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Now showing 1 - 10 of 113

Tuning of the electron g factor in defect-free GaAs nanodisks
(2015-12-15)
Yang, Li-Wei
;
Tsai, Yi-Chia
;
Li, Yiming
;
Higo, Aiko
;
Murayama, Akihiro
We theoretically study the impact of changes in surroundings on the electron ground-state effective g factor in defect-free GaAs/AlGaAs nanodisks. To perform the study, we formulate and deploy a computational efficient full three-dimensional model to describe the effective g-factor tensor in semiconductor nano-objects of complex geometry and material content. This model is based on an effective 2 x 2 conduction-band Hamiltonian which includes the Rashba and Dresselhaus spin-orbit couplings. The description is suited to clarify the important question of the controllability of the electron effective g factor in semiconductor nano-objects. The results of this theoretical study suggest that in the defect-free GaAs/AlGaAs nanodisks, the effective g factor can be tuned within a wide range by proper design of the nanodisk environment. The zz components of the electron effective g-factor tensor obtained in our simulation are in good agreement with some recent experimental observations.
Electrical characteristic fluctuation of 16-nm-gate trapezoidal bulk FinFET devices with fixed top-fin width induced by random discrete dopants
(2015-03-11)
Huang, Wen-Tsung
;
Li, Yiming
;
電機工程學系
;
電信工程研究所
;
Department of Electrical and Computer Engineering
In this work, we use an experimentally calibrated 3D quantum mechanically corrected device simulation to study the random dopant fluctuation (RDF) on DC characteristics of 16-nm-gate trapezoidal bulk fin-type field effect transistor (FinFET) devices. The fixed top-fin width, which is consistent with the realistic process by lithography, of trapezoidal bulk FinFET devices is considered in this study. For RDF on trapezoidal bulk FinFETs under the fixed top-fin width, we explore the impact of geometry and RDF on the on-/off-state current and the threshold voltage (V-th) fluctuation with respect to different channel fin angles. For the same channel doping concentration, compared with an ideal FinFET (i.e., device with a right angle of channel fin), the off-state current is large in trapezoidal bulk FinFETs with a small fin angle. Furthermore, the short-channel effect and V-th variation degrade as the fin angle is getting smaller. The magnitude of the normalized sigma V-th increases 7% when the fin angle decreases from 90 degrees to 70 degrees.
Simulation study of 14-nm-gate III-V trigate field effect transistor devices with In1-xGaxAs channel capping layer
(2015-06-01)
Huang, Cheng-Hao
;
Li, Yiming
;
電機工程學系
;
電信工程研究所
;
Department of Electrical and Computer Engineering
In this work, we study characteristics of 14-nm-gate InGaAs-based trigate MOSFET (metal-oxide-semiconductor field effect transistor) devices with a channel capping layer. The impacts of thickness and gallium (Ga) concentration of the channel capping layer on the device characteristic are firstly simulated and optimized by using three-dimensional quantum-mechanically corrected device simulation. Devices with In1-xGaxAs/In0.53Ga0.47As channels have the large driving current owing to small energy band gap and low alloy scattering at the channel surface. By simultaneously considering various physical and switching properties, a 4-nm-thick In0.68Ga0.32As channel capping layer can be adopted for advanced applications. Under the optimized channel parameters, we further examine the effects of channel fin angle and the work-function fluctuation (WKF) resulting from nano-sized metal grains of NiSi gate on the characteristic degradation and variability. To maintain the device characteristics and achieve the minimal variation induced by WKF, the physical findings of this study indicate a critical channel fin angle of 85 degrees is needed for the device with an averaged grain size of NiSi below 4x4 nm(2). (C) 2015 Author(s).
