Temperature-dependent analysis of SiC SJ-TG-IGBT with split collector for reduced losses and high breakdown voltage

Power semiconductor devices such as MOSFET/IGBT and PiN diodes are widely used as basic components for supporting infrastructure in the field of electronics, including in power conversion, industrial equipment, railways, and automobiles. Recently, increasing attention has been paid to silicon carbide (SiC) as a wide-band-gap semiconductor suitable for use in power devices with low loss and high breakdown voltage. However, basic knowledge of the material properties and reliability of SiC devices, and particularly the influence of mechanical stress on device characteristics, is still incomplete. In this paper, we evaluated the effect of mechanical stress on the electrical characteristics of SiC devices. In order to investigate the effect of stress on the SiC device characteristic, we propose a simple evaluation method using four-point bending, which is a classical method capable of applying uniaxial stress to a device. With this method, we evaluated the stress in a SiC device using residual stress measurement by Raman spectroscopy and stress simulation based on the finite element method. Our proposed experimental method is as follows. First, the SiC device was bonded with AuGe solder to a metal plate [phosphor bronze; Young’s modulus: 105 GPa; Poisson’s ratio: 0.33; dimensions: 100 mm (W) × 12 mm (L) × 2 mm (T)], and aluminum wire (wire radius: 200 μm) was also bonded to the device. Second, the prepared device was placed on the specially designed four-point bending apparatus for mechanical stress experiments. Finally, the sample was bent in compression or tension in the in-plane direction by the four-point system. The SiC device was subjected to compression or tensile stress via the metal plate. The electrical characteristics of the SiC-MOSFET were measured with a curve tracer in our proposed system. Id−Vds characteristics changed linearly as stress was applied to the device. As a result, the on-resistance was increased by 7.6% by applying a tensile stress of 300 MPa and was decreased by 1.0% by applying a compressive stress of 100 MPa at room temperature, respectively. A power device circuit with multiple chips was also simulated by SPICE based on the experimental results to confirm the effects of stress on SiC devices in a power module. Simulated MOSFET model contains stress factors obtained from experimental results. The circuit was simulated by electro-thermal coupled analysis using a one-dimensional model of the electric circuit and thermal circuit constructed in SPICE. The results show that the proposed method is powerful simulation method for power device design.

Silicon carbide (SiC) has attracted increasing attention as a material suitable for use with high breakdown voltages and at high temperatures. The effects of residual stress and thermal stress on the electrical properties are therefore a matter of growing concern. To analyze the effects, multi-physics simulation is required. The aim of this study is to present an evaluation method for SiC power modules by electro-thermal-stress coupled analysis. In this analysis, we investigate the relationship among mechanical stress, temperature, and electrical resistance in 4H-SiC MOSFET. To investigate the relationship, we used a four-point bending system that is capable of applying uniaxial stress to the SiC device. We prepared two kinds of test specimens with the uniaxial stress direction of four-point bending coinciding with the 〈112̄0〉 and 〈11̄00〉 direction of SiC. To associate the four-point bending load with the stress components in the SiC device, the four-point bending test was simulated by the finite element method. Tensile or compressive load was applied to two types of test specimens, and the internal stress of the SiC device was determined. To determine the internal stress during operation and mounting, the simple module model was also simulated by the structural analysis method. The internal stress was simulated from mounting temperature to the operating temperature. An electrical circuit and thermal circuit were constructed for the DC-DC converter in the above-described module for the coupled analysis method. The relationship among mechanical stress, temperature, and electrical resistance was incorporated into the additional resistance of the MOSFET in the electrical circuit. When an isotropic stress from −500 to 1400 MPa was applied with the SiC under the oxide film in the one parallel DC-DC converter, the change in the power conversion efficiency was about 0.16%. This indicates that our proposed method is a useful simulation method for SiC power modules.

