Ohmic Conduction Research Articles

Stable resistive switching behavior of polyvinyl alcohol coating film-based memristor under multiple operating voltages by doping AgNWs

The integration of memristive effect devices for both information storage and computation can enhance the efficiency and performance of artificial intelligence (AI) systems，the memristors based on various polymers as functional layers show high application prospects. This research introduces 5 wt% silver nanowires (AgNWs) doping into the polyvinyl alcohol (PVA) memristor device, which enables stable resistive switching (RS) behavior across multiple operating voltages. Defects from PVA and AgNWs are counterbalanced by Ag ions stimulated by AgNWs and Ag top electrode, thus reducing conductive path randomness. The device demonstrates excellent cycle durability for 300 cycles and data retention for up to 104 s. Analysis of the I-V characteristic curve reveals that the current conduction mechanism is mainly related to Ohmic conduction, Space-charge-limited conduction (SCLC), and Schottky emission mechanisms. The AgNWs simplify the structure of conductive filaments (CFs) and facilitate the formation and breakage of CFs dominated by Ag atoms, leading to the conversion between HRS and LRS of the device.

Thermal annealing effects on the electrical characteristics of alpha particles irradiated MIS device AuTa2O5GaAs

An alpha particle-irradiated MIS device made of AuTa2O5GaAs was used to study how thermal annealing affects the I-V characteristics and how the current changes with annealing temperature, radiation energy, and voltage biassing. The super-gate of the MIS structure was made by using thermal evaporation to build a 1000°A thick layer of gold under a vacuum of about 10-5 torr. At room temperature, the devices were exposed to alpha particles from the radioactive source 226Ra (0.5 Ci) with energies of 5.1, 4, 3, 1.8, and 1.2 MeV for 0–30 minutes. After 30 minutes of annealing at 150, 200, and 300 o C in a vacuum of 10-3 torr, the current-voltage (I-V) characteristics of the irradiation devices were found. During thermal annealing, different results were seen with bias voltages of 0.4, 1, and 2 V and temperatures of 150, 200, and 300 o C. Annealing the device at 150 o C doesn't change how stable it is, but annealing it at 300 o C causes ohmic conduction in the device's properties. The device's current can be fixed best when the device is heated to 200 o C and then cooled. Also, thermal annealing seems to have different effects on the I–V electrical characteristics of the devices depending on the energy of the particles and the voltage biassing.

From h‐BN to Graphene: Characterizations of Hybrid Carbon‐Doped h‐BN for Applications in Electronic and Optoelectronic Devices

AbstractHybrid two‐dimensional materials consisting of graphene and hexagonal boron nitride (h‐BN) have drawn significant interest due to their tunable bandgap and electrical properties. Considering their composition‐dependent properties, ohmic current injection and the development of h‐BN‐based optoelectronic and high‐power electronic devices should be achievable by controlling the C concentration. In this study, electrical and optical characterizations of single‐crystal h‐BN synthesized under high‐pressure and high‐temperature (HPHT) are conducted by varying C concentrations via post‐growth diffusion. Low C‐doped h‐BN (h‐BN:C) with ≈0.1 at% C exhibits nonohmic conduction within a voltage range of ±100 V at all temperatures. In contrast, high h‐BN:C (≈10 at% C) containing C domains and graphite/graphene layers shows additional luminescence peaks and initially exhibits nonohmic conduction at 298 K, which then transforms to ohmic conduction after breakdown‐like behavior at 598 K. This phenomenon, observed only in the high h‐BN:C devices, is attributed to the C‐containing conductive path formed on the channel surface through C drift and local dielectric breakdown of h‐BN mother phase, indicating that ohmic conduction itself does not guarantee the current flow in the conduction/valence bands in h‐BN:C. With these findings, the present thorough and fruitful characterizations are beneficial for the development of h‐BN:C‐based devices.

Ohmic conduction in poly (o-toluidine)–nano CuO composite based devices

Polymer nanocomposite comprising 25 weight % of nano copper oxide (n-CuO) and poly (o-toluidine) [POT] is prepared. For the first time, we report the current–voltage (I–V) characteristics of this nanocomposite. Incorporation of n-CuO modifies the structural properties of POT. The X-ray diffraction (XRD) spectra indicate the bonding of CuO with the polymer matrix. The Band gap of the samples is estimated about 1.78 ​eV. FTIR spectra reveal presence of C–H, C–C bonds. SEM image recorded reveal substitution of n-CuO inside the POT matrix. I–V characteristic recorded at different temperature implies change in conducting behaviour of the polymer nanocomposite from conducting to semiconducting nature with change in temperature.

