WO2023087123A1 - Image sensors with shielded electronics layers - Google Patents

Image sensors with shielded electronics layers Download PDF

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Publication number
WO2023087123A1
WO2023087123A1 PCT/CN2021/130782 CN2021130782W WO2023087123A1 WO 2023087123 A1 WO2023087123 A1 WO 2023087123A1 CN 2021130782 W CN2021130782 W CN 2021130782W WO 2023087123 A1 WO2023087123 A1 WO 2023087123A1
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WIPO (PCT)
Prior art keywords
sensing element
radiation
straight line
radiation absorption
collimator
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PCT/CN2021/130782
Other languages
French (fr)
Inventor
Peiyan CAO
Yurun LIU
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Shenzhen Xpectvision Technology Co., Ltd.
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Application filed by Shenzhen Xpectvision Technology Co., Ltd. filed Critical Shenzhen Xpectvision Technology Co., Ltd.
Priority to PCT/CN2021/130782 priority Critical patent/WO2023087123A1/en
Priority to TW111137643A priority patent/TW202321735A/en
Publication of WO2023087123A1 publication Critical patent/WO2023087123A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/24—Measuring radiation intensity with semiconductor detectors
    • G01T1/242—Stacked detectors, e.g. for depth information

Definitions

  • a radiation detector is a device that measures a property of a radiation. Examples of the property may include a spatial distribution of the intensity, phase, and polarization of the radiation.
  • the radiation measured by the radiation detector may be a radiation that has transmitted through an object.
  • the radiation measured by the radiation detector may be electromagnetic radiation such as infrared light, visible light, ultraviolet light, X-ray, or ⁇ -ray.
  • the radiation may be of other types such as ⁇ -rays and ⁇ -rays.
  • An imaging system may include one or more image sensors each of which may have one or more radiation detectors.
  • an imaging system comprising an image sensor which comprises: a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1; and M collimator regions respectively for the M electronics layers of the M radiation detectors, wherein there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region, and wherein for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
  • the M collimator regions are respectively on the M electronics layers.
  • the imaging system further comprises a radiation source, wherein each collimator region of the M collimator regions completely shadows the corresponding electronics layer with respect to the radiation source.
  • each collimator region of the M collimator regions has a shape of a plate having a thickness being the same as a thickness of the corresponding electronics layer.
  • the M radiation absorption layers and the M electronics layers are arranged in an alternating manner.
  • the M collimator regions comprise tungsten.
  • the radiation absorption layer of said each radiation detector is configured to generate electrical signals in response to incident X-ray photons, and wherein the electronics layer of said each radiation detector is configured to process the generated electrical signals.
  • each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein for each sensing element column of each radiation absorption layer of the M radiation absorption layers, the imaging system is configured to add final voltages of sensing elements of said each sensing element column whose voltages exceed a pre-specified threshold voltage, and wherein a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  • said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of said each sensing element column by at least a pre-specified voltage tolerance value, wherein the first sensing element is adjacent to the second sensing element, and wherein the second sensing element is between the first sensing element and the M collimator regions.
  • said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of an adjacent sensing element column by at least a pre-specified voltage tolerance value, and wherein a straight line perpendicular to the reference straight line intersects both the first and second sensing elements.
  • each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein the sensing element columns of the image sensor are arranged in multiple sensing element column groups of adjacent sensing element columns, wherein for each sensing element column group of the image sensor, the imaging system is configured to add final voltages of sensing elements of said each sensing element column group whose voltages exceed a pre-specified threshold voltage, wherein said each sensing element column group comprises N sensing element columns, N being an integer greater than 1, and wherein for each sensing element column of said each sensing element column group, a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  • a method comprising: receiving incident radiation with an image sensor of an imaging system, the image sensor comprising: a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1; and M collimator regions respectively for the M electronics layers of the M radiation detectors, wherein there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region, and wherein for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
  • the M collimator regions are respectively on and in the M electronics layers.
  • each collimator region of the M collimator regions completely shadows the corresponding electronics layer with respect to a same radiation source.
  • each collimator region of the M collimator regions has a shape of a plate having a thickness being the same as a thickness of the corresponding electronics layer.
  • the M radiation absorption layers and the M electronics layers are arranged in an alternating manner.
  • the M collimator regions comprise tungsten.
  • the radiation absorption layer of said each radiation detector is configured to generate electrical signals in response to incident X-ray photons, and wherein the electronics layer of said each radiation detector is configured to process the generated electrical signals.
  • each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns
  • the method further comprises for each sensing element column of each radiation absorption layer of the M radiation absorption layers, adding with the imaging system final voltages of sensing elements of said each sensing element column whose voltages exceed a pre-specified threshold voltage, and wherein a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  • said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of said each sensing element column by at least a pre-specified voltage tolerance value, wherein the first sensing element is adjacent to the second sensing element, and wherein the second sensing element is between the first sensing element and the M collimator regions.
  • said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of an adjacent sensing element column by at least a pre-specified voltage tolerance value, and wherein a straight line perpendicular to the reference straight line intersects both the first and second sensing elements.
  • each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein the sensing element columns of the image sensor are arranged in multiple sensing element column groups of adjacent sensing element columns, wherein the method further comprises, for each sensing element column group of the image sensor, adding with the imaging system final voltages of sensing elements of said each sensing element column group whose voltages exceed a pre-specified threshold voltage, wherein said each sensing element column group comprises N sensing element columns, N being an integer greater than 1, and wherein for each sensing element column of said each sensing element column group, a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  • Fig. 1 schematically shows a radiation detector, according to an embodiment.
  • Fig. 2 schematically shows a simplified cross-sectional view of the radiation detector, according to an embodiment.
  • Fig. 3 schematically shows a detailed cross-sectional view of the radiation detector, according to an embodiment.
  • Fig. 4 schematically shows a detailed cross-sectional view of the radiation detector, according to an alternative embodiment.
  • Fig. 5 schematically shows an imaging system including an image sensor, according to an embodiment.
  • Fig. 6 shows a flowchart generalizing the operation of the imaging system.
  • Fig. 1 schematically shows a radiation detector 100, as an example.
  • the radiation detector 100 may include an array of pixels 150 (also referred to as sensing elements 150) .
  • the array may be a rectangular array (as shown in Fig. 1) , a honeycomb array, a hexagonal array, or any other suitable array.
  • the array of pixels 150 in the example of Fig. 1 has 4 rows and 7 columns; however, in general, the array of pixels 150 may have any number of rows and any number of columns.
