Good Endurance Properties Research Articles

NiFe2O4 nanoparticles for non-volatile bipolar resistive switching memory device

The present work reports the chemical synthesis of NiFe2O4 (NFO) nanoparticles (NPs) and its use as a switching layer material in resistive switching (RS) devices. Various analytical techniques were used to confirm the phase, composition, and optical properties of the NFO NPs. With the support of the x-ray diffraction technique, crystal structure (cubic spinel) and crystallite size (20.12 nm) were determined. Field emission scanning electron microscopy confirmed the material morphology. Raman Spectroscopy and Fourier Transform Infrared Spectroscopy were applied to identify the NFO NPs functional groups. The Ag/NFO/fluorine-doped tin oxide device was fabricated, which shows bipolar RS with good endurance (104cycles) and retention (6 × 103 s) properties. Moreover, the device’s conduction and RS mechanisms were also carried out.

Solvothermal synthesis of TiO2 nanospheres for non-volatile memory and synaptic learning applications

In this study, we used the one-pot solvothermal method to synthesize the TiO2 nanospheres (NSs) and used them for non-volatile memory and neuromorphic computing applications. Several analytical tools were used to understand the structural, optical, morphological, and compositional characteristics of synthesized TiO2 NSs. The tetragonal crystal structure of anatase TiO2 was formed, according to the Rietveld refined x-ray diffraction results. The NS morphology was confirmed by field emission scanning electron microscopy and transmission electron microscopy images. X-ray photoelectron spectroscopy was probed to understand the elemental composition and electronic states of the TiO2 NSs. We specifically looked at the impact of reaction time on the structural, optical, morphological, compositional, and resistive switching (RS) properties of TiO2 NSs. The fabricated devices (Ag/TiO2 NSs/FTO) exhibit bipolar RS behavior. The optimized RS device shows good endurance (5000 cycles) and memory retention (5000 s) properties. Moreover, fabricated devices showed double-valued charge-flux characteristics, whereas charge transport was caused by the Ohmic and space charge-limited current mechanisms. Additionally, the optimized device can mimic various synaptic characteristics including potentiation-depression, excitatory post-synaptic current, and paired-pulse facilitation.

The g-C3N4-TiO2 nanocomposite for non-volatile memory and artificial synaptic device applications

Recently, 2D layered materials like graphitic carbon nitride (g-C3N4) are gaining significant attention due to their excellent structural and electronic properties. Metal oxide and g-C3N4 composite can enhance chemical and electronic properties which can ultimately enhance device performance. Given this, we report the synthesis of g-C3N4–TiO2 nanocomposite by the ex-situ (solid state reaction) method for resistive switching (RS) applications. Initially, the TiO2 nanoparticles (NPs) were optimized by using annealing them at different temperatures and composited with the g-C3N4. The devices fabricated using g-C3N4–TiO2 nanocomposite shows good RS properties at very low SET and RESET voltages (< 0.5 V), similar to the biological voltage scale. The distribution of switching voltages of all devices was studied using the cumulative probability and Weibull distribution techniques. Moreover, switching voltages were modeled and predicted using the statistical time series analysis method. All fabricated devices demonstrated the double-valued charge flux characteristics, suggesting the presence of a non-ideal memristor effect. The optimized g-C3N4-TiO2 (TiO2 NPs annealed at 450 °C) device shows good endurance and retention memory properties. Moreover, the optimized g-C3N4-TiO2 device can mimic the various bio-synaptic properties such as potentiation-depression, excitatory postsynaptic current, and paired-pulse facilitation. The charge transport results reveal that Ohmic and Child's square law dominated the conduction of the device. Based on electrical and charge transport results, a plausible filamentary RS effect is presented. This study suggested that the g-C3N4-TiO2 is beneficial for both memory and neuromorphic computing applications.

The Feasibility of Tungsten-Doped VO2 Films on Soda-Lime Glass with Low Thermal Budget by High Density Plasma Source for Smart Windows

Thermochromic W-doped VO2 thin films on soda-lime glass are successfully fabricated by co-sputtering technique using a high density plasma source, which is equipped by high power impulse magnetron sputtering (HIPIMS). A post-rapid thermal annealing of 500 °C is performed for the purpose of low thermal budget. The effect of doping amount of tungsten on thermochromic properties such as transmittance and transition temperature are addressed. The transition temperature can be lower down to 30 °C with a small amount of 4.5% tungsten added in VO2 nanocrystals. A solar regulation efficiency, ΔTsol = 10% is achieved at thicker TiO2 thickness. The competition of secondary phase of V2WO7.5 and oxygen-rich phase of V2O5 under different O2/Ar ratio is studied. The crystalline behavior of monoclinic phase is examined by X-ray diffraction (XRD) pattern and high resolution transmission electron microscope (HR-TEM). The good endurance property ensures the feasible use for the energy-saving applications.

