Brittle materials bond for flexible electronics


Rebecca Pool

Tuesday, May 14, 2019 - 15:15
Electron microscope image of the flexible sulphur-selenium dielectric alloy [Ajayan Research Group]
US-based researchers have mixed two brittle materials to make a flexible dielectric that shows promise as a separator in next-generation, flexible electronics.
An electron microscopy image of the sulphur-selenium alloy, created by researchers at Rice University, shows a layered structure without voids. 
Until now, electronics manufacturers have had to choose between brittle dielectrics with a high dielectric constant K or flexible low-K polymers; the latest material offers the best of both worlds.
“We were surprised by this discovery because neither sulphur or selenium have any dielectric properties or have a ductile nature,” says Sandhya Susarla from the Ajayan Research Group and Nanomaterials Laboratory at Rice University. “When we combined them, we started playing with the material and found out that mechanically, it behaved as a compliant polymer.”
To fabricate the alloy, Susarla and colleagues mixed sulphur and selenide powders in a mortar and pestle, and then melted the mixture at 572ºF in an inert argon atmosphere to form a dense semi-crystalline alloy.
Compression tests in a lab press revealed that the alloy recovered 96% of its previous form once the load was removed.
As Susarla explains, the repulsion of dipole moments in the selenium matrix is most responsible for the material’s ability to recover.
“There are some attractive forces in the sulphur and selenium rings that make the material stable, and there are repulsive forces that make the material incompressible,” she says.
“There are a few reports in the early 1900s on the synthesis of these materials and their viscoelastic properties,” she adds. “But since no one was interested in flexible semiconductors back then, their dielectric properties were ignored.”
According to Susarla, the new material is cheap, scalable, lightweight and elastic, and has the electronic properties necessary to be a player in the emerging field of flexible technologies.
What's more, it is stable, abundant and easy to fabricate, and should be simple to adapt for micro- and nanoscale electronics.
“The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device application,” highlights Susarla.
“Since the viscosity of this material is high, forming thin films can be a little difficult,” she adds. “That is the current challenge we are trying to deal with.”
Research is published in Science Advances.
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