SCIENCE CHINA Information Sciences, Volume 61 , Issue 2 : 022401(2018) https://doi.org/10.1007/s11432-016-9049-2

A threshold voltage and drain current model for symmetric dual-gate amorphous InGaZnO thin film transistors

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  • ReceivedNov 24, 2016
  • AcceptedMar 10, 2017
  • PublishedAug 25, 2017



This work was supported by National Natural Science Foundation of China (Grant No. 61274085) and Science and Technology Research Projects of Guangdong Province (Grant No. 2015B090909001).


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  • Figure 1

    Schematics of (a) DG a-IGZO TFT and (b) sub-gap DOS model of a-IGZO, the dotted and solid lines are sketches of free-carrier and trap-state distributions in the bandgap of a-IGZO.

  • Figure 2

    Current-voltage characteristics of DG a-IGZO TFTs from this analytical model (solid lines) and TCAD simulations (symbols) at $T$=300 K. (a) and (b) are transfer curves with $\varphi_{\rm~t}$ set as 0.05 V and 0.065 V; (c) and (d) are output curves with $\varphi_{\rm~t}$ set as 0.05 V and 0.065 V. The dashed and dotted lines represent the drift and diffusion components of drain current respectively.

  • Figure 3

    Variations of $\textit{n}\rm_{free}$, $\textit{n}\rm_{trap}$ and $\lambda$ with the gate voltage.

  • Figure 4

    Comparison of threshold voltage obtained by different definition methods under various (a) $\varphi\rm_{t}$ and (b) $\textit{V}\rm_{DS}$.

  • Figure 5

    Comparison of transfer curves between this model (solid lines) and experiment data (symbols) in (a) [10], (b) [16], with the dashed and dotted lines being the drift and diffusion drain current respectively. Values of parameters in [10]: $\textit{t}\rm_{IGZO}$=30 nm, $\textit{C}\rm_{ox}$=1.73$\times$10$^{-8}$ F$\cdot~{\rm~cm}^{-2}$, $\mu\rm_{0}$=13 cm$^{2}\cdot~{\rm~V}^{-1}\cdot~{\rm~s}^{-1}$, $\textit{g}\rm_{t}$=8.5$\times$10$^{17}$ cm$^{-3}$eV$^{-1}$, $\varphi\rm_{t}$=0.08 V, $\varphi\rm_{F0}$=0.5 V, $\textit{V}\rm_{fb}$=0.4 V, $\textit{m}$=0.7, $\gamma$=0.14. Values of parameters in [16]: $\textit{W}$/$\textit{L}$=40 $\mu$m/5 $\mu$m, $\textit{t}\rm_{IGZO}$=70 nm, $\textit{C}\rm_{ox}$=1.73$\times$10$^{-8}$ F$\cdot~{\rm~cm}^{-2}$, $\mu\rm_{0}$=6.5 cm$^{2}\cdot~{\rm~V}^{-1}\cdot~{\rm~s}^{-1}$, $\textit{g}\rm_{t}$=8.0$\times$10$^{16}$ cm$^{-3}$eV$^{-1}$, $\varphi\rm_{t}$=0.085 V, $\varphi\rm_{F0}$=0.2 V, $\textit{V}\rm_{fb}$=1.8 V, $\textit{m}$=0.9, $\gamma$=0.10.

  • Table 1   Parameters and the calculated threshold voltage in this model
    Symbol $\textit{V}\rm^{lin}\rm_{th}$ $\textit{V}\rm^{sat}\rm_{th}$ W/L $\textit{t}\rm_{IGZO}$ $\textit{C}\rm_{ox}$ $\mu\rm_{0}$ $\textit{g}\rm_{t}$ $\varphi\rm_{t}$ $\varphi\rm_{F0}$ $\textit{V}\rm_{fb}$ m
    (unit) (V) (V) ($\rm{\mu}$m/$\rm{\mu}$m) (nm) (F$\cdot$cm$^{-2}$) (cm$^{2}\cdot~{\rm~V}^{-1}\cdot~{\rm~s}^{-1}$) (cm$^{-3}\cdot~{\rm~eV}^{-1}$) (V) (V) (V)
    TFT in Figure 2(a) and (c) 0.08 $-$0.01 20/20 50 1.73$\times$10$^{-8}$ 15 1$\times$10$^{18}$ 0.05 0.3 0 0.8
    TFT in Figure 2(b) and (d) 0.11 0.14 20/20 50 1.73$\times$10$^{-8}$ 15 1$\times$10$^{18}$ 0.065 0.3 0 0.9