Cu-based fine patterns were directly fabricated using femtosecond laser reduction of Cu2O nanospheres (NSs) via nonlinear optical absorption. Cu2O NS solution films, containing Cu2O NSs, polyvinylpyrrolidone (PVP), and 2-propanol, were prepared by spin-coating of the Cu2O NS solution on glass substrates or Cu-coated glass substrates. Finer line patterns were formed by scanning the focused femtosecond laser pulses. The absorption of the Cu2O NS solution film at wavelength of the femtosecond laser pulses, 780 nm, was low, whereas the intense absorption at wavelength of 390 nm was observed. Finer patterns were obtained on the Cu-coated glass substrates than on the glass substrates. The minimum line width of 0.6 μm was obtained on the Cu-sputtered film, which was smaller than the focal spot diameter of 1.3 μm. The heat accumulation is lower on the Cu-sputtered films due to their high thermal conductivity, resulting that the line width with the sub diffraction limit was achieved. The electrical conductivity of the patterns on the glass substrates was evaluated to be 4.1×106 S/m at scanning speed of 200 μm/s and pulse energy of 0.312 nJ, which is close to that of bulk copper.
Yukinari Kondo, Mizue Mizoshiri, Junpei Sakurai, and Seiichi Hata, "Femtosecond laser direct writing of Cu-based fine patterns using Cu2O nanospheres," Proc. SPIE 10520, Laser-based Micro- and Nanoprocessing XII, 1052006 (Presented at SPIE LASE: January 30, 2018; Published: 19 February 2018); https://doi.org/10.1117/12.2287686.
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