Ultrafast Laser-Induced Thickness-Limited Sintering of Metal Nanoparticle Film for Ultrathin Flexible Microelectronic Devices

Laser sintering of metal nanoparticles (NPs) has been widely used in flexible microelectronic device fabrication, wherein the sintered layer thickness is a key factor affecting the mechanical stability and conductivity. In this work, ultrathin flexible electronic circuits on flexible substrates with robust bonds and excellent conductivity have been fabricated through ultrafast laser-induced thickness-limited sintering of the metal NP film. When the laser fluence is below the damage threshold of the metal NP film, sintered layer thickness can be controlled by the laser parameters. The maximum thickness of the dense sintered NP layer is limited to 355, 421, 491, 527, and 647 nm at laser pulse durations of 0.3, 5, 10, 15, and 20 ps, respectively. This thickness-limited sintered layer is mainly determined by the plasmonic photothermal absorption of metal NPs and heat transfer within the NP layer. Due to the nonthermal process under intense ultrafast laser irradiation, the metal–polymer interaction can be further enhanced with minimal damage on substrates. The resistivity of the as-received Ag NP film decreases to 6.32 μΩ·cm after laser sintering at a pulse duration of 20 ps. Meanwhile, the relative resistance of the NP film increases to 2.7, 1.7, and 1.03 after 10⁵ bending cycles, 500 tape peeling cycles, and water flow impinging for 60 min, respectively. This thickness-controlled ultrathin Ag NP film fabricated by ultrafast laser sintering exhibits excellent mechanical robustness and electrical conductivity, which shows great promise in ultrathin flexible microelectronic devices.