Showing papers by "John W. Palmour published in 2008"

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

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).

Critical Technical Issues in High Voltage SiC Power Devices

Abstract: In this paper, we review the state of the art of SiC switches and the technical issues which remain. Specifically, we will review the progress and remaining challenges associated with SiC power MOSFETs and BJTs. The most difficult issue when fabricating MOSFETs has been an excessive variation in threshold voltage from batch to batch. This difficulty arises due to the fact that the threshold voltage is determined by the difference between two large numbers, namely, a large fixed oxide charge and a large negative charge in the interface traps. There may also be some significant charge captured in the bulk traps in SiC and SiO2. The effect of recombination-induced stacking faults (SFs) on majority carrier mobility has been confirmed with 10 kV Merged PN Schottky (MPS) diodes and MOSFETs. The same SFs have been found to be responsible for degradation of BJTs.

4H-SiC Bipolar Junction Transistors with a Current Gain of 108

Abstract: 4H-SiC BJTs with a common emitter current gain (b) of 108 at 25°C have been demonstrated. The high current gain was accomplished by using a base as thin as 0.25 μm. The current gain decreases at high temperatures but is still greater than 40 at 300°C. The device demonstrates an open emitter breakdown voltage (BVCBO) of 1150 V, and an open base breakdown voltage (BVCEO) of 250 V. A low specific on-resistance of 3.6 mW-cm2 at 25°C was achieved. The BJTs have shown blocking capabilities over a wide range of operating temperatures up to 300°C.

Self-Heating of 4H-SiC PiN Diodes at High Current Densities

Abstract: Self-heating in high-voltage 4H-SiC PiN diodes has been studied experimentally and theoretically in dc and 8-ms single pulse modes. To simulate the self-heating, an electro-thermal model was used to calculate non-isothermal current-voltage characteristics at dc and current-time dependences at pulsed measurements. The dynamic instability of N-type was observed: the current decreases in spite of increasing of bias applied to the structure. At dc, irreversible diode degradation was found to occur at a current density of about 1700 A/cm2. Under a single current surge 8-ms pulse, the loss of thermal stability has been found at a current density of approximately 9000 A/cm2. Comparison of experimental data and simulations showed that the local temperature in the diode base at the end of the 8-ms, 9000-A/cm2 pulse reaches 2000 – 2300 K.