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., ne edles) designed for penetration of human skin which circumvent high impedan ce problems associated with layers of tbe 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-electrod e impedance of dry spiked electrodes having a size of 4 x 4 mm(2) is reduce d compared to standard electrodes using electrolytic gel and having a compa rable size, Recorded low amplitude biopotentials resulting from the activit y of the brain, (i.e, EEG signals) are of high quality, even for spiked ele ctrodes as small as 2 x 2 mm(2). The spiked electrode offers a promising al ternative to standard electrodes in biomedical applications and is of inter est in research of nem biomedical methods.