Channel Region Research Articles

3D particle-in-cell study of the electron drift instability in a Hall Thruster using unstructured grids

In a Hall Thruster, the E×B current generates a strong electron drift with respect to the ions, which can trigger plasma instabilities, such as the electron drift instability (EDI), also called the electron cyclotron drift instability. The EDI has drawn a great deal of attention in the E×B community as previous one- and two-dimensional Particle-In-Cell (PIC) studies suggest it plays a major role in the anomalous transport of electrons across the magnetic barrier. However, experiments showed that the EDI has an inherent three-dimensional nature, which cannot be accurately described in a 1D or 2D configuration. Unfortunately, due to their prohibitive computational cost, needed 3D PIC simulations remained inaccessible without scaling plasma parameters, which inevitably modified the physics in a Hall Thruster. Thanks to recent computational developments, this paper presents a 3D fully kinetic investigation of the EDI in a typical Hall Thruster channel and near plume region. The study was conducted using an unstructured grid, thus demonstrating the feasibility to model more complicated geometries in the future. The growth and development of the EDI are described along with other plasma fluctuations, possibly the signature of another plasma instability, the modified-two-stream-instability. 3D effects on the anomalous transport are also assessed and found to be lower than in an analogous 2D simulation. This is due to lower losses in 2D, which lead to the saturation of the EDI occurring at higher energy levels.

Strained topological insulator spin field effect transistor

The notion of a spin field effect transistor, where transistor action is realized by manipulating the spin degree of freedom of charge carriers instead of the charge degree of freedom, has captivated researchers for at least three decades. These transistors are typically implemented by modulating the spin orbit interaction in the transistor’s channel with a gate voltage, which causes gate-controlled spin precession of the current carriers, and that modulates the channel current flowing between the ferromagnetic source and drain contacts to implement transistor action. Here, we introduce a new concept for a spin field effect transistor which does not exploit spin-orbit interaction. Its channel is made of the conducting surface of a strained three dimensional topological insulator (3D-TI) thin film and the transistor function is elicited by straining the channel region with a gate voltage (using a piezoelectric under-layer) to modify the energy dispersion relation, or the Dirac velocity, of the TI surface states. This rotates the spins of the carriers in the channel and that modulates the current flowing between the ferromagnetic source and drain contacts to realize transistor action. We call it a strained-topological-insulator-spin-field-effect-transistor, or STI-SPINFET. Its conductance on/off ratio is too poor to make it useful as a switch, but it may have other uses, such as an extremely energy-efficient stand-alone single-transistor frequency multiplier.

Heterogeneous Structure Omnidirectional Strain Sensor Arrays With CognitivelyLearned Neural Networks.

Mechanically stretchable strain sensors gain tremendous attention for bioinspired skin sensation systems and artificially intelligent tactile sensors. However, high-accuracy detection of both strain intensity and direction with simple device/array structures is still insufficient. To overcome this limitation, an omnidirectional strain perception platform utilizing a stretchable strain sensor array with triangular-sensor-assembly (three sensors tilted by 45°) coupled with machine learning (ML) -based neural network classification algorithm, is proposed. The strain sensor, which is constructed with strain-insensitive electrode regions and strain-sensitive channel region, can minimize the undesirable electrical intrusion from the electrodes by strain, leading to a heterogeneous surface structure for more reliable strain sensing characteristics. The strain sensor exhibits decent sensitivity with gauge factor (GF) of ≈8, a moderate sensing range (≈0-35%), and relatively good reliability (3000 stretching cycles). More importantly, by employing a multiclass-multioutput behavior-learned cognition algorithm, the stretchable sensor array with triangular-sensor-assembly exhibits highly accurate recognition of both direction and intensity of an arbitrary strain by interpretating the correlated signals from the three-unit sensors. The omnidirectional strain perception platform with itsneural network algorithm exhibits overall strain intensity and direction accuracy around 98% ± 2% over a strain range of ≈0-30% in various surface stimuli environments.

