Browsing by Author "Li, YM"

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A comparative study of electrical characteristic on sub-10-nm double-gate MOSFETs
(2005-09-01)
Li, YM
;
Chou, HM
;
電信工程研究所
;
友訊交大聯合研發中心
;
Institute of Communications Engineering
We explore the structure effect on electrical characteristics of sub-10-nm double-gate metal-oxide-semiconductor field-effect transistors (DG MOSFETs). To quantitatively assess the nanoscale DG MOSFETs' characteristics, the on/off current ratio, subthreshold swing, threshold voltage (V-th), and drain-induced barrier-height lowering are numerically calculated for the device with different channel length (L) and the thickness of silicon film (T-si). Based on our two-dimensional density gradient simulation, it is found that, to maintain optimal device characteristics and suppress short channel effects (SCEs) for nanoscale DG MOSFETs, T-si should be simultaneously scaled down with respect to L. From a practical fabrication point-of-view, a DG MOSFET with ultrathin T-si will suppress the SCE, but suffers the fabrication process and on-state current issues. Simulation results suggest that L/T-si >= 1 may provide a good alternative in eliminating SCEs of double-gate-based nanodevices.
A computational efficient algorithm for protein sequence classification
(2003)
Li, YM
;
Lu, HM
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友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
In this paper we present statistical algorithms to classify the stability of proteins by their sequence. A protein sequence consists of successive amino acid codes and can be considered as multivariate categorical data. Based on the statistical variance analysis for data set in each group (stable or unstable protein), the weights are calculated and become an important clue for the effects of the combination of amino acids codes on protein stability. Once the weights for every combination of amino acid codes have been decided, we can assign each protein a score presenting its stability. The distribution of the score for a stable protein is different from the score of an unstable protein. Our algorithm is well suit in the protein stability analysis by its sequence. We propose weighting algorithms and compare them as the results of protein stability classification. It provides an alternative for the protein stability classification and a predictable result as the reference before the protein mutation.
A computational efficient method for HBT intermodulation distortions and two-tone characteristics simulation
(2001)
Huang, KY
;
Li, YM
;
Lee, CP
;
Sze, SM
;
電子工程學系及電子研究所
In this paper, a new simulation method for two-tone characteristics calculations and the third-order intercept point (OIP3) of heterojunction bipolar transistor (HBT) in large-scale time domain is proposed. Base on waveform relaxation (WR) and monotone iterative (MI) methods, we solve a set of nonlinear ordinary differential equation (ODE) of equivalent circuit. With this approach, the two-tone characteristics in frequency domain for HBTs were directly computed from time domain result with fast Fourier transform (FFT). Simulation results on a realistic HBT are presented to show the accuracy and efficiency of the method.
A computational investigation of electron energy states for vertically coupled semiconductor quantum dots
(2003)
Li, YM
;
Lu, HM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We study the electron energy state for single and vertically coupled quantum dots (QDs). Our realistic three-dimensional (3D) modeling for narrow gap semiconductor QDs considers: (1) the effective one electronic band Hamiltonian; (2) the energy- and position-dependent electron effective mass approximation; (3) a finite height hard-wall confinement potential; and (4) the Ben Daniel-Duke boundary conditions. A robust nonlinear iterative algorithm is applied to solve the model for disk- (DI-) and conical- (CO-) shaped QDs. For single QD, we find that the most stable against the dot size deviations (between dots of the same base radius) is the electron energy spectra of the CO-shaped QDs. For vertically coupled QDs with the fixed dot size, the energy spectra can be controlled by an interdot distance between two dots. Due to weak interaction of wavefunctions, electron energies of the CO-shaped coupled QDs are less dependent on the inter-distance than that of the DI-shaped coupled QDs. This investigation is related to optical spectra and useful in optoelectronics applications.
