Patent Description:
Radiation detectors may be used for many applications. One important application is imaging. Radiation 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.

Early radiation detectors for imaging include photographic plates and photographic films. A photographic plate may be a glass plate with a coating of light-sensitive emulsion. Although photographic plates were replaced by photographic films, they may still be used in special situations due to the superior quality they offer and their extreme stability. A photographic film may be a plastic film (e.g., a strip or sheet) with a coating of light-sensitive emulsion.

In the <NUM>, 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 radiation, electrons excited by radiation 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. In contrast to photographic plates and photographic films, PSP plates can be reused.

Another kind of radiation detectors are radiation image intensifiers. Components of a radiation image intensifier are usually sealed in a vacuum. In contrast to photographic plates, photographic films, and PSP plates, radiation image intensifiers may produce real-time images, i.e., do not require post-exposure processing to produce images. Radiation 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 radiation. 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 radiation image intensifiers in that scintillators (e.g., sodium iodide) absorb radiation and emit visible light, which can then be detected by a suitable image sensor for visible light. In scintillators, the visible light spreads and scatters in all directions and thus reduces spatial resolution. Reducing the scintillator thickness helps to improve the spatial resolution but also reduces absorption of radiation. A scintillator thus has to strike a compromise between absorption efficiency and resolution.

Semiconductor radiation detectors largely overcome this problem by direct conversion of radiation into electric signals. A semiconductor radiation detector may include a semiconductor layer that absorbs radiation in wavelengths of interest. When a particle of radiation is absorbed in the semiconductor layer, multiple charge carriers (e.g., electrons and holes) are generated and swept under an electric field towards electrical contacts on the semiconductor layer.

<CIT> discloses an image sensor comprising a plurality of X-ray detectors and an actuator configured to move the plurality of X-ray detectors to a plurality of position. The image sensor is configured to capture, by using the detectors, images of portions of a scene at the positions, respectively, and configured to form an image of the scene by stitching the images of the portions.

<CIT> discloses an x-ray scanner includes an x-ray source producing a fan of X-rays, an X-ray detector array, a collimator between the source and array which is fixed to the source and defines one or more slits collimating the X-ray fan into a linear X-ray beam. The array is spaced from the source such that a linear extent of the linear X-ray beam is no greater than a detector dimension of the array.

An X-ray processing unit processes detection of the linear X-ray beam by the array. A processor-controlled motor moves the X-ray source about a source movement axis to pan the linear X-ray beam and create an X-ray emission cone and moves the array correspondingly with the source. The X-ray processing unit form an X-ray scanned image of an object disposed between the collimator and the array within the X-ray emission cone when the linear X-ray beam is panned across the object.

<CIT> discloses a system for spectroscopic imaging of bodily tissue in which a scintillation screen and a charged coupled device (CCD) are used to accurately image selected tissue. An x-ray source generates x-rays which pass through a region of a subject's body, forming an x-ray image which reaches the scintillation screen.

The scintillation screen reradiates a spatial intensity pattern corresponding to the image, the pattern being detected by a CCD sensor. The image is digitized by the sensor and processed by a controller before being stored as an electronic image. Each image is directed onto an associated respective CCD or amorphous silicon detector to generate individual electronic representations of the separate images.

According to an aspect of the present invention, there an image sensor according to claim <NUM>, comprising: a plurality of radiation detectors; a mask with a plurality of radiation transmitting zones and a radiation blocking zone; and an actuator configured to move the plurality of radiation detectors from a first position to a second position and to move the mask from a third position to a fourth position; wherein while the radiation detectors are at the first position and the mask is at the third position and while the radiation detectors are at the second position and the mask is at the fourth position, the radiation blocking zone is configured to block radiation from a radiation source that would otherwise be incident on a dead zone of the image sensor and the radiation transmitting zones are configured to allow at least a portion of radiation from the radiation source that would be incident on active areas of the image sensor to pass through; wherein the actuator comprises a linear motor and a linkage; wherein the linear motor is configured to move the radiation detectors from the first position to the second position; and wherein the linkage couples the mask to the radiation detectors such that movement of the radiation detectors from the first position to the second position causes the mask to move from the third position to the fourth position.

According to an embodiment, the image sensor is configured to capture, by using the radiation detectors, an image of a first portion of a scene when the radiation detectors are at the first position and the image sensor is configured to capture, by using the radiation detectors, an image of a second portion of a scene when the radiation detectors are at the second position, wherein the image sensor is configured to form an image of the scene by stitching the image of the first portion and the image of the second portion.

According to an embodiment, the plurality of radiation detectors are spaced apart.

According to an embodiment, the image sensor further comprises a shutter configured to block the radiation from the radiation source during movement of the radiation detectors.

According to an embodiment, at least some of the plurality of radiation detectors are arranged in staggered rows.

According to an embodiment, radiation detectors in a same row are uniform in size; wherein a distance between two neighboring radiation detectors in a same row is greater than a width of one radiation detector in the same row in an extending direction of the row and is less than twice that width.

According to an embodiment, active areas of the radiation detectors tessellate the scene at the positions.

According to an embodiment, at least some of the plurality of radiation detectors comprise multiple layers of detectors.

According to an embodiment, at least some of the plurality of radiation detectors are rectangular in shape.

