SiC SBD Research Articles

Voltage Distribution in Ultra High Voltage SBD Modules with Directly Stacked SiC SBD Bare Chips in Series

Voltage Distribution in Ultra High Voltage SBD Modules with Directly Stacked SiC SBD Bare Chips in Series

The Influence to Uniform Current Distribution of SiC MOSFET Modules Based on the 3rd Quadrant Characteristics

This paper concentrated on the 3rd quadrant characteristics of 1200V/300A full SiC MOSFET modules produced by four SiC mainstream manufacturers; and compared the diode forward voltage (VSD) performances of “SiC MOSFET only” and SiC MOSFETs modules with SiC Schottky barrier parallel diode. The characteristics of the diode forward voltage showed that module A exhibits the same trend with the PiN diode, whereas modules B, C and D exhibit the characteristics of SBD. Through the failure analysis, it was verified that there is no parallel SBD in module A, meanwhile, it was assumed that modules B, C and D integrate a positive temperature characteristic SBD by wire bonding. The existence of SBD can prevent the modules from burning out due to excessive heating caused by non-uniform current distribution. From the analysis, it illustrated that the body diode can be used as the parallel SiC SBD, but further research on the uniform current distribution of the the body diode is needed.

A dry etching method for 4H-SiC via using photoresist mask

In this abstract, a novel method of 4H-SiC shallow trench etching process via directly using photoresist as a mask is proposed to fabricate SiC MOSFETs and SiC diodes which enjoy popularity in power devices. By changing the profile of photo resist mask during exposure and development, with SF6/O2 plasma alternatively attacking onto the SiC surface, different shallow trench taper angles from 45° to 85° are achieved. The described shallow trench process plays a vital role in alignment mark, declined ion implantation and JTE structure fabrication process of power device R&D and manufacturing. With the proposed method, we have successfully fabricate a 1200 V/20A SiC SBD device with breakdown voltage of 1400 V (@IR = 10 μA), and threshold voltage of 1.6 V (@ IF = 20 A), yield of 98% and uniformity less than 3% from wafer to wafer. Moreover, using photoresist directly as a SiC etching mask simplifies the etching process compared with the traditional two masks process and thus saves mass production cost and tact time.

Investigation on Degradation of SiC MOSFET Under Surge Current Stress of Body Diode

Eliminating antiparallel silicon carbide Schottky barrier diode (SiC SBD) and making use of the intrinsic body diode of SiC metal–oxide–semiconductor-field-effect transistor (SiC MOSFET) offer a cost-effectiveness solution without obviously sacrificing the conversion efficiency in some power converter applications. Although the body diode of commercial SiC MOSFET has been qualified by several manufacturers, the reliability of SiC MOSFET under repetitive surge current stress of body diode has not been sufficiently studied. In this article, the new degradation phenomena of SiC MOSFET’s gate oxide are observed, and the degradation mechanism is discussed when the intrinsic body diode of the 1200-V SiC planar gate MOSFETs was subjected to surge current stress. TCAD simulation and experimental measurements indicate that the generation and accumulation of electrons or holes within the gate oxide under surge current stress are the main reasons for the degradation of SiC MOSFET. Finally, a mitigation technique with optimal gate turn-off voltage is suggested to suppress the gate oxide degradation of the SiC MOSFET under surge current stress of its body diode.

Development of high power SiC devices for rail traction power systems

Si-based power devices have been widely used in electric locomotive and EMU, however, there are urgent requirements from the industry to have power converters with smaller size and higher performance. To meet such demands, wide band-gap (WBG) devices such as SiC power chips and modules are developed for the traction systems, and a 1.7 kV hybrid SiC power module has been used in Metro system and all SiC 3.3 kV power module has been developed. In this paper, the development of hybrid SiC and all SiC power modules are introduced from the perspectives of devices, modules and applications. SiC SBD and MOSFET chips and modules are manufactured and tested, both static and dynamic testing results are evaluated and showed that SiC devices present better performance and higher efficiency than the traditional Si IGBT modules, especially in the conditions of high temperature and high operation frequency. Based on the developed SiC modules, the urgent demand of traction converters with smaller size and lighter weight can be achieved while present advantages such as higher efficiency, power density, operation temperatures and frequency. The current challenges of SiC devices and future applications are discussed for the next generation of rail transportation.

