US Patent 6645402 - Carbon Electron Emitting Device

On occasion I will have a discussion with someone outside of the patent field about patents. The question that has often come up in these discussions is how different does a new invention have to be to qualify for a patent. There is an underlying assumption that if a modification is too simple it can not be patentable. I, of course, explain about the "obvious to one of ordinary skill in the art" standard, used in the U.S. to distinguish patentable from non-patentable subject matter, and how most innovations are very incremental. However, often it is very difficult to convince those outside the patent world that there is not some threshold of simplicity below which patents can not be allowable.

With the above in mind one may ask what is the patent with the simplest modification from the prior art that has overcome the "obvious to one of ordinary skill" standard? I would submit US Patent 6645402 as a possible candidate for this honor.

http://www.freepatentsonline.com/6645402.html

Claim 1 reads

1. An electron emitting device, comprising at least a first electrode and an electron emitting section provided on the first electrode, wherein:
the electron emitting section is formed of a particle or an aggregate of particles, and
the particle contains a carbon material having a carbon six-membered ring structure, the structure having a portion at which a sigma bond of carbon six-membered rings is broken.

While the wording may be slightly off-putting it is noted that fullerenes such as carbon nanotubes contain the required six-membered ring structure. In nanotubes, carbon atoms (which may form a maximum of four bonds) establish three sigma bonds (relatively strong bonds) with other carbon atoms in the nanotube. Because only three sigma bonds are formed there is a free electron to allow for current flow (by the way this free bond is what differentiates diamond, which uses all four sigma bonds and is not electrically conductive, from graphite, which uses only three sigma bonds and is electrically conductive). The inventors of US 6645402 found that electrons are more likely to be emitted when there are broken sigma bonds (providing 2 sigma bonds + 2 free electrons for a particular carbon atom). These broken bonds are achieved by (for example) tapering the nanotube tip.

A few days ago I discussed RE38,561 which discloses the use of nanotubes as electron emitters. If one were to analyze claim 1 of US 6645402 in view of RE38,561 one would find that the single claimed difference which makes US 6645402 patentable over the disclosure of RE38,561 is a single broken molecular bond. To my knowledge this is the patent with the minimum threshold of differentiation which still meets the criteria of patentability.