Smart glasses are widely seen as a breakthrough technology because they will project digital information directly into an individual’s line of sight. Yet real world adoption has lagged, largely since the hardware required to power these displays has been bulky and impractical. A serious obstacle comes from classical optics, which suggests that shrinking efficient light emitting pixels right down to the dimensions of the sunshine’s own wavelength shouldn’t work.
Physicists at Julius-Maximilians-Universität Würzburg (JMU) have now overcome that barrier. Using specially designed optical antennas, the team has built what they describe because the smallest pixel ever created. The research group, led by Professors Jens Pflaum and Bert Hecht, reported the advance within the journal Science Advances.
A Full HD Display on One Square Millimeter
“With the assistance of a metallic contact that enables current injection into an organic light-emitting diode while concurrently amplifying and emitting the generated light, we now have created a pixel for orange light on an area measuring just 300 by 300 nanometers. This pixel is just as vivid as a traditional OLED pixel with normal dimensions of 5 by 5 micrometers,” says Bert Hecht, describing the important thing finding of the study.
For scale, a nanometer is one millionth of a millimeter. At 300 by 300 nanometers, these pixels are extraordinarily small. In truth, a projector or display with a resolution of 1920 x 1080 pixels could fit inside an area of only one square millimeter. Such compact dimensions could allow a display to be built directly into the arms of a pair of glasses, with the projected light directed onto the lenses.
OLED technology relies on multiple ultra thin organic layers positioned between two electrodes. When electricity passes through, electrons and holes recombine contained in the lively layer. This process excites the organic molecules, which then release energy as light quanta. Because each pixel produces its own light, no separate backlight is required. That design enables deep blacks, vibrant colours, and energy efficient performance for augmented and virtual reality (AR and VR) devices.
Why Shrinking OLED Pixels Is So Difficult
Simply cutting down existing OLED designs doesn’t work on the nanoscale. The Würzburg team found that electrical current doesn’t spread evenly when the structure becomes extremely small. “As with a lightning rod, simply reducing the scale of the established OLED concept would cause the currents to emit mainly from the corners of the antenna,” says Jens Pflaum, explaining the underlying physics. The gold antenna utilized in the device is formed like a cuboid measuring 300 by 300 by 50 nanometers.
“The resulting electric fields would generate such strong forces that the gold atoms becoming mobile would progressively grow into the optically lively material,” Pflaum continues. These thread like growths, often known as filaments, would keep extending until they created a brief circuit and destroyed the pixel.
Insulation Layer Prevents Short Circuits
To resolve this problem, the researchers introduced a precisely engineered insulating layer above the optical antenna. This layer leaves only a circular opening with a diameter of 200 nanometers at the middle. By blocking current from flowing in at the sides and corners, the design ensures stable and reliable operation of the nano light-emitting diode. Under these conditions, filament formation is prevented. “Even the primary nanopixels were stable for 2 weeks under ambient conditions,” says Bert Hecht, describing the result.
The team’s next goal is to spice up efficiency beyond the present level of 1 percent and extend the colour range to cover the complete RGB spectrum. Achieving those milestones would clear the trail for a brand new generation of miniature displays “made in Würzburg.” In the longer term, displays and projectors based on this technology could grow to be so compact that they’re nearly invisible when integrated into wearable devices, from eyeglass frames to contact lenses.