Reliability issues associated with operating voltage constraints in advanced SiGe HBTs

The paper addresses many aspects of the relationship between operating voltage constraints and reliability issues in SiGe HBTs, examining breakdown-related instabilities as they relate to technology generation, device geometry, bias configuration, and operating current density. New definitions for breakdown voltage, adopted from standard measurements, are presented. Practical design and reliability implications of breakdown are explored through careful measurement and simulation using quasi-3D compact models. Overall, SiGe HBTs; biased in common-base configuration and driven by constant emitter current, are shown to possess higher stable operating voltage limits than those biased in a common-emitter configuration and driven by constant base current. However, biasing beyond the determined "safe-operating-area" can result in impedance matching and linearity issues at lower currents and significant increases in hot-carrier degradation at higher currents, and must be carefully considered from a circuit design perspective.