Materials · 1950

Zone refining

A moving molten zone sweeps impurities out of a crystal.

William Pfann demonstrated zone refining at Bell Labs in October 1950. By 1955, repeated passes supplied germanium with fewer than one impurity atom per ten billion germanium atoms. It helped supply the ultrapure material needed for reliable transistors.

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Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 2

Transistor 1947
Czochralski crystal pulling 1916

Related measurements

The dashed line marks when it first worked.

Transistors per microprocessor Latest: 58.2B transistors (2021) Source: Our World in Data