An Investigation of the Drain-Source Leakage Current Early Transients During HTRB Reliability Tests

Abstract

High Temperature Reverse Bias (HTRB) is a qualification and reliability test, where devices are subject to high temperature and reverse voltage bias for a defined amount of time (typically 1000 hours), while the drain-source leakage current is monitored. The devices can fail or exhibit patterns of failure at the early stages; hence, it is important to understand the early transient behaviour of the leakage currents while the devices are under test. Moreover, during HTRB, a large number of devices are usually stressed and monitored in parallel. In this paper, two 1200 V SiC MOSFETs of similar current ratings (trench and planar) were investigated. Different experiments have been performed to investigate the exponentially decaying transient of the drain-source leakage current, and the differences between monitoring individual discrete devices and monitoring discrete devices grouped together. Experimental results show that when stressing devices in parallel the exponential decay is common to all the devices, with the total current being the result of adding the individual leakage currents. The impact of the stress voltage applied to the devices (700 to 1000 V) and temperature (50 to 150°C) was also investigated. The results show that generally, the transient time is shorter at lower temperatures, and that it increases as the stress voltage increases. Additionally, the investigated devices showed different relaxation time constants in the orders of thousands (trench) and hundreds (planar) of seconds.