Study of the SOI layer’s impact on the electrical properties of the Heterojunction Bipolar Transistor BiCMOS55nm

The main purpose of this paper is to investigate the impact of the SOI (Silicon On Insulator) layer on the electric characteristics of a SiGe Heterojunction Bipolar Transistor (HBT), manufactured by STmicroelctronics under the industrial BiCMOS55nm technology with a DPSA-SEG (Double Poly-silicon, Self-Aligned, Selective Epitaxial Growth) architecture using COMSOL multiphysics software. We noticed that the electrical performances were improved for an HBT with a SOI substrate compared to one with a solid silicon substrate. In a second step, we have optimized the impact of the layer thickness (SOI) more precisely the thickness of the Buried OXide (BOX) in order to increase the performance of the transistor and reach a frequency in the order of Tetra hertz range $(0.5 \mathrm{THz})$. Results showed that when the layer thickness increases from 200 to $\mathbf{4 0 0} \mathbf{n m}$ both transition and the maximum oscillation frequencies increase from 340 GHz to 385 GHz and from 460 GHz to 480 GHz respectively.