On the accuracy and efficiency of substrate current calculationsfor sub-μm n-MOSFET's

The accuracy and efficiency of the self-consistent (regarding the electric field) Monte Carlo model, nonself-consistent Monte Carlo model, and the soft-threshold lucky electron model (LEM) for the calculation of substrate currents in deep sub-μm n-MOSFET's are investigated. While the two Monte Carlo models are in good agreement with the experiment, the simpler LEM model still gives reasonable results even for a 0.16 μm n-MOSFET. On the other hand, huge differences in the CPU time consumption are found and the LEM is about four orders of magnitude faster than the self-consistent Monte Carlo simulations. The nonself-consistent calculations are only one order of magnitude slower than the LEM. The good agreement with the experiment is obtained without considering the so-called surface impact ionization or any fitting of parameters on the device level     

Statistical Model for the Circuit Bandwidth Dependence of Low-Frequency Noise in Deep-Submicrometer MOSFETs

This paper covers measurement, analytical analysis, and Monte Carlo simulation of the frequency and bandwidth dependence of MOSFET low-frequency (LF) noise behavior. The model is based on microscopic device physics parameters, which cause statistical variation in the LF noise behavior of individual devices. Analytical equations for the statistical parameters are provided. The analytical model is compared to experimental data and Monte Carlo simulation results     

Physical device simulation in a shrinking world

The effect of shrinking device dimensions from micrometers to nanometers on the validity of device simulators is examined. It is shown that the assumptions underlying the drift-diffusion equation weaken when applied to small devices. Using the Monte Carlo method to simulate the microscopic motion of several thousand carriers as they travel through a device, an alternative approach that is beginning to find wide application in device engineering is discussed. Because the Monte Carlo method directly mimics carrier motion at a microscopic level, it provides highly accurate, detailed, realistic simulations of carrier transport in devices. However, it imposes a heavy computational burden, and the noise associated with the use of a relatively small sample-a few thousand electrons-sometimes limits its application. Nevertheless, its advantages continue to grow as device dimensions shrink. As the devices shrink to dimensions below 100 nm, the wave nature of electrons will play an increasingly important role, and even semiclassical Monte Carlo techniques are inadequate. Quantum approaches for use in that regime are considered     

Simulation of Schottky barrier MOSFETs with a coupled quantuminjection/Monte Carlo technique

A full-band Monte Carlo device simulator has been used to analyze the performance of sub-0.1 μm Schottky barrier MOSFETs. In these devices, the source and drain contacts are realized with metal silicide, and the injection of carriers is controlled by gate voltage modulation of tunneling through the source barrier. A simple model treating the silicide regions as metals, coupled with an Airy function approach for tunneling through the barrier, provides injecting boundary conditions for the Monte Carlo procedure. Simulations were carried out considering a p-channel device with 270 Å gate length for which measurements are available. Our results show that in these structures there is not a strong interaction with the oxide interface as in conventional MOS devices and carriers are injected at fairly wide angles from the source into the bulk of the device. The Monte Carlo simulations not only give good agreement with current-voltage (I-V) curves, but also easily reproduce the subthreshold behavior since all the computational power is devoted to simulation of channel particles. The simulations also clarify why these structures exhibit a large amount of leakage in subthreshold regime, due to both thermionic and tunneling emission. Computational experiments suggest ways to modify the doping profile to reduce to some extent the leakage     

Yield modeling of acoustic charge transport transversal filters

This paper presents a yield model for acoustic charge transport transversal filters. This model differs from previous IC yield models in that it does not assume that individual failures of the nondestructive sensing taps necessarily cause a device failure. A redundancy in the number of taps included in the design is explained. Poisson statistics are used to describe the tap failures, weighted over a uniform defect density distribution. A representative design example is presented. The minimum number of taps needed to realize the filter is calculated, and tap weights for various numbers of redundant taps are calculated. The critical area for device failure is calculated for each level of redundancy. Yield is predicted for a range of defect densities and redundancies. To verify the model, a Monte Carlo simulation is performed on an equivalent circuit model of the device. The results of the yield model are then compared to the Monte Carlo simulation. Better than 95% agreement was obtained for the Poisson model with redundant taps ranging from 30% to 150% over the minimum     

On the description of the collision terms in three-valleyhydrodynamic models for GaAs device modeling

A reduced set of transport parameters is proposed for the collision terms of the three-valley hydrodynamic model which is a faster alternative to ensemble Monte Carlo simulations. The predictions of the proposed model have been found to be in excellent agreement with transient ensemble Monte Carlo data. The reduction in the number of the transport parameters makes the model relatively easy to implement with substantial accuracy. The transport parameters which are of interest in semiclassical device modeling are presented as a function of electron energy     

