Abstract
In this study, an ink formulation was developed to prepare conductive copper thin films with compact structure by using intense pulsed light (IPL) sintering. To improve inter-particle connections in the sintering process, a cuprous oxide shell was synthesized over copper nanoparticles (CuNP). This cuprous oxide shell can be reduced by IPL with the presence of a reductant and fused to form connection between large copper particles. However, the thermal yield stress after strong IPL sintering resulted in cracks of conductive copper film. Thus, a multiple pulse sintering with an off time of 2 s was needed to reach a low resistivity of 10−5 Ω·cm. To increase the light absorption efficiency and to further decrease voids between CuNPs in the copper film, cupric oxide nanoparticles (CuONP) of 50 nm, were also added into ink. The results showed that these CuONPs can be reduced to copper with a single pulse IPL and fused with the surrounding CuNPs. With an optimal CuNP/CuONP weight ratio of 1/80, the copper film showed a lowest resistivity of 7 × 10−5 Ω·cm, ~25% conductivity of bulk copper, with a single sintering energy at 3.08 J/cm2. The ink can be printed on flexible substrates as conductive tracks and the resistance remained nearly the same after 10,000 bending cycles.
Highlights
Recent advancements in printing technology have shown the capability of fabricating highly conductive patterns for light-weight flexible electronic with conductive inks. [1] Among those inks, metal nanoparticles, such as gold [2,3] and silver, [4,5] are widely used as conductive filler due to their great conductivity
Inkjet printing processes require stable nanoparticles inks with high conductivity after long term and high temperature post-treatment
With the nature of intense local heating, the intense pulsed light (IPL) process is found to be very efficient in decomposing protective polymers, especially coupled with UV or infrared lights, [16] and IPL-sintered tracks can exhibit great conductivity close to bulk copper
Summary
Recent advancements in printing technology have shown the capability of fabricating highly conductive patterns for light-weight flexible electronic with conductive inks. [1] Among those inks, metal nanoparticles, such as gold [2,3] and silver, [4,5] are widely used as conductive filler due to their great conductivity. Recent advancements in printing technology have shown the capability of fabricating highly conductive patterns for light-weight flexible electronic with conductive inks. Inkjet printing processes require stable nanoparticles inks with high conductivity after long term and high temperature post-treatment. To resolve the high temperature sintering problem, intense pulsed light (IPL) technology has recently drawn lots of attention for metal nanoparticle sintering process. With the nature of intense local heating, the IPL process is found to be very efficient in decomposing protective polymers, especially coupled with UV or infrared lights, [16] and IPL-sintered tracks can exhibit great conductivity close to bulk copper. It has been found that inkjet printed copper oxide nanoparticles can absorb IPL to yield locally high temperatures and react with the reduction agent into conductive copper thin films. To facilitate the chemical reactions, these MOD/IPL procedures generally need more energy consumption than copper nanoparticle inks
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