Median-Time-To-Failure (MTF) of Microwave Power Transistors Under RF Conditions

For the first known time, comprehensive RF life-tests are being run on a microwave power transistor. Previous reliability predictions have been based on DC life-tests. Preliminary data indicates a median life of the order of 106 hours (> 100 years) for a state-of-the-art 30 watt L-Band device operating under normal RF operation. This exceeds the desired device reliability levels in solid-state phased array radars using this device. Tests are being run under two typical pulsed RF conditions: 120 us and 1500 us pulse width at 1.4 GHz. Data has also been generated showing MTF (mean-time-to-failure) under pulsed RF conditions is 2-6 times greater than under CW (continuous wave) conditions. Furthermore, MTF at a given pulse width is shown to be inversely related to the pulse factor. Preliminary failure analysis indicates that the predominate failure mode under extreme stress conditions is the degradation of the emitter-base junction due probably to the dissolution of the SiO2 dielectric layer by the aluminum metallization.