electronics on deck
Technology Research News
Diamonds naturally form in the thickest
part of the earth's crust, 75 or more miles deep, where more than half
a million pounds of pressure per square inch and temperatures topping
900 degrees Celsius push carbon atoms into a compact crystalline structure.
Diamonds ride to the surface in streams of molten lava when volcanoes
Only a material with unusual properties could survive such an intense
Researchers have known for a long time that pure diamond is potentially
superior to silicon in several ways that would make for better electronic
components. In theory, diamond components would be able to withstand extreme
conditions like heat, radiation and high voltage, and could boost the
bandwidth of wireless communications channels.
But it has proved difficult to make sufficiently pure diamond. Like natural
diamond, the manufactured variety tends to contain impurities and defects
that hinder their ability to conduct electricity.
Semiconductor materials used to make components that precisely guide currents
of electrons must be extremely pure. The silicon wafers used for most
of today's electronics are the purest material manufactured in large quantities,
with fewer than one impurity or defect per trillion atoms.
Researchers from ASEA Brown Boveri (ABB) in Sweden and DeBeers Industrial
Diamonds in England have brought diamond-based electronics closer to realization
by showing that it is possible to manufacture diamond pure enough to reliably
Two distinct processes are used to manufacture diamond for industrial
use. High-pressure, high-temperature (HPHT) techniques have been used
for more than 30 years to produce tiny diamonds for applications like
coating the tips and edges of cutting tools. For the past decade researchers
have been working to make more pure diamond using chemical vapor deposition
(CVD), which induces the carbon in a carbon-containing gas to accumulate
on a surface.
The ABB-DeBeers researchers' achieved success in chemical vapor deposition
"by very precise control of synthesis conditions, and ensuring that deposition
occurs under conditions of high purity," said Steven Coe, research manager
at DeBeers. "This is a case where a whole series of incremental improvements
have collectively enabled" a step forward, he said.
The manufactured diamond's charge carrier mobility, a measure of how easily
negatively charged electrons or positively-charged holes vacated by electrons
can move through a material, is actually higher than theoretical predictions,
said Jan Isberg, an ABB researcher who is now a researcher at Uppsala
University in Sweden. "We have... shown that the electronic quality of
the diamond can be improved to reach higher carrier mobilities than in
any previously-made diamond," said Isberg.
The researchers' diamond showed room temperature electron carrier mobility
as high as 4,500 square centimeters per volt second, Isberg said. This
is about three times higher than silicon. This means electric current
can travel through the diamond as fast as 45,000 centimeters per second
in the presence of a one volt electric field applied over a one millimeter-thick
area of diamond, he said.
The experiments also showed carrier lifetimes "orders of magnitude better"
than previously shown in diamond, said Isberg.
In a semiconductor substance like diamond, an electric field jolts electrons
into a higher energy state to induce current to flow; the carrier lifetime
is the average time an electron stays in this high-energy state. In natural
diamonds, carrier lifetimes are shorter than one billionth of a second.
The researchers clocked carrier lifetimes as high as two millionths of
a second in their diamond material. "The lifetime is limited by defects
and impurities in the material, so long lifetimes is an indication of
pure material," said Isberg.
Electrically viable diamond is especially valuable because of diamond's
other unusual properties. It is the hardest known substance and best known
heat conductor, and it withstands the damaging effects of electric current
better than any other known material. It is also chemically inert, offers
low friction, and is transparent to lightwaves from the ultraviolet range
to the far-infrared range.
In general, the material could enable electronic devices with "superior
performance regarding power efficiency, power density, high frequency
properties, power loss, and cooling," Isberg said.
Its ability to withstand electrical current makes it a good candidate
for higher power, higher frequency wireless devices. "You can make smaller
transistors for the same voltage levels, which improves the switching
speed and thereby [increases the] frequency," said Isberg. Transmitting
information at higher frequencies enables wireless devices with more bandwidth,
because more information can be transmitted in the same amount of time
over radio waves that are shorter and thus faster.
Diamond transistors could in theory deliver one watt of power at 100 gigahertz,
or billion cycles per second, said Isberg. This is five times faster has
been achieved using the semiconductor Gallium Arsenide.
Diamond-based electronics would also be better than existing semiconductor
materials for high-temperature applications, said Isberg. Diamond conducts
heat 15 times more efficiently than silicon, and therefore cools faster.
The ability to disburse heat quickly is a plus for electronics materials
because some of the energy that powers the transistors in devices like
computer chips is inevitably given off as waste heat. The faster the chip
and the more transistors it contains, the more heat is given off. The
fans in many of today's PCs are required to prevent the main processor
chips, which contain as many as 40 million transistors each, from overheating.
Diamond would be especially appropriate for electronics required to withstand
high-temperature environments like automobile engines and space, said
The strong chemical bond structure of diamond means that the atoms are
not easily displaced by radiation. This would make for more stable components
for radiation-detection and high-voltage devices, and for high-radiation
environments in space, said Isberg.
The researchers' next step is to construct electronic components like
transistors and diodes from the manufactured diamond material.
Simple diamond radiation and UV detectors for medical applications and
space could be ready for practical use in as few as two years, said Isberg.
Diamond diodes and transistors for use in telecommunications, high-voltage
and high-temperature applications will take four to six years to develop,
The work is an important breakthrough in this type of diamond synthesis,
said Yury Gogotsi, a professor of materials engineering at Drexel University.
"Many years of research activities and huge money invested in CVD diamond
in the past decade did not produce the films or crystals of the quality
necessary for the electronic application of diamond," he said. The initial
disappointments have in recent years slowed funding for and development
of the process, he said.
This finding may reverse that trend, said Gogotsi. "Demonstration of electronic-quality
diamond produced by CVD may result in a new wave of interest... and financial
support for the research on CVD diamond and diamond electronics."
Isberg's research colleagues were Johan Hammersberg, Erik Johansson and
Tobias Wikström of ABB, and Daniel J. Twitchen, Andrew J. Whitehead and
Geoffrey A. Scarsbrook of De Beers Industrial Diamonds in England. They
published the research in the September 6, 2002 issue of Science. The
research was funded by ABB in Sweden and De Beers.
Timeline: 2 years, 4-6 years
TRN Categories: Chemistry; Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "High Carrier Mobility
in Single-Crystal Plasma-Deposited Diamond," Science, September 6, 2002.
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