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 Decoding cement's shape promises greener concrete
08.12.2016 | Rice University

nachricht Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D
08.12.2016 | DOE/Brookhaven National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Closing the carbon loop

08.12.2016 | Life Sciences

Applicability of dynamic facilitation theory to binary hard disk systems

08.12.2016 | Physics and Astronomy

Scientists track chemical and structural evolution of catalytic nanoparticles in 3-D

08.12.2016 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>