Multielectrode arrays (MEAs) are bioelectronic interfaces. They’re made up of conductive electrodes patterned onto an insulating substrate. The MEA is usually connected to an electronic system that can record and stimulate the tissue via the conductive electrodes.
Passive arrays have only conductive electrodes in direct contact with biological tissue. This is flexible, transparent, and “biocompatible”. They benefit from a wider range of materials, meaning they’re easier to manufacture.
Active arrays have nanoscale electronics close to the electrode interface, made from a rigid CMOS substrate. They can have a high signal-to-noise ratio by amplifying and digitising the signal close to the electrode before the neural signals are exposed to environmental noise.