Stretchable Silicon May Inspire a New Wave of Electronics

Scientists have created a form of nanoscale silicon that is stretchable. The new material may help pave the way for a class of stretchable electronic devices, such as “smart” surgical gloves and personal health monitors, that are not possible to create using current technology and materials.

“Electronics that are bendable have many potential applications, but reversible stretchability is a different and much more technically challenging characteristic,” said corresponding researcher John Rogers, a materials scientist at the University of Illinois at Urbana-Champaign (UIUC), to PhysOrg.com.

Rogers and colleagues from UIUC and the University of Arizona created an ultra-thin silicon membrane from a silicon wafer and merged the membrane with a slab of a silicon-based polymer. The overall process involved several steps but, in short, the group first “pre-strained” the polymer slab, pulling it taut, before they topped it with the prepared silicon. When they released the strain the silicon buckled, resulting in a series of raised wavy ridges forming a herringbone-like pattern. The finished composite membrane is about 100 nanometers thick and can stretch biaxially – that is, in both the vertical and horizontal directions.

The group performed several stretching tests on the membrane by pulling it from various directions. Stretching it horizontally caused the herringbone pattern to straighten out. Stretching along the diagonal produced similar changes until, at full stretch, straight diagonal ridges formed. And stretching along the vertical direction – perpendicular to the waves – produced straight vertical ridges. In each case, the membrane recovered its original pattern when the strain was released.

These temporary stretching-induced structural changes occur primarily at the membrane’s central region. In its pre-stretched state, the herringbone pattern is far less pronounced at the membrane’s edges. There, the waves give way to fairly straight ridges, and thus the edge of the membrane does not have the elasticity of the central region. However, Rogers and his colleagues say that this could be an asset in certain applications. For example, a medical imaging system that is stretchable – able to conform to the contours of the human body to achieve more detailed images – might perform better if regions directly above the device’s photodetectors (which collect light reflecting from the object being imaged) are kept flat.

In their paper describing the work, in the May 8 online edition of Nano Letters, Rogers and his colleagues also discuss theoretical predictions of the membrane's behavior. They note that these predictions match their experimental observations, specifically in terms of the shape and dimensions of the waves. This theoretical component of the research, performed by UIUC scientist Young Huang, a co-author of the paper, is a significant result of their work.

Rogers and his group have previously produced structures with similar qualities: stretchy, ridged nanoribbons made of silicon and gallium arsenide. Other research groups have made circuit components consisting of stretchable metal wires connecting rigid islands. However, the nanoribbons are only stretchable lengthwise and the wire-island structures provide circuit-level stretchability rather than stretchable devices.

Citation: Won Mook Choi, Jizhou Song, Dahl-Young Khang, Hanqing Jiang, Yonggang Y. Huang, and John A. Rogers. “Biaxially Stretchable ‘Wavy’ Silicon Nanomembranes” Nano Lett., ASAP Article 10.1021/nl0706244 S1530-6984(07)00624-8

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Related stories:

Stretchable silicon camera next step to artificial retina
(PhysOrg.com) -- By combining stretchable optoelectronics and biologically inspired design, scientists have created a remarkable imaging device, with a layout based on the human eye.
Researchers demonstrate a flexible, 1-step assembly of nanoscale structures
Scientists at the University of Pennsylvania have created a one-step, repeatable method for the production of functional nanoscale patterns or motifs with adjustable features, size and shape using a single master "plate."
Foldable and stretchable, silicon circuits conform to many shapes
Scientists have developed a new form of stretchable silicon integrated circuit that can wrap around complex shapes such as spheres, body parts and aircraft wings, and can operate during stretching, compressing, folding and other types of extreme mechanical deformations, without a reduction in electrical performance.
Deflecting damage: Flexible electronics aid brain injury research
Flexible electronic membranes may overcome a longstanding dilemma faced by brain researchers: How to replicate injuries in the lab without destroying the electrodes that monitor how brain cells respond to physical trauma.
Flexible electronics could find applications as sensors, artificial muscles
Flexible electronic structures with the potential to bend, expand and manipulate electronic devices are being developed by researchers at the U.S. Department of Energy's Argonne National Laboratory and the University of Illinois at Urbana-Champaign. These flexible structures could find useful applications as sensors and as electronic devices that can be integrated into artificial muscles or biological tissues.
Chain Mail Fabric a Perfect Fit
Contemporaries of the ancient Greeks might find something familiar within the walls of the Micro and Nanotechnology Lab at the University of Illinois. In constructing a new type of smart fabric, researchers Jonathan Engel and Chang Liu have used interconnecting rings and links to create a textile looking a bit like the chain mail used by warriors dating back 2,000-plus years.
Stretchable silicon could be next wave in electronics
The next wave in electronics could be wavy electronics.
Researchers at the University of Illinois at Urbana-Champaign have developed a fully stretchable form of single-crystal silicon with micron-sized, wave-like geometries that can be used to build high-performance electronic devices on rubber substrates.
Japanese researchers eye 'e-skin' for robots
Japanese researchers say they have developed a rubber that is able to conduct electricity well, paving the way for robots with stretchable "e-skin" that can feel heat and pressure like humans.

News discussion:

Nanotechnology news