A Flexible and Switch-Matrix Addressable Active Electrode Array Based on Complementary Organic Electrochemical Semiconductor Technology

While there has been considerable recent interest in flexible and conducting polymer (CP)-based implants for interfacing with the brain, nearly all of these studies have focused on passive electrode arrays with low channel counts. Active integration of CP-based electronics for large-scale recordings, on the other hand, is limited, as the current library of active organic electronics is restricted to organic electrochemical transistors (OECTs). OECT gating is traditionally achieved over a common gate electrode and electrolyte, which limits the control of individual components in a large array. In addition, when OECTs are used for active switching operations, ion uptake of CPs poses a major issue for <i>in vivo</i> neural applications where the high ionic transients (~μA) result in the undesired activation of nearby neurons and lead to high ionic-electronic cross-talk with the adjacent OECTs. Therefore, there is a significant need for generation of alternative CP-based circuit components to generate complex organic circuitries capable of operation with internal ions to avoid interference with the measured media. In this work, we introduce a new class of organic semiconductors which can be operated by controlling the electrophoretic drift of the internally trapped cations in the channel to generate unidirectional conductivity with electrical output analogous to silicon-based diodes. We tune these organic diodes to work in complementary regime with the existing OECT configuration and demonstrate that this circuit architecture can be used to generate a switch matrix for electrode selection on the neural interface with minimal crosstalk between adjacent pixels. We further show that this topology enables the generation of ultra-thin (50-μm x 8-μm), flexible neural implants with high channel counts (32) that acquire local field potentials with high signal-to-noise ratio. To the best of our knowledge, this work is the first demonstration of active organic electrochemical circuits integrated in the front-end pixel of a fully implantable shank. Owing to their ionic-electronic conductivity, solution-based processability, and integrability with flexible, biocompatible substrates, unlike most inorganic circuit elements, CP-based circuitries are ideal to use on the neural interface.