Anti-bacterial and transparent allantoin biomaterial-based biocomposite for non-volatile memory and brain-inspired computing applications

The allantoin biomaterial-based biocomposite was utilized to fabricate resistive switching (RS) devices for non-volatile memory and brain-inspired computing applications. The polymeric phase, surface morphology, and purity of biomaterial were characterized using different analytical tools. The allantoin biofilm shows anti-bacterial and transparent properties, therefore, it can be useful for wearable electronics. Novel allantoin biomaterial-based composite device exhibits forming-free bipolar resistive switching behavior with low SET (+0.50 V) and RESET (−1.34 V) voltages, good endurance (3 × 103 cycles), and memory retention properties (103 s). Additionally, the device mimics various bio-synaptic properties such as excitatory postsynaptic current, paired-pulse facilitation, and paired-pulse depression.

Polarization of Bi2Se3 thin film toward non-volatile memory applications

In recent years, topological insulators have drawn growing interest as a unique electronic state of matter toward quantum information technology. Despite the logic devices with magnetization switching through spin–orbit torque or the topological magneto-electric effect, realizing memory devices based on topological insulators has been urged in quantum computing applications. In this work, we report the design and fabrication of a non-volatile memory device that employs polarization of Bi2Se3 thin films achieving fast memory speed, sufficient memory window, and good reliability. The Bi2Se3 film polarizes under an external electrical field with charges accumulated on the top and bottom surfaces separating the electrons and holes. Such polarization is much faster than the carrier tunneling in conventional floating-gate flash memory and ferroelectric-based memory devices. In addition, good memory retention and endurance properties have also been obtained, showing great potential in high-performance memory application in future topological insulator-involved information technology.

Gate controlled resistive switching behavior of heterostructure in the Ni-Co layered double hydroxide/graphene oxide transistor

A novel heterostructure consisting of two dimensional nanocomposite Ni-Co layered double hydroxides (Ni-Co LDHs) and graphene with adjustable Fermi levels has been studied. Transistor characteristics and memristor properties of the Ni-Co LDHs/graphene oxide heterostructure have been investigated. In consideration of Fermi energy of graphene is modulated under external applied voltage, by constructing Schottky barrier, the current and threshold voltage of the device were effectively modulated by applied different gate voltage. The Ni-Co LDHs/graphene oxide heterostructure device exhibits a good endurance property, as well as data retention property is up to 104 s. The resistive switching characteristics are achieved via the conductive filament. The performance and scheme design of this device have a good prospect in memory applications.

Multilevel resistive switching performance of TiO2-based flexible memory prepared by low-temperature sol-gel method with UV irradiation

The flexible Ag/TiO2/ITO/PET resistive switching memory is prepared by low-temperature sol-gel method with UV irradiation, and the simple method that combined the advantages of sol-gel method and low temperature can be applied to fabricate high-quality film. The flexible Ag/TiO2/ITO/PET memory device displays good resistive behavior, for instance, the narrow distributions of switching voltages, good cycle endurance, and long retention time. Meanwhile, the multilevel resistance states of the device can be realized by controlling the compliance current or reset voltages, showing the potential of applications in neural networks and high-density storge. In addition, flexibility of the Ag/TiO2/ITO/PET is studied, which exhibit good endurance and retention properties under bending condition. The I–V curves are replotted and fitted for analyzing the conductive mechanism of the device. The fitting results show that SCLC and Ohmic mechanism are main mechanisms of high resistance state and low resistance state respectively. The electrochemical and thermochemical modes are adopted to explain resistive switching behavior. Our results indicate the Ag/TiO2/ITO/PET memory has potential application in wearable and foldable electronics.

