Technology: Germanium makes the chips go faster

Technology 11 December 1993

Silicon, the tortoise of the semiconductor industry, has finally caught
up with the hare, gallium arsenide. This week researchers at IBM’s Thomas
J. Watson research centre in New York are due to announce that, by adding
a few atoms of germanium, they have made silicon chips that work as fast
as those made from gallium arsenide.

The chips they are manufacturing, called digital to analogue converters,
are used in electronic devices such as portable phones and computers. They
have about 30 000 transistors, a modest number for a silicon chip, but each
transistor can switch on or off more than a billion times every second.
Only gallium arsenide chips, which are more difficult and expensive to manufacture,
could operate at this speed before, but they require significantly more

Few technical details are currently available about these faster silicon
chips, but the principle behind them is that the variation in electrical
fields set up by the uneven distribution of germanium atoms throughout
the transistors speeds the passage of electrons through the chips. As a
result, each transistor can be switched on and off between two and four
times faster than those in conventional silicon transistors.

IBM has developed a technique called ultra-high vacuum chemical vapour
deposition to distribute the germanium atoms unevenly. The chips are put
into a vacuum chamber, and gases are let in. These gases then react to
release germanium atoms, which settle on everything inside the vacuum chamber.

Bernie Meyerson, leader of IBM’s research team, estimates that the
technique could extend the future for silicon chips by 20 to 30 years.