JP2020008587A - Method of making semiconductor x-ray detectors - Google Patents

Abstract

To provide a method of making an X-ray detector with a large area and a large number of pixels.SOLUTION: A method of making an X-ray detector comprises: preparing a substrate 122 comprising electric contacts 125, and a first chip comprising a first X-ray absorption layer 110 having an individual electrode 114; and bonding the first X-ray absorption layer 110 to the substrate 122 such that the individual electrode 114 of the first X-ray absorption layer 110 is electrically connected to the electrical contacts 125 of the substrate 122.SELECTED DRAWING: Figure 4A

Description

  The present disclosure relates to an X-ray detector, and more particularly, to a method for manufacturing a semiconductor X-ray detector.

  An x-ray detector may be a device used to measure the flux, spatial distribution, spectrum, or other property of x-rays.

  X-ray detectors can be used for many applications. One important application is imaging. X-ray imaging is a radiographic technique and can be used to reveal the internal structure of non-uniformly configured and opaque objects, such as the human body.

  Early X-ray detectors for imaging include photographic plates and films. The photographic plate may be a glass plate having a coating of a photosensitive emulsion. Although photographic plates have been replaced by photographic film, photographic plates may still be used in special circumstances due to their superior quality and extreme stability. The photographic film can be a plastic film (e.g., a strip or sheet) with a coating of the photosensitive emulsion.

  In the 1980's, stimulable phosphor plates (PSP plates) became available. The PSP plate may include a phosphor material having a color center in its lattice. When a PSP plate is exposed to X-rays, the electrons excited by the X-rays are trapped in the color center until stimulated by a laser beam that scans the plate surface. As the plate is scanned by the laser, the trapped excited electrons emit light, which is collected by a photomultiplier. The collected light is converted to a digital image. In contrast to photographic plates and films, PSP plates can be reused.

  Another type of X-ray detector is an X-ray image intensifier (intensifier). The components of an X-ray image intensifier are usually sealed in a vacuum. In contrast to photographic plates, photographic films, and PSP plates, X-ray image intensifiers can produce real-time images, ie, do not require post-exposure processing to produce the images. X-rays first strike an input phosphor (eg, cesium iodide) and are converted to visible light. The visible light then strikes the photocathode (eg, a thin metal layer containing cesium and antimony compounds), causing emission of electrons. The number of emitted electrons is proportional to the intensity of the incident X-ray. The emitted electrons are projected onto the output phosphor via the electron optical element, and cause the output phosphor to generate a visible light image.

  The scintillator operates somewhat similar to an x-ray image intensifier in that the scintillator (eg, sodium iodide) absorbs x-rays and emits visible light, and then converts the visible light with a suitable image sensor. Can be detected. In a scintillator, visible light spreads and scatters in all directions, and the spatial resolution is reduced. Reducing the thickness of the scintillator not only helps improve spatial resolution, but also reduces x-ray absorption. Therefore, scintillators must strike a compromise between absorption efficiency and resolution.

  Semiconductor X-ray detectors substantially overcome this problem by directly converting X-rays into electrical signals. Semiconductor X-ray detectors may include a semiconductor layer that absorbs X-rays of a wavelength of interest. As X-ray photons are absorbed by the semiconductor layer, multiple charge carriers (eg, electrons and holes) are generated and swept under an electric field toward electrical contacts on the semiconductor layer. The cumbersome thermal management required in currently available solid state X-ray detectors (eg, Medipix) can make it difficult or impossible to manufacture detectors with large areas and large numbers of pixels.

  Disclosed herein is a method of manufacturing a device suitable for detecting X-rays, the method comprising obtaining a substrate having a first surface and a second surface, wherein the substrate is in the substrate or An electronic system on the substrate, the substrate including a plurality of electrical contacts on the first surface, the method including obtaining a first chip including a first x-ray absorbing layer; The line absorbing layer includes an electrode, and includes joining the first chip to the substrate such that the electrode of the first X-ray absorbing layer is electrically connected to at least one electrical contact.

  According to one embodiment, the method further includes attaching the backing substrate to the first chip such that the first chip is sandwiched between the backing substrate and the substrate.

  According to one embodiment, the method further comprises obtaining a second chip comprising a second X-ray absorbing layer, wherein the second X-ray absorbing layer comprises an electrode, and wherein the second X-ray absorbing layer comprises: Bonding the second chip to the substrate such that the electrodes of the second chip are electrically connected to the at least one electrical contact.

  According to one embodiment, the gap between the first chip and the second chip is less than 100 microns.

  According to one embodiment, the first chip has a smaller area than the substrate.

  According to one embodiment, the ratio between the coefficient of thermal expansion of the first chip and the coefficient of thermal expansion of the substrate is 2 or more.

  According to one embodiment, the X-ray absorbing layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof.

  According to one embodiment, the X-ray absorbing layer is doped with chromium.

  According to one embodiment, the X-ray absorbing layer has a thickness of no more than 200 microns.

  According to one embodiment, the first chip comprises a redistribution layer (RDL) on the second surface.

  According to one embodiment, the first chip includes vias, the vias extending from the first surface to the second surface.

  According to one embodiment, the electronic system includes a first voltage comparator configured to compare the voltage of the electrode to a first threshold, and a second voltage comparator configured to compare the voltage to a second threshold. A voltage comparator, a counter configured to record a plurality of X-ray photons reaching the X-ray absorption layer, and a controller, wherein the controller determines that the absolute value of the voltage is the absolute value of the first threshold. The first voltage comparator is configured to start the time delay from the time point determined to be the above, the controller is configured to start the second voltage comparator during the time delay, and the controller is configured to: When the second voltage comparator determines that the absolute value of the voltage is equal to or greater than the absolute value of the second threshold, the number recorded by the counter is increased by one.

  According to one embodiment, the electronic system further comprises a capacitor module electrically connected to the electrode of the first X-ray absorbing layer, the capacitor module transferring charge carriers from the electrode of the first X-ray absorbing layer. Configured to collect.

  According to one embodiment, the controller is configured to activate the second voltage comparator at the beginning or end of the time delay.

