A simplified and high yield method for Micro-LED integration: Substitution of metal bumps with conductive photoresist in high-precision mass transfer

Journal article, 2025

With the rapid development of Micro-light-emitting diode (Micro-LED) technology, its application in the display field is promising. However, the precise electrical connection between Micro-LEDs and driver substrates remains a key challenge to achieve their large-scale commercialization. Conventional metal bump preparation processes usually rely on complex lift-off techniques, which not only increase the complexity of the process steps, but also face operational risks and are difficult to meet the demands of smaller pixel sizes and pitches. To this end, this study proposes an innovative approach using photoresist bumps instead of conventional metal bumps for the electrical connection between Micro-LEDs and driver substrates. By customized conductive photoresist as a conductive medium and combined with a proven photolithography process, it is possible to accurately prepare photoresist bumps to a predetermined position on the driver substrate without the need for a complex metal deposition process. This method significantly simplifies the tedious steps in the conventional process and improves the preparation efficiency and process stability. In the study, we combined the laser transfer technique with the photoresist bumping method to successfully transfer micro-LEDs with a size of 30 × 15 μm² from a sapphire substrate to a transparent 1.98-in. low-temperature polycrystalline silicon thin-film transistors (LTPS-TFT) driver substrate with high precision and good process repeatability. The technology simplifies the process while effectively reducing costs, providing technical support for the large-scale production and commercial application of Micro-LED display technology. In addition, the method relies on mature lithography technology and has the advantage of compatibility with existing semiconductor manufacturing processes, which has a strong potential for industrial promotion. Although this study focuses on the transfer process of Micro-LEDs, the proposed technological solution also has a wide range of application prospects, especially in the high-precision transfer and conductive bump preparation of other micro/nano devices.