Re-examination of the extraction of MOS interface-state density by C–V stretchout and conductance methods

The extraction of interface-state density by the stretchout of MOS C–V (Terman method) is re-examined. It is shown that the typical 1 MHz frequency is not nearly high enough to get rid of the interface-state contribution to the MOS capacitance. When coupled with a bias-dependent trap time constant (τ), this could result in a severe underestimate of the interface-state density. The 'conductance method', on the other hand, can extract the interface-state density accurately if the MOS is biased in depletion and if ω ∼ 1/τ is within the measured frequency range. Also, the robustness of the conductance method subject to errors in the estimated oxide capacitance, as well as its extendibility into regions of weak and strong inversion is investigated. Furthermore, two cases of false peaks under the conductance method are mentioned: the first due to a small tunneling leakage in thin oxides and the second due to a high density of bulk-oxide traps. (paper)