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Asymmetrical substrate-biasing effects at up to 350V operation of symmetrical monolithic normally-off GaN-on-Si half-bridges

: Mönch, Stefan; Reiner, Richard; Waltereit, Patrick; Meder, Dirk; Basler, Michael; Quay, Rüdiger; Ambacher, Oliver; Kallfass, Ingmar


Veliadis, Victor (ed.) ; Institute of Electrical and Electronics Engineers -IEEE-; IEEE Power Electronics Society:
7th IEEE Workshop on Wide Bandgap Power Devices and Applications, WiPDA 2019 : October 29-31, 2019, Raleigh, North Carolina
Piscataway, NJ: IEEE, 2019
ISBN: 978-1-7281-3760-5
ISBN: 978-1-7281-3761-2
ISBN: 978-1-7281-3762-9
Workshop on Wide Bandgap Power Devices and Applications (WiPDA) <7, 2019, Raleigh/NC>
Fraunhofer IAF ()
gallium nitride; Power integrated circuits; HEMTs; half-bridges; substrates; substrate biasing effects

The work shows that the efficiency of symmetrical monolithic normally-off GaN half-bridges on semi-floating Sisubstrate depends on load current polarity, unlike discrete half-bridges. Discrete and monolithic half-bridges with intrinsic reverse diodes were characterized up to 350V in buck and floating-buck (or boost) converters, varying load current polarity but maintaining voltage and power. Asymmetric effects from negative substrate-to-source back-gate voltage during high-side conduction are observed, which reduce the channel current depending on its polarity: In buck converters, 1st quadrant high-side conduction is degraded by significantly reduced channel current below the gate. In a floating-buck converter, 3rd quadran thigh-side conduction current bypasses the degraded gate regionthrough an intrinsic reverse diode, flowing only through the drainaccess region, which showed lower degradation from negative back-gating. A duty-cycle independent substrate terminationnetwork is proposed to shift the average value of the floating substrate voltage towards positive values, avoiding static backgatingof the high-side transistor. It is shown how vertical bufferleakage at positive substrate voltages, which is not relevant for discrete transistors, limits the monolithic half-bridge’s operationvoltage. Operation of the monolithic normally-off GaN-on-Si half-bridge with semi-floating substrate in a floating-buck (instead of a buck) converter showed efficiencies above 98% at 200W and 200V.