  According to one embodiment, the electronic system further comprises a voltmeter, and the controller is configured to cause the voltmeter to measure the voltage at the end of the time delay.

  According to one embodiment, the controller is configured to determine the X-ray photon energy based on the value of the voltage measured at the end of the time delay.

  According to one embodiment, the controller is configured to connect the electrode of the first X-ray absorbing layer to electrical ground.

  According to one embodiment, the rate of change of the voltage is substantially zero at the end of the time delay.

  According to one embodiment, the rate of change of the voltage is substantially non-zero at the end of the time delay.

  According to one embodiment, the X-ray absorbing layer comprises a diode.

FIG. 1A schematically illustrates a semiconductor X-ray detector according to one embodiment. FIG. 1B illustrates a semiconductor X-ray detector 100 according to one embodiment. FIG. 2 illustrates an exemplary top view of a portion of the detector of FIG. 1A, according to one embodiment. FIG. 3 schematically illustrates an electronic layer 120 according to one embodiment. FIG. 4A schematically illustrates a direct junction between the X-ray absorbing layer and the electronic layer. FIG. 4B schematically shows a flip chip bonding between the X-ray absorbing layer and the electronic layer. FIG. 4C schematically illustrates an electronic layer according to one embodiment. FIG. 4D shows that multiple chips can be obtained and that each chip has an X-ray absorbing layer, such as the X-ray absorbing layer shown in FIG. 1A, FIG. 1B, FIG. 2, FIG. 3, FIG. 4A, or FIG. Is schematically shown. FIG. 4E shows that the chip can be bonded to the substrate of the electronic layer. FIG. 4F schematically illustrates that the backing substrate can be attached to the chip such that the chip is sandwiched between the backing substrate and the substrate of the electronic layer. FIG. 4G schematically illustrates that the backing substrate can be attached to the chip such that the chip is sandwiched between the backing substrate and the substrate of the electronic layer. FIG. 5 schematically shows a bottom view of the electronic layer. FIG. 6A shows that the electronic layer shown in FIG. 3 enables the stacking of multiple semiconductor X-ray detectors. FIG. 6B schematically illustrates a top view of the stacked semiconductor X-ray detectors 100. FIG. 7A shows a block diagram of the electronic system of the detector of FIG. 1A or 1B, according to one embodiment. FIG. 7B shows another block diagram of the electronic system of the detector of FIG. 1A or 1B, according to one embodiment. FIG. 8 shows the time evolution of the current (upper curve) flowing through the X-ray absorbing layer diode electrode or resistor electrical contact exposed to X-rays and the corresponding electrode voltage evolution according to one embodiment. (Lower curve), wherein the current is due to charge carriers generated by X-ray photons incident on the X-ray absorption layer. FIG. 9 illustrates, in an electronic system operating in the manner shown in FIG. 8, a time change in current flowing through an electrode (upper curve) due to noise (eg, dark current) and a corresponding electrode according to one embodiment. And the change over time (lower curve). FIG. 10 illustrates the time variation of the current flowing through the electrodes of the X-ray absorbing layer exposed to X-rays (upper curve) and the way the electronic system detects incident X-ray photons at a higher rate, according to one embodiment. In operation, the time variation of the voltage of the corresponding electrode (lower curve) is schematically shown, the current being due to charge carriers generated by X-ray photons incident on the X-ray absorption layer. FIG. 11 illustrates a time change (upper curve) of current flowing through an electrode due to noise (eg, dark current) and a corresponding electrode in an electronic system operating in the manner shown in FIG. 10 according to one embodiment. And the change over time (lower curve). 12, according to one embodiment, an electronic system that operates in a manner RST is shown in Figure 10 to finish before t _e, a series of X-ray charge carriers generated by photons incident on the X-ray absorbing layer Schematically shows the time change of the current flowing through the electrode (upper curve) and the time change of the voltage of the corresponding electrode. FIG. 13 schematically illustrates a system with a solid state X-ray detector as described herein suitable for medical imaging, such as chest x-ray, abdominal x-ray, according to one embodiment. FIG. 14 schematically illustrates a system comprising a semiconductor x-ray detector described herein suitable for dental radiography, according to one embodiment. FIG. 15 schematically illustrates a cargo scanning or non-intrusive inspection (NII) system comprising a semiconductor x-ray detector as described herein, according to one embodiment. FIG. 16 schematically illustrates another cargo scanning or non-intrusive inspection (NII) system comprising a semiconductor x-ray detector as described herein, according to one embodiment. FIG. 17 schematically illustrates a whole-body scanner system with a solid state X-ray detector as described herein, according to one embodiment. FIG. 18 schematically illustrates an X-ray computed tomography (X-ray CT) system with a semiconductor X-ray detector as described herein, according to one embodiment. FIG. 19 schematically illustrates an electron microscope with a semiconductor X-ray detector as described herein, according to one embodiment.

Detailed description

  FIG. 1A schematically illustrates a semiconductor X-ray detector 100 according to one embodiment. The semiconductor X-ray detector 100 may include an X-ray absorption layer 110 and an electronic layer 120 (eg, an ASIC) for processing or analyzing electrical signals, wherein incident X-rays are generated at the X-ray absorption layer 110 I do. In one embodiment, semiconductor X-ray detector 100 does not include a scintillator. The X-ray absorbing layer 110 can include a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. Semiconductors can have a high mass extinction coefficient for the X-ray energy of interest. The X-ray absorbing layer 110 includes one or more diodes (for example, pin or p-n) formed by one or more individual regions 114 of the first doped region 111 and the second doped region 113. n). The second doped region 113 can be separated from the first doped region 111 by an optional intrinsic region 112. The individual portions 114 are separated from one another by a first doped region 111 or an intrinsic region 112. The first doped region 111 and the second doped region 113 have opposite types of doping (for example, the region 111 is p-type and the region 113 is n-type, or the region 111 is n-type and the region 113 is p-type). In the example of FIG. 1A, each of the individual regions 114 of the second doped region 113 forms a diode having a first doped region 111 and an optional intrinsic region 112. That is, in the example of FIG. 1A, the X-ray absorption layer 110 has a plurality of diodes having the first doped region 111 as a shared electrode. The first doped region 111 can also have individual parts.

