ESD protection element

1. An electrostatic discharge (ESD) protection element using an NPN bipolar transistor, comprising:

a trigger element connected at one end with a pad,

wherein said NPN bipolar transistor comprises:

a first base diffusion layer;

a collector diffusion layer connected with said pad;

a trigger tap formed on said first base diffusion layer and connected with the other end of said trigger element through a first wiring; and

an emitter diffusion layer and a second base diffusion layer each separately connected at a common junction provided at a second wiring directly connecting each of the emitter diffusion layer and the second base diffusion layer to the power supply,

wherein the emitter diffusion layer and the second base diffusion layer are formed on said first base diffusion layer, and the second wiring at which the emitter diffusion layer and the second base diffusion layer are connected is different from said first wiring.

2. The ESD protection element according to claim 1 , wherein said emitter diffusion layer is formed between said trigger tap and said second base diffusion layer.

3. An electrostatic discharge (ESD) protection element, comprising:

a trigger element connected at one end with a pad; and

an NPN bipolar transistor comprising

a first base diffusion layer,

a collector diffusion layer connected with said pad,

a trigger tap formed on said first base diffusion layer and connected with the other end of said trigger element through a first wiring, and

an emitter diffusion layer and a second base diffusion layer formed on said first base diffusion layer and connected in common to a power supply through a second wiring which is different from said first wiring, the emitter diffusion layer being formed between the trigger tap and the second base diffusion layer,

wherein an impurity concentration of said first base diffusion layer between said trigger tap and said emitter diffusion layer is higher than that of said first base diffusion layer between said second base diffusion layer and said emitter diffusion layer.

4. The ESD protection element according to claim 1 , wherein said trigger element comprises at least one diode.

5. The ESD protection element according to claim 1 , wherein said trigger element comprises a transistor having a source and a drain connected between said NPN bipolar transistor and said pad.

6. An electrostatic discharge (ESD) protection element comprising first and second NPN bipolar transistors whose collectors are connected to each other, and a trigger element,

wherein said first NPN bipolar transistor comprises:

a first base diffusion layer;

a first trigger tap formed on said first base diffusion layer and connected with one end of said trigger element through a first wiring; and

a first emitter diffusion layer and a second base diffusion layer formed on said first base diffusion layer and connected in common to said pad through a second wiring which is different from said first wiring, and

wherein said second NPN bipolar transistor comprises:

a third base diffusion layer;

a second trigger tap formed on said third base diffusion layer and connected with the other end of said trigger element through a third wiring; and

a second emitter diffusion layer and a fourth base diffusion layer formed on said third base diffusion layer and connected in common to a power supply through a fourth wiring which is different from said third wiring.

7. The ESD protection element according to claim 6 , wherein said first emitter diffusion layer is formed between said first trigger tap and said second base diffusion layer, and

wherein said second emitter diffusion layer is formed between said second trigger tap and said fourth base diffusion layer.

8. The ESD protection element according to claim 7 , wherein an impurity concentration of said first base diffusion layer between said first trigger tap and said first emitter diffusion layer is higher than that of said first base diffusion layer between said second base diffusion layer and said first emitter diffusion layer, and

wherein an impurity concentration of said third base diffusion layer between said second trigger tap and said second emitter diffusion layer is higher than that of said third base diffusion layer between said fourth base diffusion layer and said second emitter diffusion layer.

9. The ESD protection element according to claim 8 , further comprising:

a first diode connected between said pad and said one end of said trigger element; and

a second diode connected between said power supply and said other end of said trigger element.

10. The ESD protection element according to claim 6 , wherein said trigger element comprises at least one diode.

11. The ESD protection element according to claim 6 , wherein said trigger element comprises a transistor having a source and a drain connected between said NPN bipolar transistor and said pad.

12. The ESD protection element according to claim 1 , wherein the first wiring and the second wiring including the common junction of the emitter diffusion layer and the second base diffusion layer are electrically isolated from each other in a wiring layer.

13. The ESD protection element according to claim 1 , wherein when a voltage higher than a predetermined voltage is applied to the pad, trigger current flows from the trigger tap into the first base diffusion layer and subsequently flows from the first base diffusion layer to the power supply through the second base diffusion layer.

14. The ESD protection element according to claim 1 , wherein the first wiring and the second wiring including the junction of the emitter diffusion layer and the second base diffusion layer are disposed in a wiring layer, the NPN transistor being disposed in a region below the wiring layer.

15. The ESD protection element according to claim 1 , wherein the emitter diffusion layer and the second base diffusion layer are each disposed directly on the first base diffusion layer.

16. The ESD protection element according to claim 1 , wherein a resistance formed in the first base diffusion layer between a base region of the first base diffusion layer and the second base diffusion layer is connected to the power supply through the second base diffusion layer and the second wiring line.

17. The ESD protection element according to claim 16 , wherein the resistance pulls up a voltage of the base region with trigger current flowing from the trigger tap into the first base diffusion layer.