Organic thin-film transistors, integrated circuits, and light-emitting diodes

This thesis reports high-performance organic thin film transistors on glass substrates and the fastest all-organic integrated circuits reported to date. In addition, a novel fully integrated all-organic light emitting diode/thin film transistor active pixel is reported.; The process technology necessary to fabricate organic thin film transistors on arbitrary substrates was developed. Using the small-molecule hydrocarbon pentacene as the active material, thin film transistors were fabricated with field-effect mobility as large as 0.6 cm2/V-s, on/off current ratio as large as 108, and subthreshold slope as small as 0.7 V/decade.; Building on the discrete thin film transistor results, simple pentacene integrated circuits were fabricated on glass substrates. Integrated level shifting was used with normally-on transistors and resulted in circuits with sub-75-musec propagation delay per inverter stage (measured using ring oscillators). These are the fastest all-organic integrated circuits reported to date. The low current level chosen for the level shifting limits the performance of these circuits; directly driven inverters have switching rise and fall time constants below 1 musec.; A low-temperature, oxygen-free transparent contact was developed and used to fabricate organic thin film light emitting diodes. This contact avoids the possibility of oxygen injection into the organic active layer as can occur when conventional conductive metal oxide transparent contacts are used. In addition, metal oxide contacts require elevated process temperatures that are incompatible with inexpensive polymeric substrates. The low-temperature transparent contact uses an ultra-thin metal film deposited by ion-beam sputtering. Such films can have remarkably small surface roughness (typically near 1 A RMS) and become continuous and conductive at film thickness that allows more than 70% optical transmission. Using transparent palladium and aluminum contacts, organic light emitting diodes were fabricated using the small-molecule electroluminescent material 8-hydroxyquinoline aluminum and the small-molecule holetransport material tetraphenyldiamine for the organic active layers.; Finally, a novel fully integrated all-organic active-matrix emissive pixel was developed. This all-organic active pixel uses a gate-controlled organic semiconductor layer to control carrier injection into the electroluminescent device and may provide important contact advantages in addition to a simplified organic light emitting diode/organic thin film transistor control structure.