Monthly Archives: April 2010

Copper Nanoparticles for Printed Electronics

Copper Nanoparticles for Printed Electronics

In the past few years, the synthesis of Cu nanoparticles has attracted much attention because of its huge potential for replacing expensive nano silver inks utilized in conductive printing. A major problem in utilizing these copper nanoparticles is their inherent tendency to oxidize in ambient conditions. Recently, there have been several reports presenting various approaches which demonstrate that copper nanoparticles can resist oxidation under ambient conditions, if they are coated by a proper protective layer. This layer may consist of an organic polymer, alkene chains, amorphous carbon or graphenes, or inorganic materials such as silica, or an inert metal. Such coated copper nanoparticles enable achieving high conductivities by direct printing of conductive patterns. These approaches open new possibilities in printed electronics, for example by using copper based inkjet inks to form various devices such as solar cells, Radio Frequency Identification (RFID) tags, and electroluminescence devices. This paper provides a review on the synthesis of copper nanoparticles, mainly by wet chemistry routes, and their utilization in printed electronics.

copper nanoparticles for printed electronics

copper nanoparticles for printed electronics

 

At present most conductive inks are based on micron size Ag flakes. Ag powders (nano-sized particles) have been commercially available for some years. Other metals used in inks are Cu and CuO. Also these metal particles can be purchased in different particle sizes and morphologies (particles and nanowires) from tens of nanometers to micron scale flakes. Ag possesses the highest electrical conductivity among metals (6,3 * 107 S/m) and is resistant to oxidation but has a high and fluctuating price (approximately 500 €/kg in January 2014). Typically nanoparticle based inks are considerably more expensive than inks based on flakes due to higher price of nanoscale metal particles and special ink formulation.

Cu has almost the same conductivity (5,96*107 S/m) than Ag but is considerably less expensive (approximately 5 €/kg in January 2014). The challenge with Cu is its rapid oxidation in the air. Oxides are not conductive which delimits Cu usage in printed electronics applications. Cu can be protected in ink formulation by using protecting agents such as ligands. Low cost inks based on CuO contain agent which reduces oxide back to metallic copper in photonic sintering process. Still Cu ink usage, if not protected or shielded in the application, is limited to only certain, usually shorter life-time products. Advantages of nanoparticles over flakes are ability to reach same conductivity with thinner and finer printed pattern with less metallic particles, ability to use non-contact printing method with fragile substrates and ability to use lower sintering temperature which allows cheaper and temperature sensitive substrates such as plastics and paper to be used. The main challenge is the manufacturing cost and obtaining stable fluid dispersion in inks.

copper nanoparticles for printed electronics

copper nanoparticles for printed electronics

 

Printed electronics represent an emerging area of research that promises large markets due to the ability to bypass traditional expensive and inflexible silicon-based electronics to fabricate a variety of devices on flexible substrates using high-throughput printing approaches.

 

In the past few years, the synthesis of Cu nanoparticles has attracted much attention because of its huge potential for replacing expensive nano silver inks utilized in conductive printing. A major problem in utilizing these copper nanoparticles is their inherent tendency to oxidize in ambient conditions. Recently, there have been several reports presenting various approaches which demonstrate that copper nanoparticles can resist oxidation under ambient conditions, if they are coated by a proper protective layer. This layer may consist of an organic polymer, alkene chains, amorphous carbon or graphenes, or inorganic materials such as silica, or an inert metal. Such coated copper nanoparticles enable achieving high conductivities by direct printing of conductive patterns. These approaches open new possibilities in printed electronics, for example by using copper based inkjet inks to form various devices such as solar cells, Radio Frequency Identification (RFID) tags, and electroluminescence devices.

copper nanoparticles for printed electronics

copper nanoparticles for printed electronics

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