Making Flexible Screens That Won’t Crack

Researchers have developed transparent and flexible displays for electronic devices by controlling the distance and interaction between organic polymer chains.

AsianScientist (Feb. 4, 2019) – A research group in South Korea has developed an organic polymer that expands minimally when heated, paving the way for the next generation of flexible and transparent displays. They reported their findings in the journal Science Advances.

Most objects expand upon heating and shrink when cooled, a property that is measured by the coefficient of thermal expansion (CTE). Organic polymers have a relatively large CTE compared to ceramics or metals. However, thin, lightweight and planar substrates of semiconductor devices should have a low CTE comparable to prevent cracking due to the stress from thermal expansion and contraction. Therefore, matching the CTE of the semiconductor device and the substrate is crucial for successfully manufacturing display devices.

In this study, scientists led by Professor Kim Sang Youl of the Korea Advanced Institute of Science and Technology sought to control the CTE of organic polymers by varying the distance and interaction of polymer chains used. They demonstrated that the thermal expansion and contraction of polymer films can be minimized by introducing interaction forces between the polymer chains and by arranging the direction of the force perpendicularly.

The team successfully implemented this approach by modifying the chemical structure of a transparent polymeric material, poly (amide-imide) film. They showed that their film is transparent, flexible and thermally stable enough to be used in the active-matrix organic light-emitting diode fabrication process.

When the researchers developed indium gallium zinc oxide thin film transistor devices based on the newly synthesized transparent poly(amide-imide) film, they confirmed that their device could operate normally even when it was folded down to a radius of one millimeter.

“Our results suggest a way of controlling the thermal expansion of amorphous polymers similar to a level of glass without chemical cross-linking, which has long been regarded as a challenging problem. At the same time, we succeeded in making the polymer transparent and flexible. We expect that it can be applied to controlling the thermal expansion of various organic materials,” said Kim.

The article can be found at: Kim et al. (2018) Poly(amide-imide) Materials for Transparent and Flexible Displays.


Source: Korea Advanced Institute of Science and Technology; Photo: Shutterstock.
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