A CRITICAL COMPARISON OF CHARGE-PUMPING, DUAL-TRANSISTOR, AND MIDGAP MEASUREMENT TECHNIQUES

Charge-pumping, dual-transistor, and midgap estimates of radiation-ind uced interface-trap density are compared for a large number of transis tors fabricated using a wide range of processing technologies. Compari sons are shown for single-transistor midgap and charge-pumping measure ments and dual-transistor-mobility measurements. When conventional ana lysis methods are used to determine threshold voltages, there can be a s much as a factor of two difference in the density of interface traps measured by charge pumping and the dual-transistor-mobility and midga p techniques. Using the voltage that corresponds to twice the bulk pot ential, 2 phi(B), as the threshold voltage, better agreement between t he three techniques is obtained. In addition, we present a new techniq ue that combines n- and p-channel transistor charge-pumping and thresh old-voltage measurements to accurately determine the threshold-voltage shifts due to interface- and oxide-trap charge. Termed the ''dual-tra nsistor charge-pumping'' technique, it contains no adjustable paramete rs and includes a physically-based self-consistency check. The self-co nsistency check has been used to identify measurement problems and whe re 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 contri butes to interface-trap measurements.