Bidirectional switch

1. A bidirectional switch, comprising:

a semiconductor substrate of a first conductivity type having a front surface and a rear surface;

first and second adjacent thyristors connected in antiparallel extending vertically between the front surface and the rear surface of the substrate;

a vertical peripheral wall of a second conductivity type connecting the front surface of the semiconductor substrate to the rear surface and surrounding said first and second adjacent thyristors;

on the front surface, in a ring-shaped region of the substrate separating the vertical peripheral wall from the first and second adjacent thyristors, a first region of the first conductivity type, having a greater doping level than the semiconductor substrate, the first region having a shape of a band at least partially surrounding the first thyristor, wherein said first region does not extend into an adjacent region between the first and second adjacent thyristors;

a second region of the first conductivity type located in a first well of the second conductivity type extending from and in contact with said vertical peripheral wall, the second region forming a gate of the bidirectional switch for actuating both the first thyristor and second thyristor.

2. The bidirectional switch of claim 1 , wherein the second region is positioned further from the second thyristor than from the first thyristor and wherein said first region is positioned between the first thyristor and the vertical peripheral wall where said second region is located.

3. The bidirectional switch of claim 2 , wherein the second region is located on a side of the first thyristor opposite to the second thyristor.

4. The bidirectional switch of claim 2 , wherein a portion of the first region is located between the second region and the first thyristor.

5. The bidirectional switch of claim 1 , wherein the shape of a band of the first region surrounds the first thyristor in top view on three sides.

6. The bidirectional switch of claim 1 , wherein the first region is coated with a metallization which is not connected to an external terminal of the switch.

7. The bidirectional switch of claim 1 , further comprising, on the front surface, in said ring-shaped region of the substrate, a third region of the first conductivity type, having a doping level greater than that of the substrate, the third region having the shape of a portion of a band at least partially surrounding the second thyristor, wherein said third region does not extend into the adjacent region between the first and second adjacent thyristors, and wherein ends of the bands for the third and first regions are physically separated from each other by a portion of the semiconductor substrate.

8. The bidirectional switch of claim 7 , wherein the third region is coated with a metallization which is not connected to an external terminal of the switch and not connected to the first region.

9. The bidirectional switch of claim 1 , comprising:

on the rear surface, a layer of the second conductivity type and a fourth region of the first conductivity type formed in said layer and extending over a first portion of the rear surface, said layer being connected to the front surface by the vertical peripheral wall;

on the front surface, a second well of the second conductivity type separated from the vertical peripheral wall by said first region, and a fifth region of the first conductivity type formed in the second well and extending over a second portion of the front surface substantially complementary to the first portion,

wherein ends of the band for the first region are located, in top view, substantially at a same distance from the fourth region as from the fifth region.

10. The bidirectional switch of claim 9 , further comprising a first metallization coating the rear surface at the fourth region and the rear surface of said layer, and a second metallization coating the front surface at the fifth region and the front surface at the second well.

11. The bidirectional switch of claim 1 , wherein the first and second conductivity types, respectively, are type N and type P.

12. The bidirectional switch of claim 1 , wherein the band for the first region is U-shaped to surround the first thyristor in top view on three sides.

13. The bidirectional switch of claim 1 , wherein the band for the first region is C-shaped to surround the first thyristor in top view on three sides.

14. A bidirectional switch, comprising:

a semiconductor substrate having a front surface and a rear surface;

a first region of a first conductivity type within the semiconductor substrate;

a peripheral wall of a second conductivity type extending from the front surface of the semiconductor substrate to the rear surface and surrounding said first region;

a layer of the second conductivity type extending along the rear surface and connected to the peripheral wall;

a second region of the second conductivity type contained within the first region and defining a ring-shaped portion of the first region separating the peripheral wall from said second region;

a third region of the first conductivity type contained within the second region;

a fourth region of the first conductivity type located in the peripheral wall;

a fifth region of the first conductivity type contained within the layer of the second conductivity type; and

on the front surface, in said ring-shaped portion, a first partial region of the first conductivity type, having a greater doping level than the semiconductor substrate, the first partial region shaped to only partially surround both the second region and the third region.

15. The bidirectional switch of claim 14 , further comprising on the front surface, in said ring-shaped portion, a second partial region of the first conductivity type, having a greater doping level than the semiconductor substrate, the second partial region shaped to only partially surround the second region, wherein ends of the second partial region are physically separated from opposed ends of the first partial region by a portion within the ring-shaped portion.

16. The bidirectional switch of claim 14 , wherein the first partial region is U-shaped to surround the first thyristor in plan view on three sides.

17. The bidirectional switch of claim 14 , wherein the first partial region is C-shaped to surround the first thyristor in plan view on three sides.

18. The bidirectional switch of claim 14 , wherein the second region, in plan view, is rectangular in shape having opposed first and second sides and having opposed third and fourth sides, wherein the first partial region is a band that extends along the first side and partially along both the third and fourth sides.

19. The bidirectional switch of claim 18 , further comprising on the front surface, in said ring-shaped portion, a second partial region of the first conductivity type, having a greater doping level than the semiconductor substrate, the second partial region shaped to only partially surround the second region, wherein ends of the second partial region are physically physically separated from opposed ends of the first partial region by a portion within the ring-shaped portion.

20. The bidirectional switch of claim 19 , wherein the second partial region is a band that extends along the second side and partially along both the third and fourth sides.