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The Next Chip Design Challenge

The next big challenge in chip design is clear: integrated photonics.

At The ConFab in May, Bill Bottoms, chair of the integrated photonics technical working group, and co-chair of the heterogeneous integration roadmap (HIR) spoke about the changing nature of the industry and specifically the needs of photonic integration.

Bottoms said the driving force behind photonics integration is pretty straightforward: “The technology we have today can’t keep up with the expanding generation of transport and storage of data,” he said. But doing so will be a challenge. “

The integration of photonics, electronics and plasmonics at a system level is necessary. “These require heterogeneous integration by architecture, by device type, by materials and by manufacturing processes,” Bottoms said. “We’re changing the way we’re doing things.”

These kinds of changes are best thought of as system level integration. “As we move the photons as close as to the transistors as possible, we’re going to be faced with integrating everything on a simple substrate,” he said. That’s obviously a huge design challenge.

There are a large number of devices that involve photons which share the common requirement of providing a photon path either into or out of the package or both. They include: Light emitting diodes (LEDs), laser diodes, plasmonic photon emitters, photonic Integrated circuits (PICs), MEMS optical switching devices, camera modules, optical modulators, active optical cables, E to O and O to E converters, optical sensors (photo diodes and other types), and WDM multiplexers and de‐multiplexers. Many of these devices have unique thermal, electrical and mechanical characteristics that will require specialized materials and system integration (packaging) processes and equipment, Bottoms noted.

Of the biggest challenges might be thermal management: “We have things that make a lot of heat and things that can’t have their temperature change by more than a degree without losing their functionality,” Bottoms said.

The scope of the HIR Photonics Chapter includes defining difficult challenges and, where possible, potential solutions associated with: data systems and the global network, photonic components, integrating these components and subsystems into systems with the smallest size, lowest weight, smallest volume, lowest power and highest performance.

A good example of where things are headed is the chip under development at MIT spinout Ayar Labs, which recently penned a deal with GlobalFoundries to bring an optical IO system called Brilliant to market this year. The claim the chips can reduce energy usage by about 95 percent in chip-to-chip communications and increase bandwidth tenfold over their copper-based counterparts. In massive data centers — Ayar’s first target application — run by tech giants such as Facebook and Amazon, the chips could cut total energy usage by 30 to 50 percent, says CEO Alex Wright-Gladstein. “Right now there’s a bandwidth bottleneck in big data centers,” she said.

Ayar’s team integrated optical components onto silicon chips, which are fabricated using the traditional CMOS semiconductor manufacturing process. To avoid making changes to the CMOS process, the researchers focused on a new class of miniaturized optical components, including photodetectors, light modulators, waveguides, and optical filters that encode data on different wavelengths of light, and then transmit and decode it.

This year, Ayar’s first prototypes should reach U.S. data centers, with a planned 2019 commercial release. “We’re starting out solving this bottleneck problem in traditional silicon chips, but ultimately we’re excited about all the different places this technology will go,” Wright-Gladstein says. “This is going to change the availability of optics, and how the world can use optics, in ways beyond what we can predict right now.”

This issue’s cover photo is a silicon photonics chip produced at imec in Belgium, where optical devices are processed at wafer scale on 200mm and 300mm CMOS pilot lines. They include high performance devices for light modulation, switching, coupling, filtering and detection at data rates of 50GB/s and beyond. See page ?? for an interview with imec’s executive vice president Ludo Deferm.

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