According to an embodiment, at least some of the plurality of radiation detectors are hexagonal in shape.

According to an embodiment, at least one of the plurality of radiation detectors comprises a radiation absorption layer and an electronics layer; wherein the radiation absorption layer comprises an electrode; wherein the electronics layer comprises an electronics system; wherein the electronics system comprises: a first voltage comparator configured to compare a voltage of the electrode to a first threshold, a second voltage comparator configured to compare the voltage to a second threshold, a counter configured to register a number of particles of radiation reaching the radiation absorption layer, and a controller; wherein the controller is configured to start a time delay from a time at which the first voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the first threshold; wherein the controller is configured to activate the second voltage comparator during the time delay; wherein the controller is configured to cause the number registered by the counter to increase by one, if the second voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the second threshold.

According to an embodiment, the electronics system further comprises a capacitor module electrically connected to the electrode, wherein the capacitor module is configured to collect charge carriers from the electrode.

According to an embodiment, the controller is configured to activate the second voltage comparator at a beginning or expiration of the time delay.

According to an embodiment, the electronics system further comprises a voltmeter, wherein the controller is configured to cause the voltmeter to measure the voltage upon expiration of the time delay.

According to an embodiment, the controller is configured to determine energy of a particle of radiation based on a value of the voltage measured upon expiration of the time delay.

According to an embodiment, the controller is configured to connect the electrode to an electrical ground.

According to an embodiment, a rate of change of the voltage is substantially zero at expiration of the time delay.

According to an embodiment, a rate of change of the voltage is substantially non-zero at expiration of the time delay.

Disclosed herein is a system comprising the image sensor described herein and a radiation source, wherein the system is configured to perform radiography on human chest or abdomen.

Disclosed herein is a system comprising the image sensor described herein and a radiation source, wherein the system is configured to perform radiography on human mouth.

Disclosed herein is a cargo scanning or non-intrusive inspection (NII) system, comprising the image sensor described herein and a radiation source, wherein the cargo scanning or non-intrusive inspection (NII) system is configured to form an image using radiation transmitted through an object inspected.

Disclosed herein is a full-body scanner system comprising the image sensor described herein and a radiation source.

Disclosed herein is a radiation computed tomography (radiation CT) system comprising the image sensor described herein and a radiation source.

Disclosed herein is an electron microscope comprising the image sensor described herein, an electron source and an electronic optical system.

Disclosed herein is a system comprising the image sensor described herein, wherein the system is a radiation telescope, or a radiation microscopy, or wherein the system is configured to perform mammography, industrial defect detection, microradiography, casting inspection, weld inspection, or digital subtraction angiography.

<FIG> and <FIG> schematically show an image sensor <NUM>, according to an embodiment. The image sensor <NUM> may take images of different portions of a scene <NUM> while the image sensor <NUM> is at different positions (e.g., positions <NUM> and <NUM>) relative to the scene <NUM>. The image sensor <NUM> includes a plurality of radiation detectors <NUM>, a mask <NUM>, and an actuator <NUM>. The plurality of radiation detectors <NUM> may be configured to receive radiation from a radiation source <NUM> and through a portion of the scene <NUM>. The radiation detectors <NUM> of the image sensor <NUM> may be in one or more packages <NUM> that are mounted to a system printed circuit board (PCB) <NUM>.

<FIG> schematically shows a top view of one of packages <NUM> including one or more of the radiation detectors <NUM> and a PCB <NUM>, according to an embodiment. The term "PCB" as used herein is not limited to a particular material. For example, a PCB may include a semiconductor. The radiation detectors <NUM> in this package <NUM> are mounted to the PCB <NUM>. The wiring between the radiation detectors <NUM> and the PCB <NUM> is not shown for the sake of clarity. The PCB <NUM> may have an area not covered by the radiation detectors <NUM> (e.g., for accommodating bonding wires <NUM>). The radiation detectors <NUM> may each have an active area <NUM>. The active area <NUM> is sensitive to radiation. Radiation incident on the active area <NUM> may be detected by the radiation detectors <NUM>. The radiation detectors <NUM> may each have a perimeter zone <NUM> near the edges thereof. The perimeter zone <NUM> is not sensitive to incident radiation and the detectors <NUM> do not detect radiation incident on the perimeter zone <NUM>.

<FIG> schematically shows a cross-sectional view several packages <NUM> of the image sensor <NUM>, according to an embodiment. The electrical connection between the PCBs <NUM> in the packages <NUM> and the system PCB <NUM> may be made by bonding wires <NUM>. The PCB <NUM> may have an area <NUM> not covered by the radiation detectors <NUM> of the packages <NUM>, for example, to accommodate the bonding wires <NUM> on the PCB <NUM>. In an example, the packages <NUM> have gaps in between to accommodate the bonding wires <NUM> on the system PCB <NUM>. The gaps may be approximately <NUM> or more. Radiation incident on the perimeter zones <NUM>, on the area <NUM> or on the gaps cannot be detected by the radiation detectors <NUM> of the image sensor <NUM>. A dead zone of a radiation detector is the area of the radiation-receiving surface of the radiation detector, in which incident radiation cannot be detected by the radiation detector. A dead zone of a package (e.g., package <NUM>) is the area of the radiation-receiving surface of the package, in which incident radiation cannot be detected by the radiation detector or radiation detectors in the package. In this example shown in <FIG>, the dead zone of the package <NUM> includes the perimeter zones <NUM> and the area <NUM>. A dead zone (e.g., <NUM>) of the image sensor <NUM> with a group of packages (e.g., packages mounted on the same PCB, packages arranged in the same layer) includes the combination of the dead zones of the packages in the group and the gaps among the packages. An active area <NUM> of the image sensor <NUM> is the combination of the active areas <NUM> of the radiation detectors <NUM> in the image sensor <NUM>.