Electrical characteristic fluctuation of 16-nm-gate high-kappa/metal gate bulk FinFET devices in the presence of random interface traps
(2014-11-25)
Hsu, Sheng-Chia
;
Li, Yiming
;
傳播研究所
;
電機資訊學士班
;
Institute of Communication Studies
In this work, we study the impact of random interface traps (RITs) at the interface of SiOx/Si on the electrical characteristic of 16-nm-gate high-kappa/metal gate (HKMG) bulk fin-type field effect transistor (FinFET) devices. Under the same threshold voltage, the effects of RIT position and number on the degradation of electrical characteristics are clarified with respect to different levels of RIT density of state (D-it). The variability of the off-state current (I-off) and drain-induced barrier lowering (DIBL) will be severely affected by RITs with high D-it varying from 5 x 10(12) to 5 x 10(13) eV(-1) cm(-2) owing to significant threshold voltage (V-th) fluctuation. The results of this study indicate that if the level of D-it is lower than 1 x 10(12) eV(-1) cm(-2), the normalized variability of the on-state current, I-off, V-th, DIBL, and subthreshold swing is within 5%.
Finite element analysis of antireflective silicon nitride sub-wavelength structures for solar cell applications
(2010-10-01)
Lee, Huang-Ming
;
Sahoo, Kartika Chandra
;
Li, Yiming
;
Wu, Jong-Ching
;
Chang, Edward Yi
We numerically calculate the spectral reflectivity of the silicon nitride (Si(3)N(4)) sub-wavelength structure (SWS) using a two-dimensional finite element simulation. The geometry-dependent effective reflectance of the Si(3)N(4) SWS over the wavelength ranging from 400 nm to 1000 nm is examined and the structure of Si(3)N(4) SWS is further optimized for the lowest effective reflectance. A p-n junction solar cell efficiency based on the optimized Si(3)N(4) SWS is also calculated, resulting in an improvement of 0.98% in efficiency than that of single layer antireflection coatings. (C) 2010 Elsevier B.V. All rights reserved.
Shape Effect of Silicon Nitride Subwavelength Structure on Reflectance for Silicon Solar Cells
(2010-10-01)
Sahoo, Kartika Chandra
;
Li, Yiming
;
Chang, Edward Yi
;
材料科學與工程學系
;
電機工程學系
In this paper, we, for the first time, examine the spectral reflectivity of hemisphere-, cone-, cylinder-, and parabola-shaped silicon nitride (Si(3)N(4)) subwavelength structures (SWSs). A multilayer rigorous coupled-wave approach is advanced to evaluate the reflection properties of Si(3)N(4) SWSs. We optimize the aforementioned four different shapes of SWSs in terms of effective reflectance over a range of wavelength. The results of our paper show that a lowest effective reflectivity could be achieved for the optimized cone-shaped SWS as compared to hemisphere-, parabola-, and cylinder-shaped structures with the same volume. The best shape SWS is then fabricated together with a silicon (Si) solar cell, and the efficiency of the solar cell is compared with that of a solar cell with single-layer antireflection coating (ARC). An increase of 1.09% in cell efficiency (eta) is observed for the Si solar cell with a cone-shaped Si(3)N(4) SWS (eta = 12.86%) as compared with the cell with single-layer Si(3)N(4) ARCs (eta = 11.77%).
Novel Metamorphic HEMTs With Highly Doped InGaAs Source/Drain Regions for High Frequency Applications
(2010-10-01)
Sahoo, Kartika Chandra
;
Kuo, Chien-I
;
Li, Yiming
;
Chang, Edward Yi
;
傳播研究所
In this paper, we report the first result of a strained In(0.52)Ga(0.48) As channel high-electron mobility transistor (HEMT) featuring highly doped In(0.4)Ga(0.6) As source/drain (S/D) regions. A lattice mismatch of 0.9% between In(0.52)Ga(0.48) As and In(0.4)Ga(0.6) As S/D has resulted in a lateral strain in the In(0.52)Ga(0.48) As channel region, where the series resistance is reduced with highly doped S/D regions. An experimentally validated device simulation is advanced for the proposed HEMT, and the results of this paper have shown that there are 60% drive-current and 100% transconductance improvements, compared with the conventional structure. A remarkable 150-GHz increase in the cutoff frequency has been seen for the proposed structure over the conventional one as well for the shown devices.
