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Author: search.filters.author.Wu, Yu-ShengSubject: search.filters.subject.Poisson's equation

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Now showing 1 - 4 of 4
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    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.
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    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.
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    Static Noise Margin of Ultrathin-Body SOI Subthreshold SRAM Cells-An Assessment Based on Analytical Solutions of Poisson's Equation
    (2009-09-01)
    Hu, Vita Pi-Ho
    ;
    Wu, Yu-Sheng
    ;
    Fan, Ming-Long
    ;
    Su, Pin
    ;
    Chuang, Ching-Te
    This paper investigates the static noise margin (SNM) of ultrathin-body (UTB) SOI SRAM 6T/8T cells operating in the subthreshold region using analytical solutions of Poisson's equation validated with TCAD simulations. An analytical framework to calculate the SNM for UTB SOI SRAMs operating in the subthreshold region is presented. Our results indicate that for improving both read SNM (RSNM) and write SNM (WSNM), the back-gating technique is more effective in the subthreshold region than in the superthreshold region. The 6T UTB SOI subthreshold SRAM cell with the back-gating technique by increasing the strength of the pull-up transistors and decreasing the strength of the pass-gate transistors shows comparable RSNM with the 10T bulk subthreshold SRAM and an improvement in RSNM variation. Due to better electrostatic integrity, the back-gating technique (pull-up transistors with positive back-gate bias, pull-down/pass-gate transistors with negative back-gate bias) mitigates the 6T UTB SOI SRAM RSNM variation significantly with some improvement in RSNM. Increasing cell beta-ratio shows a limited improvement on RSNM and has no benefit on the SNM variability for the subthreshold operation. The UTB SOI 8T SRAM cell exhibits RSNM 2 x larger than the 6T SRAM cell in the subthreshold region. Both negative bit-line voltage (VBL) and boosted word-line voltage (VWL) are more effective than lower cell supply voltage to improve WSNM, and negative VBL shows a larger improvement in WSNM than boosted VWL.
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    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.