Smart glasses are widely recognized as a breakthrough technology because they can project digital information directly into a person’s line of sight. However, in the real world, its adoption is slow. The main reason for this is that the hardware required to power these displays is bulky and impractical. The main hurdle comes from classical optics, which suggests that scaling down efficient light-emitting pixels to the scale of light’s own wavelength should not work.
Physicists at the Julius Maximilian University of Wurzburg (JMU) have overcome that barrier. Using a specially designed optical antenna, the team built what is described as the smallest pixel ever created. A research group led by Professors Jens Pflaum and Bart Hecht reported their progress in the journal Science Advances.
1 square mm full HD display
“With the help of metal contacts that allow current injection into the organic light-emitting diode and simultaneously amplify and emit the light produced, we created a pixel of orange light on an area of just 300 x 300 nanometers. This pixel is as bright as a conventional OLED pixel, which typically has dimensions of 5 x 5 micrometers,” says Bert Hecht, describing the key findings of the research.
On a scale, a nanometer is one millionth of a millimeter. These pixels are very small at 300 x 300 nanometers. In fact, a projector or display with a resolution of 1920 x 1080 pixels fits within an area of just 1 square millimeter. Such compact dimensions could make it possible to integrate the display directly into the arm of the glasses, directing the projected light to the lenses.
OLED technology relies on multiple ultrathin organic layers placed between two electrodes. When electricity flows, electrons and holes recombine within the active layer. This process excites organic molecules and releases energy as photons. No separate backlight is required as each pixel generates its own light. This design enables deep blacks, vibrant colors, and energy-efficient performance for augmented reality (AR and VR) devices.
Why shrinking OLED pixels is so difficult
Simply scaling down existing OLED designs will not work at the nanoscale. The Würzburg team discovered that when the structures become very small, the current does not spread evenly. “Similar to a lightning rod, if you simply reduce the size of an established OLED concept, the current will be radiated primarily from the corners of the antenna,” says Jens Pflaum, explaining the basic physics. The gold antenna used in this device is shaped like a cuboid measuring 300 x 300 x 50 nanometers.
“The resulting electric field will generate forces so strong that the now mobile gold atoms will gradually grow into an optically active material,” Pflaum continues. These thread-like growths, known as filaments, continue to stretch until they cause a short circuit and destroy the pixel.
Insulating layer prevents short circuits
To solve this problem, researchers introduced a precisely engineered insulating layer on top of the optical antenna. This layer leaves only a circular opening in the center, 200 nanometers in diameter. This design ensures stable and reliable operation of nano-light-emitting diodes by blocking current inflow at edges and corners. Under these conditions, filament formation is prevented. “Even the first nanopixels were stable for two weeks under ambient conditions,” explains Bert Hecht, explaining the results.
The team’s next goals are to increase efficiency beyond the current level of 1% and extend the color range to cover the entire RGB spectrum. Achieving these milestones will pave the way for a new generation of miniature displays “Made in Würzburg”. In the future, displays and projectors based on this technology could become so compact that they are almost invisible when incorporated into wearable devices ranging from eyeglass frames to contact lenses.
