Patent Publication Number: US-11644583-B2

Title: X-ray detectors of high spatial resolution

Description:
TECHNICAL FIELD 
     The disclosure herein relates to X-ray detectors, particularly relates to X-ray detectors capable of high spatial resolution of charge carriers. 
     BACKGROUND 
     X-ray detectors may be an apparatus used to measure the flux, spatial distribution, spectrum or other properties of X-rays. 
     X-ray detectors may be used for many applications. One important application is imaging. X-ray imaging is a radiography technique and can be used to reveal the internal structure of a non-uniformly composed and opaque object such as the human body. Another important application is elemental analysis. Elemental analysis is a process where a sample of some material is analyzed for its elemental composition. 
     Early X-ray detectors include photographic plates and photographic films. A photographic plate may be a glass plate with a coating of light-sensitive emulsion. 
     In the 1980s, photostimulable phosphor plates (PSP plates) became available. A PSP plate may contain a phosphor material with color centers in its lattice. When the PSP plate is exposed to X-ray, electrons excited by X-ray are trapped in the color centers until they are stimulated by a laser beam scanning over the plate surface. As the plate is scanned by laser, trapped excited electrons give off light, which is collected by a photomultiplier tube. The collected light is converted into a digital image. 
     Another kind of X-ray detectors are X-ray image intensifiers. In an X-ray image intensifier, X-ray first hits an input phosphor (e.g., cesium iodide) and is converted to visible light. The visible light then hits a photocathode (e.g., a thin metal layer containing cesium and antimony compounds) and causes emission of electrons. The number of emitted electrons is proportional to the intensity of the incident X-ray. The emitted electrons are projected, through electron optics, onto an output phosphor and cause the output phosphor to produce a visible-light image. 
     Scintillators operate somewhat similarly to X-ray image intensifiers in that scintillators (e.g., sodium iodide) absorb X-ray and emit visible light, which can then be detected by a suitable image sensor for visible light. 
     Semiconductor X-ray detectors can directly convert X-ray into electric signals and thus offer better performance than previous generations of X-ray detectors. A semiconductor X-ray detector may include a semiconductor layer that absorbs X-ray in wavelengths of interest. When an X-ray photon is absorbed in the semiconductor layer, multiple charge carriers (e.g., electrons and holes) are generated. As used herein, the term “charge carriers,” “charges” and “carriers” are used interchangeably. A semiconductor X-ray detector may have multiple pixels that can independently determine the local intensity of X-ray and X-ray photon energy. The charge carriers generated by an X-ray photon may be swept under an electric field into the pixels. If the charge carriers generated by a single X-ray photon are collected by more than one pixel (“charge sharing”), the performance of the semiconductor X-ray detector may be negatively impacted. In applications (e.g., elemental analysis) where X-ray photon energy is determined, charge sharing is especially problematic for accurate photon energy measurement, because the energy of an X-ray photon is determined by the amount of electric charges it generates. Charge sharing can also be problematic when the location of an incident X-ray photon is to be determined. 
     SUMMARY 
     The teachings disclosed herein relate to apparatus, systems and methods for X-ray detection. More particularly, the present teachings relate to apparatus, systems and methods by X-ray detectors capable of spatial resolution of charge carriers. 
     In one example, an apparatus suitable for detecting X-ray is disclosed. The apparatus comprises: an X-ray absorption layer and a mask; wherein the mask comprises a first window and a second window, and a portion between the first window and the second window; wherein the first and second windows are not opaque to an incident X-ray; wherein the portion is opaque to the incident X-ray; and wherein the first and second windows are arranged such that charge carriers generated in the X-ray absorption layer by an X-ray photon propagating through the first window and charge carriers generated in the X-ray absorption layer by an X-ray photon propagating through the second window do not spatially overlap. 
     According to an embodiment, the first window and the second window are nearest neighbors. 
