Solution‐Processable, Transparent Polyimide for High‐Performance High‐kNanocomposite: Synthesis, Characterization, and Dielectric Applications in Transistors

Abstract

AbstractIn this study, a well‐soluble and highly transparent polyimide (PI) consisting of 9,9‐bis (3‐amino‐4‐hydroxyphenyl) fluorine (BAHPF) and 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA)) was synthesized by a high temperature polycondensation reaction. By further reacting with zirconium dioxide (ZrO2) through hydrolysis and condensation reaction, high‐kPI/ZrO2hybrid materials were prepared and demonstrated as efficient dielectric materials in the pentacene‐based organic thin film transistors (OTFTs). The influence of ZrO2loading amount in the range of 0–50 wt% on the resultant properties was first investigated. It was revealed that the decomposition temperature of the PI/ZrO2hybrid materials was increased from 445 °C to 478 °C as the incorporated ZrO2amount increased. Also, the addition of ZrO2does not impair the overall transparency of the material owing to its small particle size. All the hybrid films showed high transmittance of over 93% across the wavelengths from 400 to 800 nm. The dielectric constant of the hybrid material was increased from 4.0 to 6.1 as the ZrO2content increased from 0 to 50 wt% while the leakage current density (−2MV cm−1) was restrained to less than 5×10−7 A cm−2. Notably, the incorporation of ZrO2in the PI promoted the crystallization of pentacene grown on top of it. The pentacene‐based TFT using a hybrid material with 30 wt% ZrO2(A30) as the dielectric layer yielded the highest mobility of 1.12 cm2 V−1s−1, greatly surpassing the value (0.26 cm2 V−1s−1) of the reference device using pristine PI (A0) as the dielectric layer. To further optimize the device performance, a surface modifying layer based on a cyclic olefin copolymer was introduced at the dielectric/pentacene interface, which simultaneously flattened the dielectric's surface and passivated its surface defects. As a result, the mobility of the A30‐based TFT can be further enhanced to 3.25 cm2 V−1s−1with a much‐increased Ion/Ioffof 1.2×106. This study clearly manifests the promising potential of high‐kPI/ZrO2hybrid dielectric materials for the future development of transparent and stretchable organic components.