  • Each pixel 150 may be configured to detect radiation from a radiation source (not shown) incident thereon and may be configured to measure a characteristic (e.g., the energy of the particles, the wavelength, and the frequency) of the radiation.
  • a radiation may include particles such as photons and subatomic particles.
  • Each pixel 150 may be configured to count numbers of particles of radiation incident thereon whose energy falls in a plurality of bins of energy, within a period of time. All the pixels 150 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. When the incident particles of radiation have similar energy, the pixels 150 may be simply configured to count numbers of particles of radiation incident thereon within a period of time, without measuring the energy of the individual particles of radiation.
  • Each pixel 150 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, or to digitize an analog signal representing the total energy of a plurality of incident particles of radiation into a digital signal.
  • ADC analog-to-digital converter
  • the pixels 150 may be configured to operate in parallel. For example, when one pixel 150 measures an incident particle of radiation, another pixel 150 may be waiting for a particle of radiation to arrive. The pixels 150 may not have to be individually addressable.
  • the radiation detector 100 described here may have applications such as in an X-ray telescope, X-ray mammography, industrial X-ray defect detection, X-ray microscopy or microradiography, X-ray casting inspection, X-ray non-destructive testing, X-ray weld inspection, X-ray digital subtraction angiography, etc. It may be suitable to use this radiation detector 100 in place of a photographic plate, a photographic film, a PSP plate, an X-ray image intensifier, a scintillator, or another semiconductor X-ray detector.
  • Fig. 2 schematically shows a simplified cross-sectional view of the radiation detector 100 of Fig. 1 along a line 2-2, according to an embodiment.
  • the radiation detector 100 may include a radiation absorption layer 110 and an electronics layer 120 (which may include one or more ASICs or application-specific integrated circuits) for processing or analyzing electrical signals which incident radiation generates in the radiation absorption layer 110.
  • the radiation detector 100 may or may not include a scintillator (not shown) .
  • the radiation absorption layer 110 may include a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof.
  • the semiconductor material may have a high mass attenuation coefficient for the radiation of interest.
  • the radiation 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 intrinsic region 112.
  • the discrete regions 114 may be 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 may 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) .
  • 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.
  • the radiation absorption layer 110 has a plurality of diodes (more specifically, 7 diodes corresponding to 7 pixels 150 of one row in the array of Fig. 1, of which only 2 pixels 150 are labeled in Fig. 3 for simplicity) .
  • the plurality of diodes may have an electrical contact 119A as a shared (common) electrode.
  • the first doped region 111 may also have discrete portions.
  • the electronics layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by the radiation incident on the radiation 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 microprocessor, and memory.
  • the electronic system 121 may include one or more ADCs (analog to digital converters) .
  • the electronic system 121 may include components shared by the pixels 150 or components dedicated to a single pixel 150.
  • the electronic system 121 may include an amplifier dedicated to each pixel 150 and a microprocessor shared among all the pixels 150.
  • the electronic system 121 may be electrically connected to the pixels 150 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 radiation absorption layer 110. Other bonding techniques are possible to connect the electronic system 121 to the pixels 150 without using the vias 131.
  • the radiation absorption layer 110 including diodes
  • particles of the radiation may be absorbed and generate one or more charge carriers (e.g., electrons, holes) by a number of mechanisms.
  • the charge carriers may drift to the electrodes of one of the diodes under an electric field.
  • the electric 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 114.
  • the term “electrical contact” may be used interchangeably with the word “electrode.
  • the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete regions 114 ( “not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow to a different one of the discrete regions 114 than the rest of the charge carriers) .
  • Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete regions 114 are not substantially shared with another of these discrete regions 114.
  • a pixel 150 associated with a discrete region 114 may be an area around the discrete region 114 in which substantially all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%of) charge carriers generated by a particle of the radiation incident therein flow to the discrete region 114. Namely, less than 2%, less than 1%, less than 0.1%, or less than 0.01%of these charge carriers flow beyond the pixel 150.
  • Fig. 4 schematically shows a detailed cross-sectional view of the radiation detector 100 of Fig. 1 along the line 2-2, according to an alternative embodiment.
  • the radiation 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 material may have a high mass attenuation coefficient for the radiation of interest.
  • the electronics layer 120 of Fig. 4 is similar to the electronics layer 120 of Fig. 3 in terms of structure and function.
  • the radiation When the radiation hits the radiation absorption layer 110 including the resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of mechanisms.
  • a particle of the radiation may generate 10 to 100,000 charge carriers.
  • the charge carriers may drift to the electrical contacts 119A and 119B under an electric field.
  • the electric field may be an external electric field.
  • the electrical contact 119B may include discrete portions.
  • the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete portions of the electrical contact 119B ( “not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow to a different one of the discrete portions than the rest of the charge carriers) .
  • a pixel 150 associated with a discrete portion of the electrical contact 119B may be an area around the discrete portion in which substantially all (more than 98%, more than 99.5%, more than 99.9%or more than 99.99%of) charge carriers generated by a particle of the radiation incident therein flow to the discrete portion of the electrical contact 119B. Namely, less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact 119B.
  • Fig. 5 schematically shows an imaging system 500, according to an embodiment.
  • the imaging system 500 may include an image sensor 510, a computer 520, and a radiation source 530.
  • the radiation source 530 may send a radiation beam 532 toward an object 540 and then to the image sensor 510.
  • the object 540 is positioned between the radiation source 530 and the image sensor 510.
  • the radiation beam 532 may comprise X-rays.
  • the image sensor 510 may include a stack of 5 radiation detectors 100.
  • the 5 radiation absorption layers 110 and the 5 electronics layers 120 of the 5 radiation detectors 100 may be arranged in an alternating manner as shown. In other words, from right to left are a radiation absorption layer 110, then an electronics layer 120, then a radiation absorption layer 110, then an electronics layer 120, and so on.
  • the image sensor 510 may further include 5 collimator regions 515 respectively for the 5 electronics layers 120.
  • the 5 collimator regions 515 may be respectively on the 5 electronics layers 120 as shown.
  • the 5 collimator regions 515 may be respectively on and in direct physical contact with the 5 electronics layers 120 as shown.
  • the collimator regions 515 may comprise a material that blocks and absorbs X-rays such as tungsten.
  • any straight line intersecting the electronics layer 120.1 and being parallel to the reference straight line 519 intersects the corresponding collimator region 515.1.
  • the radiation of the radiation beam 532 from the radiation source 530 that is parallel to the reference straight line 519 and aimed at the electronics layer 120.1 is blocked by the collimator region 515.1 and therefore prevented from hitting the electronics layer 120.1.
