RF modeling approach to determining end-of-life reliability for InP-based HBTs

Abstract

Reliability testing for high-speed, compound semiconductor, heterojunction bipolar transistors (HBTs) has focused on determining device lifetimes based on changes in the DC characteristics. The work reported here considers aging effects on the RF characteristics of InP-based HBTs. In addition, an intended system life of 15 years has been assumed and we have attempted to stress the devices to approximate 15 years of circuit operation. As such, SPICE models were generated for the devices before and after the stress. The basic differences between these models are that the aged model shows increases in the emitter resistance ( R e) and in the base–collector capacitance ( C jc). The-end-of life model can be obtained from the standard model by increasing R e from 3.6 to 5.7 Ω and C jc from 20.1 to 23.4 fF. These changes lead to decreases in: transistor gain, F t, and F max, and an increase in the base–emitter voltage at typical operating conditions. No increase in low current base–emitter voltage occurs, indicating the lack of Be diffusion into the emitter. The changes in the device parameters generally fall within the normal process variations.