Influence of Epitaxial Layer Thickness on the Holding Voltage Scalability of Bi-Directional SCR Devices

Abstract

This work investigates the impact of epitaxial layer (Epi) thickness on the holding voltage ( $V_{\mathrm {h}}$ ) scalability of bidirectional silicon-controlled rectifiers (BiSCRs) in 130 nm BCD technology. Experimental results show that increasing the base lengths ( $L_{\mathrm {nb}}$ / $L_{\mathrm {pb}}$ ) of parasitic BJTs leads to a linear increase in $V_{\mathrm {h}}$ under a thicker epitaxial process ( $1.5\times $ ), while having a negligible impact in a thinner epitaxial process ( $1\times $ ). Technology computer-aided design (TCAD) simulations attribute this disparity to Epi dependent current gain variations in the parasitic NPN and PNP BJTs: thinner Epi strengthens NPN gain, dominating conduction current and suppressing $V_{\mathrm {h}}$ control via lateral base-length adjustments, while thicker Epi weakens NPN gain, enabling effective $V_{\mathrm {h}}$ tuning. These findings demonstrate that Epi thickness critically determines the efficacy of geometric design strategies for BiSCR latch-up immunity, guiding optimized ESD protection in holding-voltage sensitive applications.