Ulrich S. Schubert 1 2 Sebastian Wuenscher 1 2 Anke Teichler 1 2 Jolke Perelaer 1 2
In recent years, inkjet printing is increasingly used as a flexible and digital patterning technique in order to deposit functional materials for the manufacturing of microelectronic devices including organic light emitting diodes (OLED), organic photovoltaics (OPV), radio frequency identification tags (RFID) and organic radical batteries (ORB). Due to its minimal waste generation, its efficient handling of expensive materials and its mask-less processing, inkjet printing represents a widely accepted alternative to conventional patterning methods, such as spin-coating, vapor deposition and photolithography.
In the manufacturing process of flexible electronics, inkjet printing can be used for thin film deposition of active materials like conjugated polymers, metal ion containing small molecules as well as composites of redox active polymers and carbon nanoparticles.
Apart from the active layer materials, metal precursors, such as silver nanoparticle inks, are printed onto flexible substrates in order to provide electrical conductive antennas, electrodes, contacts and interconnects. However, silver nanoparticle inks are not conductive after printing, which is due to the presence of organic stabilizers that surround the single particles in order to prevent agglomeration in the ink and ensure processability. Therefore, a post-printing procedure is required to remove the organic material from the particle surfaces, merge the particles to a continuous network, hence yielding electrical conductive structures. This procedure is called sintering. The conventional thermal sintering requires temperatures above 200 °C and is therefore not compatible with the thermo-sensitive foils used as substrate materials. Therefore, alternative approaches, like exposure to a non-thermal plasma, are used to successfully sinter inkjet-printed silver nanoparticle inks without affecting the substrate materials. This approach allows the production of electrically conductive components on flexible substrates via inkjet-printing.
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