UW-Madison: New Fast, Flexible Computer Chips on Plastic

MADISON – New thin-film semiconductor techniques invented by University of
Wisconsin-Madison engineers promise to add sensing, computing and imaging capability
to an amazing array of materials.

Historically, the semiconductor industry has relied on flat, two-dimensional chips
upon which to grow and etch the thin films of material that become electronic
circuits for computers and other electronic devices. But as thin as those chips
might seem, they are quite beefy in comparison to the result of a new UW-Madison
semiconductor fabrication process detailed in the current issue of the Journal of
Applied Physics.

A team led by electrical and computer engineer Zhenqiang (Jack) Ma and materials
scientist Max Lagally have developed a process to remove a single-crystal film of
semiconductor from the substrate on which it is built. This thin layer (only a
couple of hundred nanometers thick) can be transferred to glass, plastic or other
flexible materials, opening a wide range of possibilities for flexible electronics.
In addition, the semiconductor film can be flipped as it is transferred to its new
substrate, making its other side available for more components. This doubles the
possible number of devices that can be placed on the film.

By repeating the process, layers of double-sided, thin-film semiconductors can be
stacked together, creating powerful, low-power, three-dimensional electronic

“It’s important to note that these are single-crystal films of strained silicon or
silicon germanium,” says Ma. “Strain is introduced in the way we form the membrane.
Introducing strain changes the arrangement of atoms in the crystal such that we can
achieve much faster device speed while consuming less power.”

For non-computer applications, flexible electronics are beginning to have
significant impact. Solar cells, smart cards, radio frequency identification (RFID)
tags, medical applications, and active-matrix flat panel displays could all benefit
from the development. The techniques could allow flexible semiconductors to be
embedded in fabric to create wearable electronics or computer monitors that roll up
like a window shade.

“This is potentially a paradigm shift,” says Lagally. “The ability to create fast,
low-power, multilayer electronics has many exciting applications. Silicon germanium
membranes are particularly interesting. Germanium has a much higher adsorption for
light than silicon. By including the germanium without destroying the quality of the
material, we can achieve devices with two to three orders of magnitude more

That increased sensitivity could be applied to create superior low-light cameras, or
smaller cameras with greater resolution.

Ma, Lagally, Materials Science and Engineering Assistant Professor Paul Evans,
Physics Associate Professor Mark Eriksson, and graduate students Hao-Chih Yuan and
Guogong Wang are patenting the new techniques through the Wisconsin Alumni Research
Foundation. The team’s work was supported in part by grants from the National
Science Foundation Materials Research Science and Engineering Center, the Department
of Energy and the Air Force Office of Scientific Research.