Sequential Design of PEALD In-Ga-Zn-O Active Layer for Enhancing TFT Stability
IEEE TRANSACTIONS ON ELECTRON DEVICES(2023)
Abstract
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.
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Key words
tft stability
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