Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) with a coplanar homojunction structure are demonstrated. The coplanar source and drain regions made of a-IGZO were formed by depositing a hydrogenated silicon nitride (SiN(X):H) layer onto the a-IGZO layer. The a-IGZO regions on which the SiN(X):H layer was directly deposited showed the low resistivity of 4.7 x 10(-3) Omega cm and degenerated conduction. The fabricated TFT showed excellent transfer and output characteristics with a field-effect mobility of 11 cm(2) V(-1) s(-1), a subthreshold swing of 0.17 V decade(-1,) and an on-to-off current ratio larger than 1 x 10(9). The width-normalized source-to-drain resistance (R(sd) W) calculated using a channel resistance method was 51 Omega cm. This TFT also showed good stability over environment change and under electrical stress. (C) 2009 Elsevier B.V. All rights reserved.