Methods of making thin film transistors comprising zinc-oxide-based semiconductor materials and transistors made thereby

• US 7,691,666 B2
• Filed: 06/16/2005
• Issued: 04/06/2010
• Est. Priority Date: 06/16/2005
• Status: Active Grant

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Levy, David H., Irving, Lyn M., Scuderi, Andrea C.
• Primary Examiner(s): Coleman; W. David
• Assistant Examiner(s): MCCALL SHEPARD, SONYA D
• Application Number:
  US11/155,436
• Publication Number:
  US 20060284171A1
• Time in Patent Office: 1,755 Days
• Field of Search: 438/149, 438/104, 257/E21.094, 257/E21.104, 257/E21.121, 257/E21.372, 257/E21.411, 257/E21.412, 257/E21.413, 257/E21.414, 257/E21.415, 257/E21.416, 257/E21.464, 257/43
• US Class Current: 438/104
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: H01L 21/02472 Oxides
• CPC Class Codes: H01L 21/02513 Microstructure
• CPC Class Codes: H01L 21/02554 Oxides
• CPC Class Codes: H01L 21/02579 P-type
• CPC Class Codes: H01L 21/02628 using solutions
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate

Abstract

A thin film transistor comprises a zinc-oxide-containing semiconductor material. Such transistors can further comprise spaced apart first and second contact means or electrodes in contact with said material. Further disclosed is a process for fabricating a thin film transistor device, wherein the substrate temperature is no more than 300° C. during fabrication.

Claims

1. A method of making a zinc-oxide-based thin film semiconductor, for use in a transistor, comprising:

(a) applying, to a substrate, a seed coating comprising a colloidal solution of zinc-oxide-based nanoparticles having an average primary particle size of 5 to 200 nm;

(b) drying the seed coating to form a porous layer of zinc-oxide-based nanoparticles;

(c) optionally annealing the porous layer of zinc-oxide-based nanoparticles at a temperature higher than the temperature of step (a) or (b);

(d) applying, over the porous layer of nanoparticles, an overcoat solution comprising a soluble zinc-oxide-precursor compound that converts to zinc oxide upon annealing, to form an intermediate composite film layer;

(e) drying the intermediate composite film layer; and

(f) annealing the dried intermediate composite film at a temperature of at least 50°

C. to produce a semiconductor film comprising zinc-oxide-based nanoparticles supplemented by additional zinc oxide material in a film layer formed by the conversion of the zinc-oxide-precursor compound during the annealing of the composite film.

2. The method according to claim 1, wherein the temperature of annealing in step (f) is about 130 to 300°

C.

3. The method according to claim 1, wherein the semiconductor film is annealed in step (f) for about 10 seconds to about 10 minutes.

4. The method of claim 1 wherein the porous layer of nanoparticles is annealed in step (c) before applying the overcoat solution.

5. The method according to claim 1, wherein the semiconductor film is optionally annealed in step (c) and/or annealed in step (f) by a laser annealing.

6. The method of claim 1 wherein the colloidal solution of zinc-oxide-based nanoparticles is applied to the substrate at a first temperature and then annealed in step (c) at a higher temperature of 50 to 500°

C., prior to applying the overcoat solution.

7. The method of claim 1 wherein the temperatures of the substrate during step (a) is 300°

C. or less.

8. The method of claim 1 wherein the optional annealing in step (c) and the annealing in step (f) is in the presence of air under ambient conditions.

9. The method of claim 1 wherein the semiconductor film has a mobility that is substantially greater than that of the seed coating alone, if annealed without the overcoat solution.

10. The method of claim 1 wherein the semiconductor film is capable of exhibiting electron mobility greater than 0.01 cm²/Vs.

11. The method of claim 1 wherein the semiconductor film exhibits a band-gap of less than about 5 eV.

12. The method of claim 1 wherein the zinc-oxide-based nanoparticles, upon heating, form a layer comprising a substantially transparent layer.

13. The method of claim 1 wherein the nanoparticles are comprised of undoped zinc oxide.

14. The method of claim 1, wherein the nanoparticles or the precursor solution comprises acceptor dopant.

15. The method of claim 1 wherein the nanoparticles are colloidally dispersed in an organic solvent.

16. The method of claim 1 wherein the seed coating is applied to the substrate at a level of 0.02 to 1 g/m² of nanoparticles, by dry-weight.

17. The method of claim 1 wherein the overcoat solution is applied at a level of 2×

104 to 0.01 moles/m² of precursor compound.

18. The method of claim 1 characterized by a molar ratio of nanoparticles, in the seed coating, to theoretically converted zinc-oxide precursor compound, in the overcoat solution, that ranges from 0.02 to 60.

19. The method of claim 1 wherein the seed coating, and/or the overcoat solution, are applied by an inkjet printer.

20. The method of claim 1 wherein the seed coating and/or the overcoat solution is applied by spin coating, extrusion coating, hopper coating, dip coating, or spray coating.