The effect of TiO2 buffer layer thickness on the thermochromic properties of VO2 thin-film fabricated by high density plasma source

Thermochromic VO2 thin films are fabricated by using high power impulse magnetron sputtering at room temperature. In order to increase the crystallinity and transparency of VO2 thin films, a barrier layer of TiO2 is deposited on the glass substrate. Then TiO2/VO2 stacks are post-annealed at a temperature of 500 °C for 3 min. The transmittance properties as functions of TiO2 and VO2 thicknesses are discussed. The effects of TiO2 thickness on the strain state of (011) and () planes of monoclinic phase are studied. The laminated film shows satisfactory optical properties with an excellent solar regulation efficiency (ΔTsol = 10.2%) and an acceptable luminous transmittance (Tlum = 41.1%) in a low-temperature state. Good endurance property is demonstrated using a thermal stress cycle of 25 °C/85 °C for 100 times.

Synthesis and room-temperature multiferroic properties of lead-free Bi4Ti3O12/NiFe2O4 nanocomposite films

Lead-free Bi4Ti3O12/NiFe2O4 nanocomposite films have been prepared via sol-gel spin-coating route. The successful phase formation of orthorhombic Bi4Ti3O12 and cubic NiFe2O4 has been confirmed using x-ray diffraction without any detectable extra phase. The scanning electron microscopy with EDS measurement reveals homogeneous and dense growth of both phases accompanied by clear interface between the two layers. The loop of magnetization versus magnetic field indicates the ferromagnetic properties at room temperature with saturation magnetization of ~257.48 emu/cm3, coercive field of ~121 Oe and remnant magnetization of ~57.03 emu/cm3. Room-temperature ferroelectric behavior is also obtained along with the good fatigue endurance properties and low leakage current density. The frequency dependence of dielectric constant displays the monotonous decreasing tendency with low dielectric loss. Moreover, evident magnetodielectric behavior is achieved in the nanocomposite films at room temperature. The coexistence of ferromagnetic and ferroelectric behavior including the appearance of magnetodielectric effect proves the room-temperature multiferroic properties in Bi4Ti3O12/NiFe2O4 nanocomposite films, which makes the films meaningful as the lead-free multiferroic systems for device applications at room temperature.

Employing defected monolayer MoS2 as charge storage materials

Recently, various two-dimensional (2D) materials have been employed in charge trapping memories as the charge trapping layer instead of conventional metal/semiconductor thin films or discrete particles. Such ultra-thin charge trapping layers are beneficial to the development of miniaturized devices, which is a trend in modern semiconductor technology. 2D MoS2 is an alternative charge trapping material, but previous investigations have been limited to their multilayers. Here, we present the study on employing monolayer MoS2 as charge trapping layer in charge trapping devices. We found that intrinsic monolayer MoS2 is less effective for charge trapping; while defective monolayer MoS2 shows enhanced charge storage capacity. By employing argon plasma treatments, we are able to control the defect density in monolayer MoS2 and the memory window of monolayer MoS2 based charge trapping devices can vary from 1.01 to 5.14 V at a sweeping voltage of ±20 V and program/erase slope from 0.06 to 0.32. Optimized devices show ∼1 ms program/erase speed, >70% charge retention after ∼7000 s and good endurance properties with >1000 cycles. The enhancement of the memory window is attributed to the localized charge tapping sites in defected monolayer MoS2. This work would provide insights for the improvement of storage capacity through defects engineering in the atomically thin 2D materials.

Improved resistive switching behavior of multiwalled carbon nanotube/TiO2 nanorods composite film by increased oxygen vacancy reservoir

The non-linear nature in the current-voltage relationship and good resistive switching characteristics were demonstrated with the help of TiO2 nanorods-functionalized multiwalled carbon nanotube (fMWCNT) composite grown by the low-cost hydrothermal method. The composites were characterized by X-ray diffraction, scanning electron microscopy, Raman, photoluminescence, and X-ray photoelectron spectroscopy to investigate the structural, morphological, and chemical composition of composite films. The resistive switching characteristics of the TiO2-fMWCNT nanocomposites were found to be strongly dependent on the fMWCNT concentration. The enhanced switching performance is associated with the surface nanostructure and chemical composition of the nanocomposites. Owing to the hierarchical rutile TiO2 nanorods and opportune fMWCNT content, the nanocomposite based device with 0.03 wt % fMWCNT exhibited the best resistive switching performance with good endurance and retention non-volatile memory properties. Interestingly, with the optimized stoichiometric composition and operation conditions, forming-free, low operational voltage, self-rectifying like properties have been simultaneously achieved, which are some of the prerequisites for next-generation memory devices. In addition to this, the double-valued charge-magnetic flux nature of the developed devices was demonstrated. The experimental current-voltage characteristics are well-matched with the Ohmic and Schottky conduction mechanisms.

