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Evaluation of Monolithic 3-D Logic Circuits and 6T SRAMs With InGaAs-n/Ge-p Ultra-Thin-Body MOSFETs
(2016-03-01)
Yu, Kuan-Chin
;
Fan, Ming-Long
;
Su, Pin
;
Chuang, Ching-Te
;
電子工程學系及電子研究所
This paper evaluates monolithic 3-D logic circuits and 6T SRAMs composed of InGaAs-n/Ge-p ultra-thin-body MOSFETs while considering interlayer coupling through TCAD mixed-mode model. This paper indicates that monolithic 3-D InGaAs/Ge logic circuits provide equal leakage and better delay performance compared with planar 2-D structure through optimized 3-D layout. The monolithic 3-D InGaAs/Ge 6T SRAMs can simultaneously improve the cell stability and performance through optimized 3-D layout. We suggest two 3-D SRAM layout designs for high performance and low power applications, respectively. Moreover, with optimized 3-D layout designs, InGaAs/Ge logic circuits exhibit larger delay improvement, and the 6T SRAMs exhibit larger read access time and time-to-write improvement compared with Si counterparts.
Analysis of Ultra-Thin-Body SOI Subthreshold SRAM Considering Line-Edge Roughness, Work Function Variation, and Temperature Sensitivity
(2011-09-01)
Hu, Vita Pi-Ho
;
Fan, Ming-Long
;
Su, Pin
;
Chuang, Ching-Te
;
電子工程學系及電子研究所
This paper analyzes stability and variability of ultrathin-body (UTB) SOI subthreshold SRAMs considering line- edge roughness (LER), work function variation (WFV), and temperature sensitivity. The intrinsic advantages of UTB SOI technology versus bulk CMOS technology with regard to the stability and variability of 6T SRAM cells for subthreshold operation are analyzed. Compared with LER, WFV causes comparable threshold voltage variation and much smaller subthreshold swing fluctuation, hence less impact on the UTB SOI subthreshold SRAMs. Even considering LER, the Lg = 40 nm UTB SOI 6T subthreshold SRAM cells still provide sufficient margin (mu RSNM/sigma RSNM > 6 at Vdd = 0.3 similar to 0.4 V) while the bulk subthreshold SRAMs with RDF fail to maintain adequate margin. Increasing temperature will increase the Vread,0 and decrease RSNM because of the degraded subthreshold swing. The RSNM of UTB SOI subthreshold SRAMs showless temperature sensitivity compared with that of bulk subthreshold SRAMs. Due to larger body effect, the back-gating technique is more efficient for the Lg = 40 nm and 25 nm UTB SOI subthreshold SRAMs compared with the bulk counterparts. By using lower threshold voltage devices with dual band-gapwork functions, the Lg = 25 nm UTB SOI subthreshold SRAMs show 31.9% reduction in sigma RSNM and 55% improvement in mu RSNM/sigma RSNM.
Analysis of Single-Trap-Induced Random Telegraph Noise on FinFET Devices, 6T SRAM Cell, and Logic Circuits
(2012-08-01)
Fan, Ming-Long
;
Hu, Vita Pi-Ho
;
Chen, Yin-Nien
;
Su, Pin
;
Chuang, Ching-Te
This paper analyzes the impacts of single-charged-trap-induced random telegraph noise (RTN) on FinFET devices in tied- and independent-gate modes, 6T static random access memory (SRAM) cell stability, and several basic logic circuits. The dependence of RTN on trap location, EOT, and temperature is evaluated through 3-D atomistic TCAD simulation. It is observed that the charged trap located near the bottom of sidewall (gate) interface and in the middle region between the source and drain will result in the most significant impact. EOT scaling and higher operating temperature improve the immunity to RTN. RTN degradation in independent-gate mode and the dependence on the location of the trap and bias-dependent current-conduction path are analyzed. We show that the planar BULK device, with larger subthreshold swing (S.S.) and comparable trap-induced V-T shift, exhibits less nominal RTN degradation than FinFET for traps placed in the worst position. However, the larger variability and surface conduction characteristic of the planar BULK device lead to broader dispersion and larger worst case RTN degradation than the FinFET device with smaller variability and volume conduction. For traps randomly placed across the interface, similar RTN amplitude dispersions are observed for FinFET and planar BULK devices except in the vicinity of distribution tail due to the strong interaction between the charged trap and discrete random dopants in planar BULK devices. For 6T FinFET SRAM cell, the READ static noise margin of 64 possible combinations from trapping/detrapping in each cell transistor is examined. Because of reduced carriers with decreasing supply voltage (V-dd), the importance of RTN on subthreshold cell stability increases. Moreover, the leakage and delay of FinFET inverters, two-way NAND, and two-to-one multiplexer are investigated using 3-D TCAD mixed-mode simulations. The RTN is found to cause similar to 24%-27% and similar to 13%-15% variations in leakage and delay at V-dd = 0.4 V, respectively, for the logic circuits evaluated.
