A wireless stimulator system-on-chip with an optically writable ID for addressable cortical microimplants

Abstract

For a profound understanding of brain function and connectivity, there is an escalating need to cover expansive cortical areas. While external recording methods such as electroencephalography (EEG) are prevalent, direct bidirectional interaction with the neural network mandates implanted electrodes. Integrating all microimplant functionalities into a single integrated circuit (IC) increases design complexities. Thus, challenges in the intricacies of distributed system networking have frustrated the drive toward implant miniaturization. In this context, we introduce addressable microimplants equipped with gate oxide-based anti-fuse (AF) Chip-IDs activated by a photodiode (PD) array. This mechanism generates a binary ID code by selectively degrading the anti-fuse gate oxide, eliminating the need for I/O PADs. These ID-equipped wireless micro-implants are distributed over vast regions, enabling bidirectional neural interfacing through recording and stimulation. We successfully fabricated an 8-channel wireless microstimulator and a spike-sensor in 180 nm CMOS, demonstrating the efficacy of the 5-bit Chip-ID in real-time networking scenarios. The system draws power from RF electromagnetic waves, receiving 1.2 V and 1 mW, and employs amplitude modulation at a 900 MHz carrier frequency for data communication. The minimum amplitude detected for demodulation was 350 mV, regenerating a 1 MHz clock and 34-bit command data. When tested, the array of eight microstimulators responded distinctly based on sequential command parameters. This IC realized in TSMC 180 nm CMOS technology, occupies only a 1 mm² area.