Monday, July 07, 2008

US Patent 7394192 - Uniform CNT distribution for field emission

When fabricating field emission devices (such as displays) using carbon nanotubes a problem of clumping can arise when low diameter nanotubes are formed resulting in an uneven distribution of tubes. Larger diameter nanotubes avoid this problem but require a higher threshold voltage for electron emission and are thus unsatisfactory. This patent from Noritake Co. teaches a manufacturing method capable of forming a mixture of large and small diameter nanotubes to provide a more even distribution without sacrificing the emission efficiency. Claim 1 reads:

1. An electron-emitting source comprising:

a plurality of first carbon nanotubes which are formed on a cathode structure made of a metal containing any one of iron, nickel, cobalt, and chromium;

a catalyst metal layer which is formed on said first carbon nanotubes and made of said metal that forms said cathode structure; and

a plurality of second carbon nanotubes which are formed on said catalyst metal layer and are thinner than said first carbon nanotubes.