Development, iplementation and verification of a physics-based Si/SiGe HBT model for millimetre-wave non-linear circuit simulations

Abstract

AbsttA physics-based large4ign model incling thermal dpendence ha ben developed fbr Si/SiGe HBT. The model takes ito acount several tefts tha ar importat for the operation of S/iGe HBTs and is directly relat to the parameter iin the fabricntio proces. Using extration procedurs fbr onyi a few parameters that iherently are difficlllt to predict, either due to uncertainties in the frication process or due to cmplex physical relations, a good agreement is found between the, model and measurmnts. The mIel has been imlemented uing a comMercia CA4Dystem fkaciitating desig of nonflinear Si/SiGe HBT *aplicons. Thus the model has been used to design and piedidt the behiour of a doubler circuit operating at 55 GHz with pg accuracy. IntoductionThe ree piopess in SiGe technology which has yeded HBT with ft of 160 GHz [I], ma it possi'bl to desi circuits for the important frequency range used in automodtive applictions For analysis and implemn~ftatioiin ofSi/SiGe HBTs in non-linear m cwave waplic ns, the access to ant ccuratephysics-bsd e4 signil model With mete diretly elaed to the fbicaion p s and describing the physical poperiews of SiGe is of grat importanCe The thermal properties of the Si/iGe HBT which plays an imnportat part in power apications has aso to be taken into account in a moSde. Such mhodl ha been developed and it is now used fbr the design and optmiat6ion of Si/SGe HBT millimetterwave frequency dublers opeting 55 Hz A modifid Ebers-Moll model, having transit time delay added to the current generator, can be shown tb sufficiently model HBT transistors a microwave frequencs [] Th model has the benefit of taking into account the physical properties of the transistr and of having only a moderate amount of cmponnts. Alo of imp£ortane is that varaion of the technologcal paraeters cartn be accuiteid foThe implementation of the model has been done in a SPICE4lke simulatrusi MDS frbm Hewlett Packard. A speial featu ca11e SDD (Symbolically Defined evice has been used for modelling the itinsicpa ofthe trasWis (the shaded part in Fig. la shows a schematic of the modelling). Embedding the inftrini prt is a shell comos oflumped circuit 61ements which accounts fbr the extirinsi transist (elements outside shide part in Fi. la) and also fbr pad parasitics.By utilizing the ability to control the curretnt iside the SDD via equations, it is possible to mathematically create a discrete analogy to the proceses occuming. Thanks to this, the ideal electron and hble injeion currents in each uncion ar treated seprily which makes the modein of the heterounctions straightfooard. Futihermore, the common base amplification factor can be decmposed. The fators ai nd q no longer need to account for the emitter injection eftfiency but only for base transport factor and a possible bulk breakdow in the spac charge regions.The current generators l and I hE have been added to empdiriclly model high injetion effecs and the surface currents occurring on a mesa device structur. The capaci s CuE and Csc have been calculated usinI the SPICE mnodl forj...

Extraction of thermal time constant in HBTs usingsmallsignal measurements

“…To achieve higher accuracy, an electrothermal model of the device can be used. Such a model has been developed and shown to accurately model SiGe HBTs from DC upto millimetre-wave frequencies [4]. It uses a modified Ebers-Moll model where the different physical processes occuring in the device are as closesly as possible modelled with lumped elements.…”

“…To model junction heating from internal power dissipation, an RC-network has been used in the model [4] where current and voltage drop has been related to internal power dissipation and device heating respectively. A thermal resistance (R T ) relates to the steady-state part and a thermal capacitance (C T ) relates to the transient part of the device heating.…”