MOS CAPACITOR-BASED, ACCUMULATING, RADIATION-SENSITIVE DETECTOR FOR OCCUPATIONAL, ENVIRONMENTAL AND MEDICAL DOSIMETRY
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 . 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.
2 . The apparatus of claim 1 , wherein the radiation-induced capacitance response is electronically measurable.
3 . The apparatus of claim 2 , wherein the apparatus comprises a capacitive readout circuit configured to measure the radiation-induced capacitance response.
4 . The apparatus of claim 3 , wherein the capacitive readout circuit comprises a capacitance to digital converter circuit.
5 . The apparatus of claim 1 , wherein the apparatus comprises a wireless transceiver integrated circuit (IC) configured to transmit a value for the absorbed radiation dose to a base station.
6 . The apparatus of claim 1 , wherein the apparatus comprises a microprocessor/wireless transceiver integrated circuit (IC) configured to transmit a value for the absorbed radiation dose to a base station.
7 . The apparatus of claim 1 , wherein the apparatus comprises an accelerometer configured to measure motion data for the apparatus.
8 . The apparatus of claim 7 , wherein the apparatus is a wearable device.
9 . The apparatus of claim 8 , wherein accelerometer is configured to provide an output to indicate whether the device is worn by a user during radiation exposure.
10 . The apparatus of claim 1 , wherein the apparatus comprises a temperature sensor configured to measure the temperature of the apparatus.
11 . The apparatus of claim 10 , wherein the apparatus is configured to output a value for absorbed radiation dose that compensates for a temperature induced drift in a capacitance response of the one or more radiation-sensitive MOSCAPs based on one or more temperature measurements made by the temperature sensor.
12 . The apparatus of claim 1 wherein the bottom conductive layer comprises a silicon substrate.
13 . The apparatus of claim 12 , where the silicon substrate comprises a p-type doped silicon substrate.
14 . The apparatus of claim 12 , wherein the apparatus comprises a conducting contact coupled to the silicon substrate, and wherein the conducting contact is configured to electrically connect the apparatus to other electronic devices.
15 . The apparatus of claim 14 , wherein the apparatus comprises a capacitive readout circuit configured to measure the radiation-induced capacitance response, and wherein the conducting contact is switchingly coupled to the capacitive readout circuit.
16 . The apparatus of claim 14 , wherein the conducting contact comprises a titanium/gold compound.
17 . The apparatus of claim 16 , wherein the conducting contact is bonded to pins on a gold-plated header.
18 . The apparatus of claim 17 , wherein the conducting contact is bonded to the pins by gold/gold thermos-compression bonding.
19 . The apparatus of claim 1 , wherein the top conductive layer comprises a polysilicon or a metal layer.
20 . The apparatus of claim 19 , wherein the apparatus comprises a conducting contact coupled to the top conductive layer, and wherein the conducting contact is configured to electrically connect the apparatus to other electronic devices.
21 . The apparatus of claim 20 , wherein the conducting contact is switchingly coupled to a biasing source.
22 . The apparatus of claim 21 , wherein the conducting contact comprises a titanium/gold compound.
23 . The apparatus of claim 22 wherein the conducting contact is bonded to pins on a gold-plated header.
24 . The apparatus of claim 23 , wherein the conducting contact is bonded to the pins by gold/gold thermos-compression bonding.
25 . The apparatus of claim 1 , wherein the oxide layer comprises a silicon dioxide layer.
26 . The apparatus of claim 1 , wherein the one or more radiation-sensitive MOSCAPs operate in inversion during radiation exposure.
27 . The apparatus of claim 1 , wherein the one or more radiation-sensitive MOSCAPs operate in depletion during a measurement of the radiation-induced capacitance response.
28 . The apparatus of claim 1 , wherein the one or more radiation-sensitive MOSCAPs operate in inversion during radiation exposure, and
wherein the one or more radiation-sensitive MOSCAPs operate in depletion during a measurement of the radiation-induced capacitance response.
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 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.