The Microbead: A Highly Miniaturized Wirelessly Powered Implantable Neural Stimulating System

TLDR

Current neural implants capable of stimulating neurons across multiple depths and regions are lacking due to significant technical obstacles. This work introduces the microbead, a fully integrated, wirelessly powered neural device designed to enable spatially selective activation of neural tissue. The microbead chip, fabricated in 130‑nm CMOS and measuring 200 µm × 200 µm, incorporates an on‑silicon coil powered by a 36‑dBm transmitter coil at a 5‑mm coupling distance, and employs a pulsed powering scheme to keep average transmitted power within safe limits. Experimental validation in a rat demonstrated successful stimulation of the sciatic nerve using 195‑µs current pulses.

Abstract

An implant that can electrically stimulate neurons across different depths and regions of the brain currently does not exist as it poses a number of obstacles that need to be solved. In order to address the challenges, this paper presents the concept of "microbead," a fully integrated wirelessly powered neural device that allows for spatially selective activation of neural tissue. The prototype chip is fabricated in 130-nm CMOS technology and currently measures 200 μm × 200 μm, which represents the smallest remotely powered stimulator to date. The system is validated experimentally in a rat by stimulating the sciatic nerve with 195-μs current pulses. To power the ultrasmall on-silicon coil, 36-dBm source power is provided to a highly optimized transmitter (Tx) coil at a coupling distance of 5 mm. In order to satisfy the strict power limit for safe use in human subjects, a pulsed powering scheme is implemented that enables a significant decrease in the average power emitted from the Tx.