In this paper theoretical benchmarking of semi-vertical and vertical gallium nitride (GaN) MOSFETs with rated voltage of 1.2 kV to 3.3 kV is performed against corresponding silicon carbide (SiC) devices. Specific design features and technology requirements for realization of high voltage vertical GaN MOSFETs are discussed and implemented in simulated structures. The main findings are that a) specific on-resistance of vertical GaN devices is expected to be 75% and 40% of that for 1.2 kV and 3.3 kV SiC MOSFETs, respectively, b) semi-vertical GaN do not offer any advantage over SiC MOSFETs for medium and high voltage devices (>1.0 kV), and c) vertical GaN has largest potential advantage for high and ultra-high voltage devices (>2.0 kV).Gallium nitride (GaN) devices experience an explosive and rapid development with new device providers entering the market at an impressive speed. However, the devices are HEMT (High Electron Mobility Transistor) type lateral devices utilizing the two-dimensional electron gas (2DEG) properties of the GaN/AlGaN interface. The required GaN layers in the devices are grown epitaxially on hetero substrates like Si, SiC, sapphire and poly-AlN using buffer layers to control the strain caused by lattice mismatch which prevents the vertical current flow. For power applications the lateral current flow close to the surface leads to thermal limitations and complicates thermal management in packaging. Furthermore, it leads to large footprint of the devices for large currents. The devices also lack the robust avalanche breakdown characteristics. At present the HEMT power devices are limited to operational voltages of less than 650V with some first devices from VisIC and iGaNPower demonstrating 1200V capability. For these reasons there is an interest in the development of vertical GaN devices opening the possibilities of small footprint and thus lower cost due to smaller chip sizes, high power densities and robust avalanche breakdown characteristics with large avalanche energy capability [1]. The development of vertical devices has been hindered by the lack of large area freestanding GaN substrates facilitating homoepitaxial growth of drift layers. An alternative are semi-vertical structures grown on Si which are the subject of this study along with true vertical structures on GaN. In addition to the material issues there are technological issues that require further attention like dopant compensation and activation and Mg implantation technology for junction termination. This paper focuses on prospective benchmarking of semi-vertical and vertical GaN MOSFETs against SiC devices. A beyond the state-of-the-art benchmarking, in wide voltage range, is missing in the literature. Most of the benchmarking publications report results of experimental structures based on state-of-the-art technology and simple junction termination [2], [3], [4].The main objective of the work has been to design competitive semi-vertical and vertical GaN structures and perform benchmarking against SiC devices in the voltage range 1.2 kV to 3.3 kV. The structures have been characterized by calculating the output, transfer and voltage blocking characteristics using default Sentaurus models. In the next step, the structures have been modified based on the experience and know-how from SiC devices. The electric field crowding occurring at the trench gate corners must be mitigated both with respect to the breakdown voltage in the bulk material and the reliability of the gate dielectric [5]. Efficient junction termination (JT) is also necessary for both types of structures. This is especially important in the semi-vertical structures where junction termination is an integral part of each device segment and has a significant impact on the resulting on-state resistance. The structure design was optimized by reducing the cell pitch and introducing a multi-cell-per-device-segment design in semi-vertical structures to improve the on-resistance. Removal of the performance limitations in the structures based on the state-of-the-art GaN technology and device cell optimization was done to make benchmarking with more mature SiC devices based on the prediction of what may become feasible beyond the state-of-the-art.1. Matteo Meneghini et al., Journal of Applied Physics, vol. 130, p. 181101, 2021.2. Oka, T. Ina, Y. Ueno and J. Nishii, 2019 31st International Symposium on Power Semiconductor Devices and ICs (ISPSD), pp. 303-306, 2021.3. A. Khadar, C. Liu, R. Soleimanzadeh and E. Matioli, IEEE Electron Device Letters, vol. 40, no. 3, pp. 443-446, 2019.4. Wei He et al., Nanoscale Research Letters, 17:14, 2022.5. Nakamura et al., 2011 International Electron Devices Meeting, pp. 26.5.1-26.5.3, 2011.

