Super-semiconductors
Graphic illustration by Jeffrey C. Chase July 26, 2022
Researchers report new material that could enable ultra-low-power electronic devices
University of Delaware mechanical engineer Bingqing Wei and an international team of colleagues have discovered a promising new material they say could pave the way for ultra-low-power electronic devices.
They call the material a super-semiconductor, a term based on two well-known words in electronics: superconductors and semiconductors. Superconductors are materials known since the early 1900s to conduct electricity with zero resistance at ultra-low temperatures, considered to range from -450 to -123 degrees Fahrenheit. Semiconductors are materials that exhibit both conductive and insulating properties, depending on temperature.
Made from cobalt and aluminum, the super-semiconductor material is 3 to 10 times more conductive than typical semiconductor materials, such as silicon, at room temperature. It exhibits ultra-low resistivity, too, meaning it allows current to flow through the material with little resistance to slow the electricity down. The researchers believe the discovery has the potential to significantly reduce power consumption and improve the performance efficiency of electronic devices.
“This is an exciting discovery in solid-state electrical conducting materials,” said Wei, professor of mechanical engineering and director of the Center for Fuel Cells and Batteries at UD.
A primer on conductive materials
Wei explained that all solid materials exhibit resistance to conducting electricity, but some more than others. Plastics, for example, are known as insulators because they do not conduct electricity. Metal alloys like copper, aluminum, gold and silver are considered good at conducting electrical current, while still other materials are in between. These in-between materials are known as semiconductors — materials that conduct current at room temperature but behave like insulating materials at ultra-low temperatures.
Modern electronics, such as diodes, transistors and computer chips, are based on silicon, a typical semiconducting material. These semiconductors rely on electrons (negative charges) and/or holes (positive charges) for their conducting behavior, but they are inefficient at conducting these charge carriers. This creates high resistance, leading to excess heat as the semiconductor operates.
“When materials become smaller and smaller in nanoscale, most of the power consumed during operation becomes heat. This heat has to be transferred outside of the system, otherwise the device will fail,” said Wei, an expert in the use of nanomaterials such as carbon nanotubes for energy storage, mainly in batteries.
So, how does the cobalt-aluminum super-semiconductor improve this problem?
“Because the material exhibits low resistance, the current passes through this super-semiconductor material more efficiently, leading to lower power consumption and producing less heat as a result,” said Wei, adding the discovery provides a potential alternative to current silicon-based semiconductors.
The researchers are working to use the material to create electrical components, such as diodes and transistors, that control the direction a current flows in modern electronics. They think these super-semiconductors would be particularly useful in what’s known as p-n junctions, which are important interfaces to control the current flow direction between semiconductor materials.
Used in computer chips, for example, Wei said super-semiconductors could dramatically decrease power consumption and extend the working time of our electronics. It’s an idea that could become very important as we add more devices to our lives.
For example, if you just consider a single personal computer in a home or business, it might seem like the power used or heat created isn’t that much to cope with, and you’d be right. The average central processing unit, or CPU chip, in a laptop uses about 45 watts per hour, little more than the 40-watt incandescent light bulb in your refrigerator. Computer chips in personal desktop computers use a little more, about 125 watts, the same electricity as a ceiling fan in your living room.
But when you combine personal computers in multiple households and businesses, plus a few supercomputers that do the heavy data-lifting for everything from weather forecasting to testing mathematical models to predicting the path of disease, you can see how this heat effect begins to multiply. Unlike their puny personal computer peers, supercomputers today typically contain 100,000 CPU chips and consume about 12.5 megawatts of power — the power consumption equivalent of a town with a population of 100,000 people.
Worldwide there are over half a billion computers.
“If we decrease the power consumption of an electronic device, you can see the benefit,” said Wei. “And this is just taking computer usage into account, it doesn’t account for other devices, such as the 2.6 billion smartphones that were sold worldwide over the last two years.”
So, how did the research team figure out that cobalt and aluminum were a winning combination?
The researchers were exploring aluminum and carbon nanotubes for infrared detector applications. They knew that shining light on small noble metallic particles (for example, gold, silver, platinum) causes what is known as a plasmonic effect, where the electric charge on the material distributes in a way that causes electrons to accumulate on the particle surface.
By using a technique called plasma etching to create space between self-assembling polystyrene spheres, the research team was able to deposit a layer of cobalt 10 nanometers thick, followed by a 100-nanometer layer of aluminum onto the spheres. For comparison, the average human hair is about 80,000 to 100,000 nanometers thick.
This layering process allowed only the metal to rest on top of the spheres, such that, when exposed to light and room temperature, it triggered this plasmonic effect and created enough energy for the free electrons in cobalt to jump to aluminum. This left the cobalt particles more positively charged than the aluminum, which the researchers theorize is what gives the material its super-semiconducting behavior.
“We're still learning. This is very new,” said Wei.
To the best of their knowledge, this is the first report of super-semiconducting behavior. The researchers have filed a provisional patent on their discovery with UD’s Office of Economic Innovation and Partnerships.
The researchers recently published their results on super-semiconductors in Applied Physics Review.
Zhigang Li, the paper’s lead author and professor in the School of Pharmaceutical and Materials Engineering at Taizhou University, China, was a visiting scholar at UD in 2018. Li is an expert on the superconducting behavior of materials. Other co-authors include Zongpeng Wang, Yanping Liu, Jigen Chen and Tainle Wang from Taizhou University; Xiangke Cui (Beijing Jiaotong University); Xiaowei Wang and Zhenhai Xia (University of North Texas); Minghu Fang (Zhejiang University); Shangshen Feng (Zhejiang Agricultural and Forestry University); and Hengji Liu (University of Science and Technology of China).
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