# Review of CMOS Integrated Circuit Technologies for High-Speed Photo-Detection
## 2 Silicon Photonics for High-Speed Data Communications
### Hybrid Integration
Not only the high-speed signal pads but also the low-speed signal pads are connected to the PIC. Subsequently, the low-speed signals are carried outside the PIC through a typical wire-bonding package. Based on this technique, the work in [43] demonstrates a 4 \(\times\) 20-Gb/s WDM transceiver and [40] implements a 56-Gb/s optical transmitter with the MZI structure. In Table 1, we summarize and compare the optical transceivers presented so far. Notably, the overall performance of the hybrid-integrated transceivers is better than that of the monolithic transceivers, especially in terms of energy efficiency. This can be attributed to the independently optimized processes of the EIC and the PIC. However, it should also be noted that recent monolithic transceivers have demonstrated significant improvement, and are comparable to their hybrid counterparts. Figure 16: Flip-chip bonded EIC directly on PIC using micro bump [56]. Figure 17: EIC flip-chip bonded to macro-PIC [43]. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & [44] & [48] & [47] & [80] & [82] & [58] & [56] & [63] \\ \hline
**Integration method** & Monolithic & Monolithic & Monolithic & Monolithic & Hybrid & Hybrid & Hybrid \\ \hline
**Technology (ECO)** & 130 nm SOI & 130 nm SOI & 130 nm SOI & 180 nm Bulk & 90 nm bulk & 65 nm bulk & 28 nm bulk & 40 mm bulk \\ \hline
**Technology (PIC)** & & & & GaAs & GaAs & 28 nm SOI & 130 nm SOI \\ \hline
**Wavelength** & 1353-155 nm & 1549-154 nm & 1560 nm & 1280-1295 nm & 850 nm & 850 nm & 156 nm & 1500 nm \\ \hline
**\# of WDM channels** & N/A & 4 & N/A & 9 & N/A & N/A & N/A & 4 \\ \hline
**Max. data rate/CH** & 10 Gb/s & 10 Gb/s & 25 Gb/s & 5 Gb/s & 25 Gb/s & 10 Gb/s & 25 Gb/s & 20 Gb/s/ \\ \hline
**Total throughput** & 20 Gb/s & 40 Gb/s & 25 Gb/s & 45 Gb/s & 25 Gb/s & 600 Gb/s & 25 Gb/s & 80 Gb/s/ \\ \hline  & & & & TX & & & \\ \hline
**Modulation type** & MZI & MZI & MRR & VCSEL & VCSEL & MRR & MRR \\ \hline ER & 5-6 dB & \(>\)4 dB & 6.9 dB & 6.9 dB & 5.1 dB & 5.6 dB & 6.5 dB & \(>\)7 dB \\ \hline
**Power/CH** & N/A & 575 mV & 208 mV & N/A & 46 mV & 69.5 mV & 72.5 mV & 23.2 mV \\ \hline
**Energy efficiency/CH** & N/A & 57.5 pF/b & 8.32 pF/b & N/A & 1.84 pF/b & 69.5 pF/b & 29.4 dB & 16.5 pF/b \\ \hline  & & & & & & & \\ \hline
**PD type** & N/A (external) & N/A (external) & Ge waveguide & S (deflect) waveguide & GaAs (top illumination) & N/A & N/A & Ge waveguide \\ \hline
**Sensitivity (BER of 10\({}^{-12}\))** & \(-\)19.5 dBm & \(-\)15 dBm & \(-\)4 dBm & \(-\)75 dBm & \(-\)6 dBm & \(\approx\) 220 Gb/s & \(-\)16 dBm (estimated) & \(-\)8 dBm & \(-\)72 dBm \\ \hline
**Power/CH** & N/A & 120 mV & 48 mV & N/A & 44.4 mV & 68.2 mV & 50 mV & 11.6 mV \\ \hline
**Energy efficiency/CH** & N/A & 12 pF/b & 1.92 pF/b & N/A & 1.78 pF/b & 6.82 pF/b & 2 pF/b & 0.73 pF/b \\ \hline
**Total power** & 25 W & 3.5 W & 256 mV & 675 mV & 90.4 mV & 8.26 W & 122.5 mV & 175.6 mV \\ \hline
**Total energy efficiency** & 125 pF/b & 87.5 pF/b & 10.2 pF/b & 15 pF/b & 3.62 pF/b & 13.77 pF/b & 4.9 pF/b & 2.2 pF/b \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of monolithic and hybrid-integrated optical transceivers.