In this work, DC and transient characteristics of a 4 diode string utilizing\ntriple-well technologies as a VDD-VSS clamp device for ESD protection are\nanalyzed in detail based on 2-dimensional device and mixed-mode simulations.\nIt is shown that there exists parasitic pnp bipolar transistor action in\nthis device leading to a sudden increase in DC substrate leakage if anode bias\nis getting high. Through transient simulations for a 2000 V PS-mode HBM\nESD discharge event, it is shown that the dominant discharge path is the one\nformed by a parasitic pnpn thyristor and a parasitic npn bipolar transistor in\nseries. Percentage ratios of the various current components regarding the\nanode current at its current peaking are provided. The mechanisms involved\nin ESD discharge inside the diode-string clamp utilizing triple-well technologies\nare explained in detail, which has never been done anywhere in the literature\nbased on simulations or measurements.
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