The Influence of Repetitive UIS on Electrical Properties of Advanced Automotive Power Transistors

Abstract

This paper investigates a degradation of three types of automotive power MOSFETs through repetitive Unclamped Inductive Switching (UIS) test typically used to evaluate the avalanche robustness of power devices. It is not uncommon in switching ap- plications that greater than the planned voltage for volt- age spikes can occur, so even the best electronic designs may encounter frequent avalanche events. Hence, there is a need to analyse the impact of repetitive avalanch- ing on the electrical performance of power transis- tors. This article focused on the shift of main electri- cal parameters: on-resistance RON , breakdown voltage VBR, threshold voltage VT H , and corresponding char- acteristics, as well as capacitances. Analysis proved that DMOS transistors are less vulnerable to repeti- tive avalanching. The most impacted parameter was on-resistance RDSon, where a 14 % increase was ob- served after 6 · 107 stress pulses. The parameters shift is attributed to hot carrier injection in the space charge region of blocking PN junction and involves mainly defects generation/activation in the drain side region of the gate oxide. For the TrenchMOS transistor, a significant shift of I − V curves was observed with considerable impact on the RON where an increase of 22 % was observed. The trench corner is verified to be the mainly degraded region by Synopsys Tech- nology Computer Aided Design (TCAD) simulations. Degradation of drain-gate capacitance CDG and input capacitance Cin was observed in all three types of anal- ysed structures. DLTS was used to verify the gener- ation/activation of defects invoked by stress. An in- crease of DLTS signal corresponding to energy levels of oxygen vacancies and impurities in SiO2 and on in- terfaces were detected on stressed samples.