Shannon meets Stackelberg on the cognitive interference channel part I: A deterministic view

AbstractIn this paper, we have combined a game‐theoretic and an information‐theoretic notions to describe the selfish behavior of each user in a two‐user linear deterministic cognitive interference channel (LD‐CIC). The two‐user LD‐CIC is the simple case of the cognitive radio technology in the high SNR regime. This model is a solution to improve the spectral efficiency in software defined network (SDN) concept in 5G. In the two‐user LD‐CIC, the information bits of the primary/licensed transmitter is a‐priori provided at the cognitive/secondary/unlicensed transmitter. So that, the cognitive transmitter can cooperate and utilize the frequency spectrum to send the information bits of the both transmitters. In information‐theoretic approaches, full cooperation is assumed between transmitters for codebook and rate selection in this channel. This may not be a realistic assumption if transmitters are selfish and are willing to maximize their own benefit. In particular, we have defined the Stackelberg equilibrium (SE) region on the capacity region of the two‐user LD‐CIC to capture the behavior of each transmitter when they compete even though one of them is informed of the other transmitter information bits. We have implemented a two‐phase Stackelberg game with the primary and cognitive transmitters acting as the leader in the first phase, and the follower in the second phase, respectively. In this implementation, both transmitters are assumed to be selfish and only interested in optimizing their own pay‐offs. The SE region is characterized as a subset of capacity region in which the transmitters cannot gain more transmission rate by individually deviating from the SE strategy. The achievability of the resultant region has been configured using a randomized Han‐Kobayashi scheme for all the channel gains. Also, we have compared the obtained SE region with the previous equilibrium regions such as Nash equilibrium (NE) region of the linear deterministic interference channel (LD‐IC). The results have shown that the SE points on the sum‐rate of the LD‐CIC capacity region are more than the NE points on the sum rate of the capacity region of LD‐IC, so the SE region of the LD‐CIC is Pareto superior to the NE region of LD‐IC.

Analytical and Physical Investigation on Source Resistance in InxGa1−xAs Quantum-Well High-Electron-Mobility Transistors

We present a fully analytical model and physical investigation on the source resistance (RS) in InxGa1-xAs quantum-well high-electron mobility transistors based on a three-layer TLM system. The RS model in this work was derived by solving the coupled quadratic differential equations for each current component with appropriate boundary conditions, requiring only six physical and geometrical parameters, including ohmic contact resistivity (ρc), barrier tunneling resistivity (ρbarrier), sheet resistances of the cap and channel regions (Rsh_cap and Rsh_ch), side-recessed length (Lside) and gate-to-source length (Lgs). To extract each model parameter, we fabricated two different TLM structures, such as cap-TLM and recessed-TLM. The developed RS model in this work was in excellent agreement with the RS values measured from the two TLM devices and previously reported short-Lg HEMT devices. The findings in this work revealed that barrier tunneling resistivity already played a critical role in reducing the value of RS in state-of-the-art HEMTs. Unless the barrier tunneling resistivity is reduced considerably, innovative engineering on the ohmic contact characteristics and gate-to-source spacing would only marginally improve the device performance.

Determining local transport properties of gas diffusion layer land-channel regions via pore network modelling

Targeted, pre-determined values of spatially-resolved liquid water saturation is achieved in the pore networks of polymer electrolyte membrane (PEM) fuel cell gas diffusion layers (GDL). An inlet selection algorithm is presented, where the local saturation of the overall substrate, channel region, and land region match the prescribed input values (within a tolerance of 2% absolute error). With this algorithm, we conduct a novel, comprehensive characterization of the influence of local saturation on local oxygen transport properties using 1721 unique saturation conditions within the GDL. The oxygen transport properties of the GDL are significantly affected by the spatial distribution of liquid water. We find that liquid water accumulation in the channel region leads to an increase in the oxygen transport resistance in the channel region of the substrate and overall substrate. The channel region saturation is a better predictor of substrate transport properties than the substrate saturation alone. The correlation between the land region saturation and the oxygen transport resistance of the substrate is weak and depends on the spatial distribution of liquid water in the land region. Land region saturation only has a strong influence on the oxygen transport resistance in the land region of the substrate.

