The expert explains why stretchable displays are more difficult to manufacture than flexible and foldable

The expert explains why stretchable displays are more difficult to manufacture than flexible and foldable

Stretch display manufacturing will be fundamentally different from flexible and foldable display manufacturing, and therefore will be much more difficult to implement. Professor Moon Dae-gyu from South Korea’s Sunchunhyan University spoke about this at a seminar on innovative methods of production and use of materials for displays.

Displays that have the ability to stretch without distorting the image displayed on them are considered by experts as an improved technology compared to flexible and roll-up displays. However, if flexible and folding displays are only pressed along one axis when folding and folding, then the stretched displays will be pressured along three axes X, Y and Z at once. shrink back to its original shape. The load on the display in this case will be proportional to how long the stretching or tension of the material will take place, and also inversely proportional to the radius of curvature of the display. That is, the smaller the radius of curvature, the stronger the load on the display structure will be. Conventional curved displays have a radius of curvature of 200 to 300 R. Large roll-up displays are 50 R and small roll-up and flexible displays are 1.4 to 5 R.

Stretching the display will cause cracks and creases in the screen. In order to create a reliable, flexible, durable and easy-to-use stretchable display, the professor said, it is necessary to simultaneously address issues associated with the development of new types of substrates, drivers and pixels.

Ceramic materials are used to produce thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs), which will be required to create stretchable displays. The latter, in turn, are solid materials, and therefore, even with a tension coefficient of 1 to 2%, they will crack and break. Microscopic LEDs (MicroLEDs) and quantum dot nanorods may be more suitable candidate materials. Currently, for the production of flexible and rollable displays, a flexible substrate with organic LEDs applied to it is used.

Ceramic materials cannot be stretched. Therefore, display substrates will need to use a different material with this property. After that, TFT and OLED layers will be added to such substrates, as well as electrical circuits, which should also have elasticity.

According to Professor Moon Te-gyu, several companies are already developing stretch display technologies. For example, Samsung Display unveiled a prototype screen at SID 2019 that used low-temperature polycrystalline silicon thin-film transistors and OLEDs. The display was mounted on a hinge and could stretch 5% up to 10,000 times. At last year’s SID, BOE showed off a very early prototype Kirigami display with a pixel density of 100 ppi and very poor color reproduction that goes into green tones. And in June of that year, LG Display was selected by the South Korean Ministry of Commerce, Industry and Energy (MOTIE) as the lead company for a national stretch display project. The main objective of the project is to create products with stretchable displays with an elongation factor of 20% by 2024.

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