Surface passivation engineering approach to fluoroacrylate-incorporated polytetrafluoroethylene for highly reliable a-IGZO TFTs

Abstract

Amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) have attracted considerable attention for cutting-edge and next-generation electronics applications because of their high field-effect mobility, low leakage current, superior uniformity, and high transparency. On the other hand, maintaining stable electrical performance under the influence of various ambient and complex operating environments is a serious application problem. Hence, a fluoroacrylate-incorporated polytetrafluoroethylene (F–P) is proposed as a new material for passivation layers (PVLs) of a-IGZO TFTs. Solution process-based F–P PVLs were introduced to overcome the intrinsically brittle nature of inorganic materials and enhance the long-term stability of organic materials because of their excellent flexibility, hydrophobicity, and chemical stability. This also provides a simple and cheaper alternative for practical applications. The F–P PVLs with different concentrations exhibited appropriate improvements in stability and electrical performance. Of these, the 1.0 wt% F–P passivated IGZO TFTs showed improved performance in saturation mobility (μ_sat) from 6.23 ± 0.21 to 7.02 ± 0.38 cm⁻² V⁻¹ s⁻¹, an on–off current ratio (I_on/I_off) from (4.05 ± 0.84) × 10⁵ to (3.75 ± 2.32) × 10⁸, and a subthreshold swing (SS) from 1.79 ± 0.30 to 0.41 ± 0.04 V per decade compared to the pristine device without the F–P PVL. After the 15 day stability test under ambient conditions, μ_sat increased from 7.02 ± 0.38 to ∼8 cm² V⁻¹ s⁻¹; I_on/I_off increased from (3.75 ± 2.32) × 10⁸ to ∼10¹⁰ and the SS values were maintained at a low level (≤0.6 V dec⁻¹). The improvement was induced by lower surface energy and better hydrophobicity from F–P PVLs, which can effectively reduce the adsorption behavior of H₂O and O₂. With a lower oxygen-related interface trap density, the electrical performances were improved by a suitable concentration-based F–P PVL. In addition, the F–P PVL can provide a long-term guarantee of stability and reliability for a-IGZO TFTs, which will have potential applications for wearable devices and multi-environment electronics devices.