WO2004095580A1 - Element detecteur pour rayons x - Google Patents

Element detecteur pour rayons x Download PDF

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Publication number
WO2004095580A1
WO2004095580A1 PCT/IB2004/050419 IB2004050419W WO2004095580A1 WO 2004095580 A1 WO2004095580 A1 WO 2004095580A1 IB 2004050419 W IB2004050419 W IB 2004050419W WO 2004095580 A1 WO2004095580 A1 WO 2004095580A1
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WO
WIPO (PCT)
Prior art keywords
collecting electrodes
detector element
conversion layer
electrodes
layer
Prior art date
Application number
PCT/IB2004/050419
Other languages
English (en)
Inventor
Augusto Nascetti
Original Assignee
Philips Intellectual Property & Standards Gmbh
Koninklijke Philips Electronics N. V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Philips Intellectual Property & Standards Gmbh, Koninklijke Philips Electronics N. V. filed Critical Philips Intellectual Property & Standards Gmbh
Publication of WO2004095580A1 publication Critical patent/WO2004095580A1/fr

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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
    • H01L27/14665—Imagers using a photoconductor layer
    • H01L27/14676—X-ray, gamma-ray or corpuscular radiation imagers

Definitions

  • the invention relates to a detector element for the detection of electromagnetic radiation, in particular x-radiation, and to an x-ray detector with such a detector element.
  • US 5 396 072 discloses a detector element for x-radiation, which has a flat conversion layer in which incident x-ray quanta are converted into free electrical charges (electron-hole pairs).
  • a ground electrode is arranged on the upper side of the conversion layer, while the lower side of the conversion layer is matricially covered with a multiplicity of collecting electrodes. In the electric field between the ground electrode and the collecting electrodes, the free charges produced by x-radiation are moved toward the collecting electrodes, where they are temporarily stored and subsequently read out by evaluation electronics.
  • the area of a collecting electrode corresponds here to an image point, or pixel, of the x-ray image that can be produced using the detector.
  • US 5 396 072 proposes a special structure of the collecting electrodes, in which they can overlap with supply and readout lines without leading to perturbing capacitive interactions. That area of the detector element which is occupied by said lines can therefore still be used for detection of x-radiation.
  • a marginal spacing must be left between the various collecting electrodes so that they are reliably insulated from one another.
  • the electric field passing through the conversion layer is therefore weaker in the edge regions of the collecting electrodes, so that charges created there are dissipated more slowly toward the collecting electrodes. This leads to perturbing residual signals during successive recordings with the detector element, and therefore to artifacts in the final image that is produced (time lag, ghosting etc.).
  • the detector element according to the invention is used for the detection of electromagnetic radiation which, in particular, may be x-radiation.
  • the detector element contains the following components: a) A conversion layer, in which incident and absorbed radiation quanta are converted into an electrical signal.
  • the electrical signal may, in particular, be formed by freely mobile electrical charges (for example electron-hole pairs).
  • the collecting electrodes may be used to dissipate free charges produced by radiation.
  • the said collecting electrodes of the detector element are arranged in an edge region thereof according to the following features: c) As seen from the viewing direction of the layer normal of the conversion layer, the at least two collecting electrodes are arranged abutting one another or overlapping in said edge region. Since the conversion layer is at least locally flat in the vicinity of a collecting electrode in question, it is possible to define its layer normal, that is to say the direction of the normal to this (local) plane. The direction of the layer normal of the conversion layer is typically also the direction of the principal radiation incidence when the detector element is being used. d) In said edge region, the two collecting electrodes in question have a distance between them as seen in a direction perpendicular to the layer normal.
  • the collecting electrodes are arranged abutting one another or overlapping, that is to say without a distance between them, as seen from the direction of the layer normal of the conversion layer (that is to say the primary incidence direction of the photons to be detected).
  • they are "in reality" spaced apart, which can be seen from a viewing direction perpendicular to the layer normal.
  • the collecting electrodes have an overlapping arrangement similar to fish scales or roof tiles.
  • the sensitive detection area defined by the collecting electrodes does not therefore have any spacing gaps between the collecting electrodes, even though the latter are also electrically insulated from one another. Maximum utilization of the sensitive area and, in particular, great homogeneity of the electric field in the conversion layer are achieved in this way, which prevents of the occurrence of delay artifacts.
  • the described scale-like arrangement of the collecting electrodes is preferably implemented not only between two collecting electrodes in a limited edge region, but also for all collecting electrodes provided on the detector element. In this way, the sensitive area of the detector element can be covered without interruption by collecting electrodes, as seen from the viewing direction of the layer normal. Maximum sensitivity of the detector element can be achieved in this way.
