Silicon-Germanium Heterojunction Bipolar Transistors for Extremely Low-Noise Applications

Citation

Bardin, Joseph Cheney (2009) Silicon-Germanium Heterojunction Bipolar Transistors for Extremely Low-Noise Applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/MCPE-4M30. https://resolver.caltech.edu/CaltechETD:etd-06092009-113849

Abstract

Historically speaking, the world of extremely low-noise solid-state amplification has been dominated by exotic technologies such as InP and GaAs HEMTs. By cryogenically cooling these devices, it is possible to realize microwave amplifiers with noise temperatures as low as 5K over decades of bandwidth. Although HEMTs can provide very low noise amplification when cooled to cryogenic temperatures, their radiometer performance is limited by intrinsic transconductance fluctuations. It is believed that bipolar devices do not suffer from this problem. As industry has invested more and more money into silicon based technologies, silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) have continued to improve and are now at the point where they are beginning to become competitive with InP HEMTs for microwave cryogenic low-noise amplifiers. Although extremely high frequency device operation has been observed at cryogenic temperatures, little work has been done on modeling the noise of cooled SiGe HBTs.

In this report, a thorough investigation into the theoretical and practical aspects of using silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) for extremely low-noise applications is presented. The dissertation is broken up into three sections:

1) Background information: The fundamentals of SiGe HBTs are presented along with a discussion of how the properties of semiconductors change at cryogenic temperatures, as well the impact that these changes have on the performance of the devices.

2) Modeling: A comprehensive study of seven state-of-the-art HBTs at temperatures ranging from 18 K to 300 K is presented. The devices are compared in terms of dc, small-signal, and noise performance, and small-signal noise models are extracted. The section concludes with a brief summary of the important conclusions regarding the performance of SiGe devices at cryogenic temperatures.

3) Applications: The models developed previously are applied to the design of several state-of-the-art LNAs in both MMIC and discrete form. Noise performance better than 2 K is achieved in the low-GHz range, which is comparable to the best InP results. The section concludes with a discussion of some high-impedance differential amplifiers which have recently been fabricated.

Thesis Files