Semiconductor radiation detector

Abstract

A radiation detector (100) comprising: a radiation absorbing layer (110) configured to absorb radiation; a discrete plurality of first electrodes (119A) on a surface of the radiation absorbing layer (110); a second electrode (119B) on the surface of the radiation absorbing layer (110); wherein each of the plurality of first electrodes (119A) is surrounded by a second electrode (119B); wherein the plurality of first electrodes (119A) do not extend into the radiation absorbing layer (110), and the second electrodes (119B) do not extend into the radiation absorbing layer (110).

Description

[Background Technology]

[0001] A radiation detector may be a device used to measure the flux, spatial distribution, spectrum, or other properties of radiation.

[0002] Radiation detectors can be used in many applications. One important application is imaging. Radiation imaging is a radiographic technique that can be used to reveal the internal structure of objects with heterogeneous composition and opaque structures, such as the human body.

[0003] Early radiation detectors used for imaging included photographic plates and photographic films. Photographic plates can be glass plates coated with a photographic emulsion. Although photographic plates have been superseded by photographic films, they may still be used in special circumstances due to their superior quality and stability. Photographic films can be plastic films (e.g., strips or sheets) coated with a photographic emulsion.

[0004] In the 1980s, photostimulated phosphor plates (PSP plates) became available. PSP plates can contain a fluorescent material with color centers in its crystal lattice. When the PSP plate is exposed to radiation, the electrons excited by the radiation are trapped in the color centers until they are excited by a laser beam scanned across the surface of the PSP plate. When the laser scans the PSP plate, the trapped excited electrons emit light, which is collected by a photomultiplier tube. The collected light is converted into a digital image. Compared to photographic negatives and film, PSP plates can be reused.

[0005] Another type of radiation detector is a radiation image intensifier. The components of a radiation image intensifier are typically sealed in a vacuum. Compared to photographic negatives, photographic film, and PSP boards, radiation image intensifiers can produce real-time images, i.e., no post-exposure processing is required to produce an image. The radiation first strikes an input phosphor (e.g., cesium iodide) and is converted into visible light. The visible light then strikes a photocathode (e.g., a thin metal layer containing a compound of cesium and antimony) and causes electron emission. The number of electrons emitted is proportional to the intensity of the incident radiation. The emitted electrons are projected onto an output phosphor through electron optics, causing the output phosphor to produce a visible light image.

[0006] Scintillators operate somewhat similarly to radiation image intensifiers, in that the scintillator (e.g., sodium iodide) absorbs radiation and emits visible light, which can then be detected by a suitable visible light image sensor. Within the scintillator, visible light propagates and scatters in all directions, reducing spatial resolution. Reducing scintillator thickness improves spatial resolution but also reduces radiation absorption. Therefore, scintillators must achieve a compromise between absorption efficiency and resolution.

[0007] Semiconductor radiation detectors largely overcome this problem by converting radiation directly into electrical signals. Semiconductor radiation detectors can include a semiconductor layer that absorbs radiation at a wavelength of interest. When a radiation particle is absorbed in the semiconductor layer, multiple charge carriers (e.g., electrons and holes) are generated, which are swept by an electric field toward electrical contacts on the semiconductor layer. The cumbersome thermal management required in currently available semiconductor radiation detectors (e.g., Medipix) can make detectors with large areas and large numbers of pixels difficult or impossible to produce. [Summary of the invention]

[0008] This article discloses a radiation detector, comprising: a radiation absorbing layer configured to absorb radiation; a plurality of discrete first electrodes located on a surface of the radiation absorbing layer; and a second electrode located on the surface of the radiation absorbing layer; wherein each of the plurality of first electrodes is surrounded by the second electrode; wherein the plurality of first electrodes do not extend into the radiation absorbing layer; and wherein the second electrode does not extend into the radiation absorbing layer.

[0009] According to one embodiment, any line located on the surface and connecting any two first electrodes of the plurality of first electrodes crosses the second electrode.

[0010] According to one embodiment, the radiation absorbing layer comprises a Group III-V semiconductor.

[0011] According to one embodiment, the III-V semiconductor is GaAs or CdZnTe (CZT).

