Cu Ion Ink for a Flexible Substrate and Highly Conductive Patterning by Intensive Pulsed Light Sintering

Abstract

Direct printing techniques that utilize nanoparticles to mitigate environmental pollution and reduce the processing time of the routing and formation of electrodes have received much attention lately. In particular, copper (Cu) nanoink using Cu nanoparticles offers high conductivity and can be prepared at low cost. However, it is difficult to produce homogeneous nanoparticles and ensure good dispersion within the ink. Moreover, Cu particles require a sintering process over an extended time at a high temperature due to high melting temperature of Cu. During this process, the nanoparticles oxidize quickly in air. To address these problems, the authors developed a Cu ion ink that is free of Cu particles or any other impurities. It consequently does not require separate dispersion stability. In addition, the developed ink is environmentally friendly and can be sintered even at low temperatures. The Cu ion ink was sintered on a flexible substrate using intense pulsed light (IPL), which facilitates large-area, high-speed calcination at room temperature and at atmospheric pressures. As the applied light energy increases, the Cu2O phase diminishes, leaving only the Cu phase. This is attributed to the influence of formic acid (HCOOH) on the Cu ion ink. Only the Cu phase was observed above 40 J cm(-2). The Cu-patterned film after sintering showed outstanding electrical resistivity in a range of 3.21-5.27 μΩ·cm at an IPL energy of 40-60 J cm(-2). A spiral-type micropattern with a line width of 160 μm on a PI substrate was formed without line bulges or coffee ring effects. The electrical resistivity was 5.27 μΩ·cm at an energy level of 40.6 J cm(-2).

Control of the Particle Distribution in Inkjet Printing through an Evaporation-Driven Sol–Gel Transition

“…Similarly, printed electronics are limited by variation of the conductivity or porosity across a printed feature. [17][18][19] Biological assays based on inkjet technology also need a uniform concentration of material across the deposit to be most effective.…”

Flash light sintered copper precursor/nanoparticle pattern with high electrical conductivity and low porosity for printed electronics

“…For this reason, copper nanoparticles have received considerable attention due to their lower cost; however, copper nanoparticles can be easily oxidized and cannot be sintered by thermal sintering under ambient conditions. To solve these problems, various sintering methods such as laser irradiation [2], microwave [13] and precursor processes [14][15][16] were studied by several researchers. These approaches have limitations in mass production because of their low throughput, high complexity, and considerable environmental obstacles (e.g., high temperature or vacuum conditions).…”

Inkjet-printed copper electrodes using photonic sintering and their application to organic thin-film transistors

“…However, Cu nanoparticle inks generally require high sintering temperatures above 300°C to obtain high conductivities [13,14]. To address this problem, photonic sintering using intense pulsed light with millisecond exposure times and a wide range of wavelengths has been reported as the most useful sintering method for the Cu nanoparticles [15][16][17][18]. A Cu nanoparticle layer can be converted to a highly conductive layer due to instantaneous heat generation within the layer accompanied by absorption of the intense pulsed light.…”

“…Some research groups have reported improvements in layer conductivity or the reduction of sintering temperature for Cu nanoparticles, however they have focused on the application to interconnect technologies on flexible polymer film at low temperatures [15][16][17][18]. There have been few reports on the application of the printed Cu electrodes to TFT [13,14].…”