A self-erasing chip for security and anti-counterfeit tech

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Self-erasing chips, developed at the University of Michigan, can help stop counterfeit electronics or issue warnings when sensitive shipments are tampered with.

Parag Deotare

Parag Deotare

They are using a new material that temporarily stores energy and changes the color of the light it emits. It extinguishes itself within a few days or can be extinguished with a flash of blue light if necessary.

"It's very difficult to tell if a device has been tampered with. It may work normally, but it can do more than it should and send information to third parties," said Parag Deotare, assistant professor of electrical engineering and computer science.

Che-Hsuan Cheng

Che-Hsuan Cheng

With a self-erasing barcode on the chip in the device, the owner could receive a notification if someone had opened it to secretly install a bugging device. Or, for example, a barcode could be written and placed on integrated circuit chips or printed circuit boards to prove that they were not opened or replaced in their travels. If the life of the barcodes were extended, they could also be written into devices as hardware analogs of software authorization keys.

Jinsang Kim

Jinsang Kim

The self-erasing chips consist of a three-atom-thick semiconductor layer on a thin film of molecules based on azobenzenes – a type of molecule that shrinks in response to UV light. These molecules in turn pull on the semiconductor, which causes it to emit slightly longer wavelengths of light.

To read the message, you need to look at it with the right kind of light. Che-Hsuan Cheng, a PhD student in materials science and engineering in Deotare's group and lead author of the Advanced Optical Materials study, is most interested in its use as a self-erasing invisible ink for sending secret messages.

This message self-destructs in seven days or can be erased with a flash of blue light. Written with UV light, the letters are characterized by molecules that shrink through energy storage and stretch the atoms of the semiconductor above. This shifts the light emitted by the semiconductor to longer wavelengths, which are represented in the visible spectrum by yellow on a blue background. Photo credit: Che-Hsuan Cheng, Exciton and Photonics Laboratory, University of Michigan.

This message self-destructs in seven days or can be erased with a flash of blue light. Written with UV light, the letters are characterized by molecules that shrink through energy storage and stretch the atoms of the semiconductor above. This shifts the light emitted by the semiconductor to longer wavelengths, which are represented in the visible spectrum by yellow on a blue background. Photo credit: Che-Hsuan Cheng, Exciton and Photonics Laboratory, University of Michigan.

The stretched azobenzene releases its stored energy naturally in the dark over a period of around seven days – a time that can be shortened by exposure to heat and light or extended when stored in a cold, dark place. Whatever was written on the chip, be it an authentication barcode or a secret message, would disappear when the azobenzene stopped stretching the semiconductor. Alternatively, it can be erased at once with a flash of blue light. Once erased, the chip can record a new message or a new barcode.

According to Deotare, the semiconductor itself is a “beyond graphene” material, as it has many similarities with the nanomaterial that was awarded the Nobel Prize. But it can also do something that graphene cannot: It emits light at certain frequencies.

The research team consisted of Jinsang Kim's group, professor of materials science and technology. Da Seul Yang, a PhD student in macromolecular and engineering sciences, designed and manufactured the molecules. Cheng then floated a single layer of the molecules on top of water and dipped a silicon wafer in the water to coat it with the molecules.

Then the chip went to Deotare's laboratory to be coated with the semiconductor. Using the “scotch tape” method, Cheng essentially taped a piece of the semiconductor tungsten diselenide and thus peeled off individual layers of the material: a sandwich of a single layer of tungsten atoms between two layers of selenium atoms. He used a kind of stamp to transfer the semiconductor onto the azobenzene-coated chip.

The next steps for research include increasing the amount of time the material can keep the message intact in order to use it as a counterfeit protection measure.

The research is funded by the Air Force Office of Scientific Research. Kim is also a professor of chemical engineering, biomedical engineering, macromolecular science and engineering, and chemistry.

The University of Michigan has filed for patent protection and is looking for commercial partners to bring the technology to market.

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