Browsing by Author "Wu, Yu-Sheng"

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A Closed-Form Quantum "Dark Space" Model for Predicting the Electrostatic Integrity of Germanium MOSFETs With High-k Gate Dielectric
(2012-03-01)
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper provides a closed-form model of the "dark space (DS)" for Ge MOSFETs with high-k gate dielectrics. This model shows accurate dependences on barrier height, surface electric field, and quantization effective mass of the channel and gate dielectric. Our model predicts that the surface DS due to quantum confinement decreases with reverse substrate bias and increasing channel doping. Our model can be also used for devices with a steep retrograde doping profile. This physically accurate model will be crucial to the prediction of the subthreshold swing and electrostatic integrity of advanced Ge devices.
Analytical Quantum-Confinement Model for Short-Channel Gate-All-Around MOSFETs Under Subthreshold Region
(2009-11-01)
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper presents an analytical model for quantum-confinement effects in short-channel gate-all-around (GAA) MOSFETs under the subthreshold region. Our analytical model accurately predicts the impact of short-channel effects and doping concentration on the quantum-confinement effects. This scalable quantum-confinement model is crucial to the ultrascaled GAA MOSFET design.
Comparison of 4T and 6T FinFET SRAM Cells for Subthreshold Operation Considering Variability-A Model-Based Approach
(2011-03-01)
Fan, Ming-Long
;
Wu, Yu-Sheng
;
Hu, Vita Pi-Ho
;
Hsieh, Chien-Yu
;
Su, Pin
This paper investigates the cell stability of recently introduced four-transistor (4T) and conventional six-transistor (6T) fin-shaped field-effect transistor static random access memory (SRAM) cells operating in a subthreshold region using an efficient model-based approach to consider the impact of device variations. Compared with the 6T cell, this paper indicates that 4T SRAM cells exhibit a better nominal READ static noise margin (RSNM) because of the reduced READ disturb. For 4T cells, the nearly ideal values of V(write, 0) and V(write, 1) guarantee the positive nominal WRITE static noise margin (WSNM) for selected cells. For half-selected cells on the selected bit line, a sufficient margin is observed between WRITE time (for selected cells) and WRITE disturb (for half-selected cells). Using the established model-based approach, the variability of subthreshold 6T and 4T SRAM cells is assessed with 1000 samples. Our results indicate that the 4T driverless cell with a larger mu RSNM and a slightly worse sigma RSNM shows a comparable mu/sigma ratio in RSNM with the 6T cell. Furthermore, for a given cell area, 4T SRAM cells using relaxed device dimensions with reduced sigma RSNM can outperform the 6T cell. For WRITE operation, 4T SRAM cells exhibit a superior WSNM, whereas the design margin between WRITE time and WRITE disturb needs to be carefully examined to ensure an adequate margin considering device variability.
Design and Analysis of Ultra-Thin-Body SOI Based Subthreshold SRAM
(2009)
Hu, Vita Pi-Ho
;
Wu, Yu-Sheng
;
Fan, Ming-Long
;
Su, Pin
;
Chuang, Ching-Te
This paper analyzes the stability, margin, and performance of Ultra-Thin-Body (UTB) SOI 6T/8T SRAM cells operating in subthreshold region. An analytical SNM model for UTB SOI 6T/8T SRAM cells operating in the subthreshold region is presented to investigate the Read SNM (RSNM) and Write SNM (WSNM). Our results indicate that back-gating technique is more effective in the subthreshold region than in the superthreshold region for improving RSNM and WSNM. The UTB SOI 6T SRAM cell with back-gating technique to increase the strength of the pull-up transistors and decrease the strength of the pass-gate transistors shows comparable RSNM in the subthreshold region with the 10T bulk subthreshold SRAM cell and an improvement in RSNM variation. Due to better electrostatic integrity, back-gating technique (pull-up PFET with positive back-gate bias, pull-down/pass-gate NFET's with negative back-gate bias) mitigates the 6T UTB SOI SRAM RSNM variation significantly with some improvement in RSNM. Increasing cell beta-ratio shows limited improvement on RSNM and has no benefit on SNM variability for subthreshold operation. The UTB SOI 8T SRAM cell exhibits RSNM 2X larger than the 6T SRAM cell in the subthreshold region. Mixed-mode device/circuit simulations show that 6T/8T UTB SOI SRAMs operating in the subthreshold region can meet/support the stability, leakage/density, and frequency requirements for intended application space of subthreshold SRAMs.
