Ensembles of autonomous, spatially distributed wireless stimulators can offer a versatile approach to patterned microstimulation of biological circuits such as the cortex. Here, we demonstrate the concept of a distributed, untethered, and addressable microstimulator, integrating an ultraminiaturized ASIC with a custom-designed GaAs photovoltaic (PV) microscale energy harvester, dubbed as an "optical neurograin (ONG)". An on-board Manchester-encoded near-infrared downlink delivers incident IR power and provides a synchronous clock across an ensemble of microdevices, triggering stimulus events by remote command. Each ONG has a unique device address and, when an incoming downlink bit sequence matches with this device identification (ID), the implant delivers a charge-balanced current stimulus to the target cortex. Present devices use 7-bit metal fuses fabricated during the CMOS process for their device ID, laser-scribed in post-processing, allowing in principle for a stimulator network of up to 128 nodes. We have characterized small ensembles of ONGs and shown a proof of concept of the system both on benchtop and in vivo rat rodent model.
Keywords: addressable; distributed; infrared; multichannel; networking; neural stimulator; wireless.