Woongje Sung

Smart grid technologies

The need for power semiconductor devices with high-voltage, high- frequency, and high-temperature operation capability is growing, especially for advanced power conversion and military applications, and hence the size and weight of the power electronic system are reduced. Development of 15-kV SiC IGBTs and their impact on utility applications is discussed.

Strategic Overview of High-Voltage SiC Power Device Development Aiming at Global Energy Savings

Advanced high-voltage (≥10 kV) silicon carbide (SiC) devices described in this paper have the potential to significantly impact the system size, weight, high-temperature reliability, and cost of modern variable-speed medium-voltage (MV) systems such as variable speed (VSD) drives for electric motors, integration of renewable energy including energy storage, micro-grids, traction control, and compact pulsed power systems. In this paper, we review the current status of the development of 10 kV-20 kV class power devices in SiC, including MOSFETs, JBS diodes, IGBTs, GTO thyristors, and PiN diodes at Cree. Advantages and weakness of each device are discussed and compared. A strategy for high-voltage SiC power device development is proposed.

Design and investigation of frequency capability of 15kV 4H-SiC IGBT

15kV 4H-SiC n-channel asymmetric and symmetric IGBTs were designed to minimize the on state and switching power loss. A Current Enhancement Layer was adopted to reduce the forward voltage drop for each IGBTs. For the asymmetric IGBT, it was found that the frequency capability of the device was affected most by adjusting the buffer region parameters such as doping concentration, thickness, and lifetime. For the symmetric IGBT, the p+ substrate doping concentration and drift region lifetime were investigated to obtain maximum switching frequency capability. A comparison of frequency capabilities between power MOSFETs, asymmetric, and symmetric IGBTs has been made. IGBTs provide lower power loss than power MOSFETs up to approximately 7 kHz.

Bevel Junction Termination Extension—A New Edge Termination Technique for 4H-SiC High-Voltage Devices

A new edge termination method, referred to as a bevel junction termination extension (Bevel-JTE), is presented for high-voltage silicon carbide devices. The 4H-SiC PiN rectifiers, with a breakdown voltage of 1600 V (~95% of the theoretical value), were fabricated using Bevel-JTEs. The Bevel-JTE technique significantly reduces the chip size by decreasing space occupied by edge termination while providing broad process latitude for parameter variations, such as implantation dose and activation anneal condition.

Monolithically Integrated 4H-SiC MOSFET and JBS Diode (JBSFET) Using a Single Ohmic/Schottky Process Scheme

This letter reports a new 900 V 4H-SiC JBSFET containing an MOSFET with an integrated JBS diode in the center area of the chip. Both MOSFET and JBS diode structures utilize the same edge termination structure,which results in 30% reduction in SiC wafer area consumption in case of 10 A rating device. In order to form a Schottky contact for the JBS diode as well as ohmic contacts for n+ source and p+ body of the MOSFET, a simple metal process flow has been newly developed. It was found that Ni can simultaneously form ohmic contacts on n+ and p+ implanted regions while it remains a Schottky contact on the n-epitaxial drift layer when it is annealed at moderate temperature (900°C for 2 min). The proposed JBSFET was successfully fabricated using a nine-mask on 6-in 4H-SiC wafers.

A Near Ideal Edge Termination Technique for 4500V 4H-SiC Devices: The Hybrid Junction Termination Extension

This letter presents a new edge termination technique named a hybrid junction termination extension (Hybrid-JTE), which combines ring-assisted JTE and multiple floating zone JTE. Based on the parameters of the drift layer specified by the wafer vendor, the measured breakdown voltage of the fabricated p-i-n diode using the Hybrid-JTE is as high as 5450 V, which is close (~99%) of the ideal parallel plane p-n junction. Furthermore, measured breakdown voltages from randomly chosen 32 p-i-n diodes across the wafer show very tight distribution: 29 diodes provide breakdown voltages higher than 5000 V at 100 μA.

10kV SiC MPS diodes for high temperature applications

This paper presents the device structure and characterization results of 10-kV 4H-SiC MPS diodes from room temperature to 200°C and compares them with JBS and PiN diodes fabricated on the same wafer. The results showed that SiC MPS diodes exhibit superior trade-off between forward voltage drop and low reverse recovery charge with increasing temperature. Results of numerical simulation are shown to explain the behavior of MPS diodes.

Area-Efficient Bevel-Edge Termination Techniques for SiC High-Voltage Devices

This paper reviews the bevel-edge termination techniques for silicon carbide (SiC) power devices, such as bevel junction termination extension (JTE), resistive-bevel termination, bevel-assisted JTE, and positive-bevel termination. The proposed bevel-edge termination techniques significantly reduce the chip size for SiC power devices. PiN diodes and test structures were fabricated to quantify the relative performance of the proposed structures. Quantitative comparison in chip size reduction, process schemes, and future research directions is discussed in detail.

A Comparative Study 4500-V Edge Termination Techniques for SiC Devices

This paper compares five edge termination techniques for SiC high-voltage devices: single zone junction termination extension (JTE), ring assisted-JTE (RA-JTE), multiple floating zone-JTE, hybrid-JTE, and floating field rings. PiN diodes with these edge terminations were fabricated on a 4.5kV-rated 4H-silicon carbide (4H-SiC) epi-layer. It was experimentally demonstrated that the Hybrid-JTE provides a nearly ideal breakdown voltage (~ 99% of the ideal parallel plane breakdown voltage) with a stable avalanche blocking behavior. RA-JTE, with tight control of the JTE implant dose, is demonstrated to be the most area-efficient edge termination structure for SiC power devices.

Wide Band Gap Semiconductor Technology for Energy Efficiency

The attributes and benefits of wide-bandgap (WBG) semiconductors are rapidly becoming known, as their use in power electronics applications continues to gain industry acceptance. However, hurdles still exist in achieving widespread market acceptance, on a par with traditional silicon power devices. Primary challenges include reducing device costs and the expansion of a workforce trained in their use. The Department of Energy (DOE) is actively fostering development activities to expand application spaces, achieve acceptable cost reduction targets and grow the acceptance of WBG devices to realize DOEs core missions of more efficient energy generation, greenhouse gas reduction and energy security within the U.S. This paper discusses currently funded activities and application areas that are suitable for WBG introduction. A detailed cost roadmap for SiC device introduction is also presented.