Electro-thermal modeling of trench-isolated SiGe HBTs using TCAD

Physical, small-signal and pulsed thermal impedance characterization of multi-finger SiGe HBTs close to the SOA edges

“…Indeed, the heat diffusion process in those technologies is confined by these isolations. Since IHP technology does not feature DTI, it leads to a reduced thermal budget [11] and a more efficient heat diffusion through the device which depends mainly on the value of the heat diffusion angle as presented fig.3 (a) and (b).…”

5. Reliability

“…Thermal issues have become a serious concern in SiGe HBTs due to the concurrent impact of the following factors: (i) the shrinking of the intrinsic device has induced a growth in power density within the base-collector SCR for a given bias condition; (ii) the trench isolation -exploited to reduce parasitics, crosstalk, and increase f MAX -limits the heat spreading since trenches are filled with materials suffering from low thermal conductivity [Rie05,dAl10,You11,Pet15]. This mechanism is even exacerbated by lateral scaling, which results in a horizontal reduction of the Si volume embraced by trenches; (iii) HBTs are operated at high current densities to boost the frequency performance, which entails a further increase in dissipated power density [Cre13].…”

“…(5.20) where k Si and k Ge are the thermal conductivities of pure Si and Ge, respectively, and c k is a bowing factor equal to 2.8 W/mK. Due to the k lowering imposed by Equation (5.20), the SiGe layer behaves as a barrier for the heat flow from the heat source to the emitter [Pet15]. The thermal conductivity is also adversely impacted by doping due to the enhanced phonon-impurity scattering, as experimentally observed in [Sla64,McC05,Lee12]; a compact formulation to account for this effect is [Lee12]:…”

Advanced thermal simulation of SiGe:C HBTs including back-end-of-line

“…Unfortunately, thermal issues have become a serious concern in SiGe HBTs due to the concurrent impact of the following factors: (i) the intrinsic device shrinking has induced a growth in power density within the base-collector depletion region; (ii) the trench isolationexploited to reduce parasitics and increase f maxgives rise to a limited heat spreading since trenches are filled with low conductivity materials [6][7][8][9]. This mechanism is even exacerbated by the lateral scaling, which results in a horizontal reduction of the Si volume embraced by trenches; (iii) HBTs are operated at high current densities to boost the frequency performance, which entails a further increase in dissipated power density [2].…”