s, the flexible BTO device still maintained excellent polarization characteristics. These results make the flexible BTO ferroelectric thin film a potential candidate for the next generation of non-volatile memories.

Multilevel Aircraft-Inverter Design Based on Wavelet PWM for More Electric Aircraft

This paper proposes a comprehensive power system designed for the use of a more electric aircraft power distribution system. Instead of traditional Nicad battery solutions as the energy source of the aircraft power system, lithium battery structures, which are a recent and promising solution in the field of aviation power systems, are modeled and analyzed. In this study, a WPWM-based, single-phase, multi-level pure sine wave static aircraft-inverter system is designed and integrated to improve the performance of conventional aircraft power systems. In the designed power system, a boost converter structure is proposed that boosts 28 VDC-to-270 VDC voltage coming from the lithium–ion battery pack and can reach a steady state in 0.032 s. The performance of the modeled WPWM-based aircraft-inverter system, compared to SPWM Bipolar and Unipolar switching techniques commonly used in single-phase inverter designs, reveals a THD reduction of approximately 27% with WPWM, resulting in a THD value below 2% for both load current and load voltage. As a result of the study, a power system that will enable the aircraft avionics, ventilation, and navigation systems to perform better than conventional power systems and comply with aircraft electric-power characteristic standards has been designed and detailed.

Improved resistive switching characteristics of solution processed ZrO2/SnO2 bilayer RRAM via oxygen vacancy differential

In this study, a solution-processed bilayer structure ZrO2/SnO2 resistive switching (RS) random access memory (RRAM) is presented for the first time. The precursors of SnO2 and ZrO2 are Tin(Ⅱ) acetylacetonate (Sn(AcAc)2) and zirconium acetylacetonate (Zr(C5H7O2)4), respectively. The top electrode was deposited with Ti using an E-beam evaporator, and the bottom electrode used an indium–tin–oxide glass wafer. We created three devices: SnO2 single-layer, ZrO2 single-layer, and ZrO2/SnO2 bilayer devices, to compare RS characteristics such as the I–V curve and endurance properties. The SnO2 and ZrO2 single-layer devices showed on/off ratios of approximately 2 and 51, respectively, along with endurance switching cycles exceeding 50 and 100 DC cycles. The bilayer device attained stable RS characteristics over 120 DC endurance switching cycles and increased on/off ratio ∼2.97 × 102. Additionally, the ZrO2/SnO2 bilayer bipolar switching mechanism was explained by considering the Gibbs free energy (ΔG o) difference in the ZrO2 and SnO2 layers, where the formation and rupture of conductive filaments were caused by oxygen vacancies. The disparity in the concentration of oxygen vacancies, as indicated by the Gibbs free energy difference between ZrO2 (ΔG o = −1100 kJ mol−1) and SnO2 (ΔG o = −842.91 kJ mol−1) implied that ZrO2 exhibited a higher abundance of oxygen vacancies compared to SnO2, resulting in improved endurance and on/off ratio. X-ray photoelectron spectroscopy analyzed oxygen vacancies in ZrO2 and SnO2 thin films. The resistance switching characteristics were improved due to the bilayer structure, which combines a higher oxygen vacancy concentration in one layer with a lower oxygen vacancy concentration in the switching layer. This configuration reduces the escape of oxygen vacancies to the electrode during RS.

The filaments control for tunning digital resistive switching in data storage application and analog behavior as an artificial synapse with CsPbBr3-based memristor

Implementation of tunable digital and analog resistive switching (RS) behaviors for memristors is crucial toward their development in data storage and energy-efficient computations. Herein, the CsPbBr3 film-based RS memristors with different switching film thickness and adaptable electrodes are constructed, which are implemented by the solution processed method. All the constructed memristors demonstrate stable bipolar switching behaviors, and in special, the gradual analog RS behavior with multi-level conductance is observed for the thin memristor, making it as the promising artificial synapse. As a comparison, the thick memristor demonstrates digital abrupt RS behavior, accompanying with a high memory window (>103), which can be applied in data storage field. Furthermore, the evolution of conductive filaments, stemming from synergetic bromine vacancies and aluminum atoms, is proposed to clarify the distinguished dynamic changes in the RS process. This work provides an optimization strategy to tune RS behavior for CsPbBr3-based RS memristors and paves the way for both data storage and artificial synapse applications.

