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Crystalline Insulator Layers in 2D Materials Enable Efficient Microelectronics

July 21, 2020 by Sam Holland

Researchers at Tu Wien (Technische Universität Wien) have introduced crystalline insulator layers to single-layer (‘2D’) materials. This offers a turning point for component miniaturisation: it provides the ability to manufacture efficient microelectronics that maintain their ideal electronic properties.

Industry Demands for Miniaturisation

Miniaturisation, of course, is integral to modern users’ increasing need for smaller, lighter devices. However, given our current rate of technological progress, the question now arises about the extent to which devices can be further miniaturised. In fact, Moore’s Law’s proponent, Gordan Moore himself, has also felt the need to refer back to his own school of thought: “We’re very close to the atomic limitation now”, the retired engineer has stated in reference to computer chips.

In fact, as the TU Wien news page explains, we already have so-called ‘2D’ materials that can have a thickness of just one atom. (While this makes the term ‘2D materials’ technically misleading, we’ll continue to use it in inverted commas, rather than its more accurate synonym, ‘single-layer materials’.) But while manufacturing one-atom-thick materials is indeed possible, the TU Wien researchers maintain that the resultant microelectronics “can only be used effectively if … combined with suitable material systems”.

As discussed shortly—and detailed further in TU Wien’s Nature Communications paper—special insulating crystals are a crucial example of such material systems.


The Limitations of Traditional Approaches to Miniaturisation

The researchers, based in TU Wien’s Faculty of Electrical Engineering, point out that silicon-based semiconductors (given the strength of their electronic properties) were initially the answer to the industry’s increasing interests in component miniaturisation.

Now, however, with components increasingly being designed at the nanometre scale, the industry is seeing a cap on the electronic potential of silicon-based layers: “These worked well for a long time,” says Professor Tibor Grasser from TU Wien’s Institute of Microelectronics, “but at some point, we reach a natural limit”. TU Wien staff attribute this limit to the problematic electronic properties that come from components with only a few atomic layers.


An atomic model of a crystalline insulator.

A graphic atomic model of Vienna University of Technology’s material of interest: a calcium fluoride crystalline insulator, which is believed to be ideal for component miniaturisation. Image Credit: TU Wien.


TU Wien’s Solution: Introduce Thin Insulators

The TU Wien researchers have proposed that the limitations of ‘2D’ materials’ electronic properties can be addressed by having the ideal substrate and insulator layer.

As Professor Grasser explains: “As it turns out, … 2D materials are only the first half of the story. The materials have to be placed on the appropriate substrate, and an insulator layer is also needed on top of it”.

But while insulator layers have in fact always been implemented within ‘2D’ materials, TU Wien’s research reflects that the traditional insulator solution, SiO₂ (silicon dioxide) is not robust enough to accommodate the requisite flow of electrons in modern miniaturised electronics. Grasser and his colleague Yury Illarionov attribute this to SiO₂’s “very disordered surface and many free, unsaturated bonds”.

Ultimately, TU Wien’s solution is to instead rely on a special class of crystals known as fluorides. The scientists explain that some of the promising crystalline insulator materials are ionic crystals, particularly calcium fluoride (CaF₂) (an atomic model of which is pictured in the middle of the above image). The researchers write in Nature Materials that the ideal materials such as CaF₂ have “surfaces … [that] are chemically inert and free of dangling bonds”.


The Upshot of Improved Insulation Layers

While the researchers praise the industry’s increasing interests in microelectronics, they maintain that their research at TU Wien reflects the need for a bigger industry focus on resistor layers. To undervalue such resistors, says Grasser, would be “like driving a Ferrari on muddy ground and wondering why you don’t set a speed record”.

What’s more, the researchers believe that the benefits are not just applicable to semiconductors and other technologies relevant to microelectronics manufacturing: the R&D points to consumer benefits, too.

Conclude the Technische Universität Wien researchers in their Nature Materials paper: “We are confident that further development of this research topic will sooner or later enable 2D electronics for commercial applications”.

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