Influences of Oxygen Plasma Posttreatment on Electrical Characteristics of Amorphous Indium–Gallium–Zinc–Oxide Thin‐Film Transistors

• Published in: Physica status solidi. A, Applications and materials science Vol. 218; no. 19
• Main Authors: Lee, Jae-Yun, Tarsoly, Gergely, Choi, Seung-Gon, Ryu, Heung-Gyoon, Kim, Sung-Jin
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.10.2021
• Subjects: Absorptivity; Electron mobility; Electrons; Gallium; Indium; Indium gallium zinc oxide; O2 plasma; Oxygen plasma; Plasma; Plasma generators; Radio frequency; Semiconductor devices; solution process; Surface properties; Thin film transistors; Threshold voltage; transmittance; Zinc oxide
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.202100205

A thin‐film transistor (TFT) using amorphous indium–gallium–zinc oxide (a‐IGZO) as an active layer is annealed at 300 °C after deposition and then treated with oxygen plasma. To analyze the effect of radio frequency (RF) power of the plasma generator on the a‐IGZO TFT, as‐deposited and plasma‐treated devices using RF power levels of 60, 120, and 180 W are fabricated and characterized. It is demonstrated that the RF power setting of the plasma generator influences the threshold voltage (V th), electron mobility, on/off current ratio and subthreshold swing of the devices alongside the transmittance and absorption coefficient of the a‐IGZO layer. The a‐IGZO TFT with oxygen plasma treatment at 60 W shows the best performance with a V th of 0.4 V, electron mobility of 14.8 cm2 V−1 s−1, an on/off current ratio of 4.8 × 108, and a subthreshold swing of 0.6 V dec−1. In addition, compared to the as‐deposited device, the bandgap widens from 3.65 to 3.72 eV, and the absorption coefficient of the 2.0–3.7 eV energy range decreases, which is due to the decreased density of tail states, and that improves electron mobility. When the RF power applied in the oxygen plasma treatment is increased to 120 and 180 W, the optical, electrical, and surface characteristics deteriorate. The amorphous indium‐gallium‐zinc‐oxide thin film is an attractive choice for transparent semiconductor applications. Exposure to oxygen plasma alters the surface morphology, optical bandgap, and composition of the film. Oxygen plasma generated at 60 W significantly enhances the electrical performance characteristics of the oxide thin‐film transistors, whereas at higher power settings the mobility and threshold voltages deteriorate.