A computational method for energy level spin splitting simulation in InAs/GaAs semiconductor quantum dots
(2002-05-01)
Li, YM
;
Voskoboynikov, O
;
Lee, CP
;
Sze, SM
;
Tretyak, O
An impact of the spin-orbit interaction on the electron quantum confinement is considered theoretically for narrow gap semiconductor cylindrical quantum dots. To study the phenomena for InAs quantum dot embedded into GaAs semiconductor matrix, the effective one electronic band Hamiltonian, the energy position dependent electron effective mass approximation, and the spin-dependent Ben Daniel-Duke boundary conditions axe considered, formulated and solved numerically. To solve the nonlinear Schrodinger equation, we propose a nonlinear iterative algorithm. This calculation algorithm not only converges for all simulation cases but also has a good convergent rate. With the developed quantum dot simulator, we study the effect of the spin-orbit interaction for narrow gap InAs/GaAs semiconductor cylindrical quantum dots. From the numerical calculations, it has been observed that the spin-orbit interaction leads to a sizeable spin-splitting of the electron energy states with nonzero angular momentum. Numerical evidence is presented to show the splitting result is strongly dependent on the quantum dot size.
A domain partition approach to parallel adaptive simulation of dynamic threshold voltage MOSFET
(2002-08-01)
Li, YM
;
Chao, TS
;
Sze, SM
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
In this paper, we present a dynamic domain partition simulation technique for parallel numerical solutions of semiconductor device equations. Based on the adaptive finite volume method, a posteriori error estimation, and monotone iterative algorithm, this dynamic load balancing approach has been successfully developed and implemented on a Linux cluster with message passing interface library. The developed simulator is then applied to calculate the physical characteristics of deep submicron dynamic threshold voltage MOSFET (DTMOS). We simulate DTMOS with two different parallel algorithms: (1) 2D dynamic load balancing for parallel domain decomposition; (2) parallel I-V point simulation. Benchmark results show that a well-designed load balancing simulation can reduce the execution time up to an order of magnitude. Compared with the measured data, the simulated results for a 0.08 mum DTMOS are demonstrated to show the accuracy and efficiency of the method. (C) 2002 Elsevier Science B.V All rights reserved.
A genetic algorithm approach to InGaP/GaAs HBT parameter extraction and RF characterization
(2003-04-01)
Li, YM
;
Cho, YY
;
Wang, CS
;
Huang, KY
;
電子工程學系及電子研究所
In this paper, a computational intelligence technique is applied to extract and simulate the stationary and high-frequency properties of heterojunction bipolar transistors (HBTs). A set of HBT circuit equations formulated with the Gummel-Poon model in time domain is solved with (1) the waveform relaxation (WR), (2) monotone iterative (MI) method, and (3) genetic algorithm (GA) with floating-point operators. The coupled nonlinear equations are decoupled and solved with the WR and MI methods in time domain, and the results obtained are used for the optimization of the characteristics with the GA method. The iteration can be terminated when the final convergent global solution is obtained. The time domain result is used in analyzing the property of the output third-order intercept point (OIP3) with the fast Fourier transform (FFT). Compared with the SPICE result, our simulation results demonstrate that this method is accurate and stable in high frequency simulation. This approach has practical applications in HBT characterization and radio frequency (RF) circuit optimal design.
A mixed lubrication model for computer simulation of extrusion processes
(2000-10-01)
Hsu , TC
;
Li, YM
;
Hung, CH
;
機械工程學系
;
Department of Mechanical Engineering
A mixed lubrication/friction model for extrusion process is developed in the present research. The model combines a rigid-plasticity finite element code to simulate the interface condition between the tooling and workpiece in the extrusion operation. The influence of surface roughness on lubricant flow is treated by using the average Reynolds equation. The active lubrication regime and appropriate friction factor were determined from the current local values of interface variables such as mean lubricant film thickness and workpiece and tooling roughness, in addition to the more traditional external variables such as interface pressure, node sliding velocity and strain rate of the workpiece. Numerical results using the coupled code include friction stress and normal pressure under different lubrication conditions are compared with experimental investigation. The discrepancy is very small and the proposed model proved to be very efficient in predicting interface friction condition in the extrusion processes.