  • a passivation layer which provides efficient electrical insulation of the collecting electrodes is arranged in said edge region, where two collecting electrodes in question adjoin each another.
  • each of the collecting electrodes consists of a main electrode and a secondary electrode, which are connected together.
  • the main electrodes of all the collecting electrodes are furthermore arranged essentially in a common plane and have a distance between them, as seen from the viewing direction of the layer normal of the conversion layer.
  • the arrangement of the main electrodes is therefore similar to the arrangement of collecting electrodes in conventional detector elements (cf. US 5 396 072).
  • the secondary electrodes are designed so that, on the one hand, they cover the aforementioned distances between the main electrodes (as seen from the viewing direction of the layer normal) while, on the other hand, they lie in a plane parallel to the main electrodes and at a distance from them.
  • each of the secondary electrodes is furthermore connected to a main electrode, so as to form an electrically integrated collecting electrode with it.
  • the two-part structure consisting of main electrodes in a first plane and secondary electrodes in a second plane has the advantage that it can be readily produced with normal semiconductor technology methods.
  • the main electrodes it is preferable for the main electrodes to be essentially designed rectangularly, and for the secondary electrodes to be arranged in the form of strips on at least two edges of the main electrodes. These are advantageously two neighboring edges of the main electrode.
  • the equivalently designed collecting electrodes may be fitted together in a regular pattern so that, overall, they cover the sensitive area without interruption.
  • the conversion layer is made of a material which has a sufficiently high sensitivity for the radiation to be detected.
  • the conversion layer may be designed for the conversion of x-ray quanta into free electrical charges, so that the detector element is suitable for use in an x-ray detector.
  • a reference electrode is generally arranged on the opposite side of the conversion layer from the collecting electrodes. It preferably extends over the surface of the side, so that it covers the total area formed by all the collecting electrodes. It is preferably furthermore essentially transparent for the electromagnetic radiation to be detected.
  • An electric field passing perpendicularly through the conversion layer, which transports the free charges resulting from the absorption of radiation toward the electrodes, can be produced between the reference electrode and the collecting electrodes by applying an electrical voltage. Uninterrupted surface coverage of the collecting electrodes in this case achieves great homogeneity of the electric field so that, on the one hand, clear-cut zonal separation takes place between the various pixels of the detector element and, on the other hand, the charges being produced are transported away with a uniform speed everywhere.
  • the detector element preferably has a large number of collecting electrodes, which are arranged matricially in rows and columns. Such matrix arrangements of collecting electrodes can be addressed and read out in the known way using row and column lines.
  • the collecting electrodes may be connected individually or in groups to corresponding evaluation electronics, which are typically located in or at of the edge of the detector surface.
  • the invention also relates to an x-ray detector for the spatially resolved detection of x-radiation, which contains an x-radiation-sensitive detector element of the type explained above, in its basic form or according to the refined variants.
  • Fig. 1 shows a schematic section through a detector element according to the prior art in the vicinity of two collecting electrodes
  • Fig. 2 shows a section corresponding to Fig. 1 through a detector element according to the invention
  • Fig. 3 shows a plan view of a subregion of a detector element according to Fig. 2 from the viewing direction of the surface normal n of the conversion layer.
  • Detector elements for x-radiation are used particularly in so-called flat dynamic x-ray detectors (FDXDs).
  • FDXDs flat dynamic x-ray detectors
  • directly converting detector elements which convert x-ray quanta into an electrical signal (for example, electron-hole pairs) in a (direct) conversion layer
  • indirectly converting detector elements have a scintillator which first converts the x-ray quanta into visible light, which is then converted in a spatially resolved way into an electrical signal (for example, electron-hole pairs) in a photodiode.
  • Directly converting detector elements will be considered below, but without the invention being restricted thereto.
  • Fig. 1 shows a section through an x-ray detector element known from the prior art, in the vicinity of two collecting electrodes 4.
  • the Figure is not true to scale and the vertical direction is instead greatly exaggerated in the vicinity of the collecting electrodes 4 compared with elsewhere, and compared with the horizontal direction (the horizontal dimension of the collecting electrodes 4 is typically of the order of 150 ⁇ m with a thickness of a few ⁇ m for the components 4, 5 and 6, and the thickness of the conversion layer 2 is typically from 100 to 1000 ⁇ m).
  • the detector element contains a directly converting flat conversion layer 2, in which the incident x-ray quanta X are converted directly into an electrical signal, that is to say free electron-hole pairs here.
