Evaluation of electronic structures in amorphous In-Ga-Zn-O using metal-oxide-semiconductor diodes fabricated with various process conditions

Electronic structures in amorphous In-Ga-Zn-O (a-IGZO) thin films were evaluated using metal-oxide-semiconductor (MOS) diodes fabricated with various process conditions. Thin film transistors (TFTs) with the corresponding process conditions were also fabricated to correlate the electronic properties with the TFT performances. It was clearly shown that trap densities of the a-IGZO films increased with the oxygen partial pressure during the sputtering of a-IGZO. The biasing voltage dependence of the transient capacitance from the MOS diodes revealed that the trap states were dominantly located near the backchannel region of the films. The subthreshold-swings of the TFTs, rather than the TFT mobilities, showed significant correlation with the estimated trap densities, consistently suggesting formation of trap states near the backchannel region of a-IGZO TFTs.