Reverse bias instabilities in bipolar power transistors with cellular layout

The different instabilities exhibited by power BJTs during inductive turn-o ff are classified, and then studied theoretically, by means of two-dimensio nal (2-D) simulator in which the device is simulated within a realistic ext ernal circuit, and experimentally, by means of a nondestructive method. It is shown that many instabilities originate by an interaction between electr ic field and charge within a single cell, which causes transit time oscilla tion phenomena. The role of the stray capacitance of the circuit in favorin g these instabilities is described. Other kinds of instability cannot be un derstood by studying a single cell but rather require accounting for the in teractions between cells. Finally, an "instability map" is used as a synthetic picture of the device behavior which ensures an easy way to link device behavior with its physica l features.