Improved Electron Transport Properties of Zn-Rich In-Ga-Zn-O Thin-Film Transistors

Amorphous transparent oxide semiconductor InGaZnO4 (IGZO)-based thin-film transistors (TFTs) have been practically used as the backplane of flat panel displays. For future higher-definition displays, alternative active materials with a higher field effect mobility (mu FE) are necessary. Although there are a few reports on InGaO3(ZnO)(m) with Zn-rich composition (IGZOm)based TFTs, their electron transport properties have not been clarified. Here, we show that a Zn-rich composition enhances the electron transport properties of IGZO(m)-TFTs. The best TFT performance was obtained for m = 7 (mu FE similar to 12 cm(2) V-1 s(-1), subthreshold swing similar to 0.1 V decade(-1), and a negligibly small bias stress shift). The carrier effective mass (m*) of IGZO(m) films was found to be 0.16 m(0), independent of the m-value. We found that mu F-E of IGZO(m)-TFT increased with the m-value for m <= 7, whereas it decreased for m > 7 due to the crystallization. The thermopower modulation analyses revealed that the effective channel thickness increased with m (m <= 7), which resulted in a longer carrier relaxation time. The present results provide an improving strategy toward new material design for next-generation TFTs with higher mu(FE) values.

Automated summary

Amorphous transparent oxide semiconductor InGaZnO4 (IGZO)-based thin-film transistors (TFTs) are widely used as the backplane for flat panel displays. In order to achieve higher-definition displays in the future, alternative active materials with higher field effect mobility (μFE) are needed. In this study, it is shown that a zinc-rich composition enhances the electron transport properties of IGZO(m)-TFTs. The best TFT performance was obtained with m = 7, and the carrier effective mass of IGZO(m) films was found to be 0.16 m(0), independent of the m-value. The present results provide a strategy for improving the design of next-generation TFTs with higher μFE values.