  • Suitable materials for the conversion layer 2 are, for example, a-Se, PbO, Pbl 2 and Hgl 2 .
  • the upper side of the conversion layer 2 is covered surface-wide by a reference electrode 1, which is transparent for x-radiation.
  • Collecting electrodes 4 which correspond to individual pixels of the x-ray image to be produced, are arranged matricially on the opposite lower side of the conversion layer 2.
  • Each of the collecting electrodes 4 is coupled at its lower side to readout electronics 6 arranged on the substrate 7.
  • the readout electronics contain, for example, capacitances for temporary storage of the charges released from the conversion layer 2, as well as a switch (thin-film transistor) which permits controlled readout of the charge signals via lines extending as rows and columns over the surface of the detector element.
  • the space remaining free between the substrate 7 and the conversion layer 2 is filled with a passivation layer 5.
  • the structure of the detector element outlined only roughly above, is described in more detail, for example, in US 5 396 072.
  • a voltage is applied between the reference electrode 1 and the collecting electrodes 4, an electric field is formed in the conversion layer 2, the field lines 3 of which are schematically indicated in Fig. 1.
  • the electric field 3 ensures that free charges produced by x-ray quanta X are dissipated toward the collecting electrodes 4 (or toward the reference electrode 1). Since the collecting electrodes 4 have a space between them in their edge regions 8 for the purpose of mutual electrical insulation, however, the electric field is inhomogeneous and attenuated in these regions.
  • the regions 8 with a lower electric field strength can lead to charge accumulation, since charges located there are dissipated more slowly.
  • the resulting delayed residual signal affects image signals being read out subsequently, and can lead to perturbing artifacts such as ghosting in the final image of the detector element.
  • a detector element according to the invention as represented in Fig. 2, is proposed in order to overcome the described problem.
  • the same reference numbers as in Fig. 1 refer to the same elements here. Essentially, only the collecting electrodes 4 are altered compared with the structure in Fig. 1, so that the other components of the detector element need not be described again.
  • the collecting electrodes 4 are constructed integrally from two electrode parts connected electrically and mechanically to each other. These are firstly the main electrode 4a, which has essentially the same shape as the (complete) collecting electrodes 4 of a conventional detector element according to Fig. 1.
  • a secondary electrode 4b which has a recumbent L-shape in the cross section shown here, is fitted to the left-hand edge of each primary electrode 4a in Fig. 2.
  • the secondary electrode 4b extends essentially in a plane parallel to the lower side of the conversion layer 2, or the plane of the main electrodes 4a, while being at a distance h from the adjacent collecting electrode.
  • the secondary electrode 4b furthermore covers the distance ⁇ in the edge region 8, which is left between the main electrodes 4a as seen from the viewing direction of the surface normal n of the conversion layer 2.
  • the edge region 8 between two collecting electrodes 4, which is covered by the secondary electrodes 4b, is filled with a passivation material 9 so that there is reliable electrical insulation between the neighboring collecting electrodes 4.
  • a passivation material 9 so that there is reliable electrical insulation between the neighboring collecting electrodes 4.
  • the effect of this, on the one hand, is that the entire lower side of the conversion layer 2 is effectively covered by collecting electrodes without interruption 4 (100% coverage), so that none of this area is lost with regard to the detection of x-radiation. It is furthermore particularly important that the electric field 3 can now extend homogeneously throughout the conversion layer 2, from the reference electrode 1 to the collecting electrodes 4.
  • FIG. 3 shows a plan view of a detail of a detector element according to Fig. 2, from the viewing direction of the surface normal n, the reference electrode 1 and the conversion layer 2 being omitted, or transparent.
  • Nine matricially arranged collecting electrodes 4 can be seen in Fig. 3, each of which consists of a main electrode 4a and a secondary electrode 4b, L-shaped in plan view, fitted to two neighboring edges of the main electrode 4a.
  • Such collecting electrodes 4 may be arranged overlapping one another in a similar way to fish scales or roof tiles in the sensitive area of the detector element.
  • a passivation layer 9 can furthermore be seen in Fig. 3. It is deposited in the edge region 8 over the spacing gaps ⁇ between the main electrodes 4a during the production of the detector element, and it covers an edge region of the main electrodes. A metal contact forming the secondary electrodes 4b is then deposited on the passivation layer 9, so that it is has contact with only one of the neighboring main electrodes 4a. Production of a detector element according to the invention may in principle be carried out with the same techniques as the production of known FDXD detectors.
  • the main advantages of the detector element are the reduction of temporal artifacts (image lag) by virtue of avoiding regions with a low field strength, efficient collection and extraction of the signal charge produced by x-radiation, and 100% coverage of the sensitive area.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Measurement Of Radiation (AREA)

