Micro-light-emitting diode displays offer high brightness, fast response, strong contrast, and low power consumption. These advantages make them promising for augmented and virtual reality, wearable devices, and other high-resolution display applications. However, producing full-colour micro-LED displays remains challenging because red, green and blue pixels must be fabricated and aligned at extremely small scales.
Quantum-dot colour-conversion layers provide a practical route toward full-colour displays. In this approach, blue micro-LEDs excite red and green quantum dots, while part of the blue light is retained as the third primary colour. The main difficulty is placing different quantum dots into precisely defined, uniform and closely spaced pixels. Conventional patterning methods can involve complex processing, limited resolution, material spreading or damage to the optical properties of the quantum dots.
In this paper published in Light: Advanced Manufacturing, Muhammad Farhan, a PhD student led by Professor Xueqiang Zhang at Beijing Institute of Technology, developed a spatially shaped femtosecond-laser method for fabricating ultrafine quantum-dot pixels. The method combines high-precision laser drilling with selective quantum-dot filling.
The researchers first coated a glass substrate with a thin SU-8 polymer layer. A femtosecond laser was then used to drill ordered microhole arrays into the polymer. Compared with a conventional Gaussian beam, the spatially shaped Bessel beam produced microholes with clearer entrances, smoother sidewalls, and reduced taper, while limiting damage to the underlying glass. By adjusting the laser conditions, the team controlled the hole diameter over a broad range and obtained high-quality nanoholes as small as 100 nm.
These microholes served as a miniature pixel mould. Red or green CdSe quantum dots were filled into selected holes and cured, while excess material was removed from the surface. Because the laser forms the empty mould before the quantum dots are introduced, the process avoids direct laser exposure of the light-emitting material. The researchers fabricated well-defined monochromatic red and green arrays and obtained reliable luminescent pixels with diameters as small as approximately 700 nm.
Sequential drilling and filling further enabled the fabrication of aligned red-and-green dual-colour arrays with clear boundaries. The resulting colour-conversion layers showed narrow-band red and green fluorescence, high colour purity and uniform pixel emission. The red and green arrays achieved luminous uniformities of approximately 90% and 97%. The corresponding colour gamut reached 111% of the NTSC standard.
This maskless, solvent-free and quantum-dot-compatible strategy provides a flexible route for producing high-resolution colour-conversion layers. Further improvements in parallel laser processing, quantum-dot filling and device integration could support larger-area fabrication and accelerate the development of full-colour micro-LED displays for AR and VR systems and other high-pixel-density applications.
