Fabrication of microelectrode arrays for neural measurements from retinal tissue

The production of high-density, large-area microelectrode arrays for neurophysiology studies requires a combination of electron beam lithography and photolithography, together with dry etch pattern transfer. The retina is one of the few parts of the animal nervous system to which the input (image) and output (ganglion) signals are accessible. To read out the signals from the ganglion cells, we have made microelectrode arrays in the transparent conductor indium tin oxide (ITO) by CH4/H-2 reactive ion etching (RIE) using a novel masking technique that avoids the usual problem of resist cross- linking. An electron beam lithography process has also been developed exploiting multiple plasma steps. The ITO layer lies on a glass substrate to allow the retinal cells and the electrode positions to be photographed using a CCD camera. SF6 RIE of vias through a thick protective silicon nitride coating deposited by plasma onto the ITO/glass permits the platinization of the electrodes. Both CH4/H-2 and SF6 RIE require low electrical damage to the ITO, which we verify