Fabrication and Properties of Amorphous In-Ga-Zn-O Material and Transistors

Abstract

Amorphous In Ga Zn O (a-IGZO) is regarded as one of the most promising materials among transparent amorphous oxide semiconductors (TAOS), owing to: carrier mobility above 5 cm/(V s), one order higher of magnitude compared to conventional amorphous semiconductors, such as amorphous Si (a-Si); potential to control carrier concentration in the range of several orders of magnitude, yielding thin lms from insulating to highly conducting ones; room-temperature fabrication and processing, and high transparency in the visible wavelength region. An unique aspect of TAOS is that the carrier mobility is not sensitive to the thin lm microstructure, as is case of conventional covalently-bonded semiconductors. This fact arises from the nature of the chemical bonding in these (n− 1)dns (n ≥ 4) metal oxides. Carrier transport in covalently-bonded materials, such as Si, is carried out primarily through anisotropic sp orbitals, so that introducing randomness into the structure greatly reduces bond overlap and carrier mobility. In TAOS, the higher ionicity of the bonding leads to a conduction band formation on spherical s orbitals. Because the overlap of s orbitals is not signi cantly altered by the introduction of structure randomness, carrier transport and, thus, mobility is insensitive to the amorphization [1]. All this facts turn a-IGZO to become a key material for next generation electronic devices, in particular for thinlm transistors (TFT), challenging silicon not only in conventional applications but opening possibilities to totally new areas, like electronic paper or ultrahigh-resolution displays for biomedical applications. Several research groups have already demonstrated the possibility of fabrication a-IGZO thin lms by using such