Reseach On Current Model Induced By Total Dose Effects In NMOS Transistors

With the aerospace technology developed rapidly, more and more electronic equipment composed of CMOS device and CMOS integrated circuits used in the aerospace engineering, however, there are lots of space articles and rays in the aerospace environment will increase the failure risk of electronic equipment. To improve the reliability of the electronic equipment, the anti-radiation studies become very important.In this article, The NMOSFET’s models of defects(fixed charge and interface states) and currents induced by Total Ionizing Dose(TID) radiation when the gate biased on zero voltage were the study object. The main study was to find the approach to build the models and demonstrate the validity and accuracy of the models.According to radiation theory, the electrical properties of NMOSFET in the Total Ionizing Dose environment and properties with different gate voltage biased were analyzed. In according with integrated circuits applied situation, the radiation model with the condition of zero gate voltage biased is studied, and proposed the related radiation experiment.The radiation experiment was carried out on both conventional and enclosed-gate n-MOSFET with different gate width and total radiation dose. And the experimental data was analyzed to obtain the influence of transfer and output characteristic with different total radiation dose, gate structure and gate with. The densities of charge and interface states were extracted via McWhorter-Winokur’s method. However the extracted results were related with gate width and the reason was analyzed, and proposed the base width to standardize the extracted results to build the current model more convenient.The model of fixed charge and interface states was established with mental-insulator- semiconductor(MIS) structure in the total ionizing dose environment, and the boundary conditions of the model was studied in detail. Even though the gate without external voltage, the electric field also existed in the oxide, it was caused by the work function difference of mental and Si and considered in the model. And then the numerical solutions was obtained by the MATLAB program, the influence of fixed charge and interface states with different gate biased, total dose and oxide thickness was analyzed. In addition, the leakage current was main existed in the bird’s beak region of conventional MOSFET fabricated with LOCOS isolation process was radiated. However, the oxide thickness of bird’s beak region was changed with gate width; it will bring more complicated to calculated radiation current, therefore, the A new approach which takes the trapped charges in the bird’s beak as equivalent charges in the gate oxide was proposed to simplify the calculation of radiation current. At last, the numerical solutions of charge model and equivalent model agree well with other paper and ours experiment data.