High-density CMOS probe array
A recording probe whose electrode sites and readout electronics are fabricated together on a single complementary metal-oxide-semiconductor (CMOS) die, so that hundreds to thousands of closely spaced sites can be integrated on a needle-thin shank. The canonical example, the Neuropixels probe, places on the order of a thousand sites along a shank a few centimetres long and reads out a selectable subset — a few hundred — through on-shank amplifiers and multiplexers.
Monolithic integration is what breaks the historical one-wire-per-electrode ceiling: amplification and analog-to-digital conversion happen at or near the sites, and time-division multiplexing routes many channels onto a handful of output lines. This is the workhorse enabling the recent steep segment of Stevenson's law in rodents and, in larger form factors, in nonhuman primates and early human research.
Neuropixels probes place on the order of a thousand sites along a single thin shank and read out several hundred at once, routinely isolating hundreds of single units across multiple regions in a freely moving mouse from one insertion.
One monolithic CMOS shank, many regions at once.
Density is bounded from below by biology, not lithography: sites spaced closer than the extracellular reach of a spike, on the order of tens of micrometres, oversample the same neurons rather than adding independent signals.