Theory and application of dual-transistor charge separation analysis

The authors describe a dual-transistor charge separation method for evaluating the radiation response of MOS transistors. This method requires that n- and p-channel transistors with identically processed oxides be irradiated under identical conditions at the same oxide electric fields. Threshold voltage shifts due to oxide-trapped and interface-trapped charge are determined from standard threshold voltage and mobility measurements by combining features of single-transistor midgap and mobility methods. These measurements can be made at currents two-five orders of magnitude higher than those required for midgap, subthreshold slope, and charge-pumping methods. The dual-transistor method contains no adjustable parameters, and includes an internal self-consistency check. The accuracy of the method is verified by comparison to midgap, subthreshold slope, and charge-pumping methods for several MOS processes and technologies. Dual-transistor measurements and analysis not only provide a useful check of single-transistor analysis methods, but also may be the charge-separation method of choice for many applications