In this study, we propose a novel and simple fabrication method of the microfluidic device, with high-aspect-ratio (HAR) microchannel for microparticle separation under viscoelastic fluid flow. To fabricate the HAR (> 10) microfluidic device comprised of the Si channel and PDMS mold, basic MEMS processes such as photolithography, reactive ion etching and anisotropic wet etching of Si wafer were used, and then plasma bonding with mechanical alignment between the Si channel and PDMS mold was conducted. The width of the microchannels was determined by the difference between the Si channel width and the master width for the PDMS mold. On the other hand, the heights of the Si channel and PDMS mold could be controlled by the KOH etching time and spin-coating speed of SU-8, respectively. The HAR microfluidic device whose microchannel had 10 μm width and 100 μm height was successfully fabricated, and used to separate microparticles without other external forces. The effect on the particle focusing position and focusing width under viscoelastic fluid was investigated, depending on the flow rate and the microparticle size. It is expected that precise manipulation as well as high-throughput separation of microparticles, can be achieved using the microfluidic device with HAR microchannel.

In this paper, we propose a novel and simple fabrication microchannel with parallelogram cross-section using anisotropic wet etching of Si wafer, and self-alignment between Si channel and PDMS mold. Single crystal Si wafer was used to fabricate microchannel and master for PDMS mold, using photolithography and anisotropic KOH etching. Si structure for microchannel and master were formed on the same Si wafer by KOH etching, and the PDMS mold was made from Si master. Thus, we could fabricate the Si microchannel and PDMS mold, with same structural height. Finally, a microchannel with parallelogram cross-section could be easily formed, through self-alignment between them. Si microchannel and PDMS mold were permanently bonded, using O₂ plasma treatment. It is expected that the fabricated microchannel with parallelogram cross-section, can be used to study inertial focusing, widely used to separate particles continuously and with high-throughput.