ESD protection design for mixed-voltage I/O buffer with substrate-triggered circuit

A substrate-triggered technique is proposed to improve the electrostatic discharge (ESD) robustness of a stacked-nMOS device in the mixed-voltage I/O circuit. The substrate-triggered technique can further lower the trigger voltage of a stacked-nMOS device to ensure effective ESD protection for mixed-voltage I/O circuits. The proposed ESD protection circuit with substrate-triggered design for a 2.5-V/3.3-V-tolerant mixed-voltage I/O circuit has been fabricated and verified in a 0.25-μm salicided CMOS process. The substrate-triggered circuit for a mixed-voltage I/O buffer to meet the desired circuit application in different CMOS processes can be easily adjusted by using HSPICE simulation. Experimental results have confirmed that the human- body-model (HBM) ESD robustness of a mixed-voltage I/O circuit can be increased ∼60% by this substrate-triggered design.