[0012] According to one embodiment, the radiation detector further comprises a plurality of guard rings located on the surface, wherein each of the plurality of first electrodes is surrounded by at least one guard ring of the plurality of guard rings; wherein the plurality of guard rings are rings of conductive material.

[0013] According to one embodiment, each of the plurality of guard rings is surrounded by the second electrode.

[0014] According to one embodiment, any line located on the surface and connecting any two guard rings of the plurality of guard rings surrounding different first electrodes of the plurality of first electrodes crosses the second electrode.

[0015] According to one embodiment, the plurality of guard rings are electrically insulated from the plurality of first electrodes and the second electrode.

[0016] According to one embodiment, the plurality of guard rings do not extend into the radiation absorbing layer.

[0017] According to one embodiment, the second electrode does not have a plurality of discrete parts.

[0018] According to one embodiment, the second electrode is configured to be electrically biased differently than the plurality of first electrodes.

[0019] According to one embodiment, the second electrode is in the shape of a grid.

[0020] According to one embodiment, said radiation is X-rays.

[0021] According to an embodiment, the radiation detector is configured to receive the radiation at the surface.

[0022] According to one embodiment, the radiation detector further comprises an electronic circuit layer comprising a plurality of first electrical contacts and a second electrical contact; wherein the electronic circuit layer is bonded to the radiation absorbing layer at the surface; wherein the electronic circuit layer substantially does not attenuate the radiation when the radiation passes through the electronic circuit layer; wherein the plurality of first electrodes are respectively connected to the plurality of first electrical contacts, and the second electrode is connected to the second electrical contact.

[0023] According to one embodiment, the electronic circuit layer is configured to bias the plurality of first electrodes and the second electrode to different voltages through the plurality of first electrical contacts and the second electrical contact.

Brief Description of the Drawings

[0024] Figure 1A A cross-sectional view of a radiation detector according to an embodiment is schematically shown.

[0025] Figures 1B to 1D Schematically illustrates perspective, top and cross-sectional views of a first electrode, a second electrode and an optional guard ring on a surface of a radiation absorbing layer of a radiation detector according to an embodiment.

[0026] Figure 2A An electronic circuit layer bonded to a radiation absorbing layer of a radiation detector according to an embodiment is schematically shown.

[0027] Figure 2B It is schematically shown that according to an embodiment, a first electrode is electrically connected to a first electrical contact through a conductive portion, and a second electrode is electrically connected to a second electrical contact through a conductive portion.

[0028] Figures 3A to 3B A component diagram of an electronic system of a radiation detector according to an embodiment is shown.

[0029] Figure 4Schematically shown are the temporal variation of the current flowing through the electrical contact (upper curve) caused by carriers generated by a pulse of visible light incident on a pixel associated with the electrical contact, and the corresponding temporal variation of the voltage of the electrical contact (lower curve).

[0030] Figures 5 to 9 Each schematically shows a system comprising a radiation detector as described herein. [Specific implementation method]

[0031] Figure 1A A cross-sectional view of a radiation detector 100 according to an embodiment is schematically shown. The radiation detector 100 may include a radiation absorbing layer 110 configured to absorb radiation from a radiation source and an electronic circuit layer 120 (e.g., an application-specific integrated circuit) bonded to the radiation absorbing layer 110 at a surface, the electronic circuit layer 120 being used to process or analyze an electrical signal generated in the radiation absorbing layer 110 by the incident radiation. In one embodiment, the radiation absorbing layer 110 includes a III-V semiconductor material, such as GaAs or CdZnTe (CZT). The semiconductor material may have a high mass attenuation coefficient for the radiation energy of interest. The radiation may be an X-ray. As Figures 1B to 1D As shown, the radiation detector 100 may further include a plurality of first electrodes 119A, a second electrode 119B, and a plurality of optional guard rings 119C located on a surface of the radiation absorbing layer 110. The plurality of first electrodes 119A, the second electrode 119B, and the plurality of optional guard rings 119C may be located between the radiation absorbing layer 110 and the electronic circuit layer 120. In one embodiment, the plurality of first electrodes 119A, the second electrode 119B, and the plurality of optional guard rings 119C do not extend into the radiation absorbing layer 110.

