Characterization Of The Total-Dose-Radiation Effects In Bipolar Transistors

Bipolar circuits are widely used in aerospace, nuclear reactor and other radioactive occasions. I was revealed that the degradation in performance of these bipolar circuits after ionizing radiation is one of the important causes that lead to degradation in reliability or even to failure of these circuits. Therefore, a study of radiation effects on bipolar transistors performance and an effective characterization technique for the evaluation of the anti-radiation capacity of bipolar devices are required urgently. With the advancement in low-frequency noise theory, it was discovered that low-frequency noise pertains a close relation with the microstructures in electronic devics, and therefor can be taken as a sensitive parameter to dignose the quality and reliability of electronic devices. From theoretical studies we know, the relative changes in low-frequency noise parameters are more significant compared with the relative change in the conventional parameters of bipolar transistors, such as current gain, before and after irradiation stress. As a result, 1/f noise was taken as an ideal probing tool to evalute and characterize the quality, reliability and anti-radiation capacity of bipolar transistors in this work.The content of this thesis was organized as follows. First, the failure modes and mechanisms of bipolar transistors under radiation stress were analyzed in datail based on the working principle of bipolar transistors and the characteristics of real radiation application environment. Second, the low-frequency noise testing technique of bipolar transistors was explored and a low-freqnecy noise testing system was built. It was validated by a large amount of measured data that, this system can accurately measure and analyze the low-frequency noise signal and extracte related parameters. Third, based on the above mentioned theoretical knowledge and testing system, both parameters of conventional current gains and low-frequency noise (1/f noise amplitude B, exponent coefficientγand conner frequency) was measured bofore and after several doses of (30krad, 90krad, 210krad, 450krad) radiation experiments. It was found that, the gain of the bipolar transistor decreases with radiation dose, whereas, the low-frequency amplitudes increase. Fourth, the gain of the bipolar transistor and the amplitudes of low-frequency noise were chosen as indicators and compared before and after radiation experiments. A new model of low-frequency noise for the characterization of radiation degradation of bipolar transistors was presented with the help of traditional 1/f noise model of bipolar transistors, and based on which a systematic characterization technique for the anti-radiation capacity was brought forward.