Investigation of the Threshold Voltage Drift in Trench-Type 1200V SiC MOSFETs Under Bipolar Dynamic Gate Stress

Since the threshold voltage (V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf>) drift of Silicon Carbide (SiC) MOSFETs under dynamic gate stress (DGS) brought reliability concerns, this study investigated the threshold voltage drift of trench-type 1200 V SiC MOSFETs under the dynamic gate bias test. The V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> drift was monitored during stress lasting for over 6×10¹¹ switching cycles under different case temperatures (25 °C, 75 °C,125 °C, 175 °C) and different positive bias voltages (20 V, 21 V, 22 V, 24 V, 26 V). The influence of such a reliability test on the on-resistance and the breakdown voltage was also investigated. Results showed that the V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> drift under dynamic gate stress was positive. The drift decreased with increasing temperature but increased with higher positive gate bias. The on-resistance increased with the positive drift of the V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf>, while the breakdown characteristics of the device remained unchanged. Besides, the mechanism of the V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> drift behavior was further studied, focusing on the trench-type electric field reconstruction under dynamic stress. The V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> drift under dynamic gate stress, followed by cross-section analysis and TCAD simulation, provides insights to improve the understanding of dynamic reliability tests of SiC MOSFETs in power applications.