Realization of thick copper conductive patterns using highly viscous copper oxide (CuO) nanoparticle ink and green laser sintering

Abstract

The demand for lower-cost and higher-thickness metallic conductive patterns is increasing in printed electronics. Copper oxide (CuO) nanoparticle (NP) ink is a promising low-cost alternative to other metal-based nanoparticle inks such as Au and Ag. In order to obtain thick printed patterns using high viscosity (207,000 cPs) CuO NP ink, a time-pressure dispenser developed in our laboratory was used. After printing the CuO patterns, we used a continuous wave (CW) green laser with a 532 nm wavelength to reduce the CuO to Cu and sinter the reduced Cu nanoparticles. However, the laser absorption depth is known to be only a few dozens of nanometers. Therefore, when the thickness of CuO patterns exceeds 10 μm, it is unclear whether the reduction and sintering can be uniformly achieved through the thickness direction. We investigated the effects of different sintering parameters on the conversion of a thick CuO nanoparticle layer with a thickness of about 34 μm to form Cu conductive patterns. Under optimal sintering conditions, we obtained a resistivity of 8.75 μΩ·cm for a Cu conductive pattern with a width of 1 mm and a thickness of 18.4 μm, which is five times higher than the bulk resistivity. After creating Cu conductive patterns, we assessed their reliability by exposing them to elevated temperatures in an air atmosphere. The findings demonstrate notable resistance to oxidation at a temperature of 250 °C for a duration of 4 h.