Impact of isolation scheme on thermal resistance and collector-substrate capacitance of SiGe HBTs

Various isolation schemes consisting of junction isolation, silicon pedestal isolation, deep trench isolation (DTI), airgap deep trench isolation and SOI with DTI are compared in terms of thermal resistance (R
_TH
) and collector-substrate capacitance (C
_CS
). Although to some extent R
_TH
and C
_CS
can be traded, airgap DTI and especially pedestal isolation perform very well, because the former results in strong reduction of C
_CS
, while the latter results in strong reduction of R
_TH
.