Doctoral Thesis: Silicon-Photonics for VLSI Systems


Event Speaker: 

Chen Sun

Event Location: 

Allen Room, 36-462

Event Date/Time: 

Monday, May 4, 2015 - 9:00am

As raw compute power of a single chip continues to scale into the multi-teraflop regime, the processor I/O communication fabric must scale proportionally in order to prevent a performance bottleneck. Electrical wires are projected to fall short of future I/O demands due to high channel losses, pin-count constraints, and crosstalk. Silicon-photonic optical links overcome the fundamental tradeoffs of electrical wires and have the potential to be integrated at chip-scale with a very large scale integrated (VLSI) CMOS electrical chip. Thus far, however, both electronic-photonic process compatibility and the difficulty of working with thermally sensitive optical devices have limited the achievable system complexity.
In this thesis, we adopt a “minimal-change” approach to silicon-photonic integration; as opposed to building a customized process for photonic devices, we instead engineer the optical devices to be compatible with a native CMOS electrical process. Using this approach, we demonstrate an integrated optical transceiver platform in a commercial 45nm CMOS SOI chip, the first such platform in a sub-100nm production CMOS line. This approach can be generalized to bulk CMOS processes, from which we enable the first demonstration of an optical link using an electronic-photonic chip fabricated in a bulk CMOS process. In both cases, the use of thermally sensitive resonant optical devices is critical for both energy-efficiency and compactness of the optical components. In order for these devices to work in a hostile thermal environment – within a VLSI chip – we show an auto-locking tuning method which keeps the resonant devices stable and is agnostic of the transmitted data sequence, making it suitable for latency-critical non-encoded communication links. Finally, we utilize these pieces to demonstrate a processor chip which uses on-chip photonic interconnects to optically communicate to distant off-chip main memory. To the best of our knowledge, this is the world’s first demonstration of an electronic-photonic processor chip.

Thesis Supervisor:

Vladimir Stojanovic

Committee Members:

Michael Watts

Srini Devadas