Molybdenum-Disulfide 2D Transistors Go Ballistic

March 2017

At the IEEE International Electron Devices Meeting, researchers presented work they say shows that molybdenum disulfide not only makes for superlative single transistors, but can be made into complex circuits using realistic manufacturing methods.

The researchers are part of Eric Pop's team. They showed transistors made from large sheets of MoS2 can be used to make transistors with 10-nanometer-long, gate having electronic properties that approach the material's theoretical limits. The devices displayed traits close to ballistic conduction, a state of very low electrical resistance that allows the unimpeded flow of charge over relatively long distances—a phenomenon that should lead to speedy circuits.

Most of the work on molybdenum disulfide so far has been what professor Eric Pop calls "Powerpoint devices." These one-off devices, made by hand in the lab, have terrific performance that looks great in a slide. This step is an important one, says Pop, but the 2D material is now maturing.

Pop Lab's transistors are not as small as the record-breaking ones demonstrated in October. What's significant is that these latest transistors maintained similar performance even though they were made using more industrial-type techniques. Instead of using Scotch tape to peel off a layer of molybdenum disulfide from a rock of the material, then carefully placing it down and crafting one transistor at a time, Pop's grad student started by growing a large sheet of the material on a wafer of silicon.

At these relatively small dimensions, the molybdenum disulfide transistors approach their ultimate electrical limit, a state called ballistic conduction. When a device is small enough (or at low enough temperature), electrons will travel through the conducting medium without scattering because of collisions with the atoms that make up the material. Transistors operating ballistically should switch very fast and enable high-performance processors. Pop estimates that about 1 in 5 electrons moves though the rusty transistors ballistically. By further improving the quality of the material (or making the transistors smaller), he expects that ratio to improve. The important thing, he says, is the way they achieved this: using methods that could translate to larger scales. "We have all the ingredients we need to scale this up," says Pop.

Eric Pop and graduate students talking during an informal lunchtime Q and A session in the Packard building.


 

Excerpted from IEEE Spectrum, "Molybdenum-Disulfide 2D Transistors Go Ballistic"