Integrated charge monitor

• US 5,753,920 A
• Filed: 07/26/1995
• Issued: 05/19/1998
• Est. Priority Date: 07/26/1995
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Soli, George A., Blaes, Brent R., Buehler, Martin G.
• Primary Examiner(s): Fields, Carolyn E.
• Assistant Examiner(s): Glick, Edward J.
• Application Number:
  US08/507,527
• Time in Patent Office: 1,028 Days
• Field of Search: 250/370.06, 250/370.07, 250/394, 250/482.1
• US Class Current: 250/370.06
• CPC Class Codes: G01T 1/02 Dosimeters G01T1/15 takes precedence
• CPC Class Codes: G01T 1/24 with semiconductor detectors
• CPC Class Codes: G01T 1/247 Detector read-out circuitry for processing gain or off-set correction H04N

Abstract

An integrated charge monitor for measuring a level of cumulative radiation exposure includes semiconductor devices having characteristics that change with a cumulative level of radiation to which the devices are exposed, different amounts of radiation shielding associated with each of the devices, and circuitry operable to separately address each of the devices to measure a change in the characteristic of the selected device due to radiation exposure. The monitor may be implemented on a single integrated circuit chip. The monitor may also be employed in performing a spectrometric analysis of radiation based on the affect of the radiation on characteristics of multiple, differently-shielded semiconductor devices.

Claims

1. An integrated charge monitor for measuring a level of cumulative radiation exposure, comprising:

a plurality of semiconductor devices, each device having a characteristic that changes with a cumulative level of radiation to which the device is exposed;

a plurality of radiation shields, each of which is associated with one of said semiconductor devices, wherein each of said shields protects its associated semiconductor device from a different amount of radiation, the plurality of radiation shields being formed from a single piece of material, a portion of the material corresponding to a first radiation shield being thinner than a portion of the material corresponding to a second radiation shield; and

circuitry operable to separately address each of said semiconductor devices to measure a change in the characteristic of the addressed semiconductor device.

2. The integrated charge monitor of claim 1, wherein the plurality of semiconductor devices are p-FETs.

3. The integrated charge monitor of claim 1, wherein the plurality of semiconductor devices are positioned on a single integrated circuit chip.

4. The integrated charge monitor of claim 1, wherein the circuitry for separately addressing the semiconductor devices comprises a multiplexer.

5. The integrated charge monitor of claim 4, wherein the plurality of semiconductor devices and the multiplexer are positioned on a single integrated circuit chip.

6. The integrated charge monitor of claim 1, wherein the plurality of semiconductor devices comprises an array of semiconductor devices.

7. The integrated charge monitor of claim 1, wherein the thinner portion of the material corresponding to the first radiation shield is formed by etching the material.

8. The integrated charge monitor of claim 1, further comprising a current supply operable to supply a current to the semiconductor devices.

9. The integrated charge monitor of claim 8, wherein the current supply is operable to supply a constant current to the semiconductor devices.

10. The integrated charge monitor of claim 9, wherein the semiconductor devices have a temperature-independent operating current at which the characteristics of the semiconductor devices are independent of temperature, and wherein the constant current produced by the current supply corresponds to the temperature-independent operating current of the semiconductor devices.

11. The integrated charge monitor of claim 1, wherein the semiconductor devices produce analog voltages corresponding to the characteristics of the semiconductor devices.

12. The integrated charge monitor of claim 11, further comprising an output circuit including an analog-to-digital converter operable to convert the analog voltages produced by the semiconductor devices to digital values.

13. An integrated charge monitor for measuring a level of cumulative radiation exposure, comprising:

a plurality of semiconductor devices, each of which has a characteristic that changes with a cumulative level of radiation to which the device is exposed, the semiconductor devices producing analog voltages corresponding to the characteristics of the semiconductor devices;

a plurality of radiation shields, each of which is associated with one of said semiconductor devices, wherein each of said shields protects its associated semiconductor device from a different amount of radiation;

circuitry operable to separately address each of said semiconductor devices to measure a change in the characteristic of the addressed semiconductor device; and

an output circuit including an analog-to-digital converter operable to convert the analog voltages produced by the semiconductor devices to digital values, wherein the output circuit includes an offset circuit operable to offset the analog voltages to produce offset analog voltages, and wherein the analog-to-digital converter is operable to convert the offset analog voltages to the digital values.

14. The integrated charge monitor of claim 13, wherein the output circuit includes an amplifier circuit operable to amplify the offset analog voltages to produce amplified offset analog voltages, and wherein the analog-to-digital converter is operable to convert the amplified offset analog voltages to digital values.

15. An integrated charge monitoring system for measuring a level of cumulative radiation exposure, comprising:

an integrated charge monitor operable to produce a signal corresponding to the level of cumulative radiation exposure, and

a processor operable to determine the level of cumulative radiation exposure based on the signal produced by the integrated charge monitor;

wherein the integrated charge monitor includes a plurality of semiconductor devices, each of which has a characteristic that changes with a cumulative level of radiation to which the device is exposed, a first of said semiconductor devices having no shielding, a single piece of material forming a plurality of radiation shields, said piece of material being associated with the semiconductor devices other than said first semiconductor device and each of said shields protecting its associated semiconductor device from a different amount of radiation than another one of the shields protects the semiconductor device associated with that shield, and circuitry operable to separately address each of the semiconductor devices to measure a change in the characteristic of the addressed semiconductor device and to produce a signal corresponding to the level of cumulative radiation exposure for that device.

16. The integrated charge monitoring system of claim 15, further comprising a second integrated charge monitor.

17. The integrated charge monitoring system of claim 16, wherein the second integrated charge monitor is identical to the first integrated charged monitor.