SiC SBDs selection method based on loss analysis of boost converter

Silicon carbide schottky barrier diodes (SiC SBDs) have much better characteristic than Si PiN diode in high voltage applications because SiC SBDs do not have recovery effect. However, simple replacing is not the most effective way. In a boost converter, the power loss caused by the SiC SBD can be divided into the conduction loss of the SiC SBD and the loss caused by the energy stored in the junction capacitance of the SiC SBD. Therefore analysis of not only the conduction loss but also the loss caused by the energy stored in the junction capacitance of the SiC SBD can realize the SiC SBD selection to improve the efficiency of the boost converter. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Physics‐based spice model on the dynamic characteristics of silicon carbide Schottky barrier diode

Silicon carbide Schottky barrier diodes (SiC SBDs) are poised to replace silicon PIN diodes as a new choice for the high power and high frequency applications. However, SiC SBDs suffer from ringing which may induce additional power losses when applied in chopper circuit, regarded as the interaction among the depletion capacitance, depletion resistance, parasitic stray inductance and series resistance. The existing SiC SBD models generally treat the resistances as constants and ignore the influence of the MOS, which deviate the switching commutation process significantly on the ringing frequency and amplitude. In this study, a more accurate Spice model of SiC SBD has been developed in which voltage dependent non-linear depletion capacitance and resistances are all considered in the transient analysis based on semiconductor physics, while the Miller capacitance of the MOS performing as a switch in the circuit is also taken into account. The improved model and analysis are validated by the better agreement with the experiments compared with the existing models on the dynamic characteristics.

Ion-Induced Anomalous Charge Collection Mechanisms in SiC Schottky Barrier Diodes

The charge induced in SiC-SBDs with different epi-layer thicknesses by ion incidence was measured to understand the mechanism of heavy-ion-induced anomalous charge collection in SiC-SBDs. SiC SBD of which epitaxial-layer thicknesses is close to ion range show larger anomalous charge collection than SBD with thicker epi-layer although the former one has lower electric field than the later one. The gains of collected charge from the SBDs suggest that the impact ionization under 0.16 - 0.18 MV/cm of the static electric field in depletion layer is not dominant mechanisms for the anomalous charge collection. It is suggested that the epitaxial-layer thickness and ion-induced transient high electric field are key to understand the anomalous charge collection mechanisms in SBDs.

A Study of Post Annealing Effects in the Repair of High Resistance Failures with Unstable Schottky Barrier Height in 4H-SiC Schottky Barrier Diode

To improve the high resistance and low Breakdown Voltage (BV) of 4H-SiC SBD, the metal annealing process is usually used to to stabilize SBH. We confirmed that post metal annealing after the chip process also stabilizes SBH by the post annealing experiment of applying failure chips (4H-SiC Ti/Al SBD) that have a forward current (IF) under 1 [A] with high resistance, because of the metal annealing process error. The result of experiments showed that the IF increment and BV decrement are proportional to the applied temperatures over 450 °C, and the second additional post annealing shows a decrease of IF and BV. Aluminum and Titanium transformation with post metal annealing made a decrease of SBH, so that the on-resistance is decreased and BV is decreased (in severe cases, the intense post annealing generates Aluminum spiking). From a result of this work, using a suitable post metal annealing, we can improve the IF of SiC SBD with a high resistance failure from the metal process event.

Nanoscale Dynamic Mechanical Analysis on Heat-Resistant Silsesquioxane Nanocomposite for Power-Device Packaging

Heat-resistance of novel mold compound made of silsesquioxane nanocomposite with silica fillers is demonstrated in a TO247 package of SiC SBD. The test specimens are exposed to thermal cycling between -50°C and 250°C, and the thermal damage of the mold are precisely evaluated by using nanoscale dynamical mechanical analysis based on nanoindentation technology. The results reveal that the excellent heat-resistance is brought by the miscibility between the thermosetting nanocomposite and silica fillers.

