Effect of sintering atmospheres on printed silver nanoparticle patterns for flexible electronics application

A unique atmosphere using formic acid was introduced to sinter silver (Ag) nanoparticles (NPs) for conductive patterns applicable for flexible electronics. Printed Ag NP patterns on flexible polyimide sheets using Ag NP ink were sintered in the atmosphere selected from air, N2, or N2-bubbled formic acid (N2-FA). Microstructures, organic residues, and electrical and mechanical properties of the sintered Ag patterns were compared, depending on sintering parameters including atmosphere, temperature, and time. The Ag NP patterns sintered in N2-FA atmosphere revealed an effective decomposition of organic materials, resulting in lower electrical resistivities and improved mechanical properties. For the Ag NP patterns sintered in N2-FA, organic residues were obtained below 5 wt% and grain sizes increased to 30–31 nm when the sintering temperature increased from 80 to 140 °C and sintering time increased up to 12 min. Less amount of organic residues and larger grain sizes contributed to achieving lower electrical resistivity of 15.7 μΩ-cm and higher hardness and modulus with their respective values of 0.184 and 8.405 GPa. The Ag NP patterns sintered in N2-FA resulted in improved electrical and mechanical properties in comparison with those sintered in air or N2. The Ag NP patterns sintered in N2-FA had enough electrical conductivity to operate light emitting diode lamps and were used to fabricate a radio frequency identification (RFID) antenna tag. From the measurement of the return loss (S11) in the RFID tags, the antenna showed a dual-band feature with two resonance frequencies of 27.76 and 33.50 MHz, which gave the ability to receive and send information in both frequencies.