  FIG. 1B illustrates a semiconductor X-ray detector 100 according to one embodiment. The semiconductor X-ray detector 100 may include an X-ray absorption layer 110 and an electronic layer 120 (eg, an ASIC) for processing or analyzing electrical signals, wherein incident X-rays are generated at the X-ray absorption layer 110 I do. In one embodiment, semiconductor X-ray detector 100 does not include a scintillator. The X-ray absorbing layer 110 can include a semiconductor material such as silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. Semiconductors can have a high mass extinction coefficient for the X-ray energy of interest. The X-ray absorption layer 110 may include a resistor without including a diode.

  When an X-ray photon strikes the X-ray absorbing layer 110, including the diode, the X-ray photon can be absorbed and generate one or more charge carriers by multiple mechanisms. X-ray photons can generate 10-100,000 charge carriers. Charge carriers can drift to the electrodes of one diode under an electric field. The electric field may be an external electric field. Electrical contacts 119B can include discrete portions that make electrical contact with discrete regions 114. In one embodiment, the charge carriers can drift in a direction such that the charge carriers generated by a single X-ray photon are not substantially shared by two different discrete regions 114 (here, "substantially" "Unshared" means that less than 5%, less than 2%, or less than 1% of these charge carriers flow to a different one of the discrete regions 114 from the rest of the charge carriers). In one embodiment, the charge carriers generated by a single X-ray photon can be shared by two different individual regions 114. FIG. 2 shows an exemplary top view of a portion of the device 100 having a 4 × 4 array of individual regions 114. Charge carriers generated by X-ray photons incident around one footprint of these individual regions 114 are not substantially shared with another of these individual regions 114. The area around the individual region 114 where substantially all (more than 95%, more than 98%, or more than 99%) of the charge carriers generated by the X-ray photons incident thereon flow into the individual region 114 is the individual region 114 Called the pixel associated with. That is, less than 5%, less than 2%, or less than 1% of these charge carriers flow across the pixel. By measuring the drift current flowing into each of the individual regions 114, or the rate of change of the voltage at each of the individual regions 114, the number of absorbed X-ray photons (related to the incident X-ray intensity) and / or the individual regions Its energy at the pixel associated with 114 can be determined. Thus, the spatial distribution (eg, an image) of the incident X-ray intensity can be measured by individually measuring the drift current into each of the arrays of individual regions 114 or by changing the voltage of each of the arrays of individual regions 114. It can be determined by measuring the rate. The pixels can be organized in any suitable array, such as a square array, a triangular array, and a honeycomb array. Pixels can have any suitable shape, such as circular, triangular, square, rectangular, and hexagonal. Pixels may be individually addressable.

  When an X-ray photon strikes the X-ray absorption layer 110, including the resistor but not the diode, the X-ray photon can be absorbed and generate one or more charge carriers by multiple mechanisms. X-ray photons can generate 10-100,000 charge carriers. Charge carriers can drift to electrical contacts 119A and 119B under an electric field. The electric field may be an external electric field. Electrical contact 119B includes a discrete portion. In one embodiment, the charge carriers may drift in a direction such that the charge carriers generated by a single x-ray photon are not substantially shared by two different discrete portions of electrical contact 119B (here, " "Substantially unshared" means that less than 5%, less than 2%, or less than 1% of these charge carriers flow to a different one of the discrete parts separate from the rest of the charge carriers) . In one embodiment, the charge carriers generated by a single X-ray photon may be shared by two different individual portions of electrical contact 119B. Charge carriers generated by X-ray photons incident around the footprint of one of these discrete portions of electrical contact 119B are not substantially shared with another of these discrete portions of electrical contact 119B. Substantially all (greater than 95%, greater than 98%, or greater than 99%) of the charge carriers generated by the X-ray photons incident thereon are separated from the electrical contacts 119B by flowing to discrete portions of the electrical contacts 119B. The area around the portion is referred to as the pixel associated with the individual portion of electrical contact 119B. That is, less than 5%, less than 2%, or less than 1% of these charge carriers flow past the pixel associated with one discrete portion of electrical contact 119B. By measuring the drift current flowing through each of the discrete portions of the electrical contact 119B, or the rate of change of the voltage at each of the discrete portions of the electrical contact 119B, the number of absorbed X-ray photons (which is Related) and / or its energy at the pixel associated with the discrete portion of the electrical contact 119B. Accordingly, the spatial distribution (eg, image) of the incident X-ray intensity can be determined by individually measuring the drift current into each of the array of discrete portions of electrical contact 119B, or by measuring the array of discrete portions of electrical contact 119B. It can be determined by measuring the rate of change of each voltage. The pixels can be organized in any suitable array, such as a square array, a triangular array, and a honeycomb array. Pixels can have any suitable shape, such as circular, triangular, square, rectangular, and hexagonal. Pixels may be individually addressable.

  The electronic layer 120 may include an electronic system 121 suitable for processing or interpreting signals generated by X-ray photons incident on the X-ray absorption layer 110. Electronic system 121 can include analog circuits such as filter networks, amplifiers, integrators, and comparators, or digital circuits such as microprocessors and memories. Electronic system 121 may include components that are shared by multiple pixels or components that are dedicated to a single pixel. For example, the electronic system 121 may include a dedicated amplifier for each pixel and a microprocessor common to all pixels. Electronic system 121 can be electrically connected to the pixel by via 131. The space between the vias can be filled with a filler material 130 that can increase the mechanical stability of the connection of the electronic layer 120 to the X-ray absorbing layer 110. Other bonding techniques are possible to connect electronic system 121 to pixels without using vias.

  FIG. 3 schematically illustrates an electronic layer 120 according to one embodiment. Electronic layer 120 includes a substrate 122 having a first surface 124 and a second surface 128. As used herein, a “surface” is not necessarily exposed and may be wholly or partially embedded. Electronic layer 120 includes one or more electrical contacts 125 on first surface 124. One or more electrical contacts 125 can be configured to be electrically connected to one or more electrodes of X-ray absorbing layer 110. Electronic system 121 may be in or on substrate 122. Electronic layer 120 includes one or more vias 126 extending from first surface 124 to second surface 128. Electronic layer 120 includes a redistribution layer (RDL) 123 on second surface 128. RDL 123 may include one or more transmission lines 127. Electronic system 121 is electrically connected to electrical contacts 125 and transmission lines 127 via vias 126.

