[John McMaster] is doing some pretty amazing work with figuring out how the circuitry in an integrated circuit works. Right now he’s reverse engineering a serial EEPROM chip one section at a time. This is a 24c02 made by ST, and he chose this particular portion of the die to examine because it looked like there were some analog components involved.
He removed the top metal using hydrofluoric acid in order to take this image. By continually removing layers this way he manages to work out the traces and even the components themselves. To help clarify the parts he uses the set of snapshots to generate a colored map using Inkscape. From there he begins labeling what he thinks the components might be, and like a puzzle the pieces start falling into place one by one. From the Inkscape drawing he lays out a schematic, then rearranges the components to make the design easier to understand. Apparently this is a Schmidt trigger.