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For system-on-chip applications with mixed-voltage I/O interfaces, I/O circuits with low-voltage devices must drive or receive high-voltage signals to communicate with other circuit blocks. With the consideration of low standby leakage in nanoscale CMOS processes, a new 2 × VDD-tolerant electrostatic discharge (ESD) clamp circuit by using only 1 × VDD devices was presented in this paper. The new ESD clamp circuit had a high-voltage-tolerant ESD detection circuit to improve the turn-on efficiency of an ESD clamp device, which consisted of a silicon-controlled rectifier (SCR) with a diode in series. This design had successfully been verified in a 65-nm CMOS process. The leakage current of this ESD clamp circuit under normal circuit operating condition was only on the order of 100 nA. The test patterns with 25- and 50-m SCR-based ESD clamp devices can achieve 2.6- and 4.8-kV human-body-model ESD robustness, respectively. Such high-voltage-tolerant ESD clamp circuits, by using only low-voltage devices with very low standby leakage current and high ESD robustness, were very suitable for mixed-voltage I/O interfaces in nanoscale CMOS processes.
Date of Publication: July 2010