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.

Insight into the Types of Alkanolamines on the Properties of Copper(II) Formate-Based Conductive Ink

Conductive inks are one of the most important functional materials for printed flexible electronic devices, and their properties determine the methods of subsequent patterning and metallization. In comparison with copper nanoparticle or nanowire inks, copper particle-free inks employing copper(II) formate (Cuf) as a precursor have attracted the interest of researchers due to their flexibility in preparation, excellent stability, and lower conversion temperature. Alkanolamines can provide Cuf with excellent solubility in alcohols while being less toxic and having a certain reducibility, making them preferable ligands in comparison with aliphatic amines and pyridine. However, there have been few studies on the effects of the alkanolamine types on the performance of Cuf inks. Also, the decomposition mechanism of copper-alkanolamine complex inks is not clear. In this work, different kinds of alkanolamines were chosen as ligands to formulate Cuf inks to address the mentioned issues. The influences of amine types on the stability, wettability, thermal decomposition behavior, and electrical performance of the formulated Cuf particle-free inks were investigated in detail. The results show that the utilization of alkanolamines could provide Cuf with excellent solubility in alcohols, resulting in an ink with good stability and favorable wetting properties. The thermal decomposition temperature and electrical performance of the formulated copper ink are largely dependent on the amine used. When amines with a longer carbon chain and more branches were utilized to prepare the ink, a decreased decomposition temperature was observed on the derived inks because of the steric hindrance effect. Copper films with good morphology and conductivity could be obtained at low temperatures by selecting the appropriate alkanolamine. Copper particle-free conductive ink from 2-amino-2-methyl-1-propanol demonstrated better morphology and electrical performance (16.09 μΩ·cm) and was successfully used for conductive circuits by direct-writing.

E-Textile by Printing an All-through Penetrating Copper Complex Ink

Wearable electronics is an emerging field in academics and industry, in which electronic devices, such as smartwatches and sensors, are printed or embedded within textiles. The electrical circuits in electronics textile (e-textile) should withstand many cycles of bending and stretching. Direct printing of conductive inks enables the patterning of electrical circuits; however, while using conventional nanoparticle-based inks, printing onto the fabric results in a thin layer of a conductor, which is not sufficiently robust and impairs the reliability required for practical applications. Here, we present a new process for fabricating robust stretchable e-textile using a thermodynamically stable, solution-based copper complex ink, which is capable of full penetrating the fabric. After printing on knitted stretchable fabrics, they were heated, and the complex underwent an intermolecular self-reduction reaction. The continuously formed metallic copper was used as a seed layer for electroless plating (EP) to form highly conductive circuits. It was found that the stretching direction has a significant role in resistivity. This new approach enables fabricating e-textiles with high stretchability and durability, as demonstrated for wearable gloves, toward printing functional e-textile.