Wireless power transfer systems and plasma generators are among the increasing number of applications that use high-frequency power converters. Increasing switching frequency can reduce the energy storage requirements of the passive elements that can lead to higher power densities or even the elimination of magnetic cores. However, operating at higher frequencies requires faster switching devices in packages with low parasitics. Wide-bandgap (WBG) power devices, such as gallium nitride (GaN) and silicon carbide (SiC) devices, have high-critical fields and high-thermal conductivity that make them good candidates for efficient high-voltage and high-frequency operations. Commercially available GaN and SiC devices have ratings targeting different applications. Lateral GaN devices dominate in lower voltage ( $C_{\text{oss}},C_{\text{iss}}$ ), which make them easy to drive at high frequencies. On the other hand, vertical SiC devices are often used in high-voltage and low-frequency applications since they have higher blocking voltages and larger gate charge than their GaN counterparts. As a result, SiC devices usually require high power and complicated gate drive circuitry. Recent work shows that in both GaN and SiC devices, losses in device $C_{\text{oss}}$ can exceed the conduction losses at high-switching frequencies and relatively high voltages under zero-voltage-switching conditions. Moreover, the $C_{\text{oss}}$ energy loss ( $E_{\text{oss}}$ ) per switching cycle increases with frequency in GaN devices but remains roughly independent of frequency in SiC devices. This means that at high frequencies, SiC devices can be preferable due to their smaller $C_{\text{oss}}$ energy loss even when taking into consideration the complexity of the gate drive circuit. In this article, we present a WBG high-voltage cascode GaN/SiC power device, combining the advantages of both a GaN and an SiC device—namely, simple gate drive requirements, $E_{\text{oss}}$ loss per cycle roughly independent of frequency, and relatively high-voltage blocking capability. Comparing this cascode GaN/SiC device with an SiC mosfet and a SiC junction gate field-effect transistor of similar voltage ratings and $R_{ds,{\text{ON}}}$ , we find that the inverter using the cascode GaN/SiC device has the highest efficiency and simplest auxiliary gate drive circuitry. Finally, integrating the cascode GaN/SiC device has the potential benefits of achieving lower $C_{\text{oss}}$ losses, higher device ratings, and better heat removal capability.

The advent of Silicon Carbide (SiC) devices has made possible high switching frequency operation of PWM power converters. In this paper, SiC devices are compared in detail with Si devices in a high power (1 MW) DC -DC converter application. The converter is designed as the building block for traction drives which requires it to operate at high power, high input voltage (11 kV) and low output voltage (800 V) levels. A dual active bridge (DAB) and a series resonant converter (SRC) topology are compared to achieve highly efficient operation. The performance and efficiency of these converters are compared by simulations using two different combinations of switches; the SiC combination consists of 10 kV/10 A SiC MOSFET at High Voltage (HV) side and 1200 V/100 A SiC MOSFET at Low Voltage side (LV), and the Silicon combination consists of 6.5 kV/10 A Si IGBT at HV side and 1200 V/100 A Silicon IGBT at LV side. For further understanding, efficiency analysis using the newly developed 15 kV/20 A SiC IGBT on the HV side is also carried out.

Wide bandgap semiconductors such as gallium nitride (GaN) and silicon carbide (SiC) offer exciting opportunities in enhancing the performance of power electronic systems in term of improved efficiency as well as higher temperature operation. Both silicon carbide and gallium nitride power semiconductor devices offer a higher voltage handling capability over their silicon power semiconductor counterparts. In this paper, the design and packaging issues for SiC power electronic modules are discussed. Several SiC devices are usually connected in parallel to increase its current handling capability in power electronic module packaging. The paralleling of these SiC devices creates unbalanced parasitic inductances which affect the dynamic switching performance for these paralleled devices. Each of the paralleled SiC devices could have different initial peak currents due to their different parasitic inductances within the module. Moreover, their fast dv/dt of the drain voltages as well as the high di/dt of the drain currents can cause spurious switching behaviors in some of the paralleled SiC devices in the power module. Layout techniques can be used to mitigate these spurious switching behaviors. However, module construction architectures and as well as module package construction are required to further mitigate these parasitic inductances. One of the many advantages of the SiC power devices is high voltage handling capability. High voltage operation of the power electronic module requires careful reduction of electric field intensification within the device as well as the module. Encapsulations with the desired dielectric breakdown strength as well as temperature performance must be applied on top of these devices to prevent premature voltage breakdown. One of the salient features of the SiC power electronic modules is high temperature operation of greater than 175°C. For high temperature operations, proper die attach must be utilized. Nano silver sintering and transient liquid phase bonding are two high temperature die attachment techniques. For high temperature operation, reliability testing for these SiC power electronic modules must be carefully considered since there is no existing international standard for reliability testing for these high-temperature power electronic modules.

