Laser-Induced Fabrication of a Transsubstrate Microelectrode Array and Its Neurophysiological Performance

Abstract

Technical problems associated with the monolithic integration of active circuitry into a high-density microelectrode array for neural recordings include passivation of the active circuit area, capacitive coupling of switching transients, and nonuniformity of the recording surface. These problems can be eliminated by implementing the passive and active elements on opposite planes of a substrate and interconnecting them with transsubstrate conductive channels. As the first step toward this integrated active transsubstrate microelectrode array (TMEA), a passive TMEA was fabricated and is reported in this paper. An array of six transsubstrate conductive channels, each 100 /tm in diameter and spaced on 100 Am centers, were made in a 7 mil thick silicon substrate using a laser-induced diffusion technique. The transsubstrate channels are metal doped p-type channels embedded in a n-type silicon wafer. The p-n junction thus formed provides good channel-to-substrate and channel-to-channel isolation. Excellent recordings were made from crayfish giant axons using TMEA. The signal-to-noise ratio was as large as 10 to 1 with no crosstalk observed between adjacent channels. The TMEA showed no degradation with long-term use.