Abstract

La présente invention se rapporte à un élément détecteur de rayonnement électromagnétique, comportant une couche de conversion (2) assurant la conversion de quanta de rayons X en signaux électriques, une électrode de référence (1) étant prévue sur la face supérieure de la couche de conversion (2) et des électrodes collectrices (4) étant disposées de façon matricielle sur la face inférieure. Les électrodes collectrices (4) constituées d'une électrode principale (4a) et d'une électrode secondaire (4b) sont imbriquées. Par conséquent, le champ électrique (3) créé entre l'électrode de référence (1) et les électrodes collectrices (4) par application d'une tension est homogène dans l'ensemble de la couche de conversion (2), ce qui évite des artefacts temporels dus à l'écoulement de charges avec retard. En outre, la zone sensible est entièrement couverte par les électrodes collectrices (4).
PCT/IB2004/050419 2003-04-24 2004-04-13 Element detecteur pour rayons x WO2004095580A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP03101127.3 2003-04-24
EP03101127 2003-04-24

Publications (1)

Publication Number Publication Date
WO2004095580A1 true WO2004095580A1 (fr) 2004-11-04

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4740824A (en) * 1985-07-18 1988-04-26 Kabushiki Kaisha Toshiba Solid-state image sensor
US5396072A (en) * 1992-08-17 1995-03-07 U. S. Philips Corporation X-ray image detector
US5895936A (en) * 1997-07-09 1999-04-20 Direct Radiography Co. Image capture device using a secondary electrode
US6172369B1 (en) * 1995-07-31 2001-01-09 Ifire Technology, Inc. Flat panel detector for radiation imaging with reduced trapped charges

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4740824A (en) * 1985-07-18 1988-04-26 Kabushiki Kaisha Toshiba Solid-state image sensor
US5396072A (en) * 1992-08-17 1995-03-07 U. S. Philips Corporation X-ray image detector
US6172369B1 (en) * 1995-07-31 2001-01-09 Ifire Technology, Inc. Flat panel detector for radiation imaging with reduced trapped charges
US5895936A (en) * 1997-07-09 1999-04-20 Direct Radiography Co. Image capture device using a secondary electrode

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