Cytosolic domain regulates the calcium sensitivity and surface expression of BEST1 channels in the HEK293 cells

BEST family is a class of Ca2+-activated Cl- channels evolutionary well conserved from bacteria to human. The human BEST paralogs (BEST1-BEST4) share significant amino acid sequence homology in the N-terminal region, which forms the transmembrane helicases and contains the direct calcium-binding site, Ca2+-clasp. But the cytosolic C-terminal region is less conserved in the paralogs. Interestingly, this domain-specific sequence conservation is also found in the BEST1 orthologs. However, the functional role of the C-terminal region in the BEST channels is still poorly understood. Thus, we aimed to understand the functional role of the C-terminal region in the human and mouse BEST1 channels by using electrophysiological recordings. We found that the calcium-dependent activation of BEST1 channels can be modulated by the C-terminal region. The C-terminal deletion hBEST1 reduced the Ca2+-dependent current activation and the hBEST1-mBEST1 chimera showed a significantly reduced calcium sensitivity to hBEST1 in the HEK293 cells. And the C-terminal domain could regulate cellular expression and plasma membrane targeting of BEST1 channels. Our results can provide a basis for understanding the C-terminal roles in the structure-function of BEST family proteins. [BMB Reports 2023; 56(3): 172-177].

Investigation of Source/Drain Recess Engineering and Its Impacts on FinFET and GAA Nanosheet FET at 5 nm Node

Impacts of source/drain (S/D) recess engineering on the device performance of both the gate-all-around (GAA) nanosheet (NS) field-effect transistor (FET) and FinFET have been comprehensively studied at 5 nm node technology. TCAD simulation results show that the device off-leakage, including subthreshold leakage through the channel (Isub) and punch-through leakage (IPT) in the sub-channel, is strongly related to the S/D recess process. Firstly, device electrical characteristics such as current density distributions, On/Off-state current (Ion, Ioff), subthreshold swing (SS), RC delay, and gate capacitance (Cgg) are investigated quantitatively for DC/AC performance evaluation and comparison according to S/D lateral recess depth (Lrcs) variations. For both device types, larger Lrcs will result in a shorter effective channel length (Leff), so that the Ion and Ioff simultaneously increase. At the constant Ioff, the Lrcs can be optimized to enhance the device’s drivability by ~3% and improve the device’s RC delay by ~1.5% due to a larger Cgg as a penalty. Secondly, S/D over recess depth (Hrcs) in the vertical direction severely affects the punch-through leakage in the Sub-Fin or bottom parasitic channel region. The NSFET exhibits less Ioff sensitivity provided that it can be well controlled under 12 nm since the bottom parasitic channel is still gated. Furthermore, with both Hrcs and Lrcs accounted for in the device fabrication, the NSFET still shows better control of the off-leakage in the intrinsic and bottom parasitic channel regions and ~37% leakage reduction compared with FinFETs, which would be critical to enable further scaling and the low standby power application. Finally, the S/D recess engineering strategy has been given: a certain lateral recess could be optimized to obtain the best drive current and RC delay, while the vertical over-recess should be in tight management to keep the static power dissipation as low as possible.

Boron Nitride-Graphene (BN-G) Bilayer as a Channel of Graphene Based Field Effect Transistor

According to the effect of the interlayer interaction of the boron nitride sheet on electronic properties, especially the energy band gap of the graphene sheet in the boron nitride-graphene (BN-G) bilayer, we propose a gapless graphene-based field effect transistor (FET). It is comprised of a boron nitride layer on top of graphene in the channel region. In this study, we investigate the transfer characteristic and output characteristic of the proposed device for different values of the interlayer distance of (BN-G) bilayer. Also, we compare the output results with simulated bilayer graphene channel FET. We find that the Ion/Ioff ratio in the proposed device shows a significant promotion compared to graphene bilayer channel FET. Our first-principles calculations show that by decreasing the inter-layer distance of (BN-G) bilayer, the energy gap increase which leads to a dipper Ioff current and an increase of Ion/Ioff ratio up to 104 for an inter-layer distance of 2.7 angstroms. Moreover, it is found that the proposed device output characteristic displays a very good saturation due to improved pinch-off of the channel.

