Terminal current noise calculations are performed for a SiGe heterojunction bipolar transistor in a wide range of
collector-emitter bias conditions. The generalized hydrodynamic (HD) model with a local temperature approach
for avalanche generation is used. The parameters of the local temperature model are calibrated by matching the
avalanche multiplication factor to results obtained by full-band Monte Carlo simulations. The noise figure calculation
results are compared with experimental values and overall good agreement is obtained. The hydrodynamic
and a drift-diffusion (DD) model are used to investigate terminal current noise due to impact-ionization. The
behavior of the current noise spectral intensity is found to be different for the two models. The Fano factor of
the collector current fluctuations is well described by the avalanche multiplication factor in the case of the DD
model, whereas the HD model evidences no correlation between the Fano factor and the avalanche multiplication
factor. The collector terminal electron transfer functions are used to discuss the difference.
Bias dependent microwave noise characteristics of high-speed 150 GHz SiGe HBTs as well as AlGaAs and InGaP HBTs were measured in the 2-26 GHz frequency range. The characteristics are compared with the compact bipolar transistor models HICUM and VBIC. For noise source analysis and decomposition, a detailed small-signal model with corresponding parameters is employed which is based on a compact model. In particular, the influence of the various noise sources and mechanisms on the minimum noise figure is investigated. As predicted by Van der Ziel, correlation between base and collector current shot noise in SiGe and AIIIBV HBTs is found to reduce NFmin for the frequency range of investigation. AIIIBV HBTs exhibit strong reduction of collector shot noise due to the conduction band peculiarity, what is not the case for SiGe based HBTs.
Noise parameters of AlGaAs/GaAs and InGaP/GaAs HBTs were measured in microwave frequency range and modeled using the small-signal equivalent circuit approach. Correlated current noise sources in the base and collector currents with thermal noise in the circuit resistive elements were accounted for by the model and yielded good agreement with the measured data. This enabled an extraction of the different noise source contributions to minimum noise figure (NFmin) in AlGaAs/GaAs and InGaP/GaAs HBTs. Decomposition of the (NFmin) in to the different contributors showed that the main noise sources in investigated HBTs are correlated base and collector current shot noise. The observed minimum of NFmin versus frequency at lower collector current is explained by the reduction of the emitter/base junction shot noise component due to the spike in the emitter/base junction and associated accumulation of the quasi-thermalized electrons forming a space charge, which screens the electron transfer through the barrier. The bias (VCE) increase creates an efficient electric field in collector/base junction, capable of 'washing out' the accumulated charge. Such shot noise reduction in HBTs could be exploited in the LNA for the RF application.
Conference Committee Involvement (2)
Noise and Information in Nanoelectronics, Sensors, and Standards II
26 May 2004 | Maspalomas, Gran Canaria Island, Spain
Noise and Information in Nanoelectronics, Sensors, and Standards