Not Science Fiction Any More: Sandia Scientists Develop Quantum Mechanical Transistor

February 11, 1998

ALBUQUERQUE, N.M. -- Improvements in the transistor of the future may rely on a radical change in operation made possible by a quantum mechanical transistor created at Sandia National Laboratories. The quantum mechanical transistor is the equivalent of turning on a light bulb without closing a switch: Electrons "tunnel" from path to path through a barrier that, according to classical physics, is impenetrable. The process takes place with extreme rapidity.

The term, "tunneling," may bring to mind moles or the highway department, but physicists use it to describe an effect in which particles, like electrons, appear in places where by rights they should not be able to go. In effect, they have tunneled under an energy barrier the same way cars use a tunnel to appear at a new location without having to drive over an impossibly high summit. The atomic-scale effect is explained only by quantum mechanical principles.

A real device, not just theory

"We have demonstrated real circuits that work and are easily fabricated," says Jerry Simmons, leader of the Sandia development team. "It is not ready to be sold yet, but it is a significant advance." The device, dubbed DELTT (Double Electron Layer Tunneling Transistor), offers promise of significant improvements in the speed of computers and in the accuracy of sensors. Sandia is a laboratory of the Department of Energy (DOE).

According to Paul Berger, professor of electrical and computer engineering at the University of Delaware, "I was impressed by the multitude of possible uses of the DELTT device, as well as by its simplicity of connectivity." Berger chaired the session at the International Electron Devices Meeting in Washington, D.C. late last year in which the first paper on the device was delivered. Sandia has applied for one patent and is preparing others on the device. A research paper on DELTT has been accepted for publication by Applied Physics Letters.

A trillion operations a second

The very fast device may run at a trillion operations a second, as have other, more primitive tunneling devices. This is roughly ten times the speed of the fastest transistor circuits currently in use. Actual speed has not yet been measured, says Simmons, because it is "not easy to measure such high speeds, which are near the limits of what can be measured with conventional equipment." The very fast device also runs at extremely low power -- tens of millivolts and microamps -- as compared with the few volts and milliamps needed by transistors currently in use.

That electrons travel so rapidly in the DELTT gallium arsenide transistor means that normal electrical processes that slow down transmission of information -- like scattering of electrons by crystal imperfections that behave much like potholes in the electrons "pathway "-- can be minimized. From Sandia's point of view as a national defense laboratory, the device might someday be put to work in satellites and smart missiles to process information faster, with less payload and much lower power consumption than today's devices.

Because the device is also tunable, it could act like an energy spectrometer on a chip. This could allow sensitive detection of chemical and biological species like nerve gas and anthrax, helping to combat bio- or chem-terrorists by allowing more rapid and reliable detection of minute concentrations of toxic materials at customs and airports, on the battlefield and via airborne platforms.

Other possible uses of the modified structure would be as an optical detector in the far infrared. Incoming photons would be used to add energy needed for a transition between electron states, causing the device to turn on in only a narrow energy band.

Actual use of the transistor by industry may be years in the future because of other engineering problems to be tackled. These include questions of temperature -- the device now works only at temperatures at or below 77 degrees Kelvin, though rapid improvements and already existing technology indicate it should be operating at room temperature by next year, says Simmons.

Another problem involves designing millions of such circuits on a chip, as is currently done with ordinary transistors. Because of the Sandia device's multifunctionality -- it has three positions, off-on-off, instead of the normal transistors-- two on-or-off states -- the same amount of work can be performed with significantly fewer transistors, and chips would have to be completely redesigned.

How it works

The technique relies in part upon the dual wave-particle nature of matter. In the device, two gallium arsenide layers, each only 150 angstroms thick, are separated by a 125 Angstrom aluminum-gallium- arsenide barrier -- the equivalent of the yards of two houses separated by a sturdy fence. Ordinarily, gallium arsenide electrons in one yard do not have the energy to climb the fence to reach the other yard. But the tiny thickness of the barrier causes the electrons to behave like waves, which can poke into the barrier.

When an electron is adjusted to have the same energy and momentum states in both regions -- something that can be done by applying a voltage to these regions -- it can pass from one region to the other without any scattering, as occurs in normal electron motion due to crystal imperfections. In effect, they tunnel under the barrier fence.

Previous attempts at building tunneling transistors had been made by researchers who created layers side by side on a surface. This proved too difficult a task for current technology to manufacture accurately at 1,000 angstroms or the even smaller dimensions necessary. A novel design change allowed Sandia researchers to stack all DELTT layers vertically, using molecular beam epitaxy (MBE) or chemical vapor deposition (CVD), which enabled single-atom layers to be grown.

MBE and CVD are the same processes used to make, among other products, semiconductor lasers for compact disc players, and are readily available technologies.

The project is funded by Sandia's Laboratory-Directed Research and Development office, which funds speculative, defense-related projects, and DOE's Defense Programs.

Sandia is a multiprogram DOE laboratory, operated by a subsidiary of Lockheed Martin Corp. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major research and development responsibilities in national security, energy, and environmental technologies and economic competitiveness.
-end-


DOE/Sandia National Laboratories

Related Electrons Articles from Brightsurf:

One-way street for electrons
An international team of physicists, led by researchers of the Universities of Oldenburg and Bremen, Germany, has recorded an ultrafast film of the directed energy transport between neighbouring molecules in a nanomaterial.

Mystery solved: a 'New Kind of Electrons'
Why do certain materials emit electrons with a very specific energy?

Sticky electrons: When repulsion turns into attraction
Scientists in Vienna explain what happens at a strange 'border line' in materials science: Under certain conditions, materials change from well-known behaviour to different, partly unexplained phenomena.

Self-imaging of a molecule by its own electrons
Researchers at the Max Born Institute (MBI) have shown that high-resolution movies of molecular dynamics can be recorded using electrons ejected from the molecule by an intense laser field.

Electrons in the fast lane
Microscopic structures could further improve perovskite solar cells

Laser takes pictures of electrons in crystals
Microscopes of visible light allow to see tiny objects as living cells and their interior.

Plasma electrons can be used to produce metallic films
Computers, mobile phones and all other electronic devices contain thousands of transistors, linked together by thin films of metal.

Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.

Researchers develop one-way street for electrons
The work has shown that these electron ratchets create geometric diodes that operate at room temperature and may unlock unprecedented abilities in the illusive terahertz regime.

Photons and electrons one on one
The dynamics of electrons changes ever so slightly on each interaction with a photon.

Read More: Electrons News and Electrons Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.