Highly Reliable Submicron InP-Based HBTs with over 300-GHz ft
ABSTRACT We have developed 0.5-μm-emitter InP-based HBTs with high reliability. The HBTs incorporate a passivation ledge structure and tungsten-based emitter metal. A fabricated HBT exhibits high collector current density and a current gain of 58 at a collector current density of 4 mA/μm2. The results of dc measurements indicate that the ledge layer sufficiently suppresses the recombination current at the emitter-base periphery. The HBT also exhibits an f t of 321 GHz and an f max of 301 GHz at a collector current density of 4 mA/μm2. The f t does not degrade even though the emitter size is reduced to as small as 0.5 μm × 2 μm. The results of an accelerated life test show that the degradation of dc current gain is due to thermal degradation of the interfacial quality of semiconductors at the passivation ledge. The activation energy is expected to be around 1.5 eV, and the extrapolated mean time to failure is expected to be over 108 hours at a junction temperature of 125°C. These results indicate that this InP HBT technology is promising for making over-100-Gbit/s ICs with high reliability.