Performance Analysis of Gate Engineered High-K Gate Oxide Stack SOI Fin-FET for 5 nm Technology

Abstract: This paper analyses the performance of 5 nm gate length gate engineered oxide stack silicon on insulator (SOI) fin field-effect transistor (OS-Fin-FET) for the first time. The high dielectric (High-K) value of the material-based gate oxide stack structure increases both the analog and the radio frequency (RF) performance of the Fin-FET device when compared to standard single gate oxide material structures. The work function of the engineered gate structure further helps in advancing the performance of the device in terms of on current (Ion), off current (Ioff) and the ratio of Ion/Ioff. The proposed OS-FinFET device improves on current (Ion) of the device by 12% in comparison to the high-K dielectric gate oxidebased FinFET device. Simulation of the device is further extended to study different electrical characteristics of the proposed device under other biasing conditions, to estimate enhanced analog and RF performance where the device is highly suitable for low power and high-speed applications. Overall, the proposed device shows improvement in existing architectures of the devices. Technology computer-aided design (TCAD) tool is used to perform entire simulations of the proposed device with 5 nm gate length. Aim: To enhance analog and RF performance of the Fin-FET device at 5 nm gate length. Background: Design of the sub-10 nm Fin-FET device undergoes charge shearing phenomena because of the minimum distance between source and drain. This problem is addressed by using High-K spacer over substrate but it leads to increase in the channel resistance and adverse short channel effects. A combination of different high-K dielectric materials can eliminate this performance. Hence most of the studies concentrated on spacer region and failed to consider channel region. This study tries to improve analog performance of the device using the approach of gate engineering with gate stack approach. Objective: The main objective of this study is to increase on current (Ion) of the device by implementing gate engineering approach, by choosing dual work function-based gate with oxide stack approach. The High-K dielectric material-based gate oxide reduces leakage current, decreases off current which will increase the ratio of Ion/Ioff. Methods: The dual work function gate material is taken with gate oxide stack approach by considering different High-K dielectric materials like HfO2, TiO2 with thin SiO2 layer as the interactive layer. Simulation of the device is carried out using TCAD Tool and results are compared with existing literature, to validate the results. Results: The proposed architecture of the Fin-FET device delivers excellent results in terms of on current and subthreshold characteristics compared to existing literature. The proposed device gives high on current of 0.027 A and current ratio of 1.08X104. Conclusion: A complete comparative analysis is carried out with existing literature on the proposed device, where the proposed device resulted in high performance. The proposed device improves 12% compared to existing literature, which is highly suitable for low power applications.

Rotation and separation of chiral active particles in a ring-shaped channel.

Transport of chiral active particles is numerically investigated in a two-dimensional ring-shaped channel. The ring-shaped channel is transversal asymmetric and can induce the directed transport (rotation) of chiral active particles. For the particles with small chirality, they slide along the outer boundary of the channel. For the particles with large chirality, the particles move along some small local circular orbits and can also exhibit directed rotation. Moreover, the rotation effect can be strongly enhanced by modifying the inner boundary geometry. Based on the study of particle rotation, we further study the separation of active particles with different chiralities. It is found that the particles with different chiralities may be distributed in different regions of the ring-shaped channel. Interestingly, these particles can be completely separated by shifting the channel's inner boundary or adding a blocking plate in the channel. Our results may be useful for understanding relevant experimental phenomena and provide a scheme for the separation of binary mixtures.

A mutational and modeling study of a binding pocket for IKs activators between KCNQ1 and KCNE1.

