Copper circuits fabricated on flexible polymer substrates by a high repetition rate femtosecond laser-induced selective local reduction of copper oxide nanoparticles

In this work, copper circuits were fabricated on flexible polyimide (PI) substrates by high repetition rate femtosecond laser-induced selective local reduction of copper oxide nanoparticles (CuO NPs). The effects of laser pulse energy and laser scanning velocity on the quality of the copper circuit were studied. By optimizing laser processing parameters, we prepared a Cu circuit of a line width of 5.5 µm and an electrical resistivity of 130.9 µΩ·cm. The Cu/O atomic ratio of the Cu circuit reaches ∼10.6 and the proportion of Cu is 91.42%. We then studied the formation mechanism of the copper circuit by simulating the temperature field under the irradiation of high repetition rate femtosecond laser pulses. The results show that the thermochemical reduction reaction induced by the high repetition rate femtosecond laser reduces CuO NPs into Cu NPs. Under the thermal effect of the high repetition rate femtosecond laser, Cu NPs agglomerate and grow to form a uniform and continuous Cu circuit.