Performance of Parallel Connected SiC MOSFETs under Short Circuits Conditions

Ruizhu Wu,Saeed Jahdi,Nereus Agbo,Simon Mendy,Jose Gonzalez,Olayiwola Alatise

doi:10.3390/en14206834

Abstract

This paper investigates the impact of parameter variation between parallel connected SiC MOSFETs on short circuit (SC) performance. SC tests are performed on parallel connected devices with different switching rates, junction temperatures and threshold voltages (VTH). The results show that VTH variation is the most critical factor affecting reduced robustness of parallel devices under SC. The SC current conducted per device is shown to increase under parallel connection compared to single device measurements. VTH shift from bias–temperature–instability (BTI) is known to occur in SiC MOSFETs, hence this paper combines BTI and SC tests. The results show that a positive VGS stress on the gate before the SC measurement reduces the peak SC current by a magnitude that is proportional to VGS stress time. Repeating the measurements at elevated temperatures reduces the time dependency of the VTH shift, thereby indicating thermal acceleration of negative charge trapping. VTH recovery is also observed using SC measurements. Similar measurements are performed on Si IGBTs with no observable impact of VGS stress on SC measurements. In conclusion, a test methodology for investigating the impact of BTI on SC characteristics is presented along with key results showing the electrothermal dynamics of parallel devices under SC conditions.

Highlights

This paper investigated the impact of variations in the threshold voltage, initial junction temperature and gate resistance on the sharing of short circuit (SC) current in parallel power devices
Current sharing in large current capacity power modules is more critical as the number of parallel devices increases
This paper shows that VGS stresses on the gate oxide of SiC MOSFETs at the rated VGS is capable of causing a change in the peak SC current and SC charge due to VTH shift

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In [15], the dependency of the short circuit performance of the SiC MOSFET on the turn-OFF VGS was investigated and the results showed that turning the device OFF with a higher negative. This paper contributes to the study of short circuits in parallel connected SiC MOSFETs by investigating the relative impacts of mismatch in (i) threshold voltage, (ii) MOSFET switching rate, and (iii) initial junction temperature. This was investigated for both planar and trench MOSFETs from three different device manufacturers.

Experimental Measurements for Short Circuits

BTI and SC Measurements

Findings

Conclusions