Design of a 250-Gbit/s SiGe HBT Electrooptic Modulator

We present a rigorous electrical and optical analysis of a highly scaled, graded-base, SiGe heterojunction bipolar transistor (HBT) electrooptic (EO) modulator. In this study, we propose a 2-D electrical model and a 3-D optical model for a graded-base SiGe HBT structure that is capable of operating at a data bit rate of 250 Gbit/s or higher. In this structure, apart from a polysilicon/low doped emitter ( width = 90 nm) and a strained SiGe graded base ( depth = 8.5 nm), a selectively implanted collector (SIC) (depth = 26 nm) is introduced. Furthermore, at a base-emitter swing of 0 to 1.0 V, this model predicts a rise time of 3.48 ps and a fall time of 0.55 ps. Optical simulations predict a π phase shift length (L_π) of 204 μm, with an extinction ratio of 13.2 dB at a wavelength of 1.55 μm.