Comparative performance evaluation of conventional and superjunction vertical 4H-silicon carbide high-voltage power mosfets

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Torky, Mohamed
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Electronic thesis
Electrical engineering
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4H-SiC exhibits a 10× higher critical breakdown field than silicon, enabling its high-voltage power devices possible to achieve >1000x smaller specific on-resistance (RON,sp) than Si-based devices at the same breakdown voltage (BV). In addition, high-voltage superjunction (SJ) devices have better performance than conventional devices due to a lower drift specific on-resistance, reducing the conduction power loss. In this thesis, we comparatively evaluate 0.6-10kV-rated, vertical power DMOS and UMOS FETs with their SJ counterparts, in 4H-SiC, in terms of their static and dynamic switching performances. The static conduction loss of these transistors is estimated from the specific on-resistance, which is calculated using analytical expressions for each region. We utilize the specific total charge QT,sp for the dynamic switching power loss, extracted from TCAD (Sentaurus) simulations. Also, the turn-on time (ton), turn-off time (toff), and switching energy loss per cycle (Esw/cycle) are determined. The specific on-resistance is reduced by 89 and 78% for SJ UMOS and DMOS, respectively, compared to their conventional counterparts at 3.3kV due to higher pillar doping and lower drift layer resistance. The QT,sp reduction is reduced by 8 and 20% at all BV ratings. The lower RON,sp of UMOS devices is due to a higher channel density than DMOS devices, hence better RCH,sp. The turn-off time is higher for UMOS FETs because of higher QT,sp, hence, higher switching energy losses per cycle. Moreover, the SJ UMOS FET with the narrowest pillar width exhibits substantial reduction (up to 24, and 99 %) in our NFOM (RON,sp . QT,sp) compared to conventional UMOS FET at 0.6 to 10kV respectively because drift layer resistance dominates at high BV ratings. Meanwhile, the reduction is 30%, 30%, and 81% in SJ DMOS at the same breakdown voltage ratings. SJ UMOS has a higher switching losses due to a 67% higher QT,sp compared to SJ DMOS, but it has a significant lower 47% in RON,sp, achieving the lowest FOM, with a reduction of 53 to at least 31% compared to SJ DMOS FET at the same BV ratings respectively because the specific on-resistance of both devices approaches the same value at high BV ratings. In summary, the SJ UMOS FET has the best performance in terms of the lowest FOM among the SJ and conventional power MOSFETs compared, inferring to have the lowest total (conduction and switching) energy loss.
May 2022
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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