The results obtain at the end of the project matches the specific objectives as described in section 1.1 of the DoA:
1. To develop simulation models and parameters suitable for analysis of diamond devices’ analysis.
This first objective has been achieved by WP2 mostly during RP2, and simulation has refined during RP3.
2. To fabricate Prototype MOS transistors in several stages 2028
The process is for the fabrication of the first Diamond MOS transistor in inversion mode, as in the proposal, has not been successful. In fact the process involves 7 main tasks carried out by at least 4 partners, ie p+/p- epitaxy (CNRS/NEEL-CEA), n epitaxy (IMEC-IAF), p+ epitaxy (CNRS/NEEL), etching (UCL-IAF). Each step was studied separately with good results. But the process flow for the full transistor fabrication involves 4 successive epilayers, and the accumulation of growth defects at the end of the epilayer growth process makes the etching impossible. No sample was obtained with sufficiently low defect at the surface, even after optimization of the process, to allow the V-shape etching.
To continue the research activity on the other work packages, we decided to replace the original diamond MOSFET by two other kind of transistors:
- Reverse Blocking MESFET. This transistor is requiring only one epilayer, with less challenging fabrication process. Expected power is much lower than the original MOSFET, but we kept the volage breakdown rating at 1kV. We did the design from scratch, then fabrication and test (WP2, 3, 4 and 5).
- SiC MOSFET. These transistors are already available commercially. Specific transistors have been chosen and integrated into the packaging and the converter to validate the design carried out in WP7, WP8 and WP9.
With this backup solution, GreenDiamond could continue its research activity towards diamond power electronics.
3. To design and develop high quality, cost-effective package solutions suitable for the robust operation of 6.52028kV and 10 kV rated devices under extreme conditions
This task is completed. The package type is SOT-227, and base plate, die-attach and topside interconnections have been developed and tested. Packaging is limited to 250°C, higher that all existing packaging, because of the lack of suitable encapsulant.
4. To develop reliability tests for normal and extreme operating conditions of the developed power devices 2028
The measurement probe stations and equipment are ready to measure any device or diamond transistor prototype.
5. To demonstrate a high voltage three-phase DC/AC high-power converter based on diamond devices 2028
A 30kV – 2W hybrid gate driver has been designed and a first prototype has been realized. Three possible topologies have been considered to deploy a HVDC or MV application. However, due to the lack of diamond power transistor, only a SiC based converter has been fabricated.
6. To disseminate the outcomes within EU and provide the foundation for industrialisation
Results have already been published and presented in scientific conferences.
The most important important event was organised just before confinement on March 22020 in Brussels. For the first time a meeting gathered companies, international bodies and academics to discuss about diamond power electronics for energy applications. In particular, for the first time a roadmap to the first industrial diamond power converter was presented, and 3 companies presented their views about the opportunities for diamond electronics for their company.
Very interesting ideas came up during the discussion time, in order to continue the research activity and transfer the technology to the companies.
Regarding the exploitation of the results, the most important is that R&D will continue toward diamond electronics, more efficient and reliable than any other technology. Activity will be reduced, or re-oriented towards other target (harsh environment signal processing electronics, aeronautics, …) because of the lack of suitable financial support. But activity will continue.
Another important element is that USA just started a 12M€ project for diamond power electronics. So technology will be developed and will emerge in the industry, led by USA or EU depending on the financial support GreenDiamond partners could obtain to continue this project at a larger scale.
