A Novel Hybrid Removal Technology for High-Aspect-Ratio SU-8 Micromolds in ECF (Electro-Conjugate Fluid) Micropumps Fabrication by UV-LIGA

• Published in: Journal of microelectromechanical systems 2018-10, Vol.27 (5), p.818-826
• Main Authors: Han, Dong, Yoshida, Kazuhiro, Kim, Joon-Wan
• Format: Article
• Language: English
• Subjects: Ablation; CO₂ laser engraving; Crosslinking; ECF micropump; Electrodes; Engraving; Etching; Fabrication; Heating systems; High aspect ratio; Lasers; LIGA process; Micropumps; Microstructure; Molds; Plasmas; SU-8 removal; triangular prism & slit electrode pair
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2018.2865201

Previously, we have developed ECF micropumps with triangular prism and slit electrode pairs (TPSEs) fabricated by the UV-LIGA. However, the previous KMPR molds have a limit to attain higher-aspect-ratio TPSEs. As a promising substitute, the ultrathick SU-8 molds are preferable for the TPSEs due to higher-aspect-ratio ability, but their difficult removal remains an annoying problem. To solve this problem, we first propose a novel hybrid removal method combining \text{C}O_{2} laser engraving with O_{2} /CF 4 plasma to achieve the fast, non-swelling, and complete removal of ultrathick SU-8 micromolds for higher-aspect-ratio TPSEs. The \text{C}O_{2} laser engraving is utilized as the main process to remove most SU-8, while the O_{2} /CF 4 plasma is adopted as the post-treatment to remove the remaining SU-8. To gather the proper fabrication conditions, we quantitatively analyze the effects of laser power, laser scan speed, and laser-pass numbers on the SU-8 ablation thickness. We successfully fabricated TPSEs of 590~\mu \text{m} and 970~\mu \text{m} in height by selectively removing SU-8 micromolds of 620 and 1100~\mu \text{m} in thickness. This achievement confirmed that our hybrid removal technology could remove the crosslinked SU-8 effectively and efficiently. We further experimentally proved the fascinating potential of our hybrid removal in improving the output performance of ECF micropumps. This promising hybrid removal opens the door to the easier fabrication of ultrathick metallic microstructures by UV-LIGA. [2017-0320]