Craig Capell

10 kV, 120 A SiC half H-bridge power MOSFET modules suitable for high frequency, medium voltage applications

The majority carrier domain of power semiconductor devices has been extended to 10 kV with the advent of SiC MOSFETs and Schottky diodes. The devices exhibit excellent static and dynamic properties with encouraging preliminary reliability. Twenty-four MOSFETs and twelve Schottky diodes have been assembled in a 10 kV half H-bridge power module to increase the current handling capability to 120 A per switch without compromising the die-level characteristics. For the first time, a custom designed system (13.8 kV to 465/√3 V solid state power substation) has been successfully demonstrated with these state of the art SiC modules up to 855 kVA operation and 97% efficiency. Soft-switching at 20 kHz, the SiC enabled SSPS represents a 70% reduction in weight and 50% reduction in size when compared to a 60 Hz conventional, analog transformer.

1000-V, 30-A 4H-SiC BJTs with high current gain

This paper presents the development of 1000 V, 30A bipolar junction transistor (BJT) with high dc current gain in 4H-SiC. BJT devices with an active area of 3/spl times/3 mm/sup 2/ showed a forward on-current of 30 A, which corresponds to a current density of 333 A/cm/sup 2/, at a forward voltage drop of 2 V. A common-emitter current gain of 40, along with a low specific on-resistance of 6.0m/spl Omega//spl middot/cm/sup 2/ was observed at room temperature. These results show significant improvement over state-of-the-art. High temperature current-voltage characteristics were also performed on the large-area bipolar junction transistor device. A collector current of 10A is observed at V/sub CE/=2 V and I/sub B/=600 mA at 225/spl deg/C. The on-resistance increases to 22.5 m/spl Omega//spl middot/cm/sup 2/ at higher temperatures, while the dc current gain decreases to 30 at 275/spl deg/C. A sharp avalanche behavior was observed at a collector voltage of 1000 V. Inductive switching measurements at room temperature with a power supply voltage of 500 V show fast switching with a turn-off time of about 60 ns and a turn-on time of 32 ns, which is a result of the low resistance in the base.

A 13 kV 4H-SiC n-Channel IGBT with Low Rdiff,on and Fast Switching

For the first time, high power 4H-SiC n-IGBTs have been demonstrated with 13 kV blocking and a low Rdiff,on of 22 mWcm2 which surpasses the 4H-SiC material limit for unipolar devices. Normally-off operation and >10 kV blocking is maintained up to 200oC base plate temperature. The on-state resistance has a slight positive temperature coefficient which makes the n-IGBT attractive for parallel configurations. MOS characterization reveals a low net positive fixed charge density in the oxide and a low interface trap density near the conduction band which produces a 3 V threshold and a peak channel mobility of 18 cm2/Vs in the lateral MOSFET test structure. Finally, encouraging device yields of 64% in the on-state and 27% in the blocking indicate that the 4H-SiC n-IGBT may eventually become a viable power device technology.

High Temperature Characterization of 4H-SiC Bipolar Junction Transistors

This paper summarizes the recent demonstration of 3200 V, 10 A BJT devices with a high common emitter current gain of 44 in the linear region, and a specific on-resistance of 8.1 mΩ- cm2 (10 A at 0.90 V with a base current of 350 mA and an active area of 0.09 cm2). The onresistance increases to 40 mΩ-cm2 at 350°C, while the DC current gain decreases to 30. A sharp avalanche behavior was observed with a leakage current of 10 μA at a collector voltage of 3.2 kV.

Ultra high voltage (>12 kV), high performance 4H-SiC IGBTs

We present our latest developments in ultra high voltage 4H-SiC IGBTs. A 4H-SiC P-IGBT, with a chip size of 6.7 mm × 6.7 mm and an active area of 0.16 cm2 exhibited a record high blocking voltage of 15 kV, while showing a room temperature differential specific on-resistance of 24 mΩ-cm2 with a gate bias of -20 V. A 4H-SiC N-IGBT with the same area showed a blocking voltage of 12.5 kV, and demonstrated a room temperature differential specific on-resistance of 5.3 mΩ-cm2 with a gate bias of 20 V. Buffer layer design, which includes controlling the doping concentration and the thickness of the field-stop buffer layers, was used to control the charge injection from the backside. Effects on buffer layer design on static characteristics and switching behavior are reported.

