ESD protection for CMOS output buffer by using modified LVTSCR devices with high trigger current

Modified designs of the low-voltage triggering semiconductor-controlled rectifier (LVTSCR) devices with high trigger current are proposed to protect the CMOS output buffer against electrostatic discharge (ESD) events in submicrometer CMOS technologies. The high trigger current is achieved by inserting the bypass diodes into the structures of the modified PMOS-trigger lateral SCR (PTLSCR) and NMOS-trigger lateral SCR (NTLSCR) devices. These modified PTLSCR and NTLSCR devices have a lower trigger voltage to effectively protect the output transistors in the ESD-stress conditions, but they also have a higher trigger current to avoid the accidental triggering due to the electrical noise on the output pad in the normal operating conditions of CMOS IC's. Experimental results have verified that the trigger current of the modified PTLSCR (NTLSCR) is increased up to 225.5 mA (218.5 mA). The noise margin to the overshooting (undershooting) voltage pulse on the output pad, without accidentally triggering on the modified NTLSCR (PTLSCR), is more than VDD + 12 V (VSS - 12 V).