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Reference : UMR5005-HERMOR-002
Workplace : VILLEURBANNE
Date of publication : Tuesday, September 03, 2019
Scientific Responsible name : Dominique Planson
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 15 October 2019
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
With the fore-coming transition from fossil energies to renewable ones (solar and/ wind energies), new challenges arise alongside with the development of HVDC and MVDC networks able to carry the electricity on long distances.
Power converters must sustain voltages well above the 10 kV threshold and be able to carry several hundreds of amperes to be viable. The semiconductor transistor located at the core of the converter is then greatly strained. No matter the successive improvements, silicon is no longer a viable technology for this range of voltages and current densities so the whole power microelectronic industry has moved on to wide bandgap materials.
Among them, Silicon Carbide (SiC) is currently the most mature one but some technological developments still remain. The current trend is to pursue voltage driven device (MOSFET, IGBT) development. While those devices are becoming more and more reliable and competitive from the electrical performances stand point, some technological barriers cannot be overcome: the on-resistivity is dramatically increased with ambient temperature in the case of MOSFET. In such a situation, bipolar devices seem to be more appalling but most of them suffers from a non-negligible on-state threshold voltage (thyristor, IGBT). Plus, the SiC-IGBT processing steps are still complex by today's standards.
Therefore, the bipolar transistor (BJT) may be the best candidate. The thesis consists in developing a SiC high-power BJT. Its noticeable specificity is to be optically driven to simplify the driver design and to save power consumption.
The objectives of this thesis subject are to design, fabricate and characterize a > 10 kV SiC Optical Driven BJT.
The design will rely on literature about SiC physics and finite element simulations (Synopsys Sentaurus) to reach the target breakdown voltage (> 10 kV). Special care will be given to gain of the device in order to turn it on optically thanks to a custom optical window. For that purpose, the SiC optical model may be calibrated if necessary. Mask layout and fabrication must include the technological means available in clean room. The processing steps will carefully be chosen to include the optical window and to keep the device structure free of defects.
The device characterization (on die or packaged) is the crucial step to validate the optical triggering of the BJT while exhibiting a breakdown voltage above 10 kV. Optical and electrical characterizations will be performed to validate the Optical SiC BJT concept for high-voltage applications.
The thesis will be held mainly at the Ampère laboratory (www.ampere-lab.fr) in the electrical energy department, on its INSA Lyon site, Bât. Leonardo De Vinci.
The candidate will join a team of ten researchers and academic staff specializing in power components with wide bandgap (SiC, GaN, Diamond).
Some of the experimental tests, including optics could be done at ISL in the Mulhouse region.
Constraints and risks
Electrical risk training will be required.
This thesis will be realized within the framework of the project ANR HV-PhotoSw, Project-ANR-18-CE05-0020.
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