Optimization Design on Active Guard Ring to Improve Latch-Up Immunity of CMOS Integrated Circuits

A new optimization design of an active guard ring has been proposed to improve latch-up immunity of CMOS integrated circuits and been successfully verified in a 0.18-μm 1.8-/3.3-V CMOS technology. Codesigned with the on-chip electrostatic discharge (ESD) protection devices (gate-ground nMOS and gate-VDD pMOS) equipped at the input-output (I/O) pad, the overshooting/undershooting trigger current during latch-up test can be conducted away through the turned-on channels of the ESD protection MOSFET's to the power rails (V_DD or V_SS). Therefore, the trigger current injecting from the I/O devices (that directly connected to the I/O pad) through the substrate to initiate the latch-up occurrence at the internal circuit blocks can be significantly reduced. Thus, the latch-up immunity of the whole chip can be effectively improved under the same placement distance between the I/O cells and the internal circuit blocks. The new proposed design is a cost-efficient solution to improve latch-up immunity and also to mention good ESD robustness of the I/O cells.