Properties of crystalline In–Ga–Zn-oxide semiconductor and its transistor characteristics.

We report, in this paper, that crystalline In–Ga–Zn-oxide (IGZO) can be formed over an amorphous surface or over an uneven surface by a sputtering process at lower than 500 °C through the purification of IGZO. Crystalline IGZO, in which no clear grain boundary is observed, shows c-axis alignment but random a- and b-axis orientations without alignment. This crystal morphology differs from other morphologies that have been known thus far, such as single crystal and polycrystal morphologies. Our model for understanding the formation of this crystal morphology [c-axis-aligned crystal (CAAC)] is also discussed. Upon thermal annealing of a deposited film at lower than 500 °C, nanocrystal regions remaining in the CAAC can be converted into the CAAC structure. Accordingly, I_off can be at the yA/µm (10⁻²⁴ A/µm) level at 85 °C. It has been proven that by utilizing normally-off characteristics even with L/W = 40 nm/40 nm (actual size: L/W = 68 nm/34 nm), the fabrication of a three-dimensional (3D) LSI with a 3D oxide semiconductor/Si hybrid structure is feasible. [ABSTRACT FROM AUTHOR]