WO2023123161A1

WO2023123161A1 - Imaging systems with image sensors for side radiation incidence during imaging

Info

Publication number: WO2023123161A1
Application number: PCT/CN2021/142884
Authority: WO
Inventors: Peiyan CAO; Yurun LIU
Original assignee: Shenzhen Xpectvision Technology Co., Ltd.
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2023-07-06
Also published as: TW202326176A

Abstract

Disclosed herein is a system comprising an image sensor (600) which comprises: M metal layers (metal layers (i), i=1,..., M) (610) and M radiation detectors (radiation detectors (i), i=1,..., M) (105). For each value of i, the radiation detector (i) (105) comprises (A) a radiation absorption layer (i) (115) which comprises multiple sensing elements (150), and (B) Ni integrated circuit chips (125) configured to process electrical signals generated in the radiation absorption layer (i) (115). M is an integer greater than 1. Ni, i=1,..., M are positive integers. The M metal layers (610) and the radiation absorption layers (i) (115), i=1,..., M together form a stack of layers.

Description

IMAGING SYSTEMS WITH IMAGE SENSORS FOR SIDE RADIATION INCIDENCE DURING IMAGING

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 a system comprising an image sensor which comprises M metal layers (metal layers (i) , i=1, …, M) and M radiation detectors (radiation detectors (i) , i=1, …, M) . For each value of i, the radiation detector (i) comprises (A) a radiation absorption layer (i) which comprises multiple sensing elements, and (B) Ni integrated circuit chips configured to process electrical signals generated in the radiation absorption layer (i) . M is an integer greater than 1. Ni, i=1, …, M are positive integers. The M metal layers and the radiation absorption layers (i) , i=1, …, M together form a stack of layers.

In an aspect, the stack comprises 2×M layers.

In an aspect, the M metal layers comprise a metal whose atomic number is at least 26.

In an aspect, the metal is tungsten, platinum, or gold.

In an aspect, the M metal layers and the radiation absorption layers (i) , i=1, …, M are arranged in an alternating manner in the stack.

In an aspect, a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and a plane perpendicular to the best-fit plane intersects all the M metal layers and does not intersect any radiation absorption layer of the radiation absorption layers (i) , i=1, …, M.

In an aspect, a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and each metal layer of the M metal layers has a thickness in a range of 50 microns to 100 microns measured in a direction perpendicular to the best-fit plane.

In an aspect, for each value of i, each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) comprises an application-specific integrated circuit (ASIC) .

In an aspect, the M metal layers are configured to block and absorb X-rays.

In an aspect, for each value of i, each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) is sandwiched between the metal layer (i) and the radiation absorption layer (i) .

In an aspect, for each value of i, the metal layer (i) comprises Pi voids, Pi being a positive integer not greater than Ni, and for each value of i, the Ni integrated circuit chips of the radiation detector (i) are within the Pi voids of the metal layer (i) .

In an aspect, Ni>Pi for each value of i.

In an aspect, Ni=Pi for each value of i, and for each value of i, the Ni integrated circuit chips of the radiation detector (i) are respectively within the Pi voids of the metal layer (i) .

In an aspect, a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and for each value of i, for each void of the Pi voids of the metal layer (i) , every straight line intersecting said each void and perpendicular to the best-fit plane intersects the radiation absorption layer (i) .

In an aspect, a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and for each value of i, a thickness of each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) measured in a direction perpendicular to the best-fit plane is less than a thickness of the metal layer (i) measured in a direction perpendicular to the best-fit plane.

In an aspect, for each value of i, each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) is not in direct physical contact with the radiation absorption layer of another radiation detector of the M radiation detectors.

In an aspect, every straight line segment having 2 ends respectively on 2 adjacent radiation absorption layers of the radiation absorption layers (i) , i=1, …, M intersects (A) at least a metal layer of the M metal layers, or (B) at least a void of a metal layer of the M metal layers.

