Imec eyes silicon photonics to solve chip I/O bottleneck

In the second and final article, the issue of adding optical input-output (I/O) to ICs is discussed with a focus on the work of the Imec nanoelectronics R&D centre that is using silicon photonics for optical I/O.

Part 2: Optical I/O

Imec has demonstrated a compact low-power silicon-photonics transceiver operating at 40 gigabits per second (Gbps). The silicon photonics transceiver design also uses 14nm FinFET CMOS technology to implement the accompanying driver and receiver electronics. 

Joris Van Campenhout“We wanted to develop an optical I/O technology that can interface to advanced CMOS technology,” says Joris Van Campenhout, director of the optical I/O R&D programme at Imec. “We want to directly stick our photonics device to that mainstream CMOS technology being used for advanced computing applications.”

Traditionally, the Belgium nanoelectronics R&D centre has focussed on scaling logic and memory but in 2010 it started an optical I/O research programme. “It was driven by the fact that we saw that electrical I/O doesn’t scale that well,” says Van Campenhout. Electrical interfaces have power, space and reach issues that get worse with each hike in transmission speed.

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The ecosystem for silicon photonics starts to take shape

Silicon photonics luminaries series

Interview 6: imec - Philippe Absil and Joris Van Campenhout

Imec has a unique vantage point when it comes to the status and direction of silicon photonics.  

The Belgium nano-electronics research centre gets to see prototype designs nearing commercialisation due to its silicon photonics integration platform and foundry service. “We allow companies to build prototypes using a robust silicon photonics technology,” says Philippe Absil, department director for 3D and optical technologies at imec.

Philippe Absil

Imec also works intimately with several partners on longer-term research, one being Huawei. This optical I/O R&D activity is part of imec’s CORE CMOS scaling R&D programme which as well as Huawei includes GlobalFoundries, Intel, Micron, Qualcomm, Samsung, SK Hynix, Sony and TSMC. The research is sufficiently far ahead to be deemed pre-competitive such that all the firms collaborate. 

For silicon photonics, the optical I/O research includes optical integration schemes, new device concepts and new materials. “The aim is to bring silicon photonics technology to the next level in order to resolve today’s challenges,” says Absil.  

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Graphene prototype modulator shown working at 10 Gigabit

• Imec's graphene electro-absorption modulator works at 10 Gigabit-per-second
• The modulator is small and has be shown to be thermally stable
• Much work is required to develop the modulator commercially

Cross-section of the graphene electro-absorption modulator. The imec work was first detailed in a paper at the IEDM conference held in December 2014 in San Francisco. Source: imec

Imec has demonstrated an optical modulator using graphene operating at up to 10 Gigabit. The Belgium nano-electronics centre is exploring graphene - carbon atoms linked in a 2D sheet - as part of its silicon photonics research programme investigating next-generation optical interconnect. Chinese vendor Huawei joined imec's programme late last year.

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