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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.
Transition energies of vertically coupled multilayer nanoscale InAs/GaAs semiconductor quantum dots of different shapes
(2005-04-01)
Li, YM
;
奈米中心
;
Nano Facility Center
The energy spectra of vertically coupled multilayer nanoscale semiconductor quantum dots (QDs) are theoretically studied using a unified three-dimensional (3D) model. The model formulation includes (1) the position-dependent effective mass Hamiltonian in a nonparabolic approximation for electrons, (2) the position-dependent effective mass Hamiltonian in a parabolic approximation for holes, (3) the finite hard wall confinement potential, and (4) Ben Daniel-Duke boundary conditions. To solve a nonlinear problem, a nonlinear iterative method is further improved in our developed 3D QD simulator. At an applied magnetic field (B), we explore the transition energy and the energy band gap of disk (DI), ellipsoid (EL)- and cone (CO)-shaped vertically coupled multilayer nanoscale semiconductor quantum dots. We find that the electron transition energy of vertically coupled rnultilayer InAs/GaAs QDs depends on their shape and is strongly dominated by the number of stacked layers (N). The interdistance (d) among InAs QDs plays a crucial role in the tunable states of these QDs. In DI-shaped vertically coupled 10-layer QDs at B = 0T and d = 1.0nm, we find approximately 40% variation in electron ground state energy, which is larger than that (similar to 20% variation) in CO-shaped QDs. In QDs at a nonzero magnetic field, the electron transition energy decreases with increasing N. In QDs with d = 1nm, the rate of decrease is low when N > 6. This results in QDs,with energy band gaps having similar dependences on N. This study implies different applications in magnetooptical phenomena and quantum optical structures.
Comparison of random-dopant-induced threshold voltage fluctuation in nanoscale single-, double-, and surrounding-gate field-effect transistors
(2006-09-01)
Li, Yiming
;
Yu, Shao-Ming
;
資訊工程學系
;
電信工程研究所
;
Department of Computer Science
In this study, we explore random-dopant-induced threshold voltage fluctuation by solving a quantum correction model. Fluctuation of the threshold voltage for three nanoscale transistors, single-, double-, and surrounding-gate (SG, DG, and AG) metal-oxide-semiconductor field-effect transistors (MOSFETs) are computationally compared. To calculate the variance of the threshold voltages of the SG, DG, and AG MOSFETs, a quantum correction model under equilibrium conditions is expanded and numerically solved using perturbation and monotone iterative methods. Fluctuation of the threshold voltage resulting from the random dopant, gate oxide thickness, channel film thickness, gate channel length, and device width are calculated for the three devices. Quantum mechanical and classical results give similar predictions for fluctuation of the threshold voltage with respect to different parameters including the dimensions of the device and the channel doping. Fluctuation increases when the channel doping concentration, channel film thickness, and gate oxide thickness increase, On the other hand, it decreases when the channel length and device width increase. Calculation results of the quantum correction model are quantitatively higher than those of classical estimation in accordance with different quantum confinement effects in nanoscale SG, DG, and AG MOSFETs. It is found that the AG MOSFET has the smallest threshold voltage fluctuation among the three device structures due to its good channel controllability. In contrast to the conventional quantum Monte Carlo approach and the small-signal analysis of the Schrodinger-Poisson equations, this computationally cost-effective quantum correction approach shows acceptable accuracy and is ready for industrial technology computer-aided design application.
Simulations for the time evolution of instantaneous resonant modes: Creation, annihilation and mode exchange
(2006-11-15)
Wu, Ten-Ming
;
Chang, S. L.
;
Tsay, Shiow-Fon
;
Tsai, K. H.
;
物理研究所
In this paper, we simulate the time evolution of the instantaneous resonant modes (IRMs), which are quasilocalized, in a model of Ga liquid. Through the simulations, we have observed the whole process from creation to annihilation of each individual IRM, and its lifetime is, therefore, estimated. We also find the exchange in character between an IRM and a non-resonant instantaneous normal mode (INM). The exchange occurs as the two INMs have very close frequencies and share a common central particle. (c) 2006 Elsevier B.V. All rights reserved.
Effect of fin angle on electrical characteristics of nanoscale round-top-gate bulk FinFETs
(2007-12-01)
Li, Yiming
;
Hwang, Chih-Hong
;
電信工程研究所
;
Institute of Communications Engineering
In this brief, electrical characteristics of 25-nm round-top-gate fin-typed field-effect transistors (FinFETs) on silicon wafers are numerically explored. With an ideal fin angle (i.e., theta = 90 degrees), the FinFETs with doped and undoped (for this case, the device has a metal gate) channels that was fabricated on silicon and silicon-on-insulator wafers are simulated and compared. With a 3-D quantum-correction-transport simulation, characteristic comparison shows that bulk FinFETs with the undoped channel possess promising electrical characteristics. By considering different short-channel effects, dependence of the device performance on the nonideal fin angle and fin height is further investigated. Optimal structure configuration for the round-top-gate bulk FinFETs is thus drawn to show the strategy of fabrication in sub-25-mn MOSFET devices.
High-Frequency Characteristic Fluctuations of Nano-MOSFET Circuit Induced by Random Dopants
(2008-12-01)
Li, Yiming
;
Hwang, Chih-Hong
;
電信工程研究所
;
Institute of Communications Engineering
As the dimension of semiconductor device shrunk into nanometer scale (nanoscale), characteristic fluctuation is more pronounced, and become crucial for circuit design. In this paper, discrete-dopant-induced characteristic fluctuation of 16-nm-gate metal-oxide-semiconductor field effect transistors (MOSFET) circuit under high-frequency regime is quantitatively studied. The circuit gain, the 3 dB bandwidth and the unity-gain bandwidth of the tested nanoscale transistor circuit are calculated concurrently capturing the discrete-dopant-number- and discrete-dopant-position-induced fluctuations in the large-scale statistically sound "atomistic" device/circuit coupled simulation. For the 16-nm-gate MOSFET circuit, the number of discrete dopants, varying from zero to 14, may result in 5.7% variation of the circuit gain, 14.1% variation of the 3 dB bandwidth, and 10.4% variation of the unity-gain bandwidth. To suppress the high-frequency characteristic fluctuations, an improved doping distribution along the longitudinal diffusion direction from the MOSFET's surface to substrate is further performed to examine the associated fluctuation. The improved vertical doping profile with less dopants locating near surface of channel effectively reduces the fluctuations of the circuit gain, the 3 dB bandwidth and the unity-gain bandwidth dramatically. Compared with the original doping profile, the reduction is 32.3%, 19.4% and 51.8%, respectively. This study provides an insight into random-dopant-induced intrinsic high-frequency characteristic fluctuations and verifies the potential fluctuation suppression technique on high-frequency characteristic fluctuations of nanoscale transistor circuit.

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