Highly conductive short chain carboxylic acid encapsulated silver nanoparticle based inks for direct write technology applications

In this study silver nanoparticles were synthesized with short chain (C6–C10) carboxylic acids as capping agents and prepared as conductive inks for fabricating electrically conductive patterns using direct write technologies. The structural characterization of as-synthesized nanoparticles revealed that the particles are spherical in shape with narrow size distribution (4.1 to 4.7 nm) and have face centered cubic crystal structure. Silver-particle-based inks were prepared by dispersing the particles in toluene and separating non-dispersing particles from the inks. The loading of silver particles in the solvent was increased with the increasing chain length of capping agents. As a result, inks with a wide range of nanoparticulate concentrations (∼3 to 66 wt%) were able to be prepared and most of these inks were stable for at least a month. All the inks exhibited shear thinning behavior and this shear thinning became more prominent for higher concentration inks. As the nanoparticle concentration of the inks was increased, surface tension was decreased and the contact angles of the inks with the Kapton® and glass were increased. Printing of microelectrodes, lines and films was carried out using aerosol jet printing and ultrasonic spray coating. The conductivity of printed microelectrodes was 10 to 87% of the bulk silver conductivity with the sintering temperatures as low as 130 to 250 °C depending on the ink used.