Fatigue lifetime evaluation of polysilicon thin films by using cyclic loading with gradually increasing amplitude

This study extends the previous fatigue test method under constant stress amplitude based on Paris’ law with two unknown parameters to evaluate the fatigue lifetime of polysilicon thin films under cyclic loading with gradually increasing stress amplitude, which gives more efficient manner. The extended method is applied to the experimental data obtained from the tests for the three specimen types with different shapes, which induce non-uniform stress distribution. The two unknown parameters in Paris’ law are evaluated by statistical analysis with maximum likelihood method based on the experimental data obtained from the fatigue tests with the gradually increasing stress amplitudes at different rates. They are then compared to those obtained by the tests with constant stress amplitudes. The confidence bounds are calculated for the two unknown parameters and give the statistical difference level at 32.8%. The lifetime difference of the fatigue curves is also analyzed with the error of the absolute value of cyclic number in logarithmic scale to be smaller than 1. The results show that the fatigue curve of polysilicon thin films could be estimated by using the two unknown parameters of the Paris’ law obtained from the new fatigue experiments with gradually increasing stress amplitude.