Ballasted polycrystalline fuse

1. A polycrystalline fuse comprising:

a first layer of polycrystalline material on a substrate;

a second layer of a silicide material on the first layer;

the first and second layers being shaped to form first and second terminal portions of a first width joined along a length of the fuse by a fuse portion of a second width narrower than the first width;

first and second contacts connected to the first and second terminal portions respectively of the second layer forming the fuse material in the fuse portion; and

the silicide material being discontinuous in one of the terminal portions of the second layer along the length of the fuse prior to programming.

2. The polycrystalline fuse of claim 1 , wherein the polycrystalline material is silicon.

3. The polycrystalline fuse of claim 1 , wherein the silicide material is one of cobalt silicide, titanium silicide, tantalum silicide and platinum silicide.

4. The polycrystalline fuse of claim 1 , wherein the discontinuity is in both of the terminal portions of the second layer.

5. The polycrystalline fuse of claim 1 , wherein the first and second contacts are connected to the first and second terminal portions of the second layer.

6. An integrated circuit comprising a fuse of claim 1 and a transistor connected to one of the contacts for driving the fuse with sufficient current to program the fuse.

7. A polycrystalline fuse comprising:

a first layer of polycrystalline material on a substrate;

a second layer of a silicide material on the first layer;

the first and second layers being shaped to form first and second terminal portions of a first width joined by a fuse portion of a second width narrower than the first width;

first and second contacts connected to the first and second terminal portions respectively of the second layer forming the fuse material in the fuse portion; and

the second layer including a third material of a higher resistance than the silicide material in one of the terminal portions and in series with the silicide material between the first and second contacts prior to programming.

8. The polycrystalline fuse of claim 7 , wherein the third material is a dielectric material.

9. The polycrystalline fuse of claim 7 , wherein the polycrystalline material is silicon.

10. The polycrystalline fuse of claim 7 , wherein the silicide material is one of cobalt silicide, titanium silicide, tantalum silicide and platinum silicide.

11. The polycrystalline fuse of claim 7 , wherein the third material is in both of the terminal portions of the second layer.

12. The polycrystalline fuse of claim 7 , wherein the first and second contacts are connected to the first and second terminal portions of the second layer.

13. An integrated circuit comprising a fuse of claim 1 and a transistor connected to one of the contacts for driving the fuse with sufficient current to program the fuse.

14. A polycrystalline fuse comprising:

a first layer of polycrystalline material on a substrate;

a fuse layer on the first layer;

the first and fuse layers being shaped to form first and second terminal portions of a first width joined by a fuse portion of a second width narrower than the first width;

first and second contacts connected to the first and second terminal portions respectively; and

the fuse layer being constructed prior to programming to have an initial current carrying capacity of half of a maximum current carrying capacity for a substantial portion of a programming period and have the maximum current carrying capacity near the end of the programming period.