Design and fabrication of microchannels for magnetohydrodynamic flow

This paper introduces a new microchannel design for magnetohydrodynamic (MHD) flow that maximizes MHD pumping power. An electromagnetic channel (EMC), which has a rectangular cross-section and electrodes that run the full length of the channels, is the key design element. EMC fabrication on Si requires a two-mask process. ICP-RIE was employed to open rectangular grooves, and then an insulation layer and a seed layer for electroplating were sputtered into these grooves. Current densities for electroplating were adjusted to obtain as planar surface as possible. However, a polishing process needed to be developed to achieve the required planarity for subsequent bonding. Profilometry showed that the surface roughness after polishing was less than 200nm. which was adequate for bonding. The conditions for the second ICP-RIE step, which opened a 10μm wide channel between the electrodes, were adjusted to protect the electrodes. Finally, HF bonding was employed to bond the wafer to an O211 glass coverplate. Bubble voltage threshold tests indicated 2.2 V could be applied within the device at 960 Hz before electrolysis created gas bubbles. These voltages are high enough to give the required pumping velocities for open tubular liquid chromatography.