Technology Research News
Shaking is a good way to break things,
especially electronic devices that contain many components. A team of
researchers at Harvard University has found that shaking can also have
the reverse effect.
The researchers have developed an assembly process that boils down to
making a cocktail -- shaken, not stirred -- of electronic components and
copper wires in a vial of hot water. The technique is one of a growing
number of self-assembly processes that could dramatically lower manufacturing
costs for electronic devices ranging from sensors to computers.
The Harvard team demonstrated their patterned self-assembly process by
making a cylindrical display about 4 millimeters in diameter that contained
113 light-emitting diodes (LEDs). The shape of the display proves the
process is not restricted to flat surfaces, which is a limitation of current
manufacturing techniques, said Heiko O. Jacobs, a member of the team who
is now an assistant professor of electrical and computer engineering at
the University of Minnesota.
The researchers began with an array of 113 copper squares that were connected
via copper wires and mounted on a plastic sheet. The squares, which measured
280 microns each, were coated with a solder that melts at relatively low
temperatures. The first steps in the process were rolling the sheet into
a cylinder, putting it in a vial of water, adding 113 280-micron-square
LEDs, and heating the water above the melting temperature of the solder.
The researchers found that they could get the LEDs to adhere to the copper
squares by gently shaking the vial by hand for one to two minutes. Tapping
the vial with a metal rod shook loose LEDs that adhered to wires between
squares or that stuck two to a square, and shaking the vial some more
got these last LEDs to stick to the right places.
The gold contacts on the bottoms of the LEDs stuck to the liquid solder
because of the same force that causes adjacent drops of liquid to merge.
Molecules on the surface of a liquid have higher energy, and are therefore
less stable, than molecules within the liquid, said Jacobs. Drops of liquid
merge because liquids naturally reduce surface area to become stable,
he said. "In our system, the solder bumps capture light emitting diodes
for the same reason," said Jacobs.
They finished the display by hand positioning another plastic sheet with
copper squares on top of the LEDs.
The advantages of the researchers' patterned self-assembly process are
that it does not require expensive machinery, it works on curved and flexible
surfaces, and it handles small components, said Jacobs. Because the process
handles smaller components it could be used to make higher-resolution
displays than are possible with conventional approaches, he added.
A display like the researchers' small cylinder prototype could be used
for a future combination pen and cell phone or similar device, said Jacobs.
Making more complicated devices that have different types of components
is likely to require shape-selective recognition and hierarchical self-assembly
techniques in addition to the researchers' cocktail-mixing approach, according
to Jacobs. Shape-selective recognition is a process for building components
with shapes that combine in only one way, said Jacobs. "Hierarchical self-assembly
is self-assembly of tiny things into small aggregates, and then further
self-assembly of the small aggregates into larger aggregates, and so on,"
The researchers' patterned self-assembly process could be put to practical
use in five to ten years, said Jacobs.
Jacobs' research colleagues were Andrea R. Tao, Alexander Schwartz, David
H. Gracias and George M. Whitesides of Harvard University. They published
the research in the April 12, 2002 issue of the journal Science. The research
was funded by the National Science Foundation (NSF), the Defense Advanced
Research Projects Agency (DARPA), the German Science Foundation and the
Swiss National Science Foundation.
Timeline: 5-10 years
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Fabrication of a Cylindrical
Display by Patterned Assembly," Science, April 12, 2002
Shake and serve
Odds not hopeless
for new Web sites
banishes browser plug-ins
Polarized light speeds
File compressor ID's authors
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link