Modification of interface properties of Au/n-GaN Schottky junction by rare-earth oxide Nd2O3 as an interlayer and its microstructural characterization

We demonstrate the impact of rare-earth Nd2O3 interlayer on the electrical properties of Au/n-GaN Schottky junction (SJ), the Au/Nd2O3/n-type GaN metal/interlayer/semiconductor (MIS) junctions were prepared and characterized. X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were employed to analyze the structural properties of the deposited Nd2O3 films on the n-GaN surface. Results confirmed that the Nd2O3 layer was formed on the n-GaN surface. The MIS junction electrical results are compared with the Au/n-GaN Schottky junction (SJ) results. Electrical outcomes demonstrated that the MIS junction revealed a good rectification behaviuor with a higher barrier height (BH) (0.66 eV) than the SJ (0.59 eV), which indicates the BH is manipulated by the Nd2O3 interlayer. The I–V, Cheung's, ΨS-V and α(V)–V plots were employed to derive BH and determined that values were similar to one another, demonstrating that the techniques used here are consistent and valid. The capacitance-frequency (C-f) and conductance-frequency (G-f) properties of SJ and MIS junction are assessed in the range of 1 kHz-1 MHz and results demonstrate that the capacitance and conductance are sturdily reliant on frequency. The estimated interface state density (NSS) of the MIS junction is less than the SJ which shows that the Nd2O3 interlayer was responsible to reduces the NSS. Results demonstrate that ohmic and space charge limited conduction mechanisms in the forward bias of the SJ and MIS junctions. Experimental outcomes established that the Schottky emission directs the reverse current in the SJ. Though, the Poole-Frenkel emission ruled reverse current in the lower bias, while the Schottky emission governs reverse current in the higher bias region of the MIS junction. Findings demonstrate that the Nd2O3 layer could be appropriate for the development of MIS/MOS devices.

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.

Effects of oxygen contents on the physical properties of MgO films and carrier transport of Au/MgO/ZnO MIS diodes

MgO films with various oxygen contents were deposited on ZnO using radio-frequency magnetron sputtering, and Au/MgO/ZnO metal-insulator-semiconductor (MIS) diodes were fabricated. The effects of various oxygen contents on the physical properties of MgO and the carrier transport in MIS diodes were studied. The crystallinity of MgO films improved with increased oxygen content up to 66%; however, the crystallinity degraded upon further increase of oxygen content up to 100%. X-ray photoelectron spectroscopy showed that the oxygen vacancies were compensated by the introduced oxygen atoms; however, the excess oxygen atoms could not fill the lattice sites and were instead absorbed on the MgO surface. The optical bandgaps of MgO films increased from 5.16 to 5.22 eV for 0 and 100% oxygen content, respectively, resulted by the suppressed oxygen vacancies. The average roughness of MgO films increased from 4.02 to 6.86 nm for 0 and 100% oxygen content, respectively. As compared to MIS diodes without oxygen content, the leakage current was reduced by approximately 300 times in MIS diodes with 66% oxygen content. At a high bias voltage (V ≥ 0.4V), MIS diodes without oxygen exhibited ohmic conduction. In contrast, MIS diodes with oxygen exhibited Fowler-Nordheim tunnelling at high bias voltages. With increasing oxygen content, the tunnelling barrier height increased to its maximum of 0.46 eV in MIS diodes with 66% oxygen content. Nevertheless, the barrier height reduced to 0.29 eV for the excess oxygen content up to 100%. However, at low-bias voltages, all MIS diodes demonstrated a direct tunnelling mechanism owing to their rectangular barriers.

Effect of annealing upon bipolar resistive switching in amorphous barium titanate (am-BTO) in Ag/am-BTO/ITO capacitor structure

The influence of annealing upon the resistive switching nature of amorphous barium titanate (am-BTO) is systematically investigated. The am-BTO thin film is fabricated on top of ITO coated glass substrate using RF-DC sputtering systems in the form of Ag/am-BTO/ITO dot point geometry. The room temperature electrical characterization shows the bipolar resistive switching characteristics. The resistive switching behaviour is diminished by increasing the temperature from RT to 600 °C. The conduction mechanism analysis is also been carried out. The ohmic and space change limited conduction mechanisms are dominated in lower and higher resistance regions respectively. The schematic representation of the proposed conduction mechanism is also drawn. The restricted movement of silver cations due to the local crystallization of BTO is presumed to be the reason for the observed reduction in switching behaviour.