The IKs current formed by the co-assembly of KCNQ1 and KCNE1 plays an important role in cardiac repolarization. Loss-of-function mutations in KCNQ1 and KCNE1 are linked to LQT syndrome. Mefenamic acid (Mef) an NSAID, and DIDS a stilbene, are known to enhance IKs currents. The present study explores in detail the role of previously identified K41-KCNE1 in Mef action as well as uncovering the KCNQ1/KCNE1 binding site(s) of Mef and DIDS. In silico experiments of drug docking on a model of IKs channel and molecular dynamic (MD) simulations were used to map critical KCNQ1 and KCNE1 residues, followed by site-directed mutagenesis and functional analysis using whole cell patch clamp. Docking procedures and MD simulations show that Mef and DIDS bind between extracellular KCNE1 residues, specifically to the subunits of the external S6 helix; neighbouring S1; and the pore turret of the opposing subunit. Mef transforms the slowly activating WT IKs current (4:4 EQ) into a current with an almost linear waveform, which causes a left shift in activation V1/2 and inhibits tail current decay at −40 mV. These effects are prevented by the K41C-KCNE1 mutation in a stoichiometric manner. MD simulations and mutagenesis scanning identified three critical residues for Mef binding: W323-KCNQ1; Y46-KCNE1; and K41-KCNE1 in which Mef effects are greatly diminished. The effect of DIDS on WT-EQ are less pronounced than Mef, and K41C-KCNE1 was unable to fully prevent effects of DIDS. Our results show that both activators bind in the same general channel region but depend on different critical residues. These findings provide insights into a common drug-induced binding site, suggesting that the chemical structure of either compound could serve as a starting point for the development of IKs agonists.

Volume relaxation of soda-lime silicate glasses below glass transition temperature

Structural relaxation is a widely known phenomenon that occurs in glassy systems, which still attracts strong industrial and research interest. Although the volume change associated with structural relaxation is well described by the Kohlrausch–Williams–Watts function, its origin, particularly from a glass structural viewpoint, is not clearly defined. To understand the behavior of structural relaxation, in this study, we performed volume relaxation evaluations, Raman spectroscopy assessments, and surface resistivity measurements before and after annealing at 50 K below the glass transition temperature Tg of soda-lime silicate glasses with the same Tg but different fragilities. The combined results indicated that the following changes in the glass structure occurred during the structural relaxation: (1) reorganization of the SiO2 network; (2) transfer of Na ions from the ion channel region into the SiO2 network region; and (3) segmentation of the ion channel region in the modified random network model.

Thermal Sensing Characteristics of Low-Voltage n-Channel Organic Field-Effect Transistors With Triple Layers of Naphthalenediimide-Containing Conjugated Polymer and Gate-Insulating Polymers

Organic field-effect transistors (OFETs) were fabricated with n-type naphthalenediimide-based conjugated polymer (N2200) as a channel layer and poly(methyl methacrylate) (PMMA)/poly(vinyl alcohol) (PVA) as a gate-insulating layer. The OFETs with the N2200/PMMA/PVA triple layers were operated with an n-channel mode at low voltages (≤5 V) and their electron mobility reached ca. 0.63 cm2/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}\cdot \text{s}$ </tex-math></inline-formula> at a drain voltage of 5 V. The drain current of OFETs was gradually increased as the temperature of channel region increased from 25 °C to 80 °C, whereas no shift in threshold voltage was measured upon the temperature variation. The relative thermal sensitivity of devices was almost linearly increased with the temperature, while a two-stage behavior by a border of ca. 35 °C was measured for specific thermal sensitivity. The present n-channel OFETs exhibited excellent thermal sensing performances upon repeated approaching/retracting tests using a heat source.

Structural basis of mammalian respiratory complex I inhibition by medicinal biguanides

The molecular mode of action of biguanides, including the drug metformin, which is widely used in the treatment of diabetes, is incompletely characterized. Here, we define the inhibitory drug-target interaction(s) of a model biguanide with mammalian respiratory complex I by combining cryo-electron microscopy and enzyme kinetics. We interpret these data to explain the selectivity of biguanide binding to different enzyme states. The primary inhibitory site is in an amphipathic region of the quinone-binding channel, and an additional binding site is in a pocket on the intermembrane-space side of the enzyme. An independent local chaotropic interaction, not previously described for any drug, displaces a portion of a key helix in the membrane domain. Our data provide a structural basis for biguanide action and enable the rational design of medicinal biguanides.

