Low-Temperature, Solution-Processed ZrO₂:B Thin Film: A Bifunctional Inorganic/Organic Interfacial Glue for Flexible Thin-Film Transistors

Abstract

A solution-processed boron-doped peroxo-zirconium oxide (ZrO₂:B) thin film has been found to have multifunctional characteristics, providing both hydrophobic surface modification and a chemical glue layer. Specifically, a ZrO₂:B thin film deposited on a hydrophobic layer becomes superhydrophilic following ultraviolet–ozone (UVO) treatment, whereas the same treatment has no effect on the hydrophobicity of the hydrophobic layer alone. Investigation of the ZrO₂:B/hydrophobic interface layer using angle-resolved X-ray photoelectron spectroscopy (AR XPS) confirmed it to be chemically bonded like glue. Using the multifunctional nature of the ZrO₂:B thin film, flexible amorphous indium oxide (In₂O₃) thin-film transistors (TFTs) were subsequently fabricated on a polyimide substrate along with a ZrO₂:B/poly-4-vinylphenol (PVP) dielectric. An aqueous In₂O₃ solution was successfully coated onto the ZrO₂:B/PVP dielectric, and the surface and chemical properties of the PVP and ZrO₂:B thin films were analyzed by contact angle measurement, atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The surface-engineered PVP dielectric was found to have a lower leakage current density (<i>J</i>_leak) of 4.38 × 10^–8 A/cm² at 1 MV/cm, with no breakdown behavior observed up to a bending radius of 5 mm. In contrast, the electrical characteristics of the flexible amorphous In₂O₃ TFT such as on/off current ratio (<i>I</i>_on/off) and electron mobility remained similar up to 10 mm of bending without degradation, with the device being nonactivated at a bending radius of 5 mm. These results suggest that ZrO₂:B thin films could be used for low-temperature, solution-processed surface-modified flexible devices