Carbon nanotube transistor fabrication
During fabrication of single-walled carbon nanotube transistor devices, a porous template with numerous parallel pores is used to hold the single-walled carbon nanotubes. The porous template or porous structure may be anodized aluminum oxide or another material. A gate region may be provided one end or both ends of the porous structure. The gate electrode may be formed and extend into the porous structure.
1. A method of making a transistor device comprising:
providing a template having a top surface and a bottom surface comprising a plurality of openings extending into the template from the top surface toward the bottom surface;
exposing the template having openings to a hydrocarbon gas at a temperature to grow carbon nanotubes in the openings;
forming a mixture of semiconducting carbon nanotubes and metallic carbon nanotubes in the openings;
forming a first electrode region on the top surface to electrically couple to the carbon nanotubes at a first point;
forming a first gate region in the template extending from a point below the top surface and below the first electrode region toward the bottom surface;
forming a second gate region in the template extending from a point below the top surface toward the bottom surface, wherein there is a first carbon nanotube and a second carbon nanotube between the first and second gate regions; and
after forming a mixture of semiconducting carbon nanotubes and metallic carbon nanotubes in the openings, removing metallic carbon nanotubes from the mixture.
2. The method of claim 1 wherein the first carbon nanotube is in a first opening and the second carbon nanotube is in a second opening, separate from the first opening.
3. The method of claim 1 wherein the first and second gate regions are electrically coupled together to form a gate electrode of the transistor device.
4. The method of claim 1 wherein the openings are extend vertically into the template.
5. The method of claim 1 wherein the first gate region extends into the template a distance from about 50 nanometers to about 1000 nanometers.
6. The method of claim 1 wherein there is a third carbon nanotube between the first and second gate regions, and the third carbon nanotube is between the first and second carbon nanotubes.
7. The method of claim 1 comprising:
forming a second electrode region below the top surface to electrically couple to the carbon nanotubes at a second point, wherein first gate region and second date regions comprise a conductive material extending at least between the first and second points;
during the removing metallic carbon nanotubes from the mixture, applying a first voltage between the first and second points of the carbon nanotubes.
8. The method of claim 7 comprising:
during the removing metallic carbon nanotubes from the mixture, applying a second voltage to the first and second gate regions.
9. The method of claim 1 wherein each opening comprises at least two carbon nanotubes.
10. The method of claim 1 wherein the temperature is at least 400 degrees Celsius.
11. The method of claim 10 wherein there are openings with carbon nanotubes in a first region of the template beside of the first gate region, the first region is not between the first and second gate regions.
12. The method of claim 1 wherein the template is provided on a substrate and the substrate is a different material than the template.
13. The method of claim 1 wherein the template is an insulator material and is provided on a substrate that is a conductor material, and the substrate is used to form a second electrode region below the top surface to electrically couple to the carbon nanotubes at a second point.
14. The method of claim 1 further comprising:
before exposing the template containing pores to a hydrocarbon gas, depositing a catalyst into the openings.
15. The method of claim 14 wherein the catalyst is at least one of cobalt or an alloy of cobalt.
16. The method of claim 14 wherein the catalyst is at least one of iron or an alloy of iron.
17. The method of claim 14 wherein the catalyst is at least one of nickel or an alloy of nickel.
18. The method of claim 1 wherein the exposing the template occurs at a temperature in a range from about 750 degrees Celsius to about 850 degrees Celsius.
19. The method of claim 1 wherein the exposing the template at a temperature in a range from about 600 degrees Celsius to about 1000 degrees Celsius.
20. The method of claim 1 wherein the removing metallic carbon nanotubes comprises:
exposing the template with mixture of carbon nanotubes to a reagent, whereby the reagent renders greater numbers of the metallic carbon nanotubes ineffective for transistor operation than semiconducting carbon nanotubes.
21. The method of claim 20 wherein the reagent is a fluid.
22. The method of claim 20 wherein the reagent is nitric acid.
23. The method of claim 1 wherein the removing metallic carbon nanotubes comprises:
applying a voltage to the first gate region that results in a current flow through the carbon nanotubes, whereby the metallic carbon nanotubes are burned off in greater numbers than the semiconducting carbon nanotubes.
24. The method of claim 23 wherein the current flow through a metallic carbon nanotube is at least 15 microamps.
25. The method of claim 23 wherein the current flow through a metallic carbon nanotube is from about 15 microamps to about 25 microamps.