Ultra-high voltage power devices are employed for management of power networks. Si-based semiconductor devices have been developed for such the power devices. Maximum breakdown voltages of Si devices are of the order of kV. When the voltage in the power network was higher than the breakdown voltage of the devices, the devices were connected in series. The series connection introduces high resistance and power loss. To overcome this series resistance problem, it has been suggested that utilization of silicon carbide (SiC) devices. SiC has much higher breakdown electric field than Si, and thus high voltage in the power networks can be managed by SiC device without the series connection. Therefore, development of ultra-high voltage SiC device will decrease resistance and power loss in the power networks. However, there are several difficulties to develop ultra-high voltage SiC devices. One of the difficulties is control of the carrier lifetime. In fact, ultra-high voltage devices are fabricated with bipolar structure, and, in the bipolar devices, the carrier lifetime is highly influential on resistance and power loss. The carrier lifetime is limited by several factors, and one of the most important factors is the surface recombination. Therefore, evaluation and control of the surface recombination is essential to develop ultra-high voltage SiC devices. In this paper, we will report evaluation techniques for the surface recombination of SiC. In addition, dependence of the surface recombination on surface treatments, crystal faces and temperature are shown. The evaluated surface recombination velocities will support development of ultra-high voltage SiC devices.

With the increasing attentions on electric vehicle (EV), hybrid electric vehicle (HEV) and Plug-in hybrid electric vehicle (PHEV), the significance of power electronics in traction power converter increased through the last decades. Having dominated for years, silicon is now reaching its material limits. As an alternative, wide band gap device such as silicon carbide (SiC) device received more attention. Market of SiC devices has been growing for years and major manufacture are now willing to participate in the SiC business. Physical properties gives SiC advantages over Si, such as high breakdown voltage, low drift region resistance, high temperature operation. For traction inverters, power loss in switches are discussed. It has been demonstrated that SiC devices have lower power losses than Si IGBT which also helps with the sizing and design of the heatsink. In DC-DC converters, the advantage of high switching frequency of SiC devices would have a hugh impact on the overall system for reducing the power loss, size of passive components and total weight. However, high cost, low productivity and reliability under harsh environment are problems facing by SiC devices currently and they are expected to be solved in the future.

Significant development of silicon carbide (SiC) material for device applications now allows circuit designers to more fully exploit its unique properties. The 4 H-SiC structure provides the most favorable characteristics to optimize device speed and power handling capabilities. These include wide bandgap (3.2 eV), high dielectric breakdown (3.5 MV/cm), and high thermal conductivity (4.9 W/cm-K) [IEEE Transactions on Electron Devices, 1993]. By combining these properties, SiC devices are able to achieve fast reverse recovery and high reverse blocking voltages, along with excellent high temperature characteristics (case temperatures above 150 C). This makes these devices ideally suited to power electronics applications, where high power levels as well as fast switching are required. Many areas dominated by ultrafast recovery silicon (Si) diodes, might therefore be better suited to the application of SiC. In order to verify the efficacy of SiC devices, temperature dependent measurements were made on a sample of fast recovery Si and SiC diodes. This paper presents the results of these measurements, comparing critical characteristics of Si and SiC devices over a range of junction temperatures up to 150 C.

The advantage of Silicon Carbide (SiC) based devices are less thermal management requirements and smaller passive components which result in higher power density. SiC devices have higher blocking voltages, lower on-state resistance and switching losses and higher thermal conductivity and operating temperatures. SiC devices can operate at higher voltages, higher frequencies and higher junction temperatures than comparable Si devices, which results in significant reduction in weight and size of the power converter and increase in system efficiency.

Silicon (Si) is the most widely used in power electronic devices. However, due to its limitations regarding blocking voltage and switching frequency, wide band gap (WBG) materials have been under extensive research. Especially, Silicon carbide (SiC) device is expected to replace the Si device in many high voltage/power application. Although the low voltage SiC device that can replace the Si device is commercially available, device for high voltage and power application is under development. In order to achieve high voltage and power, series connection of SiC devices can be considered. Besides the advantage of series connection, it causes voltage unbalance issue that must be solved. In this paper, the active gate driver (AGD) control is used to balance the voltages. A gate resistance modulation method is presented for dynamic voltage sharing. It controls the gate current to adjust dv/dt. With different time of gate resistance modulation, the dv/dt of each device is adjusted to balance the voltages. The proposed method is verified in three different cases in Matlab/Simulink.

