Micro LED, the Final Solution of Display Technology

Micro LED is a very promising solution for ultra-small screens and transparent screens. It meets the demand for high pixels and for lighting?efficiency. However, on today’s market Micro LED displays can cost tens of thousands of euros. This price is far beyond the budget of family use. But So from the birth of LED technology to the present, what is the history of LED development, and what is the relation between LED screens and another more popular display technology, LCD? This article explains how we come to Micro LED from the very first origin.?

LCD

In order to understand the advantages of LED, we need to learn something of the LCD and why this popular display has to be abandoned in the future.

The invention of liquid crystal dates back to 1888, when Austrian physiologist Friedrich Reinitzer observed the liquid crystal structure and behavior of cholesterol from carrots. Based on this discovery, German physicist Otto Lehma coined the terms “liquid crystal”. After that, the first liquid crystal display was created in 1968. From the 1970s to the 1990s, the development and manufacture of LCDs were basically in Japan, but after the 1990s the industry shifted to Korea and China, and the status of LCDs soared.

However, although LCDs are widely used, their structure and display principles have remained almost unchanged since the day they were created. The panel must be equipped with a backlight, polarizers, baseboards, a liquid crystal layer and color filter. These indispensable layers of structure reduce the lightning efficiency of LCDs. Furthermore, LCDs are limited by their backlight. When the viewing angle is exceeded, the color and brightness of the display will be largely reduced.

To overcome the energy consumption, thick layers and display angle problems associated with backlight, the only way to get around this is to look for self-emitting substances. Here comes LED

Born in 1923, the first commercialized LED was the red LED, which is still widely used today as an indicator light in remote control and for traffic signals. In 2014, blue LED was created. By now we could use the three primary colors of light, red, blue and green, to display a full-color screen. Unlike LCD, LED displays are self-emitting, consume less energy, have more brilliant colors, higher brightness and better contrast. So they are widely used in the field of giant outdoor displays. Among LED display technologies, the most crucial is the pixel, that is, the size of the LED diode. Starting with the first generation of DIPs, manufacturers of LEDs are continually looking for ways to make the diode smaller. There are three ways how the way the LED is encapsulated: DIP for Dual In-line Package, SMD for Surface Mounted Device and COB for Chip On Board. DIPs commonly used in traffic signals, where the cost is low, the diameter of the diode is large and the display is monochromatic. SMDs allows the red, green and blue light to be encapsulated together, and COBs are more suitable for small pixel pitch screens it can significantly improve the resolution of the screen.

LEDs are more representative of the future of displays than LCDs in terms of their simpler structural design. More than just rivals, they are also complementary. The backlight of an LCD is actually a whole LED light panel. Thus, controlling the backlight is one of the key issues for LCDs to improve their display quality and efficiency. Due to the backlight, LCDs cannot show a pure black but usually only a saturated color of gray. This results in a low contrast between light and dark colors across the screen and a lack of relief in the images, especially for darker areas of the screen where pictures lost their details. So LCDs changed a single backlight into several zones of backlight, creating Thus Mini LEDs. So we can understand that Mini LED is actually an LCD. Only it cuts one block of LEDs into smaller Mini LEDs to control the backlight and thus improve the contrast of the picture. But Mini LED does not fundamentally break the limit of LCD technology, the luminous efficiency is still low and the display angle is narrow. Besides from the side view of a Mini LED screen, we can observe the problem of halation.

Although LED is self-emitting, they use semiconductor materials, and the diameter of the diode is difficult to make small. It struggles to make small displays, see the screen of a phone or computer.

Engineers have therefore found organic fluorescent materials that are self-emitting when connected to electricity. The fluorescent materials are put on thin film circuits by means of Chemical Vapor Evaporation (CVD). So each pixel on the screen has its own light source and can show a picture with extremely high contrast.

Compared to the LCD, there is no liquid crystal layer, so the panel is thin and responsive. But the organic materials have a limited life span and the display brightness is low. Even with some improvements, W-OLED and WQ-OLED didn't propose a suitable outdoor display solution. Therefore, OLEDs can only be used as a temporary solution and the focus of research is still on how to reduce the diameter of the diode.

Micro LEDs were proposed in this context. Thanks to two researchers, Jiang Hongxing and Lin Jingyu, LED diameters are reduced to the micron level. Sony first released the 55-inch Crystal LED Display. Because of the small diameter of the lamp, we can put huge amount of LED into one unit area. That means we can make ultra-small screens in the size of a fingernail cap, built into VR glasses and do laser projection. At the same time, the Micro-LED display is bright enough to realistically simulate strong daylight, and when there are scenes like out of a tunnel in a game, players can truly experience the brief blindness of intense light, increasing the immersion of the game. Another important application is in transparent screen displays. As the pixel is made small, then the pitch between the pixels can be made larger per unit area, which is ideal for applications such as car windows and shop windows where high transparency is required.

But Micro-LED still has many technical problems to be solved. The micro LED transfer process is crucial in Micro LED display production. One of the challenges is the technology of mass transfer. How to "mass transfer" extremely small micro LED chip and to place them in the right place with very little room for errors. This requires accuracy, speed and Reliability.

Playnitride at Taiwan, JBD at Shanghai and VUEREAL of Canada are both leaders in micro LED display technology. However, due to low yields and highly technical barriers, the price of Micro-LED displays is prohibitive, with Sony launching a 146-inch display for $400,000 and a 219-inch one for around $800,000. As a new technology, the high price point is understandable; OLED has also experienced a downward price curve. As the ultimate display technology, Micro-LED is expected to achieve a gradual reduction in cost by the industry chain and renew of technology.