| Inkjet direct writing of functional materials provides a promising pathway towards realization of ultra-low cost, large area printed electronics on polymer substrates as an alternative to the conventional integrated circuit (IC) processes, albeit at the expense of lowered resolution (∼20-50mum). Flexible polymer substrates are chemically incompatible with resists, etchant and developers used in conventional IC processing. In practice, conventional IC fabrication processes are subject to limitations, in that they are multi-step, involve high processing temperatures, toxic waste, and are therefore expensive.; Our approach to overcome these problems entails introducing advanced laser processing combined with utilization of metal nanoparticles to inkjet direct printing. Metal nanoparticles are known to exhibit a large melting temperature depression due to thermodynamic size effect. Compared to the melting temperature of bulk gold (1063°C), 2∼3nm sized nanoparticles start to melt around 130∼140°C, a range that is compatible with plastic substrates. Hybrid metal nanoparticle inkjet printing combined with laser sintering could enhance the feature resolution and the conductor quality at least by one order without damaging the plastic substrate nor without using any conventional lithography processes. As a subtractive post process, it is demonstrated that by ablating unsintered nanoparticle film with short pulsed laser, problems encountered in the pulsed laser ablation of typical metal films at fluence lower than the ablation threshold of thin metal film formed from metal nanoparticle laser sintering, can be alleviated, enabling clean, precise and high resolution patterning. This further gives basis for a novel multilayer processing scheme; SPLA-DAT (selective pulsed laser ablation by differential ablation threshold).; Based on the nanoparticle laser sintering and ablation process, all-inkjet printed and laser processed high quality resistors (5.4mu O·cm, 1∼100mum) and capacitors (1∼10pF) were demonstrated and characterized. Finally, all-inkjet printed and laser processed OFETs (organic field effect transistors, Ion/Ioff ∼ 105, mu FE ∼ 0.01 cm2/V·s, micron to submicron channel length) combined with an air stable carboxylate-functionalized polythiophene were for the first time fabricated in a fully maskless sequence, eliminating the need for any lithographic processes by SPLA-DAT process. All processing and characterization steps were carried out at plastic-compatible low temperatures and in air under ambient pressure. |