Statistical Simulation of Static Noise Margin Variability in Static Random Access Memory
(2010-11-01)
Li, Yiming
;
Cheng, Hui-Wen
;
Han, Ming-Hung
;
傳播研究所
;
電機工程學系
In this paper, we examine the impact of random-dopant-fluctuation (RDF), process-variation-effect (PVE), and workfunction-fluctuation (WKF), on 16-nm-gate metal-oxide-semiconductor field-effect-transistor (MOSFET) static random access memory (SRAM) cells. For planar MOSFETs with a threshold voltage (V(th)) of 140mV, the nominal static noise margin (SNM) of six-transistor (6T)-SRAM with unitary cell ratio (CR) is only 20mV; and the normalized SNM fluctuations (SNM) induced by RDF, PVE, and WKF are 80%, 31%, and 48%, respectively, which may damage SRAM's operation. Two improvement approaches are further implemented; first, eight-transistor (8T)-SRAM and 6T-SRAM with increased CR are examined. Compared with the conventional 6T-SRAM, under the same Vth, the SNM of 8T-SRAM is enlarged to 233 mV and the corresponding RDF, PVE, and WKF-induced SNM are reduced to 9.5%, 6.4%, and 7%, respectively, at a cost of 30% extra chip area. Without increasing chip area, device with raised Vth, doping profile engineering and using silicon-on-insulator fin-type field-effect transistors (SOI FinFETs) are further advanced. The 6T SOI FinFETs SRAM exhibits the smallest sigma SNM, with merely 5.3%, 1.2%, and 2.3%, resulting from RDF, PVE, and WKF, respectively, where the value of SNM is equal to 125 mV.
Field emission property of carbon nanotube field emitters in triode structure fabricated with anodic aluminum oxide templates
(2008-04-01)
Li, Yiming
;
Cheng, Hui-Wen
;
Lin, Chen-Chun
;
Pan, Fu-Ming
;
材料科學與工程學系
In this work, we study the field emission (FE) properties of carbon nanotubes (CNTs) field emitters in the triode structure fabricated with anodic aluminum oxide (AAO) template. To obtain the self-consistent solution, a set of Maxwell's equations coupling with Lorentz equation are solved simultaneously using finite difference time domain (FDTD) particle-in-cell (PIC) method. The FE current is then computed with the Fowler-Nordheim equation. To validate our simulation model, we firstly calibrate the collected electron current density between the measurement data of fabricated AAO-CNTs and simulation result. We find that the high density of CNTs will result in large screening effect among adjacent emitters and reduce the strength of electric field. Consequently, it significantly affects the collected emission current density. Our prediction shows that more than three-order magnitude difference on the collected emission current density could be observed when the spacing between CNTs is decreased from 0.7 to 0.233 mu m for the explored structure with the diameter of 7 mu m. Effects of random heights and thickness of oxide on the FE property of structure are also discussed.
Analysis of field emission of fabricated nanogap in Pd strips for surface conduction electron-emitter displays
(2008-04-01)
Lo, Hsiang-Yu
;
Li, Yiming
;
Tsai, Chih-Hao
;
Pan, Fu-Ming
;
材料科學與工程學系
We study the field emission (FE) property of a nanometer-scale gap structure in a palladium strip, which was fabricated by hydrogen absorption under high-pressure treatment. A vigorous cracking process could be accompanied by extensive atomic migration during the hydrogen treatment. A three-dimensional finite-difference time-domain particle-in-cell method is adopted to simulate the electron emission in a surface-conduction electron-emitter display (SED) device. Examinations of conducting characteristics, FE efficiency, the local field around the emitter, and the current density on the anode plate with one FE emitter are conducted. The image of a light spot is successfully produced on a phosphor plate, which implies that the explored electrode with nanometer separation possesses a potential SED application. Experimental observation and numerical simulation show that the proposed structure can be used as a surface conduction electron emitter and has a high FE efficiency with low turn-on voltage and a different electron emission mechanism. This study benefits the advanced SED design for a new type of electron source.

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