STACKED RADFETS FOR INCREASED RADIATION SENSITIVITY

Hitherto, pMOS Radiation Sensitive Field Effect Transistors (RADFETs) have not been abbe to detect doses in the milli-rad range, which are r equired for low dose clinical/personnel applications. This paper repor ts on further investigation of a design approach, where RADFETs are co nnected in a stacked sequence so that increased radiation sensitivity is obtained. The radiation sensitivity obtained for 40 stacked RADFETs is approximately 220 times the single RADFET sensitivity. This enable s radiation sensitivities in the milli-rad range to be measured, Theor etical equations governing the threshold voltage of a MOS device as a function of bulk-source voltage are used to theoretically evaluate the output voltage of the stacked structure. Measurement and theory are f ound to agree closely in this analysis. % drift and % fading of the si ngle RADFET, as a function of total radiation induced shift in V-T, is similar to that of the stacked structure.