Gate-Oxide Degradation Monitoring of SiC MOSFETs Based on Transfer Characteristic With Temperature Compensation

Abstract

Gate-oxide degradation is a concern in SiC MOSFETs especially in safety critical applications such as aerospace and electric vehicles (EV). To address this concern, this paper presents an accurate gate-oxide degradation monitoring solution based on the SiC devices’ transfer characteristics. Specifically, a plug-in circuit for gate driver is proposed to extract the transconductance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g_m</i> ) and threshold voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_th</i> ) values from transfer characteristic. By using the threshold voltage as gate-oxide aging reference and transconductance as the junction temperature reference, the two precursors are combined to obtain a temperature and package degradation independent estimate of the gate-oxide health. High-temperature gate bias (HTGB) and DC power cycling tests are used to confirm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g_m</i> ’s sensitivity to gate-oxide degradation and insensitivity to package degradation in kelvin-sourced discrete SiC MOSFETs. A simple circuit is proposed for on-board <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g_m</i> measurement using the voltage drop on the common source inductance of the MOSFET. The measured <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g_m</i> is converted into digital pulse width, which can be easily measured using a microcontroller. A comprehensive comparison is presented to demonstrate the merits of the proposed method. Lastly, the accuracy and sensitivity of temperature and aging measurements using the proposed method is validated experimentally.