Organic field effect transistors

• US 20050023522A1
• Filed: 05/07/2004
• Published: 02/03/2005
• Est. Priority Date: 11/07/2001
• Status: Active Grant

• Current Assignee: Cambridge University (Government of United Kingdom)
• Original Assignee: Cambridge University (Government of United Kingdom)
• Inventors: Reynolds, Kieran John, Sirringhaus, Henning, Friend, Richard Henry, Frey, Gitti
• Granted Patent: US 7,307,277 B2
• Time in Patent Office: Days
• US Class Current: 257/40
• CPC Class Codes: H10K 10/464 Lateral top-gate IGFETs comprising only a single gate
• CPC Class Codes: H10K 10/466 Lateral bottom-gate IGFETs comprising only a single gate
• CPC Class Codes: H10K 10/468 characterised by the gate dielectrics
• CPC Class Codes: H10K 71/60 Forming conductive regions or layers, e.g. electrodes
• CPC Class Codes: H10K 85/113 Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
• CPC Class Codes: H10K 85/115 Polyfluorene; Derivatives thereof
• CPC Class Codes: H10K 85/151 Copolymers

Abstract

A field effect transistor is provided which comprises a gate electrode, a source electrode, a drain electrode, at least one organic semiconducting layer, and a hole transport layer for transferring holes from said source and drain electrodes to said organic semiconducting layer, wherein said hole transport layer comprises a layered metal chalcogenide. Processes for depositing a thin layer of a layered metal dichalcogenide on a substrate and for producing top gate structures on a layered metal chalcogenide layer in the manufacture of field effect transistors according to the invention are also provided.

Claims

1. A field effect transistor comprising;

a gate, a source, a drain, at least one organic semiconducting layer, and a hole transport layer;

wherein the hole transport layer comprises a layered metal chalcogenide.

2. The field effect transistor of claim 1, wherein the layered metal chalcogenide is a dichalcogenide or a monochalcogenide.

3. The field effect transistor of claim 2, wherein the layered metal chalcogenide is a dichalcogenide.

4. The field effect transistor of claim 3, wherein the layered metal chalcogenide is a dichalcogenide;

and wherein the metallic component is titanium, zirconium, hafnium, vanadium, tantalum, niobium, molybdenum, tungsten, or tin.

5. The field effect transistor of claim 4, wherein the metallic component is niobium, molybdenum, or tantalum.

6. The field effect transistor of claim 2, wherein the layered metal chalcogenide is a monochalcogenide.

7. The field effect transistor of claim 6, wherein the layered metal chalcogenide is a monochalcogenide;

and wherein the metallic component is gallium, indium, or thallium.

8. The field effect transistor of claim 3, wherein the the chalcogen component of the layered metal chalcogenide is sulfur or selenium.

9. The field effect transistor of claim 6, wherein the the chalcogen component of the layered metal chalcogenide is sulfur or selenium.

10. The field effect transistor of claim 1, wherein the layered metal chalcogenide has a work function of from 4 to 6.5 eV.

11. The field effect transistor of claim 10, wherein the layered metal chalcogenide has a work function of from 5 to 6.5 eV.

12. The field effect transistor of claim 1, wherein the layered metal chalcogenide is niobium diselenide, molybdenum disulfide, tin disulfide, tantalum disulfide, vanadium diselenide, indium selenide, or gallium selenide.

13. The field effect transistor of claim 12, wherein the layered metal chalcogenide is molybdenum disulfide.

14. The field effect transistor of claim 1, wherein the thickness of the metal chalcogenide layer is less than 200 nm.

15. The field effect transistor of claim 14, wherein the thickness of the metal chalcogenide layer is less than 50 nm.

16. The field effect transistor of claim 15, wherein the thickness of the metal chalcogenide layer is from 5 to 10 nm.

17. The field effect transistor of claim 1, wherein the organic semiconducting layer comprises one or more organic semiconducting materials.

18. The field effect transistor of claim 17, wherein the organic semiconducting layer comprises more than one organic semiconducting material.

19. The field effect transistor of claim 18, wherein the organic organic semiconducting material, is disposed as separate, discrete layers or as a mixture of the materials in a single layer.

20. The field effect transistor of claim 17, wherein the organic semiconducting layer comprises a semiconducting polymer selected from the group consisting of polythiophenes and copolymers having thiophene and fluorene units.

21. The field effect transistor of claim 20, wherein the semiconducting polymer is a substituted polythiophenes.

22. The field effect transistor of claim 20, wherein said organic semiconducting layer comprises a semiconducting polymer selected from the group consisting of polythiophene, poly(3-alkylthiophenes) and poly-9,9′

-dioctyl-fluorene-co-bithiophene (F8T2).

23. The field effect transistor of claim 17, wherein the organic semiconducting layer comprises a semiconducting small organic molecule selected from the group consisting of oligothiophenes containing from 3 to 6 thiophene units, pentacenes and phthlocyanines.

24. The field effect transistor of claim 17, wherein the organic semiconducting layer has a thickness of from 100 to 500 nm.

25. The field effect transistor of claim 24, wherein the organic semiconducting layer has a thickness of from 200 to 400 nm.

26. The field effect transistor of claim 1, wherein the layered metal chalcogenide acts as an interconnect and metal electrode of the device as well as acting as the hole transport layer.

27. A process for depositing a thin layer of a metal dichalcogenide on a substrate in the manufacture of a field effect transistor of claim 1, comprising the steps of:

a) intercalation of lithium atoms into the metal dichalcogenide compound;

b) addition of water to the intercalated material, the resulting hydrogen gas which is evolved between the metal dichalcogenide layers breaking up the stacking of the layers (exfoliation) so as to produce single layers of metal dichalcogenide suspended in the water;

c) addition of a water immiscible solvent to the single layer water suspension of metal dichalcogenide, followed by agitation of the resulting mixture, to produce a thin film of metal dichalcogenide which is formed at the solvent/water interface; and

d) dipping the lower end of a wet substrate, resulting in the spread of the metal dichalcogenide film as a thin oriented film on the substrate surface.

28. The process for producing top gate transistor structures on a layered metal chalcogenide layer in the manufacture of a field effect transistor of claim 1, comprising the steps of:

a) a photo resist is spun on to the layered metal chalcogenide surface;

b) the structure produced in step (a) is baked and exposed under UV to define the required source and drain pattern;

c) the layer of source and drain material is then etched through the layered metal chalcogenide layer leaving the required pattern but with a conducting layered metal chalcogenide layer in the channel;

d) the exposed layered metal chalcogenide is patterned by oxidizing the layered metal chalcogenide;

e) the photo resist is removed;

f) the organic semiconducting material is spun on top of the layered metal chalcogenide layer;

g) an insulating polymer is spun on top of the layer of organic semiconducting material deposited in step (f); and

h) the gate electrode is evaporated on the insulating polymer layer deposited in step (g).

29. The process of claim 28, wherein the metal chalcogenide layer is a dichalcogenide layer.

30. The process of claim 27, wherein the substrate is selected from the group consisting of glass, quartz and crystalline substrates of Si, GaAs, ZnSe, ZnS, GaP and InP, polyethylene terephthalate (PET) substrates and polyimide substrates.

31. The process of claim 28, wherein the substrate is selected from the group consisting of glass, quartz and crystalline substrates of Si, GaAs, ZnSe, ZnS, GaP and InP, polyethylene terephthalate (PET) substrates and polyimide substrates.