Investigation of Resistive Switching of Insulating Hafnium Nitride for Nonvolatile Memory Applications

In this study, nitrogen-rich Hafnium Nitride (HfN) featuring insulating properties was investigated for achieving resistive switching, crucial for the functionality of resistive random-access memory (ReRAM) devices. Devices were fabricated with a 15-nm HfN resistive switching layer using a Radio Frequency (RF) sputtering system. The fabricated devices successfully exhibited a bipolar switching characteristic with a high On/Off ratio (up to 104). An interesting 2-step behavior was also observed during the formation of the conduction filament which was suspected to be tied to the migration of the nitrogen ions. This is the first attempt at using HfN as the resistive switching material for nonvolatile memory applications.

Single Phase Inverter Design for Solar Panel Output Voltage

Inverter is a devices that functions to convert DC input voltage to AC. One technique for optimizing the inveter output is SPWM. In this final project, a single–phase SPWM inverter with bipolar SPWM switching is designed. This inverter has 1 phase H-Bridge spesifications, with IGBT components, resistors, warehouse and inductors where there are 4 MOSFETs that can be connected. By carrying out 3 test with different sources for a 244.44 volt DC source it produces 0,47 % harmonic, a variable DC source produces 54,81 % harmonics and for a PV sources 9,91 % harmonics. Of the three test, the largest harmonic value is by using a variable DC source. Large harmonic can affect the shape of the wave to be non-sine and the wave has lots of ripples. This simulation aims to facilitate the design of real inverter devices.

Self-Assembly of Delta-Formamidinium Lead Iodide Nanoparticles to Nanorods: Study of Memristor Properties and Resistive Switching Mechanism.

In the quest for advanced memristor technologies, this study introduces the synthesis of delta-formamidinium lead iodide (δ-FAPbI3) nanoparticles (NPs) and their self-assembly into nanorods (NRs). The formation of these NRs is facilitated by iodide vacancies, promoting the fusion of individual NPs at higher concentrations. Notably, these NRs exhibit robust stability under ambient conditions, a distinctive advantage attributed to the presence of capping ligands and a crystal lattice structured around face-sharing octahedra. When employed as the active layer in resistive random-access memory devices, these NRs demonstrate exceptional bipolar switching properties. A remarkable on/off ratio (105) is achieved, surpassing the performances of previously reported low-dimensional perovskite derivatives and α-FAPbI3 NP-based devices. This enhanced performance is attributed to the low off-state current owing to the reduced number of halide vacancies, intrinsic low dimensionality, and the parallel alignment of NRs on the FTO substrate. This study not only provides significant insights into the development of superior materials for memristor applications but also opens new avenues for exploring low-dimensional perovskite derivatives in advanced electronic devices.

Turn-off switching voltage surge analysis with dependence on IGBT cell design

Surge voltage at insulated gate bipolar transistor turn-off switching was analyzed with dependence on cell design parameters. Although drift layer thinning is effective in improving trade-off characteristics between turn-off loss E off and on-state voltage V on, voltage surge is induced due to the quickly expanding depletion layer. Therefore, the surge voltage V surge has also a trade-off relationship with V on at the same E off condition. The origin of the voltage surge was analyzed using TCAD simulation, and the total amount of remaining holes in the drift layer during turn-off switching is a key factor for the V surge. A narrow mesa structure and thick buffer layer are effective for the improvement of trade-off characteristics between V surge and V on. However, the optimum buffer layer thickness depends on the voltage-class due to the speed for punch through.

MAPbBr3 Halide Perovskite-Based Resistive Random-Access Memories Using Electron Transport Layers for Long Endurance Cycles and Retention Time.

Recent studies have focused on exploring the potential of resistive random-access memory (ReRAM) utilizing halide perovskites as novel data storage devices. This interest stems from its notable attributes, including a high ON/OFF ratio, low operating voltages, and exceptional mechanical properties. Nevertheless, there have been reports indicating that memory systems utilizing halide perovskites encounter certain obstacles pertaining to their stability and dependability, mostly assessed through endurance and retention time. Moreover, the presence of these problems can potentially restrict their practical applicability. This study explores a resistive switching memory device utilizing MAPbBr3 perovskite, which demonstrates bipolar switching characteristics. The device fabrication procedure involves a low-temperature, all-solution process. For the purpose of enhancing the device's reliability, the utilization of TPBI(2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) as an electron transfer material on the MAPbBr3 switching layer was implemented for the first time. The formation and rupture of Ag filaments in the MAPbBr3 perovskite switching layer are attributed to reduction-oxidation reactions. The TPBI is involved in the regulation of filaments during the SET and RESET processes. Hence, it can be shown that the MAPbBr3 device incorporating TPBI exhibited about 1000 endurance cycles when subjected to continuous voltage pulses. Moreover, the device consistently maintained ON/OFF ratios above 107. In contrast, the original MAPbBr3 device without TPBI demonstrated a significantly lower endurance with only 90 cycles observed. In addition, the MAPbBr3 device integrated with TPBI exhibited a retention time exceeding 3 × 103 s. The findings of this research provide compelling evidence to support the notion that electron transfer materials have promise for the development of halide perovskite memory systems owing to their favorable attributes of dependability and stability.

