Correcting the Visual Quality of MicroLED Displays for Efficient Production

MicroLEDs continue to demonstrate their advantages for the display market as an ever-growing technology that is continually being incorporated into new product lines.

These minuscule light-emitting diodes (LEDs) are individual elements that typically measure below 100 µm—about 1/10th the width of a human hair—and some are even less than 3 µm. Their benefits over other display types include faster response times, higher brightness, and lower power consumption. MicroLEDs offer the potential for wider color gamut, higher contrast ratio, and deeper blacks than LCD (liquid crystal display) and OLED (organic light emitting diode) displays.

MicroLEDs equal OLED technology for view-angle performance and response time but surpass OLED in brightness and ruggedness while consuming far less power. These benefits are driving significant investment in the technology and pushing market forecast estimates up to 330 million units shipped by 2025.1

Correcting the Visual Quality of MicroLED Displays for Efficient Production

Image Credit: Radiant Vision Systems

As the demand increases for better and higher resolutions, microLEDs are positioned to be the next technology to breakthrough in various areas of the display industry. Their tiny LED size and reduced pixel pitch produce vividly clear images. Their appeal is especially desirable for manufacturers of devices such as smartwatches, augmented reality (AR), and head-up displays (HUD): displays where high luminance and resolution are critical for visual performance in small spaces, under variable ambient lighting conditions, or at close proximity to the eye.

Quality Challenge for Emissive Displays: Non-Uniformity

To achieve the full potential of microLED display technology, some challenges must be overcome in production. Assuring the quality and uniformity of emissive displays such as OLED and microLED is a difficult task since an individual diode is its own emitter, which is independently driven. Therefore, a display consisting of millions of microLEDs can present great variability in luminance and color.

Backplane for monolithic microLED displays, from Plessy Semiconductor (Image Source).

Backplane for monolithic microLED displays, from Plessy Semiconductor (Image Source).

This variability can lead to an inconsistent appearance (non-uniform color or brightness throughout the display) that is noticeable to the viewer. Thus, a display with uniformity issues cannot be sold. Whether measuring microLEDs at the singular wafer level after deposition onto a substrate or once positioned onto the display backplane of a consumer device, microLED manufacturers need an inspection approach they can depend on to measure and quantify microLED light and color output with great accuracy to permit correction and consequently increase yields.

Variable luminance creates a non-uniform appearance in this 0.7” microLED panel (Full HD, 1920x1080) with LED size of 2µm and pixel pitch of 8µm. (Image © Jasper Display Corp.).

Variable luminance creates a non-uniform appearance in this 0.7” microLED panel (Full HD, 1920x1080) with LED size of 2µm and pixel pitch of 8µm. (Image © Jasper Display Corp.).

A display metrology system must be able to precisely identify and measure the luminance (Lv) and chromaticity (CIE x,y or u’,v’) of individual pixels and subpixels; that is, each diode, to ensure microLED device quality. Radiant’s high-resolution, low-noise ProMetric® Imaging Photometers and Colorimeters demonstrate precision measuring of microLEDs, proven to acquire accurate and repeatable luminance and chromaticity values for every single microLED beyond the capacities of competitive measurement systems.

Firstly, isolation of each pixel takes place making them ready to be quantified utilizing image analysis tools in Radiant’s TrueTest™ automated visual inspection software. Subsequently, individual correction coefficients are then calculated and applied to each microLED ensuring an equal output and uniformed display appearance. Radiant’s image-based measurement systems offer pixel-level accuracy and precision manufacturers require to properly inspect and correct microLED displays to reach the necessary standards of product quality, enabling production efficiency to meet the demands of the market.

The same microLED display shown in the prior image now has uniform luminance after measurement and correction using a ProMetric® Y29 (29-megapixel imaging photometer) with Microscope Lens using TrueTest™ Software’s demura algorithms. (Image © Jasper Display Corp.).

The same microLED display shown in the prior image now has uniform luminance after measurement and correction using a ProMetric® Y29 (29-megapixel imaging photometer) with Microscope Lens using TrueTest™ Software’s demura algorithms. (Image © Jasper Display Corp.).

Case Study: Jasper Display

Jasper Display Corporation and other display innovators selected Radiant Vision Systems to enhance the visual quality of developing technologies like microLEDs. Utilizing Jasper Display’s MicroLED Starter Kit, Radiant’s advanced pixel measurement and uniformity correction (demura) solution provides manufacturers with an assist to accomplish their goals for effective microLED display development while securing perfect visual display quality.

The ProMetric Y29 Imaging Photometer with Microscope Lens attachment has been used effectively to measure and correct luminance uniformity of microLED displays.

The ProMetric Y29 Imaging Photometer with Microscope Lens attachment has been used effectively to measure and correct luminance uniformity of microLED displays. Image Credit: Radiant Vision Systems

Watch a video case study with Jasper Display Corporation to find out more about:

  • The impact of pixel-level measurement and uniformity correction (demura) on display quality and production efficiency
  • Non-uniformity challenges in emissive displays like microLED, miniLED, and OLED
  • How Radiant’s high-resolution ProMetric® imaging system and software are applied for high-speed and accurate demura of microLED microdisplays, like those manufactured using Jasper Display’s technology

Correcting the Visual Quality of MicroLED Displays for Efficient Production

Image Credit: Radiant Vision Systems

References

  1. MicroLED Displays, report from Yole Développement, February, 2017. Retrieved from: http://www.yole.fr/MicroLEDDisplays_Market.aspx

Acknowledgments

Produced from materials originally authored by Anne Corning from Radiant Vision Systems.

This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.

For more information on this source, please visit Radiant Vision Systems.

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