Sintering Copper Nanoparticles with Photonic Additive for Printed Conductive Patterns by Intense Pulsed Light

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.

Optimization of Hybrid Ink Formulation and IPL Sintering Process for Ink-Jet 3D Printing

“…It has been confirmed that the SiO 2 particles represent an elevation of about 50 to 90 nm and have a spherical shape. In order to apply SiO 2 ink to the ink-jet printing process, it has been reported that an average particle size of about 300 nm or less must be shown to prevent blockage in the print head nozzle; most of the SiO 2 particles used in this study showed uniform inlet and spherical shapes of less than 90 nm, which was judged to meet these requirements [ 20 , 21 , 22 ]. Figure 2 c shows the contact angle of the photo-curable nano SiO 2 ink on a hydrophobic-coated glass substrate using PFTS.…”

“…Polyvinylpyrrolidone (PVP, Mw = 40,000g/mol, Sigma Aldrich, Munich, Germany) was added as a surface stabilizer and a reducing agent by sonication for 30 min. Then, ethanol (EtOH, 95%, Dae-Jung, Korea) and DEG (Diethylene glycol, 99%, Dae-Jung, Korea) were added to secure the printable and stirred at room temperature for 12 h [ 19 , 20 , 21 ].…”

Green Manufacturing of Highly Conductive Cu2O and Cu Nanoparticles for Photonic-Sintered Printed Electronics

“…Our study shows that the Cu 2 O NPs with high absorbance in UV and short visible regions are most suitable to use the light energy for sintering because the semidehydro­ascorbic acid molecules absorbed on the Cu 2 O NPs play the role of self-reduction from Cu 2 O NPs to pure metallic Cu trace. Table compares the measured electrical resistivity from various types of conductive Cu traces with optimized processing conditions. − …”

Surface and Interface Designs in Copper-Based Conductive Inks for Printed/Flexible Electronics

“…Cu oxide nanoparticles are more stable than their Cu nanoparticle counterparts. The IPL sintering can remove the oxide shells of Cu nanoparticles using the IPL-reactive protective agents, such as PVP, leaving a conductive Cu film in a short period of time (a few ms) under ambient conditions [ 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 ]. Ryu et al explained this phenomenon by oxide reduction either via an intermediate acid created by light irradiation or by hydroxyl (–OH) end groups, which act like long-chain alcohol reductants [ 100 ] ( Figure 11 ).…”

“…Besides, the adhesion strength of the two-step sintered Cu ink film indicated a 5B level compared with that of a one-step sintered case of a 3B level. Chung et al used a mixed ink of Cu nanoparticles (~100 nm) with oxide shells of 20 nm and CuO nanoparticles (50 nm) for multiple IPL sintering to increase the light absorption efficiency and further decrease voids between Cu nanoparticles in the Cu film [ 106 ]. With an optimal Cu/CuO weight ratio of 1:80, the resistivity of the Cu film reduced as low as 6.5 μΩ·cm on PET, with the single energy at 3.08 J/cm 2 .…”