Bioelectrodes for high-channel count and small form factor CMOS neural probes

SiNAPS neural probes enable continuous sub-millisecond neural activity recordings from all integrated electrodes (up to 1024) with a very small form factor implantable device. Key for this achievement was the integration of DC-coupled analog frontends within micrometric active electrode-pixels. Rather than filtering the DC electrode signal component as in conventional AC-coupled frontends, the SiNAPS electrode-pixel circuit operates with a periodic calibration that sets a DC offset compensating open circuit potential (OCP) changes of each electrode. This keeps the in-pixel amplifiers within the operational range. However, for optimal performances this circuit requires minimizing the OCP variability among all integrated electrodes. Here, we show on 4-shanks SiNAPS-probes that this variability can be controlled by the electrode material, structuring process and functionalization. Among the tested bioelectrodes, results show that evaporated platinum (Pt) functionalized with a monolayer of (3-aminopropyl) triethoxysilane (APTES) leads to less than 20 mV DC offset variability across 1024 electrodes.