Team aims world’s smallest QR code at long-term data storage

By shrinking a QR code to the size of a microbe, researchers from the Vienna University of Technology (TU Wien) and the German-Austrian start-up Cerabyte have shown that the future of the digital world could depend on ceramics, one of the oldest and most durable materials known to humans.

On December 3, the team secured a Guinness World Record for the world’s smallest QR code. Spanning just around 2 sq. micrometres, the code is about one-third the size of the previous record holder and smaller than a single bacterium. While the image is itself an achievement, the team’s methods also offer a new way for humans to store their digital legacy.

The project was led by Paul Mayrhofer, head of the Institute of Materials Science and Technology at TU Wien, along with researchers Erwin Peck and Balint Hajas. And they were motivated by data rot: the inevitable decay of magnetic and electronic storage media.

Current storage solutions like hard drives and magnetic tapes last around 10 to 30 years. They require a power supply to operate and be cooled, and need to have the data they store to be copied to new hardware to prevent loss. The TU Wien team explored ceramic-based storage as a permanent and zero-energy alternative.

To create the code, the researchers skipped traditional printing technologies in favour of atom-scale engineering, in particular a technique called focused ion beam milling.

They started with a glass substrate coated in a 15-nm-thick layer of chromium nitride, a ceramic typically used to coat industrial cutting tools because it’s very hard and excels at resisting heat and corrosion. Using a stream of electrically charged atoms as a knife, the researchers carved the QR code directly into the ceramic film.

Each individual pixel in the 29 x 29 grid measured only 49 nm. Because these pixels were roughly ten-times smaller than the wavelength of visible light, the code is physically impossible to see with a standard optical microscope. To verify the work, the team used a calibrated scanning electron microscope at the University of Vienna, which uses electrons instead of light to resolve small structures.

The effort also proved that ceramic storage could reach an information density of 130 bits per square micrometre, meaning a single A4-sized ceramic sheet could hold more than 2 TB of data. This is currently between the roughly 20 bits/μm² of LTO-9 magnetic tape and 1,500-3,000 bits/μm² of modern hard drives.

Unlike plastic-based tapes or magnetic disks, chromium nitride is chemically inert and physically stable and can survive fire, water, and millennia without degrading. And because the data has been etched rather than stored in a configuration of electromagnetic states, it doesn’t need power to persist, potentially sidestepping the need for data centres with large carbon footprints.

It does however require a powerful and expensive microscope to retrieve, although the team has said it’s developing high-speed laser writing and optical reading systems for industrial use for this purpose.

This feat is akin to Microsoft’s Project Silica, where researchers are encoding data in layers of glass using high-speed lasers, again with the aim of developing high-density data storage that can last for a long time.