Discrete GaN power electronic devices have already demonstrated their disruptive potential by significantly improving power system performance while reducing size. These components contribute to sustainable energy solutions by enhancing efficiency and minimizing material usage. With proven robustness against heavy ion and neutron radiation, p-GaN enhancement mode HEMTs enable groundbreaking innovations for space applications.
The EleGaNT project tackled three key challenges limiting the full potential of GaN technology for Point of Load (PoL) converters:
1. Reducing parasitic inductance through monolithic integration of drivers and power devices (GaN-IC).
2. Optimizing passive inductive components alongside active devices to enhance efficiency and power density.
3. Strong interaction between PoL converter design and GaN-IC design, ensuring seamless integration and improved performance.
The project plays a crucial role in strengthening Europe’s technological sovereignty by developing a non-dependent supply chain for GaN-IC technology, which has been largely dominated by Asian and North American manufacturers. It pushes the state-of-the-art by achieving a higher level of integration.
Key Results and Achievements
1. GaN-IC Performance for Space Applications:
Two learning cycles were completed, covering IC design, wafer processing, and extensive validation. GaN-IC circuits successfully passed all radiation tests hence paving the way to meet space qualification standards. A high-current PoL converter prototype was developed and tested 28V input / 3.3V – 30A output / achieving 85% efficiencty @ 1 MHz switching. Another lower-voltage but still high-current PoL converter prototype demonstrated 91.44% efficiency (5V input, 1.5V output) such as to supply large digital cores and IO periphery.
Thanks to a high level of integration and dedicated PCB-embedded packaging, a power density of 5 kW/L has been achieved and the consortium is confident that this figure can be further increased.
PCB-embedded packaging has been successfully implemented to package the IC. This packaging solution can manage custom bare chips cost-effectively, which is advantageous for aggressively competitive markets like the new space sector.
Advantages:
• Low cost
• Utilizes an industrial process from a European company
• Exhibits high reliability, as demonstrated by tests and construction analysis after exposure to temperature variations
• Favorable thermal performance with a low Rth of approximately 4°C/W
• Lower impedance circuit connections.
This technology shows great promise: while the current design is relatively large, it has the potential for size reduction and the inclusion of components on top to enhance power density and provide low impedance circuit connections.
2. Inductor Optimization for Miniaturization:
Initially, sourcing an off-the-shelf inductor capable of handling currents exceeding 100A for single-phase high-current Point-of-Load (POL) designs proved challenging. The first iteration of the inductor design successfully met the required specifications. In the subsequent design phase, the objective was to reduce the inductor's size by lowering the saturation current, making it more suitable for multi-phase applications. This second inductor was benchmarked against a Coilcraft inductor previously used by Thales, demonstrating superior performance in terms of saturation and rated currents, as well as inductance value, albeit with a slightly larger package and land pattern.
3. Exploration of Terrestrial Applications:
At the project's outset, a multi-phase buck DC-DC converter was designed and implemented using off-the-shelf discrete GaN HEMTs, capable of handling up to 24V input and 25A per phase, achieving efficiencies up to 98%. This design demonstrated competitive performance compared to existing MOSFET-based solutions. Subsequently, a GaN-IC-based design was pursued by the end of the EleGaNt project. However, the target specifications were not met due to challenges in handling the chips at the embedding partner's facility. Consequently, the buck converter was tested only at 3.5V input and a few milliamps. The test vehicle's layout could potentially be improved to accommodate higher voltages and currents. These two trials with off-the-shelf GaN HEMTs and GaN-ICs enhanced the understanding of utilizing GaN technology in designs for terrestrial applications.
