GaN-based Semi Vertical Trench MOSFET: characterization and reliability

The upcoming of new technologies in the electronics field and the theme of energy waste introduce the exigence of increasing the efficiency in power conversions through the development of new devices. In this work, the focus is on GaN implementation, whose properties make it interesting for power electronics and, in particular, for the implementation of vertical structures. The analyzed devices are Semi Vertical Trench MOSFET developed by Bosch in the field of YESvGaN European project and has been tested in the laboratories of the Advanced Characterization and Modeling of Electronics research group of the University of Padova. Three different wafers having the same layout but realized with different processing techniques and different materials have been used in this work. On each wafer different configuration of trench MOSFET and planar devices has been tested. The analysis of devices' behavior and non-idealities has been made based on different type of tests aimed at studying different aspects: at the beginning, preliminary DC characterization were done both on planar and vertical devices, with the objective of analyzing the differences between the device configurations inside the same wafer and between the same type of device on the three different wafers. In addition, an analysis of device reliability in OFF-state conditions was done to analyze breakdown phenomena to evaluate the root cause of the failure mechanism. The results indicate that the failure in OFF-state conditions is caused by the voltage between the gate and the drain and so to a failure of the gate oxide. Then, different measurements have been performed to investigate charge trapping effects: threshold voltage transient measurements were used to see the behavior of this parameter imposing different stress conditions and different temperatures; capacitance measurements (CV) were used to estimate the trapped electrons. Has been demonstrated that the devices with contact to the p-body show improved trapping properties, possibly associated to a better activation of the p-doping. In addition, has been demonstrated that the wafer with palladium as body contact results in lower trapping phenomena, probably related to a different step process during fabrication that results in a better GaN/Oxide interface.