Due to its superior electrical characteristics resultant from material properties such as high critical electric field, larger bandgap and higher thermal conductivity in comparison to Silicon (Si), Silicon Carbide (SiC) devices are becoming increasingly popular in the power electronics industry. Many SiC device types have been commercialised during the past decade. In this paper, a performance comparison between SiC MOSFET, SiC BJT and SiC SJT based bi-directional converters, targeting energy storage applications, has been made along with a Si IGBT version. Conduction losses and switching losses have been calculated and compared with the aid of measured forward I–V curves and double-pulse testing in a clamped-inductive test configuration, respectively. In order to validate the continuous operation, the device performances when operating the bi-directional converter in DC/DC conversion mode have been compared. The efficiency of the converters have been assessed at 20 and 40 kHz switching frequencies and up to 6.6 kW output powers and 27 A input current levels per half-bridge. From the results discussed, it is clear that the SiC devices surpass Si IGBTs in switching performance. During 250 V to 500 V boost conversion at 20 kHz, a loss reduction of 50.8% has been observed at a 4.9 kW power output in SiC MOSFET converter, in comparison to the Si IGBTs. At 40 kHz, peak efficiencies of 98.8% and 98.6% have been demonstrated by SiC MOSFET and SiC BJT converters, respectively. The aim of this comparison is to identify and set a guideline as to the most appropriate circumstances for using each device technology.

Using 6.5 kV Silicon (Si) IGBTs, high voltage high power DC to DC converters are realized either by multi-level converters or series connected devices based two level converters or modular multi-level converter using series connected devices two level converter as building blocks. The introduction of high voltage SiC devices (10 kV to 20 kV) reduces the component count significantly while improving the efficiency and power density of the converter. To explore further, this paper investigates the state of the art high voltage (>10 kV) SiC devices for high voltage dual active bridge (DAB) with series connected devices for high power applications. Experimental results for static and dynamic voltage balancing of 15 kV, 20 A SiC IGBT devices are given to validate the feasibility of series connection and also the experimental characterization of 10kV SiC MOSFET and 15 kV SiC IGBT with RC snubber are reported. By using energy loss data from the experimental characterization, HV side switching loss of a 1 MVA 16 kV/2 kV DAB topology has been evaluated for two independent cases with 10 kV, 10 A SiC MOSFET and 15 kV, 20 A SiC IGBT on the HV side of the converter, while using 1.7 kV Si IGBTs on LV side of the converter.

<div class="section abstract"><div class="htmlview paragraph">Efficient, small, and reliable dc-dc power converters with high power density are highly desirable in applications such as aerospace and electric vehicles, where battery storage is limited. Bidirectional full-bridge (FB) dc-dc converters are very popular in medium and high-power applications requiring regenerative capabilities. Full-bridge topology has several advantages such as: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Inherent galvanic isolation between input and output as well as high conversion ratio due to the transformer with a turns ratio <i>n</i>.</div></li><li class="list-item"><div class="htmlview paragraph">Reduction in passive component sizes due to the increase in inductor current frequency to twice the switching frequency.</div></li><li class="list-item"><div class="htmlview paragraph">Reduced voltage stresses on the low-voltage side switches and current stresses on the high-voltage side switches.</div></li></ul></div><div class="htmlview paragraph">However, due to the high number of switches, device losses increase. Use of wide-band gap (WBG) devices, such as Silicon Carbide (SiC) and Gallium Nitride (GaN) devices, in power electronic converters has shown to reduce device losses and need for extensive thermal management systems in power converters. SiC and GaN have complementary properties. SiC devices offer superior thermal performance due to their high thermal conductivity and GaN devices offer superior switching performance due to their high carrier mobility. However, state-of-the-art commercially available GaN devices can only withstand breakdown voltages up to 650 V, while SiC devices can handle up to 1700 V. Because of this shortcoming, GaN devices cannot be used in power converters for high voltage applications, despite GaN’s capability to operate at high switching frequencies with high efficiency. This work aims to exploit both the high-voltage capability of SiC devices and exceptional switching capability of GaN devices in a novel hybrid SiC-GaN based bidirectional full-bridge dc-dc converter with improved efficiency, reliability, and power density for high power applications. The proposed bidirectional converter rated at 5 kW will be designed and simulation results obtained using LT Spice circuit simulator will be presented.</div></div>

Silicon carbide (SiC) devices are attracting attention as next generation power device because of their high breakdown voltage, low conduction loss, and fast switching speed compared with conventional Silicon (Si) device. SiC power device is expected to be used in electric vehicle and hybrid electric vehicle. The large di/dt and dv/dt in fast switching operation interact with parasitic component in circuit wiring, and causes conducted noise. This study focuses on the switching behavior of SiC MOSFET and the conducted noise characteristics in a inverter. The effect of snubber circuit is evaluated with its combination of installation for SiC module.