Robust Off-State TDDB Reliability of n-LDMOS.

We report on the gate oxide reliability of n-type LDMOS which is integrated in a 90nm BiCMOS technology and is optimized to offer a robust off-state TDDB reliability performance. In contrast to previous published results, we demonstrate that off-state TDDB lifetimes show very weak dependence on the applied drain bias, Vd, thanks to the carefully optimized NWell drift region that effectively shields the channel from the deleterious high electric fields associated with high Vd operation and significantly reduces the vertical electric field across the gate oxide as shown by TCAD simulation results. TDDB lifetimes are then mainly modulated by the gate voltage and are found to be comparable to the lifetimes obtained under inversion and accumulation modes, hence enabling a reliable operation under high Vdg bias levels.