High holding voltage SCR for robust electrostatic discharge protection

A novel silicon controlled rectifier (SCR) with high holding voltage ($V_h)$ for electrostatic discharge (ESD) protection is proposed and investigated in this paper. The proposed SCR obtains high $V_h$ by adding a long N+ layer (LN+) and a long P+ layer (LP+), which divide the conventional low voltage trigger silicon controlled rectifier (LVTSCR) into two SCRs (SCR1: P+/Nwell/Pwell/N+ and SCR2: P+/LN+/LP+/N+) with a shared emitter. Under the low ESD current ($I_{ESD})$, the two SCRs are turned on at the same time to induce the first snapback with high $V_h$ ($V_{h1})$. As the $I_{ESD}$ increases, the SCR2 will be turned off because of its low current gain. Therefore, the $I_{ESD}$ will flow through the longer SCR1 path, bypassing SCR2, which induces the second snapback with high $V_h$ ($V_{h2})$. The anti-latch-up ability of the proposed SCR for ESD protection is proved by a dynamic TLP-like (Transmission Line Pulse-like) simulation. An optimized $V_{h2}$ of 7.4 V with a maximum failure current ($I_{t2})$ of 14.7 mA/$\mu m$ is obtained by the simulation. (paper)