Influence of Basal Plane Dislocation Induced Stacking Faults on the Current Gain in SiC BJTs

SiC BJTs show instability in the I-V characteristics after as little as 15 minutes of operation. The current gain reduces, the on-resistance in saturation increases, and the slope of the output characteristics in the active region increases. This degradation in the I-V characteristics continues with many hours of operation. It is speculated that this phenomenon is caused by the growth of stacking faults from certain basal plane dislocations within the base layer of the SiC BJT. Stacking fault growth within the base layer is observed by light emission imaging. The energy for this expansion of the stacking fault comes from the electron-hole recombination in the forward biased base-emitter junction. This results in reduction of the effective minority carrier lifetime, increasing the electron-hole recombination in the base in the immediate vicinity of the stacking fault, leading to a reduction in the current gain. It should be noted that this explanation is only a suggestion with no conclusive proof at this stage.

High performance, ultra high voltage 4H-SiC IGBTs

We present our latest developments in ultra high voltage 4H-SiC IGBTs. A 4H-SiC P-IGBT, with a chip size of 6.7 mm × 6.7 mm and an active area of 0.16 cm2 exhibited a record high blocking voltage of 15 kV, while showing a room temperature differential specific on-resistance of 24 mΩ-cm2 with a gate bias of -20 V. A 4H-SiC N-IGBT with the same area showed a blocking voltage of 12.5 kV, and demonstrated a room temperature differential specific on-resistance of 5.3 mΩ-cm2 with a gate bias of 20 V. Buffer layer design, which includes controlling the doping concentration and the thickness of the field-stop buffer layers, was used to control the charge injection from the backside. Effects on buffer layer design on static characteristics and switching behavior are reported.

15 kV, Large Area (1 cm2), 4H-SiC p-Type Gate Turn-Off Thyristors

In this paper, we report our recently developed 1 cm2, 15 kV SiC p-GTO with an extremely low differential on-resistance (RON,diff) of 4.08 mΩ•cm2 at a high injection-current density (JAK) of 600 ~ 710 A/cm2. The 15 kV SiC p-GTO was built on a 120 μm, 2×1014/cm3 doped p-type SiC drift layer with a device active area of 0.521 cm2. Forward conduction of the 15 kV SiC p-GTO was characterized at 20°C and 200°C. Over this temperature range, the RON,diff at JAK of 600 ~ 710 A/cm2 decreased from 4.08 mΩ•cm2 at 20°C to 3.45 mΩ•cm2 at JAK of 600 ~ 680 A/cm2 at 200°C. The gate to cathode blocking voltage (VGK) was measured using a customized high-voltage test set-up. The leakage current at a VGK of 15 kV were measured 0.25 µA and 0.41 µA at 20°C and 200°C respectively.

22 kV, 1 cm 2 , 4H-SiC n-IGBTs with improved conductivity modulation

In this paper, we report our recently developed large area 4H-SiC n-IGBTs that have a chip size of 1 cm2 and an active conducting area of 0.37 cm2. A blocking voltage of 22.6 kV has been demonstrated with a leakage current of 9 μA at a gate bias of 0 V at room-temperature. This is the highest breakdown voltage of a single MOS-controlled semiconductor switch reported to date. To improve the conductivity modulation and lower the conduction losses during the on-state, a thermal oxidation process was applied to enhance the carrier lifetime prior to the device fabrication. Compared to the devices that did not receive this lifetime enhancement process, the lifetime enhanced devices displayed nearly 1 V lower forward voltage drop with little increase in switching energy and no degradation of static blocking characteristics. A specific differential on-resistance of 55 mΩ-cm2 at 20 A and 125 °C was achieved, suggesting that bipolar power devices with thick drift regions can benefit from further enhancement of the ambipolar carrier lifetime.

Ultra high voltage MOS controlled 4H-SiC power switching devices

Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 mΩ cm2 at 25 °C, which increased to 570 mΩ cm2 at 150 °C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (VF), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.