Versatile Molecular Ink Platforms for Printed Electronics
A suite of silver and copper molecular ink (MINK) platforms formulated for the screen, inkjet, flexo, and gravure is presented. The MINK technology was developed by researchers at the National Research Council of Canada in collaboration with e2ip technologies in order to drive advancements in printed electronics. MINK is capable of producing thin, narrow, screen-printed traces with exceptional electrical (<5 mΩ/sq/mil) and mechanical properties including bending, flexing, and elongation. In addition, the decomposition temperature of the MINKs can be tuned through a selection of the metal salt molecules incorporated into the ink, enabling compatibility on substrates ranging from PET and polycarbonate to higher temperature substrates such as Kapton and glass. MINKS are also fully compatible with intense-pulsed light-based sintering protocols, enabling the production of highly conductive traces on low-temperature substrates in a high-throughput manner. A key attribute of MINKs is the production of thin (sub-micrometer) traces that are remarkably conformal and enable the development of advanced designs in printed electronics including fully printed metal−insulator−metal band-pass filters and fully printed, high-mobility thin-film transistors (TFTs) based on semiconducting single-walled carbon nanotubes with mobility values of <10 cm2 V-1 s-1 and current on/off ratios >104. Of particular note are new developments in copper-based MINKs, where 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, making them suitable for day-to-day fabrication. In a further demonstration of utility, light-emitting diodes (LEDs) can be directly soldered to IPL sintered Cu traces in a reflow oven without the need for a precious metal (silver) interlayer. The LEDs were functional not only during bending and creasing of the Cu traces to which they are soldered but also following a 3-hour exposure 180 min at 140 °C in ambient air without losing illumination intensity. Overall, these silver and copper-based MINKs provide alternative conductor material options for emerging applications such as In-Mold Electronics (IME), transparent conductive films, and advanced sensors, which can improve electrical and mechanical performance compared with traditional flake silver or nanosilver materials. In regards to IME specifically, MINK has the potential to improve the elongation tolerances in thermoforming applications.