The Challenges to Micro LED Display

In the era of artificial intelligence and big data, LED displays are no longer simple information display screens, but interactive, highly realistic and immersive information interaction terminals. Requirements are put forward for display devices that can realize three-dimensional spatial image, interactive, energy saving, thin and light, flexible folding and curling, giant size, etc. Display industry from materials, equipment, devices to manufacturing technology and the whole industry chain is entering a new revolution. Micro-LED display technology came into being. As the industry chain players continue to increase the size of the layout, who can crack the new track "key" to open the technology of the first, is very important.

01. What is Micro LED?

Micro-LED display technology is a self-luminous display technology, through the array of micron-scale LED light emitting devices (μLED) integrated on an active addressing driver substrate, to achieve individual control and lighting, so as to output display images. Micro-LED display has many advantages, such as self-lighting, high resolution, low response time, high integration, high reliability, and small size, high flexibility, easy to disassemble and merge, can be applied to any display application from small size to large size, and in many application scenarios, Micro-LED displays provide better display effects than liquid crystal displays (LCD) and organic light-emitting diode (OLED) displays.

02. Micro LED technology challenges

Despite the rapid development of Micro-LED display technology, the transformation of LED from lighting application to display application puts forward higher requirements and challenges for LED extension.

(1) Selection of substrate materials

The selection of substrate material and epitaxial technology have a crucial effect on the performance of Micro-LED devices. Because Micro-LED chips are smaller than traditional chips to 50μm, its high yield and uniformity requirements for substrate selection and epitaxial technology put forward higher requirements and challenges. When applied to high-resolution display, the injection current density of Micro-LED is very low, and the non-radiative recombination caused by defects is particularly prominent, which greatly reduces the optical output efficiency of Micro-LED. Therefore, epitaxial sheets with lower defect density are needed for Micro-LED.

At present, the substrates that can be commercialized on a large scale include sapphire, SiC and Si, etc., but these substrates as GaN epitaxial are heterogeneous epitaxial. Due to the lattice mismatch and thermal mismatch between the heterogeneous substrate and GaN epitaxial layer, the epitaxial layer has a high dislocation density. Compared with sapphire, SiC, Si and other heterogeneous substrates, GaN material as substrate can greatly improve the crystal quality of epitaxial sheet, reduce dislocation density, and improve the working life, luminous efficiency and working current density of the device. However, the preparation of GaN single crystal substrates is very difficult, and GaN substrates are very expensive and have a maximum size of only 4 inches (10.16 cm), so it is difficult to meet the needs of commercialization.

(2) Wavelength uniformity control

Micro-LED display technology is a self - lighting display technology. In the application of high resolution display, the color difference caused by the uneven emission wavelength of Micro-LED will greatly affect the display effect. To ensure the display effect, the standard deviation of wavelength variation of Micro-LED epitaxial wafer should be controlled at 0.8nm or smaller. Therefore, in the process of growing InGaN/GaN quantum well epitaxial by metal-organic chemical vapor deposition (MOCVD), the control of airflow and temperature uniformity is particularly important.


Optimizing the airflow uniformity during epitaxial growth of MOCVD plays an important role in improving the wavelength uniformity of LED. At present, Prismo UniMax, the latest domestic MOCVD device, ensures the balance of the whole temperature field during epitaxial growth by adopting the temperature control technology of the zone. Meanwhile, a series of strain control technologies such as MO source and air flow uniformity are used to improve the wavelength uniformity of LED epitaxial sheet to meet the demand of Micro-LED display. In view of the high requirement of wavelength uniformity for Micro-LED applications, the design of graphite tray can be optimized to make it with certain curvature to better match the warpage of epitaxial sheet in the epitaxial growth process, which has further improved the temperature uniformity control.