     According to an embodiment, the apparatus further comprises a first set of one or more electrodes configured to receive a signal from the incident X-ray propagating through the first window, and a second set of one or more electrodes configured to receive a signal from the incident X-ray propagating through the second window. 
     According to an embodiment, receiving the signal comprises collecting charge carriers generated by the incident X-ray. 
     According to an embodiment, the first window or the second window or both comprises one or more through holes or one or more blind holes or a combination thereof. 
     According to an embodiment, the first window or the second window or both comprises one or more through slots or one or more blind slots or a combination thereof. 
     According to an embodiment, the first window or the second window or both comprises a material different from a material of the portion. 
     According to an embodiment, the mask comprises a metal. 
     Disclosed herein is a system comprising the apparatus described above and an X-ray source. The system is configured for performing X-ray radiography on human chest or abdomen. 
     Disclosed herein is a system comprising the apparatus described above and an X-ray source. The system is configured for performing X-ray radiography on human mouth. 
     Disclosed herein is a cargo scanning or non-intrusive inspection (NII) system, comprising the apparatus described above and an X-ray source. The cargo scanning or non-intrusive inspection (NII) system is configured for forming an image based on backscattered X-ray. 
     Disclosed herein is a cargo scanning or non-intrusive inspection (NII) system, comprising the apparatus described above and an X-ray source. The cargo scanning or non-intrusive inspection (NII) system is configured to form an image using X-ray transmitted through an object inspected. 
     Disclosed herein is a full-body scanner system comprising the apparatus described above and an X-ray source. 
     Disclosed herein is an X-ray computed tomography (X-ray CT) system comprising the apparatus described above and an X-ray source. 
     Disclosed herein is an electron microscope comprising the apparatus described above, an electron source and an electronic optical system. 
     Disclosed herein is a system comprising the apparatus described above. The system is configured for measuring dose of an X-ray source. 
     Disclosed herein is a system comprising the apparatus described above. The system is an X-ray telescope, an X-ray microscopy, an X-ray micro-CT system, or a system configured to perform mammography, industrial defect detection, microradiography, casting inspection, weld inspection, or digital subtraction angiography. 
     In another example, a method of using an aforementioned apparatus is disclosed. The method comprises: placing the apparatus at a plurality of positions relative to a scene; obtaining data with the apparatus at the plurality of positions; compiling an image of the scene from the data. 
     According to an embodiment, obtaining data comprises moving the apparatus relative to the scene. 
     According to an embodiment, obtaining data further comprises moving the scene relative to the apparatus. 
     According to an embodiment, obtaining data further comprises moving a lens relative to the scene and the apparatus. 
     According to an embodiment, obtaining data in the above method further comprises measuring intensity of incident X-ray propagating through each of the windows 
     Additional advantages and novel features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The advantages of the present teachings may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  schematically shows a cross-sectional view of the detector, according to an embodiment. 
         FIG.  1 B  schematically shows a detailed cross-sectional view of the detector, according to an embodiment. 
         FIG.  1 C  schematically shows an alternative detailed cross-sectional view of the detector, according to an embodiment. 
         FIG.  2 A  shows an exemplary top view of a portion of a semiconductor X-ray detector, according to an embodiment. 
         FIG.  2 B  schematically shows that charge carriers generated by an X-ray photon diffuse as they drift. 
         FIG.  2 C  schematically shows that an X-ray photon may cause X-ray fluorescence and that the fluorescent X-ray may generate charge carriers. 
         FIG.  3 A  schematically shows an exemplary X-ray detector capable of spatial resolution of charge carriers, according to an embodiment. 
         FIG.  3 B  schematically shows another exemplary X-ray detector capable of spatial resolution of charge carriers, according to an embodiment. 
         FIG.  3 C  schematically another exemplary X-ray detector capable of spatial resolution of charge carriers, according to an embodiment. 
         FIG.  4 A  schematically shows an exemplary top view of an X-ray detector capable of spatial resolution of charge carriers, according to an embodiment. 