Highly stable two-dimensional Ruddlesden-Popper perovskite-based resistive switching memory devices.

Resistive switching random-access memory (ReRAM) devices based on organic-inorganic halide perovskites (OIHPs) have emerged as a new class of data storage devices. Recently, two-dimensional (2D) OIHPs have attracted much attention for ReRAM applications because of their structural diversity and superior stability. Here, the RS characteristics of ReRAM devices fabricated utilizing pure 2D Ruddlesden-Popper (RP) perovskite crystals, namely (TEA)2PbBr4 and (TEA)2PbI4, are reported. The RS memory devices exhibit reliable and reproducible bipolar switching properties with high ON/OFF ratio (∼104), excellent data retention of over 104 s, and good endurance characteristics of 200 cycles. This study investigates temperature-dependent RS behaviors, elucidating the creation and annihilation of a conducting pathway in the presence of an external electric field. Additionally, the RS property of 2D RP perovskite-based memory devices is found to be retained over 45 days at ambient conditions under a relative humidity of 47% ± 4%. Our findings may accelerate the technological deployment of stable 2D perovskite-based RS memory devices for successful logic application.

Study of a charge transition-driven resistive switching mechanism in TiO2-based random access memory via density functional theory.

The nature of the conducting filament (CF) with a high concentration of oxygen vacancies (VOs) in oxide thin film-based resistive random access memory (RRAM) remains unclear. The VOs in the CF have been assumed to be positively charged (VO2+) to explain the field-driven switching of RRAM, but VO2+ clusters in high concentration encounter Coulomb repulsion, rendering the CF unstable. Therefore, this study examined the oxidation state of VOs in the CF and their effects on the switching behavior via density functional theory calculations using a Pt/TiO2/Ti model system. It was concluded that the VOs in the CF are in a low oxidation state but are transformed to VO2+ immediately after release from the CF. In addition, the short-range interactions between VOs were confirmed to facilitate the rupture and rejuvenation of the CF by reducing the required activation energy. Finally, an improved switching model was proposed by considering the charge transition of VOs, providing a plausible explanation for the reported coexistence of two opposite bipolar switching polarities: the eight-wise and the counter-eight-wise polarities.

Large scale integrated IGZO crossbar memristor array based artificial neural architecture for scalable in-memory computing

Neuromorphic systems based on memristor arrays have not only addressed the von Neumann bottleneck issue but have also enabled the development of computing applications with high accuracy. In this study, an artificial neural architecture based on a 10 × 10 IGZO memristor array is presented to emulate synaptic dynamics for performing artificial intelligence (AI) computing with high recognition accuracy rate. The large area 10 × 10 IGZO memristor array was fabricated using the photolithography method, resulting in stable and reliable memory operations. The bipolar switching at −2 V–2.5 V, endurance of 500 cycles, retention of >104 s, and uniform Vset/Vreset operation of 100 devices were achieved by modulating the oxygen vacancy in the IGZO film. The emulation of electric synaptic dynamics was also observed, including potentiation-depression, multilevel long-term memory (LTM), and multilevel short-term memory (STM), revealing highly linear and stable synaptic functions at different modulated pulse settings. Additionally, electrical modeling (HSPICE) with vector-matrix measurements and simulation of various artificial neural network (ANN) algorithms, such as convolution neural network (CNN) and spiking neural network (SNN), were performed, demonstrating a linear increase in current accumulation with high recognition rates of 99.33 % and 86.46 %, respectively. This work provides a novel approach for overcoming the von Neumann bottleneck issue and emulating synaptic dynamics in various neural networks with high accuracy.

