Comparison of calculated AC to DC Hot Carrier lifetimes based on combined single MOST DC stress results and inverter simulations with AC stress measurements on single MOST´s to check the duty factor approach

DC stress Hot Carrier tests are done with varying gate stress voltage. A modeling expression is given that includes the dependency of the lifetime on Vg, in addition to the dependency on Vd and channel length L. Combined with the simulated Vg and Vd timing of an inverter this expression is used to calculate the total damage per inverter cycle and the according AC to DC lifetime ratio via a numerical integration. The simulation results are compared with results from AC stressed single MOST Hot Carrier results that use a triangular shaped gate pulse and constant drain voltage. A significant difference is found between the damage per gate pulse edge derived from the combination of DC stress data with inverter simulation result and AC stress measurement of single MOST´s. The result shows that the duty factor approach to calculate the AC lifetime is valid if the damage per single gate pulse edge is determined correctly. The damage cannot be determined correctly from DC stress test data, but can easily be measured with the triangular gate stress test on single MOST´s.