SiC Merged PiN Schottky Diode Research Articles

Reliability investigation of repeated unclamped inductive switching in a diode-clamped SiC circuit breaker

This paper investigates the reliability of a solid-state circuit breaker with a clamped SiC diode as avalanche voltage after repeated cutoff operations. In solid-state circuit breakers, a clamping element is connected in parallel with a power semiconductor switch to divert the cutoff current. The SiC merged PiN Schottky (MPS) diode is one of the candidates for clamping elements in solid-state circuit breakers because of its high avalanche tolerance and good robustness after the shocks. Reliability tests indicate that no significant electrical characteristics are found for both the SiC MOSFET and the SiC MPS diode in the proposed circuit breaker, even after more than 10,000 unclamped inductive switching (UIS) cycles. These results are based on a 400V, 50A DC distribution system with the UIS condition. The results show that the SiC MPS diode works well as a clamped element for the long-term reliability of the solid-state circuit breaker.

Electrothermal Coupling Model With Distributed Heat Sources for Junction Temperature Calculation During Surges

High junction temperature is usually the main factor leading to device failures in high-power working conditions, such as surges or avalanches. It is of great significance to obtain the junction temperature quickly and accurately. Direct measurement of junction temperature is inconvenient, and usually indirect electrical measurement combined with model calculation is used. An electrothermal coupling junction temperature calculation model with distributed heat sources is proposed in this article. This model can accurately and quickly predict the device behavior during the surge process, as well as the voltage drop and temperature changes of each part of the device, without actually performing surge tests. This article describes the theoretical basis and calculation principles of the model. By taking a commercial SiC merged PiN Schottky diode as an example, this article also explains the details of the establishment of the electrical and thermal characteristic models of the device, as well as the calculation steps of the junction temperature by the thermal coupling model. The calculated device voltage drop curve of the device is in good agreement with the measured ones, and the calculated junction temperature curve is more consistent with the device failure mechanism than the one by the traditional RC thermal circuit model.

The Impact of the Hexagonal and Circular Cell Designs on the Characteristics and Ruggedness for 4H-SiC MPS Diodes

In this article, SiC Merged PiN Schottky (MPS) diodes with hexagonal and circular cell designs are investigated and compared in terms of characteristics and ruggedness. It is demonstrated by experimental and simulated methods that the circular cell design brings better performance than the hexagonal one. Owing to the almost simultaneously triggering of the P+ island and the P+ ring of the circular cell under high current stress, the current distribution is more balanced, which significantly reduces forward voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{F}$ </tex-math></inline-formula> ) and lower energy-dissipated heat, and further enhances the surge current capability. Moreover, the circular shape can relieve the curvature effect and electric field crowding under reverse blocking conditions, thereby improving breakdown voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BV</i> ) and avalanche capability. These results suggest that circular cell design can be employed to improve the performance and ruggedness of the SiC MPS diodes.

A Comparative Study of Silicon Carbide Merged PiN Schottky Diodes with Electrical-Thermal Coupled Considerations.

A comparative study of surge current reliability of 1200 V/5 A 4H-SiC (silicon carbide) MPS (Merged PiN Schottky) diodes with different technologies is presented. The influences of device designs in terms of electrical and thermal aspects on the forward conduction performance and surge current capability were studied. Device forward characteristics were simulated and measured. Standard single-pulse surge current tests and thermal impedance measurements were carried to show their surge capability and thermal design differences. An advanced thermal RC (thermal resistance-capacitance) model, with the consideration of current distribution non-uniformity effects, is proposed to accurately calculate the device junction temperature during surge events. It was found that a thinner substrate and a hexagonal layout design are beneficial to the improvement of the bipolar conduction performance in high current mode, as well as the surge current capability. The thinner substrate design also has advantages on thermal aspects, as it presents the lowest thermal resistance. The calculated failure temperature during the surge tests is consistent with the aluminum melting phenomenon, which is regarded as the failure mechanism. It was demonstrated that, for a SiC MPS diode, higher bipolar conduction performance is conducive to restraining the joule heat, and a lower thermal resistance design is able to accelerate the heat dissipation and limit the junction temperature during surge events. In this way, the MPS diode using a thinner substrate and advanced layout design technology is able to achieve 60% higher surge current density capability compared to the other technologies.

