Effective Channel Width Research Articles

Compact modeling of sectorial split-drain magnetic field-effect transistors

Split-drain magnetic field-effect transistor (SD-MAGFET), having the key advantage of possible system integration with the mainstream CMOS technology, should be one of the key technological options for achieving better human and environmental interfacing of digital products as proposed in the More-than-Moore paradigm. However, the characteristics, the potential, and the design methodologies of this new device structure have not fully explored yet. By introducing the effective channel width concept and basing on the first principle of charge transport, we conducted a compact modeling on the magnetic sensitivity of sectorial split-drain MAGFET (SSD-MAGFET). Our model provides some intuitive views on the effects of the devices parameters, such as the sectorial angle, gap width between the two drains, effective aspect ratio, on the operation range and magnetic sensitivity. The model agrees well with the experimental results and suggests that the sensitivity-B field relationship could be approximated by two piecewise linear regions according to the field strength and there exists an optimal sector angle which is governed by the gap width and effective aspect ratio of the SSD-MAGFET.

High-performance n-channel polycrystalline germanium thin-film transistors via continuous-wave laser crystallization and green nanosecond laser annealing for source and drain dopant activation

High-quality polycrystalline germanium (poly-Ge) films have been successfully fabricated via the continuous-wave laser crystallization (CLC) process. Grain sizes as large as 0.8 μm were obtained for the poly-Ge films by CLC at 5.7 W. Furthermore, the source and drain dopants could then be effectively activated by green nanosecond laser annealing (GNS-LA). Consequently, n-channel CLC Ge thin-film transistors (TFTs) with a high field-effect mobility of 576 cm2 V−1 s−1 were demonstrated for an effective channel width of 0.86 μm and a channel length of 0.5 μm. It is shown that CLC combined with GNS-LA is effective for attaining high-performance n-channel poly-Ge TFTs.

Junctionless Transistor with Pulsed Shaped Dielectric (PSD-JNL): An Absorbing Structure for Nanoscale Aims

Junctionless devices have been recently taken into consideration for the nanoscale applications. Regarding to the reliability weakness of the conventional Silicon-on-Insulator Junctionless (SOI-JLT) in nanoscale regime, this work has proposed a novel junctionless to overcome the basic problems occurring for it. The configuration of the buried oxide in the conventional JLT has been effectively modified with converting net SiO2 dielectric to a pulsed shaped dielectric including the silicon material and SiO2 material. The new configuration leaving a pulsed shaped dielectric as the buried oxide leads to the formation of an additional depletion layer in the channel region interface with the substrate. A meaningful result is that the effective channel width in the standby mode is reduced thus decreasing the leakage current, considerably. The comparisons in the cases of both DC and AC operations revealed that the proposed structure exhibits superior electrical performance in terms of the short-channel effects, thermal features, parasitic capacitance, transcondutance, output conductance, power gains, cutoff frequency, and minimum noise figure.

Impact of geometrical parameters on the electrical performance of network-channel polycrystalline silicon thin-film transistors

The effects of geometrical parameters on the electrical characteristics of network-channel low-temperature polycrystalline silicon (LTPS) thin-film transistors (TFTs) were investigated. The grain boundary and interface trap densities were also extracted using parameters such as hole-to-hole distance, hole-branch top width, effective channel width, and area filling factor (AF). It was found that the electrical characteristics were largely dependent on AF, mainly owing to reduced trap densities. However, excessive hole formation in the network-channel structure was found to increase channel resistance and decrease drain current. These results suggest that, for a given footprint device area, denser hole patterns are preferred for achieving better electrical characteristics in novel network-channel LTPS TFTs.

Edge-Limited Valley-Preserved Transport in Quasi-1D Constriction of Bilayer Graphene.

