Stephen Daley Arthur

Recent advances in silicon carbide MOSFET power devices

Emerging silicon carbide (SiC) MOSFET power devices promise to displace silicon IGBTs from the majority of challenging power electronics applications by enabling superior efficiency and power density, as well as capability to operate at higher temperatures. This paper reports on the recent progress in development of 1200V SiC power MOSFETs. Two different chip sizes were fabricated and tested: 15A (0.225cm×0.45cm) and 30A (0.45cm×0.45cm) devices. First, the 30A MOSFETs were packaged as discrete components and static and switching measurements were performed. The device blocking voltage was 1200V and typical on-resistance was less than 50 mΩ with gate-source voltages of 0V and 20V, respectively. The total switching losses were 0.6 mJ, over five times lower than the competing devices. Next, a buck converter was built for evaluating long-term stability of the MOSFETs and typical switching waveforms are presented. Finally, the 15A MOSFETs were used for fabrication of 150A all-SiC modules. The module on-resistance values were in the range of 10 mQ, resulting in the best-in-class on-state voltage values of 1.5V at nominal current. The module switching losses were 2.3 mJ during turn-on and 1 mJ during turn-off, also significantly better than competing designs. The results validate performance advantages of the SiC MOSFETs, moving them a step closer to power electronics applications.

Silicon Carbide Integrated Circuits With Stable Operation Over a Wide Temperature Range

In this letter, silicon carbide MOSFET-based integrated circuits have been designed, fabricated, and successfully tested from -193 °C (80 K) to 500 °C. Silicon carbide single MOSFETs remained fully operational over a 700-°C wide temperature range and exhibited stable I-V characteristics. The circuits that include operational amplifier (op-amp), 27-stage ring oscillator, and buffer were tested and shown to be functional up to 500 °C with relatively small performance variation between 300 °C and 500 °C. High-temperature evaluation of these circuits confirmed stable operation and survivability of both the ring oscillator and op-amp for more than 100 h at 500 °C.

DC and Transient Performance of 4H-SiC Double-Implant MOSFETs

SiC vertical MOSFETs were fabricated and characterized, achieving blocking voltages around 1 kV and specific on-resistances as low as RSP,ON=8.3 mOmegamiddotcm2. DC and transient characteristics are shown. Room and elevated temperature (up to 200degC) 600 V/5 A inductive switching performance of the SiC MOSFETs are shown with turn-on and turn-off transients of approximately 20-40 ns.

3kV 4H-SiC Thyristors for Pulsed Power Applications

Due to the Silicon Carbide (SiC) material’s high electric field strength, wide bandgap, and good thermal conductivity, 4H-SiC thyristors are attractive candidates for pulsed power applications. With a thinner blocking layer almost an order of magnitude smaller than its Silicon (Si) counterpart, these devices promise very fast turn-on capabilities as full conductivity modulation occurs >10 times faster than comparable silicon thyristors, low leakage currents at high junction temperatures and at high voltage, and much lower forward voltage drop at high pulse currents. Our progress on the development of large area (4mm x 4mm) SiC thyristors is presented in this paper.

Device and circuit modeling of GaN/InGaN light emitting diodes (LEDs) for optimum current spreading

In this paper we use Aimspice device and circuit simulator to demonstrate that uniform current spreading does not only depend on p-transparent metal and n-GaN layers resistivities but is also a strong function of design. This is demonstrated by modeling two light emitting diode (LED) designs, A and B, which differ in the position and size of the p-contact pad. Design A exhibited better current uniformity than B because of the symmetry in the current spreading length. By keeping the resistivities of p-transparent metal and n-GaN layers fixed, the variation in current uniformity as bias current increases from 20 to 300 mA for design A is only 2% and � 9.5% for design B. The decrease in current spreading uniformity as the resistances of these layers increase is smaller in design A (2–3.5% as resistance increases from 3.8 to 6.7 X=) than design B (9.5–14.5%). A further analysis shows that the current uniformity increases as the p-transparent metal layer resistance decreases from 25 to 3.8 X=, even though, the n-GaN lateral resistance is fixed at 12 X=. This suggests better uniform current spreading in flipped chip LED design than top-emitting light emitting diodes, since LED flipped chip configuration uses thick reflective metal on top of p_GaN. Further more, current spreading uniformity increases as the thickness of p-transparent metal layer and in this model it peaked at 94.9% for a thickness of 15 nm. This is where the contact resistance, which dominates the vertical resistance of the network, had the highest value. It therefore means that the current uniformity is a function of contact resistance, which is based on the thickness of the transparent metal and ultimately affects light extraction. � 2003 Elsevier Ltd. All rights reserved.

