Ryan Haines/Android Authority
Folding screens have become commonplace in recent years, thanks in large part to Samsung’s two foldable phone lines, the Z flip other Z-fold. As other manufacturers join in, prices for foldable devices are rapidly falling, promising a new era of personal computing. But how do folding screens actually work?
Whether you’ve always been curious about how foldable screens work or haven’t thought of it yet, we’ll give you a crash course in foldable screens and the cool tech that makes them possible.
Folding screens: the basics
All displays – rigid or flexible, flat or curved, rollable or collapsible – work pretty much the same.
Simply put, millions of colored bacon combine to form the images we see on screen. There are different ways to achieve this, which results in the different displays you see, including LCD, OLEDand, more recently, micro LEDs and mini LEDs.
All of these splashes of color rest on a layer of material called the substrate. For many years, the substrate has been a thin sheet of glass – stiff, fragile glass that you can only bend before it breaks.
Then, over the past decade, display manufacturers produced flexible plastic display substrates that could bend without breaking. Plastic-based screens made possible the creation of the first phones with curved screens, such as the galaxy note edge of 2014.
The flexible substrate is only part of the equation. Scientists and engineers had to solve ridiculously difficult problems.
As technology advanced, display manufacturers found ways to increase the amount of flexibility they could safely build into a display. Above all, they have also solved the problem of durability, allowing the screens to bend thousands of times without breaking. Eventually, that 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 folding phones didn’t come out until 2019. There’s a reason folding screens have taken so long to mature — or more precisely, there are several reasons for this.
The flexible substrate is only part of the equation. Scientists and engineers had to solve ridiculously difficult problems like making substrates that were light and flexible but could withstand years of mechanical stress; ensure that all bends and folds do not affect image quality over time; create an equally flexible protective layer for the screen; and ensuring that all other technology that goes into the display is still working. When all of this was done, other smart people had thought of ways to fit flexible displays into foldable phones while still maintaining the incredibly high standards we expect from our electronic devices. Hard work indeed.
Focus on how folding screens work
Before looking at the individual components of a foldable display, it’s important to note that all of the foldable displays you see on the market today are of the OLED variety. OLED screens don’t have a backlight like LCD screens – instead, the pixels themselves emit light when powered. For this reason, OLEDs can be made approximately 30% thinner and lighter than LCDs. Associated to other advantages over LCDOLED is the first choice for flexible displays, but flexible LCD screens exist.
To understand how foldable OLED displays work, it helps to visualize the display as a very thin (and probably not very tasty) layered cake. Each layer of this high-tech cake has a specific role. These layers are laminated together in a very thin package a few fractions of a millimeter thick. Let’s go through them.
- substrate layer — Also called a board, it is the very base of the screen, which supports all the other layers. On a flexible screen, the substrate is plastic or, more rarely, metal. Most flexible displays 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 layers — Applied to the flexible substrate, the TFT (thin film transistor) layer controls the power delivery to each pixel. Think of it as an “electrical network” that connects all the pixels on the screen. On an OLED display, unlike an LCD display, each pixel can be individually controlled, enabling high contrast ratios and reduced power consumption.
- OLED layers — The light-emitting layer, made up of individual pixels, each comprising red, green and blue sub-pixels. Each pixel can achieve a certain color and brightness by varying the amount of power its sub-pixels receive. In turn, combine the pixels to form the image we see on the screen. The OLED layer is made up of several sub-layers, including a cathode, an anode, and a layer of organic electroluminescent material sandwiched between them.
- cover layers — Also called the encapsulation layer, this is the layer that seals and protects the other layers. It is also the layer that users touch when interacting with folding screens. In terms of materials, the cheapest option is polyimide (same as the substrate), while more recently we’ve seen manufacturers adopt ultra-thin glass (UTG). UTG is stronger than plastic and looks more like regular glass, while still being able to bend. UTG is what Samsung used on the latest Z Flip and Z Fold.
What else should I know about how folding screens work?
Folding screens can be inward or outward folding type. On a flip-out screen (for example, Galaxy ZFlip 3), the screen is hidden inside the device when folded, which helps with durability, but it tends to create a slight crease in the screen. On a fold-out screen (like the Huawei Mate XS 2), the screen folds around the outside of the device when folded. This leaves it exposed to scratches, but it provides a wrinkle-free look.
So read: The best foldable phones you can get
The folding screen devices we’ve seen so far only have one fold, but manufacturers have come up with device concepts that fold twice or even more. Here are some Samsung models that double fold in an “S” or “G” configuration.
Not all flexible screens bend. We’ve seen devices with rollable screens that roll up and disappear inside the body of the device. Examples include the Oppo X 2021 rollable phone or LG is crazy Rollable OLED R TV.
The display is a key aspect of how folding screens work, but it’s not the only one. The hinge can be just as important to the user experience. Manufacturers have invested a lot of resources into making sure the hinges on their foldable products work smoothly and consistently, have the right amount of “click”, and provide a smooth surface for the screen to sit on.
Another key factor is durability. By definition, foldable displays have moving parts, which opens up the possibility of water, dust, and other contaminants entering the device. Indeed, we have seen issues with debris getting lodged under the screen on some devices, which ruins the user experience and can damage the screen.
Many manufacturers have already launched or at least teased foldable screen products, including phones, laptopand even televisions. It’s easy to imagine a future where tablets, wearables, game consoles, and even home appliances have bendable screens. Innovation will also come from screens that are stretchable, wearable and even skin-integrable. In the meantime, as more resources are invested in technology, folding screens will only get better.