Two-dimensional Potential Distribution Research Articles

Two-dimensional analytical model for fully depleted SOI MOSFETs with vertical trapezoid doping including effects of the interface trapped charges

The two-dimensional (2D) potential distribution for vertical trapezoidal doping thin-body fully depleted (FD) silicon-on-insulator (SOI) devices is derived by adopting the evanescent mode analysis method, in which the 2D effects in gate oxide region, channel region and buried oxide region are taken into account. Moreover, the effects of interface trapped charge are considered. Using this potential model, the subthreshold performance of the device including subthreshold current, and subthreshold swing under various conditions have been studied. The result shows that the analytical model is good agreement with the simulated results. Therefore, it provides a feasible way of developing new 2D models for vertical trapezoidal doping thin-body FD SOI devices. Besides offering the physical insight into device physics, the analytical model provides the basic designing guidance for vertical trapezoidal doping thin-body FD SOI devices.

Numerical Solution of Electrostatic Potential Distribution on a Unit Circular Disc Using Possion Equation

In this paper, the two-dimensional electrostatic potential distribution problem has been solved numerically using the finite difference approach using Poisson’s equation in polar coordinates with Dirichlet’s boundary condition inside a unit circular disc. We also use Gauss elimination method to solve numbers of linear equations to obtain solutions of unknowns at each grid point. The numerical solution to the same problem is contrasted with the analytic solution. Finally, we examine the absolute errors throughout a range of iterations to evaluate the accuracy of the schemes.

Improved DC surface insulation performance of epoxy resin by gradient plasma fluorination

In order to improve the flashover voltage of the disc insulator in gas insulated transmission line under DC voltage, this paper considers reducing the electric field intensity on the surface by adjusting the surface conductivity distribution. Based on the joint simulation of improved particle swarm optimization algorithm and finite element, the surface conductivity gradient partition optimization model is constructed to obtain the optimal surface conductivity distribution sequence. The relationship between conductivity and treatment time is obtained by plasma fluorination, and the gradient distribution of the surface conductivity of the sample is realized by adding different ring polytetrafluoroethylene baffles. Microscopic tests are used to characterize the differences between different regions of the sample surface. The two-dimensional (2D) electric potential distribution, 2D charge density distribution, electric field intensity distribution and flashover voltage on the sample surface under pre-charging conditions are studied and compared with the simulation results. The results show that the maximum field strength of the sample with gradient treatment can be reduced by 71% and the flashover voltage can be increased by 45%. The research in this paper provides a good reference and theoretical support for the surface modification of disc insulators, such as the surface parameters with gradient distribution.

An analytical charge-based capacitance model for double-gate tunnel FETs

This paper presents an explicit capacitance model with closed-form expressions for double gate tunnel FETs (DG-TFETs). The model is based on a 2-D potential approach, considering the mobile charges in the solution. This model uses a quasi-static approach to obtain terminal capacitances. Charges associated to each electrode are calculated by adopting the Gaussian box, and then the critical terminal capacitances including the input capacitance and the Miller capacitance are analytically expressed. To derive the model, neither fitting parameter nor iterative process is used which means the proposed model can be used for SPICE modeling of TFETs . The presented model provides a physics insight to analyze transient performance in TFET-based circuits. The proposed model is in good agreement with TCAD simulation results. The model is validated for various structural and bias parameters. • Developing a simple and accurate analytical model to capture terminal capacitances of TFETs. • This analytical model can be used as SPICE model to analyze AC performance of TFET-based circuits. • Terminal charges are calculated by developing two-dimensional potential distribution and adopting Gaussian law. • The model results have been compared with simulation results to show accuracy of the model.

Characterization of acceleration zone shifting in an anode-layer-type Hall thruster RAIJIN66

The location of the ion acceleration zone has been known to affect the performance and lifetime of a Hall thruster. Herein, the magnetic field in the anode-layer-type Hall thruster RAIJIN66 was designed to shift the acceleration zone downstream beyond the discharge channel exit. To examine the effectiveness of the design concept, plasma diagnosis using an emissive probe was conducted to obtain a one-dimensional plasma profile on the channel centerline. In addition, a two-dimensional potential profile was obtained to observe the effects of the presheath on the shifted potential structure. The results proved that the acceleration zone was pushed downstream along with the shifted magnetic field. With increasing discharge voltage, the axial length of the acceleration zone contracted at around the peak of the radial magnetic flux density. The ion current density lost to the guard-ring was estimated to be 9.9 mA/cm2, which is comparable to the current density from the magnetically shielded stationary plasma thrusters. Furthermore, the measured two-dimensional potential distribution revealed the existence of a structure that attracted ions to the wall.

