Selective Direct Laser Writing of Pyrolytic Carbon Microelectrodes in Absorber-Modified SU-8

Abstract

Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 photoresist by irradiation with a low-power, 806 nm, continuous wave, semiconductor-diode laser. The SU-8 was modified by adding Pro-Jet 800NP (FujiFilm) in order to ensure absorbance in the 800 nm range. The SU-8 precursor with absorber was successfully converted into pyrolytic carbon upon laser irradiation, which was not possible without an absorber. We demonstrated that the local laser pyrolysis (LLP) process in an inert nitrogen atmosphere with higher laser power and lower scan speed resulted in higher electrical conductance. The maximum conductivity achieved for a laser-pyrolyzed line was 14.2 ± 3.3 S/cm, with a line width and thickness of 28.3 ± 2.9 µm and 6.0 ± 1.0 µm, respectively, while the narrowest conductive line was just 13.5 ± 0.4 µm wide and 4.9 ± 0.5 µm thick. The LLP process seemed to be self-limiting, as multiple repetitive laser scans did not alter the properties of the carbonized lines. The direct laser writing of adjacent lines with an insulating gap down to ≤5 µm was achieved. Finally, multiple lines were seamlessly joined and intersected, enabling the writing of more complex designs with branching electrodes and the porosity of the carbon lines could be controlled by the scan speed.

Hierarchically Porous, Laser-Pyrolyzed Carbon Electrode from Black Photoresist for On-Chip Microsupercapacitors

“…A high-power CO 2 laser (λ: 10.6 µm) was used to directly carbonize various carbon precursor materials such as polymers and metal organic frameworks (MOFs) [21][22][23]. Most photoresists have low absorption of a long-wavelength laser, preventing the photoresist from being carbonized by simple laser irradiation [24,25]. However, because the black SU-8 film showed improved absorbance against the long-wavelength laser, the CO 2 laser irradiation on a spin-coated black SU-8 film caused a photo-thermal reaction (Figure S1).…”

Enhanced Performance of Laser-Induced Graphene Supercapacitors via Integration with Candle-Soot Nanoparticles

“…In this process, LIG is produced by converting a polymeric precursor to a graphene-rich porous network of carbon through a photothermochemical reaction originating from the interaction between the laser irradiation and the polymeric substrate. − The graphene conversion can be achieved under ambient conditions, and the resulting graphene can be directly patterned in any 2D geometry using traditional laser engraving machines. While polyimide sheets have been traditionally used as the precursor substrate, many other polymeric substrates have also been explored. − Due to its inexpensive and straightforward synthesis approach, yet highly conductive and high surface-area nature, LIG has gained popularity as an efficient electrode material for several electronic applications, with flexible supercapacitors being a prominent focus. − However, the capacitance achieved from pristine LIG materials is comparatively lower. To enhance the capacitance of LIG materials, they are often modified either by doping with electroactive atoms (such as nitrogen, sulfur, and phosphorus) − or coating with electroactive materials (for example, carbonaceous material, metal oxides, − metal phosphate, metal–organic frameworks, , and MXenes. , Such modification processes often involve complicated steps, leading to increased fabrication costs and complexity, deviating from the inherent simplicity and cost-effectiveness of the LIG process.…”

Modification of Polymeric Surfaces with Ultrashort Laser Pulses for the Selective Deposition of Homogeneous Metallic Conductive Layers

“…For three-dimensional applications, on the other hand, there are a number of laser-based technologies that can be implemented. These include Laser Metal Deposition (LMD) [ 4 , 5 , 6 ], Laser Direct Writing (LDW) [ 7 , 8 , 9 , 10 ], Laser-Induced Forward Transfer (LIFT) [ 11 , 12 ], Laser-Induced Selective Activation (LISA) [ 13 , 14 ], Laser Direct Structuring (LDS) [ 15 , 16 , 17 ], and Selective Surface Activation Induced by Laser (SSAIL) [ 18 , 19 , 20 , 21 , 22 , 23 ]. Table 1 summarizes selected methods with their individual characteristics.…”