Mos capacitor-based, accumulating, radiation-sensitive detector for occupational, environmental and medical dosimetry

Abstract

A low-power wireless ionizing radiation measurement system is present that is intended to be used in a wearable dosimeter for occupational radiation monitoring. The detector element is a custom MOS capacitor that traps holes in proportion to the amount of ionizing radiation incident upon the detector, thus permanently causing a lateral shift in the CV-curve (toward more negative threshold voltage). The circuit measures the capacitance value of several redundant sensors at a given voltage in the depletion region, records this value over time and occasionally transmits the stored values to a base station. From the change in capacitance, the dose that has been delivered can be determined.

1 .- 28 . (canceled) 
     
     
         29 . An apparatus comprising:
 one or more radiation-sensitive metal oxide semiconductor capacitors (MOSCAPs) comprising:   a radiation-sensitive oxide layer disposed between a bottom conductive layer and a top conductive layer,   a microprocessor/wireless transceiver IC configured to transmit a value for an absorbed radiation dose in the radiation-sensitive oxide layer to a base station;   an accelerometer configured to measure motion data for the apparatus; and   a temperature sensor configured to measure the temperature of the apparatus,   wherein a radiation-induced capacitance response of the one or more radiation-sensitive MOSCAPs is proportional to the absorbed radiation dose in the radiation-sensitive oxide layer, and   wherein the capacitance response is electronically measurable, by a capacitive readout circuit comprising a capacitance to digital converter circuit.   
     
     
         30 . An apparatus comprising:
 one or more radiation-sensitive metal oxide semiconductor capacitors (MOSCAPs) comprising:   a radiation-sensitive oxide layer disposed between a bottom conductive layer and a top conductive layer,   wherein a radiation-induced capacitance response of the one or more radiation-sensitive MOSCAPs is proportional to an absorbed radiation dose in the radiation-sensitive oxide layer,   wherein a sensitivity of the radiation-induced capacitance response is enhanced by a time and temperature parameter of a post-oxidation annealing fabrication step.   
     
     
         31 . The apparatus of  claim 30 , wherein the radiation-sensitive oxide layer is annealed after being oxidized to thereby enhance the sensitivity of the radiation-induced capacitance response. 
     
     
         32 . The apparatus of  claim 30 , wherein the time is within a range of approximately 100-200 minutes. 
     
     
         33 . The apparatus of  claim 30 , wherein the temperature parameters are within a range of approximately 1000° C.-1200° C. 
     
     
         34 . The apparatus of  claim 30 , wherein the radiation-sensitive oxide layer has a thickness within a range of approximately 200 nm-450 nm. 
     
     
         35 . A method comprising:
 determining an absorbed radiation dose based on a radiation-induced capacitance response of one or more irradiated radiation-sensitive externally biased metal oxide semiconductor capacitors (MOSCAPs),   wherein the radiation-induced capacitance response of the one or more irradiated radiation-sensitive externally biased MOSCAPs is measured in a depletion operation regime.   
     
     
         36 . The method of  claim 35 , wherein the radiation-induced capacitance response is measured using a capacitive readout circuit. 
     
     
         37 . The method of  claim 35 , comprising applying an external bias voltage across the one or more irradiated radiation-sensitive externally biased MOSCAPs to enhance a sensitivity of the radiation-induced capacitance response of the one or more irradiated radiation-sensitive externally biased MOSCAPs. 
     
     
         38 . The method of  claim 35 , wherein the method comprises saving a value of the absorbed radiation dose to a non-transient storage medium and/or displaying the value of the absorbed radiation dose to a user. 
     
     
         39 . A method comprising:
 applying a sequence of voltages applied to one or more radiation-sensitive metal oxide semiconductor capacitors (MOSCAPs),   wherein the sequence of voltages is applied to obtain stable measurements by compensating for charging effects of applying an external active bias voltage.