Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
  • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components 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
  • H01L27/144—Devices controlled by radiation
  • H01L27/146—Imager structures
  • H01L27/14643—Photodiode arrays; MOS imagers
  • H01L27/14658—X-ray, gamma-ray or corpuscular radiation imagers
• • 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
  • G01T1/20—Measuring radiation intensity with scintillation detectors
• • 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
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/2002—Optical details, e.g. reflecting or diffusing layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
  • H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components 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
  • H01L27/144—Devices controlled by radiation
  • H01L27/146—Imager structures
  • H01L27/14601—Structural or functional details thereof
  • H01L27/14618—Containers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Definitions

• the present invention relates to a solid state X-ray detector comprising a photosensitive sensor associated with a radiation converter.
• the fields of application of this type of detector are in particular radiology: radiography, fluoroscopy, mammography, but also non-destructive testing.
• Such radiation detectors are known, for example, from French patent FR 2 605 166 in which a sensor formed from amorphous silicon photodiodes is associated with a radiation converter.
• the photosensitive sensor is generally produced from photosensitive elements in the solid state arranged in a matrix.
• the photosensitive elements are made from semiconductor materials, most often monocrystalline silicon for CCD or CMOS type sensors, polycrystalline or amorphous silicon.
• a photosensitive element comprises at least one photodiode, a phototransistor or a photo resistance. These elements are deposited on a substrate, generally a glass slab.
• the photosensitive sensor is associated with a radiation converter which comprises a layer of a scintillating substance.
• This substance has the property, when excited by such radiation, of emitting radiation of longer wavelength, for example visible or near visible light, to which the sensor is sensitive.
• the light emitted by the radiation converter illuminates the photosensitive elements of the sensor which carry out a photoelectric conversion and deliver electrical signals which can be exploited by suitable circuits.
• the radiation converter will be called a scintillator in the following description.
• Certain scintillating substances from the family of alkali halides or rare earth oxysulfides are frequently used for their good performance.
• cesium iodide doped with sodium or thallium depending on whether an emission around 400 nanometers or around 550 nanometers is desired, is known for its high absorption of X-rays and for its excellent fluorescence yield. It comes in the form of fine needles which are grown on a support. These needles are substantially perpendicular to this support and they partially confine the light emitted towards the sensor. Their finesse conditions the resolution of the detector.
• Lanthanum and gadolinium oxysulfides are also widely used for the same reasons.
• cesium iodide With regard to cesium iodide, its decomposition gives cesium hydroxide Cs + OH " and free iodine l 2 which can then combine with iodide ions to give the complex l 3 " . With regard to lanthanum oxysulfide, its decomposition gives chemically very aggressive hydrogen sulfide H 2 S.
• Humidity is extremely difficult to remove. Ambient air and the glue used to assemble the detector always contain it. The presence of moisture in the adhesive is due either to ambient air, or as a by-product of polymerization if it results from the condensation of two chemical species, which is common.
• One of the important aspects when making these detectors will be to minimize the amount of moisture initially present inside the detector, and in contact with the scintillator, and to avoid the diffusion of this humidity inside. of the sensor during its operation.
• the radiation detectors have an entry window traversed by the X-ray upstream of the scintillator.
• the scintillating substance is generally deposited on a metal support.
• the support and the scintillating substance then form the scintillator.
• the entry window must withstand without damage the thermal stresses of the deposition and treatment of the scintillator and preferably have a coefficient of expansion of the same order of magnitude as that of the scintillator and that of the sensor, more particularly that of its substrate.
• the window has a low modulus of elasticity, which makes it possible to remove differential stresses between on the one hand the window and the scintillator and on the other hand the window and the sensor, or more particularly the substrate of the sensor. This eliminates the risk of cracking of the scintillator and breakage of the sensor substrate.
• the surface condition of the entry window must also allow, in particular for cesium iodide, the finest possible needle growth, in the most uniform manner possible.
• the fineness of the needles is a quality factor for the resolution of the detector.
• the supports are aluminum.
• the transparency of aluminum to the radiation to be detected is excellent, its optical properties are good.
• After treatment of the aluminum a satisfactory surface condition can be obtained for depositing the scintillator there.
• its coefficient of expansion is very different from that of the sensor.
• This seal is necessarily flexible to absorb the differences in expansion between the support of the scintillator and the sensor during thermal cycles, and to minimize the stresses and the risks of breakage.
