Discovery at Stanford may lead to more durable electronic devices

Researchers at Stanford University have discovered that the protective layers in integrated circuit chips, the core components in electronic devices, including personal computers and smartphones, react differently to pushes and pulls of heating and cooling.

The findings, published on Monday in the journal Nature Materials, could lead to more durable electronic devices.

Deep inside electronic devices, layer upon layer of almost unimaginably small transistors and delicate circuitry shuttle electrons back and forth. It is now possible to cram 6 million or more transistors into a single layer of chips.

Designers include layers of glassy materials between the electronics to insulate and protect these delicate components against the continual push and pull of heating and cooling that often causes them to fail.

"It has always been assumed that these dense insulating materials react exactly the same way to being pushed as they do when pulled, as when they expand due to heat," said Reinhold Dauskardt, a professor of materials science and engineering at Stanford. "We found that they are actually stiffer when compressed than when stretched, and we can use this knowledge to design more durable chips and devices."

All electronic devices are in a constant state of flux. Imagine the stress upon a solar cell in the full sun of summer, or the continual calculations of the navigational app on your mobile phone. When active, the devices heat up and the components expand. When not in use, they cool and contract. This tug of war can destroy the device, Dauskardt said.

The materials' response to expansion and contraction is inherently related to the interaction within the network of particular atoms or groups of atoms, known as terminal groups, that do not fully bond during production. In compression, these terminal groups strongly repel each other to make the network stiffer. In tension, their failure to bond causes these very same atoms to interact less, making the materials less stiff and to expand more than expected as they heat up.

"There's no perfect world," Dauskardt said, who worked with doctoral candidate Joseph Burg on the project. "If you could get rid of all of the unbonded terminal groups and create an absolutely flawless material, you would not see these asymmetries, but we can't, so we have to understand and accommodate this knowledge in design."

These asymmetries will have fundamental implications on calibrating computer models used to craft new materials and electronic components. Researchers will now have to integrate these findings in their mathematical algorithms, which currently assume that the stiffness is symmetrical. In the long run, this new knowledge could improve reliability and durability of electronic devices whose delicate circuits are compromised by the continual strains of everyday use.

"This was a very surprising result. It's not something that we would have expected and it has important implications for industry," Dauskardt said, adding that "we're talking about a 250 billion U.S. dollars industry that relies on these materials and which has always assumed that these push-pull properties were symmetrical." Endit