Fabrication and characteristics of a GaN-based microcavity laser with shallow etched mesa
(2014-06-01)
Lai, Ying-Yu
;
Chou, Yu-Hsun
;
Wu, Yu-Sheng
;
Lan, Yu-Pin
;
Lu, Tien-Chang
In this work, we have developed a simple GaN-based microcavity (MC) with an intracavity shallow etched mesa. The textured GaN-based MC incorporated two high-reflectivity dielectric Bragg mirrors and an InGaN/GaN multiple quantum well with a shallow etched mesa as an optical confined structure. Lasing and transverse optical confinement characteristics have been verified by measuring devices with different mesa diameters. A quality factor (Q) of 2600 and a threshold energy of 30 nJ have been observed in a 10-mu m-diameter device. Such a cavity structure could be implanted into electrically pumped GaN vertical-cavity surface-emitting lasers for supporting efficient transverse confinement. (C) 2014 The Japan Society of Applied Physics
Fabrication and characteristics of a GaN-based microcavity laser with shallow etched mesa
(2014-06-01)
Lai, Ying-Yu
;
Chou, Yu-Hsun
;
Wu, Yu-Sheng
;
Lan, Yu-Pin
;
Lu, Tien-Chang
In this work, we have developed a simple GaN-based microcavity (MC) with an intracavity shallow etched mesa. The textured GaN-based MC incorporated two high-reflectivity dielectric Bragg mirrors and an InGaN/GaN multiple quantum well with a shallow etched mesa as an optical confined structure. Lasing and transverse optical confinement characteristics have been verified by measuring devices with different mesa diameters. A quality factor (Q) of 2600 and a threshold energy of 30 nJ have been observed in a 10-mu m-diameter device. Such a cavity structure could be implanted into electrically pumped GaN vertical-cavity surface-emitting lasers for supporting efficient transverse confinement. (C) 2014 The Japan Society of Applied Physics
Impact of Quantum Confinement on Backgate-Bias Modulated Threshold-Voltage and Subthreshold Characteristics for Ultra-Thin-Body GeOI MOSFETs
(2012-07-01)
Yu, Chang-Hung
;
Wu, Yu-Sheng
;
Hu, Vita Pi-Ho
;
Su, Pin
;
電子工程學系及電子研究所
This paper investigates the impact of quantum confinement (QC) on the backgate-bias (V-bg) modulated subthreshold and threshold-voltage (V-th) characteristics of ultra-thin-body germanium-on-insulator (UTB GeOI) MOSFETs using an analytical solution of the Schrodinger equation verified with TCAD numerical simulation. Our study indicates that the QC effect reduces the sensitivity of the subthreshold swing to V-bg. In addition, the sensitivity of V-th to V-bg can be enhanced by the QC effect particularly for electrostatically well-behaved UTB MOSFETs with triangular potential well. Aside from that, the sensitivity of V-th roll-off to V-bg is reduced by the QC effect. Since Ge and Si channels exhibit different degrees of QC due to different quantization effective mass, the impact of QC has to be considered when one-to-one comparisons between GeOI and SOI MOSFETs regarding the backgate-bias modulated threshold-voltage and subthreshold characteristics are made. Our study may provide insights for multi-V-th device/circuit designs using advanced UTB GeOI technologies.
Impact of Quantum Confinement on Short-Channel Effects for Ultrathin-Body Germanium-on-Insulator MOSFETs
(2011-01-01)
Wu, Yu-Sheng
;
Hsieh, Hsin-Yuan
;
Hu, Vita Pi-Ho
;
Su, Pin
;
電子工程學系及電子研究所
This letter investigates the impact of quantum confinement (QC) on the short-channel effect (SCE) of ultrathin-body (UTB) and thin-buried-oxide germanium-on-insulator (GeOI) MOSFETs using an analytical solution of Schrodinger equation verified with TCAD simulation. Our study indicates that, although the QC effect increases the threshold voltage (V(th)) roll-off when the channel thickness (T(ch)) is larger than a critical value (T(ch,crit)), it may decrease the V(th) roll-off of GeOI MOSFETs when the T(ch) is smaller than T(ch,crit). Since Ge and Si channels exhibit different degrees of confinement and T(ch,crit), the impact of QC must be considered when one-to-one comparisons between UTB GeOI and Si-on-insulator MOSFETs regarding the SCE are made.
Impact of Quantum Confinement on Subthreshold Swing and Electrostatic Integrity of Ultra-Thin-Body GeOI and InGaAs-OI n-MOSFETs
(2012-03-01)
Yu, Chang-Hung
;
Wu, Yu-Sheng
;
Hu, Vita Pi-Ho
;
Su, Pin
;
電子工程學系及電子研究所
This paper investigates the electrostatic integrity (EI) of ultra-thin-body (UTB) germanium-on-insulator (GeOI) and InGaAs-OI n-MOSFETs considering quantum confinement (QC) using a derived analytical solution of Schrodinger equation verified with TCAD numerical simulation. Although the electron conduction path of the high-mobility channel device can be far from the frontgate interface due to high channel permittivity, our study indicates that the quantum confinement effect can move the carrier centroid toward the frontgate and, therefore, improve the subthreshold swing (SS) of the UTB device. Since InGaAs, Ge, and Si channels exhibit different degrees of quantum confinement due to different quantization effective mass, the impact of quantum confinement has to be considered when one-to-one comparisons among UTB InGaAs-OI, GeOI, and SOI MOSFETs regarding the subthreshold swing and electrostatic integrity are made.