• flexible materials are generally permeable to moisture. This results in insufficient protection of the scintillator like this humidity, which reduces the life of the detector.
• the present invention proposes a radiation detector with an increased lifetime, the functions of which are an entry window and a seal. are not produced, as in the current state of the art, by the sole support of the scintillator.
• the subject of the invention is a solid state X-ray detector comprising a photosensitive sensor, a scintillator transforming the X-ray into radiation to which the sensor is sensitive, and an entry window traversed by the X-ray upstream of the scintillator, characterized in that the entry window is placed on the scintillator, without being fixed to the scintillator, and in that a moisture-tight sealing joint fixes the entry window and the sensor.
• the stresses to which the scintillator support was subjected are distributed between the support and the new entrance window proper.
• the scintillator support remains subject to the same reflectivity and surface condition constraints for depositing scintillator as in the state of the art.
• it is no longer subjected to the sealing and support constraints of the sealing joint. These constraints are carried over to the new additional input window.
• This structure makes it possible to define an entry window material which is compatible with the material of which the sensor is made, in particular in terms of compatibility of their respective expansion coefficients which must allow the use of a harder sealing joint, and therefore more impermeable to humidity.
• the invention can be implemented in two configurations for assembling the scintillator and the sensor.
• the scintillator substance is deposited on a support that the radiation to be detected must pass through before reaching the sensor.
• the assembly is then glued to the sensor.
• the entry window is placed on the support without being fixed to it. This keeps a degree of freedom of the input window relative to the support.
• the entry window can for example slide relative to the support to absorb possible differential expansions during changes in temperature of the detector.
• the sensor serves as a support for the scintillating substance which is then in direct and intimate contact with the sensor.
• the scintillating substance is then covered with a protective sheet.
• the first configuration allows the scintillator and the sensor to be optimized separately.
• the scintillator can then receive heat treatments, even if these are incompatible with the sensor.
• cesium iodide it is evaporated by heating and it is deposited on the support by condensing.
• An annealing operation is then carried out at approximately 300 ° C. in order to achieve an optimum fluorescence yield.
• direct deposition a compromise must be made on the annealing temperature so as not to damage the sensor.
• Another advantage of the first configuration known as the attached scintillator, is that the sensor and the scintillator are only assembled if they have been successfully tested, which improves the overall manufacturing yield.
• the second configuration called direct deposit, each time the scintillator is defective, the sensor is discarded because there is no risk of trying to recycle it.
• the thickness of adhesive for the assembly brings some losses in terms of spatial resolution of the X-ray detector and of light collection.
• the direct deposition of the scintillator on the sensor offers the best optical coupling conditions.
• the configuration in which the scintillator is carried by the support allows better management of production flows by allowing the separate production of the two elements that are the scintillator with its support on the one hand, and the sensor on the other hand.
• the cost of the support as described in the first configuration is lower than that of the sensor serving as support for the scintillating substance in the second configuration.
• the first configuration can be applied to photosensitive elements consisting of sets of several butted elements, as for example described in the French patents published under the numbers FR 2 758 654 and FR 2 758 656.
• the second configuration cannot be applied to such photosensitive assemblies made up of assemblies of several butted elements, due to the poor dimensional stability of such assemblies at a temperature of 300 ° C, which temperature is necessary for the implementation of the scintillating substance after its deposition on its support.
• the entrance window must meet the following requirements: be as transparent as possible to the radiation to be detected, be moisture-tight, and have mechanical properties compatible with the manipulations undergone by the detector.
• FIG. 1 represents a radiology detector according to the first configuration.
• FIG. 2 represents a radiology detector according to the second configuration.
• the scales are not respected for the sake of clarity.
• the first configuration known as the attached scintillator, is represented in FIG. 1.
• the radiation sensor bears the reference 1. It comprises a substrate 2, in principle a glass slab, supporting photosensitive elements 3. Each photosensitive element 3 is mounted between a row conductor and a column conductor so that it can be addressed. The conductors are not visible in the figure for the purpose of simplification.
• the photosensitive elements 3 and the conductors are generally covered with a passivation layer 4 intended to protect them from humidity.
• the sensor 1 cooperates with a scintillator 5 which in the example is optically coupled to the sensor 1 with optical glue 6.
