Reverse Voltage Sweeps Research Articles

Prediction of Device Characteristics of Feedback Field-Effect Transistors Using TCAD-Augmented Machine Learning

In this study, the device characteristics of silicon nanowire feedback field-effect transistors were predicted using technology computer-aided design (TCAD)-augmented machine learning (TCAD-ML). The full current-voltage (I-V) curves in forward and reverse voltage sweeps were predicted well, with high R-squared values of 0.9938 and 0.9953, respectively, by using random forest regression. Moreover, the TCAD-ML model provided high prediction accuracy not only for the full I-V curves but also for the important device features, such as the latch-up and latch-down voltages, saturation drain current, and memory window. Therefore, this study demonstrated that the TCAD-ML model can substantially reduce the computational time for device development compared with conventional simulation methods.

Self-rectifying threshold resistive switching based non-volatile memory of CBD/CBD grown vertical n-ZnO nanowire/p-Si heterojunction diodes

Vertically oriented ZnO nanowires are grown on p-Si substrate by employing two-step sequential chemical bath deposition technique. The ZnO nanowire exhibits n-type doping due to the presence of oxygen vacancies. The electrical characterizations of n-ZnO NWs/p-Si heterojunction diodes exhibit a self-rectifying, threshold resistive switching behavior. Such switching behavior is explained by oxygen vacancy assisted conducting filament formation mechanism. The relevant charge transport is governed by TC-SCLC and multistep recombination-tunneling processes through the interface traps. Threshold-voltage for resistive switching is observed to be increasing with increasing bias sweep rate. The device shows superior memory endurance for forward and reverse voltage sweep of 50 cycles in fast sweep mode. The ratio of HRS to LRS resistances shows one order of difference. The retention time of such resistive switching memory is recorded to be 4000 seconds, suggesting its non-volatile functionality. Thus, the n-ZnO NWs/p-Si heterojunction can be employed for fabricating promising non-volatile memory devices with excellent endurance and retentions. Copyright © 2018 VBRI Press.

Modelling the switching effect in graphene oxide-based memristors

The two-dimensionality of insulating graphene oxide sheets is attractive for use in nanoscale two-terminal devices. These structures are promising for the next generation of non-volatile resistive random access memories, with high speed, low-power consumption and excellent scalability. In this work, the transport properties of graphene oxide-based metal-insulator-metal structures are addressed. The graphene oxide was synthesized using an eco-friendly modified Hummers method. The obtained graphene oxide sheets, placed between two electrodes, were subjected to an electrical characterization measuring cycling current–voltage (I–V) curves by applying successive forward and reverse voltage sweeps. When the absolute value of the measured current is plotted in logarithmic scale versus the applied voltage, the typical butterfly-shaped curves are observed, which are better interpreted in terms of their first derivative, or differential conductivity, in order to understand the transport mechanism. The experimental I–V curves can be explained in two different ways: by modifying well-known transport models or by using typical flux-controlled memristor models. The connection between both strategies is established in this work. The analytical expressions used for the differential conductance for the low resistance state and the high resistance state lead to simple expressions for the I–V curves. The symmetry of the curves after several cycles is lost when compared to those measured on pristine devices, which might indicate the occurrence of filament forming effect, affecting the bipolar switching.

Enhanced thermally aided memory performance using few-layer ReS2 transistors

Thermally varying hysteretic gate operation in few-layer ReS2 and MoS2 back gate field effect transistors (FETs) is studied and compared for memory applications. Clockwise hysteresis at room temperature and anti-clockwise hysteresis at higher temperature (373 K for ReS2 and 400 K for MoS2) are accompanied by step-like jumps in transfer curves for both forward and reverse voltage sweeps. Hence, a step-like conductance (STC) crossover hysteresis between the transfer curves for the two sweeps is observed at high temperature. Furthermore, memory parameters such as the RESET-to-WRITE window and READ window are defined and compared for clockwise hysteresis at low temperature and STC-type hysteresis at high temperature, showing better memory performance for ReS2 FETs as compared to MoS2 FETs. Smaller operating temperature and voltage along with larger READ and RESET-to-WRITE windows make ReS2 FETs a better choice for thermally aided memory applications. Finally, temperature dependent Kelvin probe force microscopy measurements show decreasing (constant) surface potential with increasing temperature for ReS2 (MoS2). This indicates less effective intrinsic trapping at high temperature in ReS2, leading to earlier occurrence of STC-type hysteresis in ReS2 FETs as compared to MoS2 FETs with increasing temperature.

