Soft-switching power converters based on wideband-gap (WBG) transistors offer superior efficiency and power density advantages. However, at high frequencies, loss behavior varies significantly between different WBG technologies. This includes losses related to conduction and dynamic ON-resistance (RDS(ON)) degradation, also charging/discharging of input capacitance (CISS) and output capacitance (COSS). As datasheets lack such important information, we present measurement techniques and evaluation methods for soft-switching losses in WBG transistors which enable a detailed loss-breakdown analysis. We estimate the gate loss under soft-switching conditions using a simple small-signal measurement. Next, we use Sawyer-Tower (ST) and Nonlinear Resonance (NR) methods to measure largesignal COSS energy losses up to 40 MHz. Finally, we investigate the dependence of dynamic RDS(ON) degradation on OFF-state voltage using pulsed-IV measurements. We demonstrate an insightful comparison of soft-switching losses for various normally-OFF Gallium-Nitride (GaN) and Silicon-Carbide (SiC) devices. A p-GaN-gated device exhibits the most severe RDS(ON) degradation and the lowest gate loss. Cascode arrangement increases threshold voltage for GaN devices and reduces gate losses in SiC transistors; however, it leads to higher COSS losses. The study facilitates the evaluation of system losses and selection of efficient WBG devices based on the trade-offs between various sources of losses at high frequencies.
GaN transistors are being employed in an increasing number of applications thanks to their excellent performance and competitive price. Yet, GaN diodes are not commercially available, and little is known about their performance and potential impact on power circuit design. In this work, we demonstrate scaled-up GaN-on-Si Tri-Anode Schottky Barrier Diodes (SBDs), whose excellent DC and switching performance are compared to commercial Si fast recovery diodes and SiC SBDs. Moreover, the advantageous lateral GaN-on-Si architecture enables to integrate several devices on the same chip, paving the way to power integrated circuit. This is demonstrated by realizing a diode-multiplier Integrated Circuit (IC), which includes up to 8 monolithically-integrated SBDs on the same chip. The IC was integrated on a DC-DC magnetic-less boost converter able to operate at a frequency of 1 MHz. The IC performance and footprint are compared to the same circuit realized with discrete Si and SiC vertical devices, showing the potential of GaN power ICs for efficient and compact power converters.
Fig.1. (a) SEM image of a finger of the scaled up Tri-Anode SBD. The Anode contact is nanostructured into a Tri-Gate and Tri-Anode region. (b-c) Focused Ion Beam (FIB) cross-section of the Tri-Gate and Tri-Anode structure.
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