Biodegradable transient resistive random-access memory based on MoO3/MgO/MoO3 stack

High-performance biodegradable transient resistive random-access memories (RRAMs) with the structure of Mg/MoO3/MgO/MoO3/Mg have been fabricated on a polylactic acid (PLA) substrate. Without the electroforming process, the devices have high ratios of the high-resistance state (HRS)/low-resistance state (LRS) (&amp;gt;50% of devices reaching above 106 and ∼3% reaching above 1011), good retention properties (both the HRS and LRS without deterioration within 2 × 104 s), and good endurance properties (continuously switched between the HRS and LRS &amp;gt;100 times under appropriate voltage pulses). By investigating the effect of different top electrode (TE) and bottom electrode (BE) combinations (TE/BE: Mg/Mg, Pt/Mg, Mg/Pt, and Mg/Au) and different oxygen contents of MoO3 on the performance of devices, the resistive switching mechanism is revealed to be the redox of the Mg TE at the interface of Mg/MoO3. The HRS is attributed to the formation of MgO after Mg is oxidized by mobile oxygen ions or oxygen captured from adjacent MoO3 under applied voltage, while the LRS is ascribed to the dissolution of formed MgO. The fitting results of the measured data indicate that the conduction of the HRS is dominated by the Poole-Frenkel (P-F) emission and that of the LRS is governed by the Ohmic conduction. Moreover, the devices can degrade quickly in 0.9% NaCl solution within 5 h, except for the PLA substrate that is able to degrade in the human body.

Low thermal budget annealing for thermochromic VO2 thin films prepared by high power impulse magnetron sputtering

Thermochomic VO2 thin films are fabricated by using high power impulse magnetron sputtering at room temperature. In order to increase the crystallinity and transparency of VO2 thin films, first a buffer layer of TiO2 is deposited on the glass substrate. Then TiO2/VO2 stacks are post-annealed at a temperature of 500 °C for 3 min. The transmittance as functions of film thickness and O2/Ar ratio during film deposition is discussed. It is found that the O/V atomic ratio decreases with increasing O2/Ar ratio, which is due to serious inter-diffusion inside stacked layers. At high O2/Ar ratio, columnar-shaped crystals are suggested, which belongs to V2Ti3O9:Si quaternary oxide. The depth profiles of binding energies measured by X-ray photoelectron spectroscopy are compared with different O2/Ar ratios. Good endurance property for a thermal stress cycle of 25 °C/85 °C is obtained under the O2/Ar ratio of 6%. The laminated film shows satisfactory optical properties with an excellent solar regulation efficiency (ΔTsol = 10.4%) and an applicable luminous transmittance (Tlum = 35.2%) in a low-temperature state.

Control of the set and reset voltage polarity in anti-series and anti-parallel resistive switching structures

In the attempt to control the polarity of the set and reset voltages in bipolar resistive switching capacitors, we have studied the switching properties of structures consisting of either two anti-series or two anti-parallel metal-insulator-metal capacitors. The capacitors were based on hafnium oxide, and W and TiN/Ti were used as bottom and top electrodes respectively. MIM capacitors showed bipolar resistive switching behavior, with very good repetitiveness and endurance properties. Both anti-series and anti-parallel structures showed again bipolar resistive switching behavior, being the polarity of the set and reset voltages controllable by applying higher biases. In the case of anti-series configuration, there is a stretch-out in the current-voltage characteristic because the bias is applied across two different devices. Changing the polarity is equivalent to the process of write and erase of complementary resistive switching devices in crossbar arrays. In the case of anti-parallel configuration, the resistance window between both resistivity states is reduced. The control of the switching polarity has also been observed when applying a small ac signal, and measuring the conductance of the structures.

