Fabrication of submicron-sized metal patterns on a flexible polymer substrate by femtosecond laser sintering of metal nanoparticles

The femtosecond laser sintering of metal nanoparticles was studied in order to fabricate submicron-sized metal patterns on flexible polymer substrates for various applications in the electronic and photonic industries. In this process, a mode-locked Ti:sapphire laser beam was tightly focused on silver nanoparticles. To achieve a homogeneous dispersion of the silver nanoparticles, the nanoparticles were prepared using a two-phase reduction method wherein the silver nanoparticles were encapsulated by functional surfactants. The key advantage of the femtosecond laser sintering process is that it reduces the heat-affected zone during sintering, as the femtosecond (10^-15s) laser pulse is shorter than the heat diffusion time (picosecond: 10^-12s). Therefore, sintering of metal nanoparticles is limited to the laser focal spot and the thermal diffusion effect is suppressed, enabling the realization of submicron-sized metal patterns on flexible polymer substrates. Through this process, metal conductors with submicron-sized features and high conductivity were successfully fabricated. As demonstrated by the obtained results, the femtosecond laser sintering of metal nanoparticles is a novel process that offers direct, low-temperature, ultra-high-resolution results, and which will have numerous further applications in electronics and photonics.