杏吧原创

THE world鈥檚 first superconducting transistor, a long-standing goal for applied physicists, could lead to dramatically faster microchips.

Last year Andrea Caviglia and his colleagues at the University of Geneva in Switzerland 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 鈥� just above absolute zero 鈥� 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) 鈥� a mainstay of digital electronics.

鈥淭he team can switch the superconductivity on and off by applying a voltage鈥�

A conventional FET contains a sliver of a semiconducting material with a so-called 鈥渟ource鈥� electrode at one end and a 鈥渄rain鈥� electrode at the other. Above this source-drain channel is an electrode called the gate, which acts like a tap: when a 鈥渟witch-on鈥� voltage is applied to the gate, a current flows through the semiconductor channel. That current鈥檚 state 鈥� either off or on 鈥� 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鈥檚 why a superconducting FET could run much faster.

Caviglia鈥檚 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 (Nature, vol 456, p 624). 鈥淲ith no electric field, there is zero resistance between the source and drain as the device is superconducting,鈥� says 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 鈥渕uch faster than the gigahertz speeds currently available鈥�.

David Cardwell, a superconductor specialist at the University of Cambridge, thinks the work is an important breakthrough: 鈥淭his is an exciting effect and has clear potential for a new generation of high-speed transistors.鈥