Rumours started to circulate earlier in 2019 on the interest of Apple to move to microLED technology for its devices displays. First the rumours were betting on a new Apple Watch dropping OLED screen in favour of microLED. More recent rumours are shifting the application to new Mac models to appear in 2020.
But what is the microLED technology?
The flat screens we have on our televisions today, on our phone, and many other devices are composed by tiny elements, pixels that can be illuminated forming a mosaic whose tiles are so small to be invisible to our eye (at least when watched from a distance). LCD screens had pixel coloured in red, green and blue that can be turned on or off. When off they would stop light going through, when on they would let light of a given wavelenght (colour) to go through. The light comes from LED that are illuminating the back pane of the screen (backlight).
Newer technologies are getting rid of this light generating back pane. OLED, Organic Light Emitting Diode, use an organic molecule to create light of a particular wavelength. The advantage of OLED, and in general of technologies that are not needing an illuminating back pane, is that they can have a much greater contrast, since the blacks are created by switching off the diode whilst in LCD you are just placing a opaque filter on the light and this lets a little bit of light to pass through and secondly they can provide, in principle, brighter display since the light is not going through a filter (red/green/blue).
MicroLED are like OLED (same LED root!) but are not using an Organic molecule to generate light. They use Gallium Nitride (GaN) and don’t need a polarising and encapsulating layer (necessary for OLED) so the screen is thinner, as thin as 100µm, thinner than a human hair.
The problem with microLED, invented in 2000 is the difficulty in manufacturing them through an affordable industrial process. LED, per sé, are really cheap. Look at those Christmas light ribbons: they cost a few dollars and bring sparkling light to your home. They are easy and cheap to manufacture because they are (relatively speaking) “big”. MicroLED are basically a shrunken version of those Christmas LED arranged in an array.
There are several problems arising when shrinking a LED and placing it in an array. First is the fact that each single LED has to be sufficiently separated from its neighbours so that the current powering each LED does not reach an unintended one. In you Christmas strips the spacing is several cm, so there is no problem. In a television display you have to place some 8 million LED on the screen surface, the smaller the surface the higher the density, meaning the LEDs get closer and closer one another.You can in principle squeeze the LED size at will (but in doing so you are also decreasing their brightness) but you cannot decrease at will the separation. This means that as you squeeze more and more the LED you are not just diminishing the overall brightness since each one will emit less light, you will also increase the ratio of the surface that is black (the part separating the LED) to the one emitting light. Beyond a certain dimension your display becomes weaker and weaker. Researchers are trying to reverse this effect by making LED brighter but in turns this requires more power, leading to more dissipation and requiring bigger insulation. You hit a wall where pushing the envelope in one direction requires compromising in another with a net effect that is zero gain.
This is the reason why the first demos of microLED in display was the The Wall, a television developed by Samsung with a 292″ diagonal -that is 7.4 meters- (tip it might be difficult to fit it in you living room, not to mention squeezing it through the door or affording the price…).
From a manufacturing point of view the issue is how to pick up a single LED and place it, and solder it, to the right spot. Current leading manufacturing pick-and-place systems (robots) have an accuracy of 34µm whilst the precision required for cramming UHD pixels on a 55″ display is 1.5µm.
Apple, according to rumours, seems to have tackled this issue and may be getting ready to bring microLED technology to market in its new MacbookPro line next year. We’ll see. For sure if this happens we are going to see, sooner than expected, the next generation of screens, with lower power consumption, better colour quality (LED emission can be tweaked to very precise narrow wavelengths resulting in higher colour fidelity) and higher contrast (that is so much appreciated by our brain to define screen quality!).
Give it few more years and you’ll see price declining sharply. Even more interesting, the manufacturing process works by producing submodules that can be assembled to create any size and any shape. By the end of the next decade assembling technology may allow us to have that Wall passing through the door and transform our home walls into gigantic virtual windows that can display anything, entertainment, sure, but also immersive environment to fit with our mood or … improve it!