Editorial Feature

Direct Optical Lithography of Nanomaterials

In a recent study published in Science, a group of Researchers at the University of Chicago, in collaboration with the Argonne National laboratory, have recently developed a novel method they termed DOLFIN to pattern nanomaterials in an extremely precise manner. Unlike traditional photolithography methods that involve the laying down of several layers of new material on top of a polymer stencil to create miniature structures, the DOLFIN technique utilizes a different nanomaterial “ink” to create the patterns, without requiring the use of any type of stencil1. This new technique has the potential to revolutionize the way in which the electronics industry fabricates nanomaterials for their device products1.

Semiconductor lithography, otherwise known as photolithography, is the technique that is most often used to write the patterns that make up the light sensitive material called photoresist that is placed on top of a silicon polymer2. To build a circuit that consists of millions of transistors, the processes of lithography and etch pattern steps are repeated as many as 20 – 30 times in order to print and align each pattern layer on top of the previously laid printed patterns.

This process serves to connect and isolate several components of materials including conductors such as aluminum, polysilicon as well as insulators, such as silicon dioxide, silicon nitride and several others.  The selective doping of various regions of silicon results in variable conductivity of the material that is dependent on the applied voltage.

The photolithography process is used extensively in the creation of several types of electronic devices, including smart phones, tablet devices and much more. As a process that is available for large scale patterning of electronic circuits, that can be produced in both an efficient and reliable manner, photolithography processes have significantly reduced the cost of the modern smartphone as a result2.

As impressive as it sounds, the selective applicability of this technique to only a few materials and the continuous development of new electronic materials, especially nanomaterials, signals the search of an alternative to lithography technique1.

As a result of their nanoscale size, nanomaterials, exhibit unique properties that their bulk materials lack. Despite their exceptional range of properties and their potential benefits in their applications, manufacturing electronic devices based on these nanomaterials has been very difficult due to the lack of proper techniques available for their manufacturing, as well as a series of compatibility issues existing between different nanomaterials.

Multiple steps such as masking, patterning and developing sequential layers are involved in nanoscale patterning. To solve this problem, Dmitri Talapin’s team from the University of Chicago developed an “ink” made up of different nanomaterials that includes tiny crystals of metals and semiconductors.

The team of Researchers used light-responsive ligands to change the ability of the nanocrystals in specific solvents, thereby allowing for the development of nanoscale patterns by simple redispersion of nanocrystals in the dark regions. This technique does not require the utilization of photoresists because of the selective deposition of nanocrystals only in presence of light.

The chemical coatings for individual particles developed by Talapin’s team when reacted with light, transfers the pattern directly into the layer of nanoparticles below thereby wiring them into useful electronic devices. Therefore, this technique completely bypassed the laying down of polymer stencil step in the photolithography technique. Not only that, this process can also be applied to a wide range of materials used in electronic manufacturing such as semiconductors, metals, oxides or other magnetic materials3.

This new technique has a potential to find its use in development of a variety of electronics ranging from LED lights to smart phones to photo detectors and solar cells. The Researchers found that the quality of patterns obtained by using this DOLFIN technique is comparable to the patterns made with the other state-of-the-art techniques.

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References:

  1. “New method promises easier nanoscale manufacturing” – UChicago News
  2. “Lithography” – Lithoguru.com
  3. “Direct optical lithography of functional inorganic nanomaterials” Y. Wang, I. Fedin, et al. Science. (2017). DOI: 10.1126/science.aan2958.

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