Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/24—Measuring radiation intensity with semiconductor detectors
  • G01T1/241—Electrode arrangements, e.g. continuous or parallel strips or the like
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/0224—Electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
  • H01L31/085—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors the device being sensitive to very short wavelength, e.g. X-ray, Gamma-rays

Definitions

• the invention relates to a high dynamic range radiation detection device.
• highly dynamic detection device is intended to mean a device capable of detecting radiation of both low flux and high flux.
• the radiation in question may be X or ⁇ radiation, but other types of radiation, for example of the corpuscular type, could be used, such as proton beams.
• This radiation is capable of creating electrical charges within a semiconductor material in a volume of 1 order of the cubic millimeter.
• the invention finds applications in particular in the medical field. For example, for an X-ray, the X-ray used, before arriving on the detector device, passes through the body of a patient where it is absorbed in an inhomogeneous manner. The outgoing flow can therefore vary considerably locally (several decades).
• Another area is that of non-destructive testing by radiography, for example the interior of containers (loading of boats) which can have very varied absorption.
• radiation detectors for example X or ⁇
• scintillator detectors operating on an indirect detection principle: the incident photon interacts with the scintillator material by creating photons of another type, photons which are multiplied by a photomultiplier to provide a measurable electrical signal.
• Figure 1 schematically describes a detector of this type.
• the device comprises a semiconductor material 2 surrounded by two electrodes 4 and 6, supply means 8 capable of bringing the electrode 6 to an appropriate voltage (-V), means for measuring the current ( i) delivered, comprising, in the example illustrated, an amplifier 10 the output of which is looped back to the input by a capacitor 12, a switch 14 being furthermore disposed at the terminals of this capacitor.
• the device finally includes a device for measuring current (or voltage 16). • The radiation that we want to detect is referenced 20 and it passes through the semiconductor material 2.
• the operation of this device is as follows.
• the radiation 20 interacts with the semiconductor material 2 by creating electrical charges.
• the number of charges created is of an order of magnitude greater than that obtained by indirect detection by a scintillator detector.
• the electric field created in the material by the electrodes makes it possible to collect these charges on the electrodes and in particular the electrode 4. These charges are then stored in the capacitor 12 and processed in the circuit 16 which delivers a signal representative of the radiation.
• the integration capacitor 12 is dimensioned so as to be able to store the maximum amount of charge that the semiconductor material can deliver. This quantity depends on the value of the incident flux. If the flow is very high, the number of charges to be stored will be high and the capacities necessary for their storage will have to be large. These capacity values may either not exist on the electronic components market, or imply areas of integrated capacity that are too large for the space available on the circuit.
• the solution therefore consists in reducing the quantity of charges to be stored, only when the incident flux is too high. But it is essential to maintain the fundamental qualities of the detector, namely a good spatial resolution or a good contrast.
• the spatial resolution is the minimum distance which must separate the points of interaction with the material of two incident photons so that the detector can differentiate them.
• the quantity of charges to be stored cannot be reduced by simply reducing the number of photons arriving on the detector. This method, valid for high flows, would not be suitable for low flows and the detector would lose the dynamics necessary for the application.
• the number of incident photons must remain consistent because the noise of the electrical signal is proportional to 1 / vN where N is the number of photons absorbed in the entire volume of the detector.
• the object of the present invention is precisely to propose a device for detecting radiation with high dynamics which does not have these drawbacks and makes it possible to satisfy these contradictory requirements.
• the invention provides a device, the essential characteristic of which is that the polarization electrode, opposite the measurement electrode, is fragmented into conductive zones electrically isolated from each other, the supply means being capable of carrying each of these areas at an appropriate voltage.
• the incident radiation is injected in a direction perpendicular to the direction of fractionation of the polarization electrode.
• the invention therefore relates to a device for detecting energy radiation, comprising a semiconductor material capable of converting this radiation into electrical charges, a measurement electrode and a measurement circuit for measuring the current delivered by this electrode, characterized in that it further comprises polarization electrodes constituted by conductive zones electrically isolated from each other, said polarization electrodes and the measurement electrode surrounding the material and supply means capable of carrying each these conductive areas at a suitable adjustable voltage.
• the semiconductor material has the shape of a parallelepiped bar with a depth intended to be oriented parallel to the direction of the radiation, a width and a height, this bar having two parallel faces separated by said height, the measuring electrode and the bias electrodes being disposed on these faces.
• the conductive areas of the polarization electrode are in the form of rectangular strips having a length parallel to the width of the bar and a width parallel to the depth of the bar.
• the measuring electrode consists of rectangular conductive strips having a length parallel to the depth of the bar and a width parallel to the width of the bar. Fragmentation zones can take various forms, notably in rectangular bands.
• FIG. 4 shows a particular embodiment with areas of increasing widths