We investigated the quantization of the conductance of quasi-one-dimensional (quasi-1D) constrictions in high-mobility bilayer graphene (BLG) with different geometrical aspect ratios. Ultrashort (a few tens of nanometers long) constrictions were fabricated by applying an under-cut etching technique. Conductance was quantized in steps of ∼4 e2/ h (∼2 e2/ h) in devices with aspect ratios smaller (larger) than 1. We argue that scattering at the edges of a quasi-1D BLG constriction limits the intervalley scattering length, which causes valley-preserved (valley-broken) quantum transport in devices with aspect ratios smaller (larger) than 1. The subband energy levels, analyzed in terms of the bias-voltage and temperature dependences of the quantized conductance, indicated that they corresponded well to the effective channel width of a physically defined conducting channel with a hard-wall confining potential. Our study in ultrashort high-mobility BLG nano constrictions with physically tailored edges clearly confirms that physical edges are the major source of intervalley scattering in graphene in the ballistic limit.

Capillary Coatings: Flow and Drying Dynamics in Open Microchannels.

Capillary flow and drying of polymer solutions in open microchannels are explored over time scales spanning seven orders of magnitude: from capillary filling (10-3-10 s) to the formation of a dry thin film (a "capillary coating"; 102-103 s). During capillary filling, drying-induced changes (increased solids content and viscosity) generate microscale pinning events that impede contact line motion. Three unique types of pinning are identified and characterized, each defined by the specific location(s) along the contact line at which pinning is induced. Drying is shown to ultimately pin the contact line permanently, and the associated total flow distances and times are revealed to be strong functions of channel width and drying rate. In general, lower drying rates coupled with intermediate channel widths are found to be most conducive to longer flow distances and times. After the advancing contact line permanently pins, internal flows driven by uneven evaporation rates continue to drive polymer to the contact line. This phenomenon promotes a local accumulation of solids and persists until all motion is arrested by drying. The effects of channel width and drying rate are investigated at each stage of this capillary coating process. These results are then applied to case studies of two functional inks commonly used in printed electronics fabrication: a PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)) ink and a graphene ink. Although drying is shown to permanently arrest flow in both inks, both systems exhibit an increased resistance to pinning unexplained by mechanisms identified in aqueous polymer systems. Instead, arguments based on chemistry, particle size, and rheology are used to explain their novel behavior. These case studies provide insight into how functional inks can be better designed to optimize flow distances and maximize overall dry film uniformity in capillary coatings.

Effect of channel-width and chirality on graphene field-effect transistor based real-time biomolecule sensing

Graphene field-effect transistors (GFET) hold promise in biomolecule sensing due to the outstanding properties of graphene materials. Charges in biomolecules are transduced into a change in the GFET current, which allows real-time monitoring of the biomolecule concentrations. Here we theoretically evaluate the performance of GFET based real-time biomolecule sensing, aiming to better understand the width-scaling limit in GFET based biosensors. In particular, we study the effect of the channel-width and the chirality on FET sensitivity by taking the percentage change of the FET current per unit charge density as the sensing signal. Firstly, GFETs made of graphene nanoribbons (GNR) and graphene sheets (GS) show comparable sensing signals to each other when gated at 1011 – 1012 cm-2 carrier densities. Sensing signals in GNRs are enhanced when gated near the sub-band thresholds, and increase their values in wider GNRs due to the change in device conductance and quantum capacitance. Secondly, the GNR chirality is found to fine tune the sensing signals. Armchair GNRs with smaller energy bandgaps appear to have an enhanced sensing signal close to 1011 cm-2 carrier densities. These results may help understand the scaling limit in GFET based biosensors along the width direction, and shed light on forming all-electrical bio-arrays.

Comprehensive analysis of Subthreshold short channel behavior of a Dual-material gate strained trapezoidal FinFET

The current research highlights the subthreshold short channel characteristics of a novel structure namely Dual-material gate strained Trapezoidal strained FinFET. Based on the effective channel width and equivalent number of gates (ENG), we have developed a quasi-3-D scaling length model and examined device characteristics like potential and electric field. The response of the device towards the various short channel effects has also been studied in depth. The analytical results obtained have been verified using 3-D numerical device simulation results.