         FIG.  4 B  schematically shows another exemplary top view of an X-ray detector capable of spatial resolution of charge carriers, according to an embodiment. 
         FIG.  5    schematically shows an exemplary method of using an X-ray detector capable of spatial resolution of charge carriers, according to an embodiment. 
         FIG.  6 A  schematically shows an exemplary method of using an X-ray detector capable of spatial resolution of charge carriers by moving the X-ray detector relative to the scene, according to an embodiment. 
         FIG.  6 B  schematically shows another exemplary method of using an X-ray detector capable of spatial resolution of charge carriers by moving the scene relative to the X-ray detector, according to an embodiment. 
         FIG.  6 C  schematically shows another exemplary method of using an X-ray detector capable of spatial resolution of charge carriers by moving the lens, according to an embodiment. 
         FIG.  7    schematically shows a system comprising the X-ray detector described herein, suitable for medical imaging such as chest X-ray radiography, abdominal X-ray radiography, etc., according to an embodiment. 
         FIG.  8    schematically shows a system comprising the X-ray detector described herein suitable for dental X-ray radiography, according to an embodiment. 
         FIG.  9    schematically shows a cargo scanning or non-intrusive inspection (NII) system comprising the X-ray detector described herein, according to an embodiment. 
         FIG.  10    schematically shows another cargo scanning or non-intrusive inspection (NII) system comprising the X-ray detector described herein, according to an embodiment. 
         FIG.  11    schematically shows a full-body scanner system comprising the X-ray detector described herein, according to an embodiment. 
         FIG.  12    schematically shows an X-ray computed tomography (X-ray CT) system comprising an X-ray detector described herein, according to an embodiment. 
         FIG.  13    schematically shows an electron microscope comprising the X-ray detector described herein, according to an embodiment. 
         FIG.  14    schematically shows an X-ray microscope or an X-ray micro-CT system, according to an embodiment. 
         FIG.  15    schematically shows an X-ray microscope or an X-ray micro-CT system, according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings. 
     When an X-ray photon is absorbed in a semiconductor layer of an X-ray detector having an array of pixels, multiple charge carriers (e.g., electrons and holes) are generated and may be swept under an electric field towards circuitry for measuring these charge carriers. The carriers drift along the direction of the electric field and diffuse in other directions. The envelope of carrier trajectories can be roughly a conical shape. If the envelope sits on a boundary of two or more pixels of the X-ray detector, charge sharing occurs (“charge sharing” used in the present teachings means charge carriers generated from a single X-ray photon are collected by two or more pixels). Charge sharing may cause inaccurate measurement of an X-ray photon, because the energy of the X-ray photon is determined by the amount of electric charges it generates. 
     In the present teachings, charge sharing between neighboring pixels is limited by the X-ray detector that is capable of limiting diffusion of charge carriers, so that a single X-ray photon is only collected by a single pixel in the X-ray detector. 
       FIG.  1 A  schematically shows a semiconductor X-ray detector  100 , according to an embodiment. The semiconductor X-ray detector  100  may include an X-ray absorption layer  110  and an electronics layer  120  (e.g., an ASIC) for processing or analyzing electrical signals incident X-ray generates in the X-ray absorption layer  110 . In an embodiment, the semiconductor X-ray detector  100  does not comprise a scintillator. The X-ray absorption layer  110  may include a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor may have a high mass attenuation coefficient for the X-ray energy of interest. 
