"We observe no visible degradation of the sample, which indicates that this sample would still be error free after 1 million years," the researchers stated.
The disk was then tested at up to 763 Kelvin (913F) for two hours, which caused some degradation.
Optical microscope images of the same QR code left: after fabrication, center: after two hours at 613 K and right: 2 hours at 763 K (Photo: MESA Institute and University of Twente)
As the temperature was increased, the top layer of silicon cracked and reduced the number of readable QR codes. While not readable by the QR code algorithm, the QR codes themselves were not "visibly" damaged and the tungsten was still present in the material. Overall, the QR codes lost about 7% of their readable data at higher temperature tests, the researchers said.
"The misreading of the information is caused by the readout using an optical microscope without a monochromatic light source. The images are taken using a top mounted camera and contain a multitude of colors, caused by the variation in [the silicon's] thickness due to the cracking," the researches wrote. "The very simple detection software was unable to correctly assign a black or white color to multitude of colors caused by the cracking of the top silicon-nitride layer."
The design of the disc. Each pixel in the large QR codes consists of a QR code. (Source: MESA Institute and University of Twente)
Sign up for MIS Asia eNewsletters.