Experimental and modelling investigation of the influence of noise transit time and self-heating on microwave noise of Si/SiGe:C and InP/InGaAs HBTs

Abstract

The results of a comprehensive experimental and modelling investigation of high-frequency noise (HFN) of Si/SiGe:C and InP/InGaAs heterojunction bipolar transistors (HBTs) demonstrate that the key parameters to correctly model HFN for both HBTs are the self-heating (SH) effect at high collector injection levels, i.e. JC > 2–3 mA µm−2, and the noise transport time (τ) which must be included at all bias levels. In contrast, thermal noise contribution of the base–emitter junction of the Si/SiGe:C HBT, associated with the diffusive nature of electron transport at this junction because of the lack of conduction band discontinuity, is only important at operation frequencies lying in the frequency range f > fT/2. The noise analysis indicates that in order to correctly model HFN performances at any injection level and operation frequency, τ must be constant with bias and equal to the addition of base and collector transit times (τB + τC). On the other hand, at high JC levels if SH is neglected, then the amplitude of the equivalent noise resistance (Rn) will be the most impacted noise parameter for both HBTs. Concerning the InP/InGaAs HBT, if SH is off at JC = 5.5 mA µm−2, the minimum noise figure (NFmin) of the InP HBT will be underestimated by 10%.