Misconception with Pad-Based CDM ESD Protection

On-chip ESD protection is a major reliability problem to ICs. Human body model (HBM) and charged device model (CDM) are fundamentally different ESD phenomena. This review depicts a big common misconception in CDM ESD protection designs. It is well known that CDM ESD is much faster than HBM ESD, therefore, vast design efforts for CDM ESD protection has been devoted to making an CDM ESD protection device faster. Our study concludes that the commonly used pad-based ESD protection methods, while working well for “external-oriented” HBM ESD protection, are theoretically faulty for the “internal-oriented” CDM ESD protection. This misconception with pad-based CDM ESD protection designs is believed to be the root cause to the mystery of CDM ESD failures today.