• the scintillator 5 comprises a layer of scintillating substance 7, represented with a needle structure, deposited on a support 8.
• the support 8 thus carries the scintillating substance 7.
• the scintillating substance 7 belongs for example to the family of alkali halides such as cesium iodide which is particularly sensitive to wet oxidation, but it could also belong to the family of rare earth oxysulfides some members of which are also not very stable like lanthanum oxysulfide.
• the scintillator substance 7 is deposited directly on the sensor 1 and a sheet 9 covers the scintillator substance 7.
• the sheet 9 is used to protect the scintillator substance 7.
• the assembly formed by the scintillator substance 7 and the sheet 9 will bear the mark 5 and will be called scintillator as in the first configuration.
• an input window 10 is placed on the scintillator 5 without being fixed on it.
• a sealed seal 11 fixes the entry window O to the sensor 1 or more precisely to its substrate 2.
• the choice of a material for the seal is made according to the materials of the entry window and the sensor.
• the sealing joint can be made from mineral material. This type of seal has very good impermeability but it requires a high processing temperature, of the order of 400 ° C.
• the sealing joint can be made from organic material. These materials have a poorer seal than mineral materials. But on the other hand their processing temperature is lower, of the order of 200 ° C. Among the organic materials the best sealing is ensured by an epoxy adhesive
• the input window 10 for its part, can be made of any material whose coefficient of thermal expansion is close to that of the material of which the sensor 1 is formed.
• the coefficient of expansion of the input window is lower to that of aluminum.
• the entry window 10 can be covered with any deposit which can improve its reflectivity or its chemical resistance to any corrosion, which can come inter alia from residues of decomposition of the scintillator in a humid environment.
• the entrance window may include glass. The is mono component and therefore easy to implement. In addition, when the substrate 2 of the sensor 1 is produced from a glass slab, it is easy to choose a sealing joint whose compatibility is only checked with a single material, in this case glass. Carbon fibers can also be used to make the entrance window. Carbon fibers have better X-ray transparency than glass and are also less fragile. In carbon fibers, which are often held together with epoxy resin, are more difficult to seal due to their rough surface condition.
• the entrance window may include a ceramic material whose X-ray transparency is close to that of glass.
• the entrance window can also include an organic material such as polyester.
• This material has better X-ray transparency than glass. Its fragility is also less than that of glass. It is a homogeneous material having a smooth surface state when it is obtained by rolling. Nevertheless, the sealing of polyester is more difficult to achieve than that of glass.
• the support 8 of the scintillator, or the sheet 9 depending on the configuration chosen may include any metallic material such as aluminum, titanium or the like. It can also include any ceramic or organic material such as for example a polyimide, or even a composite material based on carbon fiber.
• the material chosen must be transparent to X-rays, chemically compatible with the scintillating substance, and compatible with the operations for producing a luminescent scintillator, such as for example vacuum deposition and annealing.
• the chosen material absorbs or reflects the light produced by the scintillator 5 but does not transmit it. Indeed, the light produced by the scintillator 5 is generally visible or near visible light. If the chosen material transmitted the light produced by the scintillator 5, the detector would no longer be optically impermeable to outside light, and the sensor 1 could receive outside light, which would disturb its operation.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Power Engineering (AREA)
• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
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• Condensed Matter Physics & Semiconductors (AREA)
• Electromagnetism (AREA)
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• High Energy & Nuclear Physics (AREA)
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• Spectroscopy & Molecular Physics (AREA)
• Toxicology (AREA)
• Measurement Of Radiation (AREA)
• Solid State Image Pick-Up Elements (AREA)

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• 2001
  • 2001-10-26 FR FR0113899A patent/FR2831671B1/fr not_active Expired - Lifetime
• 2002
  • 2002-10-25 US US10/492,597 patent/US7402814B2/en not_active Expired - Lifetime
  • 2002-10-25 CN CNB02821286XA patent/CN1276269C/zh not_active Expired - Fee Related
  • 2002-10-25 JP JP2003538770A patent/JP4510453B2/ja not_active Expired - Fee Related
  • 2002-10-25 EP EP02790545A patent/EP1438606A1/fr not_active Ceased
  • 2002-10-25 WO PCT/FR2002/003681 patent/WO2003036329A1/fr active Application Filing
  • 2002-10-25 CA CA002463078A patent/CA2463078C/fr not_active Expired - Fee Related

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