Papers by Author: Charlotte Jonas

Abstract: A 1 cm x 1 cm 4H-SiC N-IGBT exhibited a blocking voltage of 20.7 kV with a leakage current of 140 μA, which represents the highest blocking voltage reported from a semiconductor power switching device to this date. The device used a 160 μm thick drift layer and a 1 μm thick Field-Stop buffer layer, and showed a V_F of 6.4 V at an I_C of 20 A, and a differential R_on,sp of 28 mΩ-cm². Switching measurements with a supply voltage of 8 kV were performed, and a turn-off time of 1.1 μs and turn-off losses of 10.9 mJ were measured at 25°C, for a 8.4 mm x 8.4 mm device with 140 μm drift layer and 2 μm F-S buffer layer. The turn-off losses were reduced by approximately 50% by using a 5 μm F-S buffer layer. A 55 kW, 1.7 kV to 7 kV boost converter operating at 5 kHz was demonstrated using the 4H-SiC N-IGBT, and an efficiency value of 97.8% was reported.

Abstract: For the first time, a 1200 V 4H-SiC power MOSFET with a monolithically integrated gate buffer circuit has been demonstrated successfully. The device used a 6x10¹⁵ cm^-3 doped, 10 μm thick n-type drift layer to support 1200 V. The gate buffer circuit was built in a p-well, formed by boron ion implantation. The integrated device provided sufficient voltage isolation for the control circuit from the drain of the power MOSFET, and supported internal supply voltages up to 20 V. The operation of the integrated devices was demonstrated. A specific on-resistance (R_on,sp) of 20 mΩ-cm² was observed. The high R_on,sp was due to the limitations in NMOS pull-up circuit topology and the body effect in the 4H-SiC NMOSFET. Development of PMOS pull-up devices is recommended for future integration efforts.

Abstract: In this work, we report our recently developed 16 kV, 1 cm², 4H-SiC PiN diode results. The SiC PiN diode was built on a 120 µm, 2×10¹⁴/cm³ doped n-type SiC drift layer with a device active area of 0.5175 cm². Forward conduction of the PiN diode was characterized at temperatures from 20°C to 200°C. At high injection-current density (J_F) of 350 ~ 400 A/cm², the differential on-resistance (R_ON,diff) of the SiC PiN diode decreased from 6.08 mΩ·cm² at 20°C to 5.12 mΩ·cm² at 200°C, resulting in a very small average temperature coefficient of –5.33 µΩ·cm²/°C, while the forward voltage drop (V_F) at 100 A/cm² reduced from 4.77 V at 20°C to 4.17 V at 200°C. This is due to an increasing high-level carrier lifetime with an increase in temperature, resulting in reduced forward voltage drop. We also observed lower R_ON,diff at higher injection-current densities, suggesting that a higher carrier lifetime is needed in this lightly doped n-type SiC thick epi-layer in order to achieve full conductivity modulation. The anode to cathode reverse blocking leakage current was measured as 0.9 µA at 16 kV at room temperature.

Abstract: The latest developments in ultra high voltage 4H-SiC IGBTs are presented. A 4H-SiC P-IGBT, with a chip size of 8.4 mm x 8.4 mm and an active area of 0.32 cm², which is double the active area of the previously reported devices [1], exhibited a blocking voltage of 15 kV, while showing a room temperature differential specific on-resistance of 41 mΩ-cm² with a gate bias of -20 V. A 4H-SiC N-IGBT with the same area showed a blocking voltage of 17 kV, and demonstrated a room temperature differential specific on-resistance of 25.6 mΩ-cm² with a gate bias of 20 V. Field-Stop buffer layer design was used to control the charge injection from the backside. A comparison between N- and P- IGBTs, and the effects of different buffer designs, are presented.

Abstract: 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.

Abstract: We present our recent developments in 4H-SiC power DMOSFETs. 4H-SiC DMOSFETs with a room temperature specific on-resistance of 3.7 mΩ-cm2 with a gate bias of 20 V, and an avalanche voltage of 1550 V with gate shorted to source, was demonstrated. A threshold voltage of 3.5 V was extracted from the power DMOSFET, and a subthreshold swing of 200 mV/dec was measured. The device was successfully scaled to an active area of 0.4 cm2, and the resulting device showed a drain current of 377 A at a forward voltage drop of 3.8 V at 25oC.

Abstract: DMOSFETs fabricated in 4H-SiC with capabilities for blocking in excess of 1700V and conducting 20A continuous current in the on-state are presented. These SiC DMOSFETs remain functional to temperatures in excess of 225°C, with leakage current at 1700V at 225°C of less than 5 A with VGS = 0V. The DMOSFETs show excellent switching characteristics, with total switching energy of 1.8 to 1.95 mJ over the entire temperature range of testing (25°C to 200°C), when switched from the blocking state at 1200V to conducting at 20A in a clamped inductive load switching circuit. The electrical characteristics are compared to commercially available Si IGBTs rated to 1700V with similar current ratings as the SiC DMOSFET described herein.

Abstract: 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.

Abstract: 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).

Abstract: 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.