SCIENTIA SINICA Informationis, Volume 49 , Issue 3 : 342-360(2019) https://doi.org/10.1360/N112017-00200

Threshold voltage and DIBL effect analysis and modeling for FD-SOI MOSFET with high k + SiO$_2$ gate

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  • ReceivedOct 13, 2017
  • AcceptedMar 28, 2018
  • PublishedMar 15, 2019


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林志瑗, 杨铨让, 沙玉钧. 电磁场工程基础. 北京: 高等教育出版社, 1984.

\begin{equation}C_{{\rm edge}}=\frac{2\varepsilon}{2\pi}{\rm ln}\frac{2\pi w}{t}=\frac{\varepsilon}{\pi}{\rm ln}\frac{2\pi w}{t}, \tag{33}\end{equation} 式(A1)中$\varepsilon$是介电常数, $w$和$t$分别是栅的宽度和介质材料厚度.因此完整的栅电容是 \begin{equation}C_{{\rm g}}^\prime=\frac{\varepsilon}{\pi}{\rm ln}\frac{2\pi w}{t}+\frac{\varepsilon}{\pi}wl, \tag{34}\end{equation} 式中$l$是栅长度. 单位面积的栅电容是 \begin{equation}C_{{\rm g}}=\frac{C_{{\rm g}}^\prime}{lw}=\varepsilon\bigg[\frac{1}{t}+\frac{1}{lw\pi}{\rm ln}\frac{2\pi w}{t}\bigg], \tag{35}\end{equation} 上式表明单位面积的电容与沟道长度、介电常数、栅宽都有影响. par 下面用式(A3)计算不同介质的单位面积栅长电容. SiO$_2$介电常数是$\varepsilon_{{\rm~ox}}$, 栅介质电容是 \begin{equation}C_{{\rm ox}}=\varepsilon_{{\rm ox}}\bigg[\frac{1}{t_{{\rm ox}}}+\frac{1}{lw\pi}{\rm ln}\frac{2\pi w}{t_{{\rm ox}}}\bigg]=C_0\bigg[1+\frac{t_{{\rm ox}}}{lw\pi}{\rm ln}\frac{2\pi w}{t_{{\rm ox}}}\bigg], \tag{36}\end{equation} 式(A4)中$C_0=\frac{\varepsilon_{{\rm~ox}}}{t_{{\rm~ox}}}$, 是单位面积的平行板栅电容, 称作栅的本征电容. 若用等电容设计, 设高k材料介电常数是$\varepsilon_{{\rm~k}}$, 则有$t_{{\rm~g}}=\frac{\varepsilon_{{\rm~k}}}{\varepsilon_{{\rm~ox}}}t_{{\rm~ox}}$, 高k栅电容是 \begin{equation}C_k=\varepsilon_{{\rm k}}\bigg[\frac{1}{t_{\rm k}}+\frac{1}{\pi lw}{\rm ln}\frac{2\pi w}{t_{\rm k}}\bigg]= C_0\bigg[1+\frac{t_{\rm ox}}{\pi lw}\frac{\varepsilon_{{\rm k}}}{\varepsilon_{{\rm ox}}}\bigg({\rm ln}\frac{2\pi w}{t_{\rm ox}}-{\rm ln}\frac{\varepsilon_{{\rm k}}}{\varepsilon_{{\rm ox}}}\bigg)\bigg]. \tag{37}\end{equation}

高k + SiO$_2$栅的栅电容如图A1所示. $C_{{\rm~k+SiO_2}}$是$C_{{\rm~ox}}^\prime$与$C_{{\rm~k}}^\prime$的串联,等效电容是 \begin{equation}C_{{\rm k+SiO_2}}=\frac{C_{{\rm ox}}^\prime C_{{\rm k}}^\prime}{C_{{\rm ox}}^\prime+C_{{\rm k}}^\prime}. \tag{38}\end{equation}

等效电容设计的MOSFET SiO$_2$层厚度是$t_{{\rm~ox}}$, 令$t_{{\rm~ox}}^\prime=\alpha~t_{{\rm~ox}}~(0\leq\alpha\leq1)$是高k + SiO$_2$栅器件的SiO$_2$层厚度,等效氧化层厚度${\rm~EOT}=(1-\alpha)t_{{\rm~ox}}$, 则有 \begin{align*}& C_{{\rm ox}}^\prime=\varepsilon_{{\rm ox}}\bigg[\frac{1}{\alpha t_{{\rm ox}}}+\frac{1}{\pi lw}\bigg({\rm ln}\frac{2\pi w}{t_{\rm k}}+{\rm ln}\frac{1}{\alpha}\bigg)\bigg], \\ & C_{{\rm k}}^\prime=C_0\bigg[\frac{1}{1-\alpha}+\frac{\varepsilon_{{\rm k}}t_{\rm ox}}{\varepsilon_{{\rm ox}}\pi lw}\bigg({\rm ln}\frac{2\pi w}{t_{\rm ox}}+{\rm ln}\frac{\varepsilon_{{\rm ox}}}{\varepsilon_{{\rm k}}}+\frac{1}{1-\alpha}\bigg)\bigg]. \end{align*} 等效电容计算仅考虑高k材料的影响,故有$C_{{\rm~ox}}^\prime\approx\frac{C_0}{\alpha}$, $C_{{\rm~k}}^\prime\approx~C_0[\frac{1}{1-\alpha}+\frac{\varepsilon_{{\rm~k}}t_{\rm~ox}}{\varepsilon_{{\rm~ox}}\pi~lw}{\rm~ln}\frac{2\pi~w}{t_{\rm~ox}}]$, 式(6)的高k + SiO$_2$栅等效电容为 \begin{equation}C_{{\rm k+SiO_2}}=\frac{C_0\big[\frac{1}{1-\alpha}+\frac{\varepsilon_{{\rm k}}}{\varepsilon_{{\rm ox}}}\frac{t_{\rm ox}}{\pi lw}{\rm ln}\frac{2\pi w}{t_{\rm ox}}\big]}{\big[\frac{1}{1-\alpha}+\alpha\frac{\varepsilon_{{\rm k}}}{\varepsilon_{{\rm ox}}}\frac{t_{\rm ox}}{\pi lw}{\rm ln}\frac{2\pi w}{t_{\rm ox}}\big]} =C_0\left[1+\frac{(1+\alpha)^2\frac{\varepsilon_{{\rm k}}}{\varepsilon_{{\rm ox}}}\frac{t_{\rm ox}}{\pi lw}{\rm ln}\frac{2\pi wlw}{t_{\rm ox}}}{1+\alpha(1+\alpha)\frac{\varepsilon_{{\rm k}}}{\varepsilon_{{\rm ox}}}\frac{t_{\rm ox}}{\pi lw}{\rm ln}\frac{2\pi w}{t_{\rm ox}}}\right]. \tag{39}\end{equation}