In an aspect, every straight line segment having 2 ends respectively on 2 adjacent radiation absorption layers of the radiation absorption layers (i) , i=1, …, M intersects a metal layer of the M metal layers.

In an aspect, the system further comprises a radiation source; a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M; and a straight line parallel to the best-fit plane intersects both the radiation source and the image sensor. Also disclosed herein is a method of using this system. The method includes sending radiation from the radiation source toward the image sensor and toward an object positioned between the radiation source and the image sensor; and capturing with the image sensor an image of the object by using a portion of the radiation from the radiation source that has transmitted through the object.

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 a perspective view of another radiation detector, according to an embodiment.

Fig. 6 schematically shows a side view of an image sensor, according to an embodiment.

Fig. 7 schematically shows a side view of the image sensor, according to an alternative embodiment.

Fig. 8 schematically shows a cross-sectional view of the image sensor of Fig. 7, according to an embodiment.

Fig. 9 schematically shows an imaging system, according to an embodiment.

Fig. 10 shows a flowchart generalizing the operation of the imaging system, according to an embodiment.

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.

RADIATION DETECTOR WITH INTEGRATED CIRCUIT CHIPS

Fig. 5 schematically shows a perspective view of a radiation detector 105, according to an embodiment. In an embodiment, the radiation detector 105 may comprise a radiation absorption layer 115 and one or more integrated circuit chips 125 (e.g., 4

integrated circuit chips

125a, 125b, 125c, and 125d as shown) .

In an embodiment, the radiation detector 105 may be similar to the radiation detector 100 of Fig. 1 –Fig. 4 in that (A) the radiation absorption layer 115 of the radiation detector 105 is similar to the radiation absorption layer 110 of the radiation detector 100 in terms of structure and function, and (B) the integrated circuit chips 125 of the radiation detector 105 are similar to the electronics layer 120 of the radiation detector 100 in terms of function.

Specifically, in an embodiment, the integrated circuit chips 125 may be configured to process electrical signals generated in the radiation absorption layer 115. In an embodiment, each of the integrated circuit chips 125 may include an ASIC (application-specific integrated circuit) .

IMAGE SENSOR

Fig. 6 schematically shows a side view of an image sensor 600, according to an embodiment. In an embodiment, the image sensor 600 may include multiple radiation detectors 105 (e.g., 3 radiation detectors 105.1, 105.2, and 105.3 as shown) . The radiation detectors 105.1, 105.2, and 105.3 may include radiation absorption layers 115.1, 115.2, and 115.3 respectively.

In an embodiment, the image sensor 600 may further include multiple metal layers 610 (e.g., 3 metal layers 610.1, 610.2, and 610.3 as shown) . In an embodiment, the 3 metal layers 610.1, 610.2, and 610.3 and the 3 radiation absorption layers 115.1, 115.2, and 115.3 together form a stack of 6 layers as shown.

In an embodiment, the 3 metal layers 610.1, 610.2, and 610.3 and the 3 radiation absorption layers 115.1, 115.2, and 115.3 may be arranged in an alternating manner in the stack as shown. “Alternating manner” means that the layers in the stack are arranged in the order of a metal layer 610, then a radiation absorption layer 115, then a metal layer 610, then a radiation absorption layer 115, and so on.

In an embodiment, the metal layers 610 of the image sensor 600 may include a metal whose atomic number is at least 26 (such as tungsten, platinum, and gold) . In an embodiment, the metal layers 610 may block and absorb X-rays.

In an embodiment, with reference to Fig. 6, each of the integrated circuit chips 125 of the image sensor 600 may be sandwiched between the corresponding metal layer 610 and the corresponding radiation absorption layer 115. For example, the integrated circuit chip 125a. 1 of the radiation detector 105.1 is sandwiched between the corresponding metal layer 610.1 and the corresponding radiation absorption layer 115.1. For another example, the integrated circuit chip 125b. 1 of the radiation detector 105.1 is sandwiched between the corresponding metal layer 610.1 and the corresponding radiation absorption layer 115.1.

