Electric fields assemble devices
Technology Research News
The easiest way to assemble a device is
to provide an environment that causes it to self-assemble. As components
continue to shrink, this could become the only practical means of assembly.
In contrast, today's electronic devices are generally put together
using tiny equivalents of assembly line robots that pick up and place
components on chips. This approach can be scaled down only so far because
at a certain point natural forces cause components to stick to assembly
Researchers from the National Microelectronics Research Centre
(NMRC) in Ireland have sidestepped the problem by using electric fields
to direct the assembly process. They used the technique to cause arrays
of gallium arsenide light-emitting diodes to assemble onto silicon chips.
The method, dubbed Field Controllable Assembly, is compatible
with contemporary optoelectronics manufacturing methods, and could lead
to low-cost, rapid assembly of optical and electronic devices, said Alan
O'Riordan, a research scientist at the National Microelectronics Research
The method takes advantage of the electric charge that most objects
carry. "The response of these charges to an appropriately configured electric
field may be exploited to direct the transport and ultimately the self-assembly
of the devices," O'Riordan said.
The researchers' self-assembly device contains an array of electrodes
on a silicon surface that allows them to put electric fields of specific
configurations on the surface of the chip. The fields can be configured
to attract electric charges at a particular spot and repel it everywhere
else. The right configuration causes components to rapidly move from one
spot to another. Once the components are in place, the transport fluid
is evaporated and the components fused to the surface by melting and cooling
the chip's tin-gold contacts.
In theory, the technique could move components over distances
of up to several millimeters, according to O'Riordan.
The researchers' method is a high-throughput, non-contact, pick-and-place
technique that allows for programmable manipulation of individual components
on silicon surfaces like computer chip wafers, said O'Riordan.
A key factor of the researchers' self-assembly technique is that,
unlike many natural self-assembly processes, the objects involved are
not required to recognize the parts they must connect to.
The researchers used the method to assemble devices from 50- to
80-micron diameter light-emitting diodes, and to transport 1-micron latex
beads. A micron is one thousandth of a millimeter; the width of a human
hair is about 75 microns.
The method is scalable down to the nano level, and could eventually
be used to assemble nanoelectronic, nanophotonic, and nanoscale biotechnology
devices, said O'Riordan. A nanometer is one millionth of a millimeter.
The technique can also be used to assemble many components in
parallel. As long as the spots are about the same diameter as the components,
the method assures that each spot attracts a single component, according
to O'Riordan. For example, the researchers randomly deposited a set of
light emitting diodes in a liquid on a chip surface and configured the
electric fields on the chip to attract the diodes to an array of spots.
The method is particularly applicable to microelectrical mechanical
systems (MEMS), which incorporate moving parts into computer chips, and
optoelectronics, which convert light signals to electrical signals and
vice versa. The cost reduction the method would bring about would be particularly
useful in these manufacturing sectors, said O'Riordan.
The method could be used practically in two to five years, said
O'Riordan's research colleagues were Paul Delaney and Gareth Redmond.
The work appeared in the May, 2004 issue of Nano Letters. The research
was funded by the the European Union and Enterprise Ireland.
Timeline: 2-5 years
TRN Categories: Nanotechnology; Integrated Circuits
Story Type: News
Related Elements: Technical paper, "Field Configured Assembly:
Programmed Manipulation and Self-assembly at the Mesoscale," Nano Letters,
May, 2004; video of Field Configurable Assembly of light-emitting diodes,
July 28/August 4, 2004
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