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

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 as the threshold voltage, better agreement between the three techniques is obtained. In addition, the authors present a 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. Called the dual-transistor charge-pumping technique, it contains no adjustable parameters and includes a physically based self-consistency check