Madison (WI) - Research engineers and physicists at the University of Wisconsin-Madison have developed a method to measure how varying degrees of strain affect electronic structures in silicon, which in turn affect performance. The new model reveals just how much performance potential remains in this already strained industry.


Uniformity across the board

Strained silicon in production today is limited primarily by two factors. First, techniques used to create the product don't always produce silicon that's strained equally across its surface. This creates performance gaps and reduces the added efficiency of going strained in the first place. And second, the physics of strain have never been fully mapped out via real-world trials due to variations in manufacturing. Well, until now that is.


Measuring strain

A team of researchers led by Max Lagally, Professor of Materials Science and Engineering, have directly measured the effects of strain on electronic structures in silicon. To do this they needed a high-power, variable wavelength X-ray source. They ultimately chose a device at their on-campus Synchrotron Radiation Center. It operates alongside a monochromator, which allows extremely precise wavelength tuning - a necessity for this type of research.

By measuring how different types of extremely thin film layers of strained silicon react, the research team determined the direction and magnitude of shifts in the conduction bands. This basically means they now understand why strained silicon increases electron motility (which gives it its better performance), and to what degree based on the materials and type of strain used.


Straining samples

To produce the test samples, the team literally stretched out thin films of silicon for deposition. They strained it severely, but uniformly and to a known degree. Lagally describes the process like this, "Imagine [attaching] a ring and a hook to all four corners [of a piece of thin film silicon] and pulling equally on all four corners like a trampoline, it stretches out like that."

By creating strained silicon in this way, they were able to create samples with uniform strain across their surface. Their current work has been published online in the October 10 edition of Physical Review Letters. A print edition will soon be available.


Continued research

The team will continue their research into different types of semiconductor materials. Their hope is to produce a type of catalog showing strain-dependent band structures in all kinds of semiconductor materials with all kinds of strained membranes applied.

This work could ultimately produce semiconductor products (CPUs and telecommunications equipment) which generates less heat, uses less power and switches faster than is currently possible. If products can be created from this research, consumers will definitely see its benefits.