Visual Electrochemiluminescence Biosensor Chip Based on Distance Readout for Deoxynivalenol Detection

Visual electrochemiluminescence (ECL) biosensors do not need complex instruments or well-trained operators, which is regarded as an ideal choice for portable and low-cost detection. But traditional visual ECL biosensors are based on the change in ECL intensity, which is easily affected by environmental factors and signal acquisition processes. In this work, a visual ECL biosensor chip based on distance readout has been developed for the first time. The chip is composed of a square detection region and a visual channel region, which are modified with graphene oxide (GO) and gold nanoparticles (AuNPs)@Ti3C2 nanocomposites, respectively. Target molecules can release aptamers adsorbed on the GO surface of the detection region and further change the electrode potential of the visual channel region, which can determine the length of the long channel that generates visible ECL signals. The application of AuNPs@Ti3C2 nanocomposites can effectively enhance ECL intensity by six times. Through the unique design of the sensor chip, quantification detection can be achieved based on the length change instead of the traditional intensity change. This visual ECL sensor is successfully applied for deoxynivalenol toxin detection in actual samples, demonstrating that the introduction of the distance readout strategy into ECL sensing has a good prospect in on-site testing.

High performance nanoscale SOI MOSFET with enhanced gate control

A nanoscale SOI MOSFET structure with enhanced gate control is provided in this article. The gate is positioned in the silicon region's center and surrounded by insulating HfO2 and SiO2. Using this structure, we attempt to enhance the gate control over the channel. Furthermore, the source connection is positioned horizontally within the silicon region to generate an electric field caused by the potential difference between the gate and the source junction in the channel region. In fact, in addition to enhanced control of the gate over the channel, the idea of utilizing gate and source connections within the silicon region has led to the maximum electron temperature shifting from the channel to the drain region. Also, generating an undoped silicon region has been feasible to lower the lattice temperature. In addition, the electrical characteristics of the proposed MOSFET in both DC and AC states will be improved. The electrical features such as effective mobility, hot electron effect, electric field, and self-heating effect have been improved. The proposed structure is designed for RF applications and is studied in the 1 MHz to 500 GHz range. The frequency characteristics of the proposed structure, like the gate-source and gate-drain capacitors, S parameters, maximum unilateral power gain, transducer power gain, minimum noise figure, and noise conductance have also been enhanced.

Estimating the real contact area in lubricated hot rolling of aluminium

Predictions of the real contact area in metal forming processes are essential for the calculation of friction and, consequently, the optimisation of energy consumption and quality of rolled products. This study develops of a model for estimating the real contact area in hot rolling of a 6061 aluminium alloy based on: thermo-viscoplastic material properties, measured roll topography, and hydrodynamic and hydrostatic roles of lubricant in the contact. Results show the interplay between load and contact area, as regions of solid contact, fluid channels and pockets are formed. Quantification in a rolling pass shows both solid contact and lubricant entrapment play the major roles, which is highly determined by the topography and the flow stress of the workpiece.

Water wave models using conformal coordinates

A review of nonlinear water wave problems in complex domains is presented. These include non-smooth highly variable bottom topographies and boundaries as for example forked channel regions. The physical and mathematical relevance of each case is discussed. The Schwarz–Christoffel mapping is the common modeling tool for these different problems. The mapping produces conformal coordinates which allow the problems’ dimension to be reduced and the weakly nonlinear partial differential system of equations to be simplified. Usually conformal mapping is adopted while preserving the Laplace operator. The main focus in the present review is to highlight some water wave problems where the underlying differential operators are not invariant under the conformal change of coordinates. The Schwarz–Christoffel mapping is used to produce a boundary fitted, curvilinear conformal coordinate system. The models reported include solitary waves on branching channels, and its reduction to nonlinear waves on graphs, as well as three dimensional surface-waves propagating over highly variable ridges. Of particular interest is nonlinear water waves on graphs, which has important applications and a scarce mathematical literature. Conformal mapping plays a crucial role regarding a systematic incorporation of forking angles into the equations, as not done before, and deducing a generalized compatibility condition at the graph nodes.

GaN Vertical Transistors with Staircase Channels for High-Voltage Applications.

In this study, we propose and simulate the design of a non-regrowth staircase channel GaN vertical trench transistor, demonstrating an exceptional threshold and breakdown characteristic for high power and high frequency applications. The unique staircase design provides a variable capacitance through the gate-dielectric-semiconductor interface, which results in a high breakdown voltage of 1.52 kV and maintains a channel on-resistance of 2.61 mΩ∙cm2. Because of the variable length and doping profile in the channel region, this model offers greater flexibility to meet a wide range of device application requirements.