[0032] Figures 1B to 1D The perspective view, top view and cross-sectional view of a plurality of first electrodes 119A, a second electrode 119B and a plurality of optional guard rings 119C according to an embodiment are schematically shown. For the sake of clarity, the electronic circuit layer 120 is omitted in these figures. The height of the plurality of first electrodes 119A, the second electrode 119B and the plurality of optional guard rings 119C is Figure 1B and Figure 1D The plurality of first electrodes 119A may be discrete, and each first electrode 119A may be surrounded by a second electrode 119B, as shown in FIG. Figure 1B and Figure 1C The second electrode 119B may be in a mesh shape and may or may not have discrete portions.

[0033] According to one embodiment, Figures 1B to 1DAs shown, the optional guard ring can be a ring made of a conductive material such as aluminum or a heavily doped semiconductor. In one embodiment, each first electrode 119A is surrounded by at least one optional guard ring 119C, and each guard ring is surrounded by a second electrode 119B, as shown in FIG. Figure 1B and Figure 1C Multiple optional guard rings 119C can be used by Figure 1D The plurality of optional guard rings 119C may be electrically floating, electrically grounded, or electrically biased.

[0034] Figure 1C Schematically showing a line 216 (not necessarily a straight line) and a line 217 (not necessarily a straight line) on the surface of the radiation absorbing layer 110. Line 216 connects two first electrodes 119A. Line 217 connects two optional guard rings 119C. According to one embodiment, as Figure 1C As shown in the example in , any line (e.g., line 216) located on the surface and connecting any two first electrodes 119A among the multiple first electrodes 119A crosses the second electrode 119B; any line (e.g., line 217) located on the surface and connecting any two optional guard rings 119C among the multiple optional guard rings 119C that surround different first electrodes 119A among the multiple first electrodes 119A crosses the second electrode 119B.

[0035] Figure 2A Schematically, an electronic circuit layer 120 is shown bonded to a radiation absorbing layer 110 according to an embodiment. The electronic circuit layer 120 may include an electronic system 121 suitable for processing or analyzing signals generated from radiation incident on the radiation absorbing layer 110. The electronic system 121 may include analog circuits such as filter networks, amplifiers, integrators, and comparators, or digital circuits such as microprocessors and memories. The electronic circuit layer 120 may include a plurality of first electrical contacts 118A, a second electrical contact 118B, and a plurality of optional guard ring contacts 118C.

[0036] Figure 2BThe schematic diagram shows that, after the electronic circuit layer 120 and the radiation absorbing layer 110 are bonded, according to an embodiment, a plurality of first electrodes 119A are electrically connected (e.g., via solder balls 131) to a plurality of first electrical contacts 118A, a second electrode 119B is electrically connected (e.g., via solder balls 131) to a second electrical contact 118B, and a plurality of guard ring contacts 118C are electrically connected to a plurality of optional guard rings 119C. Even when the plurality of optional guard rings 119C are present, the plurality of guard ring contacts 118C may not be present. Other bonding techniques may connect the electronic circuit layer 120 to the radiation absorbing layer 110 without the use of solder balls. The electronic circuit layer 120 may be configured to bias the plurality of first electrodes 119A and the second electrode 119B to different voltages via the plurality of first electrical contacts 118A and the second electrical contacts 118B, respectively. For example, one or more voltage sources 122 may supply a non-zero voltage to the plurality of first electrical contacts 118A, and the second electrical contacts 118B may be connected to a virtual ground of an amplifier in the electronic system 121 .

[0037] The radiation detector may be configured to receive radiation at the surface 130 or surface 130' of the radiation absorbing layer 110, such as Figure 2B As shown. In one embodiment, radiation particles emitted from the radiation source must pass through the electronic circuit layer 120 to reach the surface 130 of the radiation absorbing layer 110. The electronic circuit layer 120 may include a radiolucent structural material that does not substantially attenuate the radiation of interest when the radiation passes through the electronic circuit layer 120. In one embodiment, more than 50% of the radiation particles incident on the electronic circuit layer 120 reach the surface 130 of the radiation absorbing layer 110. When the radiation particles strike the surface 130 of the radiation absorbing layer 110, as shown Figure 2B As shown, it may be absorbed by the radiation absorbing layer 110, and the radiation absorbing layer 110 may generate one or more carriers through various mechanisms. The radiation particles may generate 10 to 100,000 carriers. The carriers may drift to the plurality of first electrodes 119A and second electrodes 119B under the action of an electric field. The electric field can be established by biasing the plurality of first electrodes 119A and second electrodes 119B differently. According to one embodiment, the distance between one first electrode 119A in the plurality of first electrodes 119A and its nearest second electrode 119B does not exceed 2λ, where λ is the mean free path of the carriers in the radiation absorbing layer 110.

