Analysing impact of MOSFET oxide breakdown by small- and large-signal HF measurements

The impact of gate oxide breakdown on the performance of 90 nm RF-CMOS devices is studied. A thorough analysis of the S-parameter and large-signal HF measurement results confirm that the gate oxide mechanism is purely resistive. Therefore, the fundamental parameters characterizing gate oxide breakdown (i.e., the values for R/sub GS/ and R/sub GD/, and the reduction of G/sub M/) can equally well be derived from DC, small-signal HF, or large-signal HF measurements. In all cases, the same dependency on breakdown position as well as on DC bias is found. Combining these parameters with a standard HF model for a fresh device allows to predict changes in HF figures of merit without the need for time-consuming HF measurements. When no standard model is available, the added value of HF measurements is being able to estimate at which rate the impact of gate oxide breakdown reduces as function of frequency. The advantage of large-signal HF measurements over S-parameter measurements is that the visualization in terms of trajectories facilitates the interpretation, because variations in either or both resistive and capacitive components can instantly be caught.

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