Capacitor including a capacitor plate formed from a doped semiconductor

1. A capacitor comprising:

a metal plate;

a doped semiconductor plate doped with a dopant, the doped semiconductor plate having a top, a bottom and a side having an edge;

a dielectric sandwiched therebetween; and

a metallic contact coupled to the edge of the doped semiconductor plate wherein the metallic contact extends around at least a portion of the edge of the semiconductor plate.

2. A capacitor as claimed in claim 1 , wherein the metallic contact extends around at least 5% of the periphery of the semiconductor plate.

3. A capacitor as claimed in claim 2 , wherein the metallic contact extends completely around the edge of the semiconductor plate.

4. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate comprises a tongue which protrudes beyond a periphery of the metal plate for connection to the metallic contact.

5. A capacitor as claimed in claim 1 , wherein the semiconductor plate is a III V semiconductor plate.

6. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate is In x Ga 1-x As, wherein X is in the range 0 to 0.7.

7. A capacitor as claimed in claim 1 , wherein the dopant comprises Silicon.

8. A capacitor as claimed in claim 7 , wherein a concentration of the dopant is greater than 1×1017 atoms/cm 3 .

9. A capacitor as claimed in claim 7 , wherein a concentration of the dopant is greater than 5×10 17 atoms/cm 3 .

10. A capacitor as claimed in claim 7 , wherein a concentration of the dopant is greater than 1×10 18 atoms/cm 3 .

11. A capacitor as claimed in claim 7 , wherein a concentration of the dopant is greater than 2×10 18 atoms/cm 3 .

12. A capacitor as claimed in claim 1 , wherein the dopant comprises at least one of Boron or Carbon.

13. A capacitor as claimed in claim 12 , wherein a concentration of the dopant is greater than 1×10 17 atoms/cm 3 .

14. A capacitor as claimed in claim 12 , wherein a concentration of the dopant is greater than 5×10 17 atoms/cm 3 .

15. A capacitor as claimed in claim 12 , wherein a concentration of the dopant is greater than 1×10 18 atoms/cm 3 .

16. A capacitor as claimed in claim 12 , wherein a concentration of the dopant is greater than 2×10 18 atoms/cm 3 .

17. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate is a portion of larger semiconductor substrate.

18. A capacitor as claimed in claim 17 , wherein the doped semiconductor plate is provided by diffusion of the dopant into the semiconductor substrate.

19. A capacitor as claimed in claim 17 , wherein the doped semiconductor plate is provided by implantation of the dopant into the semiconductor substrate.

20. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate is deposited as a doped layer on a semiconductor substrate.

21. A capacitor as claimed in claim 1 , wherein the dielectric comprises Silicon and Nitrogen, the ratio of Silicon and Nitrogen preferably being in the range 0.5 to 2.

22. A capacitor as claimed in claim 21 , wherein the dielectric further comprises hydrogen contaminant.

23. A capacitor as claimed in claim 21 , wherein the dielectric is deposited on the doped semiconductor plate by vapour deposition.

24. A capacitor as claimed in claim 1 , wherein the dielectric comprises silicon and oxygen preferably in the ratio 0.5 to 3.

25. A capacitor as claimed in claim 24 , wherein the dielectric further comprises hydrogen contaminant.

26. A capacitor as claimed in claim 1 , wherein the dielectric is a polymer.

27. A capacitor as claimed in claim 1 , wherein the metal plate is a bond pad.

28. A capacitor as claimed in claim 1 , wherein the metallic contact extends around at least 40% of the periphery of the semiconductor plate.

29. A capacitor as claimed in claim 1 , wherein the metallic contact extends around at least 80% of the periphery of the semiconductor plate.

30. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate is In x Ga 1-x As, wherein X is in the range 0.1 to 0.6.

31. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate is In x Ga 1-x As, wherein X is in the range 0.3 to 0.6.

32. A capacitor as claimed in claim 1 , wherein the doped semiconductor plate is In x Ga 1-x As, wherein X is in the range 0.4 to 0.5.

33. A capacitor as claimed in claim 1 , wherein the dielectric comprises Silicon and Nitrogen, the ratio of Silicon and Nitrogen preferably being in the range 0.65 to 0.85.