Copper Nanoparticle Conductive Inks: Characterization and Fabrication of Inkjet Printed Flexible Electrodes

In this article, multiple commercially available copper (Cu) nanoparticle conductive inks have been investigated – both as received and in modified form, for future flexible printed electronic device fabrication and their applications. Critical fluid properties such as viscosity, surface tension, particle size measurement, and pH values have been analyzed thoroughly along with their temperature dependence for three commercial formulations, Ink 1: DM-CUI-5002 (Dycotec Materials Ltd. UK), Ink 2: Metalon® CI-004 (NovaCentrix, USA), Ink 3: Metalon® CI-005 (NovaCentrix, USA), and a fourth custom diluted version of DM-CUI-5002 (Ink 4). The mean particle sizes of the different Cu nanoparticle inks are 56.2 nm for Ink 1/ Ink 4, 8.62 nm for Ink 2, and 11.5 nm for Ink 3. The viscosities for Inks 1 – 4 are 17.14, 31.30, 13.52, and 15.02 cP respectively (20°C). The resistivity obtained for each nanoparticle ink varied from 8.89 µΩ-cm to 39.5 µΩ-cm. Fluid properties of the nanoparticle Cu inks have been optimized for inkjet printing using Fujifilm Dimatix Materials Printer – DMP 2850 based on legacy printheads and recently launched (2021) Samba G3L printheads. The electrochemical characterization of the ink/flexible inkjet printed electrodes has also been reported based on electrochemical impedance spectroscopy (EIS) measurement (phosphate buffer saline – PBS; pH 7.43). This article indicates the potential viability of utilizing commercially available Cu ink (Ink 3) for printing flexible electronics with both inkjet printheads. However, Ink 4 showed excellent performance with the lowest impedance (~ 400 Ω at 1kHz) making it a promising formulation for flexible inkjet printed Cu electronics.