Keywords: printed electronics, flexible electronics, novel printing, ultrasonic sintering
Summary:Novel and multi-material solvent-free printing process for printed electronics is developed using toner-type patterning of organic semiconductor, insulator, metal and other conductor particles, and the subsequent thin-film formation by ultrasonic sintering. Toner type printing makes circuit and device pattern of material particles by electrostatic force, although conventional toner technology was only for insulating complex materials charged by friction charging. In this work, we expanded this technology for metals and other conductive materials, for example, graphite, carbon nanotube, graphene, ZnO, Au, Ag, Cu and so on. In the electrostatic transfer patterning, approximately 10 - 30 micrometer resolution pattern printing, which depends on the material, was achieved in our laboratory in the development phase. High throughput and large area page printing are also expected in this type of technologies. On the other hand, ultrasonic sintering that enables the thin film formation and quick sintering by applying the ultrasonic vibration, was also applied on the wide range of materials. Ultrasonic sintering is a powerful tool to melt organic semiconductor and insulators, and to sinter the oxide semiconductor or metal particles in several seconds. Ultrasonic sintering generates local high temperature and instantaneous high pressure at the material interface, so we can sinter the oxides and metals on plastic film surface, and we also had demonstrated that we can make organic thin film transistor on plastic film surface. The electrostatic transfer use nearly the same principle as that used in office use toner printing, therefore that is additive, direct digital and page printing. In addition, toner printing is also environmentally friendly compared with other printing technologies because it is solvent free, saves materials, and enables easy recycling.