Ligand memory effect in purple quantum dot LEDs

We report a ligand-dependent, trap state memory effect in a purple quantum dot light emitting diode. The measured, bistable current-voltage characteristics show a high conductance state and a low conductance state. Thereby, a memory window with an ON state and an OFF state is achieved, which can be reversed by applying a negative bias. The height of the memory window depends strongly on the length of the ligand passivating the quantum dot (QD). Together with a 5 nm thick aluminum film under the hole transport layer, charges accumulate at the charge transport/quantum dot ligand interface, leading to an increase in conductance during the forward voltage sweep. During a reverse voltage sweep, previously injected charge carriers recombine until the active layer is free of charge carriers. Voltage-capacitance measurements confirm the changes in the charge carrier population within the active layer and demonstrate that they depend on both the direction of the bias sweep and ligands surrounding the QD.

Features of Tunneling Current in Superlattices with Electrical Domains

Abstract—The tunneling electron transport in GaAs/AlAs and InAs/AlSb superlattices with electric domains at room temperature is studied. At voltages above the threshold for the formation of domains, a series of maxima on the current–voltage characteristics, almost equidistant in voltage, and current hysteresis during direct and reverse voltage sweeps were found. An explanation is proposed relating the origin of these maxima to tunnel transitions between quantum wells in a triangular domain, assisted by the emission of optical phonons, and hysteresis with a transition between modes with a moving and static domain. The large asymmetry of the transition times between domain modes was found.

Resistive Switching in Reduced Graphene Oxide Incorporated Polyvinyl Alcohol Films

Reduced graphene oxide (rGO) nanoparticle incorporated thin films of polyvinyl alcohol (PVA) were spin coated on ITO coated glass substrates. I-V characteristics revealed resistive switching in these films. The ON/OFF switching ratio values varied with voltage sweep cycles. The largest switching ratios obtained were 8 orders between the high resistance state (HRS) to low resistance state (LRS) and 7 orders for the LRS to HRS. In the LRS, the electrical conduction was initially space charge limited which turned to ohmic behavior that persisted till switching occurred to HRS. In the reverse voltage sweep, the conduction in HRS was initially ohmic, which then turned into a hopping type of conduction which persisted till switching occurred to the LRS. These conduction mechanisms in LRS and HRS are qualitatively different from that of pure rGO and other PVA composite films investigated earlier.

The smooth transition from field emission to a self-sustained plasma in microscale electrode gaps at atmospheric pressure

We report on the existence of a smooth transition from field emission to a self-sustained plasma in microscale electrode geometries at atmospheric pressure. This behavior, which is not found at macroscopic scales or low pressures, arises from the unique combination of large electric fields that are created in microscale dimensions to produce field-emitted electrons and the high pressures that lead to collisional ionization of the gas. Using a tip-to-plane electrode geometry, currents less than 10 μA are measured at onset voltages of ∼200 V for gaps less than 5 μm, and analysis of the current–voltage (I-V) relationship is found to follow Fowler–Nordheim behavior, confirming field emission. As the applied voltage is increased, gas breakdown occurs smoothly, initially resulting in the formation of a weak, partial-like glow and then a self-sustained glow discharge. Remarkably, this transition is essentially reversible, as no significant hysteresis is observed during forward and reverse voltage sweeps. In contrast, at larger electrode gaps, no field emission current is measured and gas breakdown occurs abruptly at higher voltages of ∼400 V, absent of any smooth transition from the pre-breakdown condition and is characterized only by glow discharge formation.

