Research Bits: July 22

Sub-1nm gate

Researchers from Korea’s Institute for Basic Science, Sungkyunkwan University, Harvard University, and Korea Advanced Institute of Science and Technology (KAIST) found a method that enables epitaxial growth of 1D metallic materials with a width of less than 1 nm, which they used as a gate electrode of a miniaturized transistor.

The team controlled the crystal structure of molybdenum disulfide (MoS₂) at the atomic level using Van der Waals epitaxial growth to create mirror twin boundaries (MTBs) with a width of 0.4 nm in desired locations.

The channel width modulated by the electric field applied from the 1D MTB gate could be as small as 3.9 nm, the team demonstrated. They also found that a transistor based on the MTBs exhibited minimized parasitic capacitance due to its simple structure and extremely narrow gate width. [1]

Data storage metamaterial

Researchers from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), TU Chemnitz, TU Dresden and Forschungszentrum Jülich demonstrated that entire bit sequences can be stored in cylindrical domains measuring around 100nm.

“A cylindrical domain, which we physicists also call a bubble domain, is a tiny, cylindrical area in a thin magnetic layer. Its spins, the electrons’ intrinsic angular momentum that generates the magnetic moment in the material, point in a specific direction. This creates a magnetization that differs from the rest of the environment. Imagine a small, cylinder-shaped magnetic bubble floating in a sea of opposite magnetization,” said Olav Hellwig, a professor at HZDR’s Institute of Ion Beam Physics and Materials Research, in a statement.

Domain walls form at the edges of this cylindrical domain, where the direction of magnetization changes. Controlling the spin structure in the domain wall is key to using them for magnetic storage, since its clockwise or counterclockwise direction can be used directly to encode bits.

The team created a synthetic antiferromagnet using blocks of alternating layers of cobalt and platinum, separated by layers of ruthenium, and deposited them on silicon wafers. It has a vertical magnetization structure in which adjacent layer blocks have opposite directions of magnetization, resulting in a net neutral magnetization overall.

“This is where the concept of the ‘racetrack’ memory comes in. The system is like a racetrack, along which the bits are arranged like a string of pearls. The ingenious thing about our system is that we can specifically control the thickness of the layers and thus, their magnetic properties. This allows us to adapt the magnetic behavior of the synthetic antiferromagnet to enable the storage not only of individual bits, but entire bit sequences, in the form of a depth-dependent magnetization direction of the domain walls,” explained Hellwig in the press release.

Alongside the potential to overcome current data density limitations in magnetic storage devices, the approach could have applications in magnetoresistive sensors, spintronic components, and magnetic implementations of neural networks. [2]

Counterfeit chip detection

Researchers from Purdue University propose an optical anti-counterfeit detection method for semiconductor devices capable of detecting adversarial tampering features such as malicious package abrasions, compromised thermal treatment, and adversarial tearing.

A key challenge is determining when adversarial tampering has happened, or whether damage is due to natural degradation, such as physical aging at higher temperatures, packaging abrasions, and humidity impact.

The method relies on optical physical unclonable functions (PUFs) based on based on randomly patterned arrays of gold nanoparticles embedded on chips and a deep learning discriminator that uses residual, attention-based processing to extract the positions and radii of the gold nanoparticles in the random patterns and verify the authenticity of each pattern. The method was able to correctly detect tampering in 97.6% of distance matrices under worst-case tampering scenarios. [3]

References

[1] Ahn, H., Moon, G., Jung, Hg. et al. Integrated 1D epitaxial mirror twin boundaries for ultrascaled 2D MoS2 field-effect transistors. Nat. Nanotechnol. (2024). https://doi.org/10.1038/s41565-024-01706-1

[2] R. Salikhov, F. Samad, S. Schneider, D. Pohl, B. Rellinghaus, B. Böhm, R. Ehrler, J. Lindner, N. S. Kiselev, O. Hellwig: Multilayer Metamaterials with Ferromagnetic Domains Separated by Antiferromagnetic Domain Walls, Advanced Electronic Materials, 2024. https://doi.org/10.1002/aelm.202400251

[3] Blake Wilson, Yuheng Chen, Daksh Kumar Singh, Rohan Ojha, Jaxon Pottle, Michael Bezick, Alexandra Boltasseva, Vladimir M. Shalaev, Alexander V. Kildishev, “Authentication through residual attention-based processing of tampered optical responses,” Adv. Photon. 6(5) 056002 (17 July 2024) https://doi.org/10.1117/1.AP.6.5.056002