     As shown in a detailed cross-sectional view of the detector  100  in  FIG.  1 B , according to an embodiment, the X-ray absorption layer  110  may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region  111 , one or more discrete regions  114  of a second doped region  113 . The second doped region  113  may be separated from the first doped region  111  by an optional the intrinsic region  112 . The discrete portions  114  are separated from one another by the first doped region  111  or the intrinsic region  112 . The first doped region  111  and the second doped region  113  have opposite types of doping (e.g., region  111  is p-type and region  113  is n-type, or region  111  is n-type and region  113  is p-type). In the example in  FIG.  1 B , each of the discrete regions  114  of the second doped region  113  forms a diode with the first doped region  111  and the optional intrinsic region  112 . Namely, in the example in  FIG.  1 B , the X-ray absorption layer  110  has a plurality of diodes having the first doped region  111  as a shared electrode. The first doped region  111  may also have discrete portions. 
     When an X-ray photon hits the X-ray absorption layer  110  including diodes, the X-ray photon may be absorbed and generate one or more charge carriers by a number of mechanisms. An X-ray photon may generate 10 to 100000 charge carriers. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The field may be an external electric field. The electrical contact  119 B may include discrete portions each of which is in electrical contact with the discrete regions  114 . In an embodiment, the charge carriers generated by a single X-ray photon can be shared by two different discrete regions  114 . 
     As shown in an alternative detailed cross-sectional view of the detector  100  in  FIG.  1 C , according to an embodiment, the X-ray absorption layer  110  may include a resistor of a semiconductor material such as, silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof, but does not include a diode. The semiconductor may have a high mass attenuation coefficient for the X-ray energy of interest. 
     When an X-ray photon hits the X-ray absorption layer  110  including a resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. An X-ray photon may generate 10 to 100000 charge carriers. The charge carriers may drift to the electrical contacts  119 A and  119 B under an electric field. The field may be an external electric field. The electrical contact  119 B includes discrete portions. In an embodiment, the charge carriers generated by a single X-ray photon can be shared by two different contacts  119 B. 
     The electronics layer  120  may include an electronic system  121  suitable for processing or interpreting signals generated by X-ray photons incident on the X-ray absorption layer  110 . The electronic system  121  may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessors, and memory. The electronic system  121  may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system  121  may include an amplifier dedicated to each pixel and a microprocessor shared among all the pixels. The electronic system  121  may be electrically connected to the pixels by vias  131 . Space among the vias may be filled with a filler material  130 , which may increase the mechanical stability of the connection of the electronics layer  120  to the X-ray absorption layer  110 . Other bonding techniques are possible to connect the electronic system  121  to the pixels without using vias. 
       FIG.  2 A  shows an exemplary top view of a portion of the apparatus  100  with a 4-by-4 array of discrete regions  114 . Charge carriers generated by an X-ray photon incident around the footprint of one of these discrete regions  114  are not substantially shared with another of these discrete regions  114 . The area  210  around a discrete region  114  in which substantially all (more than 95%, more than 98% or more than 99% of) charge carriers generated by an X-ray photon incident therein flow to the discrete region  114  is called a pixel associated with that discrete region  114 . Namely, less than 5%, less than 2% or less than 1% of these charge carriers flow beyond the pixel, when the X-ray photon hits inside the pixel. The pixels may be organized in any suitable array, such as, a square array, a triangular array and a honeycomb array. The pixels may have any suitable shape, such as, circular, triangular, square, rectangular, and hexangular. The pixels may be individually addressable. 
     Similarly, when the 4-by-4 array in  FIG.  2 A  indicates an array of discrete portions of the electrical contact  119 B in  FIG.  1 B , the charge carriers generated by an X-ray photon incident around the footprint of one of these discrete portions of the electrical contact  119 B are not substantially shared with another of these discrete portions of the electrical contact  119 B. The area around a discrete portion of the electrical contact  119 B in which substantially all (more than 95%, more than 98% or more than 99% of) charge carriers generated by an X-ray photon incident therein flow to the discrete portion of the electrical contact  119 B is called a pixel associated with the discrete portion of the electrical contact  119 B. Namely, less than 5%, less than 2% or less than 1% of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact  119 B, when the X-ray photon hits inside the pixel. The pixels may be organized in any suitable array, such as, a square array, a triangular array and a honeycomb array. The pixels may have any suitable shape, such as, circular, triangular, square, rectangular, and hexangular. The pixels may be individually addressable. 
