Non-Newtonian Binary Cu Nanocrystal-Microcrystal Colloidal Inks for Printable Nanoscale-Soldered Conductors and RF...

Area of Science:

• Materials Science
• Nanotechnology
• Electronics Engineering

Background:

• Printed electronics require high-conductivity metal traces.
• Traditional copper inks face challenges in achieving desired thickness and conductivity for RF applications.

Purpose of the Study:

• To formulate and print high-conductivity copper traces using binary mixtures of copper nanocrystals (NCs) and microcrystals (MCs).
• To enable high-performance printed radio frequency (RF) electronic devices and components for the Internet of Things (IoT).

Main Methods:

• Formulation of Cu inks with binary mixtures of Cu NCs (~5 nm) and Cu MCs (~500 nm).
• Post-deposition treatments including solid-state NH4Cl chemical treatment and low-temperature N2 annealing.
• Printing techniques: screen printing and direct ink writing (DIW) on flexible substrates.

Main Results:

• Achieved micron-thick, high-conductivity copper traces with resistivities as low as 95 ± 22.6 μΩ·cm.
• Optimized 75 wt% NC/MC films yielded resistivities ~14.5 times that of bulk Cu after annealing.
• Fabricated screen-printed flexible RF capacitors with a quality factor (Q) of 4.89.
• Demonstrated DIW of over 100 μm thick traces.

Conclusions:

• NC-enabled processing of mixed NC/MC systems provides a viable route for manufacturable, high-frequency metal components.
• This technology supports the development of printed electronics for IoT platforms.
• The developed inks and treatments offer a pathway to high-performance printed RF devices.