A new parallel adaptive finite volume method for the numerical simulation of semiconductor devices
(2001-12-15)
Li, YM
;
Liu, JL
;
Chao, TS
;
Sze, SM
;
應用數學系
Based on adaptive finite volume approximation, a posteriori error estimation, and monotone iteration, a novel system is proposed for parallel simulations of semiconductor devices. The system has two distinct parallel algorithms to perform a complete set of I-V simulations for any specific device model. The first algorithm is a domain decomposition on I-irregular unstructured meshes whereas the second is a parallelization of multiple I-V points. Implemented on a Linux cluster using message passing interface libraries, both algorithms are shown to have excellent balances on dynamic loading and hence result in efficient speedup. Compared with measurement data, computational results of sub-micron MOSFET devices are given to demonstrate the accuracy and efficiency of the system. (C) 2001 Elsevier Science B.V. All rights reserved.
A novel numerical approach to heterojunction bipolar transistors circuit simulation
(2003-05-15)
Li, YM
;
Huang, KY
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
;
Department of Electronics Engineering and Institute of Electronics
In this paper we present a novel computational method for calculating the heterojunction bipolar transistor (HBT) physical characteristics in the time domain. To calculate the HBT high frequency properties, the Gummel-Poon equivalent circuit model is applied to replace the HBT in the circuit and a set of governing ordinary differential equations (ODEs) is formulated. We directly decouple the system ODEs and solve each decoupled ODE with the monotone iterative method in the time domain. This solution methodology proposed here has been applied to semiconductor device simulation by us earlier, and we find this method for the HBT simulation has good accuracy and converges globally. Compared with the HSPICE circuit simulator results, our results present the accuracy, efficiency, and robustness of the method. (C) 2002 Elsevier Science B.V. All rights reserved.
A numerical iterative method for solving Schrodinger and Poisson equations in nanoscale single, double and surrounding gate metal-oxide-semiconductor structures
(2005-07-01)
Li, YM
;
Yu, SM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
Numerical solution of the Schrodinger and Poisson equations (SPEs) plays an important role in semiconductor simulation. We in this paper present a robust iterative method to compute the self-consistent solution of the SPEs in nanoscale metal-oxide-semiconductor (MOS) structures. Based on the global convergence of the monotone iterative (Ml) method in solving the quantum corrected nonlinear Poisson equation (PE), this iterative method is successfully implemented and tested on the single-, double-, and surrounding-gate (SG, DG, and AG) MOS structures. Compared with other approaches, various numerical simulations are demonstrated to show the accuracy and efficiency of the method. (c) 2005 Elsevier B.V All rights reserved.
A parallel adaptive finite volume method for nanoscale double-gate MOSFETs simulation
(2005-03-01)
Li, YM
;
Yu, SM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We propose in this paper a quantum correction transport model for nanoscale double-gate metal-oxide-semiconductor field effect transistor (MOSFET) device simulation. Based on adaptive finite volume, parallel domain decomposition, monotone iterative, and a posteriori error estimation methods, the model is solved numerically on a PC-based Linux cluster with MPI libraries. Quantum mechanical effect plays an important role in semiconductor nanoscale device simulation. To model this effect. a physical-based quantum correction equation is derived and solved with the hydrodynamic transport model. Numerical calculation of the quantum correction transport model is implemented with the parallel adaptive finite volume method which has recently been proposed by us in deep-submicron semiconductor device simulation. A 20 nm double-gate MOSFET is simulated with the developed quantum transport model and computational technique. Compared with a classical transport model. it is found that this model can account for the quantum mechanical effects of the nanoscale double-gate MOSFET quantitatively. Various biasing conditions have been verified on the simulated device to demonstrate its accuracy. Furthermore. for the same tested problem, the parallel adaptive computation shows very good computational performance in terms of the mesh refinements, the parallel speedup, the load-balancing, and the efficiency. (C) 2004 Elsevier B.V. All rights reserved.
