Laser-assisted silicon etching for micro fuel cell electrode plate fabrication

Silicon electrode plates for micro fuel cells were obtained using a microfabrication process based on the micro-electromechanical system (MEMS) technology. The dry etching process involved the laser ablation technique using the highly stable Nd:YAG. This technique is suitable for micromachining silicon substrates. The total size of the electrode plate was 2.5 cm x 2.5 cm and the active reaction area was 1 cm. An increase in laser scan numbers deepened the groove being etched on the silicon sample, but it showed a saturated behavior as the number of scans became higher. The time required to etch a complete electrode plate flow field with 14 square-shaped through-holes of 0.185 cm x 0.185 cm area using laser ablation was ~30 minutes, which was much shorter than the wet etching time of more than 10 hours with the potassium hydroxide solution (KOH) solution. The laser-etched flow field achieved vertical sidewalls as per the original design, whereas the wet-etched structure achieved a typical anisotropic hole structure with sidewalls that were approximately 54o to the electrode surface due to the <100> orientation of the silicon wafer. Therefore, the laser ablation technique was chosen to produce the electrode plates for the micro fuel cell as it can save time on the etching process and produce more precise flow field dimensions for the electrode plates with less process steps compared with the conventional wet etching processes using KOH solution.