Device comprising carbon nanotube field emitter structure and process for forming device

• US 6,630,772 B1
• Filed: 04/22/1999
• Issued: 10/07/2003
• Est. Priority Date: 09/21/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.), Lucent Technologies, Inc. (Nokia Corporation), University of South Carolina
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.), University of South Carolina
• Inventors: Zhou, Otto, Bower, Christopher Andrew, Zhu, Wei
• Primary Examiner(s): Patel, Nimeshkumar D.
• Assistant Examiner(s): Santiago, Mariceli
• Application Number:
  US09/296,572
• Time in Patent Office: 1,629 Days
• Field of Search: 445/51, 445/50, 445/24, 445/49, 313/495, 313/496, 313/497, 313/306, 313/307, 313/308, 313/309, 313/310, 313/311
• US Class Current: 313/311
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: H01J 1/304 Field-emissive cathodes
• CPC Class Codes: H01J 2201/30469 Carbon nanotubes (CNTs)
• CPC Class Codes: H01J 9/025 of field emission cathodes
• CPC Class Codes: Y10S 977/842 for carbon nanotubes or fullerenes

Abstract

The invention provides improved devices containing adherent carbon nanotube films, in particular electron field emitter structures containing such films. Previously, attaining even moderate adherence of powdery or mat-like nanotubes to a substrate was difficult, because of the perfect fullerene structure of nanotubes, which tend to exhibit no dangling bonds or defect sites where chemical bonding to the substrate is able to occur. The invention overcomes these problems, and provides a strongly adherent nanotube film, by a variety of fabrication processes.

Claims

1. A process for fabricating a device, comprising the steps of:

providing a substrate, and

disposing an adherent carbon nanotube film on the substrate,

aligning at least 50 volume percent of the carbon nanotubes in substantially the same direction,

wherein the substrate comprises at least one material selected from the group consisting of carbon-dissolving elements, carbide-forming elements, and low melting point materials.

2. The process for fabricating a device according to claim 1, wherein:

the step of aligning the carbon nanotubes further comprises applying at least one of an electric field and a magnetic field while disposing the adherent carbon nanotube film on the substrate.

3. The process for fabricating a device according to claim 2, wherein the adherent carbon nanotube film is disposed on the substrate in the absence of polymeric material.

4. The process for fabricating a device according to claim 2,

the step of disposing an adherent carbon nanotube film on the substrate further comprising the steps of:

disposing carbon nanotubes on the substrate; and

heating the substrate and the carbon nanotubes to a temperature sufficient to induce at least one of;

a reaction of at least a portion of the carbon nanotubes with the carbon-dissolving elements,

a reaction of at least a portion of the carbon nanotubes with the carbide-forming elements, and

a melting of at least a portion of the low melting point materials.

5. The process for fabricating a device according to claim 2,

the step of disposing an adherent carbon nanotube film on the substrate further comprising the steps of:

forming a dispersion of carbon nanotubes in a solvent;

applying the dispersion to a surface of the substrate to coat the substrate surface; and

evaporating substantially all of the solvent to form a layer of carbon nanotubes on the surface of the substrate.

6. The process for fabricating a device according to claim 5, further comprising the steps of purifying and ultrasonicating the carbon nanotubes.

7. The process for fabricating a device according to claim 5,

the step of disposing an adherent carbon nanotube film on the substrate further comprising the step of:

heating the substrate to a temperature sufficient to induce at least one of

a reaction of at least a portion of the carbon nanotubes with the carbon-dissolving elements,

a reaction of at least a portion of the carbon nanotubes with the carbide-forming elements, and

a melting of at least a portion of the low melting point materials.

8. The process for fabricating a device according to claim 2, wherein at least 75 volume percent of the carbon nanotubes in the adherent carbon nanotube film are aligned in substantially the same direction.

9. The process for fabricating a device according to claim 1, wherein:

the step of aligning the carbon nanotubes further comprises the steps of

mixing carbon nanotubes with a polymer to form a composite material characterized by a softening temperature,

heating the composite material to a temperature above the softening temperature,

subjecting the composite material to a uniaxial load,

cooling the composite material to a temperature below the softening temperature, and

releasing the uniaxial load.

10. The process for fabricating a device according to claim 9, wherein at least 75 volume percent of the carbon nanotubes in the adherent carbon nanotube film are aligned in substantially the same direction.

11. A device comprising

a substrate, and

a carbon nanotube film formed on a surface of the substrate, the carbon nanotube film comprising at least 50 percent by volume carbon nanotubes;

wherein, at least 50 percent of the carbon nanotubes are aligned in a direction generally parallel to an alignment axis.

12. A device according to claim 11:

further wherein the alignment axis is generally perpendicular to the surface of the substrate.

13. A device according to claim 12:

further wherein the carbon nanotube film comprises an electron emitter and exhibits an electron emitter density of at least 10⁹/cm².

14. A device according to claim 13:

further wherein the electron emitter exhibits a threshold emission field of less than 20 V/μ

m at a current density of 10 mA/cm².

15. A device according to claim 14:

wherein the threshold emission field remains at a value less than 20 V/μ

m after sustaining a current density of 10 mA/cm² for at least 50 hours.

16. A device according to claim 11:

wherein the carbon nanotube film further comprises amorphous carbon; and

further wherein the proportion of amorphous carbon in the carbon nanotube film decreases as a distance from the substrate increases.

17. A device according to claim 11:

wherein the device comprises a microwave amplifier or a display.