Comparison of low-frequency noise in III-V and Si/SiGe HBTs

Abstract

The low frequency noise characteristics of double self-aligned InP/InGaAs and two types Si/SiGe heterojunction bipolar transistors (HBTs) were investigated. Spectral analysis shows no striking differences; the spectra are composed of a 1/f component and the white noise is always reached at low bias. A general trend for all the transistors was the presence of Lorentzian(s) component(s) for the smallest devices. The voltage coherence function was always one for SiGe transistors; and for the first time, it was found to be close to zero for InP devices. Concerning the 1/f noise level, both types of transistors have approximately a quadratic dependence on base current bias and an inverse dependence on the emitter area. Thus a comparison of the 1/f noise level has been made using the Kb parameter, and values around 10 9 μm 2 for SiGe HBTs and around 10 8 μm 2 for InP HBTs were found. These results are of same order of magnitude as the best published ones. The low frequency noise results suggest that excess noise sources are mainly located at the intrinsic emitter-base junction for the two type of SiGe devices, and for the for InP HBTs, a correlated noise source is located at the emitter periphery. To compare different devices and technologies, fc/fT where fT is the unity current gain frequency was studied as a function of collector current density and for some HBT technologies, fc/f T α J c . The effects of different processing conditions, designs and temperature were also investigated and will be discussed.