     As shown in  FIG.  2 A , two pixels  210  (e.g.  210 - 1  and  210 - 2 ) associated with two neighboring discrete regions  114  can be called two neighboring pixels (“neighboring pixels” used in the present teachings means pixels that are close to each other such that carriers generated from a single photon may be shared by these pixels). 
       FIG.  2 B  shows an exemplary cross-sectional view of the detector with dispersing charge carriers according to an embodiment. In a semiconductor X-ray detector, charge carriers drift toward the pixels while diffuse in all directions. Regions  210 ,  211 ,  212  or  213  schematically show spaces that a group of carriers occupy as they drift toward the pixels under an electric field into the pixels. 
       FIG.  2 C  shows that an incident X-ray photon can generate X-ray fluorescence. Namely, secondary X-ray photons such as  201 ,  202 , and  203  may be generated and they can generate additional charge carriers at locations relatively far away from where the incident photon hits. 
     The incident X-ray photon and the secondary X-ray photons can be absorbed and cause multiple charge carriers to be generated. The charge carriers may move in various directions, e.g. drift along the direction of an electric field and diffuse in other directions. In  FIG.  2 C , each circle, e.g.  2011 ,  2012 ,  2013 ,  2021 ,  2022 ,  2023 ,  2031 ,  2032  and  2033 , represents the footprint of a region of charge carriers generated by a photon occupy at a point of time. 
       FIG.  2 C  also illustrates a mechanism of charge sharing. A region the charge carriers occupy may be inside a pixel, or on a boundary of neighboring pixels (e.g. region  2033 ). 
     As discussed above, when a region that the charge carriers occupy is over a boundary of two or more neighboring pixels, charge sharing occurs, which may cause issue for energy measurement. In an embodiment, the electronic system  121  in an X-ray detector can still accurately measure the energy of an X-ray photon even if a charge sharing occurs to the carriers generated by the X-ray photon. 
     According to an embodiment, two neighboring pixels do not have to share a boundary, but can be close to each other such that carriers generated from a single photon may be shared by the two pixels. That is, charge sharing may occur on neighboring pixels, even if there is not a boundary shared by the neighboring pixels. 
     If the size of a pixel is too small, e.g. smaller than a region the charge carriers occupy when the charge carriers reach the pixel, charge sharing can happen all the time. On the other hand, if the size of a pixel is too large, it is very likely for multiple photons to hit the pixel at the same time, which can generate difficulty for accurate X-ray detection and image generation. 
       FIG.  3 A  schematically shows a semiconductor X-ray detector  100 , according to an embodiment. The semiconductor X-ray detector  100  can include an X-ray absorption layer  110  described above and a mask  301 . The mask  301  may include multiple windows such as a window  3010  and a window  3011 , and a portion  3012  separating the windows from one another. The window  3010  is the nearest neighbor of window  3011 . As used herein, a window A being the nearest neighbor of a window B means that no other window is closer to window B than window A is. The distance between two windows may be the center-to-center distance. As used herein, a center of a window is defined as the center of the three dimensional space within the window. 
     The windows are not opaque to an incident X-ray. For example, the windows may have an X-ray transmissivity of at least 80% or at least 90%. 
     The portion that separates the windows is essentially opaque to the incident X-ray. For example, the portion may have an X-ray transmissivity of at most 20% or at most 10%. 
     The windows  3010  and  3011  are arranged such that charge carriers generated in the X-ray absorption layer  110  by an X-ray photon propagating through the window  3010  and charge carriers generated in the X-ray absorption layer  110  by an X-ray photon propagating through the window  3011  do not spatially overlap. 
