SiC Power Semiconductor Devices Research Articles

Technical Trends of SiC Power Semiconductor Devices and Their Applications in Power Electronics

Technical Trends of SiC Power Semiconductor Devices and Their Applications in Power Electronics

Analytical model and optimization strategy for SiC floating junction JBS diodes

Conventional SiC power semiconductor devices are disturbed by “SiC limit”, but the floating junction (FJ) structure can overcome the limit. This article classifies FJ breakdown model into two types based on the FJ doping concentration: “Incompletely Depleted Floating Junction” (IDFJ) and “Fully Depleted Floating Junction” (FDFJ). The focus of this article is on the model establishment and design optimization of the FJ JBS diode. Analytical models of conducting state and blocking state for FDFJ are established and verified using TCAD simulation. The research findings indicate that adjusting the floating junction doping concentration can significantly improve the performance of SiC JBS diodes. An optimal Baliga's Figure of Merit (BFOM) of 12.44 GW/cm2 (BFOM = 4BV2/Ron-sp) can be achieved, which represents a 31.8% improvement over the FDFJ (non-optimal) JBS diode. These outcomes are promising and indicate that SiC JBS diodes may have many potential applications in power electronics devices.

High-Temperature Cycle Durability of Superplastic Al–Zn Eutectoid Solder Joints With Stress Relaxation Characteristics for SiC Power Semiconductor Devices

We have developed a new high-temperature Al-Zn lead-free soldering process that utilizes superplasticity to realize SiC power devices with high-temperature cycle durability. The joining process consists of an Al-78wt.%Zn preparation being sandwiched by a SiC die and an insulation substrate, an interfacial cleaning process at approximately 250-270 °C, a heating stage to reach the solid-liquid coexisting temperature of 420-430 °C, the ejection of low-melting-temperature β(Zn) from the joining area by press stress, and the transformation to a superplastic composition, i.e., Al-70 wt.% Zn at 270-310 °C. Many lamellar phases that enable superplasticity can be formed in this microstructure. This solder joint composition was proven to have a better stress-relaxation effect than eutectic Al-95wt.%Zn, and the composition shows a much higher damping capability at the maximum operating temperature of SiC devices (200 °C) than that of other joining candidates. The outstanding temperature cycle durability was verified in temperature cycle tests from -40 °C to 300 °C for 5000 cycles. This durability is due to the high-stress-relaxation effect from the superplasticity transformation realized by the lamellar structures in the Al-Zn alloy solder.

Control of Power Electronics through a Photonic Bus: Feasibility and Prospects

The ubiquitous diffusion of Power Electronic Converters (PECs) in many fields of application including traction and energy conversion suggests the possibility of new and better integration of advanced power conversion and Information and Communication Technology (ICT) services. This work investigates the possible advancements in the use of optical communication links made of plastic optical fibers for control of PECs. The optical communication link connects the switching control to the converter control, following the line of separation between the expertise of power electronic and control engineers. Control wise, a PEC is a black box compatible with any off-board controller, now immune from the Electromagnetic Interference (EMI) produced by the power switches. The redundant optical link is ready for the high switching and sampling frequencies, made possible by relying on SiC power semiconductor devices (100+ kHz). Distributed control of multiple PEC units and advanced telemetry for diagnostics and prognostics are targeted. A proof-of-concept demonstrator is presented and tested. Moreover, the possible evolution towards a power electronic cloud with remote management and orchestration is described.