Realization of Self‐Rectifying and Self‐Powered Resistive Random‐Access Memory Memristor Using [001]‐Oriented NaNbO3 Film Deposited on Sr2Nb3O10 Nanosheet at Low Temperatures

[001]‐oriented NaNbO3 films are deposited on Sr2Nb3O10/TiN/SiO2/Si substrates at 300 °C. The Sr2Nb3O10 nanosheets are used as a template to form crystalline NaNbO3 films at low temperature. The NaNbO3 films deposited on one Sr2Nb3O10 monolayer exhibit a bipolar switching curve due to the construction and destruction of oxygen vacancy filaments. Because the Sr2Nb3O10 monolayer does not act as an insulating layer, the film does not exhibit self‐rectifying properties. Self‐rectifying properties are observed in the NaNbO3 memristor, which forms on two Sr2Nb3O10 monolayers that act as tunnel barriers in the memristor. The memristor exhibits extensive rectification and on/off ratios of 48 and 15.7, respectively. Tunneling is the current conduction mechanism of the device in the low‐resistance state, and Schottky emission and tunneling are responsible for the conduction mechanism in the high‐resistance state at low and high voltages, respectively. The piezoelectric nanogenerator produced using the [001]‐oriented NaNbO3 film generates high voltage (1.8 V) and power (3.2 μW). Furthermore, endurance of the resistive random‐access memory and nonlinear transmission characteristics of the biological synapse are accomplished in the NaNbO3 memristor powered by the NaNbO3 nanogenerator. Therefore, the [001]‐oriented crystalline NaNbO3 film formed at 300 °C may be utilized for self‐rectifying and self‐powered artificial synapses.

An Electrically Resistive Switching Nonvolatile Memory System Based on PEDOT:PSS

The current density–voltage (J–V) curves of poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) are examined at room temperature, which reveal nonlinear behavior and hysteresis loop‐like patterns. Herein, the potential of the material for nonvolatile applications requiring resistive random access memory (ReRAM) is demonstrated. The resistive switching effect is explained using a Schottky barrier and the space‐charge‐limited conduction model. Additionally, dielectric and electrical characteristics are analyzed in the frequency range from 20 Hz to 10 MHz. The impedance, electric modulus, dielectric loss tangent, and AC conductivity are explored through On‐ and Off‐states of resistive switching. A modified Debye function and Jonscher's power law are used for data fitting. The resistive switching memory behavior of PEDOT:PSS are studied using J–V and chemical impedance spectroscopy (CIS) measurements. The Cu/PEDOT:PSS/Cu sandwich‐type devices show bipolar switching behavior, and an equivalent circuit model based on the impedance spectra is proposed to describe the CIS response in both states. The switching process is attributed to the electrical‐field‐induced effect of dipolar reorientation on the electrical conductivity of PEDOT:PSS at grain boundaries.

Transformation of rust iron into a sustainable product for applications in the electronic, energy, biomedical, and environment fields: Towards a multitasking approach

Utilization of waste material for value-added applications is a sustainable approach towards reduction of global waste. Herein, the waste rust iron is transformed into useful Fe2O3 nanoparticles (FNPs). Here for the first time, FNPs were uniquely utilized in multiple applications, including resistive switching (RS), tribo and piezo-electric nano-generators, magnetic hyperthermia, and toxic dyes adsorption from water. The RS characteristics of the Ag/FNPs/ITO device emphasized bipolar switching with excellent cyclic stability, endurance, and memory retention. Afterward, the FNPs based tribo and piezo-electric nanogenerator device demonstrated greater instantaneous power (5200 µW) at 10 MΩ, surpassing previously reported inorganic or garbage materials. Furthermore, the pertinency of FNPs was explored for biomedical application by induction heating studies for magnetic fluid hyperthermia (MFH). MFH revealed an increase in temperature of 14.9 °C and 23.4 °C for 5 mg and 10 mg FNPs ferrofluid, respectively, thus indicating the potential of FNPs for possible cancer treatment with biocompatibility suggestions. Finally, the adsorption study reveals that the FNPs are a promising candidate for the adsorption of safranin M.S., methylene blue, malachite green, and lemon yellow powder, (77, 78, 59, and 56 mg/g, respectively). We believe that our current study will result in a significant impact to reduce the future burden of global waste and thus encourage its utilization for value-added applications.