[0038] Figure 3A and Figure 3B Each of the diagrams shows a component of the electronic system 121 according to an embodiment. The electronic system 121 may include a first voltage comparator 301 , a second voltage comparator 302 , a counter 320 , a switch 305 , a voltmeter 306 , and a controller 310 .

[0039] The first voltage comparator 301 is configured to compare the voltage of one of the plurality of first electrical contacts 118A with a first threshold value. The first voltage comparator 301 can be configured to monitor the voltage directly or to calculate the voltage by integrating the current flowing through the electrical contact over a period of time. The first voltage comparator 301 can be controllably enabled or disabled by the controller 310. The first voltage comparator 301 can be a continuous comparator. That is, the first voltage comparator 301 can be configured to be continuously enabled and continuously monitor the voltage. The first voltage comparator 301 can be a clocked comparator, which has the advantage of low power consumption. The first threshold value can be 5-10%, 10%-20%, 20-30%, 30-40%, or 40-50% of the voltage that a single visible light pulse can generate at the electrical contact. The maximum voltage can depend on the energy of the incident radiation particle, the material of the radiation absorbing layer 110, and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV, or 200 mV.

[0040] The second voltage comparator 302 is configured to compare the voltage to a second threshold. The second voltage comparator 302 can be configured to monitor the voltage directly or to calculate the voltage by integrating the current flowing through the electrical contact over a period of time. The second voltage comparator 302 can be a continuous comparator. The second voltage comparator 302 can be controllably enabled or disabled by the controller 310. When the second voltage comparator 302 is disabled, the power consumption of the second voltage comparator 302 can be less than 1%, 5%, 10%, or 20% of the power consumption when the second voltage comparator 302 is enabled. The absolute value of the second threshold is greater than the absolute value of the first threshold. As used herein, the term "absolute value" or "modulus" of a real number x, |x|, is the non-negative value of x regardless of its sign. That is, if x>=0, then |x|=x, and if x<=0, then |x|=-x. The second threshold can be 200%-300% of the first threshold. The second threshold value can be at least 50% of the maximum voltage that an incident radiation particle can generate on the first electrical contact 118A. For example, the second threshold value can be 100mV, 150mV, 200mV, 250mV, or 300mV. The second voltage comparator 302 and the first voltage comparator 310 can be the same component. That is, the electronic system 121 can have a voltage comparator that is capable of comparing the voltage to two different threshold values at different times.

[0041] The first voltage comparator 301 or the second voltage comparator 302 may include one or more operational amplifiers or any other suitable circuits. The first voltage comparator 301 or the second voltage comparator 302 may have a high speed to allow the electronic system 121 to operate under a high flux of incident radiation particles. However, having a high speed often comes at the expense of power consumption.

[0042] Counter 320 is configured to record at least the number of radiation particles received by radiation absorbing layer 110. Counter 320 may be a software component (eg, a number stored in computer memory) or a hardware component (eg, 4017 IC and 7490 IC).

[0043] The controller 310 can be a hardware component, such as a microcontroller or microprocessor. The controller 310 is configured to initiate a time delay from the time the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of a first threshold (e.g., the absolute value of the voltage increases from an absolute value below the first threshold to a value equal to or above the absolute value of the first threshold). The term "absolute value" is used herein because the voltage can be negative or positive, depending on whether the voltage at the cathode or anode of the diode is utilized, or which electrical contact is utilized. The controller 310 can be configured to disable the second voltage comparator 302, the counter 320, and any other circuitry not required for the operation of the first voltage comparator 301 before the time the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold. The time delay can terminate before or after the voltage becomes stable, i.e., the rate of change of the voltage is substantially zero. The phrase "the rate of change of the voltage is substantially zero" means that the temporal variation of the voltage is less than 0.1% / ns. The phrase "the rate of change of the voltage is not substantially zero" means that the temporal variation of the voltage is at least 0.1% / ns.

