04-09 elastic strain map

[Image above] An example of a new “map” that plots the stability regions of a crystal as a function of elastic strain. Credit: Shi et al., PNAS (CC BY-NC-ND 4.0)

Semiconductors, the materials at the heart of modern electronics, are a massive industry that is expected to grow even larger over the next decade, reaching a projected market value of $1 trillion by 2030. Yet even as demand for these materials expands, the semiconductor industry has reached its limit in terms of processing power with current design paradigms.

If manufacturers are to meet the demand for semiconductors and improved computing performance, new materials and system structures must be identified and implemented. Elastic strain engineering (ESE) may help address this need.

In contrast to doping, which tunes a semiconductor’s properties by adding trace amounts of other elements into the material, ESE tunes a material’s properties solely through the introduction of controlled mechanical strain. This method can be an easier way to tune the properties of wide-bandgap semiconductors, such as diamond, which are difficult to dope.

Researchers first discovered the benefits of ESE to the semiconductor industry in the 1980s, when the performance of silicon-based heterostructures was doubled by applying just 1% elastic strain to the material. Manufacturers now regularly use small amounts of strain to increase the performance of their microchips.

In 2018, researchers led by Nanyang Technological University in Singapore and Massachusetts Institute of Technology in the U.S. showed that 1% strain was just the tip of the iceberg when they successfully deformed diamond nanoneedles with elastic strains of up to 9%. Since then, they published numerous papers in collaboration with other groups exploring the limits of ESE, such as this paper covered in a July 2021 CTT.

In February 2024, the researchers published their latest paper on the topic. In contrast to previous studies, which focused on answering specific open questions in the field, the new open-access paper took that knowledge and created a general “map” showing how to tune crystalline materials to produce specific thermal and electronic properties.

The map, which was created using a combination of first principles calculations and machine learning, plots the stability regions of a crystal in six-dimensional strain space. Looking at the map reveals the conditions under which a material can exist in a particular phase and when it might fail or transition to another phase.

The researchers used diamond to demonstrate the map’s potential for guiding ESE of crystalline materials. They determined that it should be possible to either increase or reduce the lattice thermal conductivity of diamond by more than 100% or by more than 95%, respectively, purely by reversible elastic strain.

In an MIT press release, senior author Ju Li, Battelle Energy Alliance Professor in Nuclear Engineering at MIT, says that “Experimentally, these properties are already accessible with nanoneedles and even microbridges.”

Achieving these results in industry, however, would require modified manufacturing processes and device designs to accommodate the increased strain. But “I think it’s definitely a great start,” says first author Zhe Shi, a postdoc in Li’s lab, in the press release. “It’s an exciting beginning to what could lead to significant strides in technology.”

The open-access paper, published in Proceedings of the National Academy of Sciences, is “Phonon stability boundary and deep elastic strain engineering of lattice thermal conductivity” (DOI: 10.1073/pnas.2313840121).