Leading in uniformity: creating excellent display effects
Uniformity is one of the key indicators of the display effect of MicroLED microdisplay chips. Since the projection size is usually more than 10,000 times the chip size, any non-uniformity will be significantly magnified in the display effect.
At the key technical level, MicroLED preparation has the most direct impact on its uniformity in terms of coating process.
Figure: Demura special high-magnification imaging brightness meter photo (pure white picture)
The first is the uniformity control of film thickness. In the process of manufacturing MicroLED chips, the thickness of the film needs to be precisely controlled to keep it highly uniform. Because the uneven film thickness will directly affect the performance of the chip, it will also cause differences in the optical properties of different areas of the chip, which will in turn affect the uniformity of luminescence. Only by controlling the film thickness within a suitable range can the overall uniformity of the chip be improved. Therefore, achieving good coating uniformity is one of the key technologies to improve chip uniformity.
The second is etching consistency. The etching process has an important impact on the structure and performance of the chip. Good etching consistency can ensure the stability and consistency of the etching process, and avoid uneven chip structure due to excessive or insufficient etching, thereby affecting uniformity. This is also a technical link that needs to be focused on and optimized in the process of improving chip uniformity.
Figure: 0.12-inch 640*480 green light Micro-LED chip uniformity reaches 98%
In terms of uniformity indicators, Hongshi Intelligent has achieved remarkable results. At present, its MicroLED chip uniformity has reached 98%, which is in a leading position in the industry. In contrast, the leading standard currently delivered by other companies is a uniformity of 90%, while most manufacturers are only 80%, and some manufacturers even avoid talking about this indicator.
In fact, there is no shortcut to improve uniformity.
Any company has gradually improved the uniformity of MicroLED chips, not overnight. Hongshi Intelligent has also experienced a development process from a lower level (60%) to a higher level (90+%) through a stable 8-inch wafer process and advanced Demura correction technology. This has also enabled Hongshi Intelligent to continuously work hard on technology research and development and process improvement, gradually accumulate experience, and make significant progress.
Screen defect control, optical coupling optimization
In terms of screen defects, the industry standard for MicroLED chip screen defects is strict. The number of bright spots must be 0, and the number of continuous dark spots exceeds 1, which is unqualified. The number of single dark spots must be controlled within 100, which places extremely high demands on product process consistency.
Because optoelectronic devices are sensitive to process consistency, temperature control, cleanliness and other conditions in production, slight changes will affect the IV curve and IL curve of a single pixel. After two years of technical research, Hongshi Intelligent successfully achieved no bright spots and no continuous dark spots, and controlled the number of single-pixel dark spots to one ten-thousandth, within 30 dark spots, reaching the industry-leading level.
Figure: Micro-LED light emission angle
In terms of optical coupling, when the MicroLED chip is coupled into the diffraction optical waveguide, increasing energy is the key requirement, and the control of the beam divergence angle is crucial. Studies have shown that when the emission half angle exceeds ±30°, it will cause significant light energy loss, greatly affecting the effective transmission and utilization of energy.
Traditional LED devices present typical Lambertian radiation characteristics, with a half-angle of luminous emission of ±60°, which limits their optical waveguide coupling efficiency. To solve this problem, Hongshi Intelligent adopts an innovative solution:
Using wafer-level micro-nano processing technology, a microlens array is prepared on the light-emitting surface of Micro-LED. Using its beam collimation characteristics, the radiation half-angle is accurately compressed to the range of ±25°-30°. Experimental verification shows that this structure increases the axial light intensity by 2.8 times, while effectively suppressing stray light outside ±35°, meeting the stringent requirements of high-density integrated optical waveguide systems for the directivity of light sources.
Production efficiency, yield and cost advantages: creating comprehensive competitiveness
The manufacturing of MicroLED micro-display chips includes eight major processes and more than 200 small processes, among which the main processes are epitaxial wafer growth, bonding and peeling, lithography, etching, coating, electrode production, chip cutting, packaging, testing and sorting. Because it operates on an extremely small scale and has extremely high precision requirements, this also leads to high process difficulty.
To make an analogy, MicroLED is a display technology composed of micron-sized LED chips. In the manufacture of MicroLED, gallium nitride is a key material commonly used in MicroLED manufacturing technology due to its excellent semiconductor properties.
At the same time, as an advanced technology used in aircraft, rockets and other fields, the material used in the transmitter of gallium nitride radar is the same as that of MicroLED, which is gallium nitride. However, gallium nitride radar generally has a large number of transmitters (about 100,000 gallium nitride power transistors), and the power uniformity and consistency of these tubes need to be guaranteed to ensure radar performance.
At present, only China and the United States can achieve gallium nitride radar technology in the world, which shows how difficult it is. However, the transmitter size of gallium nitride radar is more than 100μm×100μm, while MicroLED is only 4μm×4μm. The challenge of achieving uniformity and consistency at such a small size is even more arduous.
In terms of goals, the manufacture of MicroLED must not introduce dirt, otherwise it may affect product quality; second, it must maintain consistency, because poor consistency cannot meet the requirements of the design graphics, which in turn affects product performance and function. The core cost of the chip is the production cost rather than the material cost, so the choice of substrate size is particularly important.
Hongshi Intelligent precisely controls the uniformity of nano-level film thickness within ±3%, effectively ensuring the efficient transport of carriers; in terms of plasma etching, the anisotropy deviation is strictly controlled to <5°, ensuring the consistency of the submicron table structure morphology; at the same time, in a Class 100 clean environment, the particle contamination is controlled at the level of 0.1/cm², which minimizes the failure of the light-emitting unit.
In addition, the 8-inch silicon-based substrate selected by Hongshi Intelligent has a much higher equipment production efficiency than the 4-inch. Comparing the cost of producing a 4-inch and an 8-inch, under the same time, the production cost of the product produced by the 8-inch equipment is only 1/6 of the product produced by the 4-inch equipment, and the production cost accounts for 80% of the entire chip cost, so the production of 8-inch equipment has obvious cost advantages.
And the 8-inch is more efficient than the 4-inch, because the base of the 8-inch equipment is a standard equipment, and large wafers such as 8-inch are processed more at the same time than 4-inch. It is known that the processing volume of a single chip of 8-inch and 4-inch substrates is 2412 and 380 respectively. The one-time production efficiency of 8-inch wafers is six times that of 4-inch wafers, and the production efficiency advantage is obvious.
Moreover, Hongshi Intelligent has successfully achieved a high product yield through strict process quality control.
In the key process window, Hongshi Intelligent has expanded it to more than 85% of the theoretical value, far exceeding the industry average. Compared with the traditional 4-inch process, Hongshi Intelligent's 8-inch production line has significant advantages. The process uniformity has been improved by 2.3 times, making the product quality more stable and reliable; the single-chip production capacity has been increased by 4.8 times, greatly improving production efficiency; and the overall manufacturing cost has been reduced by 50%.
While ensuring product quality, Hongshi Intelligent has achieved significant cost optimization, providing customers with more cost-effective products and services.