  • any (i.e., every) straight line intersecting said each radiation absorption layer and being parallel to the reference straight line 519 does not intersect any collimator region of the 5 collimator regions 515.
  • any straight line intersecting the radiation absorption layer 110.1 and being parallel to the reference straight line 519 does not intersect any collimator region of the 5 collimator regions 515.
  • the radiation of the radiation beam 532 from the radiation source 530 that is parallel to the reference straight line 519 and aimed at the radiation absorption layer 110.1 is not blocked by any collimator region 515 (including the collimator region 515.1) and therefore can hit the radiation absorption layer 110.1.
  • the computer 520 may be electrically connected to the 5 electronics layers 120 of the image sensor 510. In an embodiment, the computer 520 may receive and process data from the electronics layers 120 so as to generate an image of the object 540.
  • image in the present specification is not limited to spatial distribution of a property of a radiation (such as intensity) .
  • image may also include the spatial distribution of density of a substance or element.
  • the operation of the imaging system 500 may be as follows.
  • the radiation source 530 may send the radiation beam 532 toward the object 540 and then to the image sensor 510.
  • the radiation beam 532 may include X-rays parallel to the reference straight line 519.
  • the collimator regions 515 prevent the radiation beam 532 from entering the 5 electronics layers 120 but do not prevent the radiation beam 532 from hitting the 5 radiation absorption layers 110.
  • Incident radiation hitting the 5 radiation absorption layers 110 causes electrical signals in the 5 radiation absorption layers 110.
  • the 5 electronics layers 120 may monitor and process these electrical signals and generate data accordingly.
  • the computer 520 may receive and process the data created by the 5 electronics layers 120 and generate an image of the object 540.
  • Fig. 6 shows a flowchart 600 generalizing the operation of the imaging system 500 of Fig. 5 described above, according to an embodiment.
  • an image sensor of an imaging system receives incident radiation.
  • the image sensor 510 of the imaging system 500 receives incident radiation of the radiation beam 532.
  • the image sensor comprises a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1.
  • the image sensor further comprises M collimator regions respectively for the M electronics layers of the M radiation detectors.
  • the image sensor 510 further includes 5 collimator regions 515 respectively for the 5 electronics layers 120 of the 5 radiation detectors 100.
  • step 610 there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region.
  • every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region.
  • any straight line intersecting the electronics layer 120.1 and being parallel to the reference straight line 519 intersects the corresponding collimator region 515.1.
  • step 610 for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
  • any straight line intersecting the radiation absorption layer 110.1 and being parallel to the reference straight line 519 does not intersect any collimator region of the 5 collimator regions 515.
  • the image sensor 510 and the radiation source 530 may be such that each collimator region of the 5 collimator regions 515 completely shadows the corresponding electronics layer 120 with respect to the radiation source 530.
  • each collimator region of the 5 collimator regions 515 completely shields the corresponding electronics layer 120 from radiation of the radiation source 530.
  • the collimator region 515.1 completely prevents the radiation from the radiation source 530 from hitting the corresponding electronics layer 120.1.
  • each collimator region of the 5 collimator regions 515 may have the shape of a plate having a thickness being the same as the thickness of the corresponding electronics layer 120.
  • the collimator region 515.5 has the shape of a plate having a thickness 515w being the same as a thickness 120w of the corresponding electronics layer 120.5.
  • the imaging system 500 may generate an image of the object 540 as follows. Specifically, the radiation source 530 may send the radiation beam 532 to the object 540 and then to the image sensor 510.
  • the electronics layer 120.1 may monitor the voltage of each sensing element 150 of the corresponding radiation absorption layer 110.1.
  • the voltage of a sensing element 150 may be the voltage of the electrical contact 119B (Fig. 3 and Fig 4) of the sensing element 150.
  • the electronics layers 120.1 may measure the voltage of the sensing element 150 at a time point T2 which is after T1 by a pre-specified time delay. This measured voltage may be called the final voltage. After the measurement of the final voltage of the sensing element 150, the charge carriers in the sensing element 150 that create the final voltage of the sensing element 150 may be discharged.
  • the computer 520 may add the measured final voltages of the sensing elements 150 of the same sensing element column. Note that the voltages of these sensing elements 150 exceed the pre-specified threshold voltage Vt.
  • the right most sensing element column includes 7 sensing elements 150 (4, 7) –150 (4, 1) .
  • the charge carriers caused by the photon in the sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) of the right most sensing element column are sufficient to cause the voltages of these 4 sensing elements to exceed Vt.
  • the electronics layer 120.1 measures the 4 final voltages of these 4 sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) .
  • the measured final voltages of the sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) are 6V, 5V, 8V, and 3V, respectively.
  • the computer 520 adds the 4 final voltages together resulting in a photon voltage value.
  • the imaging system 500 may perform the same operation described above and determine another photon voltage value for this photon and for this right most sensing element column.
  • the computer 520 may add all the photon voltage values for the right most sensing element column and for all the photons entering the right most sensing element column during the exposure time period. As a result, the sum of all these photon voltage values represents the total energy of all the photons hitting that right most sensing element column during the exposure time period.
  • the imaging system 500 determines 30 photon voltage values for these 30 photons.
  • the sum of all these 30 photon voltage values represents the total energy of all the 30 photons entering that right most sensing element column during the exposure time period.
  • the imaging system 500 may perform the same operation described above for the other 19 sensing element columns of the image sensor 510.
  • the 20 sums for the 20 sensing element columns represent the values of the 20 picture elements of the image of the object 540.
  • each sensing element column of the image sensor 510 corresponds to a picture element of the image of the object 540.
  • the adding of the final voltages of the sensing elements in the same sensing element column described above may not apply to bad sensing elements.
  • a sensing element 150 may be considered a bad sensing element if its final voltage exceeds the final voltage of the sensing element 150 right above it in the same sensing element column by at least a pre-specified voltage tolerance value.
  • the pre-specified voltage tolerance value is 1V
  • the final voltages of the sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) are 6V, 5V, 8V, and 3V, respectively. Because the final voltage of a sensing element 150 should decrease when the depth of the sensing element increases, the sensing element 150 (4, 5) may be considered a bad sensing element because its final voltage (8V) exceeds the final voltage (5V) of the sensing element 150 (4, 6) right above it in the right most sensing element column by at least 1V.
  • the final voltage of the bad sensing element 150 may be ignored in adding the final voltages for the sensing element column.
