A critical comparison of charge-pumping, dual-transistor, and midgap measurement techniques (MOS transistors)

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Abstract
Charge-pumping, dual-transistor, and midgap estimates of radiation-induced interface-trap density are compared for a large number of transistors fabricated using a wide range of processing technologies. Comparisons are shown for single-transistor midgap and charge-pumping measurements and dual-transistor-mobility measurements. When conventional analysis methods are used to determine threshold voltages, there can be as much as a factor of two difference in the density of interface traps measured by charge pumping and the dual-transistor-mobility and midgap techniques. Using the voltage that corresponds to twice the bulk potential, 2 phi(B), as the threshold voltage, better agreement between the three techniques is obtained. In addition, we present a new technique that combines n- and p-channel transistor charge-pumping and threshold-voltage measurements to accurately determine the threshold-voltage shifts due to interface- and oxide-trap charge. Termed the ''dual-transistor charge-pumping'' technique, it contains no adjustable parameters and includes a physically-based self-consistency check. The self-consistency check has been used to identify measurement problems and where the assumptions underlying the analysis broke down. This technique is valid in the limit of small border-trap densities and also provides the first analytic estimate of the region of the band gap that contributes to interface-trap measurements.