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

Reliability testing for high-speed, compound semiconductor, heterojunction bipolar transistors (HBTs) has focused on determining device lifetimes base d on changes in the DC characteristics. The work reported here considers ag ing effects on the RF characteristics of InP-based HBTs. In addition, an in tended system life of 15 years has been assumed and we have attempted to st ress the devices to approximate 15 years of circuit operation. As such, SPI CE models were generated for the devices before and after the stress. The b asic differences between these models are that the aged model shows increas es 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 incr easing R-e from 3.6 to 5.7 Omega and C-jc from 20.1 to 23.4 fF. These chang es lead to decreases in: transistor gain, F-t, and F-max, and an increase i n the base-emitter voltage at typical operating conditions. No increase in low current base-emitter voltage occurs, indicating the lack of Be diffusio n into the emitter. The changes in the device parameters generally fall wit hin the normal process variations. (C) 2001 Elsevier Science Ltd. All right s reserved.