Numerical and Experimental Investigations of Bipolar Membrane Fuel Cells: 3D Model Development and Effect of Gas Channel Width

Bipolar membrane fuel cells, which features a hybrid acid-alkaline membrane architecture, show great potential for practical applications because of their ability for self-humidification during operation. The principle of self-humidification behavior and associated transport mechanisms are reported in previous studies with reduced-dimension models. This paper reports on a three-dimensional model and new experimental data that further elucidate the mechanism of self-humidification, provide detailed characterization of the effects of design parameters on flow field and cell performance. The multidimensional-multiphysics model accounts for interface reaction kinetics, as well as transport of gas species, charged species and momentum. Simulations and quantitative analysis are performed for the cathode catalyst layer where water transport is critical for the electrochemical reaction therein. Three-dimensional model fully captures geometric features and gradients, and offers more comprehensive resolution of mass transport inside the cell. Based on the three-dimensional model, effects of channel width on cell performance are investigated both numerically and experimentally.

Effect of Confinement on the Aggregation Kinetics of Dilute Magnetorheological Fluids

The goal of this study is to investigate the field-driven structuration of model magnetorheological (MR) fluids in narrow gaps (below 1 mm) for high shear applications. With this in mind, we study the influence of confinement in the aggregation kinetics of dilute carbonyl iron suspensions under strong fields in rectangular microchannels using video-microscopy, image analysis and particle level dynamic simulations. Channel widths studied are ranged in the interval [75–1000 μm]. In these particular suspensions the experimental and simulation time scales according to: where λ is the Lambda parameter, is the particle surface fraction and W* is the reduced microchannel width. We show that the effect of channel width is crucial in the dynamic exponent and in the saturation (long time) mean cluster size. In contrast, it has no effect in the onset of the tip-to-tip aggregation process.

Continuous flow synthesis of monodisperse gold nanoparticles by liquid‐phase reduction method on glass microfluidic device

Monodisperse gold nanoparticles (GNPs) in aqueous dispersion were synthesised using a low-cost glass microfluidic device with a Y-shaped microchannel. The effects of channel width and flow rate on the size distribution of the synthesised GNPs were investigated. An aqueous solution of tetrachloroauric (III) acid (source of Au ions), and a mixture of an aqueous solution of sodium citrate acid (reducing agent) and tannic acid (protective agent), were injected into a microchannel in the microfluidic device by using a syringe pump. The absorption spectra at low flow rates showed sharper peaks in comparison with those at high flow rates. At the channel width of 260 μm, the full width at half maximum of the absorption peak was 79.2 nm for 0.05 ml/min and 92.9 nm for 0.06 ml/min. From transmission electron microscopy images, the GNPs synthesised using a channel width of 260 μm and flow rate of 0.05 ml/min were found to have a mean diameter of 11.5 nm and coefficient of variation of 0.09. These results confirmed that the combination of a low-flow rate and a small channel width is essential to obtain monodisperse GNPs.

High-Linearity AlGaN/GaN FinFETs for Microwave Power Applications

In this letter, we have proposed a novel AlGaN/GaN FinFET featuring T-shaped gate and extremely linearity of transconductance characteristics (Gm). The formation of AlGaN/GaN nano-fins only in the gate opening region is enabled by a developed fabrication process, which is simple and well compatible with the conventional one. When normalized to effective channel width, the fabricated FinFET delivers a 1.45 times higher current density and a 1.66 times higher output power density as high as 11.3 W/mm at 8 GHz compared with the planar HEMTs, along with clearly improved linearity characteristics thanks to a flatter Gm response afforded by much lower source access resistance. To the best of our knowledge, this is the first demonstration of superior power performance of highlinearity GaN FinFETs, indicating significant advantages of tri-gate configuration over planar HEMTs for microwave power applications.

