Improving safe operating area of nLDMOS array with embedded silicon controlled rectifier for ESD protection in a 24-V BCD process

In high-voltage technologies, silicon-controlled rectifier (SCR) is usually embedded in output arrays to provide a robust and self-protected capability against electrostatic discharge (ESD). Although the embedded SCR has been proven as an excellent approach to increasing ESD robustness, mistriggering of the embedded SCR during normal circuit operating conditions can bring other application reliability concerns. In particular, the safe operating area (SOA) of output arrays due to SCR insertion has been seldom evaluated. In this paper, the impact of embedding SCR to the electrical SOA (eSOA) of an n-channel LDMOS (nLDMOS) array has been investigated in a 24-V bipolar CMOS-DMOS process. Experimental results showed that the nLDMOS array suffers substantial degradation on eSOA due to embedded SCR. Design approaches, including a new proposed poly-bending (PB) layout, were proposed and verified in this paper to widen the eSOA of the nLDMOS array with embedded SCR. Both the high ESD robustness and the improved SOA of circuit operation can be achieved by the new proposed PB layout in the nLDMOS array.