What is Micro OLED Display ?

Micro Silicon-based OLED Display technology

OLED,or organic light-emitting diode. It takes use of organic light-emitting materials, with better performance than LCD (liquid crystal). It is called the third generation of display technology after CRT and LCD. OLED micro-display, OLEDoS, or OLED on Silicon, or Micro OLED, or silicon-based OLED, is an emerging branch of the display industry. It is a new display technology that combines semiconductor process technology and OLED technology, and uses single-crystal silicon wafers as the substrate to prepare OLED devices. It can be said that it integrates the two high-precision technologies of semiconductors and OLEDs. Silicon-based OLED is also called the "most mature" "new high-tech display product" by industry insiders. Silicon-based OLED micro-display is mainly composed of IC manufacturing technology and OLED technology. It is different from traditional mobile phones, IPADs, computers, and TV screens, and mostly refers to displays less than 2.5 inches.

Since micro OLED displays use single-crystal silicon wafers as active drive backplanes, it is easier to achieve high PPI (pixel density), high integration, small size, easy to carry, good shock resistance, and ultra-low power consumption. Currently, the main application methods are divided into two categories: immersive and penetrating.

Structural Technology

The structure of the silicon-based OLED device is as shown below, including the driver backplane and the OLED device. The driving backplane is prepared using standard CMOS processes to form pixel circuits, row and column driving circuits and other functional circuits. This step is performed in the wafer foundry. A patterned metal layer is made on top of the CMOS circuit to serve as the anode of the OLED device. This step can be prepared in a wafer foundry or a display panel factory. Then a complete OLED device is made above the anode, usually including a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, a translucent top electrode, and a thin film encapsulation layer on the top electrode. It is necessary to continue to prepare the color resist layer, and finally use a glass cover for lamination and packaging. OLED and subsequent steps are all performed in the display panel factory.

Performance characteristics

Silicon-based OLED uses mature integrated circuit CMOS technology, generally a process of more than 100 nm is sufficient, PPI can reach 3500 or even more than 5000, its pixel size is 1/10 of that of traditional display devices, and its fineness is much higher than that of traditional devices. Silicon-based OLED adopts self-luminous mode, with high brightness, generally above 1500 nit, and excellent products can reach 7000 nit, meeting the needs of VR and AR. Silicon-based OLED has fast response speed, μs level, low power consumption, about 20% smaller than LCD; bright colors, high contrast, wide operating temperature (solid-state device), all of which are essential performance requirements for high-end AR/VR glasses. In terms of IC, the driver IC and pixel circuit of the mobile phone are independent, while the driver IC and pixel circuit of silicon-based OLED are integrated together, and its technology is mainly mastered by IC design companies such as Shenzhen Yunying Valley, Beijing Digital Optical Core, and Gaoping Company in the United States. The advantage of this method is high integration, but it also brings many problems, such as high development difficulty and poor versatility. Therefore, silicon-based OLED ICs are also developing towards a 2-chip model: the driver IC is independent and highly versatile; the pixel circuit is designed separately by the display panel manufacturer, so that it can be manufactured using different CMOS process nodes to reduce costs, and the flexibility of product development will be greatly improved.

Advantages and Disadvantages

Compared with traditional AMOLED display technology, OLED microdisplay technology has the following outstanding features:

The substrate chip adopts mature integrated circuit technology and can be manufactured by integrated circuit foundries, and the manufacturing yield is much higher than the current mainstream LTPS technology.

Using single-crystal silicon, it has high mobility, stable performance, and a longer lifespan than AMOLED displays.

200mmx200mm OLED evaporation packaging equipment can meet manufacturing requirements (compatible with 8-inch wafer size), unlike AMOLED, which requires high-generation production lines.

OLED microdisplays are small in size and very easy to carry, and the near-eye display effect provided by their small size can be comparable to large-size AMOLED displays.

Compared with other microdisplay technologies, OLED microdisplay technology also has many advantages:

Low power consumption, 20% less than LCD power consumption, lighter battery weight,

Wide operating temperature, LCD cannot work at extreme temperatures such as 0℃, and must be heated by additional components, and must use cooling systems at high temperatures. All these solutions will increase the weight, volume and power consumption of the entire display. OLED is a fully solid-state device that can work in a temperature range of -46℃~+70℃ without heating and cooling.

High contrast ratio. LCD uses built-in backlight, and its contrast ratio is 60:1, while the contrast ratio of OLED microdisplay can reach 10,000:1.

Fast response speed. The time required for OLED pixel update is less than 1us, while the update time of LCD is usually 10~15ms, which is 1,000 to 1,500 times different. OLED display is smoother, thus reducing visual fatigue.

Application in AR/VR

The technologies available in the AR/VR micro display field include Micro LED, silicon-based OLED, Fast-LCD, LCoS, etc. Micro LED is not yet in mass production. Compared with other technologies, silicon-based OLED has obvious advantages such as fast response, high resolution, high contrast, low power consumption, and wide viewing angle (see the table below for specific comparison). Due to the current high cost and limited production capacity, the market penetration rate needs to be improved.

Product Market

More and more newly released and upcoming AR/VR products are using silicon-based OLED technology. AR products such as Nreal Air, Rokid Air, Lenovo Glasses T1, Mijia Glasses Camera, VR products such as GOOVIS VR, DJI Goggles 2, and the upcoming Apple MR and PS VR2 have all clearly adopted silicon-based OLED technology. The two important technical points of AR/VR glasses, optical solutions and micro-displays, need to be matched with each other. At present, the technical route of optical solutions is relatively clear: VR evolves to Pancake, and AR evolves to light waveguide. The light loss of these two optical solutions is relatively serious, so micro-displays are required to provide higher brightness. LCD cannot provide enough brightness, so manufacturers have turned their attention to silicon-based OLED and Micro LED. Compared with silicon-based OLED, Micro LED has higher brightness but is currently limited to monochrome. Color Micro LED still has a long way to go before mass production. Therefore, silicon-based OLED is the first choice for high-end AR/VR glasses at present and for a long time.