• FIG. 5 shows another particular embodiment with a succession of strips of the same width
• FIG. 6 illustrates a particular embodiment in which the two polarization and measurement electrodes are fragmented in two orthogonal directions. Description of particular embodiments
• the number of charges collected is reduced by reducing the electric field applied to the semiconductor material, therefore the voltage applied to the electrodes.
• This operating mode is never used in the prior art, since it is considered that by lowering the operating voltage, the charge carriers will migrate more slowly and be partially trapped.
• the quantity of charges stored in the capacitor will be very variable and the measured signal not very reproducible.
• the Applicant has shown that this was not the case for high energy photons (of the order of MeV). Indeed, such photons create electron-hole pairs in a large volume, whose typical cross section is of the order of 1 to a few mm 2 .
• FIG. 2 shows the measured charge C (in arbitrary units) as a function of the bias voltage V, expressed in volts.
• the (exponential) curve is regular and attests to a relationship simple between the variation of tension and the variation of quantity of collected charges.
• This first operating mode therefore makes it possible to reduce the quantity of charges to be treated while preserving the contrast. But this is done at the expense of spatial resolution.
• the invention proposes another operating mode (which can moreover be associated with the first) and which exploits the fragmentation of the polarization electrode opposite to the measurement electrode.
• a device is thus obtained whose interaction volume is adjustable depending on whether or not voltages are applied to the different bias electrodes.
• one or more zones can be energized and are therefore active for the collection of charges; other areas may have zero polarization.
• all the polarization electrodes can be connected in order to collect the maximum of charges; when the flux increases, one or more electrodes will be deactivated, that is to say for example grounded.
• the voltage can be adjusted to its optimal value, that is to say to a value high enough to obtain a quality spatial resolution.
• the volume of material involved being smaller, the number of photons participating in the creation of charges is lower which causes an increase in the value of the noise, which deteriorates the contrast.
• This operating mode therefore makes it possible to reduce the quantity of charges without losing the spatial resolution but to the detriment of the contrast.
• FIG. 4 illustrates a variant of the device intended to respond to a very large flow dynamic.
• this variant which also includes three polarization electrodes 6A, 6B and 6C, in the form of strips, the width of the conductive strips (counted parallel to the depth of the bar) changes from one strip to another according to a geometric progression of reason 10 (the width is 10 times greater for zone 6B than for zone 6A and 10 greater for zone 6C than for zone 6B).
• the length of the strips 6A, 6B, 6C counted parallel to the width 1 of the bar is substantially equal to the width of the bar.
• the first zone 6A very narrow, will be used with an optimal voltage and will make it possible to obtain information with a high spatial resolution, while the second zone 6B and possibly the third 6C will be used with a low voltage and will make it possible to obtain high contrast information.
• This variant is advantageous in the case of bundles, which diffuse in the material in a volume having a pear shape, the depth of the narrow part of the pear fixing the width of the first zone (6A).
• the first electrode will be sized to stop 99% of photons of 50 keV (low energy), the second to stop 95% of photons of a few hundred keV and the third to stop the rest high energy photons (more than 500 keV).
• the electrodes will typically have widths of 50 to 100 ⁇ m, 200 to 500 ⁇ m and 2 to 3 cm, respectively.
• This system allows with a single detector and a single electronic measurement circuit to produce three images with different energies. After processing the images, it is possible to deduce the nature of the materials which have attenuated the beam.
• FIG. 5 illustrates another case where six electrodes 6A, 6B, 6C, 6D, 6E, 6F are made up of strips of the same width. A periodic structure is thus obtained.
• the width of the strips can be, for example, 10 mm.
• the device of the invention is particularly advantageous when it is repeated a certain number of times to constitute a matrix.
• the device is then capable of determining the place of interaction of a photon with the semiconductor material: it then makes it possible to produce an image.
• the fragmentation of the electrodes does not significantly increase the size of the device, the latter can therefore be juxtaposed with other devices of the same type.
• the stamping can be carried out on the same bar but of more substantial width, with a fragmentation of the lower electrode in the direction of the depth. This is illustrated in FIG. 6.
• a device which comprises two polarization electrodes 6A and 6B and six measurement electrodes 4a, 4b, 4c, 4d, 4e, 4f constituting parallel rectangular strips at the depth of the bar.
• the material can be chosen from the group consisting of CdTe, CdZnTe, AsGa, Pbl 2 , Hgl 2 and Se.
• the device of the invention is advantageously used in the form of a CdTe parallelepiped having an entry surface of the order of 1 mm 2 , the depth of the bar being 60 mm, to have sufficient stopping power for photons of such energy.

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• General Physics & Mathematics (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Electromagnetism (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• High Energy & Nuclear Physics (AREA)
• Molecular Biology (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Health & Medical Sciences (AREA)
• Measurement Of Radiation (AREA)
• Light Receiving Elements (AREA)

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• 1999
  • 1999-05-19 FR FR9906335A patent/FR2793954B1/fr not_active Expired - Fee Related
• 2000
  • 2000-05-18 WO PCT/FR2000/001348 patent/WO2000072386A1/fr active Application Filing
  • 2000-05-18 US US09/959,465 patent/US6734431B1/en not_active Expired - Lifetime
  • 2000-05-18 EP EP00931310A patent/EP1186058A1/de not_active Ceased

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