Microfabrication, assembly, and hermetic packaging of mm-sized free-floating neural probes

Abstract

In this paper, we present a new micromachining (MEMS) fabrication process, microassembly, and hermetic packaging of free-floating neural probes (<1 mm3), wrapped with a bonding-wire coil for wireless power/data transmission and remote monitoring of hermetic sealing failure. The current prototype probe is a pushpin-shaped implantable device consisting of a mock-up integrated circuit (IC) that also serves as a substrate, stacked above a microfabricated silicon die with a 0100 μm non-plated through-hole and embedded cavities to house small surface mount (SMD) capacitors. In center of the micromachined die, a 081 μm sharpened tungsten electrode is inserted and held upright in the through-hole. Except for the tip of the electrode, the device is coated with 5 μm thick parylene-C for hermetic sealing with an additional layer of Polydimethylsiloxane (PDMS) to improve biocompatibility. The bonding-wire wound coils are carefully characterized and compared with electromagnetic simulations. Variations in the Q-factor and resonance frequency, which affect power/data transmission performance have been examined across 12 samples in terms of phase-dip amplitude, which corresponds to failure in hermetic sealing.