2.75GHz record bandwidth for GaN microLED
Scientists at the University of Illinois at Urbana-Champaign have achieved a world record modulation bandwidth of 2.75 GHz in a GaN blue microLED.
The work, just published in IEEE Electron Device Letters, provides a roadmap for the tiny emitters, showing how they can replace conventional electrical copper links to break energy and bandwidth bottlenecks in data centres and next-generation AI computing.
Optical interconnects offer a solution to the increasing demands of AI and high-performance computing, but key challenges remain in creating compact, high-performance light sources. MicroLED arrays are a promising candidate for creating massively parallel, error-free optical data links due to their compact footprint and potential for scalable integration.
The team, led by Can Bayram, tackled this challenge by designing and fabricating blue microLEDs across nearly two orders of magnitude, with diameters from 100µm down to a mere 2µm.
The team's analysis identifies the crucial sweet spots and limitations for future engineering, showing that aggressive scaling to the single-digit micrometer regime is the key. Their 5µm diameter device achieved the unprecedented record bandwidth of 2.75 GHz, while maintaining excellent linearity and stability under extreme current densities.
“By unifying modulation, linearity, and impedance measurements across such a vast scaling range, we have for the first time established a device-level roadmap for microLED transmitters in high-bandwidth optical interconnects,” said Bayram. “Our work not only sets a record but also provides a clear pathway for designers to create dense, low-energy optical channels in a compact footprint, dramatically reducing the packaging complexity of future optical networks for AI.”
The technical analysis, including Smith-chart measurements of RF power delivery, explained exactly why the standard, large-sized microLEDs were limited—primarily by junction capacitance. As they reduced the device diameter, this capacitance dropped significantly, enabling the record speeds.
However, they also identified a new critical challenge: further miniaturisation below 5 µm increases contact and current-spreading resistances, creating an impedance mismatch with standard 50-Ω radio-frequency systems. This critical insight defines the roadmap, identifying p-contact optimisation and other pad engineering as the next steps to unlock even higher performance.
They believe this work will break the data bottleneck by providing a roadmap towards dense, high-bandwidth optical links, ushering in the era of massively parallel optical communication for AI and high-performance computing.