  • a sensing element 150 is considered bad if its final voltage exceeds the final voltage of the sensing element right above it in the same sensing element column by at least a pre-specified voltage tolerance value. In an alternative embodiment, a sensing element 150 may be considered bad if its final voltage exceeds the final voltage of a sensing element of an adjacent sensing element column and at the same depth by at least a pre-specified voltage tolerance value.
  • the sensing element 150 (4, 5) may be considered a bad sensing element because its final voltage (8V) exceeds the final voltage (4V) of the sensing element 150 (3, 5) by at least 1V.
  • the sensing element 150 (3, 5) is of an adjacent sensing element column and at the same depth as the sensing element 150 (4, 5) .
  • the sensing elements 150 (3, 5) and 150 (4, 5) are at the same depth, there is a straight line which is perpendicular to the reference straight line 519 and intersects both the sensing elements 150 (3, 5) and 150 (4, 5) .
  • the computer 520 adds the measured final voltages of the sensing elements 150 of the same sensing element column. In an alternative embodiment, with all other things being the same, the computer 520 may add the measured final voltages of the sensing elements of the same sensing element column group.
  • a sensing element column group may include multiple adjacent sensing element columns of a radiation absorption layer 110.
  • the 4 sensing element columns of the radiation absorption layer 110.1 may be divided into 2 sensing element column groups each having 2 adjacent sensing element columns.
  • the first sensing element column group may include the left 2 sensing element columns
  • the second sensing element column group may include the right 2 sensing element columns.
  • the other 4 radiation absorption layers 110 of the image sensor 510 may be divided into sensing element column groups in a similar manner.

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Abstract

An imaging system(500), comprising an image sensor(510) which comprises: a stack of M radiation detectors(100) each of which comprises (A) a radiation absorption layer(110) and (B) an electronics layer(120) configured to process electrical signals generated in the radiation absorption layer(110), M being an integer greater than 1; and M collimator regions(515) respectively for the M electronics layers(120) of the M radiation detectors(100), wherein there is a reference straight line(519) for the image sensor(510) such that for each electronics layer(120) of the M electronics layers(120), every straight line(519) intersecting said each electronics layer(120) and being parallel to the reference straight line(519) intersects the corresponding collimator region(515), and wherein for each radiation absorption layer(110) of the M radiation absorption layers(110), every straight line(519) intersecting said each radiation absorption layer(110) and being parallel to the reference straight line(519) does not intersect any collimator region of the M collimator regions(515).

Description

IMAGE SENSORS WITH SHIELDED ELECTRONICS LAYERS Background
A radiation detector is a device that measures a property of a radiation. Examples of the property may include a spatial distribution of the intensity, phase, and polarization of the radiation. The radiation measured by the radiation detector may be a radiation that has transmitted through an object. The radiation measured by the radiation detector may be electromagnetic radiation such as infrared light, visible light, ultraviolet light, X-ray, or γ-ray. The radiation may be of other types such as α-rays and β-rays. An imaging system may include one or more image sensors each of which may have one or more radiation detectors.
Summary
Disclosed herein is an imaging system, comprising an image sensor which comprises: a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1; and M collimator regions respectively for the M electronics layers of the M radiation detectors, wherein there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region, and wherein for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
In an aspect, the M collimator regions are respectively on the M electronics layers.
In an aspect, the imaging system further comprises a radiation source, wherein each collimator region of the M collimator regions completely shadows the corresponding electronics layer with respect to the radiation source.
In an aspect, each collimator region of the M collimator regions has a shape of a plate having a thickness being the same as a thickness of the corresponding electronics layer.
In an aspect, the M radiation absorption layers and the M electronics layers are arranged in an alternating manner.
In an aspect, the M collimator regions comprise tungsten.
In an aspect, for each radiation detector of the M radiation detectors, the radiation absorption layer of said each radiation detector is configured to generate electrical signals in  response to incident X-ray photons, and wherein the electronics layer of said each radiation detector is configured to process the generated electrical signals.
In an aspect, each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein for each sensing element column of each radiation absorption layer of the M radiation absorption layers, the imaging system is configured to add final voltages of sensing elements of said each sensing element column whose voltages exceed a pre-specified threshold voltage, and wherein a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
In an aspect, said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of said each sensing element column by at least a pre-specified voltage tolerance value, wherein the first sensing element is adjacent to the second sensing element, and wherein the second sensing element is between the first sensing element and the M collimator regions.
In an aspect, said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of an adjacent sensing element column by at least a pre-specified voltage tolerance value, and wherein a straight line perpendicular to the reference straight line intersects both the first and second sensing elements.
In an aspect, each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein the sensing element columns of the image sensor are arranged in multiple sensing element column groups of adjacent sensing element columns, wherein for each sensing element column group of the image sensor, the imaging system is configured to add final voltages of sensing elements of said each sensing element column group whose voltages exceed a pre-specified threshold voltage, wherein said each sensing element column group comprises N sensing element columns, N being an integer greater than 1, and wherein for each sensing element column of said each sensing element column group, a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
Disclosed herein is a method, comprising: receiving incident radiation with an image sensor of an imaging system, the image sensor comprising: a stack of M radiation detectors  each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1; and M collimator regions respectively for the M electronics layers of the M radiation detectors, wherein there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region, and wherein for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
In an aspect, the M collimator regions are respectively on and in the M electronics layers.
In an aspect, each collimator region of the M collimator regions completely shadows the corresponding electronics layer with respect to a same radiation source.
In an aspect, each collimator region of the M collimator regions has a shape of a plate having a thickness being the same as a thickness of the corresponding electronics layer.
In an aspect, the M radiation absorption layers and the M electronics layers are arranged in an alternating manner.
In an aspect, the M collimator regions comprise tungsten.
In an aspect, for each radiation detector of the M radiation detectors, the radiation absorption layer of said each radiation detector is configured to generate electrical signals in response to incident X-ray photons, and wherein the electronics layer of said each radiation detector is configured to process the generated electrical signals.
In an aspect, each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein the method further comprises for each sensing element column of each radiation absorption layer of the M radiation absorption layers, adding with the imaging system final voltages of sensing elements of said each sensing element column whose voltages exceed a pre-specified threshold voltage, and wherein a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
In an aspect, said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second  sensing element of said each sensing element column by at least a pre-specified voltage tolerance value, wherein the first sensing element is adjacent to the second sensing element, and wherein the second sensing element is between the first sensing element and the M collimator regions.
