Avalanche Breakdown Delay in ESD Protection Diodes

Electrostatic discharge (ESD) protection diodes with a breakdown (BD) voltage above 50 V might exhibit a BD delay in the order of microseconds. The phenomenon is related to the low generation of seed carriers that can start an avalanche BD event by impact ionization. However, emission of carriers from deep traps, or the onset of tunneling generation, can shorten the delay to only fractions of a nanosecond. Emission from deep traps has been found strong enough to make this kind of device effective for protection under standard ESD conditions. However, the application of a bias voltage prior to a stress pulse empties the trap states and thus leads to increasing BD delay. This paper investigates the BD delay in an ESD protection diode under various bias and pulse conditions. A model for the BD delay is proposed, taking into account the different seed carrier generation mechanisms. The activation energy of the dominating deep trap can be calculated to 0.18 eV by measuring the time to BD at different temperatures.