Dec 4, 2008

Tech - World's first superconducting transistor

LONDON: Scientists have made the world's first superconducting transistor, a long-standing goal for applied physicists, which could lead to
dramatically faster microchips, promising a revolution in PCs (personal computers).

According to a report in New Scientist, Andrea Caviglia and his colleagues at the University of Geneva in Switzerland developed the transistor.

Last year, Caviglia and his colleagues grew a single crystal containing two metal oxides, strontium titanate and lanthanum aluminate, as separate segments.

At the interface of these materials, the team found a layer of free electrons called an electron gas.

At 0.3 kelvin - just above absolute zero - these electrons flow without resistance and so create a superconductor.

Now, the same group says it can switch this superconductivity on and off by applying a voltage to the interface. The result is a superconducting version of the field effect transistor (FET) - a mainstay of digital electronics.

The team can switch the superconductivity on and off by applying a voltage.

A conventional FET contains a sliver of a semiconducting material with a so-called "source" electrode at one end and a "drain" electrode at the other.

Above this source-drain channel is an electrode called the gate, which acts like a tap: when a "switch-on" voltage is applied to the gate, a current flows through the semiconductor channel.

That current's state - either off or on - can act as a digital 0 or 1.

The speed at which a FET can switch is limited by the resistance of the channel, which creates heat. Higher speeds create more heat until eventually the device burns out. That's why a superconducting FET could run much faster.

Caviglia's team made such a transistor by using the lanthanum aluminate side of its crystal as a source-drain channel and the strontium titanate layer as the gate.

"With no electric field, there is zero resistance between the source and drain as the device is superconducting," said Caviglia.

But, with an electric field applied to the strontium titanate, the dense electron gas gets shifted away from the interface and the lanthanum aluminate stops conducting current.

Caviglia said that computers using such transistors would be "much faster than the gigahertz speeds currently available".

According to David Cardwell, a superconductor specialist at the University of Cambridge, "This is an exciting effect and has clear potential for a new generation of high-speed transistors."

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