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Figure 1: Transparent conductive materials create the electrodes that control flexible and transparent displays
Flexible display technology can apply to various applications, from smartphones and wearables to automotive displays.
Flexible displays have come a long way since the first curved screens and recent developments have made it possible to create displays that are foldable, rollable and stretchable.
Among the key technical advances is the use of flexible substrates, which have revolutionised display technology, playing a pivotal role in the evolution of flexible displays. Advances in materials science have been instrumental in this development, transforming how electronic components are integrated into displays.
A hallmark of these substrates is their extraordinary thinness and pliability, making them invaluable as the foundation for electronic elements. They are typically manufactured from materials such as plastic or metal foil. They provide essential underpinning for the fabrication of displays with unparalleled resilience. Their inherent flexibility allows displays to be curved and rolled up while maintaining structural integrity.
Creating these substrates required technical prowess and a profound understanding of material properties. Engineers and scientists have explored the intricate mechanics of plastics and metal foils, harnessing their attributes to create substrates that could withstand the strains of bending and rolling.
The synergy between materials science and engineering ingenuity has produced substrates that can gracefully accommodate the dynamic requirements of flexible displays.
Beyond their physical durability, these substrates have also paved the way for a new realm of design possibilities. The disappearance of rigid constraints means designers and manufacturers are free to create new plans, for example, for displays that can be curved, rolled, or sewn into clothing.
This has led to a wide range of potential new applications in areas such as wearable devices, smartphones and smart packaging.
The adaptable nature of these substrates is opening up new possibilities for creativity and innovation in the display industry. By enabling the creation of displays that can be moulded to any shape for use in a variety of applications, they are helping to drive the development of innovative display technologies
Transparent conductive materials
Another important development has been the creation of transparent conductive materials, such as graphene. These are used in the electrodes that control the display and allow for the creation of flexible and transparent displays that can be used in applications ranging from smartphones to public information displays.
For example, Chasm Advanced Materials, a US developer and manufacturer of printed electronics and battery materials, partnered with In2tec to accelerate the commercialisation of new transparent conductive materials. Chasm offers a range of carbon nanotube (CNT) hybrid transparent conductive films used in many industries, including printed electronics and PCB manufacturing.
Improved manufacturing techniques
Improved manufacturing techniques have also played a role in developing flexible displays.
One of the most important is roll‑to‑roll processing, which allows for the mass production of flexible displays. This involves printing electronic components onto a flexible substrate, which is then rolled up to create, for instance, a scroll.
These techniques make it possible to create large quantities of flexible displays quickly and efficiently.
Stretchable OLEDs
A remarkable breakthrough from the University of Chicago’s Pritzker School of Molecular Engineering has resulted in a flexible OLED-based light array. Developed by a team led by assistant professor Sihong Wang and professor Juan de Pablo, this OLED can stretch to more than twice its original length without compromising its luminosity and image clarity. This innovation, showcased in Nature Materials, holds transformative potential for wearable electronics, health sensors and foldable screens.
Traditional OLEDs possess rigid structures due to their tight chemical bonds, rendering them non-stretchable. The challenge was to retain OLED electroluminescence while introducing stretchable polymers.
The team achieved this by using long polymers with bendable molecular chains and efficient light-emitting molecular structures. By understanding the behaviour of molecules when bent or pulled, it was possible to engineer new materials to optimise flexibility and luminescence.
Capillary-controlled robotic fins
Drawing inspiration from nature’s colour-changing creatures, such as chameleons and octopuses, engineers at the University of Illinois Urbana‑Champaign have pioneered capillary‑controlled robotic flapping fins. Paired with fluids, these fins create switchable optical and infrared light multi-pixel displays that are 1,000 times more energy efficient than traditional light-emitting devices.
Engineers from the university led a study to demonstrate that bendable fins and fluids can manipulate both colour and brightness. These displays operate on capillary forces, akin to plant water absorption processes. The polymer‑based fins can transition between straight and bent states, influencing fluid‑filled pixels to create various colours and brightness levels. This innovation not only offers unmatched versatility but also remarkable energy efficiency.
Building on the capillary‑controlled robotic fins, a subsequent study published in Nature Communications introduced displays that change shape and colour using fluids and flexible fins. The inspiration for this technology stemmed from nature’s “morphing skin”, which enables animals to blend seamlessly into their surroundings.
Led by professor Sameh Tawfick, the research introduces a new breed of 3D displays that rely on capillary forces to manipulate pixel-containing fluids. By altering the volume and temperature of these fluids, the displays can seamlessly adapt their shape, and colour and even communicate via infrared energy.
Challenges and considerations
Flexible electronics offer a world of possibilities. Applications range from wearable devices and biomedical sensors to flexible displays. However, their development has not been without challenges.
One of the foremost has been designing and manufacturing flexible components. Conventional semiconductor manufacturing relies on rigid silicon wafers, which do not align with flexible applications. Scalability and cost‑effectiveness are essential for commercial production, necessitating the development of new manufacturing processes.
Establishing robust connections between components poses another hurdle. Traditional connections, such as soldering and wire bonding, may not withstand the flexibility demanded by these devices. Innovations such as stretchable conductive inks and flexible circuit boards have emerged to address this, albeit with their own complexities and potential toxicity concerns.
Durability and reliability are paramount, given the mechanical fatigue and degradation that flexible devices may encounter. Finding materials that withstand repeated bending and environmental exposure is essential to ensure sustained performance.
The future of displays
Researchers and engineers are navigating challenges to refine these technologies further. The potential to revolutionise the display industry is undeniable. As these innovations mature, they will undoubtedly reshape how people perceive and interact with electronic devices.
Flexible display technology stands as a testament to human ingenuity and innovation. While its potential is undeniable, it is crucial to approach it with a comprehensive understanding of its challenges.
Electronics engineers working on projects involving flexible displays must be prepared to navigate the intricacies of material science, durability concerns, power efficiency, and user experience. By embracing these challenges and collaborating across disciplines, they can unlock the full potential of flexible displays and reshape the future of electronics.
