If you’ve purchased a new computer lately, like I have, you may have noticed just how fast these new machines are.
And that is largely because computer chips keep getting better and better.
Back in 1965, an American engineer named Gordon Moore observed that the number of transistors on a computer chip was doubling about every 18–24 months.
His observation and follow-up prediction came to be known as Moore’s Law.
That rapid pace of miniaturization of transistors that make up computer processors and memory chips eventually would stall out at around the year 2000, as it bumped into basic physical limits.
Until a new development that allowed for a three-dimensional architecture of semiconductor devices on a chip broke the logjam in 2007 and rapid progress resumed.
But now, scientists fear we on the edge of another semiconductor bottleneck — unless new, radical approaches are found.
The answer, according to a group of researchers, could be the application of nanotechnology.
The latter is the use of matter on an atomic, molecular, and supramolecular scale for industrial purposes.
The ability to visualize and manipulate matter at the nanoscale has led to a diverse technology that ranges from better and faster electronics and more efficient fuel usage to sensing, drug discovery and stronger, more resistant materials.
Check out this description from AzoNano.com:
“A nanometre is one-billionth of a metre: ten times the diameter of a hydrogen atom. The diameter of a human hair is, on average, 80,000 nanometres. At such scales, the ordinary rules of physics and chemistry no longer apply. For instance, materials’ characteristics, such as their colour, strength, conductivity and reactivity, can differ substantially between the nanoscale and the macro. Carbon ‘nanotubes’ are 100 times stronger than steel but six times lighter.”
Nanotechnology has the prospect of affecting the lives of all of us and already a number of applications are in the market-place.
Now researchers at MIT, the University of California at Berkeley, the Taiwan Semiconductor Manufacturing Company, and elsewhere have found a new way of making those electrical connections, which could help to unleash the potential of 2D materials and further the miniaturization of components — possibly enough to extend Moore’s Law, at least for the near future, the researchers say.
The findings are described in the journal Nature, in a paper by recent MIT graduates Pin-Chun Shen PhD ’20 and Cong Su PhD ’20, postdoc Yuxuan Lin PhD ’19, MIT professors Jing Kong, Tomas Palacios, and Ju Li, and 17 others at MIT, UC Berkeley, and other institutions.
According to a report in SciTechDaily, the direction being explored is the use of atomically thin materials instead of silicon as the basis for new transistors — but connecting those “2D” materials to other conventional electronic components has proved difficult.
“We resolved one of the biggest problems in miniaturizing semiconductor devices, the contact resistance between a metal electrode and a monolayer semiconductor material,” says Su, who is now at UC Berkeley.
The solution proved to be a simple one: the use of a semimetal, the element bismuth, to take the place of ordinary metals to connect with the monolayer material.
Such ultrathin monolayer materials, in this case molybdenum disulfide, are seen as a major contender for a way around the miniaturization limits now being encountered by silicon-based transistor technology.
But creating an efficient, highly conductive interface between such materials and metal conductors, in order to connect them to each other and to other devices and power sources, was a challenge holding back progress toward such solutions, Su says.
The interface between metals and semiconductor materials (including these monolayer semiconductors) produces 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 fall between those of metals and semiconductors, combined with proper energy alignment between the two materials, turned out to eliminate the problem.
So-called two-dimensional materials, thin sheets just one or a few atoms thick, meet all the requirements for enabling a further leap in miniaturization of transistors, potentially reducing by several times a key parameter called the channel length — from around 5 to 10 nanometers, in current cutting-edge chips, to a subnanometer scale.
A variety of such materials are being widely explored, including a whole family of compounds known as transition metal dichalcogenides.
The issue of achieving a low-resistance metal contact with such materials has also been hampering basic research on the physics of these novel monolayer materials.
Because existing connection methods have such high resistance, the tiny signals needed to monitor the behavior of electrons in the material are too weak to get through.
“There are numerous examples coming from the physics side that call for a low-contact resistance between the metal and a semiconductor. So, it’s a huge problem in the physics world as well,” Su says.
Figuring out how to scale up and integrate such systems at a commercial level could take some time and require further engineering. But for such physics applications, the researchers say, the impact of the new findings could be felt quickly.
“I think in physics, many experiments can benefit from this technology immediately,” Su says.
Nanoscale semiconductors also exhibit a widened band gap that provides these materials with a unique chemical stability at high operating temperatures.
This thermal stability provides a wide range of advantages to systems equipped with nanoscale semiconductors, especially when compared to silicon-based devices.
For example, electronic systems can eliminate the need for excess wires, connectors or cooling systems that would previously have been needed.
Besides MIT and the University of California at Berkeley, the team included researchers at Lawrence Berkeley National Laboratory, the Taiwan Semiconductor Manufacturing Company, the National Taiwan University, and King Abdullah University of Science and Technology in Saudi Arabia.
The work was supported by the National Science Foundation, the US Army Research Office, the Office of Naval research, and the US Department of Energy.
Sources: SciTechDaily, AzoNano.com, Wikipedia, MIT