UV-curable Silver Nano Inks for Direct Printing

Abstract

These instructions are an example of what a properly prepared meeting abstract should look like. Proper column and margin measurements are indicated. Metallic silver (Ag) has been extensively investigated as electrodes or conductive materials in various electronic applications because of its high conductivity and stability against oxidation. Silver inks (or pastes) for various patterning methods, such as silk screen and ink-jet printing, were developed for radio frequency identification (RFID), microelectromechanical systems (MEMS), electrodes in plasma display (PDP), embedded capacitors, and source/drain electrodes for polymer thin film transistors. Generally, they should be composed of nanometerordered silver particles in order to increase the resolution of silver patterns and decrease the sintering temperature. The silver nanoparticles in the ink should be stable against agglomeration and grain growth, because clogging in the ink jet head may be caused. Also, ink with sufficiently high silver concentration is desirable for conductivity of the patterns at the relatively low sintering temperature. Recently, silver complex inkswhich are dissolved in an organic solvent and thermally decomposed to metallic silver after patterning, have been reported because silver nanoparticle ink is unstable at high solid contents. The silver complex ink is very stable at high concentration without additional stabilizers and reducing agents. Also, physical properties such as viscosity of ink can be easily controlled by changing the solvents, because various organic solvents could be used to prepare a silver complex ink. However, these silver complex inks cannot be applied on some substrates such as PET (poly ethylene terephthalate), which are even degraded at low sintering temperature below 200, because thermal decomposition temperature of metal complexes is about 250. In order to use these silver inks in industrial applications, either the sintering temperature of metal complexes must be lowered below 200℃ (ideally less than 100℃) or non-thermal reduction method has to be developed.In this study, we have prepared silver nano inks, both silver complex ink (Ag-CI) and silver nanoparticle ink (Ag-PI), and investigated their transformation behaviors to metallic silver byUV-irradiation. The effect of irradiation time and distance from UV source as well as the concentration of silver nano ink and types of solvent upon the formation of conductive patterns were studied with SEM, XRD, TGA, and IR spectrometry. Silver films for conductivity measurement were fabricated by a spin coating method using the silver nano inks on a polyimide substrate and characterized by a 4-point probe analysis. SEM images of UV cured films indicated that Ag-CI and Ag-PI on polyimide film got agglomerated and grain growth to larger silver particles after UV-irradiation. XRD pattern of cured Ag-CI film showed diffraction peaks at 2Θ of 38, 44, 64, 77° indicating the face-centered cubic (FCC) structure (JCPDS 04-0783) of typical silver. The increase in irradiation time and the decrease in irradiation height made the peak of XRD patterns sharper, showing higher level of crystallinity of silver nanoparticles. In conclusion, UV-curable silver nano inks developed in this study would be a good alternative for electronic devices with the low sintering temperature and can be widely used in flexible display technology.