Extended T-type Inverter

Abstract This paper presents a new concept for a power electronic converter - the extended T-type (eT) inverter, which is a combination of a three-phase inverter and a three-level direct current (dc)/dc converter. The novel converter shows better performance than a comparable system composed of two converters: a T-type inverter and a boost converter. At first, the three-level dc/dc converter is able to boost the input voltage but also affects the neutral point potential. The operation principles of the eT inverter are explained and a simulation study of the SiC-based 6 kVA system is presented in this paper. Presented results show a serious reduction of the DC-link capacitors and the input inductor. Furthermore, suitable SiC power semiconductor devices are selected and power losses are estimated using Saber software in reference to a comparative T-type inverter. According to the simulations, the 50 kHz/6 kVA inverter feed from the low voltage (250 V) shows <2.5% of power losses in the suggested SiC metal oxide-semiconductor field-effect transistors (MOSFETs) and Schottky diodes. Finally, a 6 kVA laboratory model was designed, built and tested. Conducted measurements show that despite low capacitance (2 × 30 μF/450 V), the neutral point potential is balanced, and the observed efficiency of the inverter is around 96%.

Prospects for the practical use of SiC power semiconductor devices

Prospects for the practical use of SiC power semiconductor devices

A New Lead-Free Solder Joint Utilizing Superplastic Al-Zn Eutectoid Alloy for Next Generation SiC Power Semiconductor Devices

A new high-temperature lead-free solder joint which withstands up to 300°C utilizing superplasticity in the Al-Zn eutectoid alloy has been developed to realize SiC power semiconductor devices. The new solid state joining process consists of interfacial cleaning of joints utilizing superplasticity of the Al-Zn-eutectoid alloy at 250°C followed by diffusion bonding between 350 and 390°C. The bonding strength of the new joints exhibits almost the same value at the temperature range from RT to 300°C, above which it decreases slightly with increasing temperature. It is also found that the bonding strength of the new joints is 8 times as high as those of a high-temperature Pb-5wt%Sn-1.5wt%Ag solder and the Al-Zn eutectoid alloy solder without utilizing superplasticity at 250°C. The Al-Zn eutectoid alloy solder joint has shown high reliability in the temperature cycle testing between 50°C and 300°C up to 300 cycles.

Sandwich Structured Power Module for High Temperature SiC Power Semiconductor Devices

A high temperature sandwich structured power module for high temperature SiC power semiconductor devices has been accomplished. Problems were found in the high temperature building-up process of the module caused by excess warpage of the ceramic substrate. Also the high temperature operation of the power module brings an excess warpage of the structure caused by parts having different coefficients of thermal expansion (CTEs) from each other. In this paper, some countermeasures to overcome the problems are demonstrated.

High Temperature Stability and the Performance Degradation of SiC MOSFETs

SiC MOSFET devices have great potentials in future high temperature power electronics applications due to their possible higher thermal runaway temperature compared with other SiC power semiconductor devices. In this paper, the high temperature stability of SiC MOSFETs is investigated by experiments and Saber simulations. The maximum steady-state junction temperature of the SiC MOSFET is measured to exceed 250 °C and saber simulations based on experimental model estimate that the thermal runaway temperatures are close to 300 °C. In addition, performance degradation of SiC MOSFETs during high-temperature operation is observed and discussed. Experimental results show that the degradation happens during both the high temperature storage (maximum 5% RON increment) and high temperature operation process (maximum 15% RON increment). The degradations are found to recover to a close-to-initial level after 1 h recovery time at the room temperature.

Some aspects on ruggedness of SiC power devices

This article is on effects that can destroy SiC power semiconductor devices. The failure physics in SiC devices are discussed based on the well understood effects in silicon devices. In some device properties, such as surge current, short circuit, static avalanche and dynamic avalanche, SiC has significant possible advantages compared to silicon. For cosmic ray stability, there are no unique results. Regarding thermal mechanical stress on interface materials, SiC is more challenging. The same may hold for electrical stress in passivation layers at the junction termination.

