SILICON-BASED MICROELECTRODES FOR NEUROPHYSIOLOGY FABRICATED USING A GOLD METALLIZATION NITRIDE PASSIVATION SYSTEM

The multimicroelectrode probe (microprobe) is a device used in neuroph ysiology to record signals from nerve cells, Microprobes typically hav e a number of gold recording sites supported on a narrow cantilever be am which is inserted into the tissue, Conducting tracks connect the re cording sites to bonding pads on the body of the device, The metalliza tion is insulated, except at the recording sites and bonding pads, by a passivation layer, Boron etch stop techniques can be used to produce narrow cantilever beams upon which recording sites are situated, Prev iously, polysilicon interconnects were used on microprobes fabricated using boron etch stop techniques, with gold inlaid onto the recording sites using a lift-off technique, This meant that mechanical jigging w as required before the final shaping of the probes in potassium hydrox ide (or other etch) to prevent the etch from attacking the polysilicon conductors beneath the inlaid gold, The process reported here incorpo rates a gold metallization layer, in conjunction with a plasma-enhance d chemical vapor deposition (PECVD) nitride passivation layer. Since b oth these materials etch very slowly in potassium hydroxide, no mechan ical jigging, or other steps, need to be taken to protect the front of the wafer during the shaping stage, This simplifies the fabrication o f these devices.