Sep 14 2018
A new study by scientists at Soonchunhyang University in South Korea provides an understanding into the processing of copper nanoparticle ink using green laser light.
Printed electronics use standard printing methods to produce electronic devices on different substrates like plastic films, glass, and paper.
Interest in this area is increasing due to the potential to make cheaper circuits more efficiently than conventional approaches.
Kye-Si Kwon and his colleagues have previously worked with silver nanoparticle ink, but they recently turned to copper (derived from copper oxide) as a potential economical alternative.
Metallic inks composed of nanoparticles possess an advantage over bulk metals because of their lower melting points.
Although the melting point of copper is around 1,083 °C in bulk, according to Kwon, copper nanoparticles can be made to reach their melting point at just 150 to 500 °C—through a process known as sintering. Then, they can be combined and bound together.
Kwon’s team concentrates on photonic methods for heating nanoparticles by the absorption of light. “A laser beam can be focused on a very small area, down to the micrometer level,” explained Kwon and doctorate student Md. Khalilur Rahman.
Heat from the laser serves two key purposes: changing copper oxide into copper and boosting the conjoining of copper particles through melting.
A green laser was chosen for these tasks because its light (in the 500- to 800-nm wavelength absorption rate range) was thought to be best suited to the application.
Kwon was also inquisitive because, to his knowledge, the use of green lasers in this role has not been stated elsewhere.
In their experiment, his team used copper oxide nanoparticle ink available in the market, which was spin-coated onto glass at two speeds to attain two thicknesses. Then, they prebaked the material to dry out a majority of the solvent before sintering.
This is essential to cut the copper oxide film thickness and to stop air bubble explosions that might happen from the solvent unexpectedly boiling during irradiation.
After a chain of tests, Kwon’s team decided that the prebaking temperature should be a little lower than 200 °C.
The scientists also examined the optimal settings of laser power and scanning speed during sintering to improve the conductivity of the copper circuits.
They learned that the best sintered results were generated when the laser power ranged from 0.3 to 0.5 Watts.
They also discovered that to reach the preferred conductivity, the laser scanning speed should not be faster than 100 mm/second, or slower than 10 mm/second.
Furthermore, Kwon and his group examined the thickness of the film—before and after sintering—and its influence on conductivity. Kwon and his group concluded that sintering cuts thickness by as much as 74%.
In subsequent experiments, Kwon’s team will scrutinize the substrate effects on sintering. Taken together, these studies can offer answers to some of the reservations delaying printed electronics.