Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Scientists fashion semiconductors into flexible membranes


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:

More articles from Materials Sciences:

nachricht From ancient fossils to future cars
21.10.2016 | University of California - Riverside

nachricht Study explains strength gap between graphene, carbon fiber
20.10.2016 | Rice 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: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

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

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>