I was a bit stunned when I saw that Professor Mike Kelly at Cambridge University for Advanced Photonics and Electronics had claimed that structures with dimensions three nanometers or less could not be mass-produced.
I became somewhat relieved when I clicked on the source story for the above link to discover that Kelly had added that this 3-nm limit only applied to “using a top-down approach.”
My sense of relief was short lived when it seems in the source article that Kelly wasn’t really sure that a bottom-up approach could do it either since the processes used were too prone to unpredictable defects.
So, I thought I might find some respite in the original paper published by the UK’s Institute of Physics IOP (The paper is currently free if you register on the site).
The only real hopeful bit that escapes Kelly’s rather pessimistic theorem is that he doesn’t specifically discuss bottom-up approaches to manufacturing structures below 3nm, except to say, “There is a vanishing probability of generating a wide-area defect-free (especially line-defect-free) arrays.”
The main thrust of Kelly’s argument is one that is not altogether that radical, which is that you may be able to fabricate one-off structures that have dimensions below 3nm but you won’t be able to duplicate that in a full-scale manufacturing process.
While most have noted the difficulty of ramping up to a manufacturing process, or implied that new techniques would be developed to enable these manufacturing processes, Kelly is not quite as hopeful. From the IOP paper:
“If this (top-down) manufacturing process is to be based on the most modern forms of deposition (including epitaxy), e-beam or ultra-deep UV lithography and precision etching, the mainstay of microelectronics and optoelectronics fabrication, then there are strict limits described below for which one-off fabrication is possible, but manufacture is not.”
So, metaphorically speaking Kelly has laid down the gauntlet, challenging the nanoscience community to either disprove his theorem, or, if they cannot, to start developing techniques for manufacturability rather than continuing to develop structures that will never be able to be manufactured.
"If I am wrong, and a counterexample to my theorem is provided, many scientists would be more secure in their continued working, and that is good for science,” says Kelly. "If more work is devoted to the hard problem of understanding just what can be manufactured and how, at the expense of more studies of things that cannot be manufactured under the conditions of the present theorem, then that too is good for science and for technology."
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.