Moore’s Law predicts that the number of transistors that can be packed into a microchip will double every two years, eventually reaching its physical limit. Unless new methods are found, these limits could bring decades of progress to a halt. Atomically thin nanomaterials are a promising alternative to silicon-based transistors, and researchers are now looking for ways to connect them more efficiently to other chip components.
Now researchers at MIT, UC Berkeley, TSMC and elsewhere have discovered a new way to make these electrical connections that could help unlock the potential of the two-dimensional materials and further miniaturize the components, which could be enough to extend Moore’s Law.
The findings are described in the journal Nature, and the authors of the paper are recent MIT graduates Dr. Pin-Chun Shen, 20, and Dr. Cong Su, 20; postdoc Dr. Yu-Xuan Lin, 19; MIT professors Jing Kong, Tomas Palacios and Ju Li; and 17 others at MIT, the University of California, Berkeley, and other institutions.
The researchers said they solved one of the biggest problems in miniaturizing semiconductor devices, namely the contact resistance between metal electrodes and monolayer semiconductor materials, with a solution that proved to be very simple – using a semimetal, the element bismuth, to connect to the monolayer material instead of a common metal.
This ultra-thin monolayer material, in this case molybdenum disulfide, is considered a major contender to bypass the miniaturization limitations now encountered in silicon-based transistor technology. The interface between the metal and the semiconductor material, including these monolayers, creates a phenomenon called metal-induced gap state, which leads to the formation of a Schottky barrier, a phenomenon that inhibits the flow of charge carriers. The use of a semimetal, whose electronic properties are intermediate between those of a metal and a semiconductor, coupled with a proper energy alignment between the two materials, results in the elimination of this problem.
With this technique, the researchers have demonstrated miniaturized transistors with extraordinary properties that meet the requirements of future transistor and microchip technology roadmaps.
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