Electrical Properties of Sputter-Deposited InGaZnO Thin Film Transistors with an Etch Stopper

This study demonstrated the effect of a passivation layer of a siloxane-based spin-on-glass (SOG) etch stopper on the electrical properties of sputter-deposited InGaZnO thin-film transistors (IGZO TFTs). Compared to stabilities of unpassivated devices, IGZO TFTs passivated by SOG annealed at 100 degrees C in air showed better stability against positive bias stress (PBS) and much worse stability against negative bias stress (NBS), which were attributed to the reduction of ambient environmental effects by SOG and the introduction of H and C electron donors from SOG into IGZO. As the annealing temperature of SOG increases from 100 to 300 degrees C, the degradation in PBS stability and the improvement in NBS stability were observed. These are because of higher O-related acceptors and lower C-and H-related donors in IGZO, respectively, as evidenced by SIMS analysis. The best stability was achieved for the passivated TFTs with a 200 degrees C-annealed SOG, which exhibited a small threshold voltage shift (Delta V-th)of 2.1 V under PBS and a minimal Delta V-th of 1.8 V under NBS. These results show the great potential of methyl-siloxane-based SOG layers as effective passivation materials.