An ambient air sinterable Cu@Ag nanoparticle ink with exceptional oxidation resistance and stability for EMI shielding and printed RFID applications

Abstract

Though copper is cheap and offers the highest conductivity per dollar among metals, it is not as popular in printed electronics as commercial conductive inks due to its fast oxidation, even under native conditions. Herein, we developed a highly stable and durable copper ink through a core–shell approach. The chemically synthesized copper core has a quasi-spherical shape with an ∼77 nm average size and a 2–5 nm silver shell. The remarkable oxidation stability of the ink was evaluated using TGA and XPS, confirming that the particles were relatively durable up to 60 days of storage under native conditions and remained stable up to a temperature of 250 °C upon thermal treatment. The optimized silver-encapsulated copper nanoparticles were used to formulate an ambient air-sinterable ink to obtain a sheet resistance of 0.21 ± 0.06 Ω □⁻¹ (conductivity ((2.55 ± 0.72) × 10⁵ S m⁻¹) when sintered at 250 °C for 30 minutes. Further, the screen-printed patterns developed using the formulated ink have been demonstrated to be excellent for EMI shielding and RFID applications. A four-stroke printed silver-encapsulated copper nanoparticle ink showed an EMI shielding of ∼51.3 dB, corresponding to a specific shielding effectiveness value of 2960 dB cm² g⁻¹ in the Ku band. Also, the formulated ink has been deployed to print a UHF RFID antenna that showed bidirectional radiation performance with a maximum trans-receiver length of 115 cm. Additionally, the tag showed read–write capability even under extreme bent conditions.