A SU-8-Based Fully Integrated Biocompatible Inductively Powered Wireless Neurostimulator

A fully integrated minimally invasive compact polymer-based wireless neurostimulator was designed, fabricated, and characterized both in open air and in vivo. The neurostimulator (3.1 × 1.6 × 0.3 mm) consists of a planar spiral coil for wireless power supply through inductive coupling, two Schottky diodes for full-wave rectification, an application-specific integrated circuit neurostimulator circuit chip for stimulus spike signal generation, and two biphasic platinum-iridium (PtIr) stimulation electrodes. The device is fully integrated and completely embedded in biocompatible SU-8 packaging. For in vivo testing, the wireless neurostimulator was implanted subcutaneously in a rat hind limb. At the coupling power of 21 dBm (125 mW) at 394-MHz resonant frequency, stable and robust cortical responses during extended periods of wireless stimulation were recorded.