4kV Silicon Carbide MOSFETs

Doubly-implanted SiC vertical MOSFETs were fabricated displaying a blocking voltage of 4.2kV and a specific on-resistance of 23 mΩ-cm2, on a 4.5mm x 2.25mm device. Design variations on smaller (1.1mm x 1.1mm) devices showed on-resistance as low as 17 mΩ-cm2 with a blocking voltage of 3.3kV. Analysis is presented of the on-resistance and temperature dependence (up to 175°C), as well as switching performance. Switching tests taken at 1000V and 6A showed turn-on and turn-off transients of approximately 20-40ns.

Stability and 2-D Simulation Studies of Avalanche Breakdown in 4H-SiC DMOSFETs With JTE

In this paper, the stability of n-channel 4H-silicon carbide (SiC) DMOSFETs with junction termination extension (JTE) was assessed by measuring the breakdown voltage (BV) of these devices before and after bias stress at a high temperature. The BV slumped after the DMOSFET was bias stressed at 1200 V for 2 h at 175degC, and the slumped BV dynamically recovered to the prestress value during the poststress period. Computer simulation suggests that the BV slump and its recovery are dominated by the positive charge trapping/detrapping phenomena at the SiC/fleld oxide interface in the JTE structure, rather than the trapping/detrapping at the SiC/gate oxide interface in the cell structure. A positive interface charge of approximately one-third of the sheet dopant concentration of the JTE region, lowers BV by 150 V, which is the typical measured BV slump of the DMOSFETs of this paper.

Design of Area-Efficient, Robust and Reliable Junction Termination Extension in SiC Devices

This paper discusses SiC JTE design tradeoffs required to maximize device performance while minimizing consumed die area, fabrication cost and maintaining good reliability. Modeling and experimental results are provided.

MCT (MOS controlled thyristor) reliability investigation

The authors outline some of the ruggedness features observed in recent MCTs. The MCT capabilities described cover the last stages of tests performed on devices that were production-line fabricated and aimed at 400 to 1600 V blocking levels but small enough in die size to be packaged in a TO-220 or TO-218 plastic package. The goal of 100-A operation, a 1-V forward drop at 20 A, and a 1- mu s turn-off time has been achieved in 0.2 to 0.4 cm/sup 2/ production-line-fabricated MCTs. The high-current ruggedness, including di/dt, is due to low forward drop plus uniform MOS-gated turn-on. Turn-off current ruggedness is the result of small cell size and the fact that the MCT blocking junction is flat. High-temperature capability along with excellent noise capability and virtually zero Miller gate capacitance are due to the very dense off-FET shorts and the low (<1 V) FET source-drain voltage and off-FET average current.<<ETX>>

Readiness of SiC MOSFETs for Aerospace and Industrial Applications

This paper highlights ongoing efforts to validate performance, reliability and robustness of GE SiC MOSFETs for Aerospace and Industrial applications. After summarizing ruggedness and reliability testing performed on 1.2kV MOSFETs, two application examples are highlighted. The first demonstrates the 1.2kV device performance in a prototype high frequency 75kW Aviation motor drive. The second highlights the experimental demonstration of a 99% efficient 1.0MW solar inverter using 1.7kV MOSFET modules in a two-level topology switching at 8kHz. Both applications illustrate that SiC advantage is not only in improved performance, but also in significant system cost savings through simplifications in topology, controls, cooling and filtering.