Research Bits: June 17

Superlattice castellated FETs

Researchers from the University of Bristol and Northrop Grumman Mission Systems discovered a latch-effect in gallium nitride (GaN) that could lead to improved radio frequency device performance, crucial for enabling 6G devices.

“We have piloted a device technology, working with collaborators, called superlattice castellated field effect transistors (SLCFETs), in which more than 1000 fins with sub-100 nm width help drive the current. Although SLCFETs have demonstrated the highest performance in the W-band frequency range, equating to 75 gigahertz -110 GHz, the physics behind it was unknown,” explained Akhil Shaji, honorary research associate at the University of Bristol, in a statement. “We recognized it was a latch-effect in GaN, which enables the high radio frequency performance.”

The team utilized precision electrical measurements and optical microscopy to pinpoint the location where this effect occurred. “We also developed a 3D model using a simulator to further verify our observations,” said Martin Kuball, professor of physics and leader of the Centre for Device Thermography and Reliability at the University of Bristol, in a statement. “The next challenge was to study the reliability aspects of latch effect for practical applications. The rigorous testing of the device over a long duration of time showed it has no detrimental effect on device reliability or performance. We found a key aspect driving this reliability was a thin layer of dielectric coating around each of the fins. But the main takeaway was clear – the latch effect can be exploited for countless practical applications, which could help transform people’s lives in many different ways in years to come.”

Next steps for the work include further increasing the power density the devices can deliver. [1]

Compact phased-array transceiver

Researchers from the Institute of Science Tokyo, Panasonic, and Shinko Electric Industries designed an ultra-compact, low-power antenna-in-package 150 GHz radio module for 6G user equipment.

The eight-element module measures 8.4 mm by 20 mm, with 56 Gbps maximum data rates, 25.7 dBm effective radiated power, and 150 mW power consumption per element in transmission mode.

The radio module integrates a phased-array transceiver that uses an injection-locked tripling phase shifter, which eliminates the need for local oscillator buffers that can consume significant power and chip area. The design maximizes voltage amplitude while maintaining precise frequency control by connecting directly to a bi-active sub-harmonic mixer, which operates at half the local oscillator frequency and effectively cancels problematic oscillator leakage.

The researchers also integrated an antenna switch directly into the amplifier matching networks, which eliminated parasitic capacitance issues, minimized signal losses, and enabled sharing of power amplifier components between transmission and reception modes.

“While conventional modules using millimeter-wave bands have had maximum data rates of a few Gbps, this new wideband 150 GHz module enables high-capacity wireless communication at several tens of Gbps in mobile devices,” said Kenichi Okada, professor in the Department of Electrical and Electronic Engineering, Institute of Science Tokyo, in a press release. “Compared to conventional phased-array radios designed for 6G, this module achieves very high-power-density, making it suitable not only for base stations but also for compact, low-power terminal applications.” [2]

RF GaN-on-Si transistor

Researchers from imec built a gallium nitride (GaN) MOSHEMT on silicon device for high-efficiency 6G power amplifiers that achieved 27.8dBm (1W/mm) output power and 66% power-added efficiency (PAE) at 13GHz and 5V for an enhancement-mode (E-mode) device.

The result was obtained in a single device with an 8-finger gate layout, which provided the gate width needed for high output power without requiring the combined power of multiple transistors. The device combined a gate recess technique, used to shift the device into E-mode, with an InAlN barrier layer that offset the performance loss from the thinned channel.

In a separate module that was fully compatible with the E-mode transistor architecture, the team demonstrated a low contact resistance of 0.024Ω· mm using a regrown n⁺(In)GaN layer maximizing current flow and minimizing power loss.

“Reducing contact resistance is crucial for pushing output power while keeping efficiency high,” said Alireza Alian, principal member of technical staff at imec, in a release. “Our next step is to integrate this contact module into the E-mode transistor and validate the expected gains in power and efficiency, bringing the device closer to real-world 6G applications.” Simulations indicated that integrating the contact module could improve the output power density by 70%. [3]

References

[1] Kumar, A.S., Dalcanale, S., Uren, M.J. et al. Gallium nitride multichannel devices with latch-induced sub-60-mV-per-decade subthreshold slopes for radiofrequency applications. Nat Electron (2025). https://doi.org/10.1038/s41928-025-01391-5

[2] Y. Yamazaki, S. Park, T. Uchino, et al. A 150 GHz High-Power-Density Phased-Array Transceiver in 65nm CMOS for 6G UE Module. 2025 Symposium on VLSI Technology and Circuits https://www.vlsisymposium.org/wp-content/uploads/VLSI2025_Advanceprogram0611.pdf

[3] A. Alian, S. Yadav, R. ElKashlan, et al. High Power/PAE (27.8dBm/66%) Emode GaN-on-Si MOSHEMTs for 5V FR3 UE Applications. 2025 Symposium on VLSI Technology and Circuits https://www.vlsisymposium.org/wp-content/uploads/VLSI2025_Advanceprogram0611.pdf