Analytical Modeling of Switching Energy of Silicon Carbide Schottky Diodes as Functions of <italic>dI <inline-formula><tex-math notation="LaTeX">$_{\bf DS}$</tex-math></inline-formula>/dt</italic> and Temperature

SiC Schottky Barrier diodes (SiC SBD) are known to oscillate/ring in the output terminal when used as free-wheeling diodes in voltage-source converters. This ringing is due to RLC resonance among the diode capacitance, parasitic resistance, and circuit stray inductance. In this paper, a model has been developed for calculating the switching energy of SiC diodes as a function of the switching rate ( dI $_{\rm DS}/dt$ of the commutating SiC mosfet ) and temperature. It is shown that the damping of the oscillations increases with decreasing temperature and decreasing dI $_{\rm DS}/dt$ . This in turn determines the switching energy of the diode, which initially decreases with decreasing dI $_{\rm DS}/dt$ and subsequently increases with decreasing dI $_{\rm DS}/dt$ thereby indicating an optimal dI $_{\rm DS}/dt$ for minimum switching energy. The total switching energy of the diode can be subdivided into three phases namely the current switching phase, the voltage switching phase, and the ringing phase. Although the switching energy in the current switching phase decreases with increasing switching rate, the switching energy of the voltage and ringing phase increases with the switching rate. The model developed characterizes the dependence of diode's switching energy on temperature and dI $_{\rm DS}/dt$ , hence, can be used to predict the behavior of the SiC SBD.

Performance characterization of gallium nitride HEMT cascode switch for power conditioning applications

Abstract A hybrid cascoded GaN switch configuration is demonstrated in power conversion applications. A novel metal package is proposed for the packaging of a D-mode GaN MIS-HEMT cascoded with an integrated power MOSFET and a SBD. The normally-off cascode circuit provides a maximum drain current of 14.6 A and a blocking capability of 600 V. Analysis of 200 V/1 A power conversion characteristics are discussed and show the excellent switching performance in load circuits. Switching characteristics of the integral SiC SBD are also demonstrated. Finally, a 48-to-96 V boost converter is used to evaluate the benefit of GaN cascode switches. These results show that high-voltage GaN-HEMTs can be switching devices for an ultralow-loss converter circuit.

Simulation Analysis of Snubber Circuit for SiC MOSFET Inverter

SiC MOSFET, as a promising power semiconductor devices, has attracted attention from many laboratories and companies for its super performance in high temperature, high voltage and high frequency applications. To protect the devices from overvoltage induced by parasitic inductance in high frequency applications, snubber circuit is a must. In this paper, simulation of snubber circuit in a high frequency PWM inverter is invested, under different numbers of snubber circuit , parasitic parameters, different kinds of load and whether a SiC SBD exsits. Some useful conclusions are obtained to help design more perfect snubber circuit.

SiC SBD の並列接続リカバリ抑制手法の検討

SiC SBD の並列接続リカバリ抑制手法の検討

The Impact of Parasitic Inductance on the Performance of Silicon–Carbide Schottky Barrier Diodes

1200V/300A silicon carbide Schottky barrier diode (SiC SBD) and Si pin diode modules have been tested as free-wheeling diodes under conditions of clamped inductive switching over a temperature range between -40 °C and 125 °C. Over the temperature range, the turn-OFF switching energy increases by 100% for the Si pin diode, whereas that of the SiC diode is temperature invariant and is 50% less than that of the Si pin diode at 125°C. However, the SiC SBD suffers from ringing/oscillations due to an underdamped response to an RLC circuit formed among the diode depletion capacitance, parasitic inductance, and diode resistance. These oscillations contribute to additional power losses that cause the SiC SBDs to be outperformed by the Si pin diodes at -40 °C and 0 °C. The higher depletion capacitance and lower series resistance of the SiC SBD contribute to a lower damping factor compared to the Si device. Furthermore, the positive temperature coefficient of the ON-state resistance in silicon contributes to better damping at high power levels, whereas the temperature invariance of the ON-state resistance in SiC means the oscillations persist at high temperatures. SPICE simulations and experimental measurements have been used to validate analytical expressions that have been developed for the circuit damping and oscillation frequency.

