Using Pulsed-Mode Measurements of SiGe HBTs for Non-Destructive, Improved RF-SOA Estimation

We present a new approach for exploring the underlying reliability physics of SiGe HBTs, and define a new, application-relevant safe-operating area (SOA) of devices by implementing pulsed-voltage measurements. Compared to DC measurements, pulsed-mode measurements have the advantage of being non-destructive, and can be used to decouple self-heating and impact ionization to predict hard failure under large RF swings. In the present work, one of the conventional DC SOA criteria is explored as a function of pulse-width in state-of-the-art SiGe HBTs. The collector-current density ($J_{C}$) doubles at a later voltage under pulsed conditions vs. DC, resulting in an additional SOA margin of 0.8 V at peak-$f_{T}$ quiescent current. Load-pull measurements show that the devices experience hard failure at about the same bias as the new pulsed-mode SOA definition for the shortest measured pulse-width (160 ns). Load lines overlaid with the pulsed-SOA definition demonstrate that the device experiences hard failure when the RF current swing and voltage are outside the pulsed-mode SOA boundary. These results demonstrate pulsed-mode measurements as a new and useful tool wherein pulsed width can be adjusted to improve the correlation between measurements of the SOA and hard failure under application-relevant RF operating conditions. Furthermore, pulsed-mode SOA can be measured using forced voltage between the base and the emitter, often preferred for power amplifiers, which allows designers to explore more aggressive operational bias conditions that provide circuit peRFormance advantages while remaining robust to damage.