Micro-LED DUV maskless lithography; detecting counterfeit chips; two sides of GaN.
Researchers from the University of Science and Technology of China, Anhui GaN Semiconductor, and Wuhan University developed a vertically integrated micro-LED array for deep ultraviolet (DUV) maskless photolithography.
The team fabricated a DUV display integrated chip with 564 pixels-per-inch density that uses a three-dimensional vertically integrated device architecture with a AlGaN-based DUV micro-LED array and zinc oxide (ZnO)-based photodetector (PD) side-by-side via a transparent sapphire substrate. In this architecture, the UV photons emitted from the DUV micro-LED array can penetrate the transparent sapphire substrate and be captured by the PD on the backside of the substrate, enabling efficient optical signal transmission.
A self-stabilizing luminescence system with a closed-loop feedback control enabled the system to monitor fluctuations of the output light intensity of the micro-LED array and provided continuous feedback to ensure stable output power.
The team said their approach displayed a clear pattern on a silicon wafer after the maskless DUV photolithography, indicating potential in high-resolution photolithography technology. [1]
Researchers from Purdue University developed an optical counterfeit chip detection method that combines optical physically unclonable functions (PUFs) based on gold nanoparticle patterns embedded on chips with deep learning.
RAPTOR, or residual attention-based processing of tampered optical responses, is a deep learning approach that the team claims can discriminate between adversarial tampering and natural degradation, including the ability to detect malicious package abrasions, compromised thermal treatment, and adversarial tearing.
“The gold nanoparticles are randomly and uniformly distributed on the chip sample substrate, but their radii are normally distributed. An original database of randomly positioned dark-field images is created through dark-field microscopy characterization,” said Yuheng Chen, a doctoral student at Purdue, in a statement. “Gold nanoparticles can easily be measured using dark-field microscopy. This is a readily available technique that can integrate seamlessly into any stage of the semiconductor fabrication pipeline.”
“RAPTOR uses an attention mechanism for prioritizing nanoparticle correlations across pre-tamper and post-tamper samples before passing them into a residual attention-based deep convolutional classifier. It takes nanoparticles in descending order of radii to construct the distance matrices and radii from the pre-tamper and post-tamper samples,” explained Blake Wilson, a member of the Purdue team, in a statement. “We have proved that RAPTOR has the highest average accuracy, correctly detecting tampering in 97.6% of distance matrices under worst-case scenario tampering assumptions.”
The team plans to collaborate with chip-packaging researchers to further improve the nanoparticle embedding process and streamline the authentication steps. [2]
Researchers from Cornell University and Polish Academy of Sciences developed a dual-sided gallium nitride chip that combines its photonic and electronic functions simultaneously.
Gallium nitride (GaN) is used to make both power semiconductors and LEDs. “Gallium nitride (GaN) is unique among wide-bandgap semiconductors because it has a large electronic polarization along its crystal axis, which gives each of its surfaces dramatically different physical and chemical properties. The gallium, or cation, side has proved useful for photonic devices such as LEDs and lasers, while the nitrogen, or anion, side can host transistors,” noted Cornell’s David Nutt, in a press release.
Grown on a transparent GaN substrate, the device has a high electron mobility transistor (HEMT) on the nitrogen polar face that drives LEDs on the metal polar face. “To our knowledge, nobody has made active devices on both sides, not even for silicon,” said Len van Deurzen, a doctoral student at Cornell, in a release. “One of the reasons is that there’s no additional functionality you get from using both sides of a silicon wafer because it’s cubic; both sides are basically the same. But gallium nitride is a polar crystal, so one side has different physical and chemical properties than the other, which gives us extra degree in designing devices.”
To test and measure the device, the team assembled what they call a crude double-side-coated glass plate and wire-bonded one side of the wafer to it, which allowed them to probe both sides from the top. Because the GaN substrates were transparent for the entire visible range, the light was able to transmit through. The single HEMT device succeeded in driving a large LED, turning it on and off at kilohertz frequencies, sufficient for a working LED display.
Beyond LEDs, the researchers see this as a step toward enabling the convergence of photonic, electronic, and acoustic devices. [3]
[1] H. Yu, J. Yao, M. H. Memon, Y. Luo, Z. Gao, D. Luo, R. Wang, Z. Wang, W. Chen, L. Wang, S. Li, J. Zheng, J. Zhang, S. Liu, H. Sun, Vertically Integrated Self-Monitoring AlGaN-Based Deep Ultraviolet Micro-LED Array with Photodetector Via a Transparent Sapphire Substrate Toward Stable and Compact Maskless Photolithography Application. Laser Photonics Rev 2024, 2401220. https://doi.org/10.1002/lpor.202401220
[2] 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
[3] van Deurzen, L., Kim, E., Pieczulewski, N. et al. Using both faces of polar semiconductor wafers for functional devices. Nature 634, 334–340 (2024). https://doi.org/10.1038/s41586-024-07983-z
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