Functional Silver Nanoink for Direct Write Applications

Direct write (DW) technology offers a simple method of rapid manufacturing technology for printing electronic, optoelectronic devices, and complex functional devices. The key component of DW technology is the functional inks, which are colloidal suspensions of functional nanoparticles in various solvents such as aerosol or liquid form. With a DW approach, patterns or structures can be easily deposited on flexible substrates such as paper, plastics, and composites, once the solvent volatilizes or is driven off via conventional, laser, or microwave sintering. In this work, polymer-assisted silver (Ag) nanoinks were synthesized by silver salt and polymer in the water solution at relatively high silver precursor concentrations and relatively low concentration of polymers. The silver nanoparticle dispersion and morphology was examined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results showed that the size of Ag nanoparticles was in nanoscale (∼20 nm) with a narrow distribution of Ag nanoparticle sizes. The viscosity and thermal properties of synthesized silver nanoinks were characterized to determine their applicability and the lifetime. It has been shown that the synthesized silver nanoink can be printed on a flexible plastic substrate or glass substrate. The morphology of the Ag nanoink line printed on the substrate was observed by optical microscopy and scanning electron microscopy (SEM) to understand the relationship between the microstructure and wettability. Uniaxial tension tests of silver nanoink line on a Kapton film indicate that the ink can be stretched ∼20% without failure. The resistance of silver nanoink line printed on the Kapton films was also measured by four probe conductivity measurement system to assess the electrical performance. The resistivity is about 7.5 × 10⁻⁵ Ω-cm by thermal treatment at 250°C for 30 min, which is about half that of bulk silver (1.6 × 10⁻⁶ Ω-cm). Overall, the performance of the synthesized silver nanoink is comparable to a commercially available ink with lower Ag weight content at relatively low cost.