Materials Science Forum Vol. 924

Abstract: Different methods for cross-section characterization of SiC Trenched-singly-implanted vertical junction field effect transistors (TSI-VJFETs) are presented with the purpose to determine the epitaxial structure in terms of doping topography.

Abstract: The threshold voltage of SiC JFETs has been determined from transfer characteristics by employing methods commonly used in the case of MOSFETs. The extracted values have been compared with the value determined from the fitting of experimental transfer characteristics with the Schockley model equation. Moreover, the variation of the extracted threshold voltage values with respect to channel width has been employed to determine the channel concentration without taking into account the V_bi value.

Abstract: External Schottky barrier diodes (SBDs) used as free-wheel diodes should be larger in higher voltage devices to avoid bipolar degradation consequent on current conduction of body diodes in SiC MOSFETs. By embedding an external SBD into an SiC MOSFET, we achieved compact 3.3 kV and 6.5 kV SiC MOSFETs that are free from bipolar degradation. The active area of the 3.3 kV/6.5 kV samples is only about a half/quarter of the total active area of a conventional MOSFET and a coupled external SBD.

Abstract: P-type implanted metal oxide semiconductor capacitors (MOSCAPs) and metal oxide semiconductor field effect transistors (MOSFETs) have been fabricated. The characteristics of hole trapping at the interface of SiO₂/SiC are investigated through capacitance-voltage (CV) measurements with different starting voltages. The negative shift voltage ∆V_shift and the hysteresis voltages ∆V_H which caused by the hole traps in the MOSCAPs and MOSFETs are extracted from CV results. The results show that the hole traps extracted from MOSCAPs are larger than the that extracted from the threshold voltage shift in the MOSFETs. It suggests holes trapping are the primary mechanism contributing to the NBTI, but not all the holes work. Part of the hole traps are compensation by sufficient electrons in the MOSFET structure.

Abstract: In comparison to silicon based devices, MOSFETs based on silicon carbide show more complex threshold voltage variations caused by positive and negative gate bias stress. We show that the majority of the voltage shift in standard JEDEC-like bias temperature instability measurements originates from stress independent measurement parameters like timing and switching conditions. A more sophisticated bias temperature instability measurement technique using device preconditioning is presented allowing for more accurate and nearly delay time independent extraction of the permanent voltage shift component within typical industrial timescales.

Abstract: To investigate effect of stacking faults (SFs) on switching reliability, we carried out switching tests using SiC-MOSFETs containing expanded SFs. Before the switching test, current stress was applied to the internal body-diode devices under test (DUTs) to expand SFs. The circuit configuration of the switching test we used was a half-bridge type and a double-pulse gate signal was applied to the lower arm DUT. The switching-voltage was 1.8kV and switching-current increased in about 8A steps to breakdown. Reverse recovery safety operation area (RRSOA) breakdown switching-current decreased dependently on the degree of SiC-MOSFET degradation. Reverse bias SOA (RBSOA) did not decrease even if degraded SiC-MOSFETs were used.

Abstract: A new class of power MOSFET, the vertical tri-gate MOSFET, is described and analyzed. The structure can reduce the 4H-SiC MOS channel resistance by up to an order-of-magnitude, producing the same benefit as if the mobility were increased by the same factor. In this paper we outline the fabrication procedure and describe the unit processes unique to this structure.

Abstract: This paper presents a 1.2kV-rated 4H-SiC Split-Gate power MOSFET (SG-MOSFET) with superior high frequency figures-of-merit (HF-FOM). Electrical characteristics including reverse transfer capacitance and gate-to-drain charge are measured from fabricated devices on a 6-inch SiC wafer, demonstrating excellent performance. Compared to the conventional MOSFETs, the SG-MOSFET provides about 7x smaller HF-FOM [R_onxC_gd] and 2x smaller HF-FOM [R_onxQ_gd] with improved reverse transfer capacitance and gate-to-drain charge.

Abstract: In this work, TCAD modeling of a 1200 V SiC MOSFET is presented. The main focus is on modeling of the channel mobility, and the Coulomb scattering by interface traps and surface roughness are therefore included. For the Coulomb scattering, the interface trap profiles have been extrapolated from the subthreshold characteristics at room temperature, whereas the scattering due to surface roughness has been fitted by comparing to the transfer characteristics at high gate bias. A comparison with measurements for the transfer characteristic and the output characteristic is also presented. Results show that the reduction of the threshold voltage with increasing temperature and the temperature dependence of the output characteristics are properly modeled.

Abstract: The behavior of silicon carbide power MOSFETs is analyzed using TCAD device simulations with respect to conduction and switching losses. Device designs with varying breakdown voltages are simulated. The contributions to the on-state resistance are shown at room and elevated temperature. Whereas channel and substrate resistance dominate at low breakdown voltages, drift and JFET resistance dominate at high breakdown voltages. With increasing temperature, the channel resistance decreases and thus the drift resistance is the main contributor already at medium breakdown voltages. Manufacturing processes of a device can have a high influence on its losses. Variations in interface mobility, drift doping, and p-body doping can lead to a significant change of on-resistance, internal capacitances, and reverse recovery charge. For higher voltage classes the drift layer properties should be of major interest as it influences on-resistance and reverse recovery charge.