High-voltage Power Electronics Applications Research Articles

(Invited) Multi-Channel AlGaN/GaN Power Rectifiers: Breakthrough Performance up to 10 kV

High-voltage power rectifiers are widely used in renewable energy processing, electric grids, industrial motor drives, pulse power systems, among other applications. Today’s high-voltage rectifier market is dominated by bipolar Si diodes up to 6.5 kV, which suffer from slow reverse recovery. Wide-bandgap SiC unipolar diodes have been pre-commercialized up to 10 kV, which allows for a much higher switching speed. Recently, we have developed a new generation of high-voltage rectifiers based on the multi-channel AlGaN/GaN platform, which highlight a series of novel device designs incorporating the stacked two-dimensional electron gas (2DEG) channels, p-n junctions, and 3-D fin structures. With these innovations, the performances of our unipolar 1.2-10 kV multi-channel AlGaN/GaN Schottky rectifiers well exceed the Si and SiC 1-D limit, at the same time possessing a lower cost as compared to SiC counterparts. This paper reviews our efforts in the design, fabrication and characterization of these GaN devices. Our results show the tremendous promise of GaN for medium-voltage and high-voltage power electronics applications.

Stackable SiC-Embedded Ceramic Packages for High-Voltage and High-Temperature Power Electronic Applications

Abstract This study encompasses the development of a high-voltage and high-temperature–capable package for power electronic applications based on the embedding of silicon carbide (SiC) semiconductor devices in the ceramic circuit carrier such as the direct bonded copper (DBC) substrate. By sealing semiconductor devices into DBC substrates, high temperature, high voltage, and high current capability as well as high corrosion resistance can be achieved compared with the state-of-the-art printed circuit board (PCB) embedding technology. The power devices are attached with high-temperature stable solder and sinter material and are surrounded by thermal conductive ceramic and high-temperature–capable potting materials that enable the complete package to operate at 250°C or above. Furthermore, the single embedded packages can be stacked together to multilevel DBC topologies with increased voltage blocking characteristics. Thus, current limits of the PCB and low-temperature cofired ceramic–based multilayer solutions are exceeded and will be confirmed in the course of this study. This package is designed to carry out the maximal performance of SiC and future wide bandgap devices. It is a promising solution not only for applications in harsh ambient environments such as aerospace and turbine, geothermal well logging, and downhole oil and gas wells but also for hybrid electric/electric vehicle and energy conversion.

Stackable SiC Embedded Ceramic Packages for High Voltage and High Temperature Power Electronics Applications

Abstract This paper encompasses the development of a high voltage and high temperature capable package for power electronic applications based on the embedding of SiC (silicon carbide) semiconductor devices in ceramic circuit carrier such as direct bonded copper (DBC) substrate. By sealing the semiconductor devices into DBC substrates, high temperature, high voltage and high current capability as well as high corrosion resistance can be achieved compared to state-of-the-art PCB (printed circuit board) embedding technology. The power devices are attached with high temperature stable solder and sinter material, and are surrounded by thermal conductive ceramic and high temperature capable potting materials that enable the complete package to operate at 250 °C or above. Furthermore, the single embedded packages can be stacked together to multilevel DBC topologies with increased voltage blocking characteristics. Thus, current limits of PCB and LTCC (low-temperature co-fired ceramic) based multilayer solutions are exceeded and will be confirmed in the course of this study. This package is designed to carry out the maximal performance of SiC and future WBG (wide band-gap) devices. It is a promising solution for applications in harsh ambient environment such as aerospace and turbine, geothermal well logging, down hole-well oil & gas, but also applicable for HEV/EV (hybrid electric/electric vehicle) and energy conversion.

(Invited) Simulation Study of High Voltage Vertical GaN Nanowire Field Effect Transistors

Concept of vertical Gallium Nitride (GaN) nanowire field effect transistors (NWFETs) for high voltage power electronic applications is investigated through three dimensional (3D) TCAD simulations in this paper. The proposed GaN NWFET can operate either in a normally-off or a normally-on mode depending on the specific device design. A gate-all-around (GAA) structure coupled with a strong dielectric REduced SURface Field (RESURF) effect has the potential to offer blocking voltages over 900 V with very low specific on-resistance for the NWFETs. VRB 2/RON and QGD x RDS(ON) Figures of Merits (FoMs) of the NWFET are extracted and compared with other state of the art GaN, SiC and Si field effect transistors to get a comparative understanding of the potential of the NW architecture for high voltage applications.

Site Specific TEM Specimen Preparation for Characterization of Extended Defects in 4H-SiC Epilayers

Silicon carbide (SiC) is an important semiconductor for high temperature, high voltage and high power electronic applications. Unfortunately, SiC still has not reached its potential in these applications due to the presence of extended defects in epilayers, which degrade the performance of SiC-based devices. In this work, focused ion beam (FIB) is employed to prepare site-specific cross-sectional transmission electron microscopy (TEM) specimens allowing direct characterization of unwanted in-grown stacking faults (IGSFs) and basal plane dislocations (BPDs). IGSFs are known to decrease breakdown voltages and increase leakage currents in SiC diodes [1]; however, their nucleation mechanism is currently not established. BPDs can form recombination-induced stacking faults, which lead to device performance degradation over time [2]. Recently, KOH etching of the substrate was reported to cause conversion of BPDs to electrically benign threading edge dislocations (TEDs) in the epilayer. However, for some BPDs this conversion was also associated with a shift in the locations of etch pits [3]. In this study, FIB and TEM are used to explain the nucleation mechanism of IGSFs and the previously observed shift in the locations of BPDs.

