The road to Micro LED commercialization is full of twists and turns

Since Apple acquired Micro LED startup LuxVue in 2014, Micro LED, which is hailed as the next-generation display technology, has officially entered the growth stage from its infancy and has attracted global manufacturers to continue to invest resources in research and development. However, many technical barriers and equipment limitations are still difficult to overcome, resulting in the difficulty in reducing production costs. Micro LED is still on the road to commercialization.

Micro LED not only has brightness and contrast effects that surpass OLED, but also has the characteristics of fast response, low power consumption and high reliability. If it is successfully introduced into mobile devices and automotive applications, the prospects are promising. However, the manufacturing process of Micro LED is complicated, and the raw materials, process consumables, production equipment, testing instruments and auxiliary fixtures used require strict specifications and relatively strict precision.

Micro LED Wafer Manufacturing

Micro LED and LED are both based on epitaxial silicon wafers, but the requirements for Micro LED epitaxy are far more stringent than those for traditional LEDs. The size of a Micro LED chip does not exceed 100 microns, which is only 1% of a traditional LED chip. Therefore, the wavelength consistency of the epitaxy is crucial. If the wafer is uneven, it may cause chip defects and increase the cost of subsequent processes. However, most of the existing epitaxial silicon wafer production equipment is made for the production of traditional LED wafers and can hardly meet the requirements of Micro LED wafers. Furthermore, the chip process on the epitaxial wafer is also very critical and may affect subsequent processes such as wafer bonding and transfer.

In order to break through production restrictions, many epitaxy MOCVD equipment manufacturers and chip manufacturers have worked together to develop Micro LED chips to improve chip efficiency and quality while accelerating production. For example, AIXTRON announced in January this year that it had signed a Micro LED production cooperation agreement with Taiwan's Neptunium Technology, and Veeco cooperated with German Micro LED technology manufacturer ALLOS.

Micro LED Transfer Technology

To make a Micro LED display, the Micro LED chip must first be removed from the sapphire substrate and transferred to another temporary substrate, and then moved to different backplanes depending on the function and purpose. The transfer process is doubly difficult due to the extremely small chips and large number. If traditional pick and place technology is used to transfer millions of LEDs, it will inevitably be extremely time-consuming and increase production costs. In order to speed up the transfer process, many manufacturers have developed various transfer technologies, such as Pick & Place transfer, fluid assembly, laser transfer, etc. In addition, placing the Micro LED chip on the target substrate and arranging it accurately is also a difficult challenge. In order to meet the needs of different transfer methods, chip manufacturers must work closely with transfer technology manufacturers to improve overall yield and efficiency.

LEDinside, a subsidiary of TrendForce, analyzed the advantages and disadvantages of various existing transfer solutions and pointed out that Pick & Place transfer technology can be applied to chip products larger than 10 microns, but the transfer efficiency, accuracy and stability are relatively low. Although the fluid assembly technology used by manufacturers such as eLux has a faster transfer speed, it may cause chip damage during the process, so the yield cannot be guaranteed. The laser transfer technology used by Sony and start-ups such as Uniqarta and QMAT has the opportunity to transfer chips smaller than 10 microns in size, and the accuracy is improved, but the equipment cost is relatively high.

In order to maintain their current leading edge in Micro LED technology, many brands have formed alliances with mass transfer technology developers, such as Apple's acquisition of LuxVue and Osram's cooperation with X-Celeprint. Rohinni has cooperated with equipment manufacturer K&S to develop mass transfer solutions and established a joint venture with BOE to leverage its advantages in placement technology.

In addition, the U.S. Patent and Trademark Office recently announced that Apple has obtained a patent for Micro LED chip transfer and structure technology, which allows Micro LED structures with metal film layers to be more easily transferred and assembled in large quantities onto the target receiving substrate. This is one of the most challenging production processes for Micro LED displays, and it also proves that Apple is still quietly developing and laying out Micro LED technology.

Micro LED Testing and Others

Inspection is also an important part of the manufacturing process. During the production process, the Micro LED chip must be continuously tested to ensure its normal function in order to ensure chip efficiency and improve the overall yield. If defects are detected, they must be repaired. However, the miniaturization of chips also increases the difficulty of inspection. Therefore, equipment manufacturers are committed to developing more effective and accurate solutions.

In addition, backplane materials, full-color solutions and driver IC design are also bottlenecks in the production of Micro LED displays. Industry manufacturers are actively integrating the supply chain vertically and forming strategic alliances to lead Micro LED displays towards practical applications. However, before Micro LED officially moves towards commercialization, more innovative technological developments are still needed to solve the problems in the production process in order to reduce production costs and accelerate mass production.