Enhanced high temperature stability of printed Cu wirings based on large Cu particle ink, Ag element addition, and intense pulsed light sintering

Abstract

With the market expansion of printed electronics, to develop cheap Cu inks instead of expensive Ag and Au inks becomes increasingly inevitable. However, the complicated synthetic process and the poor oxidation resistance of Cu nanoparticles are likely to hinder the large scale preparation of highly stable Cu inks. And printed Cu wirings can still be easily oxidized at a high temperature, which is also an insurmountable obstacle for their practical applications. This paper provides three strategies (using submicron Cu particles instead of Cu nanoparticles, utilizing intense pulsed light (IPL) sintering, and introducing anti-oxidation elements) and develops two kinds of hybrid Cu inks of Cu particles and metal complex to address the oxidation problem of Cu inks and improve the conductivity as well as stability of sintered Cu wirings. It is determined that the in-situ formed fresh and active metal nanoparticles decomposed from metal complex play a role of nano-welders in the sintering of adjacent large Cu particles. With the intense pulsed light sintering, the created metal nanoparticles can totally grow with the large Cu particles and enable the formation of highly dense and conductive wirings (3.5 μΩ cm). In addition, it should be noted that the addition of Ag element can greatly improve the high temperature stability of printed Cu-based wirings. For example, the Cu-Ag wirings maintain a stable resistance (R/R 0 < 1.5) after 1000 bending cycles at 220°C. Therefore, these Cu-based inks can be used to create various circuits for printed flexible electronics and flexible wirings for wide band gap power electronic devices.