Writing electrical contacts on sensitive materials

NanoNextNL PhD researcher Adrie Mackus has developed a gentle way of very accurately producing components such as electrical contacts on sensitive materials such as graphene. Graphene is a highly promising material for the even faster and smaller electronics of the future. With the current methods for producing electrical contacts on chips you destroy the graphene, however. Project partner and electron microscope manufacturer FEI has applied for a patent on the new writing method.

Read this highlight
  • EN
  • NL
  • Select other language

photo: PhD researcher Adrie Mackus (credits: Bart van Overbeeke)

‘The plastic of the 21st-century’ is how graphene is often referred to. The material, which consists of a single atomic layer of carbon atoms in a characteristic honeycomb structure, could signify a revolution within electronics. It is extremely strong, exceptionally hard and conducts electricity better than copper. It could, for example, be used to produce flexible screens or for very powerful computer chips. But in order to do that you must be able to make electrical contacts on it. And with the current technology that is not yet possible. NanoNextNL PhD researcher Adrie Mackus has developed a method that is suitable for making very precise contacts on such sensitive materials.

The material graphene could signify a revolution within electronics. It is extremely strong, exceptionally hard and conducts electricity better than copper. It could, for example, be used to produce flexible screens or for very powerful computer chips.

For the current silicon-based computer chips manufacturers such as Intel make use of lithographic techniques to produce different layers with electronic components and connections: you place a thin film of the material on the silicon surface, stick a light-sensitive lacquer layer to this, illuminate that layer with the desired pattern and subsequently etch away the unwanted material of the thin film with aggressive chemicals. For sensitive nanomaterials such as graphene and carbon nanotubes this method for creating patterns is not an option, however. The chemicals corrode these materials, as a result of which they lose their functionality.

Laborious

Furthermore, this method is in all honesty highly laborious says Mackus’ supervisor Erwin Kessels from Eindhoven University of Technology: ‘Imagine you were to build a house in this manner. Then you would build a complete cube of bricks and then subsequently remove the majority of those bricks with the exception of the walls. We are searching for ways of simply building just the walls for the structures and chips.’

Combination

In his NanoNextNL project PhD researcher Adrie Mackus combined two existing techniques to directly write patterns on the surface. With an electron beam he first wrote thin lines of platinum. The beam of electrons was targeted at gaseous platinum compounds that were scattered across the surface. Only the platinum particles located in the path of the beam were deposited on the surface. Next he used a technique called atomic layer deposition (ALD) to build walls of platinum on top of the lines. Atomic layer deposition uses gases to be able to deposit materials atomic layer by atomic layer on top of pre-defined locations. Up until Mackus’ research this method was mainly used to deposit complete films of materials and not so much for making thin lines.

Highlight Elektrische contacten schrijven structuurUsing a combination of techniques, Adrie Mackus managed to write neat electrical contacts of just a few micrometres in size directly on a surface.  

Promise

Due to the major breakthrough that Mackus has managed to achieve with his approach he received his doctorate cum laude in 2013. Since then he has been a postdoc at the prestigious Stanford University. Meanwhile the researchers in Eindhoven have been working further on refining the technology, says Kessels: ‘With this technique you can make platinum contacts on chips but you can also build other nanostructures. If you want to make components with new materials such as graphene then, in principle, such a writing process works better than lithography. An approach such as that of Adrie combines the best properties of the two techniques used. And although I do not want to pretend that we have now found the final solution, I nevertheless have high expectations for it.’

Read more

NanoTextNL 2014, page 12
News item promotion Adrie Mackus
Thesis Adrie Mackus

Theme 9: Nano fabrication

Original author: Anouck Vrouwe