Fabrication and characterization of TiOx based single-cell memristive devices

Nowadays, remarkable progress has been observed in research into neuromorphic computing systems inspired by the human brain. A memristive device can behaviorally imitate the biological neuronal synapse therefore memristor-based neuromorphic computing systems have been proposed in recent studies. In this study, the memristive behaviors of titanium dioxide sandwiched between two platinum electrodes were investigated. For this purpose, three SiO2/Pt/TiOx/Pt thin films with 7.2 nm, 40 nm, and 80 nm TiOx metal-oxide layers were fabricated using a pulsed laser deposition technique. The fabrication process, structural properties, photoluminescence properties and electrical transport characterization of each thin film have been investigated. All thin films were analyzed in terms of the film stoichiometry and degree of oxidation using high-resolution x-ray photoelectron spectroscopy. By measuring the layer thickness, density, and surface roughness with the x-ray reflectivity technique, by analyzing the structural defects with photoluminescence spectroscopy and by characterizing the quasi-static electrical properties with the conventional two probes technique, we have shown that the fabricated memristive devices have bipolar digital switching properties with high ROFF/RON ratio. This type of switching behavior is applicable in random access memories. Experimental current–voltage behavior in the form of pinched hysteresis loop of the films have been modelled with generalized memristor model.

Enhanced memristive effect of laser-reduced graphene and ferroelectric MXene-based flexible trilayer memristors

Ferroelectric memory devices based on 2D materials are gaining popularity in research due to having non-volatile data storage, low power consumption and improved endurance and data retention properties. In this study, we discussed the synthesis of self-standing graphene oxide (GO) and MXene films via chemical oxidation and etching routes. As synthesized MXene (nFE-MXene) was converted into ferroelectric (FE-MXene) by heating the nFE-MXene self-standing film. XRD, SEM, EDS and elemental mapping supported crystal structure as well as chemistry of prepared material. Ferroelectric hysteresis measurements at various frequencies (100Hz–400Hz) confirmed the presence of polarization domains in FE-MXene. Graphene oxide was laser reduced (rGO) to implement as metal electrodes for metal-insulator metal (MIM) memory device architecture. Three trilayer memory systems (rGO/nFE-MXene/rGO, rGO/FE-MXene/rGO and rGO/FE-MXene/nFE-MXene/rGO) were fabricated showing non-volatile bipolar switching. The memory performances were checked for a working window of ±4V. Further, the elevated memory performance of rGO/FE-MXene/nFE-MXene/rGO memristive device at low operating voltage (˂ ±3V) is discussed for efficient working device application with an on/off ratio of 103, higher data retention (4000 s) and endurance up to 1000 cycles.

Engineering Atomic-Scale Patterning and Resistive Switching in 2D Crystals and Application in Image Processing.

The ultrathin thickness of 2D layered materials affords the control of their properties through defects, surface modification, and electrostatic fields more efficiently compared with bulk architecture. In particular, patterning design, such as moiré superlattice patterns and spatially periodic dielectric structures, are demonstrated to possess the ability to precisely control the local atomic and electronic environment at large scale, thus providing extra degrees of freedom to realize tailored material properties and device functionality. Here,the scalable atomic-scale patterning in superionic cuprous telluride by using the bonding difference at nonequivalent copper sites is reported. Moreover, benefitting from the natural coupling of ordered and disordered sublattices,controllable piezoelectricity-like multilevel switching and bipolar switching with the designed crystal structure and electrical contact is realized, and their application in image enhancement is demonstrated. This work extends the known classes of patternable crystals and atomic switching devices, and ushers in a frontier for image processing with memristors.

Crystal structure and magnetization reversal in single-layered Ruddlesden–Popper CaEuFeO4 ceramics

Magnetization reversal widely exists in ferrimagnets, which provides an opportunity to develop novel low-power-consumption memory in the future. In the present work, dense CaEuFeO4 ceramics with the single-layered Ruddlesden–Popper structure were prepared by a standard solid-state reaction process. The orthorhombic phase was determined to have the space group Bmab at room temperature. The antiferromagnetic state was observed below the Néel temperature of 338 K, and temperature-induced magnetization reversal was observed below the compensation temperature in the field cooling protocol. Moreover, field-induced magnetization reversal or bipolar magnetic switching between different fields was also observed at low temperatures. The intriguing temperature- and field-induced magnetization reversal is induced by the competition between the canted Fe3+ moment and the antiparallel Eu3+ moment induced by the Eu–Fe exchange interaction.

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.