This thesis describes the design, microfabrication, and testing of an active scalp EEG (electroencephalograph) electrode that has several distinct advantages over existing technologies. These advantages are: (1) no electrolyte used, (2) no skin preparation, (3) significantly reduced sensor size, and (4) compatibility with EEG monitoring systems. The active electrode array is an integrated system made of an array of capacitive sensors with local integrated circuitry housed in a package with batteries to power the circuitry. This level of integration was required to achieve the functional performance obtained by the electrode. The electrode consists of a silicon sensor substrate fabricated at UCD and a custom circuit substrate fabricated at Orbit Semiconductors, using a 2 μm analog CMOS technology. The circuitry was designed for low 1/f noise. One side of the sensor substrate holds four capacitive sensors with rm Si_3N _4 as the dielectric material. The opposite side holds aluminum pads for bonding to the circuit substrate. A via hole technology was developed to make electrical contact to both sides of the sensor substrate. The via holes are 200 μm square openings etched through the silicon by a reactive ion etching (RIE) process using an rm SF_6/O_2 gas mixture, oxidized, and then filled with sputtered aluminum for contacts through the substrate. The via holes have an aspect ratio of 2:1 (length of opening to depth of hole). Silicon RIE etch rates of up to 18 mu/hr were obtained under optimum conditions, using a 0.8 μm aluminum mask. The circuit and sensor substrates were bonded with silver adhesive, and wire bonding was used to make electrical contacts between the substrates. The two substrates were then integrated in a custom package for testing. The electrode was tested on an electrical test bench and on human subjects in four modalities of EEG activity, namely: (1) spontaneous EEG, (2) sensory event-related potentials, (3) brain stem potentials, and (4) cognitive event-related potentials. The performance of the dry electrode compared favorably with that of the standard wet Ag/AgCl electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio.
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- Physics: Electricity and Magnetism; Physics: Condensed Matter; Engineering: Biomedical; Engineering: Electronics and Electrical