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

Abstract

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 (μFE) 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 IGZOm-TFTs. The best TFT performance was obtained for m = 7 (μFE ∼12 cm2 V–1 s–1, subthreshold swing ∼0.1 V decade–1, and a negligibly small bias stress shift). The carrier effective mass (m*) of IGZOm films was found to be 0.16 m0, independent of the m-value. We found that μFE of IGZOm-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 μFE values.