BY NOLAN FELL
Bell Labs' physicists Hendrik Schon and Shenan Bao have developed a
field effect transistor (FET) combining both insulator and semiconductor layers within a single
The work builds on the development of a single-molecule transistorthat the
two scientists built last November and is published in Applied Physics
"The molecules have two parts," said Schon. "In the conjugated part, there
are mobile electrons. When you build up a series of molecules, the
electrons interact and determine transport properties.It is similar to
organic thin films."
The insulating part of the molecule is deposited on to a silicon substrate
through precipitation out of a solution. A controlled chemical reaction grafts
silane on to a silicon substrate, which also acts as the gate electrode.
Pyrene units are attached to the insulating hydrocarbon silane structure,
the pyrene acting as theconducting part of the molecule. A gold electrode
for the drain is then thermally evaporated through a shadow mask.
Schon and Bao then assembled an insulating alkanethiol
monolayercovering the top and side wall of the drain electrode. The
source electrode was evaporated on top of this structure. Using
this technique, Schon and Bao have succeeded in producing 2nm
"The combination of insulating and semiconducting parts could lead to true
single-molecule transistors," said Schon. "We need now to develop a more
complex molecular design and connect them to some kind of contact."
In tests at Bell Labs, Schon and Bao established a circuit with the
transistors which ran for hours without any sign of degradation and the
monolayers demonstrated stability up to 200 degrees C. Tests also
achieved mobilities of 0.05cm2/Vs and on/off current ratios of more than
This could eventually lead to transistors more than 100 times smaller than
those produced using conventional CMOS processes, but Schon does not
anticipate commercial development for a decade.
(C) 2002 EE Times.