Organic field effect transistor with an organic dielectric

1. A process of manufacturing an organic field effect device comprising the steps of

a) depositing from a solution an organic semiconductor layer; and

b) depositing from a solution a layer of low permittivity insulating material forming at least a part of a gate insulator, such that the low permittivity insulating material is in contact with the organic semiconductor layer, wherein the low permittivity insulating material is of relative permittivity from 1.1 to below 3.0 with the proviso that the low permittivity insulating material is not benzocyclobutene (BCB).

2. A process as claimed in claim 1 further comprising depositing on the other side of the layer of low permittivity insulating material from the organic semiconductor layer at least one layer of high permittivity insulating material, wherein the high permittivity insulating material is of relative permittivity higher than the low permittivity insulating material.

3. A process as claimed in claim 2 wherein the at least one layer of high permittivity insulating material is deposited from a solution.

4. A process as claimed in claim 1 wherein one or more of the layers is deposited from a solution comprising a fluoro solvent.

5. A process as claimed in claim 1 wherein one or more of the layers is deposited from solution by spin coating.

6. A process as claimed in claim 1 wherein all steps are performed at or below about 100° C.

7. An organic field effect device manufactured by the process as claimed in claim 1 .

8. An organic field effect device as claimed in claim 7 wherein the permittivity of the low permittivity insulating material is in the range 1.3 to 2.5, preferably in the range 1.5 to 2.1.

9. An organic field effect device as claimed in claim 7 wherein the device has a top gate configuration.

10. An organic field effect device as claimed in claim 7 wherein the device has a bottom gate configuration.

11. An organic field effect device as claimed in claim 7 wherein the high permittivity insulating material has a permittivity greater than 3.5, preferably greater than 10, more preferably greater than 20, and up to 200.

12. An organic field effect device as claimed in claim 11 wherein the high permittivity insulating material comprises polyvinylidene fluoride, cyanopulluane, polyvinylalcohol or other highly polar organic polymer.

13. An organic field effect device as claimed in claim 11 wherein the high permittivity insulating material comprises at least one of TiO2, Ta 2 O 5 , SrTiO 3 , Bi 4 Ti 3 O 12 , BaMgF 4 , barium zirconium titanate, barium strontium titanate or other highly polar inorganic material.

14. An organic field effect device as claimed in claim 7 wherein the thickness for the low permittivity insulating material layer is in the range 5 nm to 1 □m and the thickness of the at least one high permittivity insulating material layer is in the range 50 nm to 10 □m.

15. An organic field effect device as claimed in claim 7 wherein the gate insulator layer comprises an organic material.

16. An organic field effect device as claimed in claim 15 wherein the low permittivity insulating material layer comprises a fluoropolymer.

17. An organic field effect device as claimed in claim 15 wherein the low permittivity insulating material layer comprises a polyethylene, polypropylene, polyisobutylene, poly(4 methyl 1-pentene), polyisoprene, poly(vinyl cyclohexane) or a copolymer containing the monomer units of at least one of these materials.

18. An organic field effect device as claimed in claim 15 wherein the low permittivity insulating material layer comprises copolymers of tetrafluoroethylene and dioxoles.

19. An organic field effect device as claimed in claim 7 wherein the organic semiconductor layer has a mobility greater than 10 −5 cm 2 V −1 s −1 .

20. An organic field effect device as claimed in claim 19 wherein the organic semiconductor layer comprises a polyarylamine.

21. An organic field effect device as claimed in claim 20 wherein the organic semiconductor layer contains a monodisperse arylamine compound with a number of repeat units, n, ≧2.

22. An organic field effect device as claimed in claim 19 wherein the organic semiconductor layer comprises an oligomer or polymer containing fluorene copolymerised with an arylamine.

23. An organic field effect device as claimed in claim 19 wherein the organic semiconductor layer comprises an oligomer or polymer containing a thiophene.

24. An organic field effect device as claimed in claim 19 wherein the organic semiconductor layer comprises an oligomer or polymer containing fluorene copolymerised with a thiophene.

25. An organic field effect device as claimed in claim 19 wherein the organic semiconductor layer comprises a composite of at least two organic semiconductor species.

26. An organic field effect device as claimed in claim 19 wherein the organic semiconductor layer includes a binder polymer.

27. A process as claimed in claim 1 wherein the permittivity of the low permittivity insulating material is in the range 1.3 to 2.5.

28. A process as claimed in claim 2 wherein the high permittivity insulating material has a permittivity greater than 3.5 and up to 200.

29. A process as claimed in claim 28 wherein the high permittivity insulating material comprises polyvinylidene fluoride, cyanopulluane, polyvinylalcohol or other highly polar organic polymer.

30. A process as claimed in claim 28 wherein the high permittivity insulating material comprises at least one of TiO2, Ta 2 O 5 , SrTiO 3 , Bi 4 Ti 3 O 12 , BaMgF 4 , barium zirconium titanate, barium strontium titanate or other highly polar inorganic material.

31. A process as claimed in claim 28 wherein the thickness for the low permittivity insulating material layer is in the range 5 nm to 1 □m and the thickness of the at least one high permittivity insulating material layer is in the range 50 nm to 10 □m.

32. A process as claimed in claim 27 wherein the low permittivity insulating material layer comprises a fluoropolymer.

33. A process as claimed in claim 32 wherein the low permittivity insulating material layer comprises a polyethylene, polypropylene, polyisobutylene, poly(4 methyl 1-pentene), polyisoprene, poly(vinyl cyclohexane) or a copolymer containing the monomer units of at least one of these materials.

34. A process as claimed in claim 33 wherein the low permittivity insulating material layer comprises copolymers of tetrafluoroethylene and dioxoles.

35. A process as claimed in claim 27 wherein the organic semiconductor layer comprises a polyarylamine and has a mobility greater than 10 −5 cm 2 V −1 s −1 .