Millimeter-scale integrated and wirewound coils for powering implantable neural microsystems

Abstract

Next generation brain machine interfaces are targeting millimeter-scale implants that are freely floating and completely wireless. It is essential these systems achieve good power transmission efficiency but are also compatible with microsystem technologies. This paper presents two schemes for implementing mm-scale coils for power delivery by electromagnetic coupling — on-chip and wire-wound. A set of on-chip coils have been fabricated using a 0.35 μm CMOS technology with thick top metal option (3 μm aluminium). These achieve a maximum Q-factor of 16.37. The second approach describes wire-wound coils that have been fabricated using bondwire (25 μm gold), achieving a Q-factor of 24.54. This work develops the relevant analytical models, equivalent simulation models, and reports results using both finite element modeling (simulation) and experimental measurement of the fabricated devices. Finally, we compare results and discuss the relative merits of each approach.