As schematically shown in <FIG> and <FIG>, the mask <NUM> has a plurality of radiation transmitting zones <NUM> and a radiation blocking zone <NUM>. The radiation blocking zone <NUM> prevents the radiation incident thereon from passing through, and the radiation transmitting zones <NUM> allow at least a portion of the radiation incident thereon to pass through. The radiation blocking zone <NUM> is aligned with the dead zone <NUM> of the image sensor <NUM>. The radiation blocking zone <NUM> is configured to block radiation from a radiation source (e.g., radiation source <NUM>) that would otherwise reach the dead zone <NUM>. For example, the radiation blocking zone <NUM> is configured to prevent radiation from the radiation source <NUM> that otherwise would reach the dead zone <NUM> from reaching the scene <NUM>. The radiation transmitting zones <NUM> are aligned with the active area <NUM> of the image sensor <NUM>. The radiation transmitting zones <NUM> allow at least a portion of radiation from a radiation source (e.g., radiation source <NUM>) to reach the active area <NUM>. The positions of the radiation transmitting zones <NUM> and the radiation blocking zone <NUM> may be fixed relative to the mask <NUM>. One example of the mask <NUM> may be a metal sheet with a thickness enough for blocking radiation with holes therein. The holes may be the radiation transmitting zones <NUM> and the rest of the metal sheet may be the radiation blocking zone <NUM>.

The actuator <NUM>, as shown in <FIG> and <FIG>, is configured to move the radiation detectors <NUM> and the mask <NUM> to a plurality of positions. The actuator <NUM> has one or multiple drivers (e.g., electric motors). The actuator <NUM> is configured to move the radiation detectors <NUM> and the mask <NUM> without relative movement. In the example shown in <FIG>, the radiation detectors <NUM> are at a first position <NUM>, and the mask <NUM> is at a third position <NUM>. In the example shown in <FIG>, the actuator <NUM> moves the radiation detectors <NUM> from the first position <NUM> to a second position <NUM> and moves the mask <NUM> from the third position <NUM> to a fourth position <NUM>. At each of the positions, the image sensor <NUM> takes an image of a portion of the scene <NUM>. Namely, an image of a first portion of the scene <NUM> is captured by the image sensor <NUM> by using the radiation detectors <NUM> when the radiation detectors <NUM> are at the first position <NUM> and an image of a second portion of the scene <NUM> is captured by the image sensor <NUM> when the radiation detectors <NUM> are at the second position <NUM>. The images of the portions may be then stitched to form an image of the scene <NUM>. The images of the portions may have overlap among one another to facilitate stitching.

According to the claimed invention, while the radiation detectors <NUM> are at the first position <NUM> and the mask <NUM> is at the third position <NUM> and while the radiation detectors <NUM> are at the second position <NUM> and the mask <NUM> is at the fourth position <NUM>, the radiation blocking zone <NUM> blocks radiation from the radiation source <NUM> that would otherwise be incident on the dead zone <NUM> of the image sensor <NUM> and the radiation transmitting zones <NUM> allow at least a portion of radiation from the radiation source <NUM> that would be incident on the active areas <NUM> of the image sensor <NUM> to pass through.

The actuator <NUM> may be positioned between the scene and the radiation source <NUM>, between the scene <NUM> and the image sensor <NUM>, or at another suitable position. The actuator <NUM> may be configured to move the mask <NUM> and the radiation detectors <NUM> among multiple positions at which the image sensor <NUM> captures images of the portions of the scene <NUM>, such that the alignment between the radiation detectors <NUM> with the mask <NUM> is maintained at each of these positions.

Examples of designs of the actuator <NUM> are schematically shown in <FIG>. According to an embodiment not forming part of the claimed invention, the actuator <NUM> may comprise a first linear motor <NUM> and a second linear motor <NUM>, which may engage the mask <NUM> and the radiation detectors <NUM> respectively, as shown in <FIG>. The first linear motor <NUM> is configured to move the radiation detectors <NUM>, for example, from the first position <NUM> to the second position <NUM>. The second linear motor <NUM> is configured to move the mask <NUM>, for example, from the third position <NUM> to the fourth position <NUM>.