[0044] The controller 310 can be configured to enable the second voltage comparator during the time delay (including the start and end). In one embodiment, the controller 310 is configured to enable the second voltage comparator at the start of the time delay. The term "enable" means that the component enters an operating state (for example, by sending a signal such as a voltage pulse or logic level, by powering on, etc.). The term "disable" means that the component enters a non-operating state (for example, by sending a signal such as a voltage pulse or logic level, by powering off, etc.). The operating state can have a higher power consumption than the non-operating state (for example, 10 times higher, 100 times higher, 1000 times higher). The controller 310 itself can be disabled until the output of the first voltage comparator 301 enables the controller 310 when the absolute value of the voltage equals or exceeds the absolute value of the first threshold.

[0045] The controller 310 may be configured to increase the number recorded by the counter 320 by one if the second voltage comparator 302 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold during the time delay.

[0046] The controller 310 can be configured to cause the optional voltmeter 306 to measure the voltage when the time delay expires. The controller 310 can be configured to connect the electrical contact in the plurality of first electrical contacts 118A to electrical ground to reset the voltage and release any carriers accumulated on the electrical contact in the plurality of first electrical contacts 118A. In one embodiment, the electrical contact in the plurality of first electrical contacts 118A is connected to electrical ground after the time delay expires. In one embodiment, the electrical contact in the plurality of first electrical contacts 118A is connected to electrical ground for a limited reset time period. The controller 310 can connect the electrical contact in the plurality of first electrical contacts 118A to electrical ground by controlling the switch 305. The switch can be a transistor such as a field effect transistor (FET).

[0047] In one embodiment, the system 121 has no analog filtering networks (eg, RC networks). In one embodiment, the system 121 has no analog circuitry.

[0048] The voltmeter 306 may feed its measured voltage to the controller 310 as an analog signal or a digital signal.

[0049] The electronic system 121 may include an integrator 309 electrically connected to the electrical contact in the plurality of first electrical contacts 118A, wherein the integrator is configured to collect carriers from the electrical contact in the plurality of first electrical contacts 118A. The integrator 309 may include a capacitor located in the feedback path of the amplifier. An amplifier configured in this way is referred to as a capacitive transimpedance amplifier (CTIA). A capacitive transimpedance amplifier has a high dynamic range by preventing the amplifier from saturating and improves the signal-to-noise ratio by limiting the bandwidth in the signal path. The carriers from the electrical contact in the plurality of first electrical contacts 118A accumulate in the capacitor over a period of time ("integration period"). After the integration period terminates, the voltage of the capacitor is sampled and then reset by a reset switch. The integrator 309 may include a capacitor directly connected to the electrical contact in the plurality of first electrical contacts 118A.

[0050] Figure 4The diagram schematically illustrates the temporal variation of current flowing through one of the plurality of first electrical contacts 118A due to carriers generated by radiation particles (upper curve), and the corresponding temporal variation of voltage across one of the plurality of first electrical contacts 118A (lower curve). The voltage may be the time integral of the current. At time t0, a radiation particle strikes the radiation absorbing layer 110, carriers begin to be generated in the radiation absorbing layer 110, current begins to flow through one of the plurality of first electrical contacts 118A, and the absolute value of the voltage across one of the plurality of first electrical contacts 118A begins to increase. At time t1, the first voltage comparator 301 determines that the absolute value of the voltage equals or exceeds the absolute value of the first threshold V1, and the controller 310 initiates a time delay TD1. The controller 310 may deactivate the first voltage comparator 301 at the start of the time delay TD1. If the controller 310 was deactivated before time t1, it is activated at time t1. During the time delay TD1, the controller 310 enables the second voltage comparator 302. As used herein, the term "period" of a time delay refers to the start and end (i.e., the end) and any time therebetween. For example, the controller 310 may enable the second voltage comparator 302 when the time delay TD1 ends. If, during the time delay TD1, the second voltage comparator 302 determines that the absolute value of the voltage is equal to or exceeds the absolute value of the second threshold value V2 at time t2, the controller 310 waits for the voltage to stabilize. The voltage stabilizes at time t2 when all carriers generated by the radiation particles drift out of the radiation absorbing layer 110. e Stable. At time t s , time delay TD1 ends. At time t e or at time t e Afterwards, the controller 310 causes the voltmeter 306 to digitize the voltage and determine which bin the energy of the radiation particle falls into. The controller 310 then causes the counter 320 corresponding to the bin to increase the number recorded by one. Figure 4 In the example, time t s At time t e After that; that is, after all carriers generated by the radiation particles drift out of the radiation absorbing layer 110, the time delay TD1 ends. e cannot be easily measured, the time delay TD1 can be chosen empirically to allow enough time to collect substantially all the carriers generated by the radiation particle, but not so long as to risk another incident radiation particle. That is, the time delay TD1 can be chosen empirically so that the time t s Based on experience, at time t e After that. Time t s Not necessarily at time t eAfterwards, since once the second threshold V2 is reached, the controller 310 may ignore the time delay TD1 and wait for the time t e Therefore, the rate of change of the difference between the voltage and the dark current contribution to that voltage at time t e The controller 310 may be configured to deactivate the second voltage comparator 302 upon expiration of the time delay TD1 , or at time t2 , or any time therebetween.

