Understanding and Modeling of Diode Voltage Overshoots During Fast Transient ESD Events

Diodes in forward direction exhibit excellent ESD ruggedness and are thus widely used in both discrete and on-chip electro-static discharge (ESD) protection devices. Due to the conductivity modulation under an ESD stress, a transient voltage overshoot is observed at the beginning of a fast discharge event. Since the voltage overshoot can be harmful, understanding the origin of the overshoot is crucial to design optimized protection diodes. In this paper, it will be shown that existing models can result in much underestimated overshoot voltage, especially for diodes with a large lowly doped region. This can be attributed to the negligence of transient charge distribution in the lowly doped region. A new model that takes this effect into account as well as impact-ionization is presented.