image: Figure | Micro-patterning of quantum dot color converters using the dry liftoff photolithography method. (a) Fluorescence photograph of a glass wafer displaying different images patterned with green perovskite QDs under a UV lamp. (b) Fluorescence microscope image of patterned red CdSe/ZnS QDs, the inset shows the zoom-in view of patterned features. (c) Fluorescence microscope image of multi-color patterns integrating green perovskite QDs and red CdSe/ZnS QDs.
Credit: John Leo Velpugonda et al.
Micro-light-emitting diode (micro-LED) display technology holds significant promise for a wide range of consumer and commercial applications, such as augmented and virtual reality headsets, smartwatches, and next-generation mobile devices. A significant challenge in developing micro-LED displays is the miniaturization of individual LED elements. Existing methods involve either tedious pick-and-place processes or specialized ink which may compromise pixel optical quality.
In a new paper published in Light: Advanced Manufacturing, a team of researchers, John Leo Velpugonda, Matthew Yerich, Naresh Varnakavi, led by Professor Lih Y Lin from Department of Electrical and Computer Engineering at the University of Washington, developed a photolithography-based process for patterning solution-processed materials utilizing a dry mechanical lift-off technique and applied it to achieve high-resolution patterning of QD color converters for micro-LED displays. This method combines the scalability and high-resolution capabilities of photolithography with the versatility of patterning a wide variety of solution-processed materials while preserving their optical properties, making it highly desirable. They demonstrated the process at a wafer scale with the highest pattern resolution of ~1 μm. Additionally, they showed the universal potential of this technique by demonstrating compatibility with green perovskite QDs and red CdSe/ZnS core-shell QDs. They also achieved integration with a typical LED substrate by applying this method to micro-pattern QDs directly onto a blue GaN LED array. These researchers summarize the unique advantages and potential impacts of the technology:
“The method involves using parylene as an intermediary layer, facilitating a dry lift-off procedure in which undesired QDs are mechanically removed without the use of additional solvents. The lift-off QDs can be reused. We achieved a pattern resolution close to 1 µm, which is limited by the capability of the equipment in the fabrication facility. Since the QDs are deposited as the final step and do not undergo any further processing, their photoluminescence properties and narrow linewidth are preserved, making this technique highly attractive for applications requiring precise and reliable patterning of solution-processed materials. Additionally, preserving the optical properties of QDs is crucial for their use in optoelectronic devices, where consistent performance and efficiency are essential.”
“We used this method to create single- and multicolor patterns successfully. The parylene coatings effectively shield the underlying QD films, allowing for the creation of multicolor converter patterns through repeated use of the usual photolithography technique. Furthermore, since the method is agnostic to the materials to be patterned, QDs of different types can be integrated, which was demonstrated by the successful integration of green perovskite QDs with red CdSe/ZnS QDs. The display industry has yet to reach a consensus on the optimum QDs. InP QDs are appealing for being non-toxic, and their optical quality has improved. The universality of the dry lift-off micro-patterning method can ensure agile adaptation to any adopted materials.
“Our results demonstrate the versatility of this method for high-resolution micro-patterned solution-processed materials. Its simplicity and effectiveness also make it a promising approach for large-scale manufacturing and integration of QD-based devices, potentially lowering production costs and increasing accessibility for various applications, such as micro-LED displays.”
Journal
Light: Advanced Manufacturing
Article Title
A Universal High-Resolution Micro-Patterning Technique for Solution-Processed Materials