A spectral boundary integral method for simulating electrohydrodynamic flows in viscous drops

A weakly conducting liquid droplet immersed in another leaky dielectric liquid can exhibit rich dynamical behaviors under the effect of an applied electric field. Depending on material properties and field strength, the nonlinear coupling of interfacial charge transport and fluid flow can trigger electrohydrodynamic instabilities that lead to shape deformations and complex dynamics. We present a spectral boundary integral method to simulate droplet electrohydrodynamics in a uniform electric field. All physical variables, such as drop shape and interfacial charge density, are represented using spherical harmonic expansions. In addition to its exponential accuracy, the spectral representation affords a nondissipative dealiasing method required for numerical stability. A comprehensive charge transport model, valid under a wide range of electric field strengths, accounts for charge relaxation, Ohmic conduction, and surface charge convection by the flow. A shape reparametrization technique enables the exploration of significant droplet deformation regimes. For low-viscosity drops, the convection by the flow drives steep interfacial charge gradients near the drop equator. This introduces numerical ringing artifacts that we treat via a weighted spherical harmonic expansion, resulting in solution convergence. The method and simulations are validated against experimental data and analytical predictions in the axisymmetric Taylor and Quincke electrorotation regimes.

Resistive switching characteristics and mechanism of W/TiO2/ITO devices

In recent years, titanium oxide (TiO2)-based memristors have come under widespread investigation due to their compatibility with CMOS technology and their potential use as the forthcoming nonvolatile memories. However, the practical application of these devices requires a detailed understanding of their switching mechanism. This study examined the resistive switching and conduction mechanism of titania films on an Indium tin oxide (ITO) substrate with tungsten (W) serving as the top electrode (TE). The thin film of TiO2 was fabricated by solution processing and spin coating technique. The sol was prepared using titanium tetra isopropoxide (TTIP) and ethanol. Optical characterization was done using UV–Visible transmission spectroscopy. From the tauc plot, the band gap of films treated at 250 °C and 400 °C was found to be 3.37 eV and 3.29 eV, respectively. From the electrical analysis, a pinched hysteresis current–voltage curve was obtained, and the device exhibits stable, reversible, forming-free, and interface type resistance-switching characteristics.The homogeneous switching observed in this device is caused by oxygen vacancy-induced barrier modulation at the metal-oxide interface. The I-V data were fitted to various conduction mechanismsand it was found that ohmic conduction and Schottky emission mechanism (SE) were dominant in the low and high field regions, respectively, for both HRS and LRS.

A Facile Hydrothermal Synthesis and Resistive Switching Behavior of α-Fe2O3 Nanowire Arrays.

A facile hydrothermal process has been developed to synthesize the α-Fe2O3 nanowire arrays with a preferential growth orientation along the [110] direction. The W/α-Fe2O3/FTO memory device with the nonvolatile resistive switching behavior has been achieved. The resistance ratio (RHRS/RLRS) of the W/α-Fe2O3/FTO memory device exceeds two orders of magnitude, which can be preserved for more than 103s without obvious decline. Furthermore, the carrier transport properties of the W/α-Fe2O3/FTO memory device are dominated by the Ohmic conduction mechanism in the low resistance state and trap-controlled space-charge-limited current conduction mechanism in the high resistance state, respectively. The partial formation and rupture of conducting nanofilaments modified by the intrinsic oxygen vacancies have been suggested to be responsible for the nonvolatile resistive switching behavior of the W/α-Fe2O3/FTO memory device. This work suggests that the as-prepared α-Fe2O3 nanowire-based W/α-Fe2O3/FTO memory device may be a potential candidate for applications in the next-generation nonvolatile memory devices.

Semiconductor-to-Insulator Transition in Inter-Electrode Bridge-like Ensembles of Anatase Nanoparticles under a Long-Term Action of the Direct Current.

