Methods of making thin film transistors comprising zinc-oxide-based semiconductor materials and transistors made thereby
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.
1. A method of making a semiconductor thin film, for use in a transistor, comprising a zinc-oxide-based semiconductor, the method comprising depositing a colloidal solution of zinc-oxide-based nanoparticles on a substrate, at a temperature of 300° C. or less, wherein the nanoparticles are the reaction product of a mixture of reactants comprising an organozinc precursor compound and a basic ionic compound, wherein the nanoparticles have an average primary particle size in the range of 10 to 150 nm and are colloidally stabilized in the colloidal solution, and wherein the level of inorganic ions in the colloidal solution is below 1 mM and the level of organic compounds, or salts thereof, is below 5 mM.
2. 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 at a higher temperature of 50 to 500° C.
3. The method of claim 1 wherein the colloidal solution of zinc-oxide-based nanoparticles ise applied to the substrate at a first temperature and then annealed at a higher temperature of 100 to 250° C.
4. The method of claim 1 comprising, following drying of the deposited colloidal solution of nanoparticles, annealing the zinc-oxide-containing nanoparticles for about 1 minute to about 2 hours at a temperature of about 100 to about 250° C.
5. The method according to claim 4 , wherein the annealing is by means of a laser-annealing technique.
6. The method of claim 1 wherein the temperature of the substrate during deposition is 150° C. or less.
7. The method of claim 4 wherein the annealing is in the presence of air under ambient conditions.
8. The method of claim 1 wherein the inorganic ions and organic compounds, or salts thereof, include impurities resulting from nanoparticle formation, during the reaction of the mixture of reactants, and are removed prior to deposition.
9. The method of claim 1 wherein the inorganic ions and organic compounds, or salts thereof, include impurities resulting from nanoparticle formation and are removed prior to deposition by a technique that removes soluble impurities but not the nanoparticles.
10. The method of claim 1 wherein the inorganic ions and organic compounds, or salts thereof, include impurities resulting from nanoparticle formation and are removed prior to deposition by washing comprising a separation technique selected from the group consisting of dialysis, liquid-liquid extraction, ion-exchange, centrifugation, deionization, redispersal in a solvent carrier, and combinations thereof.
11. The method of claim 1 wherein the zinc-oxide-based nanoparticles are not stabilized by the addition of a surfactant or other organic stabilizer.
12. The method of claim 1 wherein the zinc-oxide-based nanoparticles comprise undoped zinc oxide.
13. The method of claim 1 wherein the zinc-oxide-based nanoparticles, upon heating, form a layer comprising a substantially transparent, material.
14. The method of claim 1 wherein the zinc-oxide-based nanoparticles further comprise an acceptor dopant.
15. The method of claim 1 wherein the semiconductor thin film exhibits a band gap of less than about 5 eV.
16. The method of claim 1 wherein the semiconductor thin film exhibits a field effect electron mobility that is greater than 0.01 cm 2 /Vs.
17. The method of claim 1 wherein the nanoparticles are colloidally dispersed in an organic solvent.
18. The method of claim 1 wherein the colloidal solution of zinc-oxide-based nanoparticles are applied to the substrate at a level of 0.02 to 1 g/m 2 of nanoparticles, by dry-weight.
19. The method of claim 1 wherein the colloidal solution of zinc-oxide-based nanoparticles is applied by an inkjet printer.
20. The method of claim 19 wherein the inkjet printer is a continuous or drop-on-demand inkjet printer.
21. The method of claim 1 wherein the colloidal solution of zinc-oxide-based nanoparticles is applied by spin coating, extrusion coating, hopper coating, dip coating, or spray coating.
22. The method of claim 1 wherein a semiconductor thin film is coated on a moving web substrate.
23. The method of claim 1 wherein the semiconductor thin 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 thin film, the source electrode, and the drain electrode are in any sequence as long as the gate electrode and the semiconductor thin film both contact the dielectric layer, and the source electrode and the drain electrode both contact the semiconductor thin film.
24. The method of claim 23 , wherein the gate electrode is adapted for controlling, by means of a voltage applied to the gate electrode, a current between the source electrode and the drain electrode through the semiconductor thin film.
25. The method of claim 23 , wherein the transistor has an on/off ratio of a source/drain current of at least 10 4 .
26. The method of claim 23 wherein the transistor is configured for enhancement mode operation.
27. The method of claim 1 wherein the substrate comprises a e dielectric layer that made of an inorganic or organic electrically insulating material.
28. The method of claim 1 comprising depositing the colloidal solution of zinc-oxide-based nanoparticles onto at least a portion of a surface of a dielectric layer.
29. The method according to claim 28 , wherein the dielectric layer comprises a substantially transparent material.
30. The article of claim 29 wherein the dielectric layer comprises Al 2 O 3 /TiO 2 or Al 2 O 3 .
31. The method according to claim 28 , further comprising depositing on the dielectric layer at least one material for forming a source and a drain, prior to depositing the colloidal solution of nanoparticles.
32. The method according to claim 31 , wherein the material for forming a source and a drain is ion beam sputtered deposited onto the dielectric layer, and the semiconductor film is annealed to diffusion-dope the film with the source and the drain material.
33. The method of claim 23 wherein the source, drain, and gate electrodes each independently comprise a material selected from doped silicon, metal, and conducting polymer.
34. The method of claim 33 wherein the source, drain, and gate electrode each comprise indium-tin oxide, and the substrate comprises glass.
35. The method of claim 23 wherein the transistor comprises a non-participating support that is optionally flexible.
36. The method of claim 1 comprising, not necessarily in the following order, the steps of:
(a) depositing the colloidal solution of zinc-oxide-based nanoparticles on a substrate, to form a thin film of zinc-oxide-based semiconductor material, such that the semiconductor material exhibits a field effect electron mobility that is greater than 0.01 cm 2 /Vs;
(b) 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 thin film of zinc-oxide-based semiconductor material; and
(c) forming a gate electrode spaced apart from the semiconductor material.
37. The process of claim 36 comprising, not necessarily in order, the following steps:
(a) providing the substrate;
(b) providing the gate electrode material over the substrate;
(c) providing a dielectric over the gate electrode material;
(d) depositing the thin film of the zinc-oxide-based semiconductor material over the gate dielectric; and
(e) providing the source electrode and the drain electrode contiguous to the thin film of zinc-oxide-based semiconductor material.
38. An electronic device comprising a multiplicity of thin film transistors made according to claim 1 .
39. The electronic device of claim 38 wherein the multiplicity of thin film transistors is on a non-participating support that is optionally flexible.
40. The electronic device of claim 38 wherein the electronic device is selected from the group consisting of an integrated circuit, active-matrix display, solar cell, flat panel display, active matrix imager, sensor, and rf label containing price, identification, and/or inventory information.
41. An optoelectronic display device comprising at least one display element coupled to a switch comprising an enhancement-mode, field effect transistor made according to claim 1 .
42. The optoelectronic display device of claim 41 , wherein the device comprises an active-matrix liquid-crystal display.
43. The electronic device of claim 38 wherein the electronic device is selected from the group consisting of (a) a substantially transparent, dynamic random-access memory cell, comprising a substantially transparent capacitor coupled to an enhancement-mode, field effect transistor; (b) a substantially transparent logic inverter, comprising a load device coupled to an enhancement-mode, field effect transistor; and (c) an amplifier comprising an enhancement-mode, field effect transistor, wherein the enhancement-mode, field effect transistor is made according to claim 1 .