It would be strange and even naive to think that flexible displays came out of nowhere. In fact, development in this direction has been going on for a dozen years, and Samsung showed a conceptual video of what a smartphone with a flexible screen can be back in 2014. Even then, the company thought that it could be a smartphone folded and a tablet unfolded. By the way, the wallpaper of the smartphone in the video is recognizable – it was used with the Samsung Galaxy S3.
At CES 2013, Samsung showed a working prototype of such a display. And already in 2018 at the Samsung developer conference held in San Francisco – a working prototype of such a smartphone with a foldable display. Only a year and a half was left before the announcement of the first Galaxy Fold.
How is a foldable OLED display
In essence, a flexible OLED display is just like any other display, only using a plastic substrate instead of glass, which gives it flexibility. A layer of electroluminescent organic semiconductors (which, in fact, are called OLED) is already deposited on it. The plastic substrate is made of the type of polyethylene terephthalate (aka polyethylene glycol terephthalate, PET, PET, PET, PETG, lavsan, mylar – it has a lot of marketing names registered as a trademark). We regularly use products made from it, for example, plastic bottles for drinks. These are the same PET bottles (patented, by the way, back in 1973), which use the properties of plastic to become transparent when heated, then cool sharply after they take the required shape. These materials are strong and durable, but it only seems that making a flexible OLED display based on them is a matter of technology. In fact, it was necessary to solve a number of problems associated with them. For example, encapsulation – OLED materials are destroyed upon contact with moisture and air. And regular bending (we plan to bend the screen hundreds of thousands of times while working with a smartphone) creates mechanical stress (tension) in the materials. Therefore, it took so long to solve all these problems, and we were able to see production devices with flexible displays.
Samsung’s foldable display innovation
While the Samsung Galaxy Z Fold2’s foldable display backing comes from PET, the company still calls its material glass. And I came up with a special name for it: UTG or Ultra Thin Glass – ultra-thin glass.
A very interesting solution is used to implement a feature called Flex Mode. We will talk about what it gives for the user in a separate post, and now we will touch on the mechanical implementation of the ability to fix the open screen at different angles. The developers of the smartphone called this engineering solution CAM Mechanism. It allows you to hold the screen and not close on its own at an angle of 75 and 115 degrees. The principle of the mechanics can be seen in the gif below.
Inside this mechanism looks and works as follows:
The swivel joint uses four dual CAMs – one pair on each side of the foldable display:
In addition to the complex mechanics, there was another problem with the foldable display to be addressed. In older clamshells, the swivel joint consisted of two different parts. The Galaxy Z Fold2 uses one large, unibody display that is not split in two. As a result, when bending it inevitably, the inner part of the flexible display should extend beyond the edges of the case. We overcame this problem by creating two virtual axes, between which the fold of the bent screen is hidden.
Do you think that’s all? No matter how it is. Additional space is required for this fold. And where there is free space, dust and all sorts of small crumbs from our pockets and bags constantly accumulate. All of them put additional stress on the inside of the display with each flexion and extension. Samsung engineers have considered more than a hundred (!) Ways to solve the problem. And, in the end, they created a special Sweeper brush made of carbon fiber and nylon, borrowing the idea from powerful Samsung vacuum cleaners (for example, this one) with turbo brushes rotating 20 times per second. Its bristles are just 0.87 millimeters high and clean the inside of the screen every time you open and close your smartphone.
What the foldable display looks like on the Samsung Galaxy Z Fold2
This is how the Samsung Galaxy Z Fold2’s hidden hinge mechanism looks like in action. It consists of 60 parts and is designed, according to the developers, to withstand 200 000 opening mechanism. That’s over a hundred disclosures a day for ten years.
In practice, it looks like this:
Hinges in semi-unfolded state, side view:
Outside of the hinges. Everything looks neat and reliable. With the first Fold, I went through a couple of months and did not experience any problems in working with a flexible display. I have Fold2 for several weeks now and the result is the same. All fears of how reliable the flexible screen is after the first days of use. The main thing is to remember that the manufacturer does not recommend removing the protective film – this can damage the screen and damage the smartphone display.
The fold of the screen is easily palpable in the unfolded state – it protrudes slightly, this is a feature of the technology, and the fold of the more compact Z Flip is also palpable. Perhaps they will get rid of this in the future, but so far. Personally, this does not cause any inconvenience to me from the word at all, but I do not exclude that there will be aesthetes who will not like it.
Next time we’ll talk about how good both displays are from the point of view of a special device – a colorimeter.
Five things to know about the foldable display design of the Samsung Galaxy Z Fold2
- flexibility is provided by a special substrate made of a special material called UTG (ultra-thin glass);
- it has a complex hidden hinge mechanism, consisting of 60 parts;
- special CAM mechanism provides 75 and 115 degrees of display opening for Flex Mode;
- under the screen is a Sweeper brush with 0.83 millimeter bristles that cleans the inside of the screen every time it is opened and closed;
- the screen mechanism is capable of withstanding 200,000 opening-closing cycles (more than 100 times a day for 10 years).