Manuel González Sentís, third year PhD student at IRT Saint Exupéry won the “session 2” prize during the « Journées CNES des Jeunes Chercheurs » for his thesis in 180 seconds about a new material in satellites.
Journées CNES des Jeunes Chercheurs
The contest of JC2 2018 (Journées CNES des Jeunes Chercheurs) took place in Toulouse, at Cité de l’Espace, from 10th to 13th of October. This was an opportunity for a hundred PhD students, interested in spatial activities, to present their work. Seven sessions have come and gone about invention of tomorrow’s spatial techniques and their uses. These sessions combined three minutes speeches and coffee-discussion more detailed around posters sessions and interaction with the public.
Manuel won the second session with his thesis entitled: “Characterization and modeling of failure mechanisms of GaN power transistors”
THESIS SUBJECT
“Characterization and modeling of failure mechanisms of GaN power transistors”
ABOUT HIS THESIS
The main purpose of Manuel’s thesis is to identify the electrical signature of each failure mechanisms specific to GaN devices and then, to try to find out the stress that activated each failure mechanisms.
Manuel conceived his thesis around Féline (Fiabilité ÉLectronique INtEgrée) project, which bring together industrials and academics actors like Airbus, Thales, the IETR Rennes, the IMS Bordeaux, and the LAAS-CNRS. This project focuses on robustness of electronic components and it aims to predict the fiability of components and electronic cards in an operational environment. Feline has 4 important issues: improve methods to calculate components fiability, model and characterize effects of cosmic radiations, and finally reduce costs of reclassification electromagnetic computability.
Within this framework, Manuel has been looking at the use of new materials in satellites’ energy costs uses. To overcome environment disadvantages in space (as radiation or temperature) power transistors should be equipped with components more reliable, efficient, and robust to ensure the proper functioning of the satellite throughout its mission. So far, the semi-conductor used, the Silicium, has limited physic characteristics regarding spatial missions constraint:
- Electronic components are damaged by the accumulated dose of radiation
- Active components are deficient because of solar wind particles
- Single Event Upsets (SEU) are caused by high energy protons and cosmic radiations
- Panels power decreases because of the radiation damages
Thus, the alternative would be to substitute the Silicium for the GaN, a new material for electronic, composed with Galium and Azote. The GaN has an intrinsically robustness to radiations and works in extreme temperatures. Its low intern resistance reduces losses and then, increase its efficiency. GaN allows a strong power integration thanks to its critical electric field and its high current density. Then, its switching frequency makes it possible to design lighter and more compact energy converter.
However, during his study, Manuel has been experiencing one main difficulty. When designing his ageing bench, he discovered specific failure mechanisms in GaN components, which don’t appear in the classical Silicium components: the trapping effects. Studying those effects is not an easy task because these transistors effects are really quick (microsecond) with high variations of current and tensions. Therefore, these effects decrease the energy converters’ high frequency efficiency .
Furthermore, Manuel also found a gate leakage current and a significant threshold voltage drift in aged components in his ageing bench.
Nevertheless, large-scale deployment of GaN HEMT remains limited. The aim of his thesis is to study the GaN devices specific failure mechanisms, which is unavoidable to use those devices in harsh environment under specific mission conditions.