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Junctionless transistor eases chip making

Posted: 25 Feb 2010 ?? ?Print Version ?Bookmark and Share

Keywords:junctionless transistor? chip making? CMOS?

Cross section of a silicon wire with wrap-around insulator and overlaid gate.

Scientists at the Tyndall National Institute have designed and fabricated what they claim is the first junctionless transistor.

The breakthrough is based on the deployment of a control gate around a silicon wire that measures just a few dozen atoms in diameter. The gate can be used the squeeze the electron channel to nothing without the use of junctions or doping. The development, which could simplify manufacturing of transistors at around the 10nm stage, was created a by a team led by Professor Jean-Pierre Colinge and a paper on the development has been published in Nature Nanotechnology.

It simplifies the production of transistors which also have a near-ideal sub-threshold slope, extremely low leakage currents and less degradation of mobility with gate voltage and temperature than classical transistors, the researchers have claimed. Nonetheless such device can be made to have CMOS compatibility.

Since their invention transistor- and diode-action has depended on controlling the flow of electrons across junctions giving rise to the familiar NPN and PNP notation for bipolar devices and p- and n-type FETs with sources and drains. Controlling the junction allows the current in the device to be turned on and off and it is the precise fabrication of this junction that determines the characteristics and quality of the transistor and is a major factor in the cost of production. However, as a consequence of the repeated miniaturization predicted by Moore's Law transistors at the leading edge are becoming so small that conventional transistor architectures are becoming exceedingly difficult to fabricate.

"We have designed and fabricated the world s first junctionless transistor that significantly reduces power consumption and greatly simplifies the fabrication process of silicon chips," declared Colinge, in a statement.

Wedding ring-like gate
"The current flows in a very thin silicon wire and the flow of current is perfectly controlled by a 'wedding ring' structure that electrically squeezes the silicon wire in the same way that you might stop the flow of water in a hose by squeezing it. These structures are easy to fabricate even on a miniature scale which leads to the major breakthrough in potential cost reduction," explained Colinge.

Another key challenge for the semiconductor industry is reducing the power consumption of microchips. Minimizing current leakage is one of the main challenges in today's complex transistors. "The Tyndall junctionless devices have near ideal electrical properties and behave like the most perfect transistors. Moreover, they have the potential of operating faster and using less energy than the conventional transistors used in today s microprocessors," said Colinge.

He went on to say that the junctionless transistor resembles the ideal semiconductor transistor structure, first proposed in 1925. But to-date, no-one had been able to fabricate it. He attributed the successful fabrication at Tyndall to the skill and expertise of researchers who were able to fabricate silicon nanowire with a diameter of a few dozen atoms using electron-beam writing techniques and expertise available at Tyndall.

"We are very excited by the outstanding results that Jean-Pierre has achieved," commented Tyndall CEO, Professor Roger Whatmore. "We are beginning to talk about these results with some of the world's leading semiconductor companies and are receiving a lot of interest in further development and possible licensing of the technology. These results could not have been achieved without the expertise of Jean-Pierre and his colleagues together with the state-of-the art facilities that we have at Tyndall."

- Peter Clarke
EE Times Europe

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