Samsung Researchers Prove the Viability of Commercialized ‘Stretchable’ Devices – Samsung Global Newsroom
With flexible displays established behind us, many have wondered what the next big thing in display technology will be.
Recently, freeform displays1 have gained prominence as the next generation technology that enables high resolution images and portability at the same time. While the technology is still in its infancy, extensive research has been carried out on stretchable displays (a core technology for freeform displays) that, like rubber bands, can be stretched in any direction to change shape.
Stretchable display and sensor openings
On June 4, researchers at the Samsung Advanced Institute of Technology (SAIT), Samsung's research and development center for innovative future technologies, published research results2 in the world-renowned journal "Science Advances" on a technology that overcomes the limits of stretchable devices.
Through this study, stable performance was achieved in a stretchable device with high elongation. This research was also the first in the industry to demonstrate the commercialization potential of stretchable devices as the technology can be integrated into existing semiconductor processes.
The SAIT research team was able to integrate a stretchable organic LED display (OLED) and a photoplethysmography sensor (PPG) into a single device to measure and display the user's heart rate in real time, creating the form factor "stretchable electronic skin" . The success of this test case proves that the technology can be extended to other applications. It is expected that this research will increase the acceptance of stretchable devices in the future.
▲ The SAIT research team demonstrating tensile device viability: Jong Won Chung, SAIT Organic Material Lab lead researcher (co-first author), lead researcher Youngjun Yun (corresponding author), and research team member Yeongjun Lee (co-first author)
OLED skin display that can be stretched up to 30%
One of the greatest achievements of this research was that the team was able to modify the composition and structure of "elastomer," a polymer compound with excellent elasticity and resilience, and use existing semiconductor manufacturing processes to apply it to the substrates of stretchable OLEDs. Applying displays and optical blood flow sensors for the first time in the industry. The team was then able to confirm that the sensor and display continued to function normally and showed no performance degradation when stretched up to 30%.
▲ SAIT Proto System
To put their research to the test, the SAIT researchers attached stretchable PPG heart rate sensors and OLED display systems to the inner wrist near the radial artery.3 This enabled them to confirm with the solution that wrist movement did not cause any deterioration in properties remain reliable with a skin stretch of up to 30%. This test also confirmed that the sensor and the OLED display worked stably even after 1,000 stretches. In addition, it was found that when measuring signals from a moving wrist, the sensor picks up a heartbeat signal that is 2.4 times stronger than a stationary silicon sensor.
“The strength of this technology is that you can measure your biometric data over a longer period of time without having to remove the solution while sleeping or exercising, as the patch feels like part of your skin. You can also check your biometric data immediately on the screen without having to transfer it to an external device, ”explains study leader Youngjun Yun, the corresponding author of the paper. "The technology can also be extended to use in wearable health products for adults, children and infants, as well as patients with certain diseases."
▲ Youngjun Yun, lead researcher and corresponding author
Overcoming technical challenges Wit stretchable materials and structure
Implementing stretchable display technology is proving difficult because the device usually either breaks or degrades when a display is stretched or its shape is tampered with. To overcome this problem, all materials and elements including the substrate, the electrode, the thin film transistor, the emissive material layer and the sensor must have physical ductility and the ability to maintain their electrical properties.
The SAIT researchers replaced the plastic material used in existing stretchable displays with elastomers. The system developed by the SAIT team is the first in the industry to implement a display and sensor using photolithographic processes that enable microstructuring and large-area processing.
Elastomer is an advanced material with high elasticity and resilience, but its heat sensitivity means that it can only be used to a limited extent in existing semiconductor processes. To mitigate this, the team increased the material's heat resistance by tailoring its molecular composition. They have also chemically integrated certain chains of molecules to create resistance to the materials used in semiconductor processes.
"We used an 'island' structure to reduce the stress4 caused by stretching," said research fellow Yeongjun Lee, co-first author of the paper. “In the area of the elastomer, which has a relatively low coefficient of elasticity5 and is therefore more likely to deform, more stress was induced. This has allowed us to minimize the stress on the OLED pixel area, which is more prone to such pressure. We applied a stretchable electrode material (cracked metal) that resists deformation of the elastomer area. This allowed the spaces and wiring electrodes between the pixels to expand and shrink without the OLED pixels themselves deforming. "
▲ OLED and cracked metal electrodes in an island structure
▲ Yeongjun Lee, research fellow and co-first author
Commercialization and Advanced Applications
The stretchable sensor was designed in such a way that it enables continuous heartbeat measurements with high sensitivity compared to existing permanently installed portable sensors. The solution accomplishes this by facilitating tight adhesion to the skin, thereby minimizing performance irregularities that can be caused by movement
The stretchable sensor and OLED display developed by the SAIT team were created by overcoming the limitations of existing device performance and operational processes, including those of current stretchable materials. The work of the SAIT team is particularly significant in that it has ensured the chemical and heat resistance of the elastomeric material, making the commercialization of stretchy, high resolution devices and large screens more likely in the future.
"Our research is still in the early stages, but our goal is to realize and commercialize stretchable devices by increasing system resolution, stretchability and measurement accuracy to a level that enables mass production," said Research Director Jong Won Chung, Co- First author of the paper. "In addition to the heartbeat sensor used in this test case, we plan to incorporate stretchable sensors and high-resolution freeform displays so users can monitor things like peripheral oxygen saturation, electromyogram readings, and blood pressure."
▲ Jong Won Chung, lead researcher and co-first author
1 Displays with significantly smaller pixels that allow more freedom in defining their shapes
2 Title of the article: "Standalone real-time health monitoring patch based on a stretchable organic optoelectronic system"
3 The superficial artery in the forearm, usually used to measure heart rate
4 The resistance force that is generated in a material when it is compressed, bent, twisted or acted on it by other external forces
5 Rate of elasticity, which indicates the degree to which an object stretches and deforms
6 The motion artifact effect
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