Analysis and Modeling of SiC MPS Diode and Its Parasitic Oscillation

SiC merged p-i-n Schottky (MPS) diodes have great potential in the construction of multiple power electronic circuits for their excellent static and dynamic characteristics. The ultrafast switching speed is unfortunately accompanied by undesirable parasitic oscillations, which have direct impact on the stability and reliability of these circuits. The wide use of SiC diodes is still limited by their uncertain reliability and a comprehensive diode physical model, which can be used to describe the device characteristics, including parasitic oscillations during reverse recovery, is still missing for the device safe operation. In this article, an accurate dynamic physical model based on the lumped-charge technique which can accurately estimate the switching oscillations is first developed for an SiC MPS diode considering all parasitic elements. Furthermore, the original static model is improved and many important semiconductor physical phenomenon are also included. In the end, simulation and experiments are carried out by a CETC WCSD60D330F19P SiC MPS diode to verify the proposed model.

Investigation of the avalanche ruggedness of SiC MPS diodes under repetitive unclamped-inductive-switching stress

State of the art freewheeling diodes are connected antiparallel with a switch like IGBT or MOSFET and for latter also with the internal body diode. The diodes have to be rugged enough to overcome temporary overvoltage and overcurrent conditions during transient operation. SiC merged pin Schottky (MPS) diodes are one of the superior contenders and thus it is essential to make investigations under high avalanche energy. In this work, an avalanche ruggedness of 20 A/1.2 kV SiC MPS diodes was investigated far beyond the specified maximum ratings of the device under unclamped inductive switching (UIS) measurement. The function of avalanche energy versus applied inductance was investigated under single event avalanche stress. The reliability under high repetitive avalanche energy was studied in detail. A forward voltage drift, change in the Schottky junction voltage and increase in the leakage current was observed after the high repetitive avalanche stress far beyond the safe operating area. Detailed failure analysis was made, focusing on the degradation of the metallization and possible stacking faults (SFs) in the SiC bulk. Furthermore, the temperature was determined as a function of the blocking voltage during avalanche stress.

A Physics-Based Lumped-Charge Model for SiC MPS Diode Implemented in PSPICE

This paper presents a physical lumped-charge model for an SiC merged p-i-n Schottky (MPS) diode. According to the MPS chip configuration, this paper divides the model into two parts: the bipolar subcircuit and the unipolar subcircuit. Both the two parts are modeled by the lumped-charge approach. The proposed physics-based model is also temperature dependent. The model is implemented into the PSPICE simulator in the form of an equivalent circuit. For the characterization of surge current condition that will cause chip temperature changes significantly, an accurate lumped thermal model of the module is established by the structural parameters extraction with a scanning electron microscope. Finally, the developed model is verified by Cree CAS300M12BM2 SiC power module with a 2000-A surge current through the electro-thermal co-simulation. Besides, a test setup is built up with an ultrafast infrared (IR) camera to validate the electro-thermal model in the circuit-level simulation.

Ultrahigh-Voltage SiC MPS Diodes With Hybrid Unipolar/Bipolar Operation

In this paper, ultrahigh-voltage (UHV) SiC devices with hybrid unipolar/bipolar operation are introduced and demonstrated. As the first step of such a device, a merged p-i-n Schottky (MPS) diode with an epitaxial p+-anode layer is proposed to reduce the conduction loss of a bipolar device in the low current region. A “snapback” phenomenon is intensively investigated by analytical modeling, device simulation, and experiment and a design guideline of snapback-free hybrid operating MPS diodes is presented. Using the design guideline, snapback-free MPS diodes are fabricated and forward characteristics are investigated. By using a proper edge termination structure, a UHV SiC MPS diode with breakdown voltage of 11.3 kV is demonstrated.