Optical Triggering of 4H-SiC Thyristors with a 365 nm UV LED

Direct light triggering of 4H-SiC thyristors with a 365 nm UV LED was demonstrated. Two different structures with etched and non etched gate were successfully tested. The current rise time was less than 100 ns and the delay time as short as 1.5 μs. The optical energy density necessary to switch-on a thyristor has been studied for different optical power densities and bus voltages. This work shows that the UV LED technology is becoming sufficiently powerful to switch-on SiC thyristors. Thus, an alternative, less expensive and more compact gate light source than UV laser is now possible. This can be of particular interest for very high voltage and pulse power electronic applications.

Optical triggering of SiC thyristors using UV LEDs

This reported work describes the demonstration of direct light triggering of 4H-SiC thyristors by UV LEDs. Two different structures with etched and non-etched gate were successfully tested. The current rise time was less than 100 ns and the delay time in the range 2-16 s depending on experimental conditions. The delay time dependency on the LED current is compared with simulation results. This work shows that the UV LED technology is becoming sufficiently mature to switch on SiC thyristors. Thus, an alternative, less expensive and more compact gate light source than the UV laser is now possible. This is of particular interest for very high voltage and pulse power electronic applications.

Demonstration of 13.56-MHz class-E amplifier using a high-Voltage GaN power-HEMT

A 13.56-MHz class-E amplifier with a high-voltage GaN HEMT as the main switching device is demonstrated to show the possibility of using GaN HEMTs in high-frequency switching power applications such as RF power-supply applications. The 380-V/1.9-A GaN power HEMT was designed and fabricated for high-voltage power-electronics applications. The demonstrated circuit achieved the output power of 13.4 W and the power efficiency of 91% under a drain-peak voltage as high as 330 V. This result shows that high-voltage GaN devices are suitable for high-frequency switching applications under high dc input voltages of over 100 V.

Characteristics of 6H-silicon carbide PIN diodes prototyping by laser doping

Silicon carbide PIN diodes have been fabricated using a direct-write laser-doping technique that reduces defect generation compared to the conventional ion-implantation technique. Nitrogen and aluminum were successfully incorporated into SiC as n-type and p-type dopants, respectively. Rutherford backscattering studies were conducted to compare the lattice defect generation by the laser-doping and ion-implantation techniques. No amorphization was observed in laser-doped samples, eliminating the need for high-temperature annealing. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the PIN diodes were also investigated. The silicon carbide diodes are intended for high-temperature and high-voltage power electronics applications.

Characterization of SiC Schottky diodes at different temperatures

The emergence of silicon carbide (SiC) based power semiconductor switches, with their superior features compared with silicon (Si) based switches, has resulted in substantial improvement in the performance of power electronics converter systems. These systems with SiC power devices have the qualities of being more compact, lighter, and more efficient; thus, they are ideal for high-voltage power electronics applications. In this study, commercial Si pn and SiC Schottky diodes are tested and characterized, their behavioral static and loss models are derived at different temperatures, and they are compared with respect to each other.

Characterization of hard- and soft-switching performance of high-voltage Si and 4H-SiC PiN diodes

This paper presents a study of the performance of high-voltage Si and 4H-SiC diodes in a DC-DC buck converter. Device operation in both hard- and zero-voltage switching conditions is presented with the help of measurements and two-dimensional (2-D) mixed device-circuit simulations. Experimental results show that SiC PiN diodes have a strong potential for use in high-speed high-voltage power electronics applications operating at high temperature. A combination of low excess carrier concentration and low carrier lifetime results in superior switching performance of the 4H-SiC diode over ultrafast Si diodes. Soft switching is shown to minimize the switching loss and allow operation at higher switching frequencies using Si diodes. The power loss of 4H-SiC diodes is dominated by conduction loss. Consequently, soft-switching techniques result in a marginal reduction in power loss. However, the low overall power loss implies that SiC diodes can be used at very high switching frequencies even in hard-switching configurations.

SYSTEM IMPACT OF SILICON CARBIDE POWER DEVICES

The emergence of silicon carbide- (SiC-) based power semiconductor switches, with their superior features compared with silicon- (Si-) based switches, has resulted in substantial improvements in the performance of power electronics converter systems. These systems with SiC power devices have the qualities of being more compact, lighter, and more efficient; thus, they are ideal for high voltage power electronics applications such as a hybrid electric vehicle (HEV) traction drive. More research is required to show the impact of SiC devices in power conversion systems. In this study, findings of SiC research at Oak Ridge National Laboratory (ORNL) including SiC device design and system modeling studies, will be given.

SiC and GaN High-Voltage Power Devices

ABSTRACTThe present status of development of SiC and GaN devices for high-voltage power electronics applications is reviewed. Device structures that are particularly applicable to these two wide bandgap semiconductors are considered and compared to those commonly used in silicon. The simulated and experimental performance of two-terminal rectifiers and three- terminal transistors and thyristors are compared. The effects of material parameters (mobility, ionization coefficients, lifetimes) and defects on device characteristics are pointed out. Similarities and differences between electronic and photonic device development in these semiconductors are discussed.

Evaluation of high temperature dielectric films for high voltage power electronic applications

Three high temperature films, polyimide, Teflon perfluoroalkoxy and poly-P-xylene, were evaluated for possible use in high voltage power electronic applications, such as in high energy density capacitors, cables and microelectronic circuits. The dielectric properties, including permittivity and dielectric loss, were obtained in the frequency range of 50 Hz to 100 kHz at temperatures up to 200°C. The dielectric strengths at 60 Hz were determined as a function of temperature to 250°C. Confocal laser microscopy was performed to diagnose for voids and microimperfections within the film structure. The results obtained indicate that all films evaluated are capable of maintaining their high voltage properties, with minimal degradation, at temperatures up to 200°C. However, above 200°C, they lose some of their electrical properties. These films may therefore become viable candidates for high voltage power electronic applications at high temperatures.