Forming Tip Electrodes on 3D Neural Probe Arrays Using Electroplated Photoresist

We present a new fabrication technique that provides a repeatable, uniform, and time-saving method for exposing and metallizing tip electrodes in out-of-plane neural probe arrays. In order to form active electrode sites for neural recording or stimulation, the insulation layers covering the electrodes must be selectively removed. In this process, an electroplated photoresist (EP) is used to conformally coat three-dimensional (3D) insulated silicon needles, followed by exposure and development of the resist. The resist is then used as a mask layer to remove insulation layers only around the tip of the needles. EP has several advantages as a masking layer, including uniform coverage, low deposition temperature, wide thickness range, chemical stability, and easy removal. We have used this method to de-insulate the tips of 0.5-1.5 mm long,
$20\ \mu\mathrm{m}$
-diameter silicon needles in a 3D neural recording array. We have simulated the electroplating process on these arrays using COMSOL to determine the feasibility of the technology.