Formulation of Screen-Printable Cu Molecular Ink for Conductive/Flexible/Solderable Cu Traces

Abstract

Screen printing is the most common method used for the production of printed electronics. Formulating copper (Cu) inks that yield conductive fine features with oxidation and mechanical robustness on low-temperature substrates will open up opportunities to fabricate cost-effective devices. We have formulated a screen-printable Cu metal-organic decomposition (MOD) ink comprising Cu formate coordinated to 3-(diethylamino)-1,2-propanediol, a fractional amount of Cu nanoparticles (CuNPs), and a binder. This simple formulation enables ∼70–550 μm trace widths with excellent electrical [∼8–15 mΩ/□/mil or 20–38 μΩ·cm] and mechanical properties with submicron-thick traces obtained by intense pulse light (IPL) sintering on Kapton and poly­(ethylene terephthalate) (PET) substrates. These traces are mechanically robust to flexing and creasing where less than 10% change in resistance is observed on Kapton and ∼20% change is observed on PET. Solderable Cu traces were obtained only with the combination of the Cu MOD precursor, CuNP, and polymer binder. Both thermally and IPL sintered traces showed shelf stability (<10% change in resistance) of over a month in ambient conditions and 10–70% relative humidity, suitable for day-to-day fabrication. To demonstrate utility, light-emitting diodes (LEDs) were directly soldered to IPL sintered Cu traces in a reflow oven without the need for a precious metal interlayer. The LEDs were functional not only during bending and creasing of the Cu traces but even after 180 min at 140 °C in ambient air without losing illumination intensity. High definition television antennas printed on Kapton and PET were found to perform well in the ultrahigh frequency region. Lastly, single-walled carbon nanotube-based thin-film transistors on a silicon wafer were fabricated with a screen-printed Cu source and drain electrodes, which performed comparably to silver electrodes with mobility values of 12–15 cm2 V−1 s−1 and current on/off ratios of ∼105 and as effective ammonia sensors providing parts per billion-level detection.

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

“…More recently, Deore et al formulated a screen-printable mixed ink from a CuF–3-(diethylamino)-1,2-propanediol (DEAPD) complex, together with a fractional amount of Cu nanoparticles [ 144 ]. The screen-printable mixed ink was formulated by mixing dry Cu(II) formate (40.2%), DEAPD (43.70%), Cu nanoparticles (0.40%), water (14.14%), glycerol (1.26%), and polyester binder (0.3%) in a planetary mixer for 30 min.…”

“…( f ) Volume resistivity of screen-printed Cu traces as a function of nominal line width from Cu molecular ink and IPL sintered on PET. Reprinted with permission from reference [ 144 ], Copyright American Chemical Society, 2019. ( g ) Schematic diagram: mask printing and fabrication of Cu-Ag alloy electrodes or circuits by low-temperature procuring and rapid sintering under an air atmosphere.…”

Advanced Nanomaterials, Printing Processes, and Applications for Flexible Hybrid Electronics

“…The electrical resistivity of patterns after a low temperature (120 • C) sintering treatment was approximately 5.8 × 10 −5 Ω cm. Recently, screen-printable Cu metallic oxide decomposition (MOD) ink was reported [144]. They printed Cu traces with Cu ink comprising a MOD compound, conductive filler, and binder, followed by thermal and IPL (intense pulse light) sintering.…”

Sustainable Advanced Manufacturing of Printed Electronics: An Environmental Consideration

“…Additives are used for supplementary properties, such as promoting stability, or preventing oxidation, flocculation, etc. [33]. In PE applications, binders and some of the additives act as an insulator and reduce the conductivity.…”