Impact of Surface Orientation on the Sensitivity of FinFETs to Process Variations-An Assessment Based on the Analytical Solution of the Schrodinger Equation
(2010-12-01)
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper investigates the impact of surface orientation on V(th) sensitivity to process variations for Si and Ge fin-shaped field-effect transistors (FinFETs) using an analytical solution of the Schrodinger equation. Our theoretical model considers the parabolic potential well due to short-channel effects and, therefore, can be used to assess the quantum-confinement effect in short-channel FinFETs. Our study indicates that, for ultrascaled FinFETs, the importance of channel thickness (t(ch)) variations increases due to the quantum-confinement effect. The Si-(100) and Ge-(111) surfaces show lower V(th) sensitivity to the t(ch) variation as compared with other orientations. On the contrary, the quantum-confinement effect reduces the V(th) sensitivity to the L(eff) variation, and Si-(111) and Ge-(100) surfaces show lower V(th) sensitivity as compared with other orientations. Our study may provide insights for device design and circuit optimization using advanced FinFET technologies.
Investigation of Cell Stability and Write Ability of FinFET Subthreshold SRAM Using Analytical SNM Model
(2010-06-01)
Fan, Ming-Long
;
Wu, Yu-Sheng
;
Hu, Vita Pi-Ho
;
Su, Pin
;
Chuang, Ching-Te
In this paper, the static noise margin (SNM) of FinFET static random access memory (SRAM) cells operating in the subthreshold region was investigated using an analytical solution of 3-D Poisson's equation. An analytical SNM model for subthreshold FinFET SRAM was demonstrated and validated by 3-D technology computer-aided design (TCAD) mixed-mode simulations. When compared with bulk SRAM, the standard 6T FinFET cell showed larger nominal READ SNM (RSNM), better variability immunity, and lesser temperature sensitivity of cell stability. Furthermore, examination of the stabilities of several novel independently controlled gate FinFET SRAM cells by using the proposed SNM model showed significant nominal RSNM improvements in these novel cells. However, the write ability is found to be degraded, which thus becomes an important concern for certain configurations in the subthreshold region. The result obtained indicates that the READ/WRITE word line voltage control technique is more effective than transistor sizing in improving the stability and write ability of the FinFET subthreshold SRAM. Furthermore, the impacts of process-induced variations on cell stability were also assessed. When compared with RSNM, it was found that WRITE SNM is more susceptible to process variations. While 6T is not a viable candidate for subthreshold SRAM, and 8T/10T cells must be used in bulk CMOS, the present analysis established the potential of 6T FinFET cells for subthreshold SRAM applications.
Investigation of electrostatic integrity for ultra-thin-body GeOI MOSFET using analytical solution of Poisson's equation
(2009-04-01)
Hu, Vita Pi-Ho
;
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrostatic integrity for UTB GeOI MOSFETs is examined comprehensively by using an analytical solution of Poisson's equation verified with TCAD simulation. Our results indicate that UTB GeOI MOSFETs with the ratio of channel length (L(g)) to channel thickness (T(ch)) around 5 can show comparable subthreshold swing to that of the SOI counterparts. The impact of the buried oxide thickness (T(BOX)) and back-gate bias (V(back-gate)) on the electrostatic integrity of GeOI devices is also examined.
Investigation of Electrostatic Integrity for Ultra-Thin-Body GeOI MOSFET Using Analytical Solution of Poisson's Equation
(2008)
Hu, Vita Pi-Ho
;
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The electrostatic integrity for UTB GeOI MOSFET is examined comprehensively by using analytical solution of Poisson's equation verified with TCAD simulation. Our results indicate that UTB GeOI MOSFETs with the ratio of channel length (L(g)) to channel thickness (T(ch)) around 5 can show comparable subthreshold swing to that of the SOI counterparts. The impact of buried oxide thickness (T(BOX)) and back-gate bias (V(back-gate)) on the electrostatic integrity of GeOI devices are also examined.
Investigation of Electrostatic Integrity for Ultrathin-Body Germanium-On-Nothing MOSFET
(2011-03-01)
Hu, Vita Pi-Ho
;
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper examines the electrostatic integrity of ultrathin-body (UTB) germanium-on-nothing (GeON) MOSFET using theoretically calculated subthreshold swing from the analytical solution of Poisson's equation. Our results indicate that UTB GeON MOSFETs with the ratio of channel length (L(g)) to channel thickness (T(ch)) around 4 can show comparable subthreshold swing to that of the silicon-on-nothing counterparts. The impact of buried insulator (BI) thickness (T(BI)) and BI permittivity on the electrostatic integrity of the UTB germanium channel devices are also examined.