Probing ion trajectory simulations for the HIBP diagnostics at the T-15MD tokamak

The paper presents the results of preliminary simulations of the Tl+ ion trajectories and detector grids for Heavy Ion Beam Probe (HIBP) diagnostics at the T-15MD tokamak. For these calculations, authors have developed the HIBP SOLVER software package using the Runge-Kutta method of the 4th order for solving the motion equation for the probing particles. Simulations have shown that the HIBP diagnostics at the T-15MD tokamak will allow measuring the entire radial profile of the plasma potential during one shot, including both the core and edge regions. The detector grid covers the most area of the vertical plasma cross section, so the two-dimensional potential distribution can be recovered. In the start regime (1 T, 1 MA), the beam energy will be below 300 keV, and in the standard regime (2 T, 2 MA), the beam energy will amount to 1000 keV.

A 2D channel potential modelling of symmetric double-gate MOSFET at onset of threshold condition

ABSTRACT A two-dimensional (2D) channel potential distribution is analytically derived for lightly doped double-gate MOSFET at turn-on condition of the device by solving 2D Poisson’s equation with the application of suitable boundary condition. Threshold voltage roll-off is also modelled to predict the short channel behaviour of the device at sub-threshold condition. Our derived model closely follows the 2D numerical simulation without the inclusion of any fitting parameters. It also serves as a basic step towards computing the compact modelling of DG MOSFET at threshold condition.

Transient analysis of a three-layer microbeam subjected to electric potential

ABSTRACTIn this paper, free vibration, wave propagation, and bending analyses of a sandwich microbeam integrated with piezoelectric face-sheets resting on Pasternak foundation under electric potential are presented based on the strain gradient theory and Euler–Bernoulli beam theory. The material properties of core are assumed variable along the thickness direction and piezoelectric face-sheets are assumed homogeneous piezoelectric materials. A two-dimensional electric potential distribution along the axial and transverse direction is applied on the face-sheets of microbeam. Hamilton principal is used to derive governing differential equations of motion. Three behaviors of sandwich microbeam including free vibration, wave propagation, and bending analyses are studied in this paper. Some numerical results are presented to capture the effect of important parameters of the problem such as in-homogeneous index, applied voltage, parameters of foundation, and material length scales. The numerical results indicate that the effect of electric potential along the axial direction is very small rather than one along the transverse direction where initial voltage is applied.

Analytic modeling of potential and threshold voltage for short-channel thin-body fully depleted silicon-on-insulator MOSFETs with a vertical Gaussian doping profile

We verify that one-dimensional (1D) Gaussian expression is an appropriate approximation of the vertical doping profile, which is obtained by combining perpendicular ion implantation and rapid thermal annealing (RTA), for short-channel thin-body (20–30 nm) fully depleted (FD) silicon-on-insulator (SOI) MOSFETs. The two-dimensional (2D) potential distribution of the silicon film is derived by adopting the evanescent mode analysis method, in which the potential function is broken into 1D long-channel and 2D short-channel potentials. The threshold voltage model is represented by the minimum front- and back-surface potentials of the silicon film. The application of the threshold voltage model can be extended to a 12 nm channel length. The results obtained using the models match well with the 2D numerical simulation results obtained using the Synopsys Sentaurus Device™. They provide a feasible way of developing new 2D models for nonuniform nanoscale thin-body FD-SOI devices.

Analysis of wave in a functionally graded magneto-electro-elastic nano-rod using nonlocal elasticity model subjected to electric and magnetic potentials

The purpose of this research is to present the wave propagation analysis of a functionally graded nano-rod made of magneto-electro-elastic material subjected to an electric and magnetic potential. The unified nonlocal elasticity theory and Love's rod model are used in this study. All mechanical, electrical and magnetic properties are assumed to be variable along the thickness direction based on a power law distribution. Two-dimensional electric and magnetic potential distributions due to an applied potential and a magnet at the top of the rod are considered. The governing equations of motion are obtained using equilibrium and nonlocal theory of elasticity in conjunction with the Hamilton principle. The effect of important parameters of the functionally graded magneto-electro-elastic nano-rod such as nonlocal parameters, power index, wave number, applied magnetic and electric potentials on the wave propagation characteristics is studied.

