Masatoshi Aketa

High performance SiC trench devices with ultra-low ron

We have developed SiC trench structure Schottoky diodes and SiC double-trench MOSFETs. We succeeded in improving device performance by the reduction of the electric field through the introduction of the aforementioned trench structures. The threshold voltage of the trench structure Schottky diode is 0.48V smaller than the planar. Also, the lowest on-resistance in SiC MOSFETs was achieved.

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.

4H-SiC Trench Structure Schottky Diodes

This paper presents three different structures of Schottky diodes that were fabricated with low Schottky barrier heights. To reduce the forward voltage drop, the introduction of a lower Schttoky barrier is necessary. One of key issues associated with diodes having a low Schottky barrier height and a planar structure is an excessively high leakage current. By introducing the novel trench structure, the leakage current was reduced to a reasonable level. Furthermore it was confirmed that they have minimal switching time during turn-off and high avalanche capability. Thus trench structure Schottky diodes are able to reduce not only switching losses but also conductive losses and demonstrate sufficient robustness.

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.

High-performance SiC power devices and modules with high temperature operation

The expectation for SiC devices in advanced power electronics applications for saving energy has been still larger. The 4H-SiC planer MOSFETs with high blocking voltage (1300V) and large current (40A) were fabricated. In addition, we have succeeded in fabricating the larger current (300A) 4H-SiC trench MOSFET with low-on resistance (2.6mΩcm2). And, regarding high-temperature operation, SiC IPMs can be successfully fabricated by using a new bonding soldering method which can withstand even 400°C.

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.