An analysis of false turn-on mechanism on high-frequency power devices (original) (raw)

Analysis of Performance and Reliability of Sub-kV SiC and GaN Cascode Power Electronic Devices

PhD Thesis, 2023

The reliability and performance of the power semiconductor devices are significantly critical, since the utilization of the power electronics in the field of renewable energy, electrical transportation applications. The performance of devices leads to unpredictable power losses, while their failure can cause extremely unfortunate faults in the power systems. Gallium Nitride (GaN) is one of wide bandgap materials that is advantageous, as it has low on-state resistance and internal capacitances. These features decreases the losses during switching and conduction, resulting in higher efficiency that can be a encouraging candidate for RF amplifiers or motor driving applications. Another wide bandgap material is Silicon Carbide (SiC) that is also improved the switching rates and it has thin voltage blocking layer lowering on state resistance of devices. However, SiC based MOSFET has a reliability concern regarding to the threshold voltage instability due to defects at the gate oxide layer. GaN based devices are commonly depletion mode devices due to the two dimensional gas layer at the hetero-interface in and these devices are used in cascode configuration to be used as enhancement mode. The central research focus is related to comprehensive exploration and analysis of recently commercially available GaN and SiC power cascode devices. To understand dynamic performance of GaN and SiC cascode devices, the switching and 3rd performance of these devices are investigated with double pulse test circuit. The key result is that GaN cascode outperforms SiC cascode devices with smaller gate resistors in switching transients. Then, an analytical model is developed to observe the impact their parasitic capacitances on switching performance in cascode configuration. Following that, parasitic turn-on/off of cascode devices have been observed during switching and it is investigated with crosstalk test circuit. Later, a model is created to predict the possible impact of the stray inductance on switching of the cascode devices. The threshold voltage instability is observed with biasing the terminals of cascode devices. The effect of the stress causes great drifts in threshold voltage of the discrete power cascode devices as well as power modules even with increasing temperature. The GaN cascode devices shows great drifts in their threshold voltages at high temperature after biasing gate terminal that could be related to defect density between the multiple layers of hetero-structure. Main output is GaN has threshold instability similar to SiC device after different stress conditions. Next, as for the reliability of power cascodes, their avalanche ruggedness capability have been carried out with the single pulse unclamped inductive switching test. The 650 V GaN could only withstand a single avalanche ruggedness test condition while other counterpart are able to confront more avalanche energy. Later on, their short circuit capabilities have been evaluated with a single pulse. The results shows GaN has some avalanche energy even it is very small. The effects of temperature, DC-link voltage level and gate resistor on the short circuit capability of the power cascode devices are analyzed. Lastly, to analyze the influence of thermal and electrical stress by power cycling test on power cascode devices have been studied and transfer characteristics, leakage currents and on-state resistance parameters have been observed after stressing cycles.