Optimised stacked RADFETs for micro-gray dose measurement

Abstract

This paper details the improvements in the design of stacked RADFETs for lower initial (pre-irradiation) output voltage (Vo) magnitude as well as increased radiation sensitivity. The issue of high read-out voltage has been shown to be a drawback. It is the body (bulk) effect factor that is responsible for the increased overall stack threshold voltage (V/sub T/), which is greater than the sum of the individual devices V/sub T/. This same body effect is the factor responsible for increased radiation sensitivity of stacked devices. From extensive process and device simulation and resultant circuit simulation, modified stack structures have been proposed and designed. New results of lower initial (preirradiation) output voltage as well as increased radiation sensitivity are presented here. Results in this work show radiation sensitivity values of 8.5 mV/mGy achieved with 15 stacked devices of 3060/13 W/L (/spl mu/m) geometry, with an initial output voltage of <10 V.