When Nobel Prize winner Leo Esaki discovered the tunnel diode in 1957, the super-fast, current-switching device was touted as a kind of Holy Grail for computer chip makers, but technological obstacles have so far hindered its widespread use in conventional, silicon-based circuits. In the Oct.12, 1998 issue of Applied Physics Letters, on-line Oct. 7, University of Delaware researchers--with scientists at the Naval Research Laboratory and Raytheon Systems Co.--describe promising, new tunnel diodes that may help chip makers boost silicon's speed while further shrinking chips. The technology, described in a patent disclosure, should someday benefit soldiers in the battlefield--or business people on the go, says lead researcher Paul R. Berger (above), an associate professor of electrical and computer engineering at UD, who received a 1996 National Science Foundation CAREER award for promising, young investigators.
Berger and his colleagues 'grew' highly doped (delta-doped) silicon monolayers at the Naval Research Laboratory, using a technique known as molecular beam epitaxy (MBE), at a relatively low temperature--370 degrees Celsius (698 degrees Fahrenheit). The materials were then cured or annealed at 700 to 800 degrees C. The resulting diode resembles a sandwich, with a 4-nanometer layer of pure silicon-germanium at the center, encased by delta-doped slices of boron and antimony on either side. The boron and antimony layers are then encased by silicon with opposing electrical charges, all of which is heaped atop a 'plate'--a silicon substrate with positive charge carriers. If UD's silicon-based, tunnel diodes can be combined with semiconductor circuits to boost transistor switching speeds, the breakthrough could enhance silicon chips, says Berger.