Influence of thermal phenomena on the RF behaviour of power heterojunction bipolar transistors and optimization

The thermal resistance of power devices is determined by means of a 3D heat dissipation modeling. In particular, we have evaluated the thermal resistance of Heterojunction Bipolar Transistors (HBTs) in which GaAs substrate is replaced by a substrate exhibiting a higher thermal conductivity like Diamond, Aluminium Nitride or Silicon. Thus, through use of the electrothermal model we can predict an increase of about 50 percent of the RF power at 10 GHz and at the compression point when the power device is transferred onto a diamond substrate. The different techniques we are performing to transfer the HBT active layers onto host substrates are described.