The technique could allow chip makers to make next-generation transistors based on materials other than silicon. A study also funded by Intel and Samsung

Researchers at MIT in Boston have developed a method that could allow semiconductor makers to fabricate transistors based on 2D materials by growing them on silicon wafers and other materials. The extent of this innovation could be considerable, given that ever-increasing miniaturization is taking silicon to its physical limits, i.e. losing the promising electrical properties that have made it the material at the basis of electronics. This is why electronics look to 2D materials, two-dimensional crystalline sheets as thick as a single atom.

“At the nanoscale , 2D materials can conduct electrons much more efficiently than silicon,” the MIT researchers explain. For this reason, the goal is to find a way to “engineer materials on standard silicon wafers while preserving their perfect crystalline shape”. And that’s exactly what they managed to do at the prestigious US university. A new method is a form of ‘ non-epitaxial, single crystal growth ‘, which the team has used for the first time to grow pure, defect-free 2D materials on industrial silicon wafers. Researchers have successfully fabricated a simple, functional transistor from a type of 2D material called transition metal dichalcogenides, or TMDs, that conduct electricity better than nanoscale silicon.

The study was published in Nature and, in addition to the MIT team, involving scholars from the University of Texas at Dallas, the University of California at Riverside, Washington University in Saint Louis and various institutions in South Korea. To underline that, Intel and Samsung also find a place among the lenders. Producing a 2D material has so far required a manual process whereby an atom-thin foil is carefully exfoliated from bulk material, similar to what happens in the kitchen when peeling the layers off an onion. Most bulk materials, however, are polycrystalline, meaning they have multiple crystals growing in random orientations.

Due to the different orientations, the meeting point between one crystal and another creates an electrical barrier and prevents the electrons from flowing. This requires researchers to conduct analyses in search of single crystalline regions, a tedious and lengthy process inapplicable to industrial needs. Recently, researchers have found other ways to fabricate 2D materials by growing them on wafers of sapphire. This material has a hexagonal atom pattern that encourages 2D materials to assemble in the same single-crystal orientation. But silicon wafers don’t have the hexagonal support scaffold offered by sapphire, so how do you do that?

With a trick that prevents the formation of barriers. The MIT researchers took a different approach involving conventional vapour deposition methods to “pump” atoms along a silicon wafer. First, they covered the silicon wafer with a “mask ,” a coating of silicon dioxide that they shaped into tiny pockets, each designed to trap a core. Then, they flowed a gas of atoms that settled in each pocket to form a 2D material, a TMD. This method’s pockets are the protagonists because they allow the 2D materials to assemble on the silicon wafer in the same monocrystalline orientation.