Improved reliability self-aligned C/X-band monolithic power HBT amplifiers fabricated with a low-stress process

We report extensive reliability testing and analysis on single-finger C/X-band HBTs fabricated for monolithic amplifiers with a low-stress process. The HBTs are self-aligned to maximize RF power performance, with ledge passivation and a low stress epitaxial base and dielectric overcoat to improve reliability. Bias stress testing was performed from T-jo = 185-340 degrees C, and J(co) = 25-50 kA/Cm-2. The temperature and current dependence of the various observed failure modes and mechanisms are described. Longterm (> 3000 hour), low temperature (< 250 degrees C), high current stress tests are found to be accurate indicators of how HBTs degrade under nominal operating conditions. Shorter, high temperature tests may lead to excessively optimistic predictions of activation energy and median time to failure.