Variability Analysis of Sense Amplifier for FinFET Subthreshold SRAM Applications
(2012-12-01)
Fan, Ming-Long
;
Hu, Vita Pi-Ho
;
Chen, Yin-Nien
;
Su, Pin
;
Chuang, Ching-Te
This paper investigates the impact of intrinsic random variability on the robustness of sense amplifier (SA) for fin-shaped field-effect transistor (FinFET) subthreshold static random access memory (SRAM) applications. We employ a model-assisted statistical approach to consider both fin line edge roughness (fin LER) and work function variation, which are regarded as the major variation sources in an advanced FinFET device. Our results indicate that fin LER dominates the overall variability of subthreshold SA robustness and sensing margin. In addition, it is observed that the offset voltage (V-OS) of current latch SA calculated solely from threshold voltage (V-T) mismatch underestimates the actual variation and is shown to be optimistic. For large-signal single-ended inverter sensing, we find that sense "0" hinders the allowable sensing margin and needs to be carefully designed. Compared with bulk CMOS, the superior electrostatic integrity and variability of FinFET enhance the feasibility of differential sensing in subthreshold SRAM applications.
Ultra-Low Voltage Mixed TFET-MOSFET 8T SRAM Cell
(2014-01-01)
Chen, Yin-Nien
;
Fan, Ming-Long
;
Hu, Vita Pi-Ho
;
Su, Pin
;
Chuang, Ching-Te
In this work, we propose a mixed TFET-MOSFET 8T SRAM cell comprising MOSFET cross-coupled inverters, dedicated TFET read stack and TFET write access transistors. Exploiting both the merits of TFET and MOSFET devices, the proposed SRAM cell provides significant improvement in SRAM stability, V-min and performance. The proposed cell is evaluated and compared with the conventional MOSFET 8T cell and pure TFET 8T cell using mixed mode TCAD simulations. The results indicate that the proposed mixed TFET-MOSFET cell topology is viable for ultra-low voltage operation.
Investigation and Simulation of Work-Function Variation for III-V Broken-Gap Heterojunction Tunnel FET
(2015-05)
Hsu, Chih-Wei
;
Fan, Ming-Long
;
Hu, Vita Pi-Ho
;
Su, Pin
;
電子工程學系及電子研究所
This paper investigates and compares the impacts of metal-gate work-function variation (WFV) on III-V heterojunction tunnel FET (HTFET), homojunction TFET, and FinFET devices using a novel Voronoi method to capture the realistic metal-gate grain patterns for Technology Computer Aided Design atomistic simulations. Due to the broken-gap nature, HTFET shows significantly steeper subthreshold slope and higher susceptibility to WFV near OFF state. For ON current variation, both the HTFET and homojunction TFET show better immunity to WFV than the III-V FinFET. Device design using source-side underlap to mitigate the impact of WFV on HTFET is also assessed.
