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Discrete-dopant-fluctuated threshold voltage roll-off in sub-16 nm bulk fin-type field effect transistors
(2008-04-01)
Li, Yiming
;
Hwang, Chih-Hong
;
電信工程研究所
;
Institute of Communications Engineering
The effect of the number and position of discrete dopants on device characteristics is crucial in determining the behavior of nanoscale semiconductor devices. We explore the fluctuations of threshold voltage (V(th)) roll-off in nanoscale bulk fin-type field effect transistors (FinFETs) by a three-dimensional (3D) statistically full-scale "atomistic" device simulation technique. The explored devices are of three different dimensions: 16, 22, and 30 nm(3). Discrete dopants are statistically positioned into the 3D channel region to explore associated carrier transport characteristics, concurrently capturing "dopant concentration variation" and "dopant position fluctuation". For the device with a gate length of 16 nm, the V(th) fluctuation of FinFETs is only half that of planar metal-oxide-semiconductor (MOS) FET. Compared with planar MOSFETs, the bulk FinFETs can significantly suppress the fluctuation of V(th) roll-off. The standard deviation of V(th) is proportional to (WL)(-0.25), which is better than the (WL)(-0.5) of planar devices. The superior immunity against fluctuation and the stable fluctuation of V(th) roll-off indicate the bulk FinFET to be a promising device for the sub-16 nm technology era.
Modeling of quantum effects for ultrathin oxide MOS structures with an effective potential
(2002-12-01)
Li, YM
;
Tang, TW
;
Wang, XL
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
In this paper, the effectiveness of the effective potential (EP) method for modeling quantum effects in ultrathin oxide MOS structures is investigated. The inversion-layer charge density and MOS capacitance in one-dimensional MOS structures are simulated with various substrate doping profiles and gate bias voltages. The effective mass is used as an adjusting parameter to compare results of the EP model with that of the Schrodinger-Poisson solution. The variation of this optimum parameter for various doping profiles at different gate voltages is investigated. The overestimated average inverse charge depth by the EP method is quantified and its reason explained. The EP model is a good practical simulation tool for modeling quantum effects but more work needs to be done to improve its accuracy near the interface.
Geometric variations and magnetic field effects on electron energy states of InAs/GaAs quantum rings
(2003-04-01)
Li, YM
;
Lu, HM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We study electron energy states in three-dimensional (313) narrow-gap semiconductor quantum rings with ellipsoidal-shape torus (EST) and cut-bottom EST (CBEST) under an applied magnetic field. Our model includes the effective one-electronic-band Hamiltonian, the energy- and position-dependent electron effective mass approximation, and the Ben Daniel-Duke boundary condition. It is solved by the nonlinear iterative method to obtain a "self-consistent" solution numerically. The electron energy dependence on the inner radius, height, and lateral width is investigated for InAs/GaAs quantum rings with EST and CBE T shapes. The height and lateral width play a crucial role in varying the energy spectra of the rings. When the magnetic field is applied on a fixed-size CBEST ring, we find that there is a nonperiodical transition among the lowest electron energy states. Compared with the well-known ID Aharonov-Bohm periodical oscillation, the electron energy levels increase and oscillate nonperiodically when the magnetic field is increased. Our calculation for single-electron magnetization shows that the magnetization is nonperiodical and is a negative function of magnetic field.
Electron transition energy for vertically coupled InAs/GaAs semiconductor quantum dots and rings
(2004-04-01)
Li, YM
;
Lu, HM
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We investigate the transition energy of vertically coupled quantum dots and rings (VCQDs and VCQRs) with a three-dimensional (3D) model under an applied magnetic field. The model formulation includes (1) the position-dependent effective mass Hamiltonian in the nonparabolic approximation for electrons, (2) the position-dependent effective mass Hamiltonian in the parabolic approximation for holes, (3) the finite hard-wall confinement potential, and (4) the Ben Daniel-Duke boundary conditions. We explore small VCQDs and VCQRs with disk (DI) and conical (CO) shapes. For small VCQDs and VCQRs, the electron-hole transition energy is dominated by the interdistance d which plays a crucial role in the tunable states of structures. Under zero magnetic field, there is about 25% variation in the electron ground state energy for both InAs/GaAs DI-shaped VCQDs and VCQRs with d varying from 0.4 nm to 4.8 nm. The energy spectra of the CO-shaped VCQDs are the most stable against the structure interdistance deviations (among dots and rings of the same volume). For a fixed d, VCQDs show diamagnetic shift; contrarily, VCQRs imply a nonperiodical transition among the lowest electron energy states. The energy band gap of VCQRs oscillates nonperiodically between the lowest electron and holes states as a function of external magnetic fields. Our investigation is constructive for studying the magneto-optical phenomena of the nanoscale semiconductor artificial molecules.
