Three-dimensional and multimaterial microfabrication using focused-ion-beam chemical-vapor deposition and its application to processing nerve electrodes

Abstract

One of the ways to interface electrodes to neurons is a regenerative electrode. The electrode is between the two cut end of a nerve. The cut nerve fiber regenerates through a metalized hold electrode in a two-dimensional (2D) planar of regenerative electrode. As this type of electrode has advantages enabling both the recording of signals of a single nerve fiber and the stimulation of a single nerve fiber, attempts have been made to develop it using traditional 2D microfabrication techniques. However, these traditional 2D techniques have made it difficult to process such electrodes, in particular, electrical wires that have a high density and an integrated structure. In this study, we developed a novel microfabrication method that enables three-dimensional (3D) micro/nanostructures to be fabricated that are made of several kinds of materials with focused-ion-beam chemical-vapor deposition (FIB-CVD). To demonstrate the feasibility of this technique, we designed and fabricated a modified type of regenerative nerve electrode composed of a number of microtubes, each of which worked as both the guide for nerve regeneration and the electrode channel. The 3D structures with this method were fabricated by depositing either diamondlike carbon (DLC, nonconductor) or tungsten (conductor) using a scanning 30keV Ga+ ion beam in an atmosphere of phenanthrene (C14H10) or tungsten hexacarbonyl (W(CO)6). The prototype for the electrode was fabricated with the following process. First, tungsten pillars, which worked as the electrical wiring, were deposited on the substrate by scanning the FIB in W(CO)6 gas. Next, carbon microtubes, which were used to guide the regenerated nerve fiber(s), were built up to be attached to each of the tungsten pillars by depositing DLC with a scanning FIB in C14H10 gas. These carbon microtubes (CMTs) were designed to be curved and to be spread so that they did not contact other wiring pillars, and they were gathered into one at both ends. Our FIB-CVD method made it possible to fabricate complicated 3D structures such as regenerative nerve electrodes made of several kinds of materials.