Fast turn-on of an NMOS ESD protection transistor: measurements and simulations

The transient turn-on of the parasitic bipolar transistor of an NMOS transistor was studied. The voltages appearing at internal nodes of protection and functional circuit after application of 350 ps rise-time pulses have been measured using electro-optic sampling. For very fast transients the triggering of the protection transistor shifts from an avalanche multiplication current towards a displacement current-induced triggering, thereby lowering the trigger voltage. With our circuit simulation mode we are able to predict the outcome of human body model and charged device model testing.