DRAM
DRAM is the best-documented and the most secretive of the three domains at the same time, and the split is not where most people expect it.
Well documented: architecture, the interface, circuit design, and observable behaviour. JEDEC publishes the standards free after registration. Micron publishes full datasheets with complete timing tables, mode register maps and refresh behaviour. Fifteen years of academic characterisation has measured what the datasheets leave as guardband.
Dark: process integration, capacitor formation, dielectric stacks, and yield learning. These are the actual competitive assets of a three-company oligopoly, and no amount of reading will surface them.
Be clear-eyed about entry here. DRAM fabrication is a three-company oligopoly with fabs in the $15–20B range. Coverage in this project is educational; it is not a route to market entry, and pages here will not pretend otherwise.