In an aspect, said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of an adjacent sensing element column by at least a pre-specified voltage tolerance value, and wherein a straight line perpendicular to the reference straight line intersects both the first and second sensing elements.
In an aspect, each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns, wherein the sensing element columns of the image sensor are arranged in multiple sensing element column groups of adjacent sensing element columns, wherein the method further comprises, for each sensing element column group of the image sensor, adding with the imaging system final voltages of sensing elements of said each sensing element column group whose voltages exceed a pre-specified threshold voltage, wherein said each sensing element column group comprises N sensing element columns, N being an integer greater than 1, and wherein for each sensing element column of said each sensing element column group, a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
Brief Description of Figures
Fig. 1 schematically shows a radiation detector, according to an embodiment.
Fig. 2 schematically shows a simplified cross-sectional view of the radiation detector, according to an embodiment.
Fig. 3 schematically shows a detailed cross-sectional view of the radiation detector, according to an embodiment.
Fig. 4 schematically shows a detailed cross-sectional view of the radiation detector, according to an alternative embodiment.
Fig. 5 schematically shows an imaging system including an image sensor, according to an embodiment.
Fig. 6 shows a flowchart generalizing the operation of the imaging system.
Detailed Description
RADIATION DETECTOR
Fig. 1 schematically shows a radiation detector 100, as an example. The radiation detector 100 may include an array of pixels 150 (also referred to as sensing elements 150) . The array may be a rectangular array (as shown in Fig. 1) , a honeycomb array, a hexagonal array, or any other suitable array. The array of pixels 150 in the example of Fig. 1 has 4 rows and 7 columns; however, in general, the array of pixels 150 may have any number of rows and any number of columns.
Each pixel 150 may be configured to detect radiation from a radiation source (not shown) incident thereon and may be configured to measure a characteristic (e.g., the energy of the particles, the wavelength, and the frequency) of the radiation. A radiation may include particles such as photons and subatomic particles. Each pixel 150 may be configured to count numbers of particles of radiation incident thereon whose energy falls in a plurality of bins of energy, within a period of time. All the pixels 150 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. When the incident particles of radiation have similar energy, the pixels 150 may be simply configured to count numbers of particles of radiation incident thereon within a period of time, without measuring the energy of the individual particles of radiation.
Each pixel 150 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, or to digitize an analog signal representing the total energy of a plurality of incident particles of radiation into a digital signal. The pixels 150 may be configured to operate in parallel. For example, when one pixel 150 measures an incident particle of radiation, another pixel 150 may be waiting for a particle of radiation to arrive. The pixels 150 may not have to be individually addressable.
The radiation detector 100 described here may have applications such as in an X-ray telescope, X-ray mammography, industrial X-ray defect detection, X-ray microscopy or microradiography, X-ray casting inspection, X-ray non-destructive testing, X-ray weld inspection, X-ray digital subtraction angiography, etc. It may be suitable to use this radiation detector 100 in place of a photographic plate, a photographic film, a PSP plate, an X-ray image intensifier, a scintillator, or another semiconductor X-ray detector.
Fig. 2 schematically shows a simplified cross-sectional view of the radiation detector 100 of Fig. 1 along a line 2-2, according to an embodiment. Specifically, the radiation detector 100 may include a radiation absorption layer 110 and an electronics layer 120 (which may include one or more ASICs or application-specific integrated circuits) for processing or analyzing electrical signals which incident radiation generates in the radiation absorption layer 110. The radiation detector 100 may or may not include a scintillator (not shown) . The radiation absorption layer 110 may include a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. The semiconductor material may have a high mass attenuation coefficient for the radiation of interest.
Fig. 3 schematically shows a detailed cross-sectional view of the radiation detector 100 of Fig. 1 along the line 2-2, as an example. Specifically, the radiation 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 intrinsic region 112. The discrete regions 114 may be 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 may 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 of Fig. 3, 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. 3, the radiation absorption layer 110 has a plurality of diodes (more specifically, 7 diodes corresponding to 7 pixels 150 of one row in the array of Fig. 1, of which only 2 pixels 150 are labeled in Fig. 3 for simplicity) . The plurality of diodes may have an electrical contact 119A as a shared (common) electrode. The first doped region 111 may also have discrete portions.
The electronics layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by the radiation incident on the radiation 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 microprocessor, and memory. The electronic system 121 may include one or more ADCs (analog to digital converters) . The electronic system 121 may include components shared by the pixels 150 or components dedicated to a single pixel 150. For example, the electronic system 121 may include an amplifier dedicated to each pixel 150 and a microprocessor shared among all the  pixels 150. The electronic system 121 may be electrically connected to the pixels 150 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 radiation absorption layer 110. Other bonding techniques are possible to connect the electronic system 121 to the pixels 150 without using the vias 131.
When radiation from the radiation source (not shown) hits the radiation absorption layer 110 including diodes, particles of the radiation may be absorbed and generate one or more charge carriers (e.g., electrons, holes) by a number of mechanisms. The charge carriers may drift to the electrodes of one of the diodes under an electric field. The electric 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 114. The term “electrical contact” may be used interchangeably with the word “electrode. ” In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete regions 114 ( “not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow to a different one of the discrete regions 114 than the rest of the charge carriers) . Charge carriers generated by a particle of the radiation incident around the footprint of one of these discrete regions 114 are not substantially shared with another of these discrete regions 114. A pixel 150 associated with a discrete region 114 may be an area around the discrete region 114 in which substantially all (more than 98%, more than 99.5%, more than 99.9%, or more than 99.99%of) charge carriers generated by a particle of the radiation incident therein flow to the discrete region 114. Namely, less than 2%, less than 1%, less than 0.1%, or less than 0.01%of these charge carriers flow beyond the pixel 150.
Fig. 4 schematically shows a detailed cross-sectional view of the radiation detector 100 of Fig. 1 along the line 2-2, according to an alternative embodiment. More specifically, the radiation 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 material may have a high mass attenuation coefficient for the radiation of interest. In an embodiment, the electronics layer 120 of Fig. 4 is similar to the electronics layer 120 of Fig. 3 in terms of structure and function.