高k 栅MOSFET 栅-源/漏寄生电容的半解析模型

This paper proposes a two-dimensional boundary value problem for a high-k gate dielectric MOSFET and its sidewall spacer oxide. We have calculated the two-dimensional electrical potential distribution and charge distribution. A model of parasitic capacitance between the gate and the source/drain for a MOSFET has been given. In this paper, we also analyze the relationship between these parasitic capacitances and geometry dimension parameters with a semi-analytical method. The results show that there is a smallest parasitic capacitance by changing the magnitude of gate dielectric constant. The accuracy of the method is tested by comparing the modeled results with CST (computer simulation technology) simulation results. Satisfactory agreement is observed between calculation results of the model and the prediction made by CST.

Analytical model for high-voltage SOI device with composite-k dielectric buried layer

An analytical model for a novel high voltage silicon-on-insulator device with composite-k (relative permittivity) dielectric buried layer (CK SOI) is proposed. In this structure, the composite-k buried layer is composed by alternating Si3N4 and low-k (k = 2.65) dielectric in the lateral direction. Due to the composite-k buried layer, the breakdown voltage (BV) is improved both by the vertical and lateral direction. Taking the modulation effect of accumulated interface holes into account, an analytical model is developed. In the blocking state, the proposed model revealed the mechanism of hole accumulation above the Si3N4 buried layer and investigated the modulation effect of accumulated holes on the two-dimensional (2-D) potential and electric field distributions. This analytical model is verified by the simulation results. Compared with the low-k dielectric buried layer SOI (LK SOI), simulation results show that the BV for CK SOI is enhanced by 21% and the specific on-resistance is reduced by 32%, respectively.

Modeling the Thermal Behaviors of a Lithium-Ion Battery during Constant-Power Discharge and Charge Operations

This paper reports a modeling methodology to predict the thermal behaviors of a lithium-ion battery (LIB) during constant-power discharge and charge operations. An efficient algorithm is presented to estimate the voltage and current of an LIB as a function of time in the mode of constant-power discharge and charge. The experimental discharge and charge curves at various power levels of 25, 50, 100, 150, and 250 W are compared with the modeling results to validate the two-dimensional modeling of the potential and current density distribution on the electrodes of an LIB cell during constant-power operations. The two-dimensional temperature distributions of the LIB cell as a function of time are calculated based on the modeling results of the two-dimensional potential and current density distributions. The temperature distributions obtained from the modeling agree well with the experimental measurements based on infrared imaging.

Effects of Localized Surface Charges on a Two-Dimensional Potential Distribution and Photovoltage at a Schottky Barrier of a Semiconductor Electrode

Although experimental studies have long been reporting the importance of a beneficial effect of a metal nanodot coating of a semiconductor electrode for solar energy conversion, little theoretical work has been done on quantitative analysis of the effect most probably because of mathematical difficulty in calculating a two-dimensional potential distribution in the space charge layer induced by localized surface modifications or charges. This paper reports a simple method for calculating such a two-dimensional potential distribution and clarifies how the Schottky-barrier height (or flat-band potential) is affected by localized surface charges of various sizes and separations. The results not only give an unambiguous theoretical basis to the beneficial effect of a nanodot coating but also provide effective information for analysis of kinetics in semiconductor devices with nanostructures.

A two-dimensional analytical model for the gate–source and gate–drain capacitances of ion-implanted short-channel GaAs metal-semiconductor-field effect transistor under dark and illuminated conditions

This paper presents an analytical model for the internal capacitances of short-channel ion-implanted GaAs MESFETs under dark and illuminated conditions. The device structure considered in this study is a normally-on self-aligned GaAs MESFET with indium tin oxide (ITO) as the Schottky metal for the gate electrode of the device. The gate area of the device is illuminated by an optical radiation of 0.87 μm from an external source which is coupled into the device through the semitransparent ITO metal at Schottky-gate to modulate the electrical and microwave characteristics of the device. The nonanalytic Gaussian doping profile commonly considered for the channel doping of an ion-implanted GaAs MESFET has been replaced by an analytic Gaussianlike function for the simplicity of the present model. The two-dimensional (2D) potential distribution obtained by solving the 2D Poisson’s equation by including the effect of photo-generated carriers due to the incident optical radiation has been utilized to model the depletion region width below the gate of the short-channel GaAs MESFETs. The depletion width model has then been used to model the internal gate-source and gate-drain capacitances of the device operating under both the linear and saturation regions. The effect of illumination on the Schottky junction at the gate of the MESFET has been modeled by considering an induced photo-voltage developed across the junction that is superimposed on the applied gate bias voltage. The proposed model has been verified by comparing the theoretically predicted results with simulated data obtained by using the commercially available ATLASTM 2D device simulator.