The results of experimental studies of ohmic conductivity degradation in the ensembles of nanostructured anatase bridges under a long-term effect of direct current are presented. Stochastic sets of partially conducting inter-electrode bridges consisting of close-packed anatase nanoparticles were formed by means of the seeding particles from drying aqueous suspensions on the surfaces of silica substrates with interdigital platinum electrodes. Multiple-run experiments conducted at room temperature have shown that ohmic conductivity degradation in these systems is irreversible. It is presumably due to the accumulated capture of conduction electrons by deep traps in anatase nanoparticles. The scaling analysis of voltage drops across the samples at the final stage of degradation gives a critical exponent for ohmic conductivity as ≈1.597. This value satisfactorily agrees with the reported model data for percolation systems. At an early stage of degradation, the spectral density of conduction current fluctuations observed within the frequency range of 0.01-1 Hz decreases approximately as 1/ω, while near the percolation threshold, the decreasing trend changes to ≈1/ω2. This transition is interpreted in terms of the increasing contribution of blockages and subsequent avalanche-like breakdowns of part of the local conduction channels in the bridges into electron transport near the percolation threshold.

Resistive switching performance and synaptic behavior of La-doped HfO2 thin film

Resistive random-access memory has great application prospects in developing nonvolatile memory and artificial synapse devices. In this work, lanthanum (La) doped hafnium dioxide (HfO2) (La: HfO2) thin film is fabricated by sol-gel deposition. Using gold (Au) and lanthanum nickelate (LaNiO3) as electrodes, the resistive switching performance and synaptic behavior of memristor based on La: HfO2 thin films with different doping concentrations as resistive switching layers are investigated. Current-voltage characteristics show that La-doped devices all exhibit bipolar resistive switching performance. When La doping concentration is 10%, the device shows reliable switching ratio (∼103) under 110 consecutive cycles. And the conduction mechanism of the device in high resistance state and low resistance state is analyzed by ohmic conduction and space charge limited conduction. In addition, the analog resistive switching can be obtained by increasing the voltage scanning and the result reveals that the device can be used to mimic the potentiation and depression behavior of biological synapses. Au/10% La: HfO2/LaNiO3/Si memristor effectively simulates the synaptic properties, such as long-term potentiation/depression, short-term potentiation/depression, paired-pulse facilitation and spike-time-dependent-plasticity learning rule. Furthermore, the information is classified and processed in an 8×8 pixel array. These findings will open up a unique way for the future development of nonvolatile memory and neural morphology computation.

Correlation Between Reverse Leakage Current and Electric Field Spreading in GaN Vertical SBD With High-Energy Ion Implanted Guard Rings

This work focuses on the bias-dependent reverse leakage current and carrier depletion process of vertical gallium nitride (GaN)-on-GaN Schottky barrier diodes (SBDs) with fluorine ion-implanted guard rings (GRs). The reverse leakage characteristics in the vertical GaN SBD with GRs sequentially go through ohmic conduction, thermionic field emission (TFE), and space charge limited conduction (SCLC) model as the reverse bias increases gradually. Once the traps in the implanted termination region are fully ionized, the device will undergo large leakage current at high biases. Compared with infinite area ion implanted edge termination (ET), ion-implanted GR can effectively reduce the leakage current at low biases. In addition, there are kinks in the reverse current–voltage curves, which proved to be related to the electric field spreading effect of individual GR. Based on the analysis of reverse leakage current, the electric field modulation mechanism of ion-implanted GRs is reviewed.

The Effect of Nitrogen Annealing on the Resistive Switching Characteristics of the W/TiO2/FTO Memory Device

In this paper, the effect of nitrogen annealing on the resistive switching characteristics of the rutile TiO2 nanowire-based W/TiO2/FTO memory device is analyzed. The W/TiO2/FTO memory device exhibits a nonvolatile bipolar resistive switching behavior with a high resistance ratio (RHRS/RLRS) of about two orders of magnitude. The conduction behaviors of the W/TiO2/FTO memory device are attributed to the Ohmic conduction mechanism and the Schottky emission in the low resistance state and the high resistance state, respectively. Furthermore, the RHRS/RLRS of the W/TiO2/FTO memory device is obviously increased from about two orders of magnitude to three orders of magnitude after the rapid nitrogen annealing treatment. In addition, the change in the W/TiO2 Schottky barrier depletion layer thickness and barrier height modified by the oxygen vacancies at the W/TiO2 interface is suggested to be responsible for the resistive switching characteristics of the W/TiO2/FTO memory device. This work demonstrates the potential applications of the rutile TiO2 nanowire-based W/TiO2/FTO memory device for high-density data storage in nonvolatile memory devices.

