MicroLED is one of the hottest topics in the display industry today. The technology promises breakthrough performance and big acquisitions by some of the top brands in consumer electronics have led to lots of speculation about when we’ll see this technology in the market. The biggest unanswered question for microLED is whether or not the technology can be manufactured efficiently and at scale. Quantum Dots just might have the answer.

Dr. ZhongSheng Luo, Nanosys Director of Applications Engineering, joins as a guest blogger this week to share an update on Quantum Dot color converters for microLED displays.

Quantum Dot Color Converters for MicroLED Display

MicroLED displays have been getting a ton of attention in the past couple of years due to the technology's ability to provide a high peak brightness while consuming significantly less power than incumbent display solutions like LCD and OLED. However, manufacturing true RGB microLED displays requires a complex process which tends to cause a high defect rate, driving up costs and increasing time to market.

There are two ways to manufacture microLED displays: the heterogeneous approach or the monolithic approach.

Using the heterogeneous method, sometimes called “pick and place”, individual microLEDs are made separately, broken up into individual chips, picked up by a transfer tool and then placed onto a backplane. For the monolithic approach, RGB of microLEDs are grown together on a substrate and then transferred to a backplane in batches, without needing to be broken down into separate chips for each color.

Neither option is ideal. Even with the very best manufacturing tools either approach can make it quite challenging to achieve good yields across all three colors over the millions of RGB pixels required by today’s high resolution displays.

Pick and place manufacturing requires high precision over an incredible number of operations (think millions of pixels times three colors) where the tiniest of errors can lead to dead pixels. The monolithic approach suffers from the challenge of manufacturing three different colors of LED on the same substrate. Each color LED requires different manufacturing process conditions. Combining three together can lead to poor uniformity and compromised performance.

Heterogeneous Integration (Left) and Monolithic Integration (Right) - Images Courtesy of Yole Développment

Heterogeneous Integration (Left) and Monolithic Integration (Right) - Images Courtesy of Yole Développment

This is where Quantum Dots color converters come into play. Instead of mixing red, blue and green LED chips, Quantum Dots can be applied to a single color blue microLED array that is much simpler to make. Patterned, photo-emissive quantum dots can then convert blue light into both red and green at the appropriate sub pixel locations.

Quantum dots are not only able to provide the critical requirements of high color purity, fast response time, high efficiency and high stability for MicroLED displays, they are also tunable and compatible with the MicroLED manufacturing process. Quantum Dot color converters can also simplify the electrical driving system for the display.

Perhaps most importantly, Quantum Dot color converters can significantly reduce the defect rate that is associated with pick and place manufacturing. Below is an example showing that the combined transfer defect rate for an AR/VR display can be improved by 3X by using a Quantum Dot color conversion solution.

Assumptions: 4” diagonal, 450PPI, ~1.4M pixels or ~4.2M subpixels, 200k spread subpixel or 600k continuous pixels per transfer (constant transfer area). The productivity is also improved by 3x with color conversion solution.

Assumptions: 4” diagonal, 450PPI, ~1.4M pixels or ~4.2M subpixels, 200k spread subpixel or 600k continuous pixels per transfer (constant transfer area). The productivity is also improved by 3x with color conversion solution.

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Dr.ZhongSheng Luo is the Applications Engineering Director of Nanosys Incorporation. He obtained his Bachelor and Master degree in Materials Science and Engineering from Tsinghua University, China and his Ph.D in Materials Science and Engineering from University of California Berkeley, prior to starting his career in 2005 as an Applications Engineer. Dr.Luo began his career in Nanosys Inc. as a Sr. Technical Marketing Engineer in 2009 and became the Technical Marketing Manager in 2011. In 2012, he left Nanosys to lead the advanced product development activities for optical inspection equipment in KLA-Tencor Incorporation as a Principal Application Engineer. He rejoined Nanosys in 2015 as Director of Applications Engineering. Dr. Luo is also the General Manager for Greater China.

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