A parallel monotone iterative method for the numerical solution of multi-dimensional semiconductor Poisson equation
(2003-07-01)
Li, YM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
Various self-consistent semiconductor device simulation approaches require the solution of Poisson equation that describes the potential distribution for a specified doping profile (or charge density). In this paper, we solve the multi-dimensional semiconductor nonlinear Poisson equation numerically with the finite volume method and the monotone iterative method on a Linux-cluster. Based on the nonlinear property of the Poisson equation, the proposed method converges monotonically for arbitrary initial guesses. Compared with the Newton's iterative method, it is easy implementing, relatively robust and fast with much less computation time, and its algorithm is inherently parallel in large-scale computing. The presented method has been successfully implemented; the developed parallel nonlinear Poisson solver tested on a variety of devices shows it has good efficiency and robustness. Benchmarks are also included to demonstrate the excellent parallel performance of the method. (C) 2003 Elsevier B.V. All rights reserved.
A quantum correction Poisson equation for metal-oxide-semiconductor structure simulation
(2004-07-01)
Li, YM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
In this paper, we present a quantum correction Poisson equation for metal-oxide-sermconductor (MOS) structures under inversion conditions. Based on the numerical solution of Schrodinger-Poisson (SP) equations, the new Poisson equation developed is optimized with respect to (1) the position of the charge concentration peak, (2) the maximum of the charge concentration, (3) the total inversion charge sheet density Q, and (4) the average inversion charge depth X. Instead of solving a set of coupled SP equations, this physically-based Poisson equation characterizes the quantum confinement effects of the MOS structure from the interface of silicon and oxide (Si/SiO2) with the silicon substrate. It successfully predicts distribution of the electron density in inversion layers for MOS structures with various oxide thicknesses T-ox and applied gate voltages V-G. Compared to SP results, the prediction of the proposed equation is within 3% accuracy. Application of this equation to the capacitance-voltage measurement of an n-type metal-oxide-semiconductor field effect transistor (MOSFET) produces an excellent agreement. This quantum correction Poisson equation can be solved together with transport equations, such as drift-diffusion, hydrodynamic and Boltzmann transport equations without encountering numerical difficulties. It is feasible for nanoscale MOSFET simulation.
A SPICE-compatible model for nanoscale MOSFET capacitor simulation under the inversion condition
(2002-12-01)
Tang, TW
;
Li, YM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
A SPICE-compatible charge model for nanoscale MOSFETs is proposed. Based on the solution of Schrodinger-Poisson (S-P) equations, the developed compact charge model is optimized with respect to: 1) the position of the charge concentration peak; 2) the maximum of the charge concentration; 3) the total inversion charge sheet density; and 4) the average inversion charge depth, respectively. This model can predict inversion layer electron density for various oxide thicknesses and applied voltages. Compared to the S-P results, our model prediction is within 5% of accuracy. Application of this charge quantization model to the C-V measurement produces an excellent agreement., This compact model has continuous derivatives and is therefore amenable,to a device simulator. It can also be easily incorporated into circuit simulator for modeling ultrathin oxide MOSFET C-V characteristics.
A study of the threshold voltage variations for ultrathin body double gate SOI MOSFETs
(2004)
Tang, CS
;
Lo, SC
;
Lee, JW
;
Tsai, JH
;
Li, YM
Silicon on insulator (SOI) devices have been of great interest in these years. In this paper, simulation with density-gradient transport model is performed to examine the variation of threshold voltage (VTH) for double gate SOI MOSFETs. Different thickness of silicon (Si) film, oxide thickness, channel length and doping concentration are considered in this work. According to the numerical study, both drift-difftision (DD) and density gradient (DG) models demonstrate that the thickness of Si film greatly affects the threshold voltage (5 similar to 15% variation). It is found that the thickness of Si film decreases, VTH variation increases; and the dependence relation is nonlinear. Therefore, this effect must be taken into account for the realization of double gate SOI ULSI circuit.
