Flexible, conformable, rollable, foldable and shapeable displays explained
April 04, 2018
Last year I spoke at a panel session about flexible displays. One of the topics of discussion was the range of terminology used to describe “flexible displays”. In reality, when referring to flexible displays people use different terms which mean slightly different things. While there is no standard definition for each of these terms, this article explains their most common uses.
This term is used in a variety of ways: for some, it means displays that are able to be flexed during use, for others it means displays that are flexed in the product housing such as a curved glass TV. In our view “flexible displays” are most commonly described as displays manufactured on plastic substrates – meaning that at some point during the manufacturing process the display was flexible, even if it is finally laminated onto a rigid cover glass before being integrated into the product housing.
These displays are flexible during production and can be conformed to or wrapped around surfaces. Conformable displays are needed in many applications such as automotive interiors, home appliances and in-store digital signage due to the existing curved surfaces of the products. These displays offer a degree of design freedom that is not possible with flat glass-based displays. One example of a conformable display is FlexEnable’s organic LCD (OLCD) on plastic, which can be wrapped around surfaces with a bend radius down to 10mm.
This term probably seems less ambiguous than the others – generally used to describe a display that can be tightly bended on 180° on top of itself. The question is: around what bend radius and angle must the display be bended to be considered “foldable”? It’s likely that the first foldable displays will have a large bend radius (3-5mm or so). For most people a foldable display is as thin as paper demanding a much smaller sub-millimetre bend radius. In order to reach such small bend radius organic transistors will be needed to avoid the crackable ceramic layers that they replace. There are several exciting concepts around today (for example the foldable phone by Samsung), but there aren’t any real foldable displays on the market yet.
Whilst this term is fairly clear, the requirements for bending the display are likely to vary significantly with application. For example, a 55” rollable TV might require the display to be rollable to a 20mm radius of curvature, whereas a smartphone with a pull-out display might require a 2mm radius. FlexEnable has demonstrated that by using organic transistors flexible OLED displays can be made rollable. Recently, LG showed a 65-inch OLED display prototype that could be rolled like a newspaper.
This is often used to refer not to the flexibility, but to the ability to design and cut displays into unusual (non-rectangular) shapes, whether or not they are then subsequently conformed, folded or rolled. The ability to design displays (electrically) with unusual shapes is partly determined by the performance of the thin-film transistors (TFTs) that drive them. For example, if the TFT mobility is high enough to use it for the gate driver, then this opens up many more design options. From a manufacturing perspective, it is the "cuttability" of the plastic displays that make them suitable for shaped displays. Plastic can easily be cut to unusual shapes using a laser, or a blade, both of which are much more difficult to do on glass displays. Read our blog that explains why OLCD is the only plastic display technology that enables low cost, large area and shapeable displays today.
Present and future
Each of the above terms describes different display properties and achieving them comes with different challenges. The good news is that thanks to constant innovation and investment a lot of progress has been made to bring new display technologies to the market. Phones featuring curved AMOLED displays are already on the market, while conformable and shapeable plastic OLCDs are currently being transferred into mass production by FlexEnable and its licensee Truly Semiconductors.
Not all applications will require all display properties described in this article. For example, automotive displays need to be conformable and shapeable, but not really foldable, whereas a foldable tablet or phone could change the user experience and utility of mobile devices. Flexibility in displays really is going to change how we think about displays and information in almost all aspects of our lives.