Impact of scaling on the DC/RF thermal behavior of SiGe HBTs for high-frequency applications

The temperature influence on both DC and RF performance of advanced silicon–germanium heterojunction bipolar transistors is analyzed in the temperature range from 300 to 380 K over different technological nodes. Accurate results are obtained by simulating increasingly scaled transistors through a deterministic solver of the Boltzmann Transport Equation based on the spherical harmonics expansion of the distribution function. In particular, the impact of scaling on the key performance metrics is quantified by determining the DC current gain and cut-off frequency, as well as estimating the junction temperature rise at the current corresponding to the maximum cut-off frequency. It is shown that in scaled devices the electrical behavior is less temperature sensitive, which is desirable for high-speed and high-density integrated circuit applications. Furthermore, it is found that the power reduction due to lateral scaling might weaken self-heating effects, which should be in principle exacerbated by the higher current densities and thermal resistances.