Noise modeling and SiGe profile design tradeoffs for RF applications [HBTs]

This paper investigates SiGe profile design tradeoffs for low-noise RF applications at a given technology generation (i.e., fixed minimum feature size and thermal cycle). An intuitive model relating structural parameters and biases to noise parameters is used to identify the noise limiting factors in a given technology. The noise performance can be improved by pushing more Ge into the base and creating a larger Ge gradient in the base. To maintain the SiGe film stability, the retrograding of the Ge into the collector has to be reduced, leading to a stronger f_T-I_C roll-off at high injection. Two low-noise profiles were designed and fabricated explicitly for improving minimum noise figure (NF_min) without sacrificing gain, linearity, frequency response, or the stability of the SiGe strained layer. A 0.2 dB NF_min was achieved at 2.0 GHz with an associated gain (G_assoc) of 13 dB