Design on the low-leakage diode string for using in the power-rail ESD clamp circuits in a 0.35-μm silicide CMOS process

A new design on the diode string with very tow leakage current is proposed for using in the ESD clamp circuits across the power rails. By adding an NMOS-controlled lateral SCR (NCLSCR) device into the stacked diode string, the Leakage current of this new diode string with six stacked diodes at 5-V (3.3-V) forward bias can be reduced to only 2.1 (1.07) nA at a temperature of 125 degrees C in a 0.35-mu m silicide CMOS process, whereas the previous designs have a leakage current in the order of mA, The total blocking voltage of this new design with NCLSCR can be linearly adjusted by changing the number of the stacked diodes in the diode string without causing latch-up danger across the power rails. From the experimental results, the human-body-model ESD level of the ESD clamp circuit with the proposed low-leakage diode string is greater than 8 kV in a 0.35-mu m silicide CMOS process by using neither the ESD-implantation nor the silicide-blocking process modifications.