Improvement on diode string structure for 65-nm RF ESD protection

• A new diode string structure has been developed for 65-nm ESD protection.
• It possesses a 30% lower clamping voltage, a 15% lower overshoot voltage under very fast ESD pulse.
• It has a faster turn-on speed of 0.8 ns, and a low intrinsic capacitance of 28 fF.
• It is successfully implemented in a low-noise amplifier (LNA) and achieved a ±2.5 kV human body model (HBM) ESD level.

Diode strings are frequently used for electrostatic discharge (ESD) protection of high-speed and radio-frequency (RF) I/O pins due to their low capacitance, tunable trigger voltage and simplicity of design, but they always exhibit a high clamping voltage due to the series connected on-resistance, which limits their applications in low-voltage ICs. In order to reduce to their clamping voltage, a new structure of diode string has been developed and investigated by 2-D electro-thermal simulations. Experimental results show that the improved diode string possesses a 30% lower clamping voltage, a 15% lower overshoot voltage under very fast ESD pulse, a faster turn-on speed of 0.8 ns, and a low intrinsic capacitance of 28 fF. The improved diode string is successfully implemented in a fully-integrated 3–10 GHz ultra-wide band (UWB) low-noise amplifier (LNA) based on a 65 nm CMOS process, which is shown to have minimal effects on the RF performances and achieves a ±2.5 kV human body model (HBM) ESD level.