     Multiple electrical contacts  119 B may be configured to receive a signal (e.g., detect charge carriers generated) from an X-ray photon propagating through a single window, as schematically shown in  FIG.  3 A . In one example, a first set  119 B 1  among the electrical contacts  119 B is configured to receive a signal from the incident X-ray propagating through the window  3010 ; and a second set  11962  among the electrical contacts  119 B is configured to receive a signal from the incident X-ray propagating through the window  3011 . 
     According to an embodiment, receiving the signal may include collecting charge carriers generated by the incident X-ray. When multiple electrical contacts are used to receive a signal from a single photon transmitting through a window, the signals received may be combined to arrive at the total signal from the single photon. For example, the amounts of charge carriers received by the set  119 B 1  may be summed to arrive at the total amount of charge carriers generated by a photon through the window  3010 . Because the windows  3010  and  3011  are arranged such that charge carriers generated through each window do not have spatial overlap, all the signals received by the set  119 B 1  must be from a photon incident on the detector at the window  3010  and all the signals received by the set  11962  must be from a photon incident on the detector at the window  3011 . 
     It is conceivable that various arrangements of the electrical contacts  119 B may be provided for the X-ray detector  100 . For example, as schematically shown in  FIG.  3 B , a single electrical contact  119 B 1  and  11962  are configured to respectively receive essentially all signal from an X-ray photon transmitted through the window  3010  and the window  3011 . The single electrical contact  119 B 1  and  11962  can be almost as large as the spacing between the windows  3010  and  3011  but are not necessarily that large.  FIG.  3 C  schematically shows that the mask  301  may be part of the electrical contacts  119 A. 
     The windows in the mask  301  may have any suitable shapes and arrangements. For example, the windows may have regular shapes or irregular shapes, such as round, rectangular, square, polygonal, slot or other irregular shapes. For example, the windows may be arranged in a two-dimensional array with equal or unequal window-to-window distance. One such example is schematically shown in  FIG.  4 A . The windows may be arranged in a tandem sequence, i.e., a one-dimensional array with equal or unequal window-to-window distance. One such example is schematically shown in  FIG.  4 B . The two-dimensional array arrangement of the windows may be used where spatial resolution in both directions of a scene is needed. The one-dimensional array arrangement of the windows may be used where spatial resolution in one direction of a scene is needed. 
     The mask  301  may be a metal (e.g., gold, platinum) film or other suitable materials that are efficient in blocking X-ray. 
     According to an embodiment, the windows may be blind holes, i.e. the materials in the space occupied by the windows can be partially removed by a suitable method such as etching, reaming, drilling, or milling, without breaking through to the other side of the mask. 
     According to an embodiment, the windows may be through holes, i.e. the materials in the space occupied by the windows can be completely removed by a suitable method such as etching, reaming, drilling, or milling, such that the windows are open to the both sides of the mask. The windows of one mask may be a mixture of blind holes and through holes. The windows may be patterned using a suitable technique such as a stencil or lithography. 
     The windows may be left unfilled or partially or completely filled with a material different from the rest of the mask. 
     The windows may be filled with a different material from that of the mask after being formed into either a blind hole or a through hole, and as such, the window and the portion are of different materials. For example, the filling material for the window may be aluminum. 
       FIG.  5    schematically shows a method of using the detector disclosed above. The method may include: placing the detector at a plurality of positions relative to a scene; obtaining data with the detector at the plurality of positions; compiling an image of the scene from the data. 
     As shown in  FIG.  6 A , obtaining data in the above method may include moving the detector  100  relative to the scene  60 . 
     As shown in  FIG.  6 B , obtaining data in the above method may include moving the scene  60  relative to the detector  100 . 
     As shown in  FIG.  6 C , an optical system such as a lens  61  is used to form the scene  60 , and obtaining data in the above method may include moving the lens  61  relative to the detector  100  and the scene  60 . 
     The image may be formed by measuring intensity of incident X-ray propagating through each of the windows. 
     Various exemplary embodiments of applications of the above X-ray detector are provided below. 
