Novel transmission line boosts integrated circuit performance

The integrated circuit, also known as a microchip, is the "brain" of all intelligent devices. As smart technology continues to advance and become an indispensable part of life for many, researchers are focusing more and more and making these chips more efficient and reliable.

Shenjian Zhang, a recent graduate from the School of Advanced Technology at Xi’an Jiaotong-Liverpool University, proposed a new transmission-line design characterised by a multi-layer air gap.

Transmission lines, in an integrated circuit, are responsible for transferring signals between circuits. Incorporating the air-gap design can make these lines more efficient by reducing energy dissipation.

The new transmission line also comes in a compact structure, meaning it can be applied to more advanced, smaller chips.

Zhang’s research paper was selected for the IEEE International Conference on Integrated Circuit Design and Technology 2021. The conference is one of the biggest annual conferences in the field of integrated circuits, and was held online last month.

Speaking on his innovative research, Zhang says: "Integrating air-gap layers between copper lines and the other surrounding materials can reduce distributed capacitance (when energy is stored rather than transmitted) in the transmission line significantly.”

To understand the effects of these air gaps, imagine a transmission line as an underground water pipe. Capacitance is when drops of water leak out and get stuck in the surrounding soil, gradually decreasing the amount of water in the pipe. However, with this design, the air gaps act as a buffer, reducing the places water can get stuck and making sure the highest amount of water (or in this case energy) makes it to the other side as quickly as possible.

As a result, the compact air-gap transmission line allows energy currents to be more uniformly distributed in the signal-carrying conductor.

“This technology can make future integrated chips smaller, more energy efficient and more cost-effective," Zhang explains.

3D view of the novel transmission line

This research is an extension of Zhang’s final year project, where he studied complementary metal-oxide-semiconductor fabrication and air-gap formation technologies.

Zhang’s research was mentored by Dr Sang Lam, Associate Professor at the Department of Electrical and Electronic Engineering at XJTLU.

Currently, Zhang is pursuing a doctoral degree in Microelectronics at the Hong Kong University of Science and Technology.

Reflecting on his research, Zhang believes that self-motivation is crucial. “After my mentor helped me clarify my research topic, I devoured every relevant paper I could get my hands on. It may have seemed like this behaviour was more than was necessary to complete my project, but I believe that it’s precisely because I read a lot of advanced papers, that I could write this article and was selected by the conference.”

In addition to the motivation problems faced by many researchers, Zhang says: “I also had a bit of trouble learning to use the simulation software. It was frustrating at first, but I soon ironed out any problems in the weekly mentorship and group sessions," Zhang says.

"Scientific progress is built on trial and error. In order to discover or create something valuable, first, use your imagination to come up with a solution to a problem. Then figure out how you can consistently and accurately research its effectiveness. Finally, carefully record where it failed, and see how you can improve it next time.”

Facing a long journey to his PhD, how does Zhang keep himself motivated to stay on track? "I am passionate about research, and value the freedom it gives; I can reflect on questions, explore the unknown and get inspiration anytime and anywhere. I have gained a great sense of achievement from my work," Zhang says.

By Huatian Jin
Translated by Ke Tang
Photo by Shenjian Zhang
Edited by Xinmin Han, Patricia Pieterse