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. (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.