Parasitic NPN and PNP Latch-Up Within a Single DMOS for High Voltage Reliability

This article discusses the robustness of field-plate-assisted reduced surface field effect (RESURF) DMOS designs to time-dependent latch-up within a single dielectrically isolated device. This work individually characterizes the dopant defined parasitic bipolar parallel to all MOS and uniquely describes the existence of another parasitic bipolar of opposite polarity through the generation of a backgate current as a result of weak impact ionization. These two NPN and PNP bipolar devices in a single DMOS device complete the latch-up mechanism once the product of their gains is greater than one. The characterized time-dependent nature of the increasing backgate current is accounted for by oxide charge trapping in the extended drain region, where measurements of this mechanism over a broad range of application and manufacturing variables enable a mathematical model for the time to failure to be described. Finally, the advantage of analyzing DMOS latch-up robustness in the context of individual parasitic NPN and PNP bipolar devices is shown by its ability to isolate out the separate variables feeding into each bipolar to implement robust solutions.