Top-Gate Amorphous Indium-Gallium-Zinc-OxideThin-Film Transistors With Magnesium Metallized Source/Drain Regions

Magnesium (Mg)-induced metallization of amorphous indium-gallium-zinc-oxide (a-IGZO) films is investigated to develop a self-aligned (SA) top-gate (SATG) a-IGZO thin-film transistor (TFT) technology. The high-conductive and SA a-IGZO source/drain (S/D) regions are well realized by a short time of sputtered deposition of Mg onto the a-IGZO film on a heated substrate, followed by the removal of the spare Mg on the surface in hot water. It is shown that the resistivity of the a-IGZO films is lowered to about $4 \times 10^{-{3}}\,\,\Omega $ cm from over $10^{{4}}~\Omega $ cm with a 36-s Mg deposition at $300~^{\circ }\text{C}$ . The metallization effect is believed to be the consequence of a large number of donor-like defects (oxygen vacancies) generated by oxidation–reduction reaction at the interface between the Mg and a-IGZO films. The SATG a-IGZO TFTs fabricated by the proposed technology show excellent electrical characteristics, such as a field-effect mobility of 19.5 cm $^{{2}}\text{V}^{-{1}}\text{s}^{-{1}}$ , a subthreshold swing of 0.19 V/dec, an ON-/ OFF-current ratio of over $10^{{9}}$ , a low S/D series resistance of $2.1~\Omega $ cm, a small channel length shrinking of around $0.1~\mu \text{m}$ , and a high stability against electrical stresses.