23-06-2012, 11:32 AM
MICROMECHANICS OF MACROELECTRONICS
MICROMECHANICS OF MACROELECTRONICS[.pdf (Size: 91.82 KB / Downloads: 34)
Abstract
The advent of flat-panel displays has opened the era of macroelectronics. Enthusiasm is gathering to develop
macroelectronics as a platform for many technologies, ranging from paper-like displays to thin-film solar cells,
technologies that aim to address the essential societal needs for easily accessible information, renewable energy, and
sustainable environment. The widespread use of these large structures will depend on their ruggedness, portability and
low cost, attributes that will come from new material choices and new manufacturing processes. For example, thin-film
devices on thin polymer substrates lend themselves to roll-to-roll fabrication, and impart flexibility to the products.
Introduction
For half a century, the technology of integrated circuits
has been advancing by miniaturization, squeezing more
and more transistors onto each chip. While the trend to
miniaturize features will continue in the field of microelectronics
(Semiconductor Industry Association, 2004), a
new trend to enlarge systems is gaining momentum in the
nascent field known as macroelectronics or large-area
electronics (Nathan & Chalamala, 2005). At present, the
most visible application of macroelectronics is flat-panel
displays. They entered the consumer market in the 1990s,
and are now replacing cathode-ray tubes as monitors for
televisions and computers. In such an application, transistors
need not to be smaller than, say 10 μm, but the
total surface area must be large.
Flexible Electronics with Hybrid Organic/
Inorganic Materials
Enthusiasm for organic electronics aside, it is unlikely
that many macroelectronic systems will be made entirely
of organic materials, because organic materials cannot
serve all functions of inorganic materials. Rather, most
macroelectronic systems will be made as organic/inorganic
hybrids. As an illustration, organic light-emitting devices
(OLEDs) survive only a few hours when exposed to
atmospheric oxygen and moisture. To attain a long lifetime,
an OLED must be hermetically sealed. Organic materials
are permeable to gases, so that a gas barrier must contain
an inorganic material. In such an application, the gas
barrier must also be optically transparent.
Stretchable Electronics of Patterned
Stiff Materials on Compliant Substrates
Of various modes of deformation (e.g., bending, twisting
and stretching), typically stretching is the most demanding,
easily inducing a large tensile strain. While an
elastomer substrate can recover from a large strain, inorganic
materials fracture at small strains (less than about
one percent, as discussed above). How to use these
materials to make stretchable electronic circuits remains a
challenge.
Effect of inelastic deformation of the substrate
on channel cracks in the film
Figure 3 illustrates the effect of viscoelastic deformation
of the substrate on channel cracks in the film. As discussed
above, the presence of an elastic substrate constrains
the opening of the crack in the film, and reduces
the crack driving force compared to that of a crack in the
free-standing film. For a film on a viscous substrate, however,
this constraint is gradually lost over time, so that the
crack driving force increases; for a sufficient long time, the
film is effectively free-standing.
Concluding Remarks
Low-cost, rugged macroelectronics will be a platform for
many technologies, such as paper-like displays, medical
imaging systems, and thin-film solar cells. These technologies
aim to address the essential societal needs for
easily accessible information, renewable energy, and a
sustainable environment. Macroelectronic systems are
large structures of diverse architectures, hybrid materials,
and small features.