Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists fashion semiconductors into flexible membranes

10.04.2006


University of Wisconsin-Madison researchers have demonstrated a way to release thin membranes of semiconductors from a substrate and transfer them to new surfaces-an advance that could unite the properties of silicon and many other materials, including diamond, metal and even plastic.



Led by materials science and engineering graduate student Michelle Roberts, the team reports in the April 9 issue of Nature Materials that the freed membranes, just tens of nanometers thick, retain all the properties of silicon in wafer form. Yet, the nanomembranes are flexible, and by varying the thicknesses of the silicon and silicon-germanium layers composing them, scientists can make membrane shapes ranging from flat to curved to tubular.

Most importantly, the technique stretches the nanomembranes in a predictable and easily controlled manner, says materials science and engineering professor Max Lagally, who is Roberts’ advisor. In silicon that is stretched, or under tensile strain, current flows faster-a fact engineers already exploit to help control silicon’s conductivity and produce speedier electronics. Strain also becomes important whenever different materials are integrated.


The new technique makes tuning the strain of materials simpler, while avoiding the defects that normally result. In addition, Lagally says: "We’re no longer held to a rigid rock of material. We now have the ability to transfer the membranes to anything we want. So, there are some really novel things we can do."

Potential applications, he says, include flexible electronic devices, faster transistors, nano-size photonic crystals that steer light, and lightweight sensors for detecting toxins in the environment or biological events in cells.

Although it could make controlling strain easier, the technique is not manufacturing-ready, cautions physics professor Mark Eriksson, because it requires the release of nanomembranes into solution before bonding to other materials.

"What we’ve done is a first demonstration," says Eriksson. "But now that we’ve shown the underlying principles are sound, we can begin taking the next steps."

In building electronic devices, engineers routinely layer materials with different crystal structures on top of one another, creating strain. Larger germanium atoms, for example, want to sit farther apart in a crystalline lattice than do smaller atoms of silicon. Thus, when a thin layer of silicon-germanium alloy is bonded to a thicker silicon substrate, the silicon’s lattice structure dominates, forcing the germanium atoms into unnaturally close proximity and compressing the silicon-germanium.

Scientists can then use the compressive strain in the silicon-germanium to strain a thin silicon layer grown on top, but only if the alloy’s strain is controlled. To do so, they typically deposit many layers of silicon-germanium. As layers are added and strain builds, "dislocations," or breaks in the crystal lattice, naturally develop, which give germanium atoms the extra room they need and relax some of the strain. But the technique is time-consuming and expensive, and the defects can scatter current-carrying electrons and otherwise degrade device performance.

The Wisconsin team’s goal was to integrate silicon and silicon-germanium and manage strain without having to introduce defects. The scientists made a three-layer nanomembrane composed of a thin silicon-germanium layer sandwiched between two silicon layers of similar thinness. The membrane, in turn, sat atop a silicon dioxide layer in a silicon-on-insulator substrate. To release the nanomembrane, the researchers etched away the oxide layer with hydrofluoric acid.

"When we remove the membrane, the silicon-germanium is no longer trying to fight the substrate, which is like a big rock holding it from below. Instead, it’s just fighting the two very thin silicon layers," says Lagally. "So the silicon-germanium expands and takes the silicon with it."

Pulled by the silicon-germanium, the silicon now exhibits tensile strain, which the researchers can readily adjust by varying the thicknesses of the layers. They call the technique "elastic strain sharing" because in the freed membrane, strain is balanced, or shared, between the three layers.

Levente Klein, a postdoctoral researcher working with Eriksson, also showed that the strain produced by the technique traps electrons in the top silicon layer, which is the end goal for many devices that integrate silicon and silicon-germanium, says Eriksson.

"In this research, there’s a nice synergy between the structural characteristics of the material and the consequences for electronics," he says.

Although the Wisconsin team grew their nanomembranes on silicon-on-insulator substrates, the method should apply to many substances beyond semiconductors, says Lagally, such as ferroelectric and piezoelectric materials. All that’s needed is a layer, like an oxide, that can be removed to free the nanomembranes.

"In any application where crystallinity and strain are important, the idea of making membranes should be of value," says Lagally.

Max Lagally | EurekAlert!
Further information:
http://www.wisc.edu

More articles from Materials Sciences:

nachricht Serendipity uncovers borophene's potential
23.02.2017 | Northwestern University

nachricht Switched-on DNA
20.02.2017 | Arizona State University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>