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True randomness, by inkjet printer

A microscale “memristor” with inkjet-printed electrodes offers an energy efficient and stable true random number generator for cryptography applications.

Using an atomically thin flake of boron nitride and printed silver electrodes, a KAUST-led international team of researchers has made a breakthrough in miniaturizing one of the key components of modern cryptography devices — the true random number generator (TRNG).

“TRNGs are important in data encryption where they are used to generate the keys to encrypt data before transmission by generating a stable stream of random numbers,” says KAUST’s Sebastian Pazos. “Current technologies integrate TRNGs into silicon chips in the form of large circuits that may require too much energy for some mobile applications.”

Memristors are resistive elements whose resistance can be changed by applying different voltages. These have been investigated as potential TRNGs because of the intrinsic randomness of how the atoms rearrange internally when the resistance changes. Yet inter-device variability and poor endurance and stability of the randomness over time have been intractable issues, and they have yet to be integrated with conventional circuits.

Pazos is part of Mario Lanza’s research group, which has been studying atomically thin layered materials as promising next-generation materials for applications such as memristors.

“We fabricated a memristor using a novel two-dimensional layered material called hexagonal boron nitride, on which we printed silver electrodes using a scalable, low-cost inkjet printing technology,” says Pazos. “The unique properties of the 2D h-BN are maintained after the electrode has been printed, enabling superior power and random signal generation.”

The team was pleased with the results. The experimentally fabricated device had the best performance ever reported for a TRNG in terms of stability of the random signal through time. It also had low energy consumption, easy circuit readout and high speed, with the ability to generate more than 7 million random bits per second.

“Furthermore, we demonstrated a built circuit that generates random numbers by interconnecting our memristor to a commercial microcontroller and making live experiments of random number generation on the fly,” says Pazos.

Pazos notes that the electronics used to implement the TRNG can be readily used in multiple low-power internet of things (IoT) applications, such as sensor node arrays requiring secure communication of data over wireless networks.

“Our scalable low-cost fabrication method using inkjet printing not only enables excellent performance but is key to the successful integration of these devices into low-cost complex electronics,“ Pazos says. “This work demonstrates the potential of 2D materials like h-BN to underpin a revolution in solid-state micro- and nanoelectronic devices and circuits owing to their outstanding electronic, physical, chemical and thermal properties.”

Pazos, S., Zheng, W., Zanotti, T., Aguirre, F., Becker, t., Shen, Y., Zhu, K., Yuan, Y., Wirth, G., Puglisi, F. M., Roldán, J. B., Palumbo, F. & Lanza, M. Hardware implementation of a true random number generator integrating a hexagonal boron nitride memristor with a commercial microcontroller. Nanoscale 15, 2171-2180 (2023).”

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