Mar. 28, 2008 - Researchers from the US and Singapore say they have developed a form of "stretchable" silicon IC that can wrap around complex and nonuniform shapes, and maintain electrical performance even while stretched, compressed, folded, and other types of mechanical deformations.

The work extends the U. of Illinois/Urbana-Champaign's 2005 creation of a 1D "stretchable" single-crystal silicon with micron-sized wave-like geometries, into 2D constructions with "carefully optimized mechanical layouts and structural configurations," according to John Rogers, prof. of Materials Science and Engineering at the U. of Illinois and leader of the research teams that also included Northwestern U. and Singapore's Institute of High Performance Computing.

"We've gone way beyond just isolated material elements and individual devices to complete, fully integrated circuits in a manner that is applicable to systems with nearly arbitrary levels of complexity," he said, in a statement. "The overall buckling process yields wavy shapes that vary from place to place on the integrated circuit, in a complex but theoretically predictable fashion."

In their work, described online in an advance publication from the journal Science, the researchers applied a sacrificial layer of polymer to a rigid carrier substrate, and then deposited a thin plastic coating on which the IC components were constructed, using conventional planar device fabrication techniques and printing methods for integrating aligned nanoribbon arrays of single-crystal silicon. The sacrificial polymer layer was then washed away, and the plastic coating and IC were bonded to a piece of prestrained silicone rubber. Once strain was relieved the rubber returns to its original shape, applying compressive stresses to the circuit sheet, which generate buckling patterns in a geometry allowing the circuit to be folded, or stretched, in different directions to conform to a variety of shapes and mechanical deformations.

Figure 1. Circuit diagram (top frame) and optical images of a stretchable, "wavy" silicon ring oscillator circuit on a rubber substrate, in the "as fabricated" flat state (top micrograph) and in moderate and high states of biaxial compression (middle, bottom micrographs). (Source: U. of Illinois)

The researchers say they've built ICs incorporating transistors, logic gates, ring oscillators, and differential amplifiers, exhibiting "extreme levels of bendability and stretchability," with electronic properties "comparable to those of similar circuits built on conventional silicon wafers." Potential applications, they say, include devices requiring mechanical deformations during installation/use (and thus not compatible with conventional semiconductor wafers), such as biomedical devices.

Figure 2. Mechanically stretchable, "wavy" silicon integrated circuit on a rubber substrate. (Source: U. of Illinois)