Published: Aug. 25, 2017 By

Ronggui Yang in a lab with two students.

(From left) PhD student Xin Qian, post doctoral researcher Puqing Jiang, and mechanical engineering professor Ronggui Yang in Yang's laboratory at CU Boulder.

Ronggui Yang knows people want faster, more powerful electronic devices. Whether it is a new laptop, cell phone, smart TV, or technology for electric vehicles and the electric grid, the push for products that can do more is an ever-growing market.

There is just one problem.

“Silicon chips have a fundamental limit on how small they can be," says Yang, a professor of mechanical engineering at the University of Colorado Boulder.

For decades, technology development has followed Moore's law, which says that the number of transistors on a chip doubles roughly every two years. The observation has powered advancements since 1965, directing research and development goals and long-term corporate planning.

Today, some transistors are as small as five nanometers. At that size, 16,000 of them could fit in the width of a single human hair. One chip can house billions of such small transistors.

Unfortunately, the development of newer and better chips has become more and more difficult, and both the private and public sector are increasingly concerned about the demise of Moore's law. Both DARPA and SRC are expecting to increase investment into radically new systems with novel materials and designs to power an electronic resurgence.

One solution may be two-dimensional (2D) layered semiconductors, such as graphene or transition metal dichalcogenides. The chips are so small that each stacked layer is only one to three atoms thick, presenting new possibilities for electronic devices. It is an active area of research around the world, but making the chips a reality has been problematic.

“When you get down to something that small, new physical phenomena emerge, but heat becomes an issue,” says Yang, who has been working on thermal challenges in electronics for more than 20 years. “At that scale, the thermal transport properties aren’t well understood.”

Heat generated by computers has long been a concern, and at such a tiny size, engineers have struggled just to measure what is happening, much less deal with it. Traditional thermometers do not function at that scale.

Yang believes he may have a solution. His team has published a paper demonstrating a new way to measure the thermal properties of these 2D semiconductors with a femtosecond laser. Their methodology allows them to collect measurements along and across each individual layer.

It could be a major advancement in experimental metrology, the study of measurements, but is complicated work and significant theoretical understanding is needed to obtain the information.

However, heat transfer research is Yang’s specialty. His laboratory, the Nano-enabled Energy Conversion, Storage and Thermal Management Systems (NEXT) Group, has done extensive fundamental and experimental investigations into the utilization of new materials for electronics as well as innovative cooling methods.

“We’ve been in this area for a long time,” Yang says. “This is a big project, but it has significant applications and I’m intrigued about the possibilities.”


Read the paper: Probing Anisotropic Thermal Conductivity of Transition Metal Dichalcogenides MX2 (M = Mo, W and X = S, Se) using Time-Domain Thermoreflectance. In addition to Yang, its other writers are Xiaokun Gu, a former PhD student who is now a professor at Shanghai Jiao Tong University in China; Xin Qian, a current PhD student; and Puqing Jiang, a post-doctoral researcher working in his lab.