[0051] Time t e The voltage of φ is proportional to the number of carriers generated by the irradiated particle, which is related to the energy of the irradiated particle. The controller 310 can be configured to use the voltmeter 306 to determine the energy of the irradiated particle.

[0052] After the expiration of time delay TD1 or the digitization of voltmeter 306, whichever is later, controller 310 connects the one of the plurality of first electrical contacts 118A to electrical ground during a reset period RST, allowing charge carriers accumulated at the one of the plurality of first electrical contacts 118A to flow to ground and reset the voltage. After reset period RST, electronic system 121 is ready to detect another incident radiation particle. If first voltage comparator 301 has been disabled, controller 310 can enable first voltage comparator 301 at any time before the expiration of reset period RST. If controller 310 has been disabled, controller 310 can be enabled before the expiration of reset period RST.

[0053] The radiation detector 100 described above may be used in various systems, such as the system provided below.

[0054] Figure 5 A system 9000 including a radiation detector 100 as described herein is schematically shown. The system can be used for medical imaging, such as chest radiation radiography, abdominal radiation radiography, and the like. The system includes a radiation source 1201. Radiation emitted from radiation source 1201 penetrates an object 1202 (e.g., a human body part such as the chest, limbs, or abdomen), is attenuated to varying degrees by the internal structures of object 1202 (e.g., bone, muscle, fat, and organs), and is projected onto system 9000. System 9000 forms an image by detecting the intensity distribution of the radiation.

[0055] Figure 6A system 9000 including a radiation detector 100 as described herein is schematically shown. The system can be used for medical imaging, such as dental radiation radiography. The system includes a radiation source 1301. Radiation emitted from the radiation source 1301 penetrates an object 1302, which is a portion of the oral cavity of a mammal (e.g., a human). The object 1302 may include the maxilla, palate, teeth, mandible, or tongue. The radiation is attenuated to varying degrees by different structures of the object 1302 and is projected onto the system 9000. The system 9000 forms an image by detecting the intensity distribution of the radiation. Teeth absorb more radiation than caries, infections, or periodontal ligaments. The radiation dose received by dental patients is typically small (about 0.150 mSv for a full mouth series).

[0056] Figure 7 A cargo scanning or non-intrusive inspection (NII) system 9000 is schematically shown, including a radiation detector 100 as described herein. This system can be used for luggage screening at bus stations and airports. The system includes a radiation source 1501. Radiation emitted from radiation source 1501 can penetrate luggage 1502, be differentially attenuated by the luggage's contents, and be projected onto system 9000. System 9000 forms an image by detecting the intensity distribution of the transmitted radiation. System 9000 can reveal the contents of luggage and identify items prohibited on public transportation, such as firearms, narcotics, sharp objects, and flammable materials.

