Estimation of low-dose-rate degradation on bipolar linear circuits using different accelerated evaluation methods

The linear bipolar devices and integrated circuits (ICs) which are subjected to ionizing radiation exhibit parametric degradations due to current-gain decrease, and the amount of degradation on various types of bipolar devices is much more significant at low-dose-rate than at high-dose-rate. Such an enhanced low-dose-rate sensitivity (ELDRS) is considered to be one of the major challenges for radiation-tolerance testing intended for space systems. Therefore, it is of great significance to explore an efficient and practical test for the ELDRS in the linear bipolar devices and ICs. The different experiments have been implemented on four types of bipolar ICs for evaluating their responses to low-dose-rate irradiation. The experiments involve the dose rate switching approach performed under high to low-dose-rate irradiation and temperature switching approach performed under high to low temperature irradiation. Good agreement is observed between predictive curves obtained at dose rate switching irradiation and the low-dose-rate results, and the irradiation time for the dose rate switching approach is reduced from 4 months to a week. Further, the results also suggest that the device degradation rate can affect the prediction of the total dose. This is because the curves examined at different doses have a lot of overlap when the devices with fast degradation rates are performed. In addition to temperature switching irradiation, the radiation response of the same type of device is much more significant than that obtained in low-dose rate irradiation, and this method will shorten the irradiation time to 12 h. Based on the analysis of mechanisms behind the switched dose rate and temperature irradiation, switching temperature irradiation can accelerate the release of protons and buildup of interface traps, which is the key physical mechanism for ELDRS. Firstly, a higher irradiation temperature can enhance the transport of holes and release of protons to form interface traps, resulting in the enhanced degradation occurring at first dose examined. Further, the reducing temperature sequence suppresses the hydrogen dimerization process during the irradiation that follows, which is strongly temperature dependent and contributes to interface trap annealing. Moreover, further decrease in temperature can restrict the interface trap annealing because the barrier for this process is higher and it has less opportunity to take place at lower temperature. Additionally, the hydrogen molecules converted from hydrogen dimerization may extend the liberation of protons, by the hydrogen molecules cracking mechanisms, leading to the additional degradation. Therefore, the temperature switching irradiation is shown to be a conservative and efficient method for ELDRS in bipolar devices, and this provides an insight into hardness assurance testing.