From: Max More (maxmore@primenet.com)
Date: Fri Feb 06 1998 - 14:36:28 MST
>PHYSICS NEWS UPDATE
>The American Institute of Physics Bulletin of Physics News
>Number 357 February 4, 1998 by Phillip F. Schewe and Ben Stein
>
>A QUANTUM TUNNELING TRANSISTOR, an on-off switch
>that exploits an electron's ability to pass through normally
>impenetrable barriers, has been built by Sandia researchers (Jerry
>Simmons, 505-844-8402), opening possibilities for record-speed
>transistors that can be mass-produced with current nanotechnology.
> In their device, the researchers control the flow of electrons
>between two GaAs layers (each only 15 nm thick) separated by an
>AlGaAs barrier (12 nm). Although the electrons in GaAs
>ordinarily do not have enough energy to enter the AlGaAs barrier,
>the layers are so thin (comparable in size to the electron
>wavelength) that the electrons, considered as waves rather than
>particles, can spread into the barrier and, with an appropriate
>voltage applied, out the other side. In the process, the electron
>waves do not collide with impurity atoms, in contrast to a
>traditional transistor's particlelike electrons, which are slowed
>down by these collisions. Transistors that switch on and off a
>trillion times per second--5 times faster than the current record--are
>possible with this approach. Although quantum tunneling
>transistors were first built in the late 1980s, it was originally
>infeasible to mass-produce them. Previous researchers engraved
>the ultrathin GaAs and AlGaAs features side-by-side on a surface,
>something hard to do reliably with present-day lithography.
>Therefore the Sandia researchers stacked the features vertically, by
>using readily available techniques such as molecular beam epitaxy
>which can deposit layers of material with single-atom thicknesses.
>Having made quantum-tunneling memory devices and digital logic
>gates operating at 77 K, the researchers expect room-temperature
>devices in the next year. (J.A. Simmons et al., upcoming article
>in Applied Physics Letters; figure at
>www.aip.org/physnews/graphics)
>
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