  The substrate 122 may be a thinned substrate. For example, the substrate can have a thickness of 750 microns or less, 200 microns or less, 100 microns or less, 50 microns or less, 20 microns or less, or 5 microns or less. Substrate 122 may be a silicon substrate or a substrate or other suitable semiconductor or insulator. Substrate 122 may be manufactured by grinding a thick substrate to a desired thickness.

  The one or more electrical contacts 125 may be a metal or doped semiconductor layer. For example, electrical contacts 125 may be gold, copper, platinum, palladium, doped silicon, and the like.

  Via 126 penetrates substrate 122 and electrically connects an electrical component (eg, electrical contact 125) on first surface 124 to an electrical component (eg, RDL) on second surface 128. The via 126 is sometimes referred to as a “through-silicon via”, but may be made in the substrate with a material other than silicon.

  RDL 123 may include one or more transmission lines 127. Transmission lines 127 electrically connect electrical components (eg, vias 126) in substrate 122 to bonding pads at other locations on substrate 122. The transmission line 127 may be electrically isolated from the substrate 122 except for a specific via 126 and a specific bonding pad. The transmission line 127 may be a material with a low mass extinction coefficient (eg, Al) for the X-ray energy of interest. The RDL 123 can redistribute electrical connections to more convenient locations.

  FIG. 4A schematically illustrates a direct junction between an X-ray absorbing layer 110 and an electronic layer 120, such as an individual region 114 and an electrical contact 125, at the electrode. Direct bonding is a wafer bonding process that does not use additional intermediate layers (eg, solder bumps). The bonding process is based on a chemical bond between two surfaces. Direct bonding may be at elevated temperatures, but need not be.

  FIG. 4B schematically illustrates a flip-chip bond between the X-ray absorbing layer 110 and the electronic layer 120, such as the discrete regions 114 and the electrical contacts 125, at the electrodes. Flip chip bonding uses solder bumps 199 deposited on contact pads (eg, electrodes or electrical contacts 125 of X-ray absorbing layer 110). Either the X-ray absorbing layer 110 or the electronic layer 120 is turned over, and the electrodes of the X-ray absorbing layer 110 are aligned with the electrical contacts 125. The solder bumps 199 can be melted to solder the electrodes and electrical contacts 125 together. The gap between the solder bumps 199 can be filled with an insulating material.

  FIG. 4C schematically illustrates the electronic layer 120 in one embodiment. The substrate 122 of the electronic layer 120 has a plurality of electrical contacts 125 on a first surface 124. A plurality of electrical contacts 125 may be organized into a plurality of regions 129. Electronic system 121 may be in or on substrate 122.

  FIG. 4D shows that a plurality of chips 189 can be obtained and that each chip 189 has an X-ray absorbing layer such as X-ray absorbing layer 110 shown in FIG. 1, FIG. 2, FIG. 3, FIG. 4A, or FIG. Is schematically shown. The X-ray absorption layer of each chip 189 has an electrode.

  FIG. 4E illustrates that chip 189 can be bonded to substrate 122 using a suitable bonding method, such as flip chip bonding or direct bonding as shown in FIGS. 4A and 4B. In one embodiment, each chip 189 is joined with one of the regions 129. The electrodes of each chip 189 are electrically connected to at least one of the electrical contacts 125. After chip 189 is bonded to substrate 122, the gap between two adjacent chips 189 may be less than 100 microns. The chip 189 may have a smaller area than the substrate 122. After being bonded to the substrate 122, the chips 189 may be arranged in an array. The smaller size of chip 189 relative to substrate 122 may help accommodate differences between the coefficient of thermal expansion of chip 189 and the coefficient of thermal expansion of substrate 122. The ratio between the coefficient of thermal expansion of the chip 189 and the coefficient of thermal expansion of the substrate 122 may be 2 or more. The X-ray absorbing layer of tip 189 may be less than 200 microns thick, less than 100 microns thick, or less than 50 microns thick. The smaller the thickness of the X-ray absorbing layer, the lower the possibility that charge carriers are trapped by defects in the X-ray absorbing layer, and thus the more efficient the charge collection efficiency (CCE) by the electronic system 121. The X-ray absorption layer of tip 189 may be a chromium-doped material, especially if the material is GaAs. Doping GaAs with chromium can reduce the density of EL2 defects in GaAs, and thus make the thickness of the X-ray absorbing layer thicker without losing many charge carriers in the defects ( Hence, high absorption efficiency). Substrate 122 may have vias such as via 126 shown in FIG. 3 and RDLs such as the RDL shown in FIG. 3 or FIG.

  FIGS. 4F and 4G schematically illustrate that the backing substrate 150 can be attached to the chip 189 such that the chip 189 is sandwiched between the backing substrate 150 and the substrate 122. FIG. The backing substrate 150 can provide mechanical support to the chip 189 and the substrate 122. The backing substrate 150 may be a material (eg, silicon, silicon oxide) having a low mass extinction coefficient for the X-ray energy of interest. The backing substrate 150 may also serve as an electrode to apply an electric field in the thickness direction of the X-ray absorbing layer. For better conduction, there may be a thin layer of conductor between the backing substrate 150 and the X-ray absorbing layer.

  FIG. 5 schematically shows a bottom view of the RDL 123, and other components that block the drawing are omitted. It can be seen that transmission line 127 is electrically connected to via 126 and redistributes via 126 to other locations.

  FIG. 6A shows that the electronic layer 120 shown in FIG. 3 enables stacking of multiple semiconductor X-ray detectors 100, whereby the RDL 123 and via 126 pass through multiple layers. To facilitate the routing of signal paths, the electronic system 121 described below may have low enough power consumption to eliminate large cooling mechanisms. The plurality of semiconductor X-ray detectors 100 in the stack need not be identical. For example, the plurality of semiconductor X-ray detectors 100 may be different in thickness, structure, or material.

