A failure levels study of non-snapback ESD devices for automotive applications

Abstract

Snapback ESD devices suffer from increasing danger when the protected ICs experience ESD events in powered up states. To ensure more reliable ESD protections, non-snapback ESD structures are gaining more importance in the field of automotive ESD design. Two types of on-chip non-snapback ESD devices, pn-diodes and active FET structures are investigated in this work regarding their failure levels. Characteristics of the ESD devices as well as electrical SOA of an nLDMOS are evaluated and discussed in detail with TCAD electro-thermal simulation, SPICE circuit simulation and mainly TLP measurements. Comparison of the efficiency of different ESD protections considering ESD window is also given, delivering the basic idea of choosing the right ESD devices in automotive applications.

No-Snapback LDMOS Using Adaptive RESURF and Hybrid Source for Ideal SOA

“…While the failure currents, It2, are similar for both the PN source and Hybrid Source LDMOS, the drain voltage under which this happens is significantly different. For this reason it is useful to compare the power-to-failure metric [14], Vd * Id, as shown in Fig. 9.…”

“…This enables a more direct path for holes to pass to the p+ body pick up, Fig. 14 Thus, a lower resistance is seen by the holes, and an enhancement to the electrical SOA can be expected. Previously, this resistance reduction had been in the range 21%....58% [4].…”

“…The combination of these two mechanisms, reduced body resistance and reduced electron injection from the source, are key elements in suppressing the parasitic bipolar which fundamentally changes the nature of the failure mechanism compared to a conventional LDMOS. For the conventional device, parasitic bipolar induced electrical snapback (electrical instability [14]), current filamentation and ultimately thermal failure. For the Hybrid Source LDMOS, electrical snapback is skipped and the thermal failure becomes a feature of the drain side engineering.…”