Room-Temperature Cu Direct Bonding Technology Enabling 3D Integration with Micro-LEDs

This paper describes Cu direct bonding at room temperature for wearable micro-LED display. Still, the conventional bonding methods of micro-LEDs with solder micro-bumps have heat problems during bonding and difficulty achieving a narrow pitch. Using a unique method developed in this paper, it is possible to bond micro-LEDs to a 3D-IC chiplet without using the micro-bumps. Here, The 30 x 30 arrays of 0.1-mm-square blue micro-LEDs are assembled, bonded, and interconnected on a sapphire substrate through electroplated Cu, and successful emission from the blue micro-LEDs is confirmed. The bonding strength of the room-temperature Cu direct bonding with the micro-LEDs and a yield enhancement technique is also described. Finally, we emphasize the high potential of massively parallel chiplet self-assembly using liquid surface tension.