Description of the thesis topic

Energy management is one of the greatest challenges our society will face in the 21st century. It is on this challenge that the research activities of the proposed subject are positioned; the design of new power switches is essential: it is necessary to minimize losses, to ensure better management of electrical energy, to increase performance (breakdown voltage, current rating, efficiency) and robustness by improving the intrinsic characteristics of semiconductor devices. Wide bandgap semiconductor materials such as gallium nitride (GaN) are suitable candidates to address this challenge.
To date, GaN devices are overwhelmingly lateral devices with AlGaN/GaN heterostructures. Although manufactured on large silicon substrates and therefore low cost, these devices exhibit many limitations: low threshold voltages VTH, limited breakdown voltage BV (< 1 kV) and in trade-off with power density, high dynamic on-resistances, etc. This is the reason why it is essential to manufacture vertical devices that can withstand high voltages (> 1 kV) while maintaining a small surface.
It is within this framework that the VERTIGO project, funded by the “electronic” PEPR (Priority Research Programs and Equipment) of the “France 2030” investment plan, fits.
In this project, the task of the doctoral student recruited here will be twofold:
The first phase of this thesis work aims at the design by LAAS of vertical 1200 V power transistors in connection with the CRHEA and CEA Leti laboratories, in order to define the optimal stacking of the different GaN epitaxial layers and to propose device architectures compatible with the technological means of these two laboratories which will be in charge of the technological realization of the said devices. As the project aims to manufacture purely vertical devices, bipolar structures can also be evaluated by simulation in addition to unipolar structures (FET, MOS).
In a second step, elementary functions ("senseFET", anode voltage sensor, use of the vertical parasitic bipolar, isolation and integration of functions for close control, etc.) will then be developed to go towards a monolithic integration of power functions that allow to make the most of the performance of the material. In collaboration with the LAPLACE laboratory, taking close control into account will allow better optimization of the “device-control” system, in particular on the specification of the threshold voltage and the choice of design compromises.

Work Context

To respond to the climate emergency, society has initiated a major change in terms of resource management and energy consumption, in particular by adopting alternative energy sources in transport and in buildings, thus imposing major changes in the power electronics industry. This requires new generations of power devices and conversion architectures that should lead to optimizing energy management by reducing their size (mass, volume) and being as close as possible to the actuators (motor, turbine).
Wide bandgap semiconductors, in particular gallium nitride (GaN) with its exceptional electronic properties, must make it possible to produce these active devices operating in a harsh environment (high voltage, high temperature, high frequency, radiation). It is therefore essential to develop the technological sector specific to the realization of these power devices and functions.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Additional Information

This thesis will be carried out within the framework of the VERTIGO project financed by the “electronic” PEPR (Priority Research Programs and Equipment) of the “France 2030” investment plan.