Planar process
Jean Hoerni's trick of building transistors flat beneath a protective oxide layer — the foundation of every silicon chip since.
Until 1959, transistors were built as raised "mesa" islands: exposed, dirt-sensitive and awkward to wire together. Jean Hoerni at Fairchild Semiconductor inverted the problem — diffuse the doping through windows etched in a thermally grown silicon-dioxide layer, then leave the oxide in place as passivation. The result was a flat surface on which the interconnections could be printed photolithographically.
That was the leap that made the integrated circuit manufacturable: Robert Noyce built the first monolithic IC on the planar process the following year. The same basic idea still underpins chip fabrication today, from the humble MOSFET to leading-edge logic, even as feature sizes shrank from micrometres to a handful of nanometres.