According to the claimed invention, the actuator <NUM> comprises a linear motor <NUM> and a linkage <NUM>, which engages the radiation detectors <NUM> and the mask <NUM> respectively, or vice versa, as shown in <FIG>. In the example shown, the linear motor <NUM> is configured to move the radiation detectors <NUM> from the first position <NUM> to the second position <NUM>, and the linkage <NUM> couples the mask <NUM> to the radiation detectors <NUM> such that movement of the radiation detectors <NUM> from the first position <NUM> to the second position <NUM> causes the mask <NUM> to move from the third position <NUM> to the fourth position <NUM>. In another example not forming part of the claimed invention, the linear motor <NUM> is configured to move the mask <NUM>, for example, from the third position <NUM> to the fourth position <NUM>, and the linkage <NUM> couples the radiation detectors <NUM> to the mask <NUM> such that movement of the mask <NUM> from the third position <NUM> to the fourth position <NUM> causes the radiation detectors <NUM> to move from the first position <NUM> to the second position <NUM>. In yet another example not forming part of the claimed invention, the linear motor <NUM> may drive the linkage <NUM> and the linkage <NUM> drives the mask <NUM> and the radiation detectors <NUM>. For example, the linkage <NUM> causes the mask <NUM> to move from the third position <NUM> to the fourth position <NUM> and causes the radiation detectors <NUM> to move from the first position <NUM> to the second position <NUM>.

According to one embodiment not forming part of the claimed invention, the actuator <NUM> may comprise a step motor <NUM> and a transmission <NUM>, which may engage the radiation detectors <NUM> and the mask <NUM> respectively, or vice versa, as shown in <FIG>. In the example shown, the step motor <NUM> is configured to move the radiation detectors <NUM>, for example, from the first position <NUM> to the second position <NUM>. The step motor <NUM> is also configured to drive the transmission <NUM> and the transmission <NUM> is configured to move the mask <NUM>, for example, from the third position <NUM> to the fourth position <NUM>. The transmission <NUM> may cause a displacement of the mask <NUM> at a magnitude of a displacement of the step motor <NUM> multiplied by a gear ratio of the transmission <NUM>.

As schematically shown in <FIG> and <FIG>, the image sensor <NUM> may include a shutter <NUM>. The shutter <NUM> is configured to block the radiation from the radiation source <NUM> during movements of the radiation detectors <NUM> and the mask <NUM>.

As shown in <FIG>, according to an embodiment, at least some of the radiation detectors <NUM> of the image sensor <NUM> are arranged in an array. To form an image of the scene <NUM>, the actuator <NUM> moves the radiation detectors <NUM> to multiple positions (e.g., A, B and C in <FIG>) relative to the scene <NUM>, where the image sensor <NUM> captures images (e.g., 51A, 51B and 51C) of portions of the scene <NUM> at these positions, respectively. Every point of the scene <NUM> is in at least one image of a portion. Namely, the images of the portions when stitched together cover the entire scene <NUM>. The images of the portions may have overlaps among them to facilitate stitching.

The radiation detectors <NUM> may be arranged in a variety of ways in the image sensor <NUM>. <FIG> schematically shows one arrangement, according to an embodiment, where at least some of the radiation detectors <NUM> are arranged in staggered rows. For example, detectors 100A and 100B are in the same row, aligned in the Y direction, and uniform in size; detectors 100C and 100D are in the same row, aligned in the Y direction, and uniform in size. Radiation detectors 100A and 100B are staggered in the X direction with respect to radiation detectors 100C and 100D. According to an embodiment, a distance X2 between two neighboring radiation detectors 100A and 100B in the same row is greater than a width X1 (i.e., dimension in the X direction, which is the extending direction of the row) of one radiation detector in the same row and is less than twice the width X1. Radiation detectors 100A and 100E are in a same column, aligned in the X direction, and uniform in size; a distance Y2 between two neighboring radiation detectors 100A and 100E in the same column is less than a width Y1 (i.e., dimension in the Y direction) of one radiation detector in the same column. This arrangement allows imaging of the scene as shown in <FIG>, and an image of the scene may be obtaining from stitching three images of portions of the scene captured at three positions spaced apart in the X direction.

<FIG> schematically shows another arrangement, according to an embodiment, where the radiation detectors <NUM> are arranged in a rectangular grid. For example, the detectors <NUM> may include detectors 100A, 100B, 100E and 100F as arranged exactly in <FIG>, without detectors 100C, 100D, <NUM>, or <NUM> in <FIG>. This arrangement allows imaging of the scene by taking images of portions of the scene at six positions. For example, three positions spaced apart in the X direction and another three positions spaced apart in the X direction and spaced apart in the Y direction from the first three positions.

Other arrangements may also be possible. For example, in <FIG>, the detectors <NUM> may span the whole width of the image sensor <NUM> in the X-direction, with a distance Y2 between two neighboring detectors <NUM> being less than a width of one radiation detector Y1. Assuming the width of the detectors in the X direction is greater than the width of the scene in the X direction, the image of the scene may be stitched from two images of portions of the scene captured at two positions spaced apart in the Y direction. The radiation detectors <NUM> may be arranged in multiple layers, where at least some of the plurality of radiation detectors <NUM> are arranged such that radiation incident on the dead zone <NUM> of one layer is captured by the radiation detectors in another layer.

The radiation detectors describe above may be provided with any suitable size and shapes. According to an embodiment (e.g., in <FIG>), at least some of the radiation detectors are rectangular in shape. According to an embodiment, as shown in <FIG>, at least some of the radiation detectors are hexagonal in shape. In such radiation detectors, the radiation detectors and the corresponding masks that are aligned may have the same shape.

