Multi-dimensional microelectrode arrays with on -chip CMOS circuitry for neural stimulation and recording.

Abstract

Multipoint electrical stimulation and extracellular recording in the central nervous system are two important techniques for studying the functionality of the central nervous system (CNS) and are key elements in the development of prostheses for deafness, blindness, paralysis, and other neurological disorders. This thesis presents the development of two- and three-dimensional (2D, 3D) probe structures for studying the highly complex neural interactions in the CNS using multipoint stimulation and recording. The probes are batch-fabricated on silicon wafers utilizing lithographic techniques to precisely control device geometries and allow the integration of on-chip CMOS circuitry for signal multiplexing. Bulk-silicon micromachining is used to define the silicon components, both the planar 2D probes with integrated CMOS circuitry and the passive components of 3D multi-probe arrays. Advanced techniques for forming the circuit contacts, electrode sites, and interconnect, and final release-etch corner protection are implemented to realize dramatic improvements in process yield. The probes have 400mum-spaced shanks which are 2.5mm in length by 80mum in width by 13mum in thickness. Each shank supports four electrode sites on 400mum centers and each 1000mum<super>2</super> iridium oxide site is capable of delivering 100muA of stimulus current. The on-chip circuitry was designed to provide greatest versatility while maintaining simplicity and robustness under wide process variations. The on-chip circuitry decodes the site addresses and multiplexes each of four analog channels carrying externally generated stimulation or recording signals to one of sixteen sites. The probes are microassembled with their shanks projecting through an orthogonal platform and are held parallel by silicon spacers. The 3D microassembled array utilizes specially-structured probes having 5mum-thick electroplated gold beam-leads bent at 90&deg; and ultrasonically bonded to mating pads on the platform. The 3D architecture utilizes programmable platform-based fuses to globally address arrays having variable numbers of probes. Fully-functional 2D probes as well as microassembled four-probe 256-site 3D arrays have been fabricated. The measured static power dissipation of a single probe is less than 10muW and 10MHz data-load rates have been demonstrated. The feasibility of a 16-probe, 1024-site array has been demonstrated. The first <italic>in-vivo</italic> stimulation experiments using probes with integrated CMOS circuitry have been successfully demonstrated.