Improvement of Electrical Properties and Bias Stability of InGaZnO Thin-Film Transistors by Fluorinated Silicon Nitride Passivation

Recently, oxide-based thin-film transistors (TFTs) have attracted considerable attention for applications such as active-matrix flat panel displays. Among oxide semiconductors, amorphous InGaZnO (a-IGZO) is widely accepted as a promising channel material for TFT application [1]. However, the bias induced instability is a remained issue to be solved. Ambient atmosphere includes oxygen and water, which easily absorb on the exposed a-IGZO surface and influence TFT properties; therefore, a suitable passivation layer is an essential to improve the reliability of the oxide TFTs. In this study, electrical properties of the IGZO TFTs with SiO_x, fluorinated SiN_x (SiN_X:F) passivation were investigated.

  Bottom-gate IGZO TFT with SiO_X etch-stopper was used for this experiment, and a SiO_X or SiN_X:F was deposited on the TFT as a passivation [2]. The experimental transfer characteristics (I_DS-V_GS) of the IGZO TFTs with SiO_X and SiN_X:F passivation are shown in Fig. 1(a) and 1(b), respectively. The IGZO TFT with SiN_X:F passivation showed steep subthrehold swing, low threshold voltage (V_th), and small hysteresis as compared with the SiO_X passivation. Fig. 2 shows the comparison of positive bias temperature stress (PBTS) reliability of the IGZO TFTs with SiO_X and SiN_X:F passivation. It was found that positive threshold voltage shift is significantly suppressed by SiN_X:F passivation. Influence of SiN_X:F passivation on reliability of the IGZO TFT will be presented at the conference.

  Authors would like to thank Tokyo Electron Co., Ltd. for their experimental supports on SiNx:F film.

[1]     K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, Nature. 432, 488 (2004).

[2]     M. Furuta, M. P. Hung, and J. Jiang, D. Wang, S. Tomai, H. Hayasaka, and K. Yano, ECS Trans., 54 (2013).