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Study allows transistors to switch to vacuum as medium

Posted: 04 Jul 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Nanotechnology? solid-state? vacuum? electron transport? transistors?

Nanotechnology switches back to vacuum transistors at low voltageJuly 03, 2012 // Peter Clarke

Researchers from the University of Pittsburgh have come up with a device structure which allows a switch from the solid-state back to vacuum as the medium for electron transport in transistors.

The team has proposed a metal oxide semiconductor (MOS) vertical structure with a triple layer of metal/silicon dioxide/silicon exposed on the side by a deep trench. The metal and silicon layers form the anode and cathode of the device, which is then separated by the insulating silicon dioxide. The electron transport occurs in the vertical direction through the vacuum.

A research paper entitled Metal-oxide-semiconductor field effect transistor with a vacuum channel has already been published in Nature Nanotechnology, detailing the findings of the work.

The study done by the team starts with a return to the beginnings of electronics. Solid-state transistors were invented in 1947 to replace bulky and unreliable vacuum tubes. Vacuum tube style electronics in miniature made using solid-state semiconductor manufacturing techniques have been tried before, but the concept has struggled to overcome requirements for high voltage and issue of compatibility with the incumbent solid-state CMOS technology.

A team under Hong Koo Kim, a Professor in the University of Pittsburgh's Swanson School of Engineering, has redesigned the structure of the vacuum electronic device. His team discovered that electrons trapped inside a semiconductor at the interface with an oxide or metal layer can be easily extracted out into the air. The electrons at the material interface form a sheet of charges, a two-dimensional electron gas and Kim found that the Coulombic repulsion of the electrons for each other enables the easy emission of electrons out of the silicon. This allows the creation of a low-voltage device in which the electrons travel ballistically in air in a nanometer-scale channel without any collisions or scattering.

The channel length is of the order of 20-nm and the team measured a transconductance of 20-nS per micron and an on/off ratio of 500 and turn-on gate voltage of 0.5-V under ambient conditions, according to the paper's abstract.

- Peter Clarke
??EE Times US

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