  FIG. 6B schematically illustrates a top view of the stacked semiconductor X-ray detectors 100. Each layer can have multiple detectors 100 tiled to cover a larger area. One layer of tiled detector 100 can be staggered relative to another layer of tiled detector 100, thereby eliminating gaps that cannot detect incident X-ray photons. it can.

  According to one embodiment, multiple semiconductor X-ray detectors 100 may be tiled side-by-side to form a larger detector. Each of the plurality of detectors may have a single or multiple chips. For example, for applications in mammography, the absorbing layer may be made on a single silicon wafer that can be bonded to an electronic layer made on another single silicon wafer. Four to six such detectors may be tiled side by side to form a tiled detector large enough to take a human chest x-ray image. Multiple tiled detectors may be stacked with staggered gaps in each layer.

  According to one embodiment, the semiconductor X-ray detector 100 includes a step of obtaining an X-ray absorption layer including an electrode and a step of obtaining an electronic layer, wherein the electronic layer includes a first surface and a second surface. An electrode including a substrate having a surface, an electronic system in or on the substrate, electrical contacts on a first surface, a via, and a redistribution layer (RDL) on a second surface; Bonding the X-ray absorbing layer and the electronic layer such that the RDL is electrically connected to the electrical contact, wherein the RDL comprises a transmission line; Vias extend from the first surface to the second surface, and the electronic system is electrically connected via the vias to electrical contacts and transmission lines.

  7A and 7B show configuration diagrams of an electronic system 121 according to an embodiment, respectively. 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.

  The first voltage comparator 301 is configured to compare the voltage of the electrode of the diode 300 with a first threshold. The diode may be a diode formed by a first doped region 111, one of the individual regions 114 of the second doped region 113, and an optional intrinsic region 112. Alternatively, first voltage comparator 301 is configured to compare the voltage at an electrical contact (eg, a discrete portion of electrical contact 119B) to a first threshold. The first voltage comparator 301 may be configured to directly monitor the voltage and may be configured to calculate the voltage by integrating the current flowing through the diode or electrical contact over a period of time. The first voltage comparator 301 may be controllably activated or deactivated by the controller 310. The first voltage comparator 301 may be a continuous comparator. That is, the first voltage comparator 301 may be configured to operate continuously to monitor the voltage continuously. The first voltage comparator 301 configured as a continuous comparator reduces the likelihood that the system 121 will miss the signal generated by the incident X-ray photons. The first voltage comparator 301 configured as a continuous comparator is particularly suitable when the incident X-ray intensity is relatively high. The first voltage comparator 301 may be a clock comparator having an advantage of low power consumption. The first voltage comparator 301, configured as a clock comparator, can cause the system 121 to miss the signal generated by some incident X-ray photons. When the incident X-ray intensity is low, the possibility of mistaken incident X-ray photons is low because the time interval between two consecutive photons is relatively long. Therefore, when the incident X-ray intensity is relatively low, the first voltage comparator 301 configured as a clock comparator is particularly suitable. The first threshold is 5-10%, 10-20%, 20-30%, 30-40%, or 40-50% of the maximum voltage that one incident X-ray photon can produce in a diode or resistor. There may be. The maximum voltage may depend on the energy of the incident X-ray photons (ie, the wavelength of the incident X-ray), the material of the X-ray absorbing layer 110, and other factors. For example, the first threshold may be 50 mV, 100 mV, 150 mV, or 200 mV.

The second voltage comparator 302 is configured to compare the voltage with a second threshold. The second voltage comparator 302 may be configured to monitor the voltage directly, and may be configured to calculate the voltage by integrating the current flowing through the diode or electrical contact over a period of time. The second voltage comparator 302 may be a continuous comparator. The second voltage comparator 302 may be controllably activated or deactivated by the controller 310. When the second voltage comparator 302 is stopped, the power consumption of the second voltage comparator 302 is less than 1% and less than 5% of the power consumption when the second voltage comparator 302 is activated. , Less than 10% or less than 20%. The absolute value of the second threshold is larger than the absolute value of the first threshold. As used herein, the term "absolute value" or "modulus" | x | of a real number x is a non-negative value x regardless of its sign. That is,

The second threshold may be between 200% and 300% of the first threshold. The second threshold may be at least 50% of the maximum voltage that one incident X-ray photon can generate in a diode or resistor. For example, the second threshold may be 100 mV, 150 mV, 200 mV, 250 mV, or 300 mV. The second voltage comparator 302 and the first voltage comparator 310 may be the same component. That is, the system 121 can have one voltage comparator that can compare the voltage with two different thresholds at different times.

  First voltage comparator 301 or 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 can have a high speed that allows the system 121 to operate under a high flux of incident X-rays. However, in many cases, having high speed sacrifices power consumption.

  Counter 320 is configured to record a plurality of X-ray photons reaching a diode or resistor. Counter 320 may be a software component (eg, a number stored in computer memory) or a hardware component (eg, 4017 IC and 7490 IC).

  Controller 310 may be a hardware component such as a microcontroller or a microprocessor. The controller 310 determines that the absolute value of the voltage is equal to or greater than the absolute value of the first threshold (for example, the absolute value of the voltage is changed from a value lower than the absolute value of the first threshold to a value equal to or greater than the absolute value of the first threshold). ) And the first voltage comparator 301 determines that the time delay starts. Absolute values are used here because the voltage at the cathode or anode of the diode or the voltage can be negative or positive depending on whether an electrical contact is used. Before the first voltage comparator 301 determines that the absolute value of the voltage is equal to or greater than the absolute value of the first threshold value, the controller 310 controls the second voltage comparator 302, the counter 320, and the first voltage comparison unit. Other circuits not required for the operation of the unit 301 may be configured to be stopped. The time delay can end before or after the voltage has settled, ie, the rate of change of the voltage is substantially zero. The stage "the rate of change of the voltage is substantially zero" means that the time change of the voltage is less than 0.1% / ns. The stage "the rate of change of the voltage is substantially non-zero" means that the time change of the voltage is at least 0.1% / ns.