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  • Figure 1

    High k + SiO$_2$ gate FD-SOI MOSFET structure diagram

  • Figure 2

    Calculates the coordinate system of the high k + SiO$_2$ gate FD-SOI MOSFET

  • Figure 3

    $\varepsilon_{{\rm~k}}=22$ high k dielectric high k + SiO$_2$ gate FD-SOI MOSFET front gate surface potential with the gate voltage changes

  • Figure 4

    High k + SiO$_2$ gate FD-SOI MOSFET front gate surface potential along the channel length distribution.protect łinebreak (a) $\varepsilon_{{\rm~k}}=7.5$ medium; (b) $\varepsilon_{{\rm~k}}=22$ medium

  • Figure 5

    High k and high k + SiO$_2$ gate FD-SOI MOSFET threshold voltage algorithm flow chart

  • Figure 6

    (a) High k gate, high k + SiO$_2$ gate and SiO$_2$ gate FD-SOI MOSFET threshold voltage and channel length relationship; (b) the relationship between threshold voltage and channel length of high k + SiO$_2$ gate FD-SOI MOSFET with different media

  • Figure 7

    FD-SOI MOSFET threshold voltage and the device's physical structure and material parameters of the relationship. (a) High k gate material unchanged, change the Si film doping concentration; (b) all parameters remain unchanged, only change the thickness of the Si film; (c) high k material unchanged, only change the ratio of high k layer and SiO$_2$ layer; (d) the high k material and device structure remain unchanged, changing only the back gate oxide thickness; (e) high k material and structure unchanged, plus different back gate voltage

  • Figure 8

    High k + SiO$_2$ gate FD-SOI MOSFET threshold voltage and dielectric constant relationship, the abscissa is the high k material dielectric constant. (a) Long channel (60 nm) situation; (b) the channel length is 20 nm short channel condition; (c) different thickness of the high k + SiO$_2$ gate, the channel length is 20 nm situation

  • Figure 9

    (a) The diagrammatic sketch for the leakage electric field intensity of two sides between the gate; (b) the edge effect discussed in the paper

  • Figure 10

    Surface potential distribution of SiO$_2$ gate, high k gate and high k + SiO$_2$ gate FD-SOI MOSFETs. protect łinebreak (a) The channel length is the surface potential $\phi_{\rm~f}(x)$ of 110 nm; (b) the channel length is 20 nm, the surface potential $\phi_{\rm~f}(x)$;protect łinebreak (c) the barrier map of (b), the unit is V

  • Figure 11

    20 nm channel length FD-SOI MOSFET $V_{{\rm~GS}}=0.3$ V, $V_{{\rm~GS}}$ and barrier height difference $\nabla\Phi$ diagram

  • Table 1   Capacitor capacitance per unit area of SiO$_2$ gate, high k + SiO$_2$ gate and high k gate
    Channel length ($l$) 110 nm 20 nm
    Gate capacitance of SiO$_2$ ($C_{\rm~ox}$) (1+0.0664)$C_0$ (1+0.365)$C_0$
    Gate capacitance of high k + SiO$_2$ ($C_{\rm~k+SiO_2}$) (1+0.157)$C_0$ (1+0.637)$C_0$
    Gate capacitance of high k ($C_{\rm~k}$) (1+0.295)$C_0$ (1+1.623)$C_0$
  • Table 2   Figure $V_{\rm~GS}=0.3$ V, 20 nm channel FD-SOI MOSFET surface potential $\phi_{\rm~f}(x)$ data
    $X$ (nm) 50.00 50.8 52.4 55.1 60.00 64.9 67.6 69.2 70.0
    *SiO$_2~\phi_{\rm~f}(x)$ SILVACO 0.5852 0.5174 0.4577 0.4089 0.4042 0.4827 0.5854 0.6859 0.7852
    Model 0.5828 0.5250 0.4771 0.4332 0.4234 0.5041 0.5947 0.7221 0.7807
    *High k + SiO$_2~\phi_{\rm~f}(x)$ SILVACO 0.5852 0.5213 0.4705 0.4330 0.4345 0.5077 0.5979 0.6886 0.7852
    Model 0.5829 0.5288 0.4885 0.4534 0.4516 0.5247 0.6037 0.6818 0.7804
    *High k$~\phi_{\rm~f}(x)$ SILVACO 0.5852 0.5608 0.5305 0.5033 0.5140 0.5949 0.6787 0.7420 0.7852
    Model 0.5824 0.5469 0.5218 0.5007 0.5076 0.5756 0.6415 0.7306 0.7785

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