Materials Science Forum Vols. 717-720

Abstract: This paper aims to introduce a solid-state fault isolation device (FID) for the short circuit protection application in the power distribution systems. The key performance of a FID is to have a low on-state loss and a strong short circuit safe operating area (SCSOA). As a FID, a novel 15kV 4H-SiC field controlled diode (FCD) with a p+buried layer is proposed to provide an improved trade-off between the on-state forward voltage drop and the saturation current. Dynamic response to the fault and the application example of the proposed FCD are described in this paper.

Abstract: The process technology for the fabrication of 4H-SiC Static Induction Transistors (SITs) has been developed. Conventional contact UV lithography and self-aligned techniques have been employed. Al-outdiffusion following Rapid Thermal Annealing (RTA) has been determined as the cause for the increased reverse leakage and early forward turn-on of the gate-source junction. The fabricated transistors, exhibited a specific R_ON value in the region of 2mΩ•cm² and 80 V turn-off voltage.

Abstract: SiC power module with low loss and high reliability was developed by utilizing IEMOSFET and SBD. The IEMOSFET is the SiC MOSFET with high channel mobility in which the channel region is the p-type carbon-face epitaxial layer with low acceptor concentration. Elemental technologies for the high channel mobility and the high reliability of the gate oxide have been developed to realize the excellent characteristics by the IEMOSFET. The SBD was designed so as to minimize the forward voltage drops and the reverse leakage current. For the fabrication of these SiC power devices, the mass production technology such as gate oxidation, ion implantation and following activation annealing have been also developed.

Abstract: We present our recent developments in 4H-SiC power DMOSFETs. 4H-SiC DMOSFETs with a room temperature specific on-resistance of 3.7 mΩ-cm2 with a gate bias of 20 V, and an avalanche voltage of 1550 V with gate shorted to source, was demonstrated. A threshold voltage of 3.5 V was extracted from the power DMOSFET, and a subthreshold swing of 200 mV/dec was measured. The device was successfully scaled to an active area of 0.4 cm2, and the resulting device showed a drain current of 377 A at a forward voltage drop of 3.8 V at 25oC.

Abstract: We have investigated the thermal behavior of our recently developed 1200 V, 200 A 4H-SiC power DMOSFETs operating from 20°C up to 300°C. Compared to the first generation SiC DMOSFET that was commercially released early this year, this 4H-SiC power DMOSFET shows a ~ 50% reduction in the total specific on-resistance at room temperature. Temperature dependence of the key parameters of this MOSFET, such as on-resistance, threshold voltage, and the MOS channel mobility, are reported in this paper. The MOSFET showed normally-off characteristics throughout the entire experimental temperature range. Different temperature dependence of the total on-resistance in different temperature regimes has been observed.

Abstract: The trench gate structure MOSFET, with its lack of JFET resistance, is one of the structures able to achieve low on-state resistance [1,2]. In 2008, this group succeeded in fabricating 790V SiC trench MOSFETs with the lowest R_on,sp (1.7 mΩcm²) at room temperature. However these devices had issues regarding oxide destruction at the trench bottom during high drain-source voltage application. In order to improve this problem, this group developed the double-trench MOSFET structure. This structure has both source trenches and gate trenches. This paper compares two kinds of trench MOSFETs: the conventional, single trench structure and a double-trench structure. Also, the latest characteristics are presented.

Abstract: Significant advancement has been made in the gate oxide reliability of SiC MOS devices to enable the commercial release of Cree’s Z-FET™ product. This paper discusses the key reliability results from Time-Dependent-Dielectric-Breakdown (TDDB) and High Temperature Gate Bias (HTGB) measurements that indicate that the SiC MOSFETs can demonstrate excellent lifetime and stable operation in the field.

Abstract: A paradigm shift in the development and utilization of power semiconductor switch technology is proposed. This new "top down" approach begins with the field-reliability of a power semiconductor switch in a power converter circuit is subjected to long-term repetitive-switching under stressful field-operating conditions. This approach is derived from extensive field-reliability data collected on state-of-the-art silicon power MOSFETs in compact computer/telecom power supplies that clearly suggests that power MOSFET field-failures were primarily caused by bulk material defects. A careful survey of power switch technologies reported to-date in Silicon Carbide (SiC) and Gallium Nitride (GaN) further suggests that excessive bulk material defects have predominantly hindered the development and commercialization of cost-effective, high-performance, and reliable high-power devices. A reliability-driven approach is likely to "unlock" the vast potential of SiC (and GaN for moderate power levels) power device technology for high-voltage and high-power switching electronics in order to impact transformative changes.

Abstract: SiC power device is expected to have high breakdown voltage with low on resistance, which cannot be attainable for conventional Si device. This study evaluates the switching performance of high voltage SiC MOSFETs with comparing to that of conventional Si power MOSFET having equivalent breakdown voltage. To this end, turn-on and turn-off switching operation of MOSFETs are assessed with resistive load for same conduction current density. Though the on resistance of SiC MOSFETs are quite lower than Si MOSFET, especially for trench gate type. But, SiC MOSFETs have larger terminal capacitance. Therefore, SiC MOSFETs show slower switching speed than Si MOSFETs for same current density condition.

Abstract: Threshold voltage (VT) instability remains an important issue for the performance, reliability, and qualification of SiC power MOSFET devices. The direct application of existing reliability test standards to SiC power MOSFETs can in some cases result in an inconsistent pass/fail response for a given device. To ensure SiC MOSFET device reliability, some modifications to existing test methods may be necessary..