Monte Carlo simulation of impact ionization in SiGe HBTs

Measurements and Monte Carlo simulations of impact ionization in the base-collector region of SiGe HBTs are presented. A device with low germanium concentration (graded from 0 to 12%) is considered and no differences are found between the experimental multiplication factor in that device and the corresponding silicon control. Because impact ionization (II) occurs inside the bulk-Si collector, phonon and II scattering rates for bulk silicon can be used in the Monte Carlo simulation, avoiding the need to model the strained SiGe layers. Full-Band Monte Carlo simulations are shown to reproduce the multiplication factors measured in SiGe devices featuring different collector profiles     

Physics-based modeling of submicron GaN permeable base transistors

We present the first physics-based nonstationary modeling of a submicron GaN permeable base transistor. Three different transport models are compared: drift-diffusion, energy balance, and ensemble Monte Carlo. Transport parameters and relaxation times used by the carrier transport equations are consistently derived from particle simulation. The current-voltage (I-V) characteristics predicted with the energy balance model are in good agreement with those obtained from direct Monte Carlo device simulation. On the other hand, the drift-diffusion approach appears to be inadequate for the device under study, even if improved high-field mobility models are adopted     

Modeling hot-electron gate current in Si MOSFET's using a coupleddrift-diffusion and Monte Carlo method

A coupled two-dimensional drift-diffusion and Monte Carlo analysis is developed to study the hot-electron-caused gate leakage current in Si n-MOSFETs. The electron energy distribution in a device is evaluated directly from a Monte Carlo model at low and intermediate electron energies. In the region of high electron energy, where the distribution function cannot be resolved by the Monte Carlo method due to limited computational resources, an extrapolation technique is adopted with an assumption of a Boltzmann tail distribution. An averaging method is employed to extract the effective electron temperature. Channel hot electron injection into a gate via quantum tunneling and thermionic emission is simulated, and electron scattering in the gate oxide is taken into account. The calculated values of gate current are in good agreement with experimental results. The simulation shows that the most serious hot electron injection occurs about 200-300 Å behind the peak of average electron energy due to a delayed heating effect     

A comparison of Monte Carlo and cellular automata approaches forsemiconductor device simulation

A detailed comparison of Monte Carlo and cellular automata approaches as applied to the study of nonequilibrium transport and semiconductor device simulation is presented. It is shown that the novel cellular automata (CA) technique enjoys all benefits of the more traditional Monte Carlo (MC) method, while at the same time allowing considerably higher performances     

Alloy scattering and high field transport in ternary and quaternary III–V semiconductors

A technique is described for the estimation of the influence of random potential alloy scattering on the high field transport properties of quaternary III–V semiconductors obtained by Monte Carlo simulation. The approach is based on an extension of a theoretical model for scattering in the ternary alloys. The magnitude of the scattering potential is an important parameter in alloy scattering, and three proposed models for calculating this potential are discussed. These are the energy bandgap difference, the electron affinity difference, and the heteropolar energy difference for the appropriate binary compounds.The technique is used in the Monte Carlo method to study the influence of alloy scattering on the transport properties of III–V quaternary alloys. The results of this study are used in a device model to estimate device parameters for FETs.     

Fast and accurate statistical characterization of standard cell libraries

With devices entering the nanometer scale process-induced variations, intrinsic variations and reliability issues impose new challenges for the electronic design automation industry. Design automation tools must keep the pace of technology and keep predicting accurately and efficiently the high-level design metrics such as delay and power. Although it is the most time consuming, Monte Carlo is still the simplest and most employed technique for simulating the impact of process variability at circuit level. This work addresses the problem of efficient alternatives for Monte Carlo for modeling circuit characteristics under statistical variability. This work employs the error propagation technique and Response Surface Methodology for substituting Monte Carlo simulations for library characterization.The techniques are validated and compared using a production level cell library using a state-of-the-art 32 nm technology node and statistical device compact model. They require electrical simulation effort linear to the number of devices, thus from one to two orders of magnitude speed-up is obtained compared to Monte Carlo analysis with the error on standard deviation and mean being smaller than 2% for the Response Surface Methodology, as compared to errors of 7% when using linear sensitivity analysis.     

Coupled Monte Carlo-drift diffusion analysis of hot-electroneffects in MOSFETs

A general method of calculating the substrate current for n-MOSFETs, using a two-dimensional conventional device simulator coupled with a full-band-structure Monte Carlo simulation, has been enhanced through the use of efficient estimators and statistical weighting of the high-energy electrons. The detailed physics of hot-electron effects in MOSFETs is explained on the basis of the energy distribution as a function of the spatial variables. Monte Carlo results show that the distribution function in the region of the device that makes the largest contribution to the substrate current does not fit a Maxwell-Boltzmann function. The effective cooling of the distribution, due in part to energy loss to impact ionization, is shown clearly. The results of the Monte Carlo calculation are used to evaluate the validity of the assumption of a constant mean path for inelastic scattering used in various analytic treatments. The calculated values of substrate current are compared to experimental results     

Analytical modeling of single electron transistor for hybrid CMOS-SET analog IC design

