Micromachined electrodes for biopotential measurements

We describe the microfabrication, packaging and testing of a micromachined dry biopotential electrode, (i.e., where electrolytic gel is not required). It consists of an array of micro-dimensioned, very sharp spikes, (i.e., needles) designed for penetration of human skin which circumvent high impedance problems associated with layers of the outer skin. The spikes are etched in silicon by deep reactive ion etching and are subsequently covered with a silver-silverchloride (Ag-AgCl) double layer. The electrode-skin-electrode impedance of dry spiked electrodes having a size of 4/spl times/4 mm/sup 2/ is reduced compared to standard electrodes using electrolytic gel and having a comparable size. Recorded low amplitude biopotentials resulting from the activity of the brain, (i.e., EEG signals) are of high quality, even for spiked electrodes as small as 2/spl times/2 mm/sup 2/. The spiked electrode offers a promising alternative to standard electrodes in biomedical applications and is of interest in research of new biomedical methods.