Abstract
In recent years, additive manufacturing has been evolving towards flexible substrates for the fabrication of printable electronic devices and circuits. Generally polymer-based, these emerging substrates suffer from their heat sensitivity and low glass-transition temperatures. As such they require new highly-localized sintering processes to treat the electronic inks without damaging the polymer-based substrate. Laser-based sintering techniques have shown great promises to achieve high-quality sintering locally, while controlling the heat penetration to preserve the polymer substrates integrity. In this report, we explore new optimization pathways for dynamic laser-based sintering of conductive silver inks. Multiple passes of a pulsed laser are first performed while varying pulse train frequencies and pulse energies as an attempt to optimize the properties of the silver inks. Then, time-domain pulse shaping is performed to alter the properties of the conductive inks. Together, these pathways allow for the careful control of the time-domain laser energy distribution in order to achieve the best electronic performances while preserving the substrate’s integrity. Sheet resistance values as low as 0.024Ω/□ are achieved, which is comparable to conventional 1-hour oven annealing, with the processing time dramatically reduced to the milisecond range. These results are supported by finite element modeling of the laser-induced thermal dynamics.
Highlights
It was shown that microsecond-pulsed lasers allow careful control of the irradiation to reach thermal equilibrium for the different materials present in ink solutions[20,21]
We have demonstrated that controlling time-domain energy distribution is paramount for optimizing the laser sintering process on various conductive heterogeneous nanoparticle-based silver ink formulations
By means of the Institut National d'Optique (INO) Master Oscillator Pulsed Arbitrary Waveform (MOPAW) pulse-shaping laser system, we have shown the ability to perform rapid thermal treatment of printed inks on low-temperature susbtrates, while locally controlling the ink properties and limiting thermal penetration to the top-most printed layer
Summary
It was shown that microsecond-pulsed lasers allow careful control of the irradiation to reach thermal equilibrium for the different materials present in ink solutions[20,21]. This aspect is critical as the heterogeneous nature of these printable inks leads to complex heating dynamics and phase transitions, including the evaporation of different organic solvents and surfactants with the sintering of nanoparticles. Finite-element method (FEM) simulation of the thermal effects occurring during laser-mater interactions with time-domain pulse-shaping modulation is consistent with our experimental observations that controlling the heating rate for the sintering process gives rise to improved conductivity for the printed silver nanoparticle-based inks
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