Hirokazu Asahara

Performance and reliability improvement in SiC power MOSFETs by implementing AlON high-k gate dielectrics

We have developed AlON high-k gate dielectric technology that can be easily implemented into both planar and trench SiC-based MOSFETs. On the basis of electrical characterization and numerical simulation, the thickness ratio of the AlON layer to the SiO2 interlayer and nitrogen content in AlON film were carefully optimized to enhance device performance and reliability.

Demonstration of 3 kV 4H-SiC reverse blocking MOSFET

The authors developed 3 kV 4H-SÍC reverse blocking (RB) metal-oxide-semiconductor field-effect transistors (MOSFETs) for the first time. To achieve reverse blocking capability, the n+-substrate layer was removed by polishing, and both a Schottky contact and edge-termination structure were introduced onto the wafer backside. Fabricated SiC RB MOSFETs exhibited good Schottky characteristics, and measured differential specific on-resistance was 20 mΩ·cm2. Both forward and reverse blocking voltages of RB MOSFETs are higher than 3 kV. On-state power loss of a developed RB MOSFET is 35% lower than that of anti-serially connected standard 3 kV SiC MOSFETs, demonstrating the advantage of the developed RB MOSFET as a high-voltage bi-directional switch.

Electrical Characterization of 1.2 kV-Class SiC MOSFET at High Temperature up to 380°C

Dynamic and static characteristics of SiC power MOSFETs at high temperature up to 380°C were investigated. Investigated devices have exhibited a behavior as a normally-off MOSFET even at such high temperature as 380°C. Temperature dependence of the MOSFET characteristics are reported in this paper, such as threshold voltage (VTH), on-resistance, internal gate resistance, and turn-on and turn-off losses (EON, EOFF). EON decreases and EOFF increases with increased temperature. Temperature dependence of switching losses is affected by transfer time of VDS, which was mainly determined from VTH.

Estimation of junction temperature at failure of SiC DMOSFETs in UIS test

Junction temperature of SiC DMOSFETs at device failure in unclamped inductive switching test has been estimated to be 960 K, and mechanism of the avalanche failure was discussed. The junction temperature was estimated from the extrapolation of temperature dependence of avalanche voltage. The estimated junction temperature was too low for SiC to behave as an intrinsic semiconductor, which suggests the failure occurred not in semiconductor, but in other materials such as oxides and electrode metals.

Reliability-aware design of metal/high-k gate stack for high-performance SiC power MOSFET

Advanced metal/high-k gate stack technology for SiC-based power MOSFET was demonstrated. We found that the Hf incorporation into aluminum oxynitride (HfAlON gate insulator) combined with TIN electrode effectively improves the stability of threshold voltage under both negative and positive bias temperature stresses. Since the relative permittivity of HfAlON increases with increasing Hf content, peak transconductance enhancement up to 3.4 times with acceptable reliability margin was achieved in the state-of-the-art trench MOSFET by implementing TiN/HfA10N(Hf50%) gate stack.

Investigation of thermal runaway of reverse-biased silicon carbide schottky barrier diode

SiC devices are expected to operate at much higher temperature than Si devices. However, commercially available SiC devices are limited to the temperature almost same as Si devices. In order to operate SiC devices at high temperature, it is necessary to improve package technology and to design SiC devices properly for high temperature. In this study, robustness against thermal runaway of SiC-SBD is evaluated. SiC-SBD with a heat-sink is thermally stable, and can operate even at Ta = 250 °C without thermal runaway.

High-Temperature Characteristics of 3-kV 4H-SiC Reverse Blocking MOSFET for High-Performance Bidirectional Switch

Novel 3-kV 4H-SiC reverse blocking (RB) metal–oxide–semiconductor field-effect transistors (MOSFETs) have been demonstrated for high-voltage bidirectional switching applications. To achieve RB capability, a series Schottky barrier diode structure was introduced onto the backside of the 4H-SiC MOSFET. The developed SiC RB MOSFET exhibits bidirectional blocking voltage over 3 kV and a differential specific on-resistance of 20

Cathodoluminescence Study of SiO2/4H-SiC Structures Treated with High-Temperature Post-Oxidation Annealing

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Flatband Voltage Shift Depending on SiO2/SiC Interface Charges in 4H-SiC MOS Capacitors with AlON/SiO2 Stacked Gate Dielectrics

cm2 at room temperature. In an inductive-load switching measurement, the RB MOSFET showed good turn-ON/-OFF characteristics at 1 kV. The bidirectional switch configured by the developed RB MOSFETs exhibited lower ON-state power loss than the series connection of the standard SiC MOSFETs at wide range of temperature and operation current, demonstrating the advantage of the SiC RB MOSFET as a high-performance bidirectional switch.

THIN FILM, METHOD OF FORMING THE SAME, AND SEMICONDUCTOR LIGHT-EMITTING ELEMENT COMPRISING THE THIN FILM

The radiative defect centers in thermally-grown SiO2/4H-SiC structures with high-temperature post-oxidation annealing (POA) in various ambient gas, i.e. Ar, H2, and NOx, were examined using cathodoluminescence (CL) measurement. It was found that radiative centers with an extremely high luminescent efficiency were remained at the SiO2/SiC interfaces after Ar-POA and FGA. Thus, these defect centers are very stable against high-temperature annealing and reducing ambient. In contrast, NOx-POA significantly reduced amounts of the radiative defects that might be related to channel mobility improvement in SiC-MOSFETs.