Teng Zhang soutient sa thèse le 13/12/2018 à 10:00.
Lieu : amphi Émilie du Châtelet (bibliothèque INSA).
Title : Contribution to condition monitoring of silicon carbide MOSSFET based power module
Jury :
- Rapporteurs : Jean-Guy Tartarin (LAAS, Toulouse), Jinshun Bi (Académie chinoise des sciences)
- Examinateurs : Marie-Laure Locatelli (Laplace, Toulouse), Sandrine Juillaguet (Charles Coulomb, Montpellier)
- Encadrement : Dominique Planson, Christophe Raynaud
Abstract :
Due to the increasing appeal to the high voltage, high temperature and high frequency application, Silicon Carbide (SiC) is continuing attracting world’s attention as one of the most competitive candidate for replacing silicon in power electric field. Meanwhile, it is important to characterize the defects in semiconductors and to investigate their influences on power devices since they are directly linked to the carrier lifetime. Moreover, reliability that is also affected by defects becomes an unavoidable issue now in power electrics.
Defects, including point defect and extended defects, can introduce additional energy levels in the bandgap of SiC due to various metals such as Ti, Fe or imperfect lattice itself. As one of the widely used defect characterization method, Deep Level Transient Spectroscopy (DLTS) is superior in determining the activation energy , capture cross section and defect concentration as well as the defect profile in the depletion region thanks to its diverse testing modes and advanced numerical analysis.
Determination of Schottky Barrier Height (SBH) has been confusing for long time. Apart from experimental measurement according to I-V or C-V characteristics, various models from Gaussian distribution of SBH to potential fluctuation model have been put forward. Now it was found that these models are connected with the help of flat-band barrier height . The Richardson plot based on along with the potential fluctuation model becomes a powerful tool for SBH characterization. SBHs with different metal contacts were characterized, and the diodes with multi-barrier are verified by different models.
Electron defects in SiC were studied with Schottky and PiN diodes, while hole defects were investigated under strong injection condition on PiN diodes. 9 electron levels and 4 hole levels are commonly found in 4H-SiC. A linear relationship between the extracted and log( ) indicates the existence of the intrinsic temperature of each defects. However, no obvious difference has been found related to either barrier inhomogeneity or contact metal. Furthermore, the electron traps near interface and fixed positive charges in the oxide layer were investigated on SiC power MOSFETs by High Temperature Gate Bias (HTGB) and Total Ionizing Dose (TID) caused by irradiation. An HTGB-assist-TID model was established in order to explain the synergetic effect.
Two carrier freeze-out regions were found near 40 K and 100 K that will degenerate the accuracy of tradition capacitance DLTS test. Meanwhile, certain defect concentration can be reduced by high temperature annealing, that is also a cause to the multi-barrier effect. Special attentions were paid on defects with tiny activation energy at extremely low temperature as well as the abnormal DLTS signal caused by negative-U centers. Irregular switch on DLTS transient (i.e. between capture and emission) is found related to width of detection zone in depletion region.
Future works are mainly focused on interface characterization as well as improvement on trapping models at low temperature. In addition, the stress effect especially introduced by the characterization method should be paid attention as well.
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