Chip-first active-matrix fabrication approach for effective connection of TFT backplanes to micro-LEDs

Micro-LEDs are a major advancement in visual display technology, offering high brightness, efficiency, and long lifespan. However, their high cost stems from low-yield fabrication processes that struggle to reliably connect millions of microscopic LEDs to the display backplane. Faulty pixel identification, repair strategies, and dual redundancy have enabled the production of working displays with superior image quality due to their high dynamic range. However, inspection only identifies issues; it doesn’t resolve them, and repair costs time and money. Therefore, there is a need to enhance micro-LED fabrication quality through innovative processes.

This presentation introduces a chip-first strategy, where micro-LEDs are placed face down on a substrate with contact pads facing upwards. A pre-polymer layer is spin-coated, patterned, and cured to form via hole connections above the anode and cathode pads. A metal layer is then sputtered and patterned to connect the LEDs, without using eutectic bonding or laser sintering. Organic thin-film transistor (OTFT) materials are applied in multiple layers using conventional tools, yielding a high-quality display through low-temperature processes (<150°C). The low temperature prevents damage to micro-LEDs, is eco-friendly by using less energy, and allows the use of a wider range of transparent plastic substrates with better optical qualities. The lowest temperature tested so far is 80°C. The presentation will show the structure of the chip-first backplane and its corresponding cross-sectional structure. OTFT transfer curves and an image of the 100x180 monochrome 2.2” display are also presented. Turn-on yield of the wired-up micro-LEDs is high, with no failures detected in over 18,000 devices.