Electrostatic discharge (ESD) protection design for mixed-voltage I/O interfaces has been one of the key challenges of system-on-a-chip (SOC) implementation in nano-scale CMOS processes. The on-chip ESD protection circuit for mixed-voltage I/O interfaces should meet the gate-oxide reliability constraints and prevent the undesired leakage current paths. This paper presents an overview on the design concept and circuit implementations of the ESD protection designs for mixed-voltage I/O interfaces without using the additional thick gate-oxide process. The ESD design constraints in mixed-voltage I/O interfaces, the classification and analysis of ESD protection designs for mixed-voltage I/O interfaces, and the designs of high-voltage-tolerant power-rail ESD clamp circuit are presented and discussed.

A new design on the electrostatic discharge (ESD) protection scheme for CMOS IC operating in power-down-mode condition is proposed. By adding a VDD_ESD bus line and diodes, the new proposed ESD protection scheme can block the leakage current from I/O pin to VDD power line to avoid malfunction during power-down-mode operating condition. During normal circuit operating condition, the new proposed ESD protection schemes have no leakage path to interfere with the normal circuit functions. The whole-chip ESD protection design can be achieved by insertion of ESD clamp circuits between VSS power line and both VDD power line and VDD ESD bus line. Experimental results have verified that the human-body-model (HBM) ESD level of this new scheme can be greater than 7.5 kV in a 0.35-μm silicided CMOS process. Furthermore, output-swing improvement circuit is proposed to achieve the full swing of output voltage level during normal circuit operating condition.

This paper presents a new electrostatic discharge (ESD) protection design for input/output (I/O) cells with embedded silicon-controlled rectifier (SCR) structure as power-rail ESD clamp device in a 130-nm CMOS process. Two new embedded SCR structures without latchup danger are proposed to be placed between the input (or output) pMOS and nMOS devices of the I/O cells. Furthermore, the turn-on efficiency of embedded SCR can be significantly increased by substrate-triggered technique. Experimental results have verified that the human-body-model (HBM) ESD level of this new proposed I/O cells can be greater than 5 kV in a 130-nm fully salicided CMOS process. By including the efficient power-rail ESD clamp device into each I/O cell, whole-chip ESD protection scheme can be successfully achieved within a small silicon area of the I/O cell.

New diode structures without the field-oxide boundary across the p/n junction for ESD protection are proposed. A NMOS (PMOS) is especially inserted into the diode structure to form the NMOS-bounded (PMOS-bounded) diode, which is used to block the field oxide isolation across the p/n junction in the diode structure. The proposed N(P)MOS-bounded diodes can provide more efficient ESD protection to the internal circuits, as compared to the other diode structures. The N(P)MOS-bounded diodes can be used in the I/O ESD protection circuits, power-rail ESD clamp circuits, and the ESD conduction cells between the separated power lines. From the experimental results, the human-body-model ESD level of ESD protection circuit with the proposed N(P)MOS-bounded diodes is greater than 8 kV in a 0.35-μm CMOS process.

Electrostatic discharge (ESD) protection design for mixed-voltage I/O interfaces has been one of the key challenges of system-on-a-chip (SOC) implementation in nanoscale CMOS processes. This paper presents an overview on the design concept and circuit implementations of the ESD protection designs for mixed-voltage I/O interfaces without using the additional thick gate-oxide process. The ESD design constraints in mixed-voltage I/O interfaces, the classification, and analysis of ESD protection designs for mixed-voltage I/O interfaces are presented and discussed.