Laser-induced forward transfer of multi-layered structures for OTFT applications

We report on the one-step laser printing of multi-layered organic-based field effect transistors, using thin films of bis(2-phenylethynyl) end-substituted terthiophene (diPhAc-3 T) as semiconductor, parylene-C (Py-C) as dielectric and silver (Ag) as gate electrode, respectively. The laser-induced forward transfer (LIFT) process was used to transfer pixels from donor to receiver substrates. The latter included pre-designed source and drain gold electrodes to form complete organic thin films transistors (OTFTs). Such laser-induced forward transfer used a single 50 ps duration pulse delivered by a Nd:YAG laser operating at 355 nm to print transistor pixel arrays under ambient temperature. The pixels (350 μm sized-squares, and 700 ± 40 nm in thickness), fabricated in the top gate configuration, were investigated for their current-voltage characteristics immediately after printing. Electrical characterization demonstrated that the laser printed transistor is fully functional with hole mobilities of 4 × 10 ^-4 cm ² /V s, a threshold voltage V _t near -10 V, I _on /I _off ratio near to 10 ⁴ -10 ⁵ and the sub-threshold slope (S) of 14-18 V/decade. The efficient cohesion between the three different layers composing the pixels offers an exceptionally high strength to laser printing, while maintaining the electrical properties.