Effect of eccentricity on junction and junctionless based silicon nanowire and silicon nanotube FETs

In this paper, the effect of eccentricity on Junction-based Silicon Nanowire FET, Junction-based Silicon Nanotube FET, Junctionless-based Silicon Nanowire FET, and Junctionless-based Silicon Nanotube FET is investigated. Three kinds of eccentric structures are considered here. The impact of eccentricity on effective gate oxide thickness thereby gate oxide capacitance, and effective channel width are studied using 3D numerical simulations. Average radius of an ellipse is used to generate a model which captures the impact of eccentricity on gate oxide capacitance, and verified using TCAD simulations in MOS nanowire structure. The impact of eccentricity on ON current (ION), OFF current (IOFF), ION/IOFF ratio, and Unity gain cutoff frequency are investigated. Eccentricity increases the effective gate oxide thickness, the effective channel width, ION, and IOFF but reduces ION/IOFF ratio.

Statistical Dependence of Gate Metal Work Function on Various Electrical Parameters for an n-Channel Si Step-FinFET

This paper presents a 3-D statistical simulation study of an n-channel Si step-FinFET due to work-function variability depending on grain orientation of metal gate. The statistical fluctuation induced by metal gate granularity on threshold-voltage ( $\sigma {V}_{T}$ ), ON current ( $\sigma I_{ \mathrm{\scriptscriptstyle ON}}$ ), and OFF current ( $\sigma {I}_{ \mathrm{\scriptscriptstyle OFF}}$ ) are estimated for a wide range of channel length and effective fin width for varying average grain size using Technology Computer Aided Design simulator. We investigated the effect of grain on magnitude of variability and also on shapes of various electrical parameters of distribution. The results indicate that $\sigma {V}_{T}$ decreases for increase in each dimension of the device. The value of $\sigma {I}_{ \mathrm{\scriptscriptstyle ON}}$ , and $\sigma {I}_{ \mathrm{\scriptscriptstyle OFF}}$ reduces as channel length increases. However, $\sigma {I}_{ \mathrm{\scriptscriptstyle ON}}$ and $\sigma {I}_{ \mathrm{\scriptscriptstyle OFF}}$ increase as fin width increases. The distribution of electrical parameters is near to normal for small grain size and becomes bimodal at large grain size. The proposed structure shows excellent behavior in terms of threshold-voltage ( ${V}_{T}$ ), subthreshold swing, and current ratio ( ${I}_{ \mathrm{\scriptscriptstyle ON}}/I_{ \mathrm{\scriptscriptstyle OFF}}$ ) compared with conventional FinFET at high temperature. It is found that the hot carrier effect reduces with increased effective channel width.

Effectiveness of flow obstructions in enhancing electro-osmotic flow

In this paper the influence of obstructions on microchannel electro-osmotic flow is investigated for the first time. To carry out such a study, regular obstructions are introduced into microchannels and flow rates are numerically calculated. The effect of channel width on flow rates is analysed on both free and obstructed channels. The solid material considered for channel walls and obstructions is silicon, and the electrolyte is deionised water. The parameters studied include channel width, obstruction size and effective porosity of the channel. The effective porosity is varied between 0.4 and 0.8 depending on other chosen parameters. The results clearly demonstrate that, under the analysed conditions, introduction of obstructions into channels wider than 100,upmu hbox {m} enhances the flow rate induced by electro-osmosis.

FE-analysis of Channel Width Effects on Spring-back Characteristics in the U-bending Process

In this study, the effects of channel width on spring-back characteristics in the U-bending process were investigated using the finite element method (FEM) and laboratory experiments. Based on the stress distribution analysis, it was found that there were no changes to the bending and reversed bending stresses in the workpiece, when a pressure pad was used. In contrast, without a pressure pad, the channel width directly affected the bending and reversed bending stresses, which resulted in changes to the spring-back characteristics. These results confirmed that the effect of channel width on the spring-back characteristics could be neglected in the case of U-bending with a pressure pad but that it should be strictly considered in the case of U-bending without a pressure pad. The FEM simulation results showed good agreement with the experimental results in terms of both the bend angles and bending forces.

