Thursday, October 13, 2016

University of Minnesota has developed Atomic Layer Lithography by ALD to create long narrow nano gaps

We have entered the era of atomic level processing by the introduction of atomic layer deposition (ALD), etching (ALE), cleaning (ALC) and so on in semiconductor manufacturing for advanced CMOS and Memory devices. Especially because of the delay of EUV Lithography ALD has proven to save continued device scaling by implementation in multiple patterning techniques so that scaliong can go on.

Here is yet another interesting technique where ALD is used in a sense to create extremely narrow channels with atomic precision governed by ALD - Atomic Layer Lithography.

As reported by Nanotechweb - Gold nanogap electrodes trap tiny particles

Researchers at the University of Minnesota in Minneapolis have invented a new ultralow power technique to trap nanoparticles in the sub-10 nm gaps between two gold electrodes. The technique, which overcomes many of the problems encountered in traditional dielectrophoresis experiments, could help make portable biosensors.

(a) Fabrication scheme using atomic layer lithography. An Al2O3 layer of desired thickness (that is, gap size) is deposited using ALD on a patterned gold film. A second layer of gold is evaporated, such that the first and second metal layers are not in contact. The top gold layer is then peeled off using adhesive tape, exposing the Al2O3-filled nanogap between the two gold electrodes. (b) An array of nanogap electrodes of desirable length is patterned by photolithography and ion milling on a 1 cm long nanogap. Courtesy: Nanotechweb & Nano Lett.

Nanotechweb reports that in 2011, a student (Xiaoshu Chen) figured out how to make vertically-oriented gaps as small as 1 nm over a centimeter length scale, which accordingly is not possible by any other method.

“As a result, we were able to make long and narrow gaps using atomic layer deposition (ALD), which is a robust manufacturing technique for coating ultra-thin films to construct insulating gaps in the sidewalls of patterned metals (see figure above). Thanks to the nature of ALD, we can precisely control the width of the gap, and after depositing metals on the other side of the ALD coating, nanogaps naturally form."

“What makes this atomic layer lithography technique so unique and appealing is that we can expose the nanogaps using just Scotch tape, he tells “This was a rather surprising discovery that Chen made. Since many labs around the world have access to ALD tools (and indeed Scotch tape!), this means that other researchers could practise our technique, easily and inexpensively.” 

Full article:  Gold nanogap electrodes trap tiny particles