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 (IESD), 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.