Laser-micromachined, chip-scaled ceramic carriers for implantable neurostimulators

Abstract

Hermetic encapsulation of long-term implantable devices using ceramics has been investigated over several decades. Our studies focus on the miniaturization of ceramic encapsulations for large numbers of stimulation channels. Laser-patterning of screen printed platinum (Pt) paste on cofired ceramics has been shown to enable the construction of features comparable in size to classical screen printing. A novel technique for embedding Pt structures into the surface of Al(2)O(3) substrates is shown to produce features with a line width minimum of 20 μm and a pitch of 40 μm. Polishing the ceramic substrates enables flip-chip bonding of application specific integrated circuits (ASIC) using gold stud bumps. A new technique for fine tuning of an ASIC stimulator with stud bump bridges is described. The technique eliminates the need for wire bond loops and increases reliability and integration density of the system, which are major requirements used to construct a visual prosthesis or other implantable devices requiring miniaturization. The methods for laser-patterned Pt tracks in alumina for fine pitch structures are described. Feasibility studies for flip-chip bonding and stud bump bridges were undertaken and the results were found to be promising.