Fabrication of MEMS structure with nano-gap using photo-assisted electrochemical etching

In this paper, MEMS comb structures with several tens of nanometer gap and ultra high aspect ratio more than 125:1 has been achieved using modified photo-assisted electrochemical etching method. It is possible to control the gap of the comb structure from 50 nm to 1 mu m by adjusting the intensity of the light source, which is unusually blue LED (light emitting diodes) in this experiment. By changing the bias and the composition of electrolyte that consists of H2O or DMF (Dimethyl-formamide) based 5% HF (Hydrofluodic acid) and 20% ethanol as a wetting agent, the characteristics of the etching were observed. Finally MEMS comb structure with uniform 200 nm gap and 25 mu m depth was well defined.