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The Challenge and Progress of “Foldable AMOLED Display”

Learn more about foldable OLEDs

The Foldable AMOLED Display can signify the original momentous application designed for displays with great flexibility. But to make this technology a reality, manufacturers should first overcome the challenges like fatigue and high stress within the foldable part. The authors from ITRI or Taiwan’s Industrial Technology Research Institute have made a proposal of several approaches to overcome the challenges. They also describe the demonstrated modules for AMOLED with 5mm folding radius.
When the cathode-ray tubes were introduced, they altered the display of information by allowing dynamic content. This became the initial wave of the upheaval of displays. Apparently, “thin-film-transistor liquid-crystal displays” have marked the start of the next wave of the upheaval. They allowed the recognition of PCs and mobile devices.

Even though the TFT-LCD became an ultimate achievement for mobile devices, the existing LCD for glass substrate is smaller for most applications. Bigger screens of tablets boost the fragility and weight of gadgets that are not portable. Consumer product manufacturers have tried to resolving these issues through increased display size and reduced tablet weight.
But, none of these methods are ideal. Up to date, consumers carry or own phones and tablets at the same time. The challenge is to produce seamless info synch among devices.

Form Factors Flexibility

Because of the limitations of existing mobile devices, it is necessary to change the basic display form factor. The concept has been proposed some years ago for flexible displays with plastic LCDs which are short-lived. For instance, in 1998, Sharp made its announcement for its product with “twisted-nematic liquid-crystal display” according to plastic instead of glass substrate.
The intention of the proposal is to generate lighter yet harder to break panels. But, some technical issues have seemed to obstruct the realization of the project. Some of the issues are the cell gap control difficulty, image quality that is poor for plastic substrate as well as the inferior “thermo mechanical properties” of the plastic in relation to glass.
Recently, both major obstacles for the making of flexible displays are represented by inadequate suitability of flexible substrate as well as the challenge in producing flexible displays through current TFT equipment and processes. At ITRI, it started addressing two major issues ten years ago. The outcome was “Flexible Universal Plane” tech, developed and proposed in ITRI Display Center which received R&D 100 Award and Innovation Gold Award by Wall Street Journal in year 2010.
And the best way to provide the third wave display upheaval, FlexUp Technologies Corp., a new company was obtained from 2014 DTC in order to give a flexible substrate solution to non-display and display industries like solar panels, touch sensors, digital radiography and OLED lighting.
Advantages of the AMOLED Display
AMOLED Display, in comparison to the TFT-LCD, is more striking when it comes on flexible substrates. Due to the self-emissive property, there is no longer a need to use a light guide plate, backlight or brightness enhancement film to allow display which is simpler to flex, bend, or fold. This is better with simple structure while providing high-video rate, low-power consumption and wide-color gamut.
Huge display companies like LG and Samsung have disclosed and adopted the flexible AMOLED display formally in their business tech as well as product roadmaps during the yearly SID Symposium. Japan’s “Semiconductor Energy Laboratory Co” has also presented curved and tri-fold flexible displays with high resolution during the Display Innovation 2014 and Display Week 2014 Symposium held in Japan.
The “tri-fold AMOLED display” is believed to better show an ultimate app for flexible display. There are actually some application modes with regard to tri-fold gadgets. Carry mode for device fold and close that can simply be placed in pockets or purse. This mode helps prevent scratches from the display screen. The smartphone is utilized in receiving or making calls.
The design helps to provide a handy or even a foldable device without hassle to data synchronization. The flexible display weighs lesser than glass based material due to plastic film as substrate. ITRI strongly believes that such apps can be realized through folding radius of 5mm or even lesser.
Mechanics for Folding
There are numerical inputs like the layer structure, mechanical strength and layer thickness in order to measure stress distribution. The materials utilized are the usual OLED chemicals and some common materials like SiN and SiO2. According to the recommended real life terms, the foldable displays should survive one hundred thousand fold-unfold cycles with no breakage or degradation signs.
Substrate Technology
A robust and highly reliable TFT backplane tech is vital since OLED displays need limited amount of “electrical current” for the achievement of needed gray-scale lighting. This gives higher demand on switching device performance as compared to typical LCD panels that generally need storage and loading o “predetermined voltage level”. Any difference in TFT performance among display elements via panel may result to the same visible deficiencies for image display.
Designing a flexible “AMOLED display” needs using high-temperature methods and highly accurate control for flexible substrate by the time of fabrication process. This is completed though the utilization of unique FlexUp method of flexible substrate coating with glass carrier through feeble intermediate bonding agent layer without tough edge bond.
Right after the process of fabrication, the next and ultimate step is detaching the flexible AMOLED panel without any smash up on the display.
Demonstration of AMOLED Display
DTC effectively demonstrated some “foldable AMOLED Display” types of modules during the “Touch Taiwan 2014 Exhibition”. The items include folding radii of 7.5 and 5 mm with various folding modes such as the display bent outward, inward and even with a tri-fold mode. After so many years of improvement, this “foldable AMOLED Display” is characterized as an excellent app when it comes to flexible displays on the market.
The new “form factor injects” are essential for the design in mobile and other wearable display items. The challenges must embody greater opportunities for innovative engineers and scientists.

Schematic of a flexible OLED Display





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