There’s a new contender for the world’s thinnest piece of electronics — and at three atoms thick, it’s going to be hard to beat.
Researchers have discovered a new process for producing ultra-thin transistors, according to a paper published today in Nature. The devices are made from an experimental material known as a transition metal dichalcogenide — also called a TMD. TMDs are exciting because they’re so thin, usually appearing as films of just a few atoms, with properties that make them useful for building solar cells, light detectors, or semi-conductors. It's an exciting prospect for physicists and manufacturers alike, but making the materials work consistently has proved extremely difficult.
Today's result unearths the best process yet for manufacturing the materials, giving new hope that the material might someday give rise to atomically thin circuits and sensors. "Our work pushes TMDs to the technologically relevant scale, showing the promise of making devices on that scale," said Saien Xie, one of the lead authors of the paper. "In principle there is no barrier toward commercial viability."
If the finding does hold up, it could result in a real breakthrough for future generations of electronics. Modern chip manufacturers are already reaching the upper density limit for silicon chips, leading some to predict the end of Moore's Law. If electronics are going to keep getting smaller and faster, we'll need an ultra-thin material that can pack circuits even tighter without overheating or breaking down. It's hard to say whether TMD and graphene will fit the bill — they might still prove unwieldy, leaving chipmakers to make do with silicon — but for anyone dreaming of nanoscale electronics, today's result is an encouraging sign.
TMDs are most often discussed alongside another cutting-edge ultra-thin material: graphene. Both materials can be produced in thicknesses of just a few atoms, which has led many researchers to call them "two-dimensional materials." Used in conjunction, they could eventually produce a new class of atom-thin electronics, either resulting in paper-thin devices — or allowing manufacturers to fit an unprecedented number of circuits into something the same size as a modern processor.
The Nature paper details a new way of producing TMD, more successful and stable than any previous method. The researchers turned to a proven industrial technique known as "metal organic chemical vapor deposition (or MOCVD). The process starts with two commercially available precursor compounds — diethylsulfide and a metal hexacarbonyl compound — mixed on a silicon wafer and baked at 550 degrees Celsius for 26 hours in the presence of hydrogen gas. The result was an array of 200 ultra-thin transistors with good electron mobility and only a few defects. Just two of them failed to conduct, leaving researchers with a 99 percent success rate.
It's the best production result TMDs have had so far, suggesting the material might one day be used to make ultra-thin electronics. Still, the next step is making sure it can be produced consistently. "The report of new properties is important in order to understand the material, but there is a lack of systematic research on synthesis methods," said Humberto Gutierrez, a physicist at the University of Louisville who also works on ultra-thin materials and was not involved in the paper. "Many of the [previously] reported conditions using chemical vapor deposition cannot be reproduced from one laboratory to another, and the large area films have very low crystal quality."
Hammering out those inconsistencies is crucial if researchers are going to build workable devices out of the new materials. The researchers will also need to be able to produce the TMDs at a lower temperature if they’re going to be used in conventional electronics, as many auxiliary materials will combust at 550 Celsius. Still, the biggest concern now is simply expanding on the current results. If researchers can produce the ultra-thin transistors consistently, there will be lots of opportunities to refine the process in the future.