Japanese writer and publicist based in Eindhoven, The Netherlands
Yuqing Jiao, Associate Professor in the Department of Electrical Engineering of Eindhoven University of Technology (Photo: TU/e)
As AI technology advances, the amount of data being transferred between servers in data centers is growing at an unprecedented rate. Semiconductor chips have been continually evolving to process this rapidly growing data. To perform faster and more energy-efficiently, semiconductor devices must reduce their sizes, but they are now approaching their physical limits.
Further miniaturisation, speed enhancement, and energy efficiency improvements of chips require a new look at how data are transported and processed in the chips. One promising technology is photonic integrated circuits (PICs). These chips use photons in addition to electrons, and they are expected to break the performance limitations of conventional electronic chips.
At Eindhoven University of Technology (TU/e), located in the Dutch province of Brabant, research on PICs using a material called indium phosphide (InP) has been conducted for more than 20 years. Based on this research, an InP-based PIC foundry called “SMART Photonics” has already been established, and TU/e is now working on the next-generation chip technology, looking at 10-15 years further into the future.
Jiao Yuqing, associate professor in the Department of Electrical Engineering of TU/e explains more about his research.
Making Photonic Chips Even Smaller, Faster, and More Energy-Efficient
While PICs can be made from materials such as silicon (Si) or silicon nitride (SiN), each with its unique characteristics, those being developed at TU/e utilise indium phosphide (InP). Unlike Si and SiN, InP can create both “passive optical components” such as optical switches and "active optical components" like lasers. This ability to integrate all photonic functions onto one single chip results in lower optical loss, improved performance, and reduced costs.
InP-based PICs are already being used in the data and telecommunications industries and are now penetrating new markets such as neuromorphic computation (computation technology that mimics neurons, the nerve cells of the brain), AI training, and remote sensing, such as LiDAR (a technology that uses laser light to measure the distance to objects and the surrounding environment with high precision).
Although the use of photonics for such applications is still relatively less mature, semiconductor giants such as Intel and TSMC (Taiwan Semiconductor Manufacturing Company) have recently started incorporating PICs into their manufacturing flow.
A PIC wafer fabricated at TU/e. Jiao's research is done on the entire wafer, not on chip basis. (Photo: TU/e)
Associate Professor Yuqing Jiao’s research represents the cutting-edge of InP-based PIC technology.
“How can we make PICs 100 to 1000 times denser, smaller, faster, and more energy-efficient? We are researching the completely new design of PICs and the development of their manufacturing process,” Jiao explains.
The key to increasing PIC density lies in the design of the diode (a component that allows the flow of electricity to go one way). Layering semiconductor materials of varying thicknesses create the diode.
“We need to compress the diode into a smaller size, but it should still contain all the photons, and it should allow the electrons to pass through. This calls for new research and optimisation into how photons and electrons interact within an extremely small structure”.
In recent experiments, Jiao and his co-workers achieved several new track records pushing the speed of the photonic devices beyond 100 GHz. This is approximately twice the speed of commercially available communication systems today.
3D integration: Combining and Converging Electronics and Photonics
In addition to InP-based PICs, Associate Professor Jiao is working on a technology that integrates PICs and electronic ICs (EICs) in a three-dimensional structure.
“It is called ‘heterogeneous integration technology,’ which combines chips made of different materials (such as InP and Si) and different functions (such as electronic and photonics) into one. We are exploring 3D integration by stacking PICs on top of electronic circuits on the same wafer” Jiao explains.
Heterogeneous integrated circuits that combine electronics and photonics on a single chip (Image: TU/e)
In conventional chip packages, PIC and EIC chips are placed side by side and they are connected with wires that are several millimeters long. However, with 3D integration, the two chips are stacked together, shortening the wires by a factor of a hundred to 10 micrometers. This decreases signal delay and dramatically improves performance.
“A major bottleneck of chip performance is the wires used in packages. No matter how fantastic your chip is, its performance is limited by the wires. So, by breaking this bottleneck, we can unleash the true performance of the chips.”
The 3D integration of electronics and photonics also leads to cost reductions.
“For example, a data center for training AI requires the transmission of huge amounts of data, and the transmission alone accounts for about half of the total electricity bill. But suppose we can bring the photonics that transmit the light and the electronics that compute closer together. In that case, we really save a lot of energy waste on the chip interconnections and reduce the electricity bill for that. Furthermore, the improved performance of the chips will pave the way for new applications. The development of this technology will benefit us both economically and socially,” Jiao said.
Walking a path, nobody has taken before
Jiao's research is complex, requiring knowledge of both electronics and photonics and a deep dive into semiconductor nanotechnologies; he explains the difficulty of combining two different materials.
“The power of combining different materials is enormous. However, materials may not be directly compatible with each other, and they may behave in different ways during the manufacturing process and during operation. It is very challenging to make sure that both the electronics and photonics operate as good as they originally are, even after 3D integration. Recently, a technological breakthrough showed that 3D integration was possible. The next step is to research on a design methodology that allows the two to work seamlessly together”.
Currently, Jiao's research focuses on InP-based PICs and heterogeneous integration technology. However, he mentions that high-performance electronics will become a third key theme. Electronics play a crucial role in heterogeneous integration. Mainstream electronics are based on Si. But InP material can unleash electronics' performance and make the latter more than ten times faster.
“No one has ever achieved a true 3D integration of electronics and photonics before, so there is limited literature from which we can learn. We are the pioneers. It's a step-by-step learning process, working with generations of PhD students,” said Jiao.
Clean room “Nano Lab” at TU/e (Photo: TU/e)
In pursuing this research, Jiao is also looking to collaborate with related companies and other universities. He hopes to actively exchange information with companies and universities in Japan, where the semiconductor industry is reviving.
“Researchers at Japanese universities tend to dedicate themselves to one technology to the point of perfection, which I don’t see much here In the Netherlands. So, I think it is worth combining the two and learning from each other at an academic level. I am also very interested in what the Japanese industry is aiming for. We are also looking for opportunities for cooperation at the industrial level.”
Associate Professor Jiao's challenge continues to advance step by step, involving researchers in Japan and worldwide. Stepping on uncharted paths, he is paving the way for innovations that will transform our world.
Contact: TU/e Electronic Engineering Department, Yuqing Jiao Associate Professor
https://www.tue.nl/en/research/researchers/yuqing-jiao