A physically based compact analytical single electron transistor (SET) model is proposed for hybrid CMOS-SET analog circuit simulation. The modeling approach is based on the "orthodox theory" of single electron tunneling, and valid for single or multi gate, symmetric or asymmetric devices and can also explain the background charge effect. The model parameters are physical device parameters and an associated parameter extraction procedure is reported. The device characteristics produced by the proposed model are verified with Monte Carlo simulation for large range of drain to source voltages (|V/sub DS/|/spl les/3e/C/sub /spl Sigma//) and temperatures [T/spl les/e/sup 2//(10k/sub B/C/sub /spl Sigma//)] and good agreements are observed. The proposed model is implemented in a commercial circuit simulator in order to develop a computer-aided design framework for CMOS-SET hybrid IC designs. A series of SPICE simulations are successfully carried out for different CMOS-SET hybrid circuits in order to reproduce their experimental/Monte Carlo simulated characteristics.     

Monte Carlo surface scattering simulation in MOSFET structures

The Monte Carlo method has been applied to MOSFET devices with the gate lengths less than 1 µm. The electric field in the channel was obtained by an analytical approach. Since the classical situation is approached in the submicrometer gate device, the partial diffusive model is employed for surface scattering process. Transient phenomena such as velocity overshoot have been predicted with drain biases causing a large field gradient in the channel. Comparison of the results of the Monte Carlo simulation with those obtained by an analytical approach based on static mobility shows that the carrier transit time in the channel is shorter (as much as two times) than that predicted by the analytical approach for a 0.3 µm gate device.     

Extraction of Transport Dynamics in AlGaN/GaN HFETs Through Free Carrier Absorption

The importance of AlGaN/GaN heterostructure field-effect transistor (HFETs) in high-power high-frequency applications is now well established. However, detailed information on high-field mobilities, velocity–field relations, carrier temperature, and momentum and energy relaxation times are not available. In this paper we carry out theoretical simulations based on Monte Carlo techniques to show that transport dynamics can be effectively extracted through free carrier absorption. Using short pulses of infrared radiation, it is possible to obtain the velocity–field curve by fitting the absorption spectrum without heating the device. We show this by solving the classical transport equation and then verify the results through Monte Carlo simulations. With the model presented it would be possible to extract carrier dynamics from experimentally measured results. Our work suggests that free carrier absorption experiments on AlGaN/GaN HFETs would provide important transport information, which would be very useful in device design and modeling.     

Potential design and transport property of 0.1-μm MOSFET withasymmetric channel profile

This paper describes potential design and transport property of a 0.1-μm n-MOSFET with asymmetric channel profile, which is formed by the tilt-angle ion-implantation after gate electrode formation. The relation between device performance and transport property of the asymmetric 0.1-μm device is explored by Monte Carlo simulations, and measured electrical characteristics. The self-consistent Monte Carlo device simulation coupled with a process simulator reveals higher electron velocity at the source end of the channel and velocity overshoot at the source side of the channel, and the smaller high-energy tail of the distribution in the drain. This transport property creates high drain current, large transconductance, and low substrate current of the 0.1-μm n-MOSFET with asymmetric channel profile     

Reliability Assessment of Microgrid Using Sequential Monte Carlo Simulation

Sequential Monte Carlo simulation method is introduced to the reliability assessment of microgrid,and a Weibuil distribution wind speed model is built to simulate the hourly wind speed of a specific site.Wind turbine generator model combined with a two-state reliability model is applied to Monte Carlo simulation method,and results show that the wind turbine reliability model works well with sequential Monte Carlo simulation.A two-state reliability model of micro gas turbine and a load model from IEEE reliability test system(IEEE RTS)are also introduced to the reliability evaluation of microgrid.Case studies show that Monte Carlo simulation method is flexible and efficient dealing with microgrid consisting of renewable resources with fluctuation characteristics.     

A quantum correction based on Schrodinger equation applied to Monte Carlo device simulation

A full-band Monte Carlo model has been coupled to a Schrodinger equation solver to account for the size quantization effects that occur at heterojunctions, such as the oxide interface in MOS devices. The overall model retains the features of the well-developed semi-classical approach, by treating self-consistently the Schrodinger solution as a correction to the particle-based Monte Carlo. The simulator has been benchmarked by comparing results for MOS capacitors and double gate structures with a self-consistent quantum solution, showing that the proposed approach is efficient and accurate. This quantum correction methodology is extended to device simulation, by accounting for the interplay between confinement and transport through a parameter which we call "transverse" temperature. This approach appears to be valid even for nanometer-scale devices in which nonequilibrium ballistic transport is occurring. We present simulations of a 25-nm MOSFET and compare results obtained with and without the quantum correction.     

全表格化的稳态Monte Carlo模拟

<正> 一、引言 Monte Carlo模拟的方法可以较精确地反映材料和器件内部的热电子效应和热噪声的影响。它的限制主要在于耗费了大量的计算机时间。通过实践,本文提出了Monte Carlo模拟的全表格化处理方法。这种方法能以少量存贮空间为代价,大幅度减少计算时间,并保证足够精度。