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CMOS-Photonic Integration Thermally Sensitive

As published in the journal Nature, CMOS transistors have been integrated with optical-resonator circuits using complex on-chip sensors and heaters to maintain temperature to within 1°C. While lacking the laser-source, these otherwise-fully-integrated solutions demonstrate both the capability as well as the limitation of trying to integrate electronics and photonics on a single-chip. The Figure shows a simplified schematic cross-section of the device.

Full chip cross-section (not to scale) from the silicon substrate to the C4 solder balls, showing the structures of electrical transistors, waveguides, and contacted optical devices. The minimum separation between transistors and waveguides is <1 μm, set only by the distance at which evanescent light from the waveguide begins to interact with the structures of the transistor. Full chip cross-section (not to scale) from the silicon substrate to the C4 solder balls, showing the structures of electrical transistors, waveguides, and contacted optical devices. (Source: Nature)

Lead author Chen Sun—affiliated with UC Berkeley and MIT, as well as with commercial enterprise Ayar Labs, Inc.—developed the thermal tuning circuitry, designed the memory bank, implemented the ‘glue-logic’ between various electronic components, and performed top-level assembly of electronics and photonics. The main limitation is the temperature control, since deviation by more than 1°C results in loss of coupling that otherwise provides for P2M/M2P transceivers:

* Waveguide Loss – 4.3 dB/cm,
* Tx and Rx Data Rate – 2.5 Gb/s,
* Tx Power – 0.02 pJ/bit,
* Rx Power – 0.50 pJ/bit, and
* Ring Tuning Control Power – 0.19 pJ/bit, so
* Total power consumption = 0.71 pJ/bit.

The Register reports that this prototype has a bandwidth density of 300 Gb/s per square millimetre, and needs 1.3W to shift a Tb/s straight from the die to off-chip memory. A single chip integrates >70 million transistors and 850 photonic components to provide microprocessor logic, memory, and interconnect functions.

—E.K.

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