1. Field
Example embodiments relate to a method for fabricating an organic thin film transistor. Other example embodiments relate to a method for fabricating a high-performance organic thin film transistor with minimized or decreased contact resistance and increased charge carrier mobility in which an organic semiconductor material may be oxidized and selectively reduced by appropriate treatment, e.g., UV irradiation, to ensure stability of interfaces between a semiconductor layer and source/drain electrodes.
2. Description of the Related Art
Solution-processable organic thin film transistors are devices which may include a semiconductor layer formed of an electrically conductive organic polymer, e.g., polyacetylene, polythiophene and/or polyphenylene. These types of organic thin film transistors may have advantages in that semiconductor layers may be formed by printing processes at ambient pressure and the overall fabrication procedure may be achieved at reduced costs by roll-to-roll processes using plastic substrates. Accordingly, solution-processable organic thin film transistors may be expected to be useful in various applications, e.g., driving devices of active displays and plastic chips for use in smart cards and inventory tags.
Conventional organic thin film transistors may include several constituent elements, e.g., a substrate, a gate electrode, a gate insulating layer, a semiconductor layer and source/drain electrodes, and provide interfaces between these elements, including interfaces between the semiconductor layer and the source/drain electrodes, an interface between the semiconductor layer and the gate insulating layer, interfaces between the source/drain electrodes and the gate insulating layer. Improvements in the performance of constituent elements of organic thin film transistors as well as the stability of interfaces between the respective elements may be required to maximize or increase the performance characteristics of the organic thin film transistors.
Control of the interfacial structure between a semiconductor and source/drain electrodes of organic thin film transistors and an improvement in the electrical properties at interfaces between the constituent elements may be directly connected with the characteristics of the transistors and may be thus regarded as important in improving the characteristics of the transistors. When organic thin film transistors based on a conjugated polymer as a material for a semiconductor layer use a metal (e.g., gold (Au)) as a material for source/drain electrodes, the interfacial characteristics between the semiconductor layer and the metal electrodes may be deteriorated, causing an increase in contact resistance. Ohmic contact between the semiconductor layer and the source/drain electrodes may not be achieved, and instead, a Schottky barrier may be formed, which is the main cause of undesirable characteristics of the transistors.
Various attempts have been made to solve these problems. For example, the related art discloses the production of high-conductivity PEDOT/PSS electrodes by adding an organic solvent having a high dielectric constant. The conductivity of the PEDOT/PSS electrodes may be comparable to that of conventional ITO electrodes, but may not match the conductivity of gold (Au), which is the most conventional electrode material.