<FIG> schematically shows a cross-sectional view of one radiation detector <NUM>, according to an embodiment. The radiation detector <NUM> may include a radiation absorption layer <NUM> and an electronics layer <NUM> (e.g., an ASIC) for processing or analyzing electrical signals incident radiation generates in the radiation absorption layer <NUM>. In an embodiment, the radiation detector <NUM> does not comprise a scintillator. The radiation absorption layer <NUM> 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 radiation energy of interest.

As shown in a detailed cross-sectional view of the radiation detector <NUM> in <FIG>, according to an embodiment, the radiation absorption layer <NUM> may include one or more diodes (e.g., p-i-n or p-n) formed by a first doped region <NUM>, one or more discrete regions <NUM> of a second doped region <NUM>. The second doped region <NUM> may be separated from the first doped region <NUM> by an optional intrinsic region <NUM>. The discrete regions <NUM> are separated from one another by the first doped region <NUM> or the intrinsic region <NUM>. The first doped region <NUM> and the second doped region <NUM> have opposite types of doping (e.g., region <NUM> is p-type and region <NUM> is n-type, or region <NUM> is n-type and region <NUM> is p-type). In the example in <FIG>, each of the discrete regions <NUM> of the second doped region <NUM> forms a diode with the first doped region <NUM> and the optional intrinsic region <NUM>. Namely, in the example in <FIG>, the radiation absorption layer <NUM> has a plurality of diodes having the first doped region <NUM> as a shared electrode. The first doped region <NUM> may also have discrete portions.

When a particle of radiation hits the radiation absorption layer <NUM> including diodes, the particle of radiation may be absorbed and generate one or more charge carriers by a number of mechanisms. A particle of radiation may generate <NUM> to <NUM> 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 119B may include discrete portions each of which is in electrical contact with the discrete regions <NUM>. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of radiation are not substantially shared by two different discrete regions <NUM> ("not substantially shared" here means less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow to a different one of the discrete regions <NUM> than the rest of the charge carriers). Charge carriers generated by a particle of radiation incident around the footprint of one of these discrete regions <NUM> are not substantially shared with another of these discrete regions <NUM>. The pixel <NUM> associated with a discrete region <NUM> may be an area around the discrete region <NUM> in which substantially all (more than <NUM>%, more than <NUM>%, more than <NUM>%, or more than <NUM>% of) charge carriers generated by a particle of radiation incident therein flow to the discrete region <NUM>. Namely, less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow beyond the pixel.

As shown in an alternative detailed cross-sectional view of the detector <NUM> in <FIG>, according to an embodiment, the radiation absorption layer <NUM> 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 radiation energy of interest.

When a particle of radiation hits the radiation absorption layer <NUM> including a resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms. A particle of radiation may generate <NUM> to <NUM> charge carriers. The charge carriers may drift to the electrical contacts 119A and 119B under an electric field. The field may be an external electric field. The electrical contact 119B includes discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of radiation are not substantially shared by two different discrete portions of the electrical contact 119B ("not substantially shared" here means less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers). Charge carriers generated by a particle of radiation incident around the footprint of one of these discrete portions of the electrical contact 119B are not substantially shared with another of these discrete portions of the electrical contact 119B. The pixel <NUM> associated with a discrete portion of the electrical contact 119B may be an area around the discrete portion in which substantially all (more than <NUM>%, more than <NUM>%, more than <NUM>% or more than <NUM>% of) charge carriers generated by a particle of radiation incident therein flow to the discrete portion of the electrical contact 119B. Namely, less than <NUM>%, less than <NUM>%, less than <NUM>%, or less than <NUM>% of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact 119B.

The electronics layer <NUM> may include an electronic system <NUM> suitable for processing or interpreting signals generated by particles of radiation incident on the radiation absorption layer <NUM>. The electronic system <NUM> may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessor, and memory. The electronic system <NUM> may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system <NUM> may include an amplifier dedicated to each pixel and a microprocessor shared among all the pixels. The electronic system <NUM> may be electrically connected to the pixels by vias <NUM>. Space among the vias may be filled with a filler material <NUM>, which may increase the mechanical stability of the connection of the electronics layer <NUM> to the radiation absorption layer <NUM>. Other bonding techniques are possible to connect the electronic system <NUM> to the pixels without using vias.

<FIG> schematically shows that the radiation detector <NUM> may have an array of pixels <NUM>. The array may be a rectangular array, a honeycomb array, a hexagonal array or any other suitable array. Each pixel <NUM> may be configured to detect a particle of radiation incident thereon, measure the energy of the particle of radiation, or both. For example, each pixel <NUM> may be configured to count numbers of particles of radiation incident thereon whose energy falls in a plurality of bins, within a period of time. All the pixels <NUM> may be configured to count the numbers of particles of radiation incident thereon within a plurality of bins of energy within the same period of time. Each pixel <NUM> may have its own analog-to-digital converter (ADC) configured to digitize an analog signal representing the energy of an incident particle of radiation into a digital signal. The ADC may have a resolution of <NUM> bits or higher. Each pixel <NUM> may be configured to measure its dark current, such as before or concurrently with each particle of radiation incident thereon. Each pixel <NUM> may be configured to deduct the contribution of the dark current from the energy of the particle of radiation incident thereon. The pixels <NUM> may be configured to operate in parallel. For example, when one pixel <NUM> measures an incident particle of radiation, another pixel <NUM> may be waiting for a particle of radiation to arrive. The pixels <NUM> may be but do not have to be individually addressable.

