1.2 Tbps/cm2 Enabling Silicon Photonics IC Technology Based on 40-nm Generation Platform

Abstract

Optical transmitter and receiver ICs, each with a footprint of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\text{25 mm}}^{2}$</tex-math></inline-formula> , were fabricated using a silicon photonics platform based on 40-nm-node CMOS technology. High-speed transmissions of data at 300 Gbps were demonstrated. The wire-type waveguide (WG) in the transmitter IC had a width of 350 nm and a height of 200 nm, and in the completed optical IC, it showed low propagation loss (1.62 dB/cm) for the O-band transverse electric mode and low propagation loss variation (0.15 dB/cm) at 3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">σ</i> . The coupling loss of the grating couplers was reduced to 2.7 dB by using an apodization structure with a narrow trench width of 70 nm. The wafer-scale reproducibility of the WG width was excellent, as confirmed by a spectral variation analysis using a large number of the microring resonators. The surface-illumination photodetectors (PDs) of the optical receiver were made using a germanium epitaxial film and had a leakage current of less than 10 nA at 3 V and a responsivity of 0.75 A/W. The modulation efficiency of the PN-junction-type Mach–Zehnder modulators of the optical transmitter was 1.3 V⋅cm at 0 V. The uniformity of the PDs and modulators on a 300-mm wafer was very high. By using the fabricated optical transmitter and receiver ICs, data transmissions at up to 12 × 25 Gbps in the O band (1.3 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m) were demonstrated. Furthermore, low-loss filtering operation in 1:4 channel delayed interferometer-based demultiplexing was shown to enable even faster data transmissions. These results indicate that our silicon photonics platform is very useful for fabricating wideband optical ICs.