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Gate Oxide Reliability of 4H-SiC MOSFETs

Liu, Tianshi
http://rave.ohiolink.edu/etdc/view?acc_num=osu1650571907493669

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
SiC power MOSFETs have received increasing attention in electric vehicle (EV) applications. Due to the safety-critical nature and the operational lifetime requirement of the automotive industry, the long-term integrity of the gate oxides of SiC power MOSFETs is a primary concern. This dissertation evaluates the gate oxide reliability of recently manufactured commercial SiC power MOSFETs from various vendors. In addition, research work on the oxide lifetime evaluations and the failure mechanisms under different operating conditions is also included. We first analyze the gate leakage current behaviors and the corresponding failure mechanisms of recently manufactured commercial 1.2 kV SiC power MOSFETs under different oxide electric fields. Due to the effects of positive and negative charge trapping in the oxide, distinct gate leakage current behaviors are observed under different oxide electric fields. The threshold voltage shift measurements show that impact-ionization-induced hole trapping is the cause of the leakage current behavior and the primary failure mechanism under high oxide electric fields. We also show that the near interface oxide traps affect gate leakage current behaviors under different temperatures. When a significant amount of near interface oxide traps exist within the oxide, the breakdown voltage of the MOSFET decreases at elevated temperatures, and a "cross-over" phenomenon occurs. Therefore, gate leakage current measurements under different temperatures can be used as an indicator for gate oxide quality. Constant-voltage time-dependent dielectric breakdown (TDDB) measurements are applied to the commercial SiC power MOSFETs under moderate and high oxide electric fields. Different electric field acceleration parameters under different oxide electric fields are observed. The gate leakage current and threshold voltage shift measurements confirm that the impact-ionization-induced hole trapping is the cause of higher field acceleration parameters under high oxide electric fields. It is also demonstrated that a higher leads to lifetime overestimation under normal operating conditions. Therefore, constant voltage TDDB measurements must be performed at lower oxide electric fields to avoid hole trapping and establish more reliable lifetime predictions. The effects of surface defects on the gate oxide reliability and yield of large-area SiC power MOSFETs are also studied. Yield analyses are applied to defect maps of 6-inch commercial SiC n-type wafers. The results show that the defect density needs to be reduced to 0.2 cm-2 or lower to obtain more than 80% yield for manufacturing the 200A SiC power MOSFETs desired by the automotive industry. TDDB measurements are conducted on commercially available SiC power MOSFETs with different current ratings (i.e., different device areas). Degradation of oxide lifetime prediction and more spread-out oxide failure times are observed for the larger commercial power MOSFETs. Detailed discussion on the gate oxide screening process and the comparison of the gate oxide reliability between planar and trench SiC power MOSFETs are also included.
Anant Agarwal, Dr. (Advisor)
Hugh Urban, Dr. (Committee Member)
Wu Lu, Dr. (Committee Member)
Marvin White, Dr. (Committee Member)
Electrical Engineering

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Citations

  • Liu, T. (2022). Gate Oxide Reliability of 4H-SiC MOSFETs [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1650571907493669

    APA Style (7th edition)

  • Liu, Tianshi. Gate Oxide Reliability of 4H-SiC MOSFETs. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1650571907493669.

    MLA Style (8th edition)

  • Liu, Tianshi. "Gate Oxide Reliability of 4H-SiC MOSFETs." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1650571907493669

    Chicago Manual of Style (17th edition)

osu1650571907493669
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© , some rights reserved.Creative Commons License Gate Oxide Reliability of 4H-SiC MOSFETs by Tianshi Liu is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by The Ohio State University and OhioLINK.
Release 3.2.12