The Influence of Ink Chemistry on the Microstructure Evolution and GHz RF Response of Printed Ag Transmission Lines.

High-frequency transmission is limited to the skin depth in metals. Because poor conductivity cannot be compensated for by increasing the conductor thickness as with DC, optimal transport properties are prerequisites for radio frequency (RF) use. Structural and chemical analyses of transmission lines printed using a traditional ink consisting of Ag nanoflakes in a dispersing phase revealed that optimized thermal treatments yielded thorough burnout of the binder, significant grain growth, elimination of the pore volume, and electrical responses that were comparable to values obtained for thermally evaporated, fully dense Ag controls. Specifically, a low DC resistivity of 2.3 µΩ·cm (1.4× bulk Ag) and RF transmission coefficients of 0.87 and 0.75 at 5 GHz and 10 GHz, respectively, were measured in the nanoflake Ag prints. Conversely, in transmission lines printed from a metal-organic decomposition ink, residual chemical contamination impeded diffusion and densification, yielding greater porosity, small grains that are pinned, and a degraded RF response. Reasonably good porosity approximations were obtained from a model based on percolation theory. The results indicate that contaminants at interfaces and pore surfaces impede diffusion, pore elimination, and full densification, and further, alter carrier dynamics and degrade RF response.

Molecular copper decomposition ink for printable electronics.

Nanostructured metal materials are the frontrunners of numerous electronic advancements. While realizing such potential, it is indispensable to address their oxidation and stability drawbacks, which are due to their high surface energies. Here, we report printable and air-stable molecular metal ink materials from metal-organic decomposition by using copper ions, including both copper formate and aqueous copper-amine complexes. By complexing copper formate with amines, the decomposition temperature of the printed molecular copper ink can be achieved at 100 °C, while maintaining its electric conductivity. The printed copper conductors exhibit a high electric conductivity of 35 MS m-1 (>50% of bulk copper's electric conductivity at room temperature) and an electromagnetic interference shielding effectiveness of 63 dB. The findings shown here of the molecular decomposition ink are promising for applications in printable electronics.