Skip to main content


Modeling and Analysis of an 80-Gbit/s SiGe Heterojunction Bipolar Transistor Electrooptic Modulator


Fast modulation of optical signals with low-cost devices is of great interest to many fields, ranging from on-chip or intra-chip interconnections to Si photonics for telecommunication. The NSF funded IGERT Trainees Mitchell R. LeRoy and Ryan Clarke under the supervision of John McDonald IGERT faculty and Professor of Electrical Engineering at Rensselaer Polytechnic Institute, Troy, NY presented a rigorous electrical and optical analysis of a strained and graded base SiGe Heterojunction Bipolar Transistor (HBT) electrooptic (EO) modulator.

In their work they proposed a 2-D model for a graded base SiGe HBT structure that is capable of operating at a data bit rate of 80 Gbit/s or higher. In this structure, apart from a polysilicon/monosilicon emitter (Width = 0.12 um) and a strained SiGe graded base (Depth = 40 nm), a selectively implanted collector (SIC) (Depth = 0.6 um) is introduced. See Figure (left panel). Furthermore, the terminal characteristics of this new device modeled using MEDICI are closely compared with the SiGe HBT in the IBM production line, suggesting the possibility of fast deployment of the EO modulator using established commercial processing. At a subcollector depth of 0.4 um and at a base-emitter swing of 0 to 1.1 V, this model predicts a rise time of 5.1 ps and a fall time of 3.6 ps. Optical simulations predict a pi phase shift length L of 240.8 um with an extinction ratio of 7.5 dB at a wavelength of 1.55 um. See Figure (right panel) for a mode profile for the HBT with subcollector thicknesses of 0.4 um and under the bias of 1.1 V. Additionally, the tradeoff between the switching speed, pi phase shift length L and propagation loss with a thinner subcollector is analyzed and reported in their paper published in IEEE Photonic Journal, Volume 3, Number 1, February 2011.

Address Goals

The design and analysis of 80-Gbit/s SiGe Heterojunction Bipolar Transistor advance the frontiers of terahertz electronics knowledge. It also has potential applications in on-chip or intra-chip interconnections and Si photonics for telecommunication. It keeps the US in a leading position of terahertz electronics and engineering.

In the process of designing and testing of the 80-Gbit/s SiGe Heterojunction Bipolar Transistor, the IGERT trainees and collaborators learned to work together and developed science and engineering skills as well as disseminated findings to society through outreach activities and professional conferences.