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

Abstract

Gate-oxide degradation is a concern in silicon carbide (SiC) MOSFETs especially in safety-critical applications such as aerospace and electric vehicles (EVs). To address this concern, this article presents an accurate gate-oxide degradation monitoring solution based on SiC devices’ transfer characteristics. Specifically, a plug-in circuit for gate driver is proposed to extract the transconductance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{m}$ </tex-math></inline-formula> ) and threshold voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{\mathrm{ th}}$ </tex-math></inline-formula> ) values from transfer characteristic. 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{m}$ </tex-math></inline-formula> ’s sensitivity to gate-oxide degradation and insensitivity to package degradation in kelvin-source discrete SiC MOSFETs. A simple circuit is proposed for on-board <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{m}$ </tex-math></inline-formula> measurement using the voltage drop on the common-source inductance of the MOSFET. The measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g_{m}$ </tex-math></inline-formula> is converted into digital pulsewidth, which can be easily measured using a microcontroller. A comprehensive comparison is presented to demonstrate the merits of the proposed method. Finally, the accuracy and sensitivity of temperature and aging measurements using the proposed method are validated experimentally.