The image sensor <NUM> described above may be used in various system such as those provided below.

<FIG> schematically shows a system comprising the image sensor <NUM> as described herein. The system may be used for medical imaging such as chest radiation radiography, abdominal radiation radiography, etc. The system comprises a radiation source <NUM>. Radiation emitted from the radiation source <NUM> penetrates an object <NUM> (e.g., a human body part such as chest, limb, abdomen), is attenuated by different degrees by the internal structures of the object <NUM> (e.g., bones, muscle, fat and organs, etc.), and is projected to the image sensor <NUM>. The image sensor <NUM> forms an image by detecting the intensity distribution of the radiation.

<FIG> schematically shows a system comprising the image sensor <NUM> as described herein. The system may be used for medical imaging such as dental radiation radiography. The system comprises a radiation source <NUM>. Radiation emitted from the radiation source <NUM> penetrates an object <NUM> that is part of a mammal (e.g., human) mouth. The object <NUM> may include a maxilla bone, a palate bone, a tooth, the mandible, or the tongue. The radiation is attenuated by different degrees by the different structures of the object <NUM> and is projected to the image sensor <NUM>. The image sensor <NUM> forms an image by detecting the intensity distribution of the radiation. Teeth absorb radiation more than dental caries, infections, periodontal ligament. The dosage of radiation received by a dental patient is typically small (around <NUM> mSv for a full mouth series).

<FIG> schematically shows a cargo scanning or non-intrusive inspection (NII) system comprising the image sensor <NUM> as described herein. The system may be used for luggage screening at public transportation stations and airports. The system comprises a radiation source <NUM>. radiation emitted from the radiation source <NUM> may penetrate a piece of luggage <NUM>, be differently attenuated by the contents of the luggage, and projected to the image sensor <NUM>. The image sensor <NUM> forms an image by detecting the intensity distribution of the transmitted radiation. The system may reveal contents of luggage and identify items forbidden on public transportation, such as firearms, narcotics, edged weapons, flammables.

<FIG> schematically shows a full-body scanner system comprising the image sensor <NUM> as described herein. The full-body scanner system may detect objects on a person'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 a radiation source <NUM>. Radiation emitted from the radiation source <NUM> may backscatter from a human <NUM> being screened and objects thereon, and be projected to the image sensor <NUM>. The objects and the human body may backscatter radiation differently. The image sensor <NUM> forms an image by detecting the intensity distribution of the backscattered radiation. The image sensor <NUM> and the radiation source <NUM> may be configured to scan the human in a linear or rotational direction.

<FIG> schematically shows a radiation computed tomography (Radiation CT) system. The radiation CT system uses computer-processed radiations 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 radiation CT system comprises the radiation detector <NUM> described herein and a radiation source <NUM>. The radiation detector <NUM> and the radiation source <NUM> may be configured to rotate synchronously along one or more circular or spiral paths.

<FIG> schematically shows an electron microscope. The electron microscope comprises an electron source <NUM> (also called an electron gun) that is configured to emit electrons. The electron source <NUM> may have various emission mechanisms such as thermionic, photocathode, cold emission, or plasmas source. The emitted electrons pass through an electronic optical system <NUM>, which may be configured to shape, accelerate, or focus the electrons. The electrons then reach a sample <NUM> and an image detector may form an image therefrom. The electron microscope may comprise the image sensor <NUM> as described herein, for performing energy-dispersive radiation 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 radiations 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 a radiation. The number and energy of the particles of radiation emitted from the sample can be measured by the image sensor <NUM>.

The image sensor <NUM> described here may have other applications such as in a radiation telescope, or a radiation microscopy, or wherein the image sensor <NUM> is configured to perform mammography, industrial defect detection, microscopy or microradiography, casting inspection, non-destructive testing, weld inspection, or digital subtraction angiography, etc. It may be suitable to use this image sensor <NUM> in place of a photographic plate, a photographic film, a PSP plate, a radiation image intensifier, a scintillator, or another semiconductor radiation detector.

The electronics layer <NUM> in the radiation detector <NUM> may include an electronic system <NUM> suitable for processing or interpreting or correcting signals generated by particles of radiation incident on the pixels <NUM> comprising radiation absorption layer <NUM>. The electronic system <NUM> may include an analog circuitry such as a filter network, amplifiers, integrators, and comparators, or a digital circuitry such as a microprocessor, and a memory. The electronic system <NUM> may include components shared by the pixels or components dedicated to a single pixel. For example, the electronic system <NUM> may include an amplifier dedicated to each pixel and a microprocessor shared among all the pixels. The electronic system <NUM> may be electrically connected to the pixels by vias <NUM>. Space among the vias may be filled with a filler material <NUM>, which may increase the mechanical stability of the connection of the electronics layer <NUM> to the radiation absorption layer <NUM>. Other bonding techniques are possible to connect the electronic system <NUM> to the pixels without using vias.

<FIG> and <FIG> each show a component diagram of the electronic system <NUM>, according to an embodiment. The electronic system <NUM> may include a first voltage comparator <NUM>, a second voltage comparator <NUM>, a counter <NUM>, a switch <NUM>, an optional voltmeter <NUM>, and a controller <NUM>.

