Researchers at the University of Toronto have created
a semiconductor device that outperforms today's conventional
chips -- and they made it simply by painting a liquid
onto a piece of glass.
The finding, which represents the first time a so-called "wet" semiconductor
device has bested traditional, more costly grown-crystal
semiconductor devices, is reported in the July 13
issue of the journal Nature.
"Traditional ways of making computer chips, fibre-optic
lasers, digital camera image sensors – the building
blocks of the information age – are costly in time,
money, and energy," says Professor Ted Sargent of
the Edward S. Rogers Sr. Department of Electrical
and Computer Engineering and leader of the research
group. Conventional semiconductors have produced
spectacular results -- the personal computer, the
Internet, digital photography -- but they rely on
growing atomically-perfect crystals at 1,000 degrees
Celsius and above, he explains.
The Toronto team instead cooked up semiconductor
particles in a flask containing extra-pure oleic
acid, the main ingredient in olive oil. The particles
are just a few nanometres (one billionth of a metre)
across. The team then placed a drop of solution on
a glass slide patterned with gold electrodes and
forced the drop to spread out into a smooth, continuous
semiconductor film using a process called spin-coating.
They then gave their film a two-hour bath in methanol.
Once the solvent evaporated, it left an 800 nanometre-thick
layer of the light-sensitive nanoparticles.
At room temperature, the paint-on photodetectors
were about ten times more sensitive to infrared rays
than the sensors that are currently used in military
night-vision and biomedical imaging. "These are exquisitely
sensitive detectors of light," says Sargent, who
holds a Canada Research Chair in Nanotechnology. "It's
now clear that solution-processed electronics can
combine outstanding performance with low cost."
The U of T development could be of critical importance
to both research and industry, according to John
D. Joannopoulos, a Professor at MIT. "The ability
to realize low-cost, paintable, high-performance
designer semiconductors for use as short-wavelength
infrared detectors and emitters is of enormous value
for a wide range of communications, imaging and monitoring
applications," says Joannopoulos, the Francis Wright
Davis Professor of Physics and director of the Institute
for Soldier Nanotechnologies at the Massachusetts
Institute of Technology.
"The key to our success was controlled engineering
at the nanometre lengthscale: tailoring colloidal
nanocrystal size and surfaces to achieve exceptional
device performance," says lead author Gerasimos Konstantatos,
a doctoral researcher at UofT. "With this finding,
we now know that simple, convenient, low-cost wet
chemistry can produce devices with performance that
is superior compared to that of conventional grown-crystal
The research was supported by the Natural Sciences
and Engineering Research Council (NSERC) of Canada
through its Idea to Innovation (I2I) Program, the
Canada Foundation for Innovation; the Province of
Ontario through the Ontario Centres of Excellence
and the Canada Research Chairs program.
Contact: Ted Sargent
University of Toronto