In-Ga-Zn-Oxide Semiconductor and Its Transistor Characteristics

Abstract

It is revealed that c-axis aligned crystal In-Ga-Zn oxide (CAAC-IGZO) and nanocrystalline IGZO films have high-density crystalline morphologies (5.9−6.3 g/cm3) and are very stable under electron-beam irradiation in transmission electron microscope observation. The electrical properties are suitable for practical use. We attempted to reproduce a previously reported amorphous IGZO film with no ordering. However, we were not able to confirm its existence; rather, we found nanocrystals with a width of 1−3 nm and a thickness of 0.7−0.8 nm. Furthermore, it is apparent that the amorphous-like film has low density (higher than or equal to 5.0 g/cm3 and lower than 5.9 g/cm3), and thus is an unstable material in which nanocrystals change when subjected to electron-beam irradiation. We fabricated field-effect transistors using CAAC-IGZO and examined their switching characteristics. As a result of microfabrication scaling, cutoff frequencies of 2 GHz and 1.5 GHz were obtained when the channel lengths were 60 nm and 100 nm, respectively. Switching characteristics in the order of GHz were obtained by microfabrication scaling with a field effect mobility of 5−10 cm2/V s, which opens new possibilities for oxide semiconductor large-scale integration.