  Controller 310 may be configured to activate the second voltage comparator during a time delay (including start and end). In one embodiment, controller 310 is configured to activate a second voltage comparator at the beginning of the time delay. The term "activate" refers to activating a component (e.g., by transmitting a signal, such as a voltage pulse or logic level, or by providing power). The term "deactivate" means to deactivate a component (e.g., by transmitting a signal such as a voltage pulse or logic level, or by shutting off power). The operating state may have higher power consumption (eg, 10 times higher, 100 times higher, 1000 times higher) than the non-operating state. The controller 310 itself may be stopped until the output of the first voltage comparator 301 activates the controller 310 when the absolute value of the voltage is equal to or greater than the absolute value of the first threshold.

  If the second voltage comparator 302 determines that the absolute value of the voltage is greater than or equal to the absolute value of the second threshold during the time delay, the controller 310 increases the number recorded by the counter 320 by one. It may be configured as follows.

  Controller 310 may be configured to cause voltmeter 306 to measure the voltage at the end of the time delay. Controller 310 may be configured to connect the electrodes to electrical ground, reset the voltage, and discharge the charge carriers stored on the electrodes. In one embodiment, the electrodes are connected to electrical ground after the end of the time delay. In one embodiment, the electrodes are connected to electrical ground for a limited reset time. Controller 310 may connect the electrodes to electrical ground by controlling switch 305. The switch may be a transistor such as a field effect transistor (FET).

  In one embodiment, system 121 does not have an analog filter network (eg, an RC network). In one embodiment, system 121 has no analog circuitry.

  The voltmeter 306 can supply the measured voltage to the controller 310 as an analog or digital signal.

The system 121 may include a capacitor module 309 electrically connected to the electrodes of the diode 300 or its electrical contacts, wherein the capacitor module is configured to collect charge carriers from the electrodes. The capacitor module can include a capacitor in the feedback path of the amplifier. An amplifier configured in this way is called a capacitive transimpedance amplifier (CTIA). CTIA has a high dynamic range so that the amplifier does not become saturated, and improves the signal-to-noise ratio by limiting the bandwidth of the signal path. Charge carriers from the electrodes, a period ( "integration period") (e.g., as shown in FIG. _8, t 0 ~t _1, or between _t 1 ~t ₂₎ accumulate on the capacitor. After the integration period ends, the capacitor voltage is sampled and reset by the reset switch. The capacitor module can include a capacitor directly connected to the electrode.

FIG. 8 shows the time variation of the current flowing through the electrodes (upper curve) due to the charge carriers generated by the X-ray photons incident on the diode or resistor, and the time variation of the corresponding electrode voltage (lower curve). Are schematically shown. Voltage may be the integral of current over time. At time t ₀ , the X-ray photons strike the diode or resistor, charge carriers begin to build up in the diode or resistor, current begins to flow through the electrode or resistor of the diode, and the absolute value of the voltage at the electrode or electrical contact Begins to increase. At time _{t 1,} the first voltage comparator 301 determines that the absolute value of the voltage is greater than or equal to the absolute value of the first threshold value V1, the controller 310 starts a time delay TD1, the controller 310 starts the TD1 Sometimes, the first voltage comparator 301 can be stopped. If the controller 310 is to stop before _{t 1,} the controller 310 is activated by _{t 1.} During TD1, the controller 310 activates the second voltage comparator 302. As used herein, the term "time delay" means the start and end (ie, end) and any time in between. For example, the controller 310 can activate the second voltage comparator 302 at the end of TD1. During the TD1, the second voltage comparator 302, if the absolute value of the voltage at time t ₂ is equal to or more than the absolute value of the second threshold value, the controller 310 sets the number recorded by the counter 320 1 Just increase. At time t _e, all charge carriers generated by the X-ray photons, drift out of the X-ray absorbing layer 110. At time _{t s,} time delay TD1 is completed. In the example of FIG. 8, time t _s is after time t _e , ie, TD 1 ends after all charge carriers generated by the X-ray light have drifted out of X-ray absorption layer 110. Therefore, the rate of change of voltage is substantially zero at t _s. Controller 310, the end time or t ₂ of TD1, or at any time in between, it may be configured to stop the second voltage comparator 302.

  Controller 310 may be configured to cause voltmeter 306 to measure the voltage at the end of time delay TD1. In one embodiment, controller 310 causes voltmeter 306 to measure the voltage after the rate of change of the voltage is substantially zero after expiration of time delay TD1. The voltage at this time is proportional to the amount of charge carriers generated by the X-ray photons related to the energy of the X-ray photons. Controller 310 may be configured to determine the energy of the X-ray photons based on the voltage measured by voltmeter 306. One way to determine energy is to bin the voltage. The counter 320 can have a sub-counter for each bin. If the controller 310 determines that the energy of the X-ray photons enters the bin, the controller 310 can increase the number recorded in the sub-counter for that bin by one. Thus, the system 121 may be able to detect X-ray images and may be able to resolve the X-ray photon energy of each X-ray photon.

  After the end of TD1, controller 310 connects the electrodes to electrical ground during reset period RST, allowing charge carriers stored on the electrodes to flow to ground and reset the voltage. After the RST, the system 121 is ready to detect another incident X-ray photon. Implicitly, the rate of incident X-ray photons that the system 121 can handle in the example of FIG. 8 is limited by 1 / (TD1 + RST). If the first voltage comparator 301 is stopped, the controller 310 can activate it at any time before the RST ends. If the controller 310 is stopped, the controller 310 may be started before the RST ends.

