In Silicon Saxony, the German location with world-leading microelectronics and semiconductor manufacturers as well as research institutions, work is done every day on forward-looking innovations. Fraunhofer FEP, as part of this closely meshed network, is the leading institute for the development of customer- and application-specific microdisplays and sensors based on OLED-on-silicon technology.
The institute’s steady microdisplay developments in recent years have been driven by various requirements such as pixel density, energy efficiency, color, brightness or frame rate. Thus, Fraunhofer FEP created a wide variety of microdisplays in full color or monochrome from ultra-low power versions to high-resolution variants for use in augmented (AR) and virtual reality (VR) applications and other wearables.
The majority of microdisplays on the market are currently developed and manufactured on 200 mm wafers in 250 nm to 90 nm CMOS process nodes. At Fraunhofer FEP, these are also established design technologies in collaboration with various semiconductor manufacturers, depending on requirements and customer needs. The realization of microdisplays on 300 mm wafers has been rare so far. This is due on the one hand to technical reasons, such as the availability of suitable transistors for the corresponding control of the OLED, and on the other hand to economic reasons.
Independently of this, however, the market’s requirements for image quality, pixel density and integrated functionality are continuously increasing. For this reason, the Fraunhofer researchers have looked at the scaling effects in smaller CMOS technologies and investigated the use of 300-mm backplane processes as part of the “Backplane” project funded by the SMWA. In this context, the researchers have now succeeded in making the next major leap forward in development: For the first time, they realized an OLED microdisplay with tiny 2.5 µm pixels (corresponding to 10,000 dpi) at a display diagonal of 0.18 inch. This demonstrated the feasibility of developing displays based on 28 nm small-node technology on 300 mm wafers and realized the world’s smallest pixels of an OLED microdisplay.
Philipp Wartenberg, department head for IC and system design, explains about the new technology: “In small technology nodes, so-called small-node technologies, there is always the challenge of realizing the voltages required for driving in complex photonic systems. Thanks to an interdisciplinary research team and a completely new type of display architecture, we have succeeded in doing this for the first time in this project, while at the same time realizing extremely small pixels with a size of just 2.5 µm. With this very important development step, we will be able to offer our customers and partners even greater development scope in the future with an even higher resolution on a smaller surface area. In addition, the small-node technology enables novel control concepts that further reduce power consumption, which is important for mobile applications. We were able to demonstrate this, for example, through an on-demand, flexible drive method as well as a scalable architecture.”
The newly developed OLED microdisplays have a resolution of 1440 x 1080 pixels in monochrome or 720 x 540 pixels in full color. On the one hand, the flexible display architecture allows the refresh rate to be reduced to 0 Hz in extreme cases when the display content remains unchanged, thus avoiding all unnecessary data transfer – an enormous advantage for power consumption. Conventional displays require a minimum refresh rate here, regardless of content. On the other hand, the new microdisplay also allows frame rates of up to 480 Hz in extreme cases – internally even up to several kHz. This is made possible by a programmable sequence control in combination with a display-integrated frame buffer.
Depending on the design, the new displays can be used in lifestyle products such as sports glasses or as head-mounted displays in motorcycle helmets, in industrial scenarios for wearables in logistics or for remote maintenance solutions. The now even smaller dimensions pave the way to even more ergonomic systems.
On the part of Fraunhofer FEP, the new OLED microdisplays will be offered as evaluation kits to provide interested customers with access and testing opportunities for their own system integration and to enable joint customer-specific microdisplay developments with industry. They will also be presented live for the first time at the SID Display Week 2023, May 23-25, in Los Angeles, USA, at the German joint booth at Fraunhofer FEP, booth #1110, and in other presentations.
About the Backplane project.
Backplane – Deep-submicron CMOS process technology for driving integrated microdisplays and evaluation circuits of optical sensors.
Funder: Saxon State Ministry of Economics, Labour and Transport
Funding code: 100392259
Term: 31.12.2019 – 31.10.2022
Further links.
www.fep.fraunhofer.de
