Thermoset polymers consisting of novolac and melamine derivatives as insulators for organic thin-film transistors

Abstract

A potential gate dielectric material that can be cured and processed at low temperatures was designed and synthesized via the cross-linking of bisphenol A novolac (Novolac) and hexamethoxymethylmelamine (HMMM) in the presence of a catalytic amount of p-toluenesulfonic acid. The thin films of the prepared insulator, Novolac-MM, were completely solidified after cross-linking at 100 °C. Metal–insulator–metal (MIM) devices and pentacene-based p-type organic thin-film transistors (OTFTs) using the synthesized polymer as a dielectric layer were fabricated and compared to poly(vinylphenol)-based materials. Novolac-MM devices showed low leakage current (<10⁻⁸ A cm⁻²) and higher hole mobility (0.31 cm² V⁻¹ s⁻¹) than PVP devices (0.23 cm² V⁻¹ s⁻¹). Flexible OTFTs using Novolac-MM were also fabricated, and were found to be processable at low temperatures.