Intelligent BSIM4 model parameter extraction for sub-100 nm MOSFET era
(2004-04-01)
Li, YM
;
Cho, YY
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We present. in this paper, an intelligent extraction technique for obtaining a set of optimal model parameters of the Berkeley short-channel insulated gate field effect transistor model 4 (BSIM4) for sub-100nm metal-oxide-semiconductor field effect transistors (MOSFETs). Based on the genetic algorithm (GA), the monotone iterative Levenberg-Marquardt (MI-LM) method, and the neural network (NN) algorithm, this novel approach can perform simultaneous BSIM4 parameter extraction with more than 16 sub-100 nm MOSFETs in a global sense. Before extraction, all input measured I-V data are preprocessed by statistical reduction and sampling procedures. The GA and MI-LM method are then applied to calculate all parameters. The NN algorithm is used to trace the errors of I-V curves and their first derivatives, and also to inspect the variations of physical quantities. Once parameters are found, the postprocess will identify a sensible searching path so that the solution engine continues evolution until parameters reach specified stopping criteria. Good accuracy is obtained for the 90 nm NMOSFETs by several testing cases. Compared with manual fitting processes, this methodology overcomes the conventional inconvenience and is cost-effective in automatic parameter extraction. It bridges device fabrication technology and system-on-a-chip (SOC) design.
Statistical Simulation of Metal-Gate Work-function Fluctuation in High-kappa/Metal-Gate Devices
(2010)
Yu, Chia-Hui
;
Han, Ming-Hung
;
Cheng, Hui-Wen
;
Su, Zhong-Cheng
;
Li, Yiming
In this work, we statistically examine the emerging high-kappa / metal gate work-function fluctuation (WKF) induced threshold voltage (V(th)) fluctuations in 16-nm-gate MOSFET devices. Our Monte-Carlo model extensively evaluates the impact of WKF for different technology node, metal grain size, and gate material. This model provides us to identify suitable materials and fabrication processes that can significantly reduce the impact of Vth fluctuation owing to WKF. First, four kinds of gate material are examined and TiN possesses the smallest Vth fluctuation. For fabrication process, a fast deposition of metal at lower temperature prevents the metal grain not to grow to large size result in a smaller variation. In addition, an idea of modeling multilayer metal gate WKF is also presented and discussed, in which the first layer plays the most important role, compared with other layers, for the fluctuation suppression.
Simulation of electrical characteristics of surrounding- and omega-shaped-gate nanowire FinFETs
(2004)
Tang, CS
;
Yu, SM
;
Chou, HM
;
Lee, JW
;
Li, YM
In this paper, electrical characteristics of sub-10 not nanowire FinFETs are investigated using a three-dimensional (3D) quantum correction simulation. Two different nanowire FinFETs, surrounding-gate FinFET and omega-shaped-gate one, are simulated with density-gradient-based model and compared in terms of on/off current, turn-on resistance, gate capacitance. It is found that the characteristic difference between surrounding-gate FinFET and omega-shaped-gate FinFET with a 70% coverage is insignificant. However, the former possesses better DIBL effect than that latter with different coverage ratios. Our examination presented here is useful in the fabrication of omega-shaped nanowire FinFETs.
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.
Statistical Analysis of Metal Gate Workfunction Variability, Process Variation, and Random Dopant Fluctuation in Nano-CMOS Circuits
(2009)
Hwang, Chih-Hong
;
Li, Tien-Yeh
;
Han, Ming-Hung
;
Lee, Kuo-Fu
;
Cheng, Hui-Wen
This work for the first time estimates the influences of the intrinsic parameter fluctuations consisting of metal gate workfunction fluctuation (WKF), process variation effect (PVE) and random dopant fluctuation (RDF) on 16-nm-gate planar metal-oxide-semiconductor field effect transistors (MOSFETs) and circuits. The WKF and RDF dominate the threshold voltage fluctuation; however, the WKF brings less impact on the gate capacitance due to the screening effect of the inversion layer. The fluctuation of timing characteristics depends on the threshold voltage fluctuation, and therefore is proportional to the trend of threshold voltage fluctuation. For an amplifier circuit, the high-frequency characteristics, the circuit gain, the 3dB bandwidth, the unity-gain bandwidth power, and the power-added efficiency, are explored consequently. Similar to the trend of the cutoff frequency, the PVE and RDF dominate both the device and circuits characteristic fluctuations due to the significant gate capacitance fluctuations and the WKF is less important at this simulation scenario. The extensive study assesses the fluctuations on circuit performance and reliability, which can in turn be used to optimize nanoscale MOSFET and circuits.
Parameterized Display Performances Behavioral Modeling and Optimization for TFT-LCD Panel
(2009)
Huang, Hsuan-Ming
;
Li, Yiming
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we implement a systematical method for thin film transistor liquid-crystal display (TFT-LCD) design optimization and sensitivity analysis. Based upon a three-dimensional (3D) field solver, Simulation Program with Integrated Circuit Emphasis (SPICE), and a Design of Experiments, we construct a second-order response surface model (RSM) for the performances of an interested TFT-LCD panel. The constructed RSMs are reduced using a step-wise regression. The adequacy and accuracy using the normal residual plots and their residual of squares are verified. According to the constructed models, we then analyze the sensitivity of the performances by considering the design parameters as changing factors (i.e., the size variation, position shift and driving setting) under an assumption of Gaussian distribution. We also could apply the models to optimize the designed circuit. The designing parameters of these models are selected and optimized to fit the designing target of the examined circuit by the genetic algorithm in our unified optimization framework. This computational statistics method can predict the TFT-LCD performances and show the engineering practicability in display panel industry.

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