128-Channel deep brain recording probe with heterogenously integrated analog CMOS readout for focal epilepsy localization

We present the development and characterization of a stereoelectroencephalography (SEEG) probe with integrated active complementary metal-oxide-semiconductor (CMOS) electronics that allows to record simultaneously from 128 individual channels. This channel count is unprecedented for depth probes and enabled by novel microfabrication and assembly processes. The probe comprises eight cylindrical macroelectrodes, each with an area of 3.1×2.5 mm
²
, similar to commercially available SEEG probes. In addition, 120 microelectrodes with a diameter of 35 µm and an impedance at 1 kHz of 332 kΩ are integrated for single-unit activity recording. The interconnection bottleneck is resolved by the integration of analog readout electronics. In total, eight CMOS chips are integrated inside the probe along its length, each multiplexing 16 recording channels onto one output line. The CMOS chips first amplify the neural signals with a gain factor of 100 and filter them in the frequency band of interest, i.e. 40 mHz to 10 kHz. Each output channel is buffered to drive the output leads at a power consumption of 12 µW/channel.