Hoerni buried transistor junctions under oxide — the process every chip still uses

In 1956 William Shockley started a semiconductor laboratory in Mountain View, California, hiring bright graduates in physics, chemistry and metallurgy. In 1957 eight of them — the 'traitorous eight', including Jean Hoerni, Gordon Moore and Robert Noyce — resigned together and founded Fairchild Semiconductor, funded by Sherman Fairchild. The eight began working with silicon, the cheap substrate they knew from Shockley's lab.

Hoerni's answer to making silicon devices dependable was the planar process. His patent application of May 1, 1959, describes a wafer of N-type silicon coated entirely with silicon oxide, holes opened in that coating by photoresist or etching, and an impurity diffused through the opening — so the junction's edges end up beneath the oxide layer rather than exposed. A second diffusion through another window builds the transistor; contacts are alloyed through further apertures. The patent, 'Method of manufacturing semiconductor devices', was granted as US 3,025,589 on March 20, 1962.

The effect was decisive. The Engineering and Technology History Wiki records that Fairchild pioneered the planar process developed by Hoerni and that it made other transistor processes obsolete; among the first customers for Fairchild's planar silicon transistors was IBM. And when Robert Noyce conceived the integrated circuit — the form the Nobel Foundation describes as manufactured in practice with silicon as semiconductor, silicon dioxide as insulator and aluminium as conductor — it was Hoerni's flat, oxidised wafer that made it buildable.

Grow an oxide blanket and keep junctions buried

The oxide does two jobs at once: it defines where dopants enter during fabrication and then shields the finished junctions, which is why the patent's junction edges sit 'beneath the oxide layer'.

Because everything happens on a flat wafer through photolithographic windows, devices are made in batches — many at once, by repeating one cycle — instead of one at a time.

Protected junctions do not degrade from contact with the surroundings, which is what made silicon devices dependable enough to sell at volume.

The economics followed the physics: Fairchild's planar transistors displaced competing processes outright, and an early demanding customer — IBM — validated the yield.

The surface you etch can also protect. Hoerni stopped fighting silicon's oxide and used it as both stencil and shield — one layer, two jobs, on a wafer a batch process repeats endlessly.

The planar process became the manufacturing route for the integrated circuit, and Fairchild dominated the early analog IC market while fending off Texas Instruments. Hoerni left Fairchild in 1961 to head the new semiconductor division of Teledyne, consulted for Union Carbide, Hughes Aircraft and Fujitsu, and founded Intersil in 1967. He later put a US$1 million endowment behind schools and health services for the Balti people of the Karakoram, and died in January 1997.