Enhanced flexibility and environmental durability of copper electrode produced with conductive ink containing silane coupling agents with diamine and ether spacer

Cu-based conductive inks are more cost effective than silver-based ones for flexible electronics. However, it is challenging to simultaneously ensure the mechanical flexibility, environmental oxidation durability, and low resistance of the sintered Cu electrodes. To achieve this goal, Cu-based conductive inks including silane coupling agents are developed and used to produce flexible Cu electrodes on cellulose paper after air–atmosphere sintering. The key factor to achieve the mechanical flexibility and environmental oxidation durability at the same time is the use of aminoethyl-aminopropyltrimethoxysilane (AEAPTMS) or 3-glycidoxypropyltrimethoxysilane (GPTMS). Negligible resistance change is observed in the sintered Cu electrode with AEAPTMS, even after 1000 repeated bending cycles with a bending radius of 5 mm and exposure at 60 °C/80% RH for 7 days. Especially, Cu electrodes produced using GPTMS show improved flexibility with negligible resistance change even after 10,000 bending cycles. To demonstrate the applicability of these Cu electrodes, a flexible paper-based movement sensor is successfully fabricated from the present Cu-based ink. This approach using silane coupling agents will contribute to the reliable operation of Cu-based flexible devices with high mechanical and environmental durability.