Device feasibility and performance improvement methodologies for thin film transistors using In-Ga-Sn-O channels prepared by atomic-layer deposition

Abstract

Thin film transistors (TFTs) using In-Ga-Sn-O (IGTO) active channel layers, which were prepared by atomic-layer deposition (ALD) techniques, were fabricated and characterized with exploring the optimum IGTO channel compositions and the process conditions for the formation of gate-stack structures. The introduction of an O3 oxidant was confirmed to secure a wider process window, which was explained by hydrogen incorporation from the protection layer/gate insulator stacked layers into the IGTO active channel. The cationic compositions of the IGTO thin films were controlled by subcyclic ratio design of each precursor. When the number of In-Ga precursor subcycles increased from 4 to 6, the Ga/Sn ratio increased from 3.5 to 4.0, leading to marked improvements in the VON characteristics of the fabricated IGTO TFTs. It was found from a comparative analysis on the device characteristics that the Ga/Sn ratio in the IGTO channel had a more dominant effect on the VON characteristics rather than the In/Ga ratio. The device using the channel with a cationic composition of 5.8:4.0:1.0 (In:Ga:Sn) exhibited the field-effect mobility of 19.1 cm2/V s, the subthreshold swing of 0.22 V/dec, and the threshold voltage (VTH) of 0.22 V, which corresponded to the best device characteristics among the fabricated devices. Furthermore, the VTH shifts were examined to be +0.4 and −0.4 V in positive and negative bias stress conditions, respectively, demonstrating excellent gate-bias stress stabilities. The obtained results suggest the device feasibility and fabrication process validity for the TFT applications using IGTO active channel layers prepared by ALD techniques.

Improvement in Short-Channel Effects and Bias-Stress Stability of Vertical Thin-Film Transistors Using Atomic-Layer-Deposited In–Ga–Sn–O Channels

“…These values were suggested to be far lower compared with those obtained from the conventional planar-channel devices. 18,19 Actually, the back-channel scattering has been reported to be a main origin to degrade the carrier mobility for the oxide-channel VTFT due to a considerable amount of defect sites and uneven surface roughness, which might be generated during the formation process of spacer sidewalls. 11 Additionally, the back-channel scattering effect might worsen as the area of the channel defined on the uneven back-channel surface increases, causing significant deterioration in the transports of carriers.…”

“…In advance, the ALDderived IGTO thin films were newly introduced as channel materials for planar-channel TFTs with variations in cationic compositions, demonstrating their good device operations and reliabilities. 18 In addition, the ALD IGTO TFTs with a submicrometer channel length as short as 500 nm were verified in terms of the SCEs, suggesting that the optimum process conditions could be determined by modulating the ALD IGTO channel compositions for improving both requirements of SCEs and contact properties for nanoscale IGTO TFTs. 19 Therefore, in this work, IGTO VTFTs were fabricated by means of the ALD process and characterized for achieving high-performance 3D-structured device elements.…”

“…Actually, we have executed a series of works for implementing the ALD IGTO VTFTs as well as for securing their promising device performance. In advance, the ALD-derived IGTO thin films were newly introduced as channel materials for planar-channel TFTs with variations in cationic compositions, demonstrating their good device operations and reliabilities . In addition, the ALD IGTO TFTs with a submicrometer channel length as short as 500 nm were verified in terms of the SCEs, suggesting that the optimum process conditions could be determined by modulating the ALD IGTO channel compositions for improving both requirements of SCEs and contact properties for nanoscale IGTO TFTs .…”

Analysis on Contact Resistance and Effective Channel Length of Thin Film Transistors Using Composition-Modified In–Ga–Zn-O Active Channels Prepared with Atomic Layer Deposition and Various Electrode Materials

“…In contrast, the introduction of Ga or Zn suppresses carrier generation and stabilizes amorphous network of IGZO, respectivley . In addition, strategic modulations in electronic natures of gate-stack structures including gate insulator (GI) layers and electrodes can facilitate the improvement in device characteristics of the ALD IGZO TFTs. − Thus, to properly secure the ALD process conditions for the formation of IGZO channel layers in future scaled devices, various device parameters should be extensively explored for the ALD IGZO TFTs in terms of the device scaling. − …”