Superior Memory of Er-Doped TiO2 Nanowire MOS Capacitor

The capacitive memory of erbium (Er)-doped nanowire (NW) has been reported. The TiO2 and Er:TiO2 NWs’ active layer sandwiched between Au and Si has been used for this study. The capacitance ( ${C}$ )–voltage ( ${V}$ ) and conductance ( ${G}$ )–voltage ( ${V}$ ) characteristics have been studied for different high frequencies ranging from 1 to 10 MHz. Most importantly, ${C}$ – ${V}$ hysteresis for various sweeping voltages (±2, ±4, ±6, ±8, and ±10 V) was measured for both the devices. Er:TiO2 NW device depicted an extreme ${C}$ – ${V}$ hysteresis as well as memory window of ~3.52 V at ±10 V. Moreover, Er:TiO2 NW device also exhibited a low value of interface trap density ${D}_{\mathrm{it}} \sim 8.72\times 10^{{10}}$ eV−1cm−2 and good endurance and retention properties.

Electric-field-controllable nonvolatile multilevel resistance switching of Bi0.93Sb0.07/PMN-0.29PT(111) heterostructures

Electric-field switchable multilevel nonvolatile resistance states are achieved at room temperature in Bi0.93Sb0.07/0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3(111) (PMN-0.29PT) heterostructures. During the initial poling of the PMN-0.29PT, the variation of the resistance of the Bi0.93Sb0.07 film with the electric field tracks the variation of the electric-field-induced in-plane strain of the PMN-0.29PT effectively, revealing that the resistance switching is dominated by the ferroelectric-domain-switching-induced lattice strain but not the domain-switching-induced polarization charges. A relative resistance change ΔR/R ∼ 7% at 300 K and up to ∼10% at 180 K were achieved near the coercive field EC of the PMN-0.29PT(111) substrate. At least five stable resistance states with good endurance properties could be obtained at room temperature by precisely controlling the electric-field pulse sequence as a result of the nonvolatile remnant strain transferring from the PMN-0.29PT to the film, providing a simple and energy efficient way to construct multistate resistive memory.

An Organic Bipolar Resistive Switching Memory Device Based on Natural Melanin Synthesized From Aeromonas sp. SNS

A Ag/melanin/SS memristive device with remarkably good endurance and retention properties is demonstrated using natural melanin isolated from bacterium Aeromonas sp. SNS. Purified and characterized melanin is used for the development of a non‐volatile memory device. The device is operated under electroforming‐free mode and requires only ±0.6 V resistive switching voltage. 2 × 104 switching cycles endurance is achieved with an approximately 10X memory window at 0.2 V read voltage. In addition to this, the low resistance state (LRS) and high resistance state (HRS) are stable over 103 s without any observable degradation in the resistance states. Standard deviation and coefficient of variation of LRS and HRS are very small compared to other memory devices reported in the literature. Furthermore, the Ag/melanin/SS memristive device shows rich nonlinear behavior and possesses negative differential resistance effect during positive bias. Charge transportation in the device is due to the ohmic and space charge limited current. The formation and breaking of the conductive filament are responsible for the bipolar resistive switching effect due to hybrid electronic‐ionic charge transportation. Rich I–V characteristics, very low switching voltage, and remarkable nonvolatile memory performance make melanin a strong candidate for next generation organic non‐volatile memory devices.

Impact of Device Area and Film Thickness on Performance of Sol-Gel Processed ZrO2RRAM

A sol-gel-processed ZrO2 layer was used as an active layer for a resistive random-access memory (RRAM). With top Ag electrodes, the fabricated devices show conventional bipolar switching memory properties. The impacts of device size and ZrO2 film thickness on device performance were investigated. The scaling of the device area and the successful increase in ZrO2 film thickness increased the high-resistance state (HRS)/low-resistance state (LRS) ratio values and improved the non-volatile memory properties, such as retention and endurance. The fabricated ITO/ZrO2/Ag RRAM shows good retention and endurance properties. The HRS and LRS were found to last for 104 s without any significant degradation.

A remarkable performance of CH 3 NH 3 PbI 3 perovskite memory based on passivated method

Organic-inorganic hybrid perovskite materials, such as CH3NH3PbI3, had been widely applied in resistive switching access memory device. In this work, we demonstrated nonvolatile memory devices based on CH3NH3PbI3 that had been passivated by oleic acid, which reduced the defects of perovskite layer, causing storage window and stability improved. Meanwhile, the device showed good endurance properties and outstanding reproducibility. The fitting results indicated that the properties changed from space-charge limited conduction to Schottky emission at HRS. This illustrated that the concentration of defect in perovskite layer was decreased and the mechanism of resistive switching transformed from ion migration to barrier modulation. These results suggested that perovskite memory based on oleic acid passivation had great potential to be used in high-performance memory devices.