Recent research in VLSI, MEMS and power devices with practical application to the ITER and dream projects

Several MEMS (Micro Electro-Mechanical Systems) devices have been analysed and simulated. The new proposed model of SiC MPS (Merged PIN-Schottky) diodes is in full agreement with the real MPS devices. The real size DLL (Dynamic Lattice Liquid) simulator as well as the research on modelling and simulation of modern VLSI devices with practical applications have been presented. Based on experience in the field of ATCA (Advanced Telecommunications Computing Architecture) based systems a proof-of-concept DAQ (data acquisition) system for ITER (International Thermonuclear Experimental Reactor) have been proposed.

An accurate electro-thermal model for merged SiC PiN Schottky diodes

The paper presents a SiC merged PiN Schottky diode model dedicated to the dynamic as-well-as very accurate static simulation. The model takes into account the temperature dependence of device characteristics and combines in a single model the behaviour typical for bipolar and unipolar devices. The presented electro-thermal simulations of the diode produce accurate results, consistent with the measurements. The dynamic model verification has been also presented on the example of a boost power converter.

Influence of series resistance and cooling conditions on I–V characteristics of SiC merged PiN Schottky diodes

The paper presents the exemplary electro-thermal models of merged PiN Schottky diode – a diode with the parallel PiN junction, protecting the device against the uncontrolled voltage rise, causing so-called thermal runaway. In the presented models, the conductivity modulation effect in the PiN junction is taken into account. The influence of the PiN junction on the non-isothermal I – V characteristics of MPS diodes, for various cooling conditions, is discussed. It is shown, that the thermal runaway is possible, in spite of presence of protecting PiN junction.

Investigations of SiC merged pin Schottky diodes under isothermal and non‐isothermal conditions

AbstractThe paper concerns the problem of SPICE modeling of the merged pin Schottky (MPS) diodes. In the paper, the SPICE electrothermal model (ETM) of the SiC MPS diodes proposed by Infineon Technologies is investigated. The model was verified experimentally by comparing the calculated and the measured d.c. characteristics of the diode IDT06S60C. Some modifications of the model resulting in the improvement of its accuracy at d.c. analysis are proposed. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Demonstration of high voltage (600–1300 V), high current (10–140 A), fast recovery 4H-SiC p-i-n/Schottky(MPS) barrier diodes

In this work, the design, fabrication, and testing of improved, high power 4H-SiC merged p-i-n/Schottky(MPS) diodes, in the 600–1300 V voltage range, are described. Both DC and transient test results are presented. The diodes were designed with a multi-step junction termination extension (MJTE) to improve the blocking voltage. The MJTE design allows full utilization of the superior breakdown properties of SiC. At 600 V, the highest forward current capability of a packaged MPS diode showed a current of 50 A at 2 V and 140 A at 4 V. At 1300 V, the current was 4 A at 2 V and 10 A at 4 V. In addition, the SiC MPS diode reverse voltage showed excellent suppression of the Schottky leakage current at temperatures up to 250 °C. The transient properties were measured with an inductively loaded half-bridge inverter circuit at high current and high temperatures (high- T). Results showed that the replacement of Si freewheeling diodes by SiC diodes results in far less storage charge in the diodes and substantial reduction in diode turn-off energy loss, especially at high- T. Switching measurements at currents up to 230 A compared a SiC MPS and a state-of-the-art Si diode; the MPS showed a 47% energy loss reduction at room temperature and 84% at 200 °C. The IGBT energy loss reduction, when using an MPS diode, was 15% at room temperature and 45% at 150 °C. The use of MPS diodes should result in improved efficiency when used in power electronics applications.