Direct Writing of High-Resolution, High-Quality Pure Metal Patterns on Smooth Transparent Substrates by Laser-Induced Forward Transfer Followed by a Novel Laser Treatment

Additive manufacturing of high-resolution conductive metallic patterns is the current focus of interest for several different applications. The print of sensors, antennas, and screens on transparent materials enables the manufacture of smart structural electronics. Laser-induced forward transfer (LIFT) is a direct write technique capable of depositing microdroplets of metals from the solid phase by means of laser irradiation. Patterns are achieved by printing drops in a sequential fashion. Due to high heat conductivity of metals, droplets solidify before smearing; therefore, LIFT-printed structures exhibit high surface roughness, which harms their functioning and limits their applications. Herein, a new procedure is developed for the fabrication of continuous metallic lines at the micrometer resolution on smooth transparent substrates, using a combination of subnanosecond LIFT and a laser melting post-treatment. The melting process is conducted using laser pulses with the timescale of a microsecond. It is shown how one can find an optimized melting process to achieve smooth lines, without introducing oxidation or balling effect. In addition, choosing the proper alloy ensures strong adhesion of the printed structure.