The first voltage comparator <NUM> is configured to compare the voltage of at least one of the electric contacts 119B to a first threshold. The first voltage comparator <NUM> may be configured to monitor the voltage directly or calculate the voltage by integrating an electric current flowing through the electrical contact 119B over a period of time. The first voltage comparator <NUM> may be controllably activated or deactivated by the controller <NUM>. The first voltage comparator <NUM> may be a continuous comparator. Namely, the first voltage comparator <NUM> may be configured to be activated continuously and monitor the voltage continuously. The first voltage comparator <NUM> may be a clocked comparator. The first threshold may be <NUM>-<NUM>%, <NUM>%-<NUM>%, <NUM>-<NUM>%, <NUM>-<NUM>% or <NUM>-<NUM>% of the maximum voltage one incident particle of radiation may generate on the electric contact 119B. The maximum voltage may depend on the energy of the incident particle of radiation, the material of the radiation absorption layer <NUM>, and other factors. For example, the first threshold may be <NUM> mV, <NUM> mV, <NUM> mV, or <NUM> mV.

The second voltage comparator <NUM> is configured to compare the voltage to a second threshold. The second voltage comparator <NUM> may be configured to monitor the voltage directly or calculate the voltage by integrating an electric current flowing through the diode or the electrical contact over a period of time. The second voltage comparator <NUM> may be a continuous comparator. The second voltage comparator <NUM> may be controllably activate or deactivated by the controller <NUM>. When the second voltage comparator <NUM> is deactivated, the power consumption of the second voltage comparator <NUM> may be less than <NUM>%, less than <NUM>%, less than <NUM>% or less than <NUM>% of the power consumption when the second voltage comparator <NUM> is activated. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term "absolute value" or "modulus" |x| of a real number x is the non-negative value of x without regard to its sign. Namely, <MAT>. The second threshold may be <NUM>%-<NUM>% of the first threshold. The second threshold may be at least <NUM>% of the maximum voltage one incident particle of radiation may generate on the electric contact 119B. For example, the second threshold may be <NUM> mV, <NUM> mV, <NUM> mV, <NUM> mV or <NUM> mV. The second voltage comparator <NUM> and the first voltage comparator <NUM> may be the same component. Namely, the system <NUM> may have one voltage comparator that can compare a voltage with two different thresholds at different times.

The first voltage comparator <NUM> or the second voltage comparator <NUM> may include one or more op-amps or any other suitable circuitry. The first voltage comparator <NUM> or the second voltage comparator <NUM> may have a high speed to allow the system <NUM> to operate under a high flux of incident particles of radiation. However, having a high speed is often at the cost of power consumption.

The counter <NUM> is configured to register at least a number of particles of radiation incident on the pixel <NUM> encompassing the electric contact 119B. The counter <NUM> may be a software component (e.g., a number stored in a computer memory) or a hardware component (e.g., a <NUM> IC and a <NUM> IC).

The controller <NUM> may be a hardware component such as a microcontroller or a microprocessor. The controller <NUM> is configured to start a time delay from a time at which the first voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold (e.g., the absolute value of the voltage increases from below the absolute value of the first threshold to a value equal to or above the absolute value of the first threshold). The absolute value is used here because the voltage may be negative or positive, depending on whether the voltage of the cathode or the anode of the diode or which electrical contact is used. The controller <NUM> may be configured to keep deactivated the second voltage comparator <NUM>, the counter <NUM> and any other circuits the operation of the first voltage comparator <NUM> does not require, before the time at which the first voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The time delay may expire before or after the voltage becomes stable, i.e., the rate of change of the voltage is substantially zero. The phase "the rate of change of the voltage is substantially zero" means that temporal change of the voltage is less than <NUM>%/ns. The phase "the rate of change of the voltage is substantially non-zero" means that temporal change of the voltage is at least <NUM>%/ns.

The controller <NUM> may be configured to activate the second voltage comparator during (including the beginning and the expiration) the time delay. In an embodiment, the controller <NUM> is configured to activate the second voltage comparator at the beginning of the time delay. The term "activate" means causing the component to enter an operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by providing power, etc.). The term "deactivate" means causing the component to enter a non-operational state (e.g., by sending a signal such as a voltage pulse or a logic level, by cut off power, etc.). The operational state may have higher power consumption (e.g., <NUM> times higher, <NUM> times higher, <NUM> times higher) than the non-operational state. The controller <NUM> itself may be deactivated until the output of the first voltage comparator <NUM> activates the controller <NUM> when the absolute value of the voltage equals or exceeds the absolute value of the first threshold.

The controller <NUM> may be configured to cause at least one of the number registered by the counter <NUM> to increase by one, if, during the time delay, the second voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold.

The controller <NUM> may be configured to cause the optional voltmeter <NUM> to measure the voltage upon expiration of the time delay. The controller <NUM> may be configured to connect the electric contact 119B to an electrical ground, so as to reset the voltage and discharge any charge carriers accumulated on the electric contact 119B. In an embodiment, the electric contact 119B is connected to an electrical ground after the expiration of the time delay. In an embodiment, the electric contact 119B is connected to an electrical ground for a finite reset time period. The controller <NUM> may connect the electric contact 119B to the electrical ground by controlling the switch <NUM>. The switch may be a transistor such as a field-effect transistor (FET).

