Elsevier

Microelectronic Engineering

Volume 87, Issue 10, October 2010, Pages 2019-2023
Microelectronic Engineering

Influence of the channel layer thickness on electrical properties of indium zinc oxide thin-film transistor

https://doi.org/10.1016/j.mee.2009.12.081Get rights and content

Abstract

Thin-film transistors (TFTs) were fabricated on SiO2/n+–Si substrates using amorphous binary In2O3–ZnO (a-IZO) films with different thickness for active channel layers deposited by the rf magnetron sputtering at room temperature. The performance of devices was found to be thickness dependent. With the active layer thickness from 33 to 114 nm, the field-effect mobility μFE increased from 1.60 to 4.59 cm2/V s, the threshold voltage VTH decreased from 62.26 to 20.82 V, and the subthreshold voltage swing S decreased from 4.06 V/decade to 1.30 V/decade. Further, the dependence of TFTs’ electrical properties on active layer thickness was investigated in detail on the basis of free carrier density and interface scattering.

Introduction

Recently, transparent oxide semiconductors (TOSs) have been widely explored for their wide applications. Especially TOSs, such as ZnO [1], [2], ZnMgO [3], Zn–Sn–O (ZTO) [4], SnO2 [5], Ga2O3 [6], In–Ga–O (IGO) [7], In2O3 [8], In–Sn–O (ITO) [9], In–Ga–Zn–O [10], [11] and so on, can be used as active channel layer for transparent thin-film transistors (TTFTs) with higher field-effect mobility compared with the conventional a-Si (amorphous Si) TFT. Among these oxides, IZO is one of potential candidates used as the active layer, because of its excellent optical transmission, high mobility, chemical stability, thermal stability, and smooth surface [12]. Moreover, all these properties are attainable even in amorphous phase, which implies IZO films could be deposited at room temperature for large area applications. Thus, a-IZO films allow for the development of inexpensive transparent and flexible electronic circuits [13].

Some previous work [14], [15], [16] reported that the channel layer thickness is one of vital factors affecting the performance of the TFT. In our study, a-IZO TFTs were fabricated with active layer thickness ranging from 33 to 114 nm in order to investigate the influence of active layer thickness on electrical properties of the TFTs.

Section snippets

Experimental

The a-IZO TFTs with a bottom gate structure were fabricated on a heavily-doped Si substrate with 300 nm thick SiO2 formed via thermal oxidation. The schematic cross-sectional diagram of a-IZO TFT is illustrated in Fig. 1. The Si (the resistivity ρ < 0.01 Ω cm) and the SiO2 (capacitance per unit area Ci = 10 nF/cm2) served as the substrate/gate electrode and the TFT gate dielectric, respectively. The SiO2 surface was ultrasonically cleaned with acetone (5 min), ethanol (5 min), and deionized water (5 min)

Results and discussion

Fig. 2 shows the XRD profile and spectra of refractive index of IZO films with different thickness. In Fig. 2A, only diffraction peaks of the substrate Si appeared at 2θ = 25.71° and 2θ = 28.47° in the XRD spectra. This indicates that both the as-deposited and RTA-treated IZO thin films are amorphous, which is in accord with Ref. [17]. The as-deposited IZO TFTs did not exhibit field-effect transistor characteristics, but the post-RTA-treated ones did. It is concluded that RTA process could improve

Conclusion

In this work, a-IZO thin-film transistors were fabricated with different thick channel layers. The as-deposited and RTA-treated IZO thin films are found to be amorphous. It is noted that the properties of devices got better with increasing the active layer thickness, in the range of 33–114 nm. We believed that this phenomenon was induced by the free carrier and interface scattering. It is concluded that the semiconductor thickness plays a vital role on the electrical performances of TFTs based

Acknowledgments

The authors are grateful for the financial supports of the key project of the Natural Science Foundation of Zhejiang province, China (Grant No. 0804201051), Special Foundation of President of the Chinese Academy of Sciences (Grant No. 080421WA01).

References (26)

  • C.Y. Tsay et al.

    Surf. Coat. Technol.

    (2007)
  • R.E. Presley et al.

    Solid-State Electron.

    (2006)
  • L. Zhang et al.

    Solid State Commun.

    (2008)
  • P. Barquinha et al.

    J. Non-Cryst. Solids

    (2006)
  • A. Soltani et al.

    Diamond Relat. Mater.

    (2007)
  • R.L. Hoffman et al.

    Appl. Phys. Lett.

    (2003)
  • J.F. Wager

    Science

    (2003)
  • H.Q. Chiang et al.

    Appl. Phys. Lett.

    (2005)
  • R.E. Presley et al.

    J. Phys. D: Appl. Phys.

    (2004)
  • K. Matsuzaki et al.

    Appl. Phys. Lett.

    (2006)
  • L. Wang et al.

    Nat. Mater.

    (2006)
  • M. Takaaki et al.

    Appl. Phys. Lett.

    (2005)
  • Y. Hisato et al.

    Appl. Phys. Lett.

    (2006)
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