Silicon photonics
Why is a configuration used in which the chip with optical devices (PIC) and the chip with electronic circuits such as drivers and TIAs (EIC) are fabricated separately and then stacked and connected?
- AOptical devices and high-speed transistors fundamentally cannot be built together on the same wafer at all
- BEach can use its best-suited fabrication process, and short connections reduce parasitic capacitance for higher speed and lower power
- CThe farther apart the PIC and EIC are placed, the smaller the interconnect capacitance and the faster the signal travels
Show answer and explanation
Answer: B. Each can use its best-suited fabrication process, and short connections reduce parasitic capacitance for higher speed and lower power
Optical devices need only dimensions of a few hundred nm and can be made in relatively old process generations, whereas drivers and TIAs operating at several tens of GHz are better made in advanced CMOS or SiGe processes with fast transistors. Putting them on separate chips allows the optimal process to be chosen for each. Stacking them vertically with microbumps or hybrid bonding then makes the connections very short, reducing parasitic capacitance and inductance and contributing to higher speed and lower power consumption. Products using monolithic integration, which builds photonic and electronic circuits on the same chip, are also in commercial use.