One of the guiding predictions in the fields of electronics and computing is Moore's Law, which says that the number of transistors on a microchip double about every two years. Now that conventional technologies are reaching their physical limits, researchers are looking for alternative methods to create more powerful devices.

The basis of modern electronics is the use of silicon, a semiconductor material, and one of the potential directions of improving electronics is by finding an alternative to this material. Researchers are looking into atomically thin materials instead of silicon. However, one persisting problem is that connecting these 2D transistors together, or with conventional electronic components, has remained challenging.

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Now, in a new study from MIT, the University of California Berkeley, and the Taiwan Semiconductor Company have found a new way of bridging this gap, which could make these atomically thin materials a feasible replacement for silicon. The new 2D transistors could further miniaturize devices, enough to extend Moore's Law in the near future, according to the researchers.

Researchers were able to demonstrate this new electronic connection in the report "Ultralow contact resistance between semimetal and monolayer semiconductors," appearing in the latest Nature journal. The team includes recent MIT graduates, professors, and 17 other collaborators from other institutions.

A Chip of Molybdenum Disulfide
(Photo: Materialscientist via Wikimedia Commons)

Beyond the Physical Limits of Moore's Law

"We resolved one of the biggest problems in miniaturizing semiconductor devices, the contact resistance between a metal electrode and a monolayer semiconductor material," says Cong Su, a recent MIT Ph.D. graduate and now with UC Berkeley, in an MIT press release.

To work around this problem, researchers used the semimetal bismuth as a replacement for conventional metals used in electronics. They used the new material to connect with the atomically thin materials for the application.

In their study, they used molybdenum disulfide, which is viewed as a promising candidate among atomically thin materials to work around the supposed physical limits hindering Moore's Law in semiconductor devices. However, another challenge awaits progress in this field: the creation of an efficient and highly conductive interface between these materials and metal conductors to create a connection between them.

To bridge this gap, researchers had to induce a phenomenon called a metal-induced gap state between the metal and semiconductor materials. This state creates a so-called Schottky barrier, which prevents charge carriers from flowing through. However, the use of a semimetal - a substance whose electrical behavior is between that of a metal and a semiconductor - with the proper energy alignment could eliminate the problem.

The Fabrication of 2D Transistors

With the use of atomically thin materials - materials only a few atoms thick - researchers can now develop these "2D transistors" and potentially reduce a key parameter in electronics called "channel length" by several times. From conventional materials of 5 to 10 nanometers in cutting-edge ICs, the new material could take the channel length down to a fraction of a nanometer. These materials include a whole class of materials called the transition metal dichalcogenides - and molybdenum disulfide used by researchers belong to this group.

While the possibility of using these materials is being explored, researchers say that scaling up and integrating these 2D transistors to a commercially feasible level could require further studies. Despite this, its applications in physics can already be felt, with Su suggesting that experiments could benefit from the new breakthrough immediately.


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