When the radiation hits the radiation absorption layer 110 including the resistor but not diodes, it may be absorbed and generate one or more charge carriers by a number of  mechanisms. A particle of the radiation may generate 10 to 100,000 charge carriers. The charge carriers may drift to the  electrical contacts  119A and 119B under an electric field. The electric field may be an external electric field. The electrical contact 119B may include discrete portions. In an embodiment, the charge carriers may drift in directions such that the charge carriers generated by a single particle of the radiation are not substantially shared by two different discrete portions of the electrical contact 119B ( “not substantially shared” here means less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%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 the 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. A pixel 150 associated with a discrete portion of the electrical contact 119B may be an area around the discrete portion in which substantially all (more than 98%, more than 99.5%, more than 99.9%or more than 99.99%of) charge carriers generated by a particle of the radiation incident therein flow to the discrete portion of the electrical contact 119B. Namely, less than 2%, less than 0.5%, less than 0.1%, or less than 0.01%of these charge carriers flow beyond the pixel associated with the one discrete portion of the electrical contact 119B.
IMAGING SYSTEM AND IMAGE SENSOR
Fig. 5 schematically shows an imaging system 500, according to an embodiment. In an embodiment, the imaging system 500 may include an image sensor 510, a computer 520, and a radiation source 530.
In an embodiment, the radiation source 530 may send a radiation beam 532 toward an object 540 and then to the image sensor 510. In other words, the object 540 is positioned between the radiation source 530 and the image sensor 510. The radiation beam 532 may comprise X-rays.
In an embodiment, the image sensor 510 may include a stack of 5 radiation detectors 100. In an embodiment, the 5 radiation absorption layers 110 and the 5 electronics layers 120 of the 5 radiation detectors 100 may be arranged in an alternating manner as shown. In other words, from right to left are a radiation absorption layer 110, then an electronics layer 120, then a radiation absorption layer 110, then an electronics layer 120, and so on.
In an embodiment, the image sensor 510 may further include 5 collimator regions 515 respectively for the 5 electronics layers 120. In an embodiment, the 5 collimator regions 515  may be respectively on the 5 electronics layers 120 as shown. In an embodiment, the 5 collimator regions 515 may be respectively on and in direct physical contact with the 5 electronics layers 120 as shown. In an embodiment, the collimator regions 515 may comprise a material that blocks and absorbs X-rays such as tungsten.
In an embodiment, there is a reference straight line 519 for the image sensor 510 such that for each electronics layer of the 5 electronics layers 120, any (i.e., every) straight line intersecting said each electronics layer and being parallel to the reference straight line 519 intersects the corresponding collimator region 515.
For example, for the electronics layer 120.1 of the radiation detector 100.1, any straight line intersecting the electronics layer 120.1 and being parallel to the reference straight line 519 intersects the corresponding collimator region 515.1. As a result, the radiation of the radiation beam 532 from the radiation source 530 that is parallel to the reference straight line 519 and aimed at the electronics layer 120.1 is blocked by the collimator region 515.1 and therefore prevented from hitting the electronics layer 120.1.
In an embodiment, for each radiation absorption layer of the 5 radiation absorption layers 110, any (i.e., every) straight line intersecting said each radiation absorption layer and being parallel to the reference straight line 519 does not intersect any collimator region of the 5 collimator regions 515.
For example, for the radiation absorption layer 110.1 of the radiation detector 100.1, any straight line intersecting the radiation absorption layer 110.1 and being parallel to the reference straight line 519 does not intersect any collimator region of the 5 collimator regions 515. As a result, the radiation of the radiation beam 532 from the radiation source 530 that is parallel to the reference straight line 519 and aimed at the radiation absorption layer 110.1 is not blocked by any collimator region 515 (including the collimator region 515.1) and therefore can hit the radiation absorption layer 110.1.
In an embodiment, the computer 520 may be electrically connected to the 5 electronics layers 120 of the image sensor 510. In an embodiment, the computer 520 may receive and process data from the electronics layers 120 so as to generate an image of the object 540.
The term “image” in the present specification is not limited to spatial distribution of a property of a radiation (such as intensity) . For example, the term “image” may also include the spatial distribution of density of a substance or element.
OPERATION OF IMAGING SYSTEM
In an embodiment, the operation of the imaging system 500 may be as follows. In an embodiment, the radiation source 530 may send the radiation beam 532 toward the object 540 and then to the image sensor 510. In an embodiment, the radiation beam 532 may include X-rays parallel to the reference straight line 519.
As a result, the collimator regions 515 prevent the radiation beam 532 from entering the 5 electronics layers 120 but do not prevent the radiation beam 532 from hitting the 5 radiation absorption layers 110. Incident radiation hitting the 5 radiation absorption layers 110 causes electrical signals in the 5 radiation absorption layers 110. In response, in an embodiment, the 5 electronics layers 120 may monitor and process these electrical signals and generate data accordingly. In response, in an embodiment, the computer 520 may receive and process the data created by the 5 electronics layers 120 and generate an image of the object 540.
FLOWCHART FOR GENERALIZATION OF OPERATION
Fig. 6 shows a flowchart 600 generalizing the operation of the imaging system 500 of Fig. 5 described above, according to an embodiment. In step 610, an image sensor of an imaging system receives incident radiation. For example, in the embodiments described above, with reference to Fig. 5, the image sensor 510 of the imaging system 500 receives incident radiation of the radiation beam 532.
In addition, in step 610, the image sensor comprises a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1. For example, in the embodiments described above, with reference to Fig. 5, the image sensor 510 includes a stack of 5 radiation detectors 100 each of which comprises (A) a radiation absorption layer 110 and (B) an electronics layer 120 configured to process electrical signals generated in the radiation absorption layer 110 (here, M=5>1) .
In addition, in step 610, the image sensor further comprises M collimator regions respectively for the M electronics layers of the M radiation detectors. For example, in the embodiments described above, with reference to Fig. 5, the image sensor 510 further includes 5 collimator regions 515 respectively for the 5 electronics layers 120 of the 5 radiation detectors 100.
In addition, in step 610, there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each  electronics layer and being parallel to the reference straight line intersects the corresponding collimator region. For example, in the embodiments described above, with reference to Fig. 5, for the electronics layer 120.1, any straight line intersecting the electronics layer 120.1 and being parallel to the reference straight line 519 intersects the corresponding collimator region 515.1.
In addition, in step 610, for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions. For example, in the embodiments described above, with reference to Fig. 5, for the radiation absorption layer 110.1, any straight line intersecting the radiation absorption layer 110.1 and being parallel to the reference straight line 519 does not intersect any collimator region of the 5 collimator regions 515.
OTHER EMBODIMENTS
COLLIMATOR REGIONS COMPLETELY SHADOW ELECTRONICS LAYERS
In an embodiment, with reference to Fig. 5, the image sensor 510 and the radiation source 530 may be such that each collimator region of the 5 collimator regions 515 completely shadows the corresponding electronics layer 120 with respect to the radiation source 530. In other words, each collimator region of the 5 collimator regions 515 completely shields the corresponding electronics layer 120 from radiation of the radiation source 530. For example, the collimator region 515.1 completely prevents the radiation from the radiation source 530 from hitting the corresponding electronics layer 120.1.
