Femtosecond laser sintering of metal nanoparticles for high-performance flexible circuits

Soft electronics that integrate metal thin film on flexible substrate play a pivotal role in wearable health monitoring systems, personalized medical devices and human-machine interactions. With the ever-increasing demand for devices with high performance, miniaturization, and extended longevity, solving problems such as poor electrical properties, limited mechanical reliability, and potential substrate damage has become a key issue in the laser sintering of metal nanoparticle thin films on flexible substrates. In this work, we propose a method to sinter silver nanoparticles into dense films on flexible substrates using a synergistic combination of laser-induced thermal effects and shockwaves enabled by precise ultrafast laser thermomechanical regulation. Under optimal conditions, the thin silver film fabricated using the proposed method shows near-full-density microstructure with outstanding electrical conductivity and mechanical reliability. The electrical resistivity, as validated by four-point probe measurements, is as low as approximately 1.4 times that of the bulk material and shows only a slight change after 100,000 bending cycles, significantly outperforming conventional laser sintering methods. Consequently, the proposed method represents a significant advancement in flexible circuit fabrication technology, demonstrating strong potential to obtain highly conductive electronic circuits with robust mechanical reliability.