Research: Sub-femtoliter inkjet printing
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A process to print electrically conducting metal lines with a width of 2 µm and a spacing of 1 µm
directly on top of small‑molecule organic semiconductor films has been developed. This allows organic p‑channel and n‑channel organic thin‑film transistors (TFTs) with a channel length of 1 µm to be manufactured in a top‑contact geometry. Unlike regular inkjet printers, which dispense ink droplets with a volume of several picoliters and create dots with a diameter of 30 to 50 µm, the inkjet system utilized here dispenses droplets with a volume of less than 1 femtoliter and a diameter of less than 1 µm in air. Because of the small size of the droplets, the organic solvent evaporates before the droplets reach the semiconductor surface, so that spreading on the surface is efficiently suppressed. The ink consists of monodispersed silver nanoparticles with a diameter of 2 to 3 nm. Because of the small size of the nanoparticles, a relatively low sintering temperature of 130 °C is sufficient to remove the dispersing agent and fuse the nanoparticles into homogeneous metallic lines with near-bulk electrical conductivity. At this low sintering temperature the morphology of the organic semiconductors is not disturbed. Using a thin gate dielectric based on a combination of an oxygen‑plasma‑grown metal oxide and a molecular self‑assembled monolayer, we have prepared pentacene p‑channel and F16CuPc n‑channel TFTs as well as complementary inverters with excellent low‑voltage characteristics. Organic Transistor Lab (Takao Someya) Back to Research |
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