Researchers Demonstrate Virus-Sized LEDs — and a TFT with Pixels Thinner Than a Human Hair

Researchers from Zhejian University and the University of Cambridge have taken the concept of display resolution to an absolute extreme, developing a monochrome display with pixels made up of LEDs around the same size as the width of a human hair — while demonstrating individual LEDs too small to see under even a powerful optical microscope.

"In this work, we report the downscaling of micro- and nano-PeLEDs [perovskite LEDs] with characteristic pixel lengths from hundreds of micrometres down to about 90nm," the research team writes of its breakthrough. "This translates to a pixel density of 127,000 PPI [Pixels Per Inch], a record among all classes of LED arrays. The devices are lithographically patterned to feature localized electrical contacts that define the active pixels and prevent non-radiative losses at the pixel boundaries."

The team's ultra-high-resolution prototype display — which, at 127,000 PPI, is around 240 times higher than a flagship smartphone — is based on thin-film transistor (TFT) technology, the same as powers many modern displays, but with scaled-down LEDs manufactured using crystalline perovskites. These, the researchers say, can deliver the same performance as traditional micro-LEDs but at a dramatically reduced manufacturing cost — and with the possibility to scale down to below 100nm, around the same size as a virus.

"The device architecture of the micro- and nano-PeLEDs consists of glass/indium tin oxide (ITO)/SiO₂/electron-transport layer (or hole-transport layer)/perovskite/hole-transport layer (or electron-transport layer)/metal electrode," the researchers explain. "High-quality micro and nano pixels with characteristic lengths down to about 90nm can be obtained. When the pixel length is reduced to about 100nm, the sidewall/pixel area ratio reaches 20%, approaching the limit of reliable fabrication using the method we developed."

To prove the concept, the researchers built the world's smallest LED display — by some considerable margin: each pixel measures 70×95μm, less than the width of a human hair. Separately, the team also proved that the concept scales by creating individual LEDs, in a variety of colors, measuring roughly the same size as a virus, as small as 90nm. Proving that these LEDs worked, though, was more of a challenge: an optical microscope, no matter how powerful, can't resolve objects the size of viruses, which meant the team had to employ more complex solutions: an Ocean Optics QE Pro spectrometer, to measure the light spectrum emitted by the LEDs, and a hyperspectral microscope.

While LEDs so small you can't actually see them may not seem that useful, the creation of the display — using existing commercial manufacturing technologies — shows that the idea scales; the team suggests that the PeLEDs could replace traditional micro-LEDs in devices like virtual and augmented reality (VR and AR) headsets to boost resolutions while bringing down production costs.

The team's work has been published in the journal Nature under closed-access terms.