Computational Model of the Mark-IV Electrorefiner: Two-Dimensional Potential and Current Distributions

A computational model of the Mark-IV electrorefiner is currently being developed as a joint project between Idaho National Laboratory, Korea Atomic Energy Research Institute, Seoul National University, and the University of Idaho. As part of this model, the two-dimensional potential and current distributions within the molten salt electrolyte are calculated for U3+, Zr4+, and Pu3+ along with the total distributions, using the partial differential equation solver of the commercial Matlab software. The electrical conductivity of the electrolyte solution is shown to depend primarily on the composition of the electrolyte and to average 205 mho/m with a standard deviation of 2.5 × 10–5% throughout the electrorefining process. These distributions show that the highest potential gradients (thus, the highest current) exist directly between the two anodes and cathode. The total, uranium, and plutonium potential gradients are shown to increase throughout the process, with a slight decrease in that of zirconium. The distributions also show small potential gradients and very little current flow in the region far from the operating electrodes.

On the maximum thickness of the space-charge region of reverse biased p +-n junctions with a positive bevel

Two-dimensional potential and electric-field strength distributions in edge regions of sharply asymmetric reverse biased p +-n junctions with a positive bevel were numerically simulated. It was shown that the maximum thickness of the space-charge region W nM nonmonotonically depends on the angle θ between the bevel surface and junction plane: the function W nM (θ) reaches a maximum at θ decreasing from 60° to 35° as the parameter Q s /ɛ s ɛ0 EvM increases from 0 to 0.02 (here Q s is the surface charge density, ɛ s ɛ0 is the absolute permittivity of the semiconductor, and E vM is the maximum field strength in the space-charge region of the p +-n junction far from the bevel). The results obtained may be useful in designing high-voltage thyristors based on Si, SiC, and other materials.

Two-dimensional potential and charge distributions of positive surface streamer

Information on the potential and the field profile along a surface discharge is required for quantitatively discussing and clarifying the propagation mechanism. The sensing technique with a Pockels crystal has been developed for directly measuring the potential and electric field distribution on a dielectric material. In this paper, the Pockels sensing system consists of a pulse laser and a CCD camera for measuring the instantaneous two-dimensional potential distribution on a 25.4 mm square area with a 50 µm sampling pitch. The temporal resolution is 3.2 ns which is determined by the pulse width of the laser emission. The transient change in the potential distribution of a positive surface streamer propagating in atmospheric air is measured with this system. The electric field and the charge distributions are also calculated from the measured potential profile. The propagating direction component of the electric field near the tip of the propagating streamer reaches 3 kV mm−1. When the streamer stops, the potential distribution along a streamer forms an almost linear profile with the distance from the electrode, and its gradient is about 0.5 kV mm−1.

Graphical Estimation of Interfacial Capacitance of PEM Fuel Cells from Impedance Measurements

Graphical methods were used to extract values of constant-phase element (CPE) parameters and interfacial capacitance from the high-frequency part of impedance data collected on a polymer electrolyte membrane (PEM) fuel cell. The impedance data were recorded as a function of current density, time, temperature, backpressure, and flow channel and gas diffusion layer design. The effective capacitance was estimated under the assumption that the CPE behavior could be attributed to two-dimensional (2D) potential and current distributions. The value of the interfacial capacitance was reduced when the cell was operated under dry or flooded conditions. The interfacial capacitance decreased with time over a time scale consistent with the approach to a steady state. In addition to providing insight into physical processes, the parameters obtained from graphical methods can be used for model reduction when regressing impedance data. The methodology presented can be applied to electrochemical systems for which the high-frequency data reveal CPE behavior caused by 2D potential and current distributions.

Modeling of the subthreshold current and subthreshold swing of fully depleted short-channel Si–SOI-MESFETs

A model for the subthreshold current and subthreshold swing of fully depleted short-channel Si–SOI-MESFETs is presented in the paper. The subthreshold current of the device is modeled empirically by an exponential function of gate–source and drain–source voltages. The short-channel effects have been included in terms of some empirical constants in the model which have been finally derived from the two-dimensional potential distribution function of the device. The subthreshold swing characteristics of the device are obtained using the subthreshold current model. The validity of the proposed model is shown by comparing the theoretical data with the simulation results obtained by using the ATLAS™ device simulation software.