Xu Yang, Jinchai Li, Xuhui Peng, Chunfeng Zhao, Chao Chen, Xiaowei Zhang, Jinliang Lin, Donghua Li, Yuefen Chen, Zhaoxia Bi, Feng Qin, Cheng Li, Kai Huang, Junyong Kang & Rong Zhang
Accepted: Jul 29, 2024 Published: Oct 17, 2024
DOI:10.1007/s11432-024-4111-9
Abstract
MicroLED display is considered one of the most promising technologies for next-generation displays. However, the high manufacturing cost has been a major obstacle to its accessibility to the general consumer market, and mass transfer, an essential process to achieve cost-effective manufacturing, has not yet reached commercial maturity. Critical issues, such as microLED chips, transfer equipments, and process materials, need to be addressed for the mass transfer technologies. In this work, we present a 1.63-inch full color microLED display module fabricated with laser mass transfer, which has a pixel density of 403 pixels per inch (PPI), the highest resolution ever achieved in the industry using mass transfer technologies. The laser mass transfer is realized with three process nodes: laser lift-off, laser induced forward transfer, and carrier bonding. Each node has been well explored to improve yields. Insights into the present progress and the future development of the laser mass transfer will be shared in this work.
Introduction to Micro-LED Technology
Micro-LED display technology involves the high-density integration of miniaturized semiconductor light-emitting diodes (LEDs) arranged in a matrix on a single chip. This interdisciplinary application merges LED chip technology with flat panel display manufacturing. Compared to LCD and OLED technologies, Micro-LED displays offer significant advantages in brightness, response time, power consumption, transparency, and stability, making them widely regarded as the next-generation mainstream display technology. Achieving an efficient, precise, and high-yield mass transfer integration is a critical concern shared by both academia and industry. Among the many transfer techniques available, laser mass transfer has emerged as a leading solution, holding great promise for the commercialization of Micro-LED technology.
Recent Breakthroughs in Research
Recently, a collaborative research team from Xiamen University, the Xiamen Institute of Future Display Technology, and Tianma published a paper titled “Super Retina TFT Based Full Color MicroLED Display via Laser Mass Transfer” in SCIENCE CHINA Information Sciences. The paper delves into the key technological challenges associated with laser mass transfer integration for ultra-high pixel density TFT-based Micro-LED full-color displays, systematically analyzing the challenges faced in processes such as laser lift-off, laser transfer repair, and panel bonding in terms of craftsmanship, equipment, and materials. The team innovatively proposed new methods and technologies to enhance transfer efficiency and yield, successfully fabricating a TFT-based Micro-LED full-color display with a pixel density of 403 PPI, marking a significant breakthrough in Micro-LED display technology.
Key Innovations
1. High-Quality Substrate Lift-off Using Laser Uniform Illumination
Current methods for laser lift-off (LLO) of patterned substrate (PSS) GaN-based Micro-LEDs using a 266 nm wavelength semiconductor-pumped solid-state laser (DPSS) face challenges such as narrow processing windows and the risk of chip breakage and edge damage. To address this, the team simulated the energy distribution at the PSS-GaN interface using photon tracing methods and proposed a laser uniform illumination scheme that achieved high-quality substrate lift-off for GaN-based Micro-LED chips, with yields exceeding 99%.
2. Multi-Factor Correlation Decision Scheme for Laser Mass Transfer
In light of the stringent requirements for positioning accuracy and yield in ultra-high pixel density Micro-LED full-color displays, the team introduced a multi-factor correlation decision scheme for the laser mass transfer process. This scheme includes:
- A comprehensive assessment of the interaction mode between the laser and transfer adhesive for adhesive type selection.
- Correlation control of laser energy range and adhesive thickness to ensure high-precision, high-yield transfer without damage.
- In-situ repair of defective chips using automatic optical inspection (AOI) and photoluminescence (PL) detection.
Through the application of this decision-making framework, the team conducted a comprehensive evaluation and optimization of factors influencing transfer material properties, laser irradiation energy, and chip irradiation damage, significantly enhancing the efficiency, precision, and yield of laser mass transfer. The transfer efficiency reached 36 kk/h, with first-pass yields of 99.87% for blue and green chips and 99.76% for red chips. Further repairs using a 266 nm laser achieved a post-repair yield of 99.999%.
Conclusion
Leveraging these innovative techniques, the research team successfully manufactured a TFT-based Micro-LED full-color display with an impressive resolution of 403 PPI using laser mass transfer for the first time.
Senior Engineer Yang Xu and Professor Li Jinchai from Xiamen University, along with Professor Huang Kai and Academician Zhang Rong from the Chinese Academy of Sciences, are the co-authors of this study. The research received funding from national key research programs, the Fujian Natural Science Foundation, and Xiamen Science and Technology Plans. The team will continue to delve into Micro-LED material epitaxy, device development, and transfer integration, enhancing the deep integration of industry, academia, and research to promote rapid industry development.
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