Practical Challenges of High-Power IGBT's I-V Curve Measurement and Its Importance in Reliability Analysis

Abstract

This paper examines the practical challenges of simplified setups aimed at achieving high-power IGBTs' I-C-V-CE curve. The slope of this I-V curve (which is defined as on-resistance R-CE) and the point where the V-CE-V-GE curve visibly bends (threshold gate voltage) can be suitable failure precursor parameters to determine an IGBT's health condition. A simplified/affordable design for these specific measurements can be used for in-situ condition monitoring or field testing of switching devices. First, the possible I-V curve measurement methods are discussed in detail in order to prevent self-heating. The selected design includes two IGBTs in which the high-side IGBT was the device under test (DUT) with a constant gate voltage (V-GE) of 15 V. Then, the low-side IGBT was switched by a short pulse (50 mu s) to impose a high-current pulse on the DUT. The V-CE-V-GE curve was also extracted as an important failure-precursor indicator. In the next stage, a power-cycling test was performed, and the impact of degradation on the IGBT was analyzed by these measurement methods. The results show that after 18,000 thermal cycles, a visible shift in I-V curve can be seen. The internal resistance increased by 13%, while the initial collector-emitter voltage and voltage at the knee point in the V-CE-V-GE curve slightly changed. It is likely that in our case, during the performed power-cycling test and aging process, the bond wires were most affected, but this hypothesis needs further investigation.