21. The method of claim 1 wherein patterned semiconductor thin films are coated on a web substrate.

22. The method of claim 1 wherein the semiconductor film is an active layer in a field effect transistor comprising a dielectric layer, a gate electrode, a source electrode and a drain electrode, and wherein the dielectric layer, the gate electrode, the semiconductor film, the source electrode, and the drain electrode are in any sequence as long as the gate electrode and the semiconductor film both contact the dielectric layer, and the source electrode and the drain electrode both contact the semiconductor film.

23. The method of claim 1 wherein the substrate comprises a dielectric layer made from an inorganic or organic electrically insulating material.

24. The method of claim 1 wherein the transistor further comprises a non-participating support that is optionally flexible.

25. The method of claim 1, for fabricating a thin film semiconductor device, comprising subsequent to step (f):

(g) forming a spaced apart source electrode and drain electrode, wherein the source electrode and the drain electrode are separated by, and electrically connected with, the semiconductor film; and

(h) forming a gate electrode spaced apart from the semiconductor film.

26. The method of claim 1 comprising, not necessarily in order, the following steps:

(a) providing the substrate;

(b) providing a gate electrode material over the substrate

(c) providing a dielectric layer over the gate electrode material;

(d) forming the semiconductor film over the gate dielectric; and

(e) providing a source electrode and a drain electrode contiguous to the semiconductor film.

27. The method of claim 1 wherein the substrate is flexible.

28. The method of claim 1 wherein steps (a) through (f) are carried out in its entirety below a peak temperature of 150°

C.

29. The method of claim 1 wherein the colloidally stable dispersion of zinc-oxide-based nanoparticles has been colloidally stabilized by charge in the absence of surfactant.

30. The method of claim 19 wherein the inkjet printer is a continuous or drop-on-demand inkjet printer.

31. The method of claim 22, wherein the gate electrode is adapted for controlling, by means of a voltage applied to the gate electrode, a current between the source and drain electrodes through the semiconductor film.

32. The method of claim 22, wherein the transistor has an on/off ratio of a source/drain current of at least 104.

33. The method of claim 22 wherein the transistor is configured for enhancement mode operation.

34. The method of claim 22 wherein the source, drain, and gate electrodes each independently comprise a material selected from doped silicon, metal, and conducting polymer.

35. The method of claim 22 wherein the source, drain, and gate electrode each comprise indium-tin oxide and the substrate comprises glass.

36. The method of claim 23 comprising depositing the seed coating onto at least a portion of a surface of the dielectric layer.

37. The method of claim 26 wherein the method further comprises step (f) wherein metal contacts are applied to the upper surface of the semiconductor film.

38. The method according to claim 36 wherein the dielectric layer comprises a substantially transparent material.

39. The method according to claim 36, further comprising depositing on the dielectric layer at least one material for forming a source and a drain prior to depositing the seed coating.

40. The method of claim 37 wherein the steps are performed in the order listed.

41. The method of claim 38 wherein the dielectric layer comprises Al₂O₃/TiO₂ or A₁2O₃.

42. The method according to claim 39, wherein the material for forming a source and a drain is ion beam sputtered deposited onto the dielectric layer, and annealing is employed to diffusion dope the semiconductor film with the source and drain material.

43. A method of inkjet printing a semiconductor film on a substrate element comprising carrying out the process of claim 1, further comprising:

i) providing an inkjet printer that is responsive to digital data signals;

ii) loading a first printhead with said seed coating;

iii) in step (a), applying to the substrate, the seed coating by printing in response to the digital data signals;

iv) loading a second printhead with said overcoat solution;

v) in step (d), applying over the porous layer of nanoparticles, the overcoat solution by printing using in response to the digital data signals; and

vi) in step (f) annealing the printed substrate.

44. A method of making a zinc-oxide-based thin film semiconductor, for use in a transistor, comprising:

(a) applying, to a substrate, a seed coating comprising a colloidally stable dispersion of zinc-oxide-based nanoparticles having an average primary particle size of 5-200 nm;

(b) drying the seed coating to form a porous layer of zinc-oxide-based nanoparticles;

(c) optionally annealing the porous layer of zinc-oxide-based nanoparticles at a temperature higher than the temperature of step (a) or (b);

(d) applying, over the porous layer of nanoparticles, an overcoat solution comprising a soluble zinc-oxide-precursor compound that converts to zinc oxide upon annealing, to form an intermediate composite film layer;

(e) drying the intermediate composite film layer; and

(f) annealing the dried intermediate composite film at a temperature of at least 50°

C. to produce a seminconductor film comprising zinc-oxide-based nanoparticles supplemented by additional zinc oxide material formed by the conversion of the zinc-oxide-precursor compound during the annealing of the composite film layer,

wherein the semiconductor film is an active layer in a field effect transistor comprising a dielectric layer, a gate electrode, a source electrode and a drain electrode, wherein the dielectric layer, the gate electrode, the seminconductor film, the source electrode, and the drain electrode are in any sequence as long as the gate electrode and the seminconductor film both contact the dielectric layer, and the source electrode and the drain electrode both contact t the seminconductor film, and wherein the entire process of making the semiconductor film is carried out below a maximum support temperature of 300°

C.