An experimental investigation of RF safe-operating-area (SOA) in SiGe HBTs on SOI

The RF safe-operating-area of a variety of both bulk and thick-film SOI SiGe HBTs SiGe has been investigated using DC and pulsed-mode output characteristics, as well as RF gain and linearity measurements. SOI SiGe HBTs are found to suffer more from self-heating than bulk devices under DC operating conditions, as expected, due to their naturally higher thermal resistance. However, in terms of RF performance, operation of SiGe HBTs on SOI beyond the traditionally-defined safe-operating-area showed only minor degradation in RF metrics, and improved RF linearity. High-injection phenomena are suggested as possible explanations for the observed suppression of self-heating-induced degradation and thermal runaway in these SiGe HBTs on SOI operating under RF operating conditions.