In an embodiment, the system <NUM> has no analog filter network (e.g., a RC network). In an embodiment, the system <NUM> has no analog circuitry.

The voltmeter <NUM> may feed the voltage it measures to the controller <NUM> as an analog or digital signal.

The electronic system <NUM> may include an integrator <NUM> electrically connected to the electric contact 119B, wherein the integrator is configured to collect charge carriers from the electric contact 119B. The integrator <NUM> can include a capacitor in the feedback path of an amplifier. The amplifier configured as such is called a capacitive transimpedance amplifier (CTIA). CTIA has high dynamic range by keeping the amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. Charge carriers from the electric contact 119B accumulate on the capacitor over a period of time ("integration period"). After the integration period has expired, the capacitor voltage is sampled and then reset by a reset switch. The integrator <NUM> can include a capacitor directly connected to the electric contact 119B.

<FIG> schematically shows a temporal change of the electric current flowing through the electric contact 119B (upper curve) caused by charge carriers generated by a particle of radiation incident on the pixel <NUM> encompassing the electric contact 119B, and a corresponding temporal change of the voltage of the electric contact 119B (lower curve). The voltage may be an integral of the electric current with respect to time. At time to, the particle of radiation hits pixel <NUM>, charge carriers start being generated in the pixel <NUM>, electric current starts to flow through the electric contact 119B, and the absolute value of the voltage of the electric contact 119B starts to increase. At time t<NUM>, the first voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller <NUM> starts the time delay TD1 and the controller <NUM> may deactivate the first voltage comparator <NUM> at the beginning of TD1. If the controller <NUM> is deactivated before t<NUM>, the controller <NUM> is activated at t<NUM>. During TD1, the controller <NUM> activates the second voltage comparator <NUM>. The term "during" a time delay as used here means the beginning and the expiration (i.e., the end) and any time in between. For example, the controller <NUM> may activate the second voltage comparator <NUM> at the expiration of TD1. If during TD1, the second voltage comparator <NUM> determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold V2 at time t<NUM>, the controller <NUM> waits for stabilization of the voltage to stabilize. The voltage stabilizes at time te, when all charge carriers generated by the particle of radiation drift out of the radiation absorption layer <NUM>. At time ts, the time delay TD1 expires. At or after time te, the controller <NUM> causes the voltmeter <NUM> to digitize the voltage and determines which bin the energy of the particle of radiation falls in. The controller <NUM> then causes the number registered by the counter <NUM> corresponding to the bin to increase by one. In the example of <FIG>, time ts is after time te; namely TD1 expires after all charge carriers generated by the particle of radiation drift out of the radiation absorption layer <NUM>. If time te cannot be easily measured, TD1 can be empirically chosen to allow sufficient time to collect essentially all charge carriers generated by a particle of radiation but not too long to risk have another incident particle of radiation. Namely, TD1 can be empirically chosen so that time ts is empirically after time te. Time ts is not necessarily after time te because the controller <NUM> may disregard TD1 once V2 is reached and wait for time te. The rate of change of the difference between the voltage and the contribution to the voltage by the dark current is thus substantially zero at te. The controller <NUM> may be configured to deactivate the second voltage comparator <NUM> at expiration of TD1 or at t<NUM>, or any time in between.

The voltage at time te is proportional to the amount of charge carriers generated by the particle of radiation, which relates to the energy of the particle of radiation. The controller <NUM> may be configured to determine the energy of the particle of radiation, using the voltmeter <NUM>.

After TD1 expires or digitization by the voltmeter <NUM>, whichever later, the controller <NUM> connects the electric contact 119B to an electric ground for a reset period RST to allow charge carriers accumulated on the electric contact 119B to flow to the ground and reset the voltage. After RST, the system <NUM> is ready to detect another incident particle of radiation. If the first voltage comparator <NUM> has been deactivated, the controller <NUM> can activate it at any time before RST expires. If the controller <NUM> has been deactivated, it may be activated before RST expires.

Claim 1:
An image sensor (<NUM>) comprising:
a plurality of radiation detectors (<NUM>);
a mask (<NUM>) with a plurality of radiation transmitting zones (<NUM>) and a radiation blocking zone (<NUM>); and
an actuator (<NUM>) configured to move the plurality of radiation detectors from a first position to a second position and to move the mask from a third position to a fourth position;
wherein while the radiation detectors are at the first position and the mask is at the third position and while the radiation detectors are at the second position and the mask is at the fourth position, the radiation blocking zone is configured to block radiation from a radiation source (<NUM>) that would otherwise be incident on a dead zone (<NUM>) of the image sensor and the radiation transmitting zones are configured to allow at least a portion of radiation from the radiation source that would be incident on active areas (<NUM>) of the image sensor to pass through;
wherein the actuator comprises a linear motor (<NUM>) and a linkage (<NUM>);
wherein the linear motor is configured to move the radiation detectors from the first position to the second position; and
wherein the linkage couples the mask to the radiation detectors such that movement of the radiation detectors from the first position to the second position causes the mask to move from the third position to the fourth position.