Patent ID: 6172368
Filing Date: 2001-01-09
Classification: G01T

Abstract:
A method of monitoring ionizing radiation using an insulated gate field effect transistor dosimeter having a source and a drain formed in a substrate, a floating gate separated from the substrate by an insulating layer, a control gate overlapping a first part of the floating gate and insulated therefrom, and a charging gate overlapping a second part of the floating gate and insulated therefrom, the second part being remote from a channel between the source and drain, the method comprising the steps of:(i) maintaining potential differences between the substrate, source, drain and control gate lower than a maximum normal operating voltage of the device;(ii) pre-charging the floating gate by establishing a potential difference between the charging gate and the control gate, monitoring a parameter dependent upon a threshold voltage of the transistor and increasing the potential difference to transfer charge between the charging gate and the floating gate through the insulating layer material between the floating gate and the charging gate until a predetermined threshold voltage is established without involving excessive electric field stress in the region of the channel;(iii) with the substrate, source, drain, control gate and charging gate maintained at a common electrical potential, exposing the dosimeter to the ionizing radiation;(iv) following such irradiation, measuring a parameter affected by change in the charge applied to the floating gate and determining the amount of such ionizing radiation absorbed by the transistor in dependence upon the difference between floating gate charge before and after irradiation.