Isolated SCR ESD device

An isolated silicon controlled rectifier (SCR) electro-static discharge (ESD) device comprising:

• a substrate;
• a first well located in the substrate, which is floating and has a first conductivity type, wherein the first well is not included with a high density doped region having the first conductivity type for connection with the pad;
• a first high density doped region having a second conductivity type for electrical connection with a pad, wherein the first high density doped region is located in the first well;
• a second well nearby the first well and having the second conductivity type;
• a second high density doped region located in the second well and having the second conductivity type;
• a third high density doped region located in the second well and having the first conductivity type,
• wherein the first high density doped region, the first well, the second well, and the third high density doped region constitute an SCR;
• and
• a fourth high density doped region located at one or more of the following locations:
• (1) at a junction area between the first and second wells,
• (2) in the first well and with a predetermined distance from the junction area between the first and second wells, or
• (3) in the second well and with a predetermined distance from the junction area between the first and second wells.