Ryan Haines / Android Authority
Folding screens have become a common sight in recent years, thanks in large part to Samsung’s two lines of foldable phones, the Z Flip and Z Fold. As other manufacturers join in, prices for foldable devices are rapidly going down, promising a new era of personal computing. But how does the folding screen actually work?
Whether you’ve always been curious about how folding screens work or haven’t considered it yet, we’ll give you a crash course in foldable displays and the great technology that makes them possible.
Read also: Display specifications and terms explained: resolution, contrast, color gamut, and more
Folding Screen: The Basics
All displays – rigid or flexible, flat or curved, rollable or folding – work in roughly the same way.
Simply put, millions of color spots combine to form the images that appear on the screen. There are various ways to achieve this, resulting in various displays including LCD, OLED, and more recently, Micro-LED and Mini-LED.
All those spots of color sit on a layer of material called the substrate. For many years, the substrate has been a thin sheet of glass—hard, fragile glass you can only flex so much before it breaks.
Then in the past decade, display manufacturers produced display substrates made of flexible plastics that can bend without breaking. The plastic-based display made it possible to manufacture the first phones with a curved display, like the 2014 Galaxy Note Edge.
The flexible substrate is only part of the equation. Scientists and engineers had to solve some ridiculously difficult problems.
As technology advanced, display manufacturers figured out ways to increase the amount of flex they could safely build into a screen. Importantly, they also solved the durability problem, allowing the screen to bend thousands of times without breaking. Eventually, this path led us to today’s folding screens, which can fold almost like a sheet of paper.
Manufacturers have been teasing folding screens for over a decade, but the first foldable phone only surfaced in 2019. There’s a reason why folding screens take so long to mature – or more accurately, there are a number of reasons.
The flexible substrate is only part of the equation. Scientists and engineers had to solve ridiculously difficult problems such as those that are lightweight and flexible but can withstand years of mechanical stress; ensuring that all bending and folding does not affect image quality over time; Creating an even flexible protective layer for the screen; And making sure all the other technology that goes into the display is still working. When all this was done, other smart people had to devise ways to incorporate flexible displays into folding phones while maintaining the high standards expected of their electronics. Really difficult job.
A closer look at how the folding screen works
Before we look at the individual components of a foldable screen, it’s important to note that most of the folding screens you see on the market today are of the OLED variety. OLED screens do not have a backlight like LCDs – instead, the pixels themselves emit light when power is applied to them. Because of this OLED can be made about 30% thinner and lighter than LCD. Coupled with other advantages over LCD, OLED is the first choice for flexible screens, but flexible LCD displays do exist.
To understand how a foldable OLED display works, it’s helpful to view the display as a very thin (and probably not very tasty) layer cake. Each layer of this hi-tech cake has a specific role. These layers are then laminated together into a very thin package that is fractions of a millimeter thick. Let’s go through them.
- substrate layer — Also called the board, it is the very basis of the screen, which supports all the other layers. On flexible displays, the substrate is made of plastic or, less commonly, metal. Most flexible screen devices today use a substrate made of a polymer plastic called polyimide (PI). In addition to being flexible and insulating, polyimide has high mechanical strength and thermal stability.
- TFT layer – Applied on top of the flexible substrate, the TFT (thin-film transistor) layer controls the power delivery to each pixel. Think of it as the “power grid” that connects all the pixels on the display. On OLED screens, unlike LCDs, each pixel can be controlled individually, leading to higher contrast rates and lower power consumption.
- OLED layer — The light-emitting layer is made up of individual pixels, each of which has red, green, and blue sub-pixels. Each pixel can affect a certain color and brightness by changing the amount of power its sub-pixel receives. In turn, the pixels combine to form the image that we see on the display. The OLED layer is made up of several sub-layers, including a cathode, an anode, and a layer of organic light-emitting material sandwiched between them.
- cover layer — Also called the encapsulation layer, it is the layer that seals and protects the other layers. It is also the layer that users touch when interacting with the folding screen. In terms of materials, the cheaper option is polyimide (similar to substrate), whereas recently, we have seen manufacturers adopt ultra-thin glass (UTG). The UTG is harder than plastic and feels like regular glass, while still being able to bend. UTG is what Samsung is using on the latest Z Flip and Z Fold.
What else should I know about how folding screens work?
Folding screens can be of in-folding or out-folding type. On an in-folding display (for example, the Galaxy Z Flip 3), the display is hidden inside the device when folded, which helps with durability, but it does create a slight crease on the screen. On an out-folding display (like the Huawei Mate XS 2), the display tilts to the outside of the device when folded. This leaves it exposed to scratches, but it does provide a crease-free aspect.
Read also: The best foldable phones you can get
Folding screen devices we’ve seen so far have only one fold, but manufacturers have shown concepts of devices that fold up twice or even more. Here are some Samsung designs that fold up twice in an “S” or “G” configuration.
Not all flexible display devices fold up. We have seen devices with rollable displays that roll up and disappear inside the body of the device. Examples include the OPPO X2021 rollable phone or LG’s Crazy OLED R rollable TV.
The display is an important aspect of how the folding screen works, but it’s not the only one. The hinge can be just as important to the user experience. Manufacturers put a lot of resources into making sure that the hinges in their foldable products work smoothly and consistently, have the right amount of “snap” and provide a smooth surface for displays to sit on.
Another important factor is durability. By definition, foldable screens have moving parts, which opens up the possibility of water, dust, and other contaminants entering the device. In fact, we have noticed debris accumulation under the screen on some devices, which ruins the user experience and can damage the screen.
Read also: What is screen burn and how can you prevent it?
Several manufacturers have already released or at least teased foldable screen products, including phones, laptops and even TVs. It’s easy to imagine a future where tablets, wearables, gaming consoles and even home appliances feature tilted screens. Innovation will come from stretchable, wearable and even skin-embedded displays. Meanwhile, as more resources are invested in the technology, the folding screen will only get better.
notes
