OLED microdisplays: bright, high-contrast and ultra-low power

Wearables, diagnostic equipment, or sensor technology – microdisplays can be found in a multitude of applications. Thanks to OLED technology, these solutions are energy efficient and deliver high contrast, making smaller and smaller displays possible.

M.Eng. Philipp Wartenberg knows all about microdisplays and their shrinking size and their many potential applications. In this COMPAMED-tradefair.com interview, the Head of IC and System Design at Fraunhofer FEP talks about the Institute’s new OLED stacks and reveals their importance for the microdisplays.

Mr. Wartenberg, the OLED microdisplay family has grown. In what way are the "new family members" expanding your portfolio?

Philipp Wartenberg: The ultra-low power OLED microdisplay family was previously only available in monochrome. Now versions in dual-color and the whole palette of their mixed colors are being added to the mix. Compared to the monochrome version, the number of pixels (pixel density) has been doubled, meaning the pixel size has been cut in half in this setting. The extended color display delivers more applications for the ultra-low power microdisplays. Examples include image rendition pertaining to thermal cameras. The applications benefit from low power consumption because of their longer battery runtime or smaller batteries. It facilitates lighter and more portable systems, making them ideally suited for wearables.

How does the development of the new OLED stacks impact the displays?

Wartenberg: New OLED stacks expand the possible applications of microdisplays because they can affect their characteristics significantly. They impact the color fidelity, color gamut, brightness, and lifetime of the microdisplays, just to name a few aspects. A clever combination of different materials allows you to construct displays that also emit in the near infrared (NIR) range and can therefore be used for multispectral, structured imaging systems with visible and NIR radiation. This includes applications in medical technology, biology, and automation.

You also develop customized solutions. Which applications or areas do the microdisplays cover in this context? Are there other conceivable options?

Wartenberg: Apart from the aforementioned applications, microdisplays are an essential component of VR/AR and MR glasses. They can also display navigation instructions in bicycle and motorcycle helmets, not to mention their use in industrial applications in the logistics, plant maintenance, and assembly areas. Since these are microchips, we can integrate other functions, such as sensor components. This also makes intelligent microdisplays possible, an example of which is our bi-directional microdisplays. Aside from the display, they also contain a camera function, which makes them attractive for a variety of applications, including medical diagnostics and therapy. Industrial applications are another area, but also security equipment where they double as high-precision optical fingerprint sensors.

Here are a few concrete examples: amid a pandemic, a combination of heat sensor and display technologies can indicate to the nursing staff whether a patient has a fever; the integrated sensors in the bi-directional microdisplay can be used as an eye-tracking system, which helps to overcome physical barriers to communication. In metal welding processes, the technology enables a welder to track the thermal image at a weld seam. All these are examples of the vast potential of microdisplays as near-to-eye applications.

What are the smallest microdisplays in the FEP portfolio and how much smaller can they still get?

Wartenberg: The size of a microdisplay is always based on the respective application and parameters like resolution – meaning the number of pixels a screen can show – and pixel size, which is specified by the optics and CMOS technology. It also plays a role whether it is a monochrome display, meaning it only requires one (sub)pixel, or a colored display, which typically requires a red, green and a blue subpixel. We conduct research from different angles at the Fraunhofer FEP. Apart from the trend towards ever smaller pixel sizes, this also includes research into highly efficient and application-adapted CMOS-integrable light sources, innovative, highly integrated CMOS circuits and system-on-chip (SoC) solutions, and the development of customer and application-specific microdisplays and processes.