Flow behaviours and boundary slip of nitrogen-oxygen mixture confined in nanochannel

Molecular dynamics simulations have been carried out to study the Couette flow of nitrogen-oxygen mixture confined in parallel-plate nanochannels. The simulation results show that the shear stress linearly increases with the increase of the shear rate when the channel width is a constant, implying that the shear viscosity of the gas flow is constant in our simulations, which increases with the channel width. However, as the channel width reaches a threshold, the effect of channel width on fluid viscosity decreases gradually. The slip velocity decreases with increasing the solid-gas coupling strength and the number density of the gas molecules. Interestingly, the shear viscosity of fluid confined in the nanochannels increases with enlarging the component ratio of nitrogen. The particular issue at nanoscale is that the solid-like structure is extremely easy to form at the gas flow boundaries for the nitrogen molecules confined in the parallel-plate nanochannels.

Zinc tin oxide thin film transistor: Effect on channel isolation and channel width

The n-channel field-effect thin-film transistors (TFTs) with amorphous zinc tin oxide as an active layer has been investigated. The transparent ZTO thin films deposited at room temperature using rf magnetron sputtering have an optical bandgap of 3.3 eV. Before the fabrication of TFT postdeposition annealing of the film was carried out 300°C for 1 hour. The channel layer on Si/SiO2 substrate was deposited in two different structures, isolating each device from the neighboring devices and without isolation. The isolation of active material improves TFT performance by reducing the gate leakage current and parasitic bias stress. The on-off ratio and subthreshold swing were significantly changed from 2.3x103 and 0.73 V/dec to 2.55x106 and 0.23 V/dec respectively on isolation. The effect of channel width on the TFT parameters such as saturated mobility, subthreshold swing and threshold voltage are also studied. The threshold voltage decreases with increasing channel width but mobility and subthreshold swing are relatively constant. The threshold voltage decreased from 19 V to 11 V when the channel width increased. It may be due to the increasing parasitic resistance between the source/drain contacts and the ZTO channel layer.

Flow behaviours and boundary slip of nitrogen-oxygen mixture confined in nanochannel

Molecular dynamics simulations have been carried out to study the Couette flow of nitrogen-oxygen mixture confined in parallel-plate nanochannels. The simulation results show that the shear stress linearly increases with the increase of the shear rate when the channel width is a constant, implying that the shear viscosity of the gas flow is constant in our simulations, which increases with the channel width. However, as the channel width reaches a threshold, the effect of channel width on fluid viscosity decreases gradually. The slip velocity decreases with increasing the solid-gas coupling strength and the number density of the gas molecules. Interestingly, the shear viscosity of fluid confined in the nanochannels increases with enlarging the component ratio of nitrogen. The particular issue at nanoscale is that the solid-like structure is extremely easy to form at the gas flow boundaries for the nitrogen molecules confined in the parallel-plate nanochannels.

Channel width effect on the operation of 4H-SiC vertical JFETs

SiC JFETs may have the lowest overall losses of switching devices and can operate at temperatures over 400 °C. Over different junction field-effect transistor (JFET) designs, the trenched and implanted (TI) gate vertical JFET (TI-VJFET) is very attractive since it may have the lowest on-resistance and its fabrication does not require epitaxial overgrowth or multiple angled implantation. 4H-SiC TI-VJFETs have been fabricated with self-aligned nickel silicide source and gate contacts using a process sequence that greatly reduces process complexity as it includes only four lithography steps. Different design factors, including channel width, channel length, and mesa height, are considered. The effect of the channel geometry on the electrical characteristics has been studied by varying their width (1.5–5 µm). The specific ON resistance (RON) of the fabricated devices, at VGS = 0 V, varied from 12.5 to 6.2 mΩ cm2 with increasing the channel width. The effect of the channel width was more tremendous on the breakdown voltage of the transistors passing from 80 to 500 V, showing the importance of the static-induction effect (saddle point potential influenced by drain potential) on the transistor blocking characteristics. Indeed, the blocking voltage gain is varying from 50 to single digit values when increasing the channel width. The physical reason is that the blocking gain to first order depends exponentially on the channel dimensions as the drain-source current is exponentially related to the saddle point potential.