Polymer thin film transistors with self-aligned gates fabricated using ink-jet printing

Abstract

Polymer thin film transistors (TFTs) with self-aligned gates have been fabricated by using a one step prepatterning technique in combination with ink-jet printing. The TFTs the authors show here are of the bottom gate configuration, whereby the gate electrode dimensions are defined by microembossing a polymer film which is supported by another polymer layer acting as a buffer. The deposition of the aluminium gates into the depressions of the embossed film was realized by thermal evaporation and subsequent lift-off technique. The buffer layer was then etched by using the gate electrodes as mask to create a thickness contrast. By taking the advantage of this thickness contrast a self-assembled molecule monolayer was applied by soft-contact printing on a spin coated dielectric layer to generate a series of banks with a sufficiently high wetting contrast for subsequent ink-jet deposition of the source and drain electrodes. Self-aligned bottom gated TFTs with channel lengths from several to several tens of micrometers have been fabricated. For TFTs with poly(9,9-dioctylfluorene-co-bithiophene) as an active layer, a hole mobility of 4.5×10−3cm2V−1s−1 and an on/off current ratio of 104 was achieved. By using a similar process TFTs with self-aligned top gates have also been fabricated.