       FIG.  7    schematically shows a system comprising the semiconductor X-ray detector  100  described herein. The system may be used for medical imaging such as chest X-ray radiography, abdominal X-ray radiography, etc. The system comprises an X-ray source  1201 . X-ray emitted from the X-ray source  1201  penetrates an object  1202  (e.g., a human body part such as chest, limb, abdomen), is attenuated by different degrees by the internal structures of the object  1202  (e.g., bones, muscle, fat and organs, etc.), and is projected to the semiconductor X-ray detector  100 . The semiconductor X-ray detector  100  forms an image by detecting the intensity distribution of the X-ray. 
       FIG.  8    schematically shows a system comprising the semiconductor X-ray detector  100  described herein. The system may be used for medical imaging such as dental X-ray radiography. The system comprises an X-ray source  1301 . X-ray emitted from the X-ray source  1301  penetrates an object  1302  that is part of a mammal (e.g., human) mouth. The object  1302  may include a maxilla bone, a palate bone, a tooth, the mandible, or the tongue. The X-ray is attenuated by different degrees by the different structures of the object  1302  and is projected to the semiconductor X-ray detector  100 . The semiconductor X-ray detector  100  forms an image by detecting the intensity distribution of the X-ray. Teeth absorb X-ray more than dental caries, infections, periodontal ligament. The dosage of X-ray radiation received by a dental patient is typically small (around 0.150 mSv for a full mouth series). 
       FIG.  9    schematically shows a cargo scanning or non-intrusive inspection (NII) system comprising the semiconductor X-ray detector  100  described herein. The system may be used for inspecting and identifying goods in transportation systems such as shipping containers, vehicles, ships, luggage, etc. The system comprises an X-ray source  1401 . X-ray emitted from the X-ray source  1401  may backscatter from an object  1402  (e.g., shipping containers, vehicles, ships, etc.) and be projected to the semiconductor X-ray detector  100 . Different internal structures of the object  1402  may backscatter X-ray differently. The semiconductor X-ray detector  100  forms an image by detecting the intensity distribution of the backscattered X-ray and/or energies of the backscattered X-ray photons. 
       FIG.  10    schematically shows another cargo scanning or non-intrusive inspection (NII) system comprising the semiconductor X-ray detector  100  described herein. The system may be used for luggage screening at public transportation stations and airports. The system comprises an X-ray source  1501 . X-ray emitted from the X-ray source  1501  may penetrate a piece of luggage  1502 , be differently attenuated by the contents of the luggage, and projected to the semiconductor X-ray detector  100 . The semiconductor X-ray detector  100  forms an image by detecting the intensity distribution of the transmitted X-ray. The system may reveal contents of luggage and identify items forbidden on public transportation, such as firearms, narcotics, edged weapons, flammables. 
       FIG.  11    schematically shows a full-body scanner system comprising the semiconductor X-ray detector  100  described herein. The full-body scanner system may detect objects on a person&#39;s body for security screening purposes, without physically removing clothes or making physical contact. The full-body scanner system may be able to detect non-metal objects. The full-body scanner system comprises an X-ray source  1601 . X-ray emitted from the X-ray source  1601  may backscatter from a human  1602  being screened and objects thereon, and be projected to the semiconductor X-ray detector  100 . The objects and the human body may backscatter X-ray differently. The semiconductor X-ray detector  100  forms an image by detecting the intensity distribution of the backscattered X-ray. The semiconductor X-ray detector  100  and the X-ray source  1601  may be configured to scan the human in a linear or rotational direction. 
       FIG.  12    schematically shows an X-ray computed tomography (X-ray CT) system comprising the semiconductor X-ray detector  100  described herein. The X-ray CT system uses computer-processed X-rays to produce tomographic images (virtual “slices”) of specific areas of a scanned object. The tomographic images may be used for diagnostic and therapeutic purposes in various medical disciplines, or for flaw detection, failure analysis, metrology, assembly analysis and reverse engineering. The X-ray CT system comprises the semiconductor X-ray detector  100  described herein and an X-ray source  1701 . The semiconductor X-ray detector  100  and the X-ray source  1701  may be configured to rotate synchronously along one or more circular or spiral paths. 