In an embodiment, with reference to Fig. 6, a best-fit plane 620 passes through all the sensing elements 150 of one of the 3 radiation absorption layers 115.1, 115.2, and 115.3 (e.g., the radiation absorption layer 115.1 as shown) . Note that the best-fit plane 620 is perpendicular to the page; therefore, the best-fit plane 620 is represented by a straight line. In an embodiment, the structure of the image sensor 600 may be such that there exists at least a plane (e.g., plane 630) that (A) is perpendicular to the best-fit plane 620, (B) intersects all the metal layers 610, and (C) does not intersect any radiation absorption layer 115. In other words, structurally, all the metal layers 610 protrude in the same direction (e.g., upward as shown) from the image sensor 600. Note that the plane 630 is chosen to be perpendicular to the page; therefore, the plane 630 is represented by a straight line.

In an embodiment, with reference to Fig. 6, each of the metal layers 610 may have a thickness in a range of 50 microns to 100 microns measured in a direction perpendicular to the best-fit plane 620. For example, the thickness 640 of the metal layer 610.1 measured in a direction perpendicular to the best-fit plane 620 is in a range of 50 microns to 100 microns.

In an embodiment, with reference to Fig. 6, the structure of the image sensor 600 may be such that every straight line segment having 2 ends respectively on 2 adjacent radiation absorption layers 115 intersects a metal layer 610. For example, every straight line segment having 2 ends respectively on the 2 adjacent radiation absorption layers 115.1 and 115.2 intersects the metal layer 610.2.

In an embodiment, the integrated circuit chips 125 of different radiation detectors 105 may be staggered. For example, a line perpendicular to the stack and that goes through one integrated circuit chip may not go through another integrated circuit chip.

ALTERNATIVE EMBODIMENTS OF IMAGE SENSOR

Fig. 7 schematically shows the image sensor 600 of Fig. 6 as viewed from a viewpoint 650, according to an alternative embodiment. Fig. 8 schematically shows a cross-sectional view of the image sensor 600 of Fig. 7 along a line 8-8, according to an embodiment.

In an embodiment, with reference to Fig. 7 –Fig. 8, each of the metal layers 610 may include one or more voids 612 (e.g., 4 voids 612a. 1, 612b. 1, 612c. 1, and 612d. 1 of the metal layer 610.1 as shown) . In an embodiment, for each radiation detector 105, the integrated circuit chips 125 of said each radiation detector 105 may be respectively within the voids 612 of the corresponding metal layer 610. For example, for the radiation detector 105.1, the 4 integrated circuit chips 125a. 1, 125b. 1, 125c. 1, and 125d. 1 of the radiation detector 105.1 are respectively within the 4 voids 612a. 1, 612b. 1, 612c. 1, and 612d. 1 of the corresponding metal layer 610.1.

In general, the number of voids 612 of each metal layer 610 may be equal to or smaller than the number of integrated circuit chips 125 of the corresponding radiation detector 105. The case where the number of voids 612 of a metal layer 610 is equal to the number of integrated circuit chips 125 of the corresponding radiation detector 105 is described above.

In the case where the number of voids 612 of a metal layer 610 is smaller than the number of integrated circuit chips 125 of the corresponding radiation detector 105, at least one of the voids 612 holds multiple integrated circuit chips 125. For example, with reference to Fig. 7 –Fig. 8, if the voids 612a. 1 and 612b. 1 are replaced by a larger void (not shown) , then the larger void may hold the 2 integrated circuit chips 125a. 1 and 125b. 1. In other words, the 2 integrated circuit chips 125a. 1 and 125b. 1 are within the larger void. Note that in this case, the metal layer 610.1 has 3 voids: the void 612c. 1, the void 612d. 1, and the larger void mentioned above.

