Hybrid Passivation for Foldable Indium Gallium Zinc Oxide Thin-Film Transistors Mediated by Low-Temperature and Low-Damage Parylene-C/Atomic Layer Deposition-AlOx Coating

Indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) are primary components in active integrated electronics, such as displays and sensor arrays, which heavily involve high-throughput passivation techniques during multilayer fabrication processes. Though oxide compound semiconductors are commonly used for providing uniform and robust passivation, it usually causes performance degradation on IGZO TFTs during passivation process. Herein, a parylene-C and aluminum oxide (AlOx) hybrid passivation approach are introduced to reduce the damage during AlOx atomic layer deposition (ALD), which results in high-performance depletion-mode IGZO TFT to be fabricated on polyethylene naphthalate (PEN) substrate with enhanced bias stability. Compared with parylene-C passivation, the hybrid-passivated IGZO TFTs exhibit excellent saturation mobility (7.9 cm(2) (V s)(-1)), ON/OFF ratio (107), hysteresis window (0.73 V), and bias stability (1.44 and -0.27 V threshold voltage shift, V-ds = 20 V). Based on systematic Mott-Schottky and X-ray diffraction characterizations, it is found that TFT performance enhancement is originated from their doping density variation that resulted from a parylene-C/ALD-AlOx microstructural hybridization. Finally, this method is implemented to wafer-scale integrated circuits with high uniformity and a flexible 10 x 10 IGZO TFT backplane matrix on a PEN substrate (2.5 cm x 2.5 cm).