Physicists' study demonstrates silicon's energy-harvesting power

August 26, 2019

A University of Texas at Dallas physicist has teamed with Texas Instruments Inc. to design a better way for electronics to convert waste heat into reusable energy.

The collaborative project demonstrated that silicon's ability to harvest energy from heat can be greatly increased while remaining mass-producible.

Dr. Mark Lee, professor and head of the Department of Physics in the School of Natural Sciences and Mathematics, is the corresponding author of a study published July 15 in Nature Electronics that describes the results. The findings could greatly influence how circuits are cooled in electronics, as well as provide a method of powering the sensors used in the growing "internet of things."

"Sensors go everywhere now. They can't be constantly plugged in, so they must consume very little power," Lee said. "Without a reliable light source for photovoltaic energy, you're left needing some kind of battery -- one that shouldn't have to be replaced."

Thermoelectric generation is a highly green energy source, converting a difference in temperature into electrical energy.

"In a general sense, waste heat is everywhere: the heat your car engine generates, for example," Lee said. "That heat normally dissipates. If you have a steady temperature difference -- even a small one -- then you can harvest some heat into electricity to run your electronics."

Sensors embedded beneath a traffic intersection provide an example of convenient thermoelectric power.

"The heat from tires' friction and from sunlight can be harvested because the material beneath the road is colder," Lee said. "So no one has to dig that up to change a battery."

The primary hurdles for widespread thermoelectric harvesting have been efficiency and cost, he said.

"Thermoelectric generation has been expensive, both in terms of cost per device and cost per watt of energy generated," Lee said. "The best materials are fairly exotic -- they're either rare or toxic -- and they aren't easily made compatible with basic semiconductor technology."

Silicon, upon which so much technology relies, is the second-most abundant element in Earth's crust. It has been known since the 1950s to be a poor thermoelectric material in its bulk, crystalline form. But in 2008, new research indicated that silicon performed much better as a nanowire -- a filamentlike shape with two of its three dimensions less than 100 nanometers. For comparison, a sheet of paper is about 100,000 nanometers thick.

"In the decade since those experiments, however, efforts to make a useful silicon thermoelectric generator haven't succeeded," Lee said.

One barrier is that the nanowire is too small to be compatible with chip-manufacturing processes. To overcome this, Lee and his team relied on "nanoblades" -- only 80 nanometers thick but more than eight times that in width. While that is still much thinner than a sheet of paper, it's compatible with chip-manufacturing rules.

Study co-author Hal Edwards, a TI Fellow at Texas Instruments, designed and supervised fabrication of the prototype devices. He turned to Lee and UT Dallas to further study what the devices could do.

"A deep dive for these novel measurements, detailed analysis and literature comparisons requires a university group," Edwards said. "Professor Lee's analysis identified key metrics in which our low-cost silicon technology competes favorably with more exotic compound semiconductors."

Lee explained that the nanoblade shape loses some thermoelectric ability relative to the nanowire.

"However, using many at once can generate about as much power as the best exotic materials, with the same area and temperature difference," he said.

The team's circuit-design solution combined an understanding of nanoscale physics with engineering principles. One key realization was that some previous attempts failed because too much material was used.

"When you use too much silicon, the temperature differential that feeds the generation drops," Lee said. "Too much waste heat is used, and, as that hot-to-cold margin drops, you can't generate as much thermoelectric power.

"There is a sweet spot that, with our nanoblades, we're much closer to finding than anyone else. The change in the form of silicon studied changed the game," he added.

Lee said that the advanced silicon-processing technology at Texas Instruments allows for efficient, inexpensive manufacturing of a huge number of the devices.

"You can live with a 40% reduction in thermoelectric ability relative to exotic materials because your cost per watt generated plummets," he said. "The marginal cost is a factor of 100 lower."

Gangyi Hu PhD'19, who finished his doctorate in physics at UT Dallas in May, is the study's lead author. He produced the computer modeling to determine the number of nanoblades per unit area that will produce the most energy without reducing the temperature difference.

"We optimized the configuration of our devices to place them among the most efficient thermoelectric generators in the world," Hu said. "Because it's silicon, it remains low-cost, easy to install, maintenance-free, long-lasting and potentially biodegradable."

Lee said the work was also novel because they used an automated industrial manufacturing line to fabricate the silicon integrated-circuit thermoelectric generators.

"We want to integrate this technology with a microprocessor, with a sensor on the same chip, with an amplifier or radio, and so on. Our work was done in the context of that full set of rules that govern everything that goes into mass-producing chips," Lee said. "Over at Texas Instruments, that's the difference between a technology they can use and one they can't."

Edwards vouched for the multiple advantages of collaborating with UT Dallas, including recruiting.

"I find my collaborations with professor Lee's group to be very valuable," Edwards said. "I also value the opportunity to get to know students well, so that I can help them to find roles within TI. One of my close TI colleagues was professor Lee's PhD student during one of our earlier collaborations."
-end-
Lee's research is supported by the National Science Foundation through the Grant Opportunities for Academic Liaison with Industry (GOALI) program, and the work at UT Dallas was performed in the Texas Analog Center of Excellence (TxACE) laboratory.

University of Texas at Dallas

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.