Journal
IEEE TRANSACTIONS ON ELECTRON DEVICES
Volume 68, Issue 12, Pages 6147-6153Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TED.2021.3117749
Keywords
Aluminum oxide; atomic layer deposition (ALD); hydrogen permeability; indium-gallium-zinc-oxide; silicon oxide
Funding
- LG Display
- Ministry of Trade, Industry and Energy (MOTIE) [20010402]
- Korea Evaluation Institute of Industrial Technology (KEIT) [20010402] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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An ALD sandwich structure was developed for depositing both semiconductor and gate insulator, revealing a hydrogen accumulation effect between Al2O3 and ALD IGZO interface layer leading to deterioration in electrical performance. TFTs with ALD SiO2 buffer and gate insulator demonstrated favorable electric properties, while an optimized structure using both SiO2 and Al2O3 exhibited excellent TFT characteristics with improved stability after hydrogen annealing.
Atomic layer deposition (ALD) has been studied extensively to employ oxide semiconductor thin film transistor (TFT) including both active layer and gate insulator (GI). Herein, we developed an ALD sandwich structure, which deposits both semiconductor and GI by ALD. In contrast to the previous results using sputter In-Ga-Zn-O (IGZO), ALD sandwich structure IGZO TFT exhibited severe deterioration in its electrical performance when the Al2O3 was adopted for both buffer layer and GI application. Through measurement of hydrogen permeability of ALD insulators and secondary ion mass spectroscopy of each sandwich structure after annealing, we found a hydrogen accumulation effect between Al2O3 and ALD IGZO interface layer, which caused deterioration of electrical performance. In contrast, TFTs with ALD SiO2, which has proper hydrogen diffusivity, chosen as the buffer and GI had favorable electric properties of 28.17 cm(2)/V.s, 0.20 V/dec, 0.96, and 0.12 V for the mobility, V-th, subthreshold swing (SS), and hysteresis. In this regard, an optimized GI structure via the ALD SiO2 and Al2O3 in situ process based on excellent interface formation with the semiconductor and hydrogen barrier performance, respectively, was developed. This functional GI structure consisting of SiO2 and Al2O3 exhibited excellent TFT characteristics (27.52 cm(2)/V.s, 0.24 V/dec, and 1.07 V for the mobility, SS, and V-th, respectively) with improved stability even after hydrogen annealing, which was used to examine the resistance to external hydrogen, showing a threshold voltage shift of -0.15 V and a SS shift of 0.01 V/dec.
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