Sequential Design of PEALD In-Ga-Zn-O Active Layer for Enhancing TFT Stability

The accelerating downscaling of transistorsin recent years has resulted in significant attention beingpaid to the development of amorphous oxide semiconductors, such as indium-gallium-zinc oxide (IGZO) using atomic layer deposition (ALD). To improve electrical perfor-mance, indium (In)-rich base IGZOs have been developed,but the increased In content in these materials can lead toissues with carrier control and crystallization. In this study,a newly designed plasma-enhanced ALD (PEALD) supercycle is proposed to suppress the crystallinity and electroncarriers in In-rich IGZO. By inserting Ga(2)O(3 )and ZnO into the In(2)O(3 )sublayer using carefully PEALD sequences,the crystallinity of In(2)O(3 )was effectively suppressed bythe lattice mismatch between the layers. As a result, the subthreshold swing (SS) characteristics in IGZO thin-film transistors (TFTs) improved from 0.42 to 0.23 V/decade.Additionally, positioning an insulating Ga2O3 layer between the In(2)O(3 )sublayer reduced the number of carriers, leading to a shift in the threshold voltage (Vth) from-4.63 to-1.83 V. Furthermore, the suppressed crystallinity and sta-ble Ga-O bonding between the In(2)O(3 )layers improved there liability of the IGZO TFTs, as evidenced by the decreasein the Vthshift from 3.75 to 0.83 V under positive biasstress (PBS). This new approach of controlling the ALD supercycles to insert different materials into the In(2)O(3 )layer provides a groundbreaking method for suppressing crystallization and controlling carriers in In-rich IGZO thin films.It constitutes a breakthrough in addressing the trade offbetween mobility and stability.