Thermal fatigue of Ag flake sintering die-attachment for Si/SiC power devices

Emerging SiC power semiconductor devices are expected to work under the high temperature condition of 250–300 °C while the operation of Si devices is limited up to 180 °C. The die-bonding materials for emerging SiC power devices hence need to have sufficient capability in such extreme operating environments. In this study, we investigated the thermomechanical reliability of the die-attach technology using Ag flake paste, which can be processed by low-temperature and low-pressure sintering. The Ag flakes start to sinter immediately after the organic dispersant layer is removed from the flake surface at 160 °C, and die-bonding consequently becomes possible. The tested Si die-attachments joining with the paste maintained high strength (23 MPa) up to 1,000 thermal cycles from −40 to 180 °C. The stable microstructures without crack and no interfacial debonding assure the reliability of the Ag flake paste die-attach of Si. SiC die-attachments also maintained their high strength (24 MPa) up to 1,000 cycles of −40 and 250 °C, though a slight degradation appeared after 1,000 cycles. The debondings at the sintered Ag flake paste layer/SiC wafer interface were affected to the joining strength with the Ag flake paste. The obtained results indicate that our Ag flake paste die-attach can be applied to both Si and SiC power devices capable of high temperature operations.

Realistic Simulations on Reverse Junction Characteristics of SiC and GaN Power Semiconductor Devices

This paper presents a practical methodology for realistic simulation on reverse characteristics of Wide Bandgap (WBG) SiC and GaN p-n junctions. The adjustment on certain physic-based model parameters, such as the trap density and photo-generation for SiC junction, and impact ionization coefficients and critical field for GaN junction are described. The adjusted parameters were used in Synopsys Medici simulation to obtain a realistic p-n junction avalanche breakdown voltage. The simulation results were verified through benchmarking against independent data reported by others.

Power devices in Polish National Silicon Carbide Program

The paper is devoted to the Polish Government Program “New Technologies Based on Silicon Carbide for High Temperature, High Power and High Frequency Applications”. The program consists of three general tasks, aimed at: SiC bulk and substrate material fabrication, SiC device manufacturing and SiC device applications, respectively. In the contribution the main assumptions and goals of the program are given, and the executed and evaluated part of the research is presented in the field of the design and manufacturing of SiC power semiconductor devices.

Power Conversion With SiC Devices at Extremely High Ambient Temperatures

This paper evaluates the capability of SiC power semiconductor devices, in particular JFET and Schottky barrier diodes (SBD) for application in high-temperature power electronics. SiC JFETs and SBDs were packaged in high temperature packages to measure the dc characteristics of these SiC devices at ambient temperatures ranging from 25degC (room temperature) up to 450degC. The results show that both devices can operate at 450degC, which is impossible for conventional Si devices, at the expense of significant derating. The current capability of the SiC SBD does not change with temperature, but as expected the JFET current decreases with rising temperatures. A 100 V, 25 W dc-dc converter is used as an example of a high-temperature power-electronics circuit because of circuit simplicity. The converter is designed and built in accordance with the static characteristics of the SiC devices measured under extremely high ambient temperatures, and then tested up to an ambient temperature of 400degC. The conduction loss of the SiC JFET increases slightly with increasing temperatures, as predicted from its dc characteristics, but its switching characteristics hardly change. Thus, SiC devices are well suited for operation in harsh temperature environments like aerospace and automotive applications.

A new edge termination technique for SiC power devices

SiC is a promising material for future power semiconductor devices due to its superior material property. Edge termination for SiC power devices remains a subject of significant interest. In this paper, available edge termination techniques are briefly reviewed and various field plate termination techniques are systematically studied. Field plate termination techniques have the advantage of being simple with fabrication process and that it avoids defects induced reverse leakage current associated with implantation based JTE terminations. It is revealed in detail for the first time that severe electric field crowding in the oxide for field plate technique will cause reliability concern and limit device breakdown voltage. Based on the analysis, a new technique is proposed to minimize field crowding in the dielectric material. Dielectric reliability concerns are alleviated and a relatively high percentage of ideal breakdown voltage is achieved with the proposed termination structure. The proposed structure is simple and can be a promising termination technology for SiC power semiconductor devices.