High holding voltage cascoded LVTSCR structures for 5.5-V tolerant ESD protection clamps

This paper presents a new design concept for the control of the holding voltage of LVTSCR ESD protection structures by realizing a negative feedback in the p emitter. The negative feedback is implemented by the creation of a voltage drop using embedded circuit elements. The final clamp voltage is tuned to exceed the power supply level, thus eliminating the potential for latchup. The design is validated by ESD pulse measurements performed on test structures with cascoded, triggered LVTSCRs for 5.5-V tolerant I/O pins in an 0.18-mum CMOS process. The results of the first part of the study were used to propose another design for the LVTSCR with a high holding voltage based on emitter area reduction. The proposed device is validated using three-dimensional simulations and experimental analysis.