COLLIMATOR REGIONS –SHAPE AND THICKNESS
In an embodiment, with reference to Fig. 5, each collimator region of the 5 collimator regions 515 may have the shape of a plate having a thickness being the same as the thickness of the corresponding electronics layer 120. For example, the collimator region 515.5 has the shape of a plate having a thickness 515w being the same as a thickness 120w of the corresponding electronics layer 120.5.
IMAGE GENERATION –ADDING FINAL VOLTAGES
In an embodiment, with reference to Fig. 5, the imaging system 500 may generate an image of the object 540 as follows. Specifically, the radiation source 530 may send the radiation beam 532 to the object 540 and then to the image sensor 510.
In an embodiment, regarding the radiation detector 100.1, the electronics layer 120.1 may monitor the voltage of each sensing element 150 of the corresponding radiation absorption layer 110.1. The voltage of a sensing element 150 may be the voltage of the electrical contact 119B (Fig. 3 and Fig 4) of the sensing element 150.
In an embodiment, if the electronics layers 120.1 finds that the voltage of a sensing element 150 of the radiation absorption layer 110.1 exceeds a pre-specified threshold voltage Vt at a time point T1, then the electronics layer 120.1 may measure the voltage of the sensing element 150 at a time point T2 which is after T1 by a pre-specified time delay. This measured voltage may be called the final voltage. After the measurement of the final voltage of the sensing element 150, the charge carriers in the sensing element 150 that create the final voltage of the sensing element 150 may be discharged.
In an embodiment, the computer 520 may add the measured final voltages of the sensing elements 150 of the same sensing element column. Note that the voltages of these sensing elements 150 exceed the pre-specified threshold voltage Vt.
For example, with reference to Fig. 5, assume that Vt=2V, and that an X-ray photon (not shown) of the radiation beam 532 enters the right most sensing element column of the radiation absorption layer 110.1. The right most sensing element column includes 7 sensing elements 150 (4, 7) –150 (4, 1) . Assume further that the charge carriers caused by the photon in the sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) of the right most sensing element column are sufficient to cause the voltages of these 4 sensing elements to exceed Vt. As a result, the electronics layer 120.1 measures the 4 final voltages of these 4 sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) . Assume that the measured final voltages of the sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) are 6V, 5V, 8V, and 3V, respectively. Then, the computer 520 adds the 4 final voltages together resulting in a photon voltage value. Specifically, the photon voltage value for this photon and for the right most sensing element column is 6V+5V+8V+3V=22V.
Assume that another X-ray photon later enters the same right most sensing element column. In an embodiment, the imaging system 500 may perform the same operation described above and determine another photon voltage value for this photon and for this right most sensing element column.
In an embodiment, for an exposure time period, the computer 520 may add all the photon voltage values for the right most sensing element column and for all the photons  entering the right most sensing element column during the exposure time period. As a result, the sum of all these photon voltage values represents the total energy of all the photons hitting that right most sensing element column during the exposure time period.
For example, assume that 30 photons of the radiation beam 532 one by one enter the right most sensing element column during the exposure time period. As a result, the imaging system 500 determines 30 photon voltage values for these 30 photons. The sum of all these 30 photon voltage values represents the total energy of all the 30 photons entering that right most sensing element column during the exposure time period.
In an embodiment, the imaging system 500 may perform the same operation described above for the other 19 sensing element columns of the image sensor 510. As a result, because the image sensor 510 has 5 × 4 = 20 sensing element columns, the 20 sums for the 20 sensing element columns represent the values of the 20 picture elements of the image of the object 540. Note that each sensing element column of the image sensor 510 corresponds to a picture element of the image of the object 540.
IGNORING BAD SENSING ELEMENTS –COMPARE WITH SENSING ELEMENT RIGHT ABOVE AND IN SAME COLUMN
In an embodiment, the adding of the final voltages of the sensing elements in the same sensing element column described above may not apply to bad sensing elements. In an embodiment, a sensing element 150 may be considered a bad sensing element if its final voltage exceeds the final voltage of the sensing element 150 right above it in the same sensing element column by at least a pre-specified voltage tolerance value.
For example, assume that the pre-specified voltage tolerance value is 1V, and assume that the final voltages of the sensing elements 150 (4, 7) , 150 (4, 6) , 150 (4, 5) , and 150 (4, 4) are 6V, 5V, 8V, and 3V, respectively. Because the final voltage of a sensing element 150 should decrease when the depth of the sensing element increases, the sensing element 150 (4, 5) may be considered a bad sensing element because its final voltage (8V) exceeds the final voltage (5V) of the sensing element 150 (4, 6) right above it in the right most sensing element column by at least 1V.
In an embodiment, the final voltage of the bad sensing element 150 may be ignored in adding the final voltages for the sensing element column. In the example above, the computer 520 may add 6V+5V+3V=14V for the right most sensing element column (i.e., the final voltage (8V) of the bad sensing element 150 (4, 5) is ignored) .
ALTERNATIVE EMBODIMENTS
BAD SENSING ELEMENT –COMPARE WITH ADJACENT SENSING ELEMENT OF SAME DEPTH
In the embodiments described above, a sensing element 150 is considered bad if its final voltage exceeds the final voltage of the sensing element right above it in the same sensing element column by at least a pre-specified voltage tolerance value. In an alternative embodiment, a sensing element 150 may be considered bad if its final voltage exceeds the final voltage of a sensing element of an adjacent sensing element column and at the same depth by at least a pre-specified voltage tolerance value.
In the example described above, assume that the pre-specified voltage tolerance value is 1V, and that the final voltage of sensing element 150 (3, 5) is 4V. Then, the sensing element 150 (4, 5) may be considered a bad sensing element because its final voltage (8V) exceeds the final voltage (4V) of the sensing element 150 (3, 5) by at least 1V. Note that the sensing element 150 (3, 5) is of an adjacent sensing element column and at the same depth as the sensing element 150 (4, 5) . Note also that because the sensing elements 150 (3, 5) and 150 (4, 5) are at the same depth, there is a straight line which is perpendicular to the reference straight line 519 and intersects both the sensing elements 150 (3, 5) and 150 (4, 5) .
