1322 IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 61, NO. 4, AUGUST 2019 Voltage-Dependent Capacitance Extraction of SiC Power MOSFETs Using Inductively Coupled In-Circuit Impedance Measurement Technique Zhenyu Zhao , Student Member, IEEE, Kye Yak See , Senior Member, IEEE, Wensong Wang , Member, IEEE, Eng Kee Chua, Senior Member, IEEE, Arjuna Weerasinghe , Zhenning Yang , Student Member, IEEE, and Wayne Chen Abstract—The voltage-dependent capacitances of silicon carbide power metal–oxide–semiconductor field-effect transistors (MOS- FETS) affect the switching characteristics and have a direct impact on the electromagnetic compatibility (EMC) performance of the power conversion circuit. To predict and mitigate the potential im- pact on EMC in the early design phase, the capacitances have to be obtained accurately. In this paper, a novel method is proposed based on an inductively coupled in-circuit impedance measurement technique. The proposed method extracts the voltage-dependent capacitances of a MOSFET under its actual biased voltage without making any direct electrical contact, and hence eliminates poten- tial safety hazards. Once the inductive probes are characterized, there is no need to re-calibrate the setup prior to each measure- ment, and therefore, it simplifies the whole measurement process. The accuracy of the extracted voltage-dependent capacitances for the SiC power MOSFET has been validated experimentally. Index Terms—Inductively coupled in-circuit impedance mea- surement, power metal–oxide–semiconductor field-effect tran- sistors (MOSFETs), silicon carbide (SiC), voltage-dependent capacitances. I. INTRODUCTION C OMPARED with conventional power semiconductor de- vices, wide-bandgap power semiconductor devices, such as silicon carbide (SiC) power metal–oxide–semiconductor field-effect transistors (MOSFETs), are gaining more popularity due to their lower ON-resistance, higher switching frequency, Manuscript received December 3, 2018; revised February 28, 2019 and April 6, 2019; accepted April 30, 2019. Date of publication May 15, 2019; date of current version August 13, 2019. This work was supported by the SMRT-NTU Smart Urban Rail Corporate Laboratory with funding support from the National Research Foundation, SMRT, and Nanyang Technological University under the Corp Lab@University Scheme. This paper was presented in part at the 2018 IEEE Symposia in Singapore/Long Beach, Singapore/Long Beach, CA, USA, July 30–August 3, 2018. (Corresponding author: Zhenyu Zhao.) Z. Zhao, K. Y. See, W. Wang, E. K. Chua, A. Weerasinghe, Z. Yang are with the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (e-mail:, zhao0245@e.ntu.edu.sg; ekysee@ntu. edu.sg; uscnuaa@gmail.com; ekchua@ntu.edu.sg; harshaya001@e.ntu.edu.sg; zhenning002@e.ntu.edu.sg). W. Chen is with SMRT Corporation Ltd., Singapore 179102 (e-mail:, wayne.chen@smrt.com.sg). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEMC.2019.2914704 higher blocking voltage, and higher rated junction temperature [1]–[4]. However, the higher switching frequency has led to undesirable oscillations at the rising and falling edges caused by the resonance of the interelectrode capacitances of the SiC power MOSFET and the circuit loop inductances [5]–[7]. Such oscillations can reduce the system’s reliability due to their as- sociated electromagnetic interference (EMI) [8], [9]. In order to predict and mitigate the negative effects in the early design phase, the capacitances have to be obtained [10]–[12]. Since the capacitances are voltage dependent [13], knowing their values over the entire voltage operating range is necessary. Several methods have been reported to obtain these voltage- dependent capacitances. One of them is applying the finite ele- ment method to extract the capacitances [14] but it requires the detailed geometrical structure and material information of the SiC power MOSFET, which may not always be readily available due to the intellectual property protection. Another method is to use an LCR meter or an impedance analyzer [15] but it requires many additional accessories, such as dc blocking capacitors, ac blocking inductors, resistors and, protection diodes. Time- domain reflectometry method has also been reported [13] but proper isolation is necessary to ensure the measurement setup be disconnected from the ground. Also, this method is only limited to obtain the output capacitance of the MOSFET. A multi-probe approach was also proposed [16] but laborious calibrations are necessary before each measurement, and its accuracy is highly dependent on the selected calibration resistors [17]. Besides the above-mentioned methods, a power device analyzer is also available in the market. It requires to connect a specific bias-tee to extract the voltage-dependent capacitances under high volt- age biasing conditions [18]. As the bias-tee has direct electrical contact with the high voltage dc power supply, added protection devices are necessary for safety hazard compliance. This paper proposes an alternative approach based on an in- ductively coupled in-circuit impedance measurement technique. The measurement setup of the proposed method has no direct electrical contact with the SiC power MOSFET that is biased with high dc voltage, and hence eliminates potential safety haz- ards without introducing additional protection devices. In ad- dition, the measurement setup is relatively simple and easy to implement. Furthermore, once the inductive probes are charac- terized, there is no need to re-calibrate the setup before each 0018-9375 © 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.