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SCIENCE CHINA Information Sciences, Volume 62, Issue 6: 062404(2019) https://doi.org/10.1007/s11432-018-9429-2

Short-channel effects on the static noise margin of 6T SRAM composed of 2D semiconductor MOSFETs

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  • ReceivedJan 15, 2018
  • AcceptedMar 27, 2018
  • PublishedJan 18, 2019

Abstract

This paper investigates the influence of the short-channel effects (SCEs) on the static noise margin (SNM) of 6T (6 transistors) SRAM composed of 2D MOSFETs. An analytical all-region I-Vmodel for short-channel complementary 2D MOSFETs has been developed, and a simulation model has been built to calculate SNM with the consideration of SCEs and velocity saturation. The results show that there exists an optimal value of channel length ($L_{\rm~opt}$ where SNM reaches a maximum, and $L_{\rm~opt}$is approximately three times the scale length. In the region where ${L}>~{L_{\rm~opt}}$, SNM increases slightly as Ldecreases because of velocity saturation, while in the region where ${L}<~{L_{\rm~opt}}$, SNM decreases rapidly as Ldecreases as the SCEs are dominant. The worst case of SNM reduction due to the threshold voltage ($V_T$) fluctuation is investigated, and the maximum $V_T$tolerance is studied as a function of L. In an SRAM with a scale length of 5 nm, as Ldecreases from 15 nm to 5 nm, SNM decreases from 155 mV to 98 mV, and the maximum $V_T$tolerance decreases from 126 mV to 105 mV.


Acknowledgment

This work was supported by Applied Basic Research Programs of Science and Technology Department of Sichuan Province, China (Grant No. M110103012016JY0044).


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  • Figure 1

    (Color online) Structure of 2D DG MOSFET.

  • Figure 2

    (Color online) (a) The $I_{\rm~sd}$-$V_{\rm~gs}$ characteristic for P-type 2D DG MOSFETs ($L_{\rm~g}$= 5 nm, W= 5 nm, $V_{\rm~sd}$= 0.7 V); (b) the $I_{\rm~ds}$-$V_{\rm~gs}$ characteristic for N-type 2D DG MOSFETs ($L_{\rm~g}$= 5 nm, W= 5 nm, $V_{\rm~ds}$=0.7 V).

  • Figure 3

    (Color online) (a) $I_{\rm~ds}$-$V_{\rm~gs}$characteristic of N-type 2D DG MOSFET with different channel lengths; (b) $I_{\rm~ds}$-$V_{\rm~ds}$characteristic with different channel lengths at $V_{\rm~gs}$= 0.25 V; (c) $I_{\rm~ds}$-$V_{\rm~ds}$characteristic with different channel lengths at $V_{\rm~gs}$= 0.7 V. The widths of all devices in the figure are equal to their channel length to normalize the current.

  • Figure 6

    (a) SNM with various channel lengths; (b) comparison of SNM between SRAM cell composed of 2D DG MOSFETS and Si DG MOSFET.

  • Figure 7

    (Color online) (a) SNM curves with the decrease in channel length (velocity saturation is dominant); (b) SNM curves with the decrease in channel length (short-channel effect is dominant).

  • Figure 8

    (Color online) (a) SNM vanishes due to technology fluctuation; (b) maximum threshold voltage tolerance with the change in channel length. The dash lines show the butterfly curves when all the transistors have the same threshold voltage. The solid lines show the occurrence of SNM vanishing.

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