A 12.5mg mm-Scale Inductively-Powered Light-Directivity-Enhanced Highly-Linear Bidirectional Optogenetic Neuro-Stimulator

The design, development, and experimental validation of a mm-scale self-contained bidirectional optogenetic stimulator are presented. A novel current-mode LED driving circuit architecture is employed that allows for fully-linear control of optical stimulation up to I-LED=10m A, with the smallest reported 200mV headroom, significantly boosting the electrical-to-optical energy conversion efficiency. The system's energy efficiency is further improved by inkjet printing of custom-designed optical mu lenses on top of the device to enhance the generated light directivity. Our results show a 30.46x irradiance (optical power per area) improvement for the same electrical power consumption. In addition to the two stimulation channels, the SoC integrates two recording channels for LFP recording and digitization, and is powered through an on-chip coil with PTE=2.24%. Full experimental SoC electrical and optical characterization and in vitro measurement results are reported.