Wednesday, November 30, 2022

Flexible screens – how is it possible


Flexible screens have long belonged to that special kind of innovation that has existed for many years in the form of concepts, but still does not materialize in serial models. And now it happened – the first “bent” smartphones from Samsung and Huawei went on sale. So, it’s time to figure out how the flexible display technology was implemented, what problems the developers pursued, and what chips they managed to offer.

Who needs it

  1. First of all, designers and marketers considered flexible screens as an opportunity to create devices that can be laid out. The idea is to have a compact device that fits in your pocket, but if necessary, transform it into a device with twice the screen size. Just imagine: with a flick of the wrist, a smartphone turns… a smartphone turns… a smartphone turns into an elegant tablet !

However, nothing funny. They all succeeded!

  1. Another possible plus is the creation of large multimedia devices with a roll-up screen that could be rolled up and unwound, which would save space and at the same time not “spoil” a modern interior. This already exists and is being sold – roll-up TVs are produced by LG .
  2. It is obvious that the non-linear shape of the screen can be useful in the production of some kind of “encircling” products, such as bracelets, straps for wearing in the form of a smart watch on the wrist. Or for installing the display in some curvilinear structures, for example, in a car dashboard.
  3. As a plus, a flexible device (as if by default) is provided with an increased impact resistance of the display. Obviously, a soft screen should not shatter when dropped, nor should it break/crack in a jeans pocket.
  4. If glass is not used in a flexible screen (and it cannot be there in any way due to the known rigidity of this material), then in general the device should become significantly thinner, and also noticeably lose weight. And, theoretically, for the same reason, the cost of a flexible display should be lower.

Problems in the manufacture of flexible screens
As usual, there should always be a couple of fly in the ointment in a barrel of honey. The list of problems to be solved turned out to be not so small.

  1. Let’s say the screen itself was made flexible, and by itself it can work quietly, for example, as a photo frame. But what about complex devices in which it covers the entire area of ​​the case (smartphones, tablets)? After all, it is impossible to bend the camera module, speaker or chip with a processor and memory. And yet they have not yet come up with flexible batteries, but they are quite large.
  2. The flexible screen will not contain glass, which performs a protective and, so to speak, shaping/bearing function for placing thin-film transistors. Instead, you need to use a film for external protection and a flexible polymer substrate as a base. A number of questions immediately arise: how reliably will the film protect the matrix from mechanical damage, how quickly after repeated bends and fractures will it get damaged and lose its tightness, will it be possible to apply a practical oleophobic coating on it, and how long will it last?
  3. Of course, the actual problem for flexible matrices is the problem of reducing the permissible bending radius, as well as increasing the number of cycles until the so-called “artifacts” appear. The fact is that the usual relatively elastic OLED-matrix, even with one normal inflection, receives damage to the conductive layers and fails.
  4. It also proved to be very difficult to make sure that the area of ​​the screen, which constantly bends, fully retains its touch control capabilities.
  5. If a gadget with a flexible screen will have a clamshell form factor, then how to achieve the durability of mechanical parts (hinges, hinges, cables) in the fracture zone? In parallel with this, it is necessary to somehow implement a reliable mechanism for fixing the device in the unfolded and folded state.
  6. Folding smartphones made using this technology will have a screen with about twice the area. And this means that the device will consume more energy – you will have to fight for increased autonomy.

Formation of technology
Fantasists have dreamed of flexible screens for a long time. Technologists have been working on their development for decades, but constantly rested on the need to use glass. The first more or less functional flexible devices were made using E-Ink technology. The e-paper is remarkable in that inside the silicone sheet in dark oil capsules are negatively charged light particles. Depending on whether voltage is applied to a particular pixel capsule, the user will see it either white or black – and this is how a characteristic black-and-white text / image appears.

At first, readers were made on “electronic ink” using glass substrates, then they learned to use plastic as a substrate, which made it possible to create screens in the form of a flexible polymer sheet. Then there were various devices with curved screens, such as bracelets. However, electronic paper could not compete with conventional displays – first of all, because of the unacceptably long screen refresh time, which makes it impossible to fully interactively use E-Ink devices.

The next step on the road to triumph is the development of screens with OLED (organic light-emitting diode), AMOLED, PMOLED technology. Two features of OLED displays became key:

The multilayer thin film structure can be assembled using flexible polymers instead of glass.
Each LED is illuminated separately, so they can work normally on a curved matrix.

First, in 2011, the then still showing signs of life, Nokia showed its prototype of the elastic Kinetic smartphone. He could not only bend and twist, but also controlled through various “body movements”.

In 2013, Samsung made its first big statement when it introduced the flexible YOUM display. It became the prototype of the “proprietary” technology FAMOLED (Flexible Active Matrix Organic Light Emitting Diode – a flexible active matrix of organic light emitting diodes), which was applied in 2019 in the Galaxy Fold smartphone .

Then the developers of the South Korean concern made a spectacular soft photo frame. But with a promising smartphone, such a sensation did not happen. The maximum that could be created at that time was to form (and then “glaze”) a curved edge of the screen from a flexible OLED matrix, which went to the side edge of the smartphone. It turned out beautifully, plus, besides, text messages were displayed on this sidewall of the screen – they could be read without even opening the smartphone in a book case.

Then there was relative silence for several years. It was possible to create flexible screens, but to make a fully flexible smartphone – here the designers ran into the inexorable laws of physics. But the market requires constant movement, so something new still had to see the light.

  1. Foldable smartphones from Huawei and Samsung
    So, sales of the long-awaited Samsung Galaxy Fold and Huawei Mate X models have started. What can we say about them? Pioneers! “To touch the future”, “a new chapter in the history of mobile technologies”, “to discover the incredible” – all this, of course, is there.

In fact, we have devices that can be used both as smartphones and as tablets. The Galaxy Fold has a 7.3-inch AMOLED screen when unfolded, while the Mate X has an 8-inch display. By the way, manufacturers warn that in the middle of the flexible screen, traces of folding the device can be seen – this is normal for him.

Both devices can hardly be called fully flexible – they are precisely foldable, that is, they consist of two halves, united by hinged loops with a locking mechanism. The engineers worked on the bugs – after the first unsuccessful tests, the design of the connecting module was improved and now we are promised up to 200,000 smooth closing and opening.

The folded out screens are almost square in shape and are well suited for working in multiple windows with multiple applications. Applications easily and quickly transform into a smaller screen when you close the device.

The battery in both devices is implemented double (one battery is located in each half of the “book”), the total capacity is 4380 for the Galaxy Fold and 4500 mAh for the Mate X. As a result, the devices provide up to 13 hours of Internet browsing (via Wi-Fi or LTE ) and up to 20 hours of video playback. Naturally, they have fast charging and a number of smart energy saving systems.

As for performance, cameras, communications, design – here, as they say, full stuffing. Most of the shortcomings that were identified in the raw test specimens, the engineers seem to have corrected. Although it will be possible to draw more or less reasonable conclusions regarding reliability and practicality after some time of using serial models by ordinary users in real field conditions. The price (more than 2,000 dollars) for these flagships is not at all humane yet, but it will definitely drop when the hype passes a little, and the pioneering companies “recapture” the funds spent on development at least a little.


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