A three-dimensional simulation of electrostatic characteristics for carbon nanotube array field effect transistors
(2005-08-01)
Li, YM
;
Chou, HM
;
Lee, JW
;
Lee, BS
;
電子物理學系
We, in this paper, study the electrostatic characteristics and the gate capacitances for carbon nanotube (CNT) array field effect transistors (FETs). The explored CNT-array FET is with three configurations of gate electrode, the top gate, the wrap around gate, and the bottom gate. Taking the pitch distance of structures and the gate length of CNT FET into consideration, a three-dimensional (3D) electrostatic simulation are performed by using an adaptive finite volume method, where different gate capacitance are calculated and compared. It is found that there is at least a 20% difference in calculating the gate capacitance between the 2D and 3D modeling and simulations. Our 3D simulation shows that a wrap around gate gives the largest gate capacitance among structures. A bottom gate possesses the weakest gate controllability. Effects of the pitch distance and the gate length on the gate capacitances of CNT-array FET are investigated. Results of the 3D electrostatic simulations can be applied to estimate the magnitude of the on-current of CNT FETs. (c) 2005 Elsevier B.V. All rights reserved.
A time-domain approach to simulation and characterization of RF HBT two-tone intermodulation distortion
(2003-10-01)
Huang, KY
;
Li, YM
;
Lee, CP
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
In this paper, we evaluate the two-tone intermodulation distortion for heterojunction bipolar transistors (HBTs) operated at RF. We directly solve the nonlinear differential equations of the HBT large-signal model in time domain by employing the waveform-relaxation and monotone-iterative methods. Based on time-domain results, sinusoidal waveform outputs are transformed into the frequency domain with the fast Fourier transform. Furthermore, the output third-order intercept-point values of the HBT are computed with the spectra. Results for a fabricated InGaP HBT under different testing conditions are reported and compared among the HSPICE results, the results with harmonic balance methodology, and the measured data. Comparisons among these results show that our method demonstrates its superiority over the conventional approaches. This characterization alternative has allowed us to study RF device properties, perform thermal consumption and sensitivity analysis, and extract model parameters.
A two-dimensional quantum transport simulation of nanoscale double-gate MOSFETs using parallel adaptive technique
(2004-07-01)
Li, YM
;
Yu, SM
;
奈米中心
;
友訊交大聯合研發中心
;
Nano Facility Center
In this paper we apply a parallel adaptive solution algorithm to simulate nanoscale double-gate metal-oxide-semiconductor field effect transistors (MOSFETs) on a personal computer (PC)-based Linux cluster with the message passing interface (MPI) libraries. Based on a posteriori error estimation, the triangular mesh generation, the adaptive finite volume method, the monotone iterative method, and the parallel domain decomposition algorithm, a set of two-dimensional quantum correction hydrodynamic (HD) equations is solved numerically on our constructed cluster system. This parallel adaptive simulation methodology with 1-irregular mesh was successfully developed and applied to deep-submicron semiconductor device simulation in our recent work. A 10 nm n-type double-gate MOSFET is simulated with the developed parallel adaptive simulator. In terms of physical quantities and refined adaptive mesh, simulation results demonstrate very good accuracy and computational efficiency. Benchmark results, such as load-balancing, speedup, and parallel efficiency are achieved and exhibit excellent, parallel performance. On a 16 nodes PC-based Linux cluster, the maximum difference among CPUs is less than 6%. A 12.8 times speedup and 80% parallel efficiency are simultaneously attained with respect to different simulation cases.
A unified quantum correction model for nanoscale single- and double-gate MOSFETs under inversion conditions
(2004-08-01)
Li, YM
;
Yu, SM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
In this paper a unified quantum correction charge model for nanoscale single- and double-gate MOS structures is presented. Based on the numerical solution of Schrodinger-Poisson equations, the developed quantum correction charge model is mainly optimized with respect to (i) the left and right positions of the charge concentration peak, (ii) the maximum of the charge concentration, (iii) the total inversion charge sheet density, and (iv) the average inversion charge depth, respectively. For nanoscale single- and double-gate MOS structures, this model predicts inversion layer electron density for various oxide thicknesses, silicon film thicknesses, and applied voltages. Compared to the Schrodinger-Poisson results, our model prediction is within 2.5% of accuracy for both the single- and double gate MOS structures on average. This quantum correction model has continuous derivatives and is therefore amenable to a device simulator.