Photonics and Sustainable Chip Manufacturing

Sustainability was a trending topic among the presentations at this year’s SPIE Defense + Commercial Sensing. It was a fitting subject, given that the annual event spanned a week that included Earth Day 2024.

At the symposium plenary on AI/ML + Sustainability, Massachusetts Institute of Technology principal research scientist Anu Agarwal began her slide presentation with a picture of her broken cell phone. She was citing this not-uncommon-experience to highlight how repair and recyclability is not part of the DNA of the microelectronics industry.

“Of course, I took it into the store,” Agarwal said of the broken phone. “And what they told me was, ‘Yep, sure, no problem, we can get you a new phone [with a] free upgrade.’”

“But I didn’t want a new phone,” she continued. “I wanted this one fixed. And they said that's going to cost me $200. So, what's wrong with this picture? I get a new phone for free, but fixing my old phone is going to cost me 200 bucks?”

There’s something wrong with the industry, Agarwal said, when a product like a cell phone cannot be designed to make repair more affordable and much easier to do. She noted that more than a trillion microchips in a wide range of devices like cell phones were sold in 2023, an industrial output that each year requires on the order of 150 Kw of energy, 800 million cubic meters of water, and is altogether responsible for some 500 megatons of CO2 equivalent emissions. Demand for microchips in coming years is expected to soar by some 70 percent and require a workforce growth of at least one million people, up from the current two million.  Most of the pollution from semiconductor manufacturing, she notes, is due to market growth.

Agarwal said that the issue of workforce growth has brought her to consider “handprints” as well as “footprints” when it comes to industry sustainability. By that she means what are the actions companies and individuals can take to reduce carbon emissions by remote work, remote meetings, all of the optional behaviors that are not inherent to manufacturing itself.

“If you look at sustainability reports across the industry, they’re apples to oranges,” Agarwal said. “They cannot be compared. Some people are talking about water recycling, some people are talking about electricity generation and how they reduce it. Some are talking about how they reduce process emissions.”

She suggests a standardized approach that considers categories of environmental impact that will matter the most for production and product lifecycle. And from there, “what highest responsibility do we have to reduce footprints? And what major opportunities do we have?  In the future I see, we will develop objective, quantitative answers as to how we can add footprints and handprints to our lifecycle analysis. We can look at manufacturing, all across the supply chain from design to production, to use—determine the processes that are the main contributors [to sustainability], touch those first, and then move down the chain.”

Among the many ways the chip industry could become more sustainable, Agarwal said, innovation in photonic chips and/or the coupling of photonic and electronic chips offers great promise. “Can we get away from copper interconnects?” she asked. “Photonic interconnects—they’re not new ideas. People have called them co-packaged optics. And this is the trend in the industry over the last 20 years, the [optical] fibers coming closer and closer to the switch in the package. Decreasing the copper length is definitely happening, but we need to do more.” She advocates innovation in chip-to-chip coupling, moving electronic and photonic circuits together on an optical interposer.

With electronic/photonic convergence, Agarwal said, the microelectronics industry can decrease energy consumption when devices are in use, and photonics nodes could be coupled to legacy electronic nodes. This would allow simpler exchange of modular parts, and easier repairs of components with longer lifecyles than their electronic counterparts. “We need to find a way to, reduce, reuse, recycle, and of course, add to our vocabulary the idea of repair for sustainability.”

“The idea is we need to drive sustainability in the microchip industry proactively not as a compliance approach. And we need to accelerate the change to promote sustainability,” she said.  “A sustainable Future is not guaranteed unless we act.”