Performance Investigation of Dynamic Characteristics of Power Semiconductor Diodes

Utilization of SiC SBD diodes in DC-DC converter applications is discussed. First reverse recovery effect of various diodes’ structures and its elimination is being described. Experimental measurements have been done and consequently data were converted into continuous form for graphic interpretation in dependence on switching frequency, supply voltage and load current. Accordingly, the utilization of new progressive materials of power SBD diodes on SiC technology is being described, whereby measurements were done also at higher (150C) temperatures. This measurements show key differences in dynamic characteristic between each diodes and therefore proper selection of diode and optimization of power supply should be done. It is concerned SiC SBD diode structures versus Si UltraFast and HyperFast diodes rated for 600V. Ill. 9, bibl. 22 (in English; summaries in English, Russian and Lithuanian).

Characteristics of a SiC SBD with semi-superjunction structure

A novel SiC semi-superjunction-Schottky Barrier Diode (Semi-SJ-SBD) structure is proposed, which is the combination of super-junction (SJ) structure and conventional drift region structure. The proposed structure can significantly reduce the specific on-resistance (Ron-sp) and improve the forward characteristics. The breakdown voltage (VB) and specific on-resistance (Ron-sp) in different SJ depth and width are studied using two-dimensional simulator Medici and compared with conventional SiC SBD. The results show that Ron-sp is greatly reduced (greater than 10%) with VB unchanged (less than 4%) when the SJ width is chosen as 2—3 μm and SJ depth is deeper than 5 μm.

Electrical characterizations of Neutron-irradiated SiC Schottky diodes

Neutrons with an average energy of 9.8±0.8 MeV were irradiated onto silicon carbide Schottky diodes. After bombardment at a fluency of 2.75×1011 neutron/cm2, the Schottky barrier height, ideality factor, and the leakage currents remained unchanged. The electrical properties began to deteriorate after bombardment at a fluency of 5.5×1011 neutron/cm2. In this study, we demonstrate that SiC SBD is robust under neutron irradiations and is well suited for space operations up to bombardments at a fluency of 2.75×1011 neutron/cm2.

Normally-Off 1400V/30A 4H-SiC DACFET and its Application to DC-DC Converter

Large (3.6 x 3.6 mm2) chips of the SiC DACFET were fabricated and mounted in TO220 packages. The drain-source avalanche breakdown voltage without any gate bias (Vgs=0V) is measured to be >1400V. The SiC DACFET keeps the normally-off characteristics even at 150°C. Ron and specific Ron of the SiC DACFET is measured to be 62mΩ and 6.7 mΩcm2 at RT while those at 150°C change to 107 mΩ and 11.6 mΩcm2. The 400V / 3 kW DC-DC switched-mode power-conversion circuit with 100kHz switching was fabricated using the SiC DACFET and the SiC SBD. The turn-off switching loss reduces dramatically using the SiC-DACFET down to 77μJ/pulse which is less than 1/10 of that using the Si-IGBT.

Electrical Characteristics Temperature Dependence of 600V-Class Deep Implanted Gate Vertical JFET

A 4H-SiC 600 V class Deep-Implanted gate Vertical JFET (DI-VJFET) is examined. The DI-VJFET exhibited a specific on-resistance of 13 mΩcm2, drain current of 5 A, and a blocking-voltage of 600 V. In this paper, the very high temperature dependence (R.T.~ 400 oC) of the I-V characteristics is measured and the dominant factor of the on-resistance and the blocking-voltage is discussed. Moreover, the switching waveform of SiC DI-VJFET with SiC SBD is measured by using a half bridge, double-pulse circuit with inductive load at R.T. and 200 oC. The turn-off time is 300 ns at an inductance of 4 mH and an external gate resistance of 100 Ω.