Organic thin film transistor using silver electrodes by the ink-jet printing technology

We have developed a conductive ink containing silver nanoparticles from which the electrodes for organic thin film transistor were directly patterned by ink-jet printing. Nano-sized silver particles having ∼ 20 nm diameter was used for a direct metal printing. Silver conductive ink was printed on the heavily doped n-type silicon wafer with 200-nm thick thermal SiO₂ layer as a substrate. To achieve a high line resolution and smooth conductive path, the printing conditions such as the inter-drop distance, stage moving velocity and temperature of the pre-heated substrates were optimized. After the heat-treatment at temperatures of 200 °C for 30 min, the printed silver patterns exhibit metal-like appearance and the conductivity. To fabricate a coplanar type TFTs, an active material of semiconducting oligomer, α,ω-dihexylquaterthiophene (DH4T) in a chlorobenzene was deposited between the ink-jet printed silver electrodes by drop casting. The OTFT with the ink-jetted source/drain electrodes shows general performance characteristics with good saturation behavior and no significant contact resistance as compared to the one with vacuum deposited electrodes. The electrical characteristic parameters of OTFT show the mobility of 1.3 × 10^{- 3} cm² V^{- 1} s^{- 1} in the saturation regime, on/off current ratio over 10³, and threshold voltage of about - 13 V.