Three Implementations of MicroLED

MicroLED currently knows three processes and is expected to use the fastest film transfer technology

    The MicroLED technology process can be divided into chip-level welding epitaxial welding and film transfer according to different implementation methods:

    Chip-bonding (chip bonding): The LED is directly cut into micro-scale MicroLED chips, and then SMT technology or COB technology is used to connect micro-scale MicroLED chips one by one to the display substrate.

    Epitaxial wafer bonding: Inductively Coupled Plasma Ion Etching (ICP) on the epitaxial thin film layer of an LED to directly from a micro-scale micro-LED epitaxial thin film structure, and then the LED wafer (including the epitaxial layer and the substrate ) Directly bonded to the drive circuit substrate, and finally the substrate is stripped using a physical or chemical mechanism, leaving only the Micro-LED epitaxial thin film structure on the drive circuit substrate to form the display element.

        Thin film transfer: Micro-level MicroLED epitaxial thin film structure is formed by peeling off the LED substrate to carry a LED epitaxial thin film layer with a temporary substrate and then inductively coupled plasma etching; or by using inductively coupled plasma ion etching to form a micron-sized MicroLED epitaxial thin film. The structure, by peeling off the LED substrate, carries the LED epitaxial thin film structure through the temporary substrate.

Figure: microLED different process technology features

   At present, the microLED large-screen applications represented by Sony mainly adopt the chip-level welding method; while Apple is promoting the thin-film transfer technology, which is more suitable for small and medium-size displays. Here we introduce only the film transfer technology that Apple will adopt: MicroLED film transfer technology flow can be simply described as 1) MicroLED chip preparation; 2) MicroLED chip transfer; 3) Mount the TFT substrate and driver IC to complete the product package.

MicroLED chip preparation, flip-chip process is the trend

        The preparation process of MicroLED chips is similar to that of traditional LED chips. The blue-green light chip is only used as an example to introduce the production process: LED chips are produced by performing technical processes such as PSS pattern substrate, LED epitaxial growth, and chip processing on a sapphire substrate material. MicroLED chips are much smaller (a few microns) in size than ordinary LED chips, but the existing etching technology can handle micrometer-level chips completely, and there is no technically significant difficulty. The following is a brief introduction to each link of LED chip growth:

  Sapphire substrate growth epitaxial wafer (blue-green LED LED chip)

        First, the sapphire material is patterned on the PSS substrate. The purpose of this step is to realize multiple reflections of light in the substrate by etching a regularly arranged cone on the surface of the sapphire substrate so as to achieve the external light extraction of the chip. Light efficiency. Thereafter, an undoped buffer layer (U-GaN), an N-type gallium nitride (N-GaN), an active layer (MQWs, a multiple quantum well), and a P-type gallium nitride layer (P-GaN) are sequentially grown on the PSS layer. ).