Revolutionising short-circuit reliability
Engineers from China have demonstrated that the introduction of a thin AlGaN barrier can deliver a substantial hike in the short-circuit reliability of the GaN HEMT.
The III-N transistors produced by the team – a partnership between researchers at the University of Electronic Science and Technology of China, Sichuan Ai-Link Technology Company, and Shenzhen Pinghu Laboratory – withstand up to 12,000 repetitive short-circuit cycles at a bus voltage of 450 V. In comparison, commercial GaN HEMTs running under those conditions fail at the third cycle.
According to spokesman Qi Zhou, an affiliate of the University of Electronic Science and Technology of China, Shenzhen Institute of Advanced Study and UESTC, their devices’ robustness will help efforts to drive the, broader adoption of GaN power devices in high-reliability power-conversion applications.
Devices produced by Zhou and co-workers are strong on a number of fronts – they combine the exceptional switching performance and power density that GaN is renowned for with a level of fault robustness that’s comparable with established silicon and SiC technologies.
These assets will be welcomed by designers of motor drives, industrial inverters, UPS systems, renewable-energy converters, and electric-vehicle powertrains. In all these applications, short-circuit faults may occur during abnormal operating conditions, and power devices must withstand the resulting irregularities until system-level protection detects the fault and safely shuts down the device.
So crucial is the need for short-circuit capability that it’s part of standardised testing, says Zhou.
The team’s devices, fabricated from 150 mm GaN-on-silicon epiwafers, feature a 2 µm-thick GaN buffer, a 2.85 µm-thick AlGaN/GaN superlattice, a GaN channel, and an AlGaN barrier with a thickness of 11 nm. Processing produced HEMTs with a p-GaN length of 1.42 µm, a single gate field plate of 3.32 µm, and a source field plate length of 2.4 µm.
Zhou admits that this design may not appear that radical, since it relies on just reducing the thickness of the AlGaN barrier. “However, the underlying design is not simply a matter of making the AlGaN barrier thinner, because the barrier is closely coupled with the p-GaN gate and the overall device structure.”
Note that if the barrier is too thin, it could shift the threshold voltage, leading to a reduction in the available gate-control margin, as well as increases in gate-drive requirements and associated turn-on losses. “This is particularly important for enhancement-mode devices, where the threshold voltage must remain sufficiently positive to ensure robust normally-off operation,” says Zhou.
Another concern that can arise if the barrier is too thin is an overwhelming increase in the electric field across the gate stack. A stronger field may facilitate gate-current injection, potentially increasing static gate leakage and electrical stress on the gate structure.
Zhou and co-workers avoid all these issues, while still benefitting from a reduced barrier thickness that substantially enhances the transient gate current during a short-circuit event. “This distinction is central to our design: the objective is not to increase gate current indiscriminately, but to maintain low static gate leakage while obtaining a strong transient gate-current response during a short-circuit fault to provide the adaptive short-circuit protection to the device.”
Benchmarking of the team’s devices shows that they outperform 1.2 kV SiC MOSFETs and 650 V silicon power transistors.
One of the next goals for the team is to further optimise its AlGaN barrier and p-GaN gate structure, together with the relevant epitaxial and device parameters.
In parallel, efforts will be directed at systematically investigating the effects of gate resistance and gate-drive conditions on transient gate-current response and short-circuit behaviour.
Pictured above: The short-circuit capability of GaN HEMTs with a thin AlGaN barrier compare favourably with other forms of power device
Reference
N. Yang et al. IEEE Trans. Power Electron. (2026) To be published
