Effects Of Secondary Electron Imbalance On Radiation Effects Of Typical Devices

Absorbed dose is the most important physical quantity in the study of radiation effect.The variation law of the electronic device parameters with the absorbed dose is the basis for the study of radiation effect.Internal absorbed dose of device are not able to be measured directly due to small size of electronic devcies.At present,irradiation tests are performed by applying electrical bias to the electronic device placed on a circuit board for irradiation,measuring the absorbed dose of current location of the device instead of the actual absorbed dose of the sensitive area of the device.There was great difference in geometry size of different type device.For a thinner device,the thicknesses for packaging material above sensitive layer and substrate under sensitive layer are thinner.In this situation secondary electron equilibrium condition is not satisfied in the sensitive area of a thinner device.Actual absorbed dose could be smaller than irradiated dose measured by the dosimeter at the same position,thus it will result in underestimation to radiation damage of electronic devices.Therefore,it is very necessary to study the influence of the secondary electron non-equilibrium on the actual absorbed dose of the device and evaluate the magnitude of error of radiation effect caused by the influence.In this thesis,CC4069 inverters with dual-in-line plastic package are selected as the experimental devices.The absorbed doses of the device sensitive area in irradiation experimental model were measured by high spatial resolution dosimetric method and the difference between the absorbed doses of the device and the nominal dose measured by the dosimeter were analyzed by Monte Carlo simulation.Combined with the measurement of the irradiation sensitive parameter threshold voltage of CC4069 inverter,we have analyzed and evaluated the influence extent of the secondary electron non-equilibrium condition to the absorbed doses of the device sensitive area and radiation effect.The results of this study will provide accurate reference data for research of radiation effect and verification of radiation hardening of the electronic device and are of important significance in improving the accuracy of radiation effect and radiation hardness assessment of electronic devices to ensure safe operation and life of spacecrafts.The main work and results in this thesis are as follows:The effects of total dose irradiation with ⁶⁰Co?-rays on CC4069 inverter were studied.The threshold voltage for PMOS and NMOS were measured by ⁶⁰Co?rays under different bias conditions during irradiation.We have obtained the change relation of threshold voltage shift for PMOS and NMOS under turn-on and cut-off bias conditions with the nominal dose and analyzed the change mechanism.This work has laid a foundation for study the influence of the secondary electron non-equilibrium on the radiation effect of the device.A dose measurement system of small size and high spatial resolution was established,and the absorbed dose of the device model and equilibrium does at the same position were measured in irradiation test using the system.The results of measurement indicate that the absorbed dose of the device model is only 86.93%of the equilibrium dose.The result proves that the absorbed dose of the device model which does not satisfy the secondary electron equilibrium condition is smaller than the equilibrium dose at the same position.The Monte Carlo device model was built.The absorbed dose distributions of⁶⁰Co?irradiation in various layers of CC4069 inverter are calculated and the absorbed dose of SiO₂ sensitive layer is also obtained.At the same time,the equilibrium dose in the secondary electron equilibrium state is calculated under the same irradiation conditions.The dose of the device sensitive layer is only 83.52%of the equilibrium dose.This result shows that the secondary electron non-equilibrium has influence on the radiation effect research.The results from Monte Carlo simulation are consistent with the experimental measuring results.The curve of threshold voltage drift for PMOS and NMOS under turn-on and cut-off bias conditions is corrected with the dose of the device sensitive layer obtained by Monte Carlo simulation.The threshold voltage drift under PMOS cut-off bias exceeds the failure criterion.Failure analysis with modified device absorbed dose shows that the radiation test under the secondary electron non-equilibrium condition will affect the assessment of radiation hardening of devices and the radiation hardening of the device is overestimated by 16.5%.