FIG. 9 illustrates electrodes in a system 121 operating in the manner illustrated in FIG. 8 due to noise (eg, dark current, background radiation, scattered x-rays, fluorescent x-rays, shared charge from adjacent pixels). The time variation of the flowing current (upper curve) and the time variation of the corresponding electrode voltage (lower curve) are schematically shown. At time _{t 0,} noise begins. If the noise is not so great that the absolute value of the voltage exceeds the absolute value of V1, controller 310 does not activate second voltage comparator 302. At time _{t 1,} which is determined by the first voltage comparator 301, if the absolute value of noise enough than the absolute value of V1 voltage greater, the controller 310 starts a time delay TD1, controller 310 of TD1 At the start, the first voltage comparator 301 can be stopped. During TD1 (eg, at the end of TD1), controller 310 activates second voltage comparator 302. The noise is not considered so great during TD1 that the absolute value of the voltage exceeds the absolute value of V2. Therefore, the controller 310 does not increase the number recorded by the counter 320. At time _{t e,} noise it is completed. At time _{t s,} time delay TD1 is completed. Controller 310 may be configured to stop second voltage comparator 302 at the end of TD1. Controller 310 may be configured to cause voltmeter 306 to not measure the voltage unless the absolute value of the voltage exceeds the absolute value of V2 during TD1. After the end of TD1, controller 310 connects the electrodes to electrical ground during reset period RST, allowing charge carriers stored on the electrodes to flow to ground as a result of noise and reset the voltage. I do. Therefore, the system 121 can be very effective in denoising.

FIG. 10 shows the time course of the current flowing through the electrodes (upper curve) due to charge carriers generated by X-ray photons incident on a diode or resistor, and that the system 121 operates at a rate faster than 1 / (TD1 + RST). Figure 5 schematically shows the corresponding electrode voltage changes over time (lower curve) when operating to detect incident X-ray photons. Voltage may be the integral of current over time. At time t ₀ , the X-ray photons strike the diode or resistor, charge carriers begin to form at the diode or resistor, current begins to flow through the diode's electrodes or resistor's electrical contacts, and the voltage at the electrodes or electrical contacts The absolute value of begins to increase. At time _{t 1,} the first voltage comparator 301 determines that the absolute value of the voltage is greater than or equal to the absolute value of the first threshold value V1, the controller 310 starts a short time delay TD2 than TD1, controller 310 At the start of TD2, the first voltage comparator 301 can be stopped. If the controller 310 is to stop before _{t 1,} the controller 310 is activated by _{t 1.} During TD2 (eg, at the end of TD2), controller 310 activates second voltage comparator 302. During the TD2, the second voltage comparator 302, if the absolute value of the voltage at time t ₂ is equal to or more than the absolute value of the second threshold value, the controller 310 sets the number recorded by the counter 320 1 Just increase. At time t _e, all charge carriers generated by the X-ray photons, drift out of the X-ray absorbing layer 110. At time _{t h,} time delay TD2 is completed. In the example of FIG. 10, is prior to time t _h time t _e, i.e. TD2, all charge carriers generated by the X-ray photons is completed before drifting out of the X-ray absorbing layer 110. Therefore, the rate of change of voltage is substantially non-zero at t _h. Controller 310, the end time or t ₂ of TD2, or at any time in between, it may be configured to stop the second voltage comparator 302.

Controller 310, extrapolating the voltage at t _e the voltage as a function of time during the TD2, it may be configured to determine the energy of X-ray photons using extrapolated voltage.

After TD2 has expired, controller 310 connects the electrodes to electrical ground during reset period RST, allowing charge carriers stored on the electrodes to flow to ground and reset the voltage. In one embodiment, RST is terminated before the _{t e.} The rate of change of voltage after RST is substantially be a non-zero, because all of the charge carriers generated by the X-ray photons, out of the X-ray absorbing layer 110 at the end of the RST before t _e It is not drifting. the rate of change of voltage after t _e is substantially zero, the voltage after t _e is stabilized to the residual voltage VR. In one embodiment, RST is terminated after t _e or t _e, the rate of change of voltage after RST substantially be a zero, since all of the charge carriers generated by the X-ray photons, t _{This is because, at e} , it drifts out of the X-ray absorption layer 110. After the RST, the system 121 is ready to detect another incident X-ray photon. If the first voltage comparator 301 is stopped, the controller 310 can activate it at any time before the RST ends. If the controller 310 is stopped, the controller 310 may be started before the RST ends.

FIG. 11 illustrates electrodes in a system 121 operating in the manner shown in FIG. 10 due to noise (eg, dark current, background radiation, scattered X-rays, fluorescent X-rays, shared charge from adjacent pixels). The time variation of the flowing current (upper curve) and the time variation of the corresponding electrode voltage (lower curve) are schematically shown. At time _{t 0,} noise begins. If the noise is not so great that the absolute value of the voltage exceeds the absolute value of V1, controller 310 does not activate second voltage comparator 302. At time _{t 1,} which is determined by the first voltage comparator 301, if the absolute value of noise enough than the absolute value of V1 voltage greater, the controller 310 starts the time delay TD2, the controller 310, the TD2 At the start, the first voltage comparator 301 can be stopped. During TD2 (eg, at the end of TD2), controller 310 activates second voltage comparator 302. The noise is not considered to be so great during TD2 that the absolute value of the voltage exceeds the absolute value of V2. Therefore, the controller 310 does not increase the number recorded by the counter 320. At time _{t e,} noise it is completed. At time _{t h,} time delay TD2 is completed. Controller 310 may be configured to stop second voltage comparator 302 at the end of TD2. After the end of TD2, the controller 310 connects the electrodes to electrical ground during a reset period RST, allowing charge carriers stored on the electrodes to flow to ground as a result of noise and reset the voltage. I do. Therefore, the system 121 can be very effective in denoising.

12, RST is the system 121 that operates in the manner shown in FIG. 10 to be terminated before the t _e, the electrode due to the charge carriers generated by a series of X-ray photons incident on the diode or resistor The time variation of the flowing current (upper curve) and the time variation of the corresponding electrode voltage (lower curve) are schematically shown. The voltage curve due to the charge carriers generated by each incident X-ray photon is offset by the residual voltage before that photon. The absolute value of the residual voltage increases continuously for each incident photon. If the absolute value of the residual voltage exceeds V1 (see the dotted rectangle in FIG. 12), the controller starts a time delay TD2, and the controller 310 can stop the first voltage comparator 301 at the start of TD2. . If there are no other X-ray photons incident on the diode or resistor during TD2, the controller connects the electrodes to electrical ground during the reset time RST at the end of TD2, thereby resetting the residual voltage. Thus, the residual voltage does not cause the number recorded by the counter 320 to increase.

