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Green Electronics with Diamond Power Devices

Periodic Reporting for period 2 - GreenDiamond (Green Electronics with Diamond Power Devices)

Reporting period: 2016-05-01 to 2017-10-31

14 European research centers and firms coming from 6 European countries will during 4 years - May 2015 to April 2019 - develop diamond based power electronics devices. 3 to 30 times better than the actual used materials, diamond will enable to diminish loses, thermal requirements and the weight, through the higher blocking voltages, of the current devices and to enhance at the same time the overall reliability and performances.

Power electronics is used for more efficient renewable energy production and distribution including in highly-efficient electricity distribution over long distances via High Voltage Direct Current power lines (HVDC) as well as in the better control of loads in switching power supplies and variable-speed drives for motors that drive fans, pumps, and compressors. Even with state-of-the-art electric equipment, the transformation of the electrical energy occurs with significant losses (for example 9% in Spain from the source to the point of use), because available semiconductors aren’t ideal for high power. In future smart grids involving delocalised renewable energy sources, these energy losses become even more important, since power electronics are needed throughout the grid to monitor and control the ever-changing supply and demand of low-carbon electricity transiting through the grid. This is even more critical in the case of offshore wind farms where an efficient energy transportation technology, such as HVDC, is required.
The key to the efficient transmission and conversion of low-carbon electrical energy is the improvement of power electronic devices, which must be durable and reliable in high power high power environments to eliminate the need for auxiliary systems. “Green electronics”, i.e. highly efficient electronic devices are crucially important for our future energy system as they will increase the efficiency of electricity production and distribution with very disruptive gains expected at the system level. First estimation gives a factor of 4 improvement, ie 75% reduction in losses, representing about 10 MW energy saving on a 300 MW HVDC converter. They will also provide more flexibility, facilitating the introduction of variable and distributed sources of renewable energies into the grid.
Silicon is a well-established starting material that has addressed the requirements of energy conversion for more than 50 years. However, it is widely recognised (as shown in research roadmaps on power semiconductor devices) that a real step-improvement in Power Electronics will be obtained by employing devices based on wide bandgap semiconductor materials. Wide bandgap semiconductor materials have superior electrical characteristics for power devices when compared to silicon. Power electronic devices based on wide bandgap semiconductor materials will result in substantial improvements in the performance of power electronics systems by offering higher blocking voltages, improved efficiency and reliability, as well as reduced thermal requirements thus leading to realisation of more efficient green electronic systems. Among wide bandgap semiconductors, diamond is considered to be the ultimate semiconductor for applications in high power electronics due to its exceptional properties. Its dielectric breakdown strength is 3 times higher than in SiC and more than 30 times better than in Si. In addition, the carrier mobility is very high for both carrier types and the thermal conductivity is unsurpassed.

The objectives of the GreenDiamond project are therefore to fabricate the first high power electronic device in diamond that is competitive with existing wide-band-gap semiconductor technologies, and realise the first power converter using these diamond devices, opening new commercial and industrial opportunities. The GreenDiamond prototypes at 6.5kV and 10kV operating voltages based on Diamond MOSFETs will address the key requirements for low carbon energy power electronics applications:
- Lower power losses and more energy efficient operation in high voltage applications
- Novel more efficient power converter topologies (integrated switching cell)
- Enhanced thermal properties (lower losses at higher temperature) which will result in simplified thermal management and improved reliability in harsh operating environments
- Higher current density than Si, SiC or GaN transistors
- Higher voltage capability than Si, SiC or GaN transistors
- Compatibility with Si processes
- Improved reliability in harsh operating environment..
After 30 Months of work, we can mention the following achievements:
- The design tool of the diamond transistor is operational. That's the first ever design tool dedicated to diamond electronic devices. Models will be continuously improved all along the project taking into account experimental results, but results are already very good and accurate enough to design the first transistors.
- The best source of diamond plates for device fabrication as been identified. The main criteria were the crystallographic quality that was assessed mainly by X-ray topography at the European synchrotron with an exceptional sensitivity. This source expect to deliver 2 inches diamond plates in the future of high quality. The project starts with reduced size, but keeping in mind upscaling.
- Surface treatment before active layer fabrication have been identified, leading to low roughness and high crystallographic quality. Technology modules are still being studied, such as growth and epitaxy. The first transistor has not been fabricated yet.
- On the packaging side, key materials have been identified to allow high temperature et and reliability.
- Test set-up have been up-graded to be able to measure diamond transistors exceptional properties in voltage, current and switching time.
- Technology transfer to industrial partner was started, adaptation to industrial equipment is in progress
GreenDiamond will accelerate the development from TRL2 to TRL4 of promising technologies for Power Electronics with no negative environmental, resource or safety issues. The vision of the consortium is to enable
highly integrated, cost competitive and reliable diamond power electronics devices and components to improve functionality, reliability, and efficiency of next-generation, low-carbon components and systems.

Current technology has an efficiency of 96% (for Self-Commutated Voltage-Sourced Converters (SC/VSC)). According to a recent study based on Si IGBT devices, is reasonable to think that the future diamond MOSFET power converters would lead to an efficiency of around 99%, reducing losses by 75%. The use of GreenDiamond higher voltage devices would significantly reduce the quantity of the auxiliaries, leading to reduced losses, cost and physical space as well improved reliability. For offshore applications, the reduction of space (and weight) requirement will enable a much lower cost overall and, therefore, an attractive system solution.

The following impacts are thus expected from the successful completion of the GreenDiamond project:
- Increasing the reliability and operating lifespan of components
- Considerable improvement of power-electronic devices’ performance
- Reducing initial and maintenance costs
- Improving efficiency