Cellulose-Derivative-Based Gate Dielectric for High-Performance Organic Complementary Inverters.

been realized using organic thin-fi lm transistors (OTFTs) as the essential element. In the majority of these applications OTFTs are integrated either in the form of arrays or as digital logic. The fundamental building block of digital logic is the inverter, a circuit that inverts an input signal. Much work has been devoted in the last fi ve years to design unipolar inverters using p-typeonly OTFTs. [ 18‐23 ] Unfortunately, unipolar logic based on single gate OTFTs always suffers from high power consumption and low noise margin coupled with high noise margin variability and therefore impedes the fabrication of complex circuits having hundreds or more logic gates. [ 19,22,23 ] In this context, it stands

Electron transport processes in on/off states of a single alkyl-tailed metal complex molecular switch

Voltammograms and current–voltage (I–V) characteristics are measured to elucidate electron transport processes in the bistable conducting states of single molecular junctions of a molecular switch, alkyl-tailed RuII terpyridine complexes. (1) On the basis of the Ru-centered electrochemical reaction data, the electron transport rate increases in the mixed self-assembled monolayer (SAM) of RuII terpyridine complexes, indicating strong electronic coupling between the redox center and the substrate, along the molecules. (2) In a low-conducting state before switch-on, I–V characteristics are fitted to a direct tunneling model, and the estimated tunneling decay constant across the RuII terpyridine complex is found to be smaller than that of alkanethiol. (3) The threshold voltages for the switch-on from low- to high-conducting states are identical, corresponding to the electron affinity of the molecules. (4) A high-conducting state after switch-on remains in the reverse voltage sweep, and a linear relationship of the current to the voltage is obtained. These results reveal electron transport paths via the redox centers of the alkyl-tailed RuII terpyridine complexes, a molecular switch.

Investigation of the hysteresis phenomenon of an a‐Si:H TFT at an elevated temperature for AMOLED displays

Abstract— The temperature dependence of the hysteresis of an a‐Si:H TFT has been investigated. An a‐Si:H TFT pixel driving scheme has been proposed and investigated. This scheme can eliminate changes in the organic light‐emitting diode (OLED) current caused by hysteresis of an a‐Si:H TFT. The VTH of the a‐Si:H TFT was changed according to the gate‐voltage sweep direction because of the hysteresis of the a‐Si:H TFT. The variation of VTH for a a‐Si:H TFT decreased from 0.41 to 0.17 V at an elevated temperature of 60°C because the sub‐threshold slope (s‐slope) of the a‐Si:H TFT, in the reverse voltage sweep direction, increased more than in the forward voltage sweep direction due to a greater increase in the initial electron trapped charges than the hole charges. Although the OLED current variation caused by hysteresis decreased (∼14%) as the temperature increased, the error in the OLED current needed to be improved in order to drive the pixel circuit of AMOLED displays. The proposed pixel circuit can apply the reset voltage (−10 V) before the data voltage for the present frame that was written to fix the sweep direction of the data voltage. The variation in the OLED current caused by hysteresis of the a‐Si:H TFT was eliminated by the fixed voltage sweep direction in the proposed pixel circuit regardless of operating temperature.

Non-equilibrium response of MOS devices to a linear voltage ramp—I. Bulk discrete traps

A study is presented of MOS devices containing discrete bulk traps, subjected to a triangular voltage waveform, such that the rate of change of voltage is sufficiently high to take the device into the non-equilibrium mode of operation. Consequently, the dynamics of the system response are related to the parameters of the traps involved in the generation and recombination processes occurring within the device. The technique is in contrast with Kuhn's method in which the device, and hence the various generation and recombination processes, are always in quasi-equilibrium. Analytical parametric equations relating the current, and hence the small-signal capacitance and the gate voltage to the width of the depletion region, are obtained. From these equations current and small-signal capacitance vs gate voltage plots are obtained as a function of sweep rate and temperature, for both forward and reverse voltage sweeps. These plots are rich in structure, and physical discussion relating to the salient features of these plots is presented. Suggestions are made of how various device parameters such as generation rate and life-time, trap density, and capture cross-section, can be extracted from the theory.