Cu Patterning Using Femtosecond Laser Reductive Sintering of CuO Nanoparticles under Inert Gas Injection

Abstract

In this paper, we report the effect of inert gas injection on Cu patterning generated by femtosecond laser reductive sintering of CuO nanoparticles (NPs). Femtosecond laser reductive sintering for metal patterning has been restricted to metal and metal-oxide composite materials. By irradiating CuO-nanoparticle paste with femtosecond laser pulses under inert gas injection, we intended to reduce the generation of metal oxides in the formed patterns. In an experimental evaluation, the X-ray diffraction peaks corresponding to copper oxides, such as CuO and Cu2O, were much smaller under N2 and Ar gas injections than under air injection. Increasing the injection rates of both gases increased the reduction degree of the X-ray diffraction peaks of the CuO NPs, but excessively high injection rates (≥100 mL/min) significantly decreased the surface density of the patterns. These results qualitatively agreed with the ratio of sintered/melted area. The femtosecond laser reductive sintering under inert gas injection achieved a vacuum-free direct writing of metal patterns.

Femtosecond Laser-Based Additive Manufacturing: Current Status and Perspectives

“…The DW process is a widely used AM technology for such microfabrication of conductive micropatterns using Ag, Au and Cu metals [150,151]. Among these, Cu is considered to be the key material for low-cost printing [152]. Further, the ultrafast lasers, such as ns and fs lasers, are preferred over CW lasers in micro-level fabrication because of the smaller spot sizes, lower HAZs, and less substrate damage [149,153].…”

“…The HAZs were also minimal and there was lower substrate damage for the ns and fs lasers compared to CW laser sintering [142]. Mizoshiri [53,152] utilised an fs-laser-based DW additive manufacturing process to fabricate copper-based microsensors for temperature sensing. This was achieved through reductive sintering of CuO.…”

“…In this experiment, Cu 2 Orich sensing parts and Cu-rich electrodes were 3D printed. Though laser reductive sintered metal oxide NPs were reported to have higher resistivity than laser sintered metal NPs, their absorption of irradiated light was higher [152]. Figure 8 shows the Cu NPs spin-coated substrate irradiated with a femtosecond laser to form Cu-and Cu 2 O-rich micropatterns.…”

“…Mizoshiri et al [152] carried out laser-reduced sintering patterning in an inert gas (N 2 /Ar) environment and were able to produce lower copper oxide (CuO/Cu 2 O) generation in the fabricated sample. They used a pulse duration of 120 fs, a laser wavelength of ~780 nm, a scanning speed from 5 to 10 mm/s, a pulse energy of 0.74 nJ and a pulse repetition rate of 80 MHz [152]. Their investigations revealed that as the injection rate of inert gases (N 2 and Ar) increased, lower metal oxides were produced, but the fabricated samples had lower surface densities.…”

Flexible Ni/NiOx-Based Sensor for Human Breath Detection

“…The laser direct patterning (LDP) process, which enables electrode patterning without the photolithography process, has been extensively developed to fabricate flexible/stretchable devices due to the fact of its simple yet high-precision process and low thermal stress applied to heat-sensitive substrates [ 16 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Nanoparticle inks, including various nanomaterials, such as Au [ 31 , 32 ], Ag [ 33 , 34 ], CuO x [ 35 , 36 ], Cu [ 37 , 38 , 39 ], and NiO x [ 40 , 41 ], have been widely utilized in the process to produce conductor or semiconductor electrodes. In our previous studies, flexible Ni and/or NiO x electrodes fabricated by the LDP process, which induces reductive sintering of the NiO x thin film owing to the reaction between nanoparticles and the reducing agents in the nanoparticle ink, have been applied to various flexible devices including temperature sensors, touchscreen panels, and high-temperature heaters [ 16 , 24 , 26 , 42 , 43 , 44 ].…”