Performance and Reliability Characterization of 1200 V Silicon Carbide Power MOSFETs and JFETs at High Temperatures

Abstract

1200 V Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) and Junction Field Effect Transistors (JFETs) have been characterized at high operational temperatures. For packaged JFETs obtained from a collaborating manufacturer, the threshold shift (ΔVT) was measured under both static and dynamic voltage stress and, in all cases, was less than 2 mV, which is within the measurement margin of error. Temperatures up to 250°C and stress times as long as 200 hours were evaluated. As a comparison, commercially available SiC MOSFETs demonstrated shifts of up to 300 mV after 30 minutes of static gate stress at 175°C. In addition, results from unpackaged JFET die at temperatures up to 525°C show ΔVT values of less than 10 mV for all stress conditions. Although VT remained unchanged for the duration of the test for both static and dynamic stress conditions, under dynamic stress conditions the JFET packaged parts demonstrated a linear increase in sub-threshold leakage current of around 15.6 nA per hour; in contrast, the MOSFET devices showed an exponential increase in sub-threshold leakage under dynamic stress. The increase in sub-threshold leakage current could be recovered temporarily, but long-term behavior was consistent with cumulative damage.

6.5 kV SiC normally-off JFETs — Technology status

“…The well-known material, processing and cost issues associated with SiC devices has begun to subside, and with the development of 6" SiC substrates, this trend will continue. The SiC MOSFET is gaining acceptance, however the SiC MOS interface still suffers from reliability issues as compared to the SiC JFET [11]. For or this study, a normally-off 6.5 kV SiC JFET is compared to a super-cascode, where five normally-on 1.2 kV rated SiC JFETs are stacked serially with a low voltage Si-MOSFET to form a 6.0 kV rated switch exhibiting the desired normally-off behavior.…”

Series-connection of SiC normally-on JFETs

“…The experimental work in [1] has shown that, under both static and dynamic gate bias stress conditions, the SiC JFET devices have remarkably stable threshold voltages with a drift measured to be less than 10 millivolts at temperatures up to 250°C for 200 hours for packaged parts and 525°C for bare die. As a comparison, commercially available second-generation SiC MOSFETs demonstrate threshold voltage shifts of up to 300 millivolts after 30 minutes of static gate stress at 175°C.…”