Charlotte Jonas

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.

Design and Characterization of High-Voltage 4H-SiC p-IGBTs

High-voltage p-channel 4H-SiC insulated gate bipolar transistors (IGBTs) have been fabricated and characterized. The devices have a forward voltage drop of 7.2 V at 100 A/cm2 and a -16 V gate bias at 25degC, corresponding to a specific on-resistance of 72 mOmega ldr cm2 and a differential on-resistance of 26 mmOmega ldr cm2. Hole mobility of 12 cm2/V ldr s in the inversion channel with a threshold voltage of -6 V was achieved by optimizing the n+ well doping profile and gate oxidation process. A novel current enhancement layer was adopted to reduce the JFET resistance and enhance conductivity modulation by improving hole current spreading and suppressing the electron current conduction through the top n-p-n transistor. Inductive switching results have shown that the p-IGBT exhibited a turn-off time of ~1 mus and a turn-off energy loss of 12 m J at 4-kV dc-link voltage and 6-A load current at 25degC. The turn-off trajectory from the measured inductive load switching waveforms and numerical simulations shows that the p-IGBT had a near-square reverse bias safe operating area. Numerical simulations have been conducted to achieve an improved tradeoff between forward voltage drop and switching off energy by investigating the effects of drift layer lifetime and p-buffer layer parameters. The advantages of SiC p-IGBTs, such as the potential of very low ON-state resistance, slightly positive temperature coefficient, high switching speed, small switching losses, and large safe operating area, make them suitable and attractive for high-power high-frequency applications.

Design and Fabrications of High Voltage IGBTs on 4H-SiC

For the first time, SiC planar p-IGBTs with 5.8 kV of blocking voltage have been fabricated and characterized. The device exhibits a differential on-resistance of ~ 570 mOmegamiddotcm2 at the gate bias of -30 V at 25degC, and decreases to ~ 118 mOmegamiddotcm2 at 200degC, ~108 mOmega middot cm 2 at 300degC, respectively. The median hole mobility in the inversion channel is 2.3 cm2/Vmiddots, and increases gradually with temperature. The effects of p-type field stopper layer and JFET region implantation to device current conduction capability were investigated. Numerical simulations have shown that to improve IGBT on-resistance, it is critical to achieve a high carrier lifetime in both drift region and JFET region, and a high value of inversion layer hole mobility

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.

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.

12 kV 4H-SiC p-IGBTs with Record Low Specific On-Resistance

DC characteristics of 4H-SiC p-channel IGBTs capable of blocking -12 kV and conducting -0.4 A (-100 A/cm2) at a forward voltage of -5.2 V at 25°C are demonstrated for the first time. A record low differential on-resistance of 14 mW×cm2 was achieved with a gate bias of -20 V indicating a strong conductivity modulation in the p-type drift region. A moderately doped current enhancement layer grown on the lightly doped drift layer effectively reduces the JFET resistance while maintains a high carrier lifetime for conductivity modulation. A hole MOS channel mobility of 12.5 cm2/V-s at -20 V of gate bias was measured with a MOS threshold voltage of -5.8 V. The blocking voltage of -12 kV was achieved by Junction Termination Extension (JTE).

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.

Development of 15 kV 4H-SiC IGBTs

We present our latest developments in ultra high voltage 4H-SiC IGBTs. A 6.7 mm x 6.7 mm 4H-SiC N-IGBT with an active area of 0.16 cm2 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. A 4H-SiC P-IGBT exhibited a record high blocking voltage of 15 kV, while showing a differential specific on-resistance of 24 mΩ-cm2. A comparison between P- and N- IGBTs in 4H-SiC is provided in this paper.

Performance of 60 A, 1200 V 4H-SiC DMOSFETs

Large area (8 mm x 7 mm) 1200 V 4H-SiC DMOSFETs with a specific on-resistance as low as 9 m•cm2 (at VGS = 20 V) able to conduct 60 A at a power dissipation of 200 W/cm2 are presented. On-resistance is fairly stable with temperature, increasing from 11.5 m•cm2 (at VGS = 15 V) at 25°C to 14 m•cm2 at 150°C. The DMOSFETs exhibit avalanche breakdown at 1600 V with the gate shorted to the source, although sub-breakdown leakage currents up to 50 A are observed at 1200 V and 200°C due to the threshold voltage lowering with temperature. When switched with a clamped inductive load circuit from 65 A conducting to 750 V blocking, the turn-on and turn-off energies at 150°C were less than 4.5 mJ.