Fabrication of an organic thin-film transistor by inkjet printing

A nanocomposite as the gate insulating film of thin film transistors (TFTs) is prepared by blending cross-linked poly(4-vinylphenol) and high-k TiO ₂ nanoparticles to enhance the permittivity of the gate dielectric and reduce operating voltage of TFTs. A pearl mill is used to grind up the agglomerations and dispersant to well stabilize the dispersion of the nanoparticles in the polymer matrix for inks. A dielectric film with the nanocomposite is made via mask-free inkjet printing. By adjusting the parameters of inkjet printing, including voltage, frequency, and waveform, a dielectric film with low roughness is accomplished after curing at 190 °C using an ink with 3 wt% TiO₂. A pentacene-TFT with a top contact structure on a glass substrate is fabricated based on the inkjet-printed gate dielectric, which has a low leakage current density and a high current ratio. The TFT exhibits p-channel TFT characteristics with a high field-effect mobility (a saturation mobility of ~-0.49 cm² V^-1 s^-1) and low-voltage operation (<6 V), indicating that these nanocomposite dielectric materials can be used in low-cost high-performance printable electronics.