Electrical charge transport properties of caesium tin chloride perovskite microrods: An analysis of microstructure conductivity and charge trapping

This study presents the electrical charge transport properties of caesium tin chloride (CsSnCl3) perovskite microrods. The as-synthesized microstructure rods were characterized using XRD, FESEM, EDS, and elemental mapping. The current–voltage (I-V) characteristics of microstructures were recorded. The I-V analysis demonstrates that as the side length of a microrod varies from 356 µm to 136 µm, the conductivity, barrier height, and ideality factor changes from 3.08 × 10−4 to 1.32 × 10−4 S/m, 0.84 eV to 0.78 eV, and 2.09 to 2.86, respectively. The charge transport investigation revealed that the sample exhibited ohmic conduction at a lower voltage and trap charge-limited conduction (TCL) after a transition voltage. The discrete trap charge concentration was found to be in the order of 1014 /m3 in the TCL region. The excellent conductivity of microstructure rods and the low trap charge concentration suggest that microrods have the potential for use in optoelectronic device applications.

Resistive switching behavior in ZnO:Ca thin films deposited by a pulsed laser deposition technique

Calcium-doped ZnO (CZO) nanopowders were synthesized using the sol–gel method. The structural characteristics were investigated by X-ray diffraction (XRD) and the analysis reveals that our samples are crystalized in a wurtzite hexagonal structure. The morphological properties and the chemical composition of the nanoparticles were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The obtained powders are stoichiometric with crystallites in a nanometric scale aggregated in micrometric particles. Then, pulsed laser deposition (PLD) technique was used to grow Ca-doped ZnO thin films with different doping concentrations (1, 3, and 5%), on p-type Si substrates. The Ca doping effect on the electrical properties of the CZO films was investigated by current–voltage characteristics. A resistive switching (RS) effect was observed in the ITO/ZnO:Ca/Au structures. The RS behavior is dependent on the Ca doping concentration. The charge transport mechanisms of the devices were studied. In the positive bias voltage region, the transport is dominated by Ohmic and space-charge limited conduction mechanisms under low and high electric fields, respectively.

Elucidating the Conducting Mechanisms in a Flexible Piezoresistive Pressure Sensor Using Reduced Graphene Oxide Film in Silicone Elastomer

Sensors as a composite film made from reduced graphene oxide (rGO) structures filled with a silicone elastomer are soft and flexible, making them suitable for wearable applications. The sensors exhibit three distinct conducting regions, denoting different conducting mechanisms when pressure is applied. This article aims to elucidate the conduction mechanisms in these sensors made from this composite film. It was deduced that the conducting mechanisms are dominated by Schottky/thermionic emission and Ohmic conduction.

Multilevel resistive switching with negative differential resistance in Al/NiO/ZnFe2O4/ITO ReRAM device

The Resistive Random Access Memory devices have emerged as an energy-efficient alternative to Von Neumann computers by enabling in-memory computing. Here we demonstrate bipolar resistive switching in thin films of Nickel oxide (NiO) and Zinc Ferrite (ZFO) using a simple Al/NiO/ZFO/ITO configuration, making them a possible candidate for the next generation memory devices. The fabricated device demonstrated excellent resistive switching behavior with high endurance for up to 1000 cycles, good retention for more than 104 s, and a good resistance ratio of HRS to LRS ∼102. Ohmic conduction was observed in the LRS, while in the HRS, along with ohmic conduction, space charge limited current (SCLC) and Schottky mechanisms were observed. Besides the LRS and HRS, a number of stable intermediate resistance states can also be obtained during the RESET process using different stop voltages, which makes the current device a multilevel resistive switching device.

Enhanced resistive switching performance of spinel MnCo2O4 resistive random access memory devices: Effects of annealing temperatures and annealing atmospheres

The spinel MnCo2O4 (MCO) thin films were fabricated on Pt/Ti/SiO2/Si substrates for resistive memories via sol-gel spin-coating deposition method under different annealing temperatures and annealing atmospheres. The 650oC-annealing Pt/MCO/Pt device shows better bipolar resistance switching parameters than the devices annealed at 600 °C and 700 °C. The nitrogen-annealing Pt/MCO/Pt device exhibits optimum resistance switching parameters due to increasing of the oxygen-vacancies proportion, formation of confined and stable conductive filaments, and suppressing of the randomness of oxygen vacancies. The carrier transportation mechanisms of the devices with numerous oxygen-vacancies content in low resistance state (LRS) and high resistance state (HRS) are dominated by Ohmic conduction and Schottky emission, respectively. For the devices with fewer oxygen-vacancies content, the conduction mechanisms at LRS and HRS can be described by nearest-neighboring hopping conduction and space-charge-limited current model, respectively. This work indicates that the spinel MCO films have good potential application in resistive random access memory.