Effect of P-type Guard ring on the Turn-on Characteristics of Diode-triggered SCR

In this paper, the influence of inner p-type guard ring (PGR) on the triggering characteristics of diode-triggered silicon-controlled rectifier (DTSCR) is studied. The ESD characteristics of conventional DTSCR with and without inner PGR are measured with the transmission line pulsing (TLP) tester. The results indicate that lower trigger voltage of DTSCR can be obtained by floating the internal PGR, which enhances the current conduction ability of the parasitic SCR in DTSCR essentially. A stronger parasitic SCR can provide a current discharge path with lower resistance before the main SCR is turned on, thus reducing the trigger voltage of the device. Furthermore, two improved structures of DTSCR are also considered, which further confirms the auxiliary triggering effect of parasitic SCR or parasitic PNPNPN structure in these devices.