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 highconductive 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 x 10
^-3
Ωcm from over 10
⁴
Ωcm with a 36-s Mg deposition at 300 °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
V
^-1
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 Ωcm, a small channel length shrinking of around 0.1 μm, and a high stability against electrical stresses.