update.357 (fwd)

[Jim Choate]

Forwarded message:

> Date: Wed, 4 Feb 1998 11:01:53 -0500 (EST)
> From: physnews at aip.org (AIP listserver)
> Subject: update.357
> 
> 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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