Advantages of Using a PMOS FET Dosimeter in High-Dose Radiation Effects Testing

In this paper data are presented that show the response, i.e., shift in threshold voltage, Δ VT, as a function of dose, D, up to a megarad for radiation-soft PMOS transistors employed as dosimeters. The relationship between Δ VT and D was determined with a calibrated Co-60 gamma-ray source. The PMOS dosimeters were operated with the threshold voltage continuously indicating, i.e., the VT mode. The Co-60 results are compared to data obtained with 10-MeV electrons from the Naval Research Laboratory (NRL) Linac. The linac data were taken at different dose rates, and they do not show an obvious dose rate dependence. Also, the Co-60 and linac data overlap well within the expected experimental uncertainties. The use of the PMOS dosimeter operating in the VT mode for high total dose measurements is compared briefly to other systems that can be employed in performing such measurements. Specifically, the PMOS dosimeter usage is compared to that of Ca F2:Mn thermoluminescent dosimeters (TLDs) and commercially available radiachromic nylon film dosimeters. These latter two dosimeter systems, and especially the TLDs, are frequently employed in radiation testing because of their ease of use. Other dosimeter systems, such as the p-i-n diode, are not considered since they are more difficult to use than the systems being compared. The significance of the present work lies in the fact that it demonstrates how important the PMOS dosimeter can be in the high-dose testing of microelectronic devices.