In an embodiment, with reference to Fig. 8, the structure of the image sensor 600 may be such that, for each void 612 of each metal layer 610, every straight line intersecting said each void 612 and perpendicular to the best-fit plane 620 intersects the corresponding radiation absorption layer 115. For example, for the void 612a. 1 of the metal layer 610.1, every straight line intersecting the void 612a. 1 and perpendicular to the best-fit plane 620 intersects the corresponding radiation absorption layer 115.1. For another example, for the void 612b. 1 of the metal layer 610.1, every straight line intersecting the void 612b. 1 and perpendicular to the best-fit plane 620 intersects the corresponding radiation absorption layer 115.1.

In an embodiment, with reference to Fig. 8, the thickness of each integrated circuit chip 125 measured in a direction perpendicular to the best-fit plane 620 may be less than the thickness of the corresponding metal layer 610 measured in a direction perpendicular to the best-fit plane 620. For example, the thickness 127 of the integrated circuit chip 125a. 1 measured in a direction perpendicular to the best-fit plane 620 is less than the thickness 640 of the corresponding metal layer 610.1 measured in a direction perpendicular to the best-fit plane 620.

In an embodiment, with reference to Fig. 8, each integrated circuit chip 125 of a radiation detector 105 is not in direct physical contact with the radiation absorption layer 115 of another radiation detector 105. For example, the integrated circuit chip 125a. 2 of the radiation detector 105.2 is not in direct physical contact with any radiation absorption layer 115 of the other radiation detectors 105.1 and 105.3. For another example, the integrated circuit chip 125b. 2 of the radiation detector 105.2 is not in direct physical contact with any radiation absorption layer 115 of the other radiation detectors 105.1 and 105.3.

In an embodiment, with reference to Fig. 8, the structure of the image sensor 600 may be such that every straight line segment having 2 ends respectively on 2 adjacent radiation absorption layers 115 intersects (A) at least a metal layer 610, or (B) at least a void 612. For example, every straight line segment having 2 ends respectively on the 2 adjacent radiation absorption layers 115.1 and 115.2 intersects (A) at least the metal layer 610.2, or (B) at least a void 612 of the metal layer 610.2.

IMAGING SYSTEM

Fig. 9 schematically shows an imaging system 900, according to an embodiment. In an embodiment, the imaging system 900 may include a radiation source 910 and the image sensor 600 of Fig. 8 (or the image sensor 600 of Fig. 6) .

In an embodiment, with reference to Fig. 9, the radiation source 910 and the image sensor 600 may be arranged such that a straight line (not shown) parallel to the best-fit plane 620 intersects both the radiation source 910 and the image sensor 600. This arrangement allows for side radiation incidence during imaging using the image sensor 600.

In an embodiment, the radiation source 910 may send radiation 912 toward the image sensor 600 and toward an object 920 positioned between the radiation source 910 and the image sensor 600. In an embodiment, the image sensor 600 may capture an image of the object 920 by using a portion of the radiation 912 from the radiation source 910 that has transmitted through the object 920. The term “image” in the present application 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.

FLOWCHART FOR GENERALIZATION OF OPERATION OF IMAGING SYSTEM

Fig. 10 shows a flowchart 1000 generalizing the operation of the imaging system 900 of Fig. 9. In step 1010, radiation is sent from the radiation source toward the image sensor and toward an object positioned between the radiation source and the image sensor. For example, in the embodiments described above, with reference to Fig. 9, the radiation 912 is sent from the radiation source 910 toward the image sensor 600 and toward the object 920 positioned between the radiation source 910 and the image sensor 600.

In step 1020, the image sensor captures an image of the object by using a portion of the radiation from the radiation source that has transmitted through the object. For example, in the embodiments described above, with reference to Fig. 9, the image sensor 600 captures an image of the object 920 by using a portion of the radiation 912 from the radiation source 910 that has transmitted through the object 920.

