Thermal management characterization for 4H-SiC power devices: modeling, optimization, and analysis.

The growing demand for efficient and reliable power management solutions in electric vehicles has led to the emergence of innovative technologies based on silicon (Si) and silicon carbide (SiC). These semiconductor materials offer significant advantages, such as high electrical resistance, excellent thermal conduction, and the ability to operate in high temperature environments. The above features make them ideal for high-power applications, including inverters, high-speed on-board chargers based on high-performance MOSFETs and diodes. For example, on-board chargers face peculiar thermal challenges in order to ensure reliability and durability in the automotive framework in the presence of harsh environments. Power losses can occur during the switching phase in the circuit and can cause a significant temperature rise inside the cabinet, compromising the all system lifetime. Therefore, it is essential to develop effective thermal strategies to manage and dissipate the heat generated during the operation of chargers. During the thesis work, a scalable fast charger solution for automotive applications, capable of managing a power flow of 7 kW, was studied and proposed. In order to accurately assess the high temperatures reached by the active silicon and silicon carbide devices during normal operation, at steady state and at the maximum permissible power, an extensive thermal simulation using COMSOL Multiphysics will be conducted. COMSOL Multiphysics is a sophisticated simulation software that provides an advanced modeling environment very suitable for addressing the study of the thermal behavior of Si and SiC devices in the proposed charger. Using the software, it will be possible to evaluate the overall thermal performance of the system and get the heat dissipation and temperatures reached inside the devices in different operating conditions. The model obtained can be used to evaluate the reliability and lifetime of the inverter. To support the market requirement, the production of ever greater volumes of SiC devices is required. This point is reflected in the production process which requires to be optimized not only to obtain high devices performance, but also to optimize production yield and thus satisfy market demands. Among the different steps involved in the device production, we focused on the Wafer Level Annealing (WLA) technique that is largely was explored in order to study the thermal stability of 4H-SiC silicon carbide substrates. This represent a thermal process which take place after the growth of SiC substrate before epitaxy. WLA involves controlled treatments at temperatures below 1600 ºC in the argon atmosphere. Using some characterization techniques such as Micro-Raman spectroscopy, atomic force microscopy and Electrostatic Force Microscopy. It will be possible to study the effect of heat treatments on the crystallographic structure of SiC substrates. Special attention will be paid to the graphitization process that can occur during heat treatments, which leads to SiC devices failures. The above represents a small contribution to the progress of power applications based on silicon carbide technology and may suggest a path to new innovative solutions in the field of power management in electric vehicles. This will contribute to the advancement of power applications based on silicon carbide technology and pave the way for innovative new solutions in the field of power management in electric vehicles.