COLUMN GROUPS VS. INDIVIDUAL COLUMNS
In the embodiments described above, the computer 520 adds the measured final voltages of the sensing elements 150 of the same sensing element column. In an alternative embodiment, with all other things being the same, the computer 520 may add the measured final voltages of the sensing elements of the same sensing element column group. A sensing element column group may include multiple adjacent sensing element columns of a radiation absorption layer 110.
For example, the 4 sensing element columns of the radiation absorption layer 110.1 may be divided into 2 sensing element column groups each having 2 adjacent sensing element columns. Specifically, the first sensing element column group may include the left 2 sensing element columns, and the second sensing element column group may include the right 2 sensing element columns. The other 4 radiation absorption layers 110 of the image sensor 510 may be divided into sensing element column groups in a similar manner. As a result, in total, the image sensor 510 has 2 × 5 = 10 sensing element column groups each having 2 adjacent sensing element columns. As a result, the resulting image of the object 540 should have 2 × 5 =  10 picture elements (each picture element of the image corresponds to a sensing element column group) .
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.

Claims (22)

  1. An imaging system, comprising an image sensor which comprises:
    a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1; and
    M collimator regions respectively for the M electronics layers of the M radiation detectors,
    wherein there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region, and
    wherein for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
  2. The imaging system of claim 1, wherein the M collimator regions are respectively on and in direct physical contact with the M electronics layers.
  3. The imaging system of claim 1, further comprising a radiation source,
    wherein each collimator region of the M collimator regions completely shadows the corresponding electronics layer with respect to the radiation source.
  4. The imaging system of claim 1,
    wherein each collimator region of the M collimator regions has a shape of a plate having a thickness being the same as a thickness of the corresponding electronics layer.
  5. The imaging system of claim 1,
    wherein the M radiation absorption layers and the M electronics layers are arranged in an alternating manner.
  6. The imaging system of claim 1, wherein the M collimator regions comprise tungsten.
  7. The imaging system of claim 1,
    wherein for each radiation detector of the M radiation detectors, the radiation absorption layer of said each radiation detector is configured to generate electrical signals in response to incident X-ray photons, and
    wherein the electronics layer of said each radiation detector is configured to process the generated electrical signals.
  8. The imaging system of claim 1,
    wherein each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns,
    wherein for each sensing element column of each radiation absorption layer of the M radiation absorption layers, the imaging system is configured to add final voltages of sensing elements of said each sensing element column whose voltages exceed a pre-specified threshold voltage, and
    wherein a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  9. The imaging system of claim 8,
    wherein said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of said each sensing element column by at least a pre-specified voltage tolerance value,
    wherein the first sensing element is adjacent to the second sensing element, and
    wherein the second sensing element is between the first sensing element and the M collimator regions.
  10. The imaging system of claim 8,
    wherein said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of an adjacent sensing element column by at least a pre-specified voltage tolerance value, and
    wherein a straight line perpendicular to the reference straight line intersects both the first and second sensing elements.
  11. The imaging system of claim 1,
    wherein each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns,
    wherein the sensing element columns of the image sensor are arranged in multiple sensing element column groups of adjacent sensing element columns,
    wherein for each sensing element column group of the image sensor, the imaging system is configured to add final voltages of sensing elements of said each sensing element column group whose voltages exceed a pre-specified threshold voltage,
    wherein said each sensing element column group comprises N sensing element columns, N being an integer greater than 1, and
    wherein for each sensing element column of said each sensing element column group, a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  12. A method, comprising:
    receiving incident radiation with an image sensor of an imaging system, the image sensor comprising:
    a stack of M radiation detectors each of which comprises (A) a radiation absorption layer and (B) an electronics layer configured to process electrical signals generated in the radiation absorption layer, M being an integer greater than 1; and
    M collimator regions respectively for the M electronics layers of the M radiation detectors,
    wherein there is a reference straight line for the image sensor such that for each electronics layer of the M electronics layers, every straight line intersecting said each electronics layer and being parallel to the reference straight line intersects the corresponding collimator region, and
    wherein for each radiation absorption layer of the M radiation absorption layers, every straight line intersecting said each radiation absorption layer and being parallel to the reference straight line does not intersect any collimator region of the M collimator regions.
  13. The method of claim 12, wherein the M collimator regions are respectively on and in direct physical contact with the M electronics layers.
  14. The method of claim 12,
    wherein each collimator region of the M collimator regions completely shadows the corresponding electronics layer with respect to a same radiation source.
  15. The method of claim 12,
    wherein each collimator region of the M collimator regions has a shape of a plate having a thickness being the same as a thickness of the corresponding electronics layer.
  16. The method of claim 12,
    wherein the M radiation absorption layers and the M electronics layers are arranged in an alternating manner.
  17. The method of claim 12, wherein the M collimator regions comprise tungsten.
  18. The method of claim 12,
    wherein for each radiation detector of the M radiation detectors, the radiation absorption layer of said each radiation detector is configured to generate electrical signals in response to incident X-ray photons, and
    wherein the electronics layer of said each radiation detector is configured to process the generated electrical signals.
  19. The method of claim 12,
    wherein each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns,
    wherein the method further comprises for each sensing element column of each radiation absorption layer of the M radiation absorption layers, adding with the imaging system final voltages of sensing elements of said each sensing element column whose voltages exceed a pre-specified threshold voltage, and
    wherein a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
  20. The method of claim 19,
    wherein said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of said each sensing element column by at least a pre-specified voltage tolerance value,
    wherein the first sensing element is adjacent to the second sensing element, and
    wherein the second sensing element is between the first sensing element and the M collimator regions.
  21. The method of claim 19,
    wherein said adding the final voltages does not apply to a first sensing element of said each sensing element column whose final voltage exceeds a final voltage of a second sensing element of an adjacent sensing element column by at least a pre-specified voltage tolerance value, and
    wherein a straight line perpendicular to the reference straight line intersects both the first and second sensing elements.
  22. The method of claim 12,
    wherein each radiation absorption layer of the M radiation absorption layers comprises multiple sensing elements which are arranged in multiple sensing element columns,
    wherein the sensing element columns of the image sensor are arranged in multiple sensing element column groups of adjacent sensing element columns,
    wherein the method further comprises, for each sensing element column group of the image sensor, adding with the imaging system final voltages of sensing elements of said each sensing element column group whose voltages exceed a pre-specified threshold voltage,
    wherein said each sensing element column group comprises N sensing element columns, N being an integer greater than 1, and
    wherein for each sensing element column of said each sensing element column group, a straight line parallel to the reference straight line intersects all sensing elements of said each sensing element column.
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