Design of a 250-Gbit/s SiGe HBT

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 ðwidth ¼ 90 nmÞ and a strained SiGe graded base ðdepth ¼ 8: 5n m Þ, a selectively implanted collector (SIC) ðdepth ¼ 26 nmÞ 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 aphase shift length ðL� Þ of 204 � m, with an extinction ratio of 13.2 dB at a wavelength of 1.55 � m.