  FIG. 13 schematically illustrates a system including the semiconductor X-ray detector 100 described herein. This system may be used for medical imaging, such as chest radiography, abdominal radiography. The system includes an X-ray source 1201. X-rays radiated from the X-ray source 1201 penetrate an object 1202 (for example, a human body part such as a chest, a limb, and an abdomen), and internal structures of the object 1202 (for example, bones, muscles, fat, and organs) ) And is projected to the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 detects an X-ray intensity distribution and forms an image.

  FIG. 14 schematically illustrates a system including the semiconductor X-ray detector 100 described herein. This system may be used for medical imaging, such as dental radiography. The system includes an X-ray source 1301. X-rays emitted from an X-ray source 1301 pass through an object 1302 that is part of the mouth of a mammal (eg, a human). The object 1302 may include a maxilla, palate, teeth, mandible, or tongue. The X-rays are attenuated to different extents by different structures of the object 1302 and are projected on the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 detects an X-ray intensity distribution and forms an image. Teeth absorb x-rays more than caries, infected areas, and periodontal ligaments. Dental patients receive a generally low dose of X-ray radiation (a series of doses throughout the mouth of about 0.150 mSv).

  FIG. 15 schematically illustrates a cargo scanning or non-intrusive inspection (NII) system comprising a semiconductor X-ray detector 100 as described herein. The system can be used for inspection and identification of goods in transportation systems such as shipping containers, vehicles, ships, luggage, and the like. The system includes an X-ray source 1401. X-rays emitted from the X-ray source 1401 can be backscattered from an object 1402 (eg, a shipping container, a vehicle, a ship, etc.) and projected on the semiconductor X-ray detector 100. Different internal structures of the object 1402 can backscatter X-rays differently. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of the backscattered X-rays and / or the energy of the backscattered X-ray photons.

  FIG. 16 schematically illustrates another cargo scanning or non-intrusive inspection (NII) system comprising a semiconductor X-ray detector 100 as described herein. This system can be used for luggage screening at public transport and airports. The system includes an X-ray source 1501. X-rays emitted from the X-ray source 1501 pass through the package 1502, are attenuated differently depending on the contents of the package, and can be projected on the semiconductor X-ray detector 100. The semiconductor X-ray detector 100 detects an intensity distribution of transmitted X-rays and forms an image. The system can reveal the contents of the baggage and identify items that are prohibited by public transport, such as firearms, drugs, cutlery, and combustible materials.

  FIG. 17 schematically illustrates a whole-body scanner system including the semiconductor X-ray detector 100 described herein. Whole body scanner systems can detect objects of the human body for security screening without physically removing or physically touching the clothing. Whole body scanner systems are capable of detecting non-metallic objects. The whole-body scanner system includes an X-ray source 1601. X-rays emitted from the X-ray source 1601 can be backscattered from the person 1602 and its object to be screened and projected onto the semiconductor X-ray detector 100. The object and the human body can separately backscatter X-rays. The semiconductor X-ray detector 100 forms an image by detecting the intensity distribution of backscattered X-rays. The semiconductor X-ray detector 100 and X-ray source 1601 can be configured to scan a person in a linear or rotational direction.

  FIG. 18 schematically shows an X-ray computed tomography (X-ray CT) system. X-ray CT systems use computerized X-rays to generate tomographic images (virtual "slices") of specific areas of an object to be scanned. The tomographic images can be used for diagnostic and therapeutic purposes in various medical fields or for defect detection, failure analysis, metrology, assembly analysis and reverse engineering. The X-ray CT system includes the semiconductor X-ray detector 100 described in this specification and an X-ray source 1701. Semiconductor X-ray detector 100 and X-ray source 1701 can be configured to rotate synchronously along one or more circular or spiral paths.

  FIG. 19 schematically shows an electron microscope. The electron microscope includes an electron source 1801 (also called an electron gun) configured to emit electrons. Electron source 1801 may have various emission mechanisms, such as a thermionic, photocathode, field emission, or plasma source. The emitted electrons pass through an electron optical system 1803, which may be configured to shape, accelerate, or focus the electrons. The electrons then reach the sample 1802, from which an image detector can form an image. The electron microscope can include a semiconductor X-ray detector 100 described herein for performing energy dispersive X-ray spectroscopy (EDS). EDS is an analytical technique used for elemental analysis or chemical characterization of a sample. When electrons enter the sample, they cause a characteristic emission of X-rays from the sample. The incident electrons excite the electrons in the inner shell of the atoms in the sample, and can emit the electrons from the inner shell while creating an electron hole in which the electrons were present. The electrons from the outer higher energy shell then fill the hole, and the energy difference between the higher and lower energy shells can be emitted in the form of X-rays. The number and energy of X-rays emitted from the sample can be measured by the semiconductor X-ray detector 100.

  The semiconductor X-ray detector 100 described here is an X-ray telescope, X-ray mammography, industrial X-ray defect detection, X-ray microscope or microradiography, X-ray casting inspection, X-ray non-destructive inspection, X-ray welding inspection , X-ray digital subtraction angiography, etc. It may be appropriate to use this semiconductor X-ray detector 100 instead of a photographic plate, photographic film, PSP plate, X-ray image intensifier, scintillator, or other semiconductor X-ray detector.

  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 not limitation, and the true scope and spirit of the invention is set forth by the following claims.

Claims (20)

A method of manufacturing a device suitable for detecting X-rays,
Obtaining a substrate having a first surface and a second surface,
The substrate includes an electronic system within or on the substrate,
The substrate includes a plurality of electrical contacts on the first surface;
Obtaining a first chip including a first X-ray absorbing layer,
The first X-ray absorption layer includes an electrode;
Bonding the first chip to the substrate such that the electrode of the first X-ray absorbing layer is electrically connected to at least one of the electrical contacts.   The method of claim 1, further comprising attaching the backing substrate to the first chip such that the first chip is sandwiched between the backing substrate and the substrate. Further comprising obtaining a second chip comprising a second X-ray absorbing layer,
The second X-ray absorbing layer includes an electrode;
2. The method of claim 1, further comprising joining the second chip to the substrate such