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

A system, comprising an image sensor which comprises:

M metal layers (metal layers (i) , i=1, …, M) ; and

M radiation detectors (radiation detectors (i) , i=1, …, M) ,

wherein for each value of i, the radiation detector (i) comprises (A) a radiation absorption layer (i) which comprises multiple sensing elements, and (B) Ni integrated circuit chips configured to process electrical signals generated in the radiation absorption layer (i) ,

wherein M is an integer greater than 1,

wherein Ni, i=1, …, M are positive integers, and

wherein the M metal layers and the radiation absorption layers (i) , i=1, …, M together form a stack of layers.
The system of claim 1, wherein the stack comprises 2×M layers.
The system of claim 1, wherein the M metal layers comprise a metal whose atomic number is at least 26.
The system of claim 3, wherein the metal is tungsten, platinum, or gold.
The system of claim 1, wherein the M metal layers and the radiation absorption layers (i) , i=1, …, M are arranged in an alternating manner in the stack.
The system of claim 1,

wherein a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and

wherein a plane perpendicular to the best-fit plane intersects all the M metal layers and does not intersect any radiation absorption layer of the radiation absorption layers (i) , i=1, …, M.
The system of claim 1,

wherein a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and

wherein each metal layer of the M metal layers has a thickness in a range of 50 microns to 100 microns measured in a direction perpendicular to the best-fit plane.
The system of claim 1, wherein for each value of i, each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) comprises an application-specific integrated circuit (ASIC) .
The system of claim 1, wherein the M metal layers are configured to block and absorb X-rays.
The system of claim 1, wherein for each value of i, each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) is sandwiched between the metal layer (i) and the radiation absorption layer (i) .
The system of claim 1,

wherein for each value of i, the metal layer (i) comprises Pi voids, Pi being a positive integer not greater than Ni, and

wherein for each value of i, the Ni integrated circuit chips of the radiation detector (i) are within the Pi voids of the metal layer (i) .
The system of claim 11, wherein Ni>Pi for each value of i.
The system of claim 11,

wherein Ni=Pi for each value of i, and

wherein for each value of i, the Ni integrated circuit chips of the radiation detector (i) are respectively within the Pi voids of the metal layer (i) .
The system of claim 13,

wherein a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and

wherein for each value of i, for each void of the Pi voids of the metal layer (i) , every straight line intersecting said each void and perpendicular to the best-fit plane intersects the radiation absorption layer (i) .
The system of claim 13,

wherein a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and

wherein for each value of i, a thickness of each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) measured in a direction perpendicular to the best-fit plane is less than a thickness of the metal layer (i) measured in a direction perpendicular to the best-fit plane.
The system of claim 13, wherein for each value of i, each integrated circuit chip of the Ni integrated circuit chips of the radiation detector (i) is not in direct physical contact with the radiation absorption layer of another radiation detector of the M radiation detectors.
The system of claim 13, wherein every straight line segment having 2 ends respectively on 2 adjacent radiation absorption layers of the radiation absorption layers (i) , i=1, …, M intersects (A) at least a metal layer of the M metal layers, or (B) at least a void of a metal layer of the M metal layers.
The system of claim 1, wherein every straight line segment having 2 ends respectively on 2 adjacent radiation absorption layers of the radiation absorption layers (i) , i=1, …, M intersects a metal layer of the M metal layers.
The system of claim 1, further comprising a radiation source,

wherein a best-fit plane passes through all sensing elements of a radiation absorption layer of the radiation absorption layers (i) , i=1, …, M, and

wherein a straight line parallel to the best-fit plane intersects both the radiation source and the image sensor.
A method of using the system of claim 19, comprising:

sending radiation from the radiation source toward the image sensor and toward an object positioned between the radiation source and the image sensor; and

capturing with the image sensor an image of the object by using a portion of the radiation from the radiation source that has transmitted through the object.