Impacts of Work Function Variation and Line-Edge Roughness on TFET and FinFET Devices and Logic Circuits
(2014)
Chen, Chien-Ju
;
Chen, Yin-Nien
;
Fan, Ming-Long
;
Hu, Vita Pi-Ho
;
Su, Pin
In this paper, we analyze the variability of III-V homojunction tunnel FET (TFET) and FinFET devices and logic circuits operating in near-threshold region. The impacts of work function variation (WFV) and fin line-edge roughness (fin LER) on TFET and FinFET device Ion, Ioff, Cg, two-way NAND delay, switching energy and leakage power are investigated and compared using 3D atomistic TCAD mixed-mode Monte-Carlo simulations. The results indicate that WFV and fin LER have different impacts on ION and IOFF. The delay variability of two-way NAND is aggravated by the Miller capacitance of TFET and FinFET devices.
Evaluation of TFET and FinFET Devices and 32-Bit CLA Circuits Considering Work Function Variation and Line-Edge Roughness
(2015)
Chen, Chien-Ju
;
Chen, Yin-Nien
;
Fan, Ming-Long
;
Hu, Vita Pi-Ho
;
Su, Pin
In this paper, we comprehensively investigate the impacts of work function variation (WFV) and fin line-edge roughness (fin LER) on III-V homojunction tunnel FET (TFET) and FinFET devices and 32-bit carry-look-ahead adder (CLA) circuits operating in near-threshold region using atomistic 3D TCAD mixed-mode simulations and HSPICE simulations with look-up table based Verilog-A models calibrated with TCAD simulation results. The results indicate that at low operating voltage (<0.3V), the CLA circuit delay and power-delay product (PDP) of TFET are significantly better than FinFET even with the impacts of random variations. As the operating voltage decreases, the performance advantage of TFET CLA becomes more significant due to its better I-on and C-g,C-ave and their smaller variability. However, the leakage power of TFET CLA is larger than FinFET CLA due to the worse I-off variability of TFET devices.
Impacts of NBTI and PBTI on Ultra-Thin-Body GeOI 6T SRAM Cells
(2015)
Hu, Vita Pi-Ho
;
Fan, Ming-Long
;
Su, Pin
;
Chuang, Ching-Te
;
電子工程學系及電子研究所
This paper investigates the impacts of Negative and Positive Bias Temperature Instabilities (NBTI and PBTI) on the stability and performance of Ultra-Thin-Body (UTB) GeOI 6T SRAM cells compared with the SOI counterparts. Worst case stress scenarios for Read and Write operations are analyzed. For UTB GeOI SRAM cells, PBTI dominates the degradations in RSNM, HSNM, cell Read access time, and Time-to-Write, while for UTB SOI SRAM cells, NBTI dominates the degradations in RSNM, HSNM, and Time-to-Write. WSNM only slightly degrades due to NBTI/PBTI. Threshold voltage design and Word-Line Under-Drive (WLUD) Read-Assist techniques are analyzed to compensate the stability degradation due to NBTI/PBTI for UTB GeOI SRAM cells. Compared with the nominal UTB GeOI SRAM cells with low Vth design, UTB GeOI SRAM cells with high Vth design suffer less NBTI/PBTI degradations and exhibit significant improvement in RSNM and HSNM, and comparable performance compared with the nominal UTB SOI SRAM cells.
Evaluation of Monolayer and Bilayer 2-D Transition Metal Dichalcogenide Devices for SRAM Applications
(2016-02-01)
Yu, Chang-Hung
;
Fan, Ming-Long
;
Yu, Kuan-Chin
;
Hu, Vita Pi-Ho
;
Su, Pin
For the first time, we comprehensively evaluate 6T SRAM stability and performance using monolayer and bilayer transition metal dichalcogenide (TMD) devices based on the ITRS 2028 (5.9 nm) node. Our study indicates that, with excellent device electrostatics and superior stability, the monolayer TMD is favored for low-power SRAM applications, while the bilayer TMD, with higher carrier mobility, is more suitable for relaxed channel length and high-performance SRAM applications.

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