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

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<sub>m</sub></i> ) and threshold voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V<sub>th</sub></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<sub>m</sub></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<sub>m</sub></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<sub>m</sub></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.

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Internal Bump Cracking Risk Assessment for Flip Chip Ball Grid Array Package During Board Level Reliability Test Through Finite Element Analysis

The performance of semiconductor devices during board-level reliability (BLR) thermal cycling tests continues to be a concern in different applications. The primary focus of those BLR tests is to evaluate the fatigue life of external solder joints between the package and printed circuit board (PCB). For flip-chip ball grid array (FCBGA) package technology, internal solder bumps can also crack and result in open electrical failure. This type of BLR failure has yet to be widely reported in the literature. This article presents failures due to internal solder bump cracks during the BLR test. Failure analysis (FA) clearly shows the cracking location strongly depends on bump density. Finite Element Analysis (FEA) based simulation is performed to understand the failure mechanism. Unlike the standard BLR modeling approach, which focuses on predicting external solder joint fatigue life with correlated data, simulation here has to capture the entire internal bump pattern in the global BLR model. The need to capture the entirety of the bump scheme poses a significant challenge to managing the global model size with a reasonable meshing count and running time. Therefore, a customized post-process approach is developed to analyze bump density impact and enable design optimization.

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