The World's Smallest Pixel is Available in Würzburg
Researchers in Würzburg have created an image element with an edge length of only 300 nanometers. This is approximately half the wavelength of light.
How about a high-resolution display in the temple of your glasses?
(Image: Iren_Geo/Shutterstock.com)
Researchers at Julius-Maximilians-Universität Würzburg (JMU) have built the world's smallest pixel. It emits orange light with a wavelength of 650 nanometers but has an edge length of 30 nanometers, making it only 90 square micrometers in size. (A nanometer is one millionth of a millimeter; a micrometer is one thousandth of a millimeter.) Theoretically, more than 3000x3000 pixels would fit into one square millimeter. This would not be achievable with classical optics.
Screens consist of many image elements, so-called pixels (picture elements). In modern screens, each pixel consists of a light-emitting diode that emits light waves. This is proven technology as long as the pixels do not need to be too small. If they shrink into the range of the wavelength of the emitted light, classical optics fail. The smaller the screen, the fewer pixels fit on it, and the lower the resolution becomes. For particularly small screens that are intended to have high resolutions at the same time, such as contact lenses with built-in screens, new approaches beyond classical optics are therefore required.
Tiny optical antennas, mostly made of gold, help here by concentrating light energy more precisely than any lens. However, optical antennas have a tendency to emit energy mainly at their corners. “The resulting electric fields would lead to such strong forces that the gold atoms would become mobile and grow piece by piece into the optically active material,” explains Professor Jens Pflaum from JMU. These outgrowths, called “filaments,” lead to a short circuit over time, destroying the pixel.
Insulation helps
The group of experimental physicists around Würzburg researchers Cheng Zhang and Björn Ewald has come up with a solution: insulation. The corners of the optical antennas are covered in such a way that only a circular opening of 200 nanometers in diameter remains open in their center. The antenna must emit its energy there. According to the researchers, filaments no longer form, which makes the tiny organic light-emitting diodes (OLED) durable. “Even the first nanopixels were stable for two weeks under normal room conditions,” says Professor Bert Hecht, impressed.
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At the same time, the tiny pixels shine brightly: 3,000 candelas per square meter (nits) exceed the brightness of current high-end smartphones like the Pixel 10. However, the efficiency is still very low at one percent. Furthermore, any desired color is currently available as long as orange is desired. JMU is continuing to work on these limitations with the goal of a new generation of screens “made in Würzburg.”
This lecture by Professor Paul Leiderer from the University of Konstanz, for example, provides information on the basics of optical antennas:
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In addition to Zhang and Ewald, the JMU research group includes Leo Siebigs, Luca Steinbrecher, Maximilian Rödel, Thomas Fleischmann, and Monika Emmerling. They work under the aegis of the aforementioned Professors Pflaum and Hecht. The report Individually addressable nanoscale OLEDs was recently published in the journal Science Advances.
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