Distribution of flat-band voltages in laterally nonuniform MIS capacitors and application to a test for nonuniformities

Interface states and lateral nonuniformities produce very similar abnormalities in the
C-V
curves of MIS capacitors. The effect of a laterally nonuniform distribution of fixed charge in the insulator can be characterized by a flat-band-voltage distribution function. Here we present a simple, approximate method for determining this distribution from the quasi-static and high-frequency
C-V
curves of the capacitor, and we apply the result to a test for distinguishing between interface states and laterally nonuniform fixed charge. The test is based on a principle that is implicit in the results of an analysis previously published by Brews and Lopez; namely, that interface states and lateral nonuniformities cannot produce identical distortions in both the quasi-static and high-frequency
C-V
curves. The presence of either lateral nonuniformities or interface states can be tested by assuming all
C-V
distortion to be due to the other cause. The
C-V
curves are regenerated under this assumption, and discrepancies between the measured and regenerated curves indicate the presence of the effect assumed not to be present.