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Song, Qihao

Publications and source records attributed to Song, Qihao.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Output Capacitance Loss of GaN HEMTs in Steady-State Switching

The output capacitance (C OSS ) loss, a loss produced when the device’s output capacitor is charged and discharged, has become a concern for GaN high electron mobility transistors (HEMTs) in high-frequency applications. This work presents a new, easy-to-implement method for the C OSS loss characterization based on the unclamped inductive switching (UIS) setup. As compared to prior approaches, this method involves the device’s ON-state conduction and could measure the C OSS loss in a single pulse and the steady-state switching. The C OSS loss of three types of mainstream commercial GaN HEMTs is characterized, which exhibit some common dependencies including a non-monotonic relation with the dv/dt (or resonance frequency), a linear relation with the ON-state current, a power-law relation with the peak blocking voltage, and little temperature dependence. In addition, their C OSS losses all show minimal distinctions in a single pulse and the steady-state switching, despite the increased on-resistance in the steady-state switching. Furthermore, this suggests that the traps accounting for the C OSS loss possess different de-trapping time constants as compared to the traps governing the dynamic on-resistance. Finally, a unified model is established to describe the C OSS loss of all three types of GaN HEMTs. These results provide important references for the high-frequency application of GaN HEMTs and new insights into the physical origin of their C OSS loss.1

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DOE OSTI2023

2 kV, 0.7 mΩ•cm2 Vertical Ga2O3 Superjunction Schottky Rectifier with Dynamic Robustness

We report the first experimental demonstration of a vertical superjunction device in ultra-wide bandgap (UWBG) Ga 2 O 3 . The device features 1.8 μm wide, 2×10 17 cm -3 doped n-Ga 2 O 3 pillars wrapped by the charge-balanced p-type nickel oxide (NiO). The sidewall NiO is sputtered through a novel self-align process. Benefited from the high doping in Ga 2 O 3 , the superjunction Schottky barrier diode (SJ-SBD) achieves a ultra-low specific on-resistance (R ON,SP ) of 0.7 mΩ•cm 2 with a low turn-on voltage of 1 V and high breakdown voltage (BV) of 2000 V. The R ON,SP ~BV trade-off is among the best in all WBG and UWBG power SBDs. The device also shows good thermal stability with BV > 1.8 kV at 175 °C. In the unclamped inductive switching tests, the device shows a dynamic BV of 2.2 kV and no degradation under 1.7 kV repetitive switching, verifying the fast acceptor depletion in NiO under dynamic switching. Such high-temperature and switching robustness are reported for the first time in a heterogeneous superjunction. These results show the great potential of UWBG superjunction power devices.

Qin, Yuan↗
DOE OSTI2023

Origin of Soft-Switching Output Capacitance Loss in Cascode GaN HEMTs at High Frequencies

Output capacitance (C OSS ) loss (E DISS ) is produced when the C OSS of a power device is charged and discharged, which ideally should be a lossless process. This loss was recently revealed to be a crucial concern for GaN high electron mobility transistors (HEMTs) in high-frequency soft-switching applications. Among various GaN devices, the composite-type, cascode GaN HEMT was reported to show the largest E DISS with a voltage dependence distinct from discrete GaN HEMTs. However, the physical origins of the EDISS in cascode GaN HEMTs remain unclear. This work fills this gap by identifying three loss components and, for the first time, experimentally quantifying them in the multi-MHz resonant switching. These loss components include a) the avalanche loss of Si MOSFET, b) the intrinsic E DISS of GaN HEMT, and c) the Si avalanche-induced GaN turn-ON loss. The last component was found to dominate E DISS at high voltage. By eliminating the Si avalanche and the associated loss components (a) and (c), the E DISS of cascode GaN HEMTs can be reduced by up to 75% at the price of an increase in output charge and switching transition time. Furthermore, these results provide new physical insights and practical guidelines to trim the soft-switching loss of cascode GaN HEMTs in high-frequency applications.

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DOE OSTI2021

True Breakdown Voltage and Overvoltage Margin of GaN Power HEMTs in Hard Switching

This work studies the dynamic breakdown voltage (BV) and overvoltage margin of a 650-V-rated commercial GaN power HEMT in hard switching. The dynamic BV measured in the hard switching circuits is over 1.4 kV, being 450 V higher than the static BV measured in the quasi-static I-V sweep. The device can survive at least 1 million hard-switching overvoltage pulses with 1.33 kV peak overvoltage (~95% dynamic BV). Recoverable device parametric shifts are observed after the 1-million pulses, featuring small reductions in threshold voltage and on-resistance. These shifts are different from the ones after the hard-switching pulses without overvoltage and are attributable to the trapping of the holes produced in impact ionization. Furthermore, these results suggest that the BV and overvoltage margin of GaN HEMTs in practical power switching can be significantly underestimated using the static BV. Index Terms— GaN, HEMT, power electronics, hard switching, breakdown voltage, overvoltage, ruggedness, reliability.

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