Investigation of random dopant fluctuation for multi-gate metal-oxide-semiconductor field-effect transistors using analytical solutions of three-dimensional Poisson's equation
(2008-04-01)
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This paper investigates the random dopant fluctuation of multi-gate metal-oxide-semi conductor field-effect transistors (MOSFETs) using analytical solutions of three-dimensional (3D) Poisson's equation verified with device simulation. Especially, we analyze the impact of aspect ratio on the random dopant fluctuation in multi-gate devices. Our study indicates that with a given total width, lightly doped fin-type FET (FinFET) shows the smallest threshold voltage (V(th)) dispersion because of its smaller Vth sensitivity to the channel doping. For heavily doped devices, quasi-planar shows smaller V(th) dispersion because of its larger volume. The Vth dispersion caused by random dopant fluctuation may still be significant in the lightly doped channel, especially for tri-gate and quasi-planar devices.
Investigation of scaling for multi-gate MOSFETs using analytical solution of 3-D Poisson's equation
(2007)
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
Investigation of Static Noise Margin of FinFET SRAM Cells in Sub-threshold Region
(2009)
Fan, Ming-Long
;
Wu, Yu-Sheng
;
Hu, Vita Pi-Ho
;
Su, Pin
;
Chuang, Ching-Te
This paper investigates the Static Noise Margin (SNM) of FinFET SRAM cells operating in sub-threshold region using analytical solution of 3D Poisson's equation. An analytical SNM model for sub-threshold FinFET SRAM is demonstrated and validated by TCAD mixed-mode simulations. The stabilities of several novel independently controlled-gate FinFET SRAM cells are examined. Significant nominal RSNM improvements are observed in these novel cells. However, Write-ability is degraded and becomes an important concern for certain configurations in sub-threshold region. Our result indicates that R/W word-line (WL) voltage control technique is more effective than transistor sizing for improving the Write-ability of the FinFET sub-threshold SRAM. While 6T cell is not a viable candidate for sub-threshold SRAM and 8T/10T cells must be used in bulk CMOS, our analysis establishes the feasibility and viability of 6T FinFET cells for sub-threshold SRAM applications.
Investigation of Static Noise Margin of Ultra-Thin-Body SOI SRAM Cells in Subthreshold Region using Analytical Solution of Poisson's Equation
(2009)
Hu, Vita Pi-Ho
;
Wu, Yu-Sheng
;
Fan, Ming-Long
;
Su, Pin
;
Chuang, Ching-Te
This paper investigates the Static Noise Margin (SNM) of Ultra-Thin-Body (UTB) SOI SRAM cells operating in subthreshold region using analytical solution of Poisson's equation validated with TCAD simulations. An analytical SNM model for UTB SOI SRAM cells operating in subthreshold region is presented. Our results indicate that back-gate bias (V(bg)) can mitigate the Read SNM (RSNM) variability of UTB SO[ SRAM cells in the subthreshold region, and the improvement of SNM variability is more significant than superthreshold region. Increasing cell beta-ratio shows limited improvement on RSNM and has no benefit on SNM variability for subthreshold operation. The UTB SOI 8T SRAM cell exhibits RSNM 2X larger than the 6T SRAM cell in subthreshold region.
Investigation of Switching-Time Variations for Nanoscale MOSFETs Using the Effective-Drive-Current Approach
(2010-02-01)
Wu, Yu-Sheng
;
Fan, Ming-Long
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
This letter investigates the impacts of random dopant fluctuation (RDF) and line edge roughness (LER) on the switching-time (ST) variation for nanoscale MOSFETs using the effective-drive-current (I(eff)) approach that decouples the ST variation into transition-charge (Delta Q) and I(eff) variations. Although the RDF has been recognized as the main variation source to the threshold-voltage variation, this letter indicates that the relative importance of LER increases as the ST variation is considered.
Quantum Confinement Effect in Short-Channel Gate-All-Around MOSFETs and Its Impact on the Sensitivity of Threshold Voltage to Process Variations
(2009)
Wu, Yu-Sheng
;
Su, Pin
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We have proposed an analytical model for quantum confinement effects in short-channel Gate-All-Around (GAA) MOSFETs. This model accurately predicts the eigen-energy shift and eigen-function modulation caused by the short channel effects in lightly doped GAA devices. It shows that the threshold voltage (V(th)) variation due to channel diameter variation is larger than that due to channel length variation because of the significant quantum confinement in ultra-scaled devices. Our model indicates that the channel diameter of GAA MOSFETs can be optimized to reduce the V(th) variation,