[0057] Figure 8 A whole-body scanner system 9000 including a radiation detector 100 as described herein is schematically shown. The whole-body scanner system 9000 can detect objects on the human body for security screening purposes without requiring physical undressing or physical contact. The whole-body scanner system is capable of detecting non-metallic objects. The whole-body scanner system includes a radiation source 1601. Radiation emitted from the radiation source 1601 can be backscattered from a person being screened 1602 and objects thereon and projected onto the system 9000. Objects and the human body can backscatter radiation differently. The system 9000 forms an image by detecting the intensity distribution of the backscattered radiation. The system 9000 and the radiation source 1601 can be configured to scan a person in a linear or rotational direction.

[0058] Figure 9A radiation computed tomography (radiation CT) system is schematically shown. A radiation CT system uses computer-processed radiation to produce tomographic images (virtual "slices") of specific regions of a scanned object. The tomographic images can be used for diagnostic and therapeutic purposes in various medical disciplines, or for defect detection, failure analysis, metrology, assembly analysis, and reverse engineering. The radiation CT system includes the radiation detector 100 and radiation source 1701 described herein. The radiation detector 100 and radiation source 1701 can be configured to rotate synchronously along one or more circular or spiral paths.

[0059] The radiation detector 100 described herein may have other applications, such as radiation telescopes, radiation mammography, industrial radiation defect detection, radiation microscopy or microradiography, radiation casting inspection, radiation nondestructive testing, radiation weld inspection, radiation digital subtraction angiography, etc. The system 9000 may be adapted to replace photographic plates, photographic films, photostimulated phosphor plates (PSP plates), radiation image intensifiers, scintillators, or another semiconductor radiation detector.

[0060] Although 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

1. A radiation detector comprising: a radiation absorbing layer configured to absorb radiation; a plurality of first electrodes, located on a surface of the radiation absorbing layer, wherein the plurality of first electrodes are discrete; as well as a second electrode located on the surface of the radiation absorbing layer; wherein each of the plurality of first electrodes is surrounded by the second electrode; wherein the plurality of first electrodes do not extend into the radiation absorbing layer; and The second electrode does not extend into the radiation absorbing layer.

2. The radiation detector according to claim 1, wherein Any line located on the surface and connecting any two first electrodes of the plurality of first electrodes crosses the second electrode.

3. The radiation detector according to claim 1, wherein The radiation absorbing layer includes a Group III-V semiconductor.

4. The radiation detector according to claim 3, wherein: The III-V semiconductor is GaAs or CdZnTe.

5. The radiation detector according to claim 1, further comprising a plurality of guard rings located on the surface, wherein: Each of the plurality of first electrodes is surrounded by at least one guard ring of the plurality of guard rings; wherein the plurality of guard rings are rings of conductive material. The radiation detector according to claim 5 , wherein: Each of the plurality of guard rings is surrounded by the second electrode.

7. The radiation detector according to claim 5, wherein Any line located on the surface and connecting any two guard rings of the plurality of guard rings surrounding different first electrodes of the plurality of first electrodes crosses the second electrode.

8. The radiation detector according to claim 5, wherein The plurality of guard rings are electrically insulated from the plurality of first electrodes and the second electrode.

9. The radiation detector according to claim 5, wherein: The plurality of guard rings do not extend into the radiation absorbing layer.

10. The radiation detector according to claim 1, wherein The second electrode does not have a plurality of discrete portions.

11. The radiation detector according to claim 1, wherein: The second electrode is configured to be electrically biased differently than the plurality of first electrodes.

12. The radiation detector according to claim 1, wherein The second electrode has a mesh shape.

13. The radiation detector according to claim 1, wherein The radiation is X-rays.

14. The radiation detector according to claim 1, wherein The radiation detector is configured to receive the radiation at the surface.

15. The radiation detector of claim 1 , further comprising an electronic circuit layer, the electronic circuit layer comprising a plurality of first and second electrical contacts; in, The electronic circuit layer is bonded to the radiation absorbing layer at the surface; wherein, when the radiation passes through the electronic circuit layer, the electronic circuit layer does not substantially attenuate the radiation; The plurality of first electrodes are respectively connected to the plurality of first electrical contacts, and the second electrode is connected to the second electrical contact.

16. The radiation detector according to claim 15, wherein: The electronic circuit layer is configured to bias the plurality of first electrodes and the second electrode to different voltages through the plurality of first electrical contacts and the second electrical contact.

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