       FIG.  13    schematically shows an electron microscope comprising the semiconductor X-ray detector  100  described herein. The electron microscope comprises an electron source  1801  (also called an electron gun) that is configured to emit electrons. The electron source  1801  may have various emission mechanisms such as thermionic, photocathode, cold emission, or plasmas source. The emitted electrons pass through an electronic optical system  1803 , which may be configured to shape, accelerate, or focus the electrons. The electrons then reach a sample  1802  and an image detector may form an image therefrom. The electron microscope may comprise the semiconductor X-ray detector  100  described herein, for performing energy-dispersive X-ray spectroscopy (EDS). EDS is an analytical technique used for the elemental analysis or chemical characterization of a sample. When the electrons incident on a sample, they cause emission of characteristic X-rays from the sample. The incident electrons may excite an electron in an inner shell of an atom in the sample, ejecting it from the shell while creating an electron hole where the electron was. An electron from an outer, higher-energy shell then fills the hole, and the difference in energy between the higher-energy shell and the lower energy shell may be released in the form of an X-ray. The number and energy of the X-rays emitted from the sample can be measured by the semiconductor X-ray detector  100 . 
       FIG.  14    schematically shows an X-ray microscope or an X-ray micro-CT system  1900  comprising the semiconductor X-ray detector  100  described herein, according to an embodiment. The X-ray microscope  1900  may include an X-ray source  1901 , a focusing optics  1904 , and the detector  100  for detecting the resulting X-ray image of the sample  1902 . 
     The X-ray source  1901  may be a microfocus X-ray source with a size of 5 to 20 μm. The focusing optics  1904  may help to focus the X-ray irradiated from the X-ray source  1901  into a focal point  1905 , which forms a tiny virtual source. The focal point  1905  may have a size of 1 to 100 nm. 
     The sample  1902  may be mounted on a sample holder  1903 . The sample holder  1903  may be configured to move or rotate the sample  1902 . For example the sample holder  1903  may include a piezoelectric driver. 
     In an example shown in  FIG.  15   , the X-ray source  1901  may include one or more sub-sources (e.g., highly collimated X-ray beams). The sub-sources may be configured to illuminate portions of the sample  1902  and generate sub-images  1909  of these portions. One way to generate the sub-sources is by using a two-dimensional grating. The portions may be spatially non-overlapping with one another. The sub-images may be spatially non-overlapping with one another. The detector  100  may be configured such that its windows are aligned with at least some of the sub-images. The sub-sources (e.g., beams scanning) and the detector  100  may be moved in a way to capture a sub-image of every portion of the sample  1902 . This configuration allows reduced exposure to X-ray by not illuminating a portion of the sample where an image of that portion is not to be captured by the detector  100 . 
     The focusing optics  1904  may be a Fresnel zone plate. A Fresnel zone plate, like most refractive optics that can be used as the focusing optics  1904 , has chromatic aberration. Therefore, focal lengths of the Fresnel zone plate are different for X-rays with different wavelengths or frequencies. In this case, the focal point  1905  is determined with respect to X-rays with a predetermined wavelength or a predetermined small range of wavelengths. 
     The focusing optics  1904  may be a focusing optics based on multi-reflections. In this case, the focal point  1905  is determined with respect to X-rays with all wavelengths of interest. 
     The sample  302  may be a piece of life organ or tissue, with a thickness of 100 μm or below. The sample  1902  may be placed close to the focal point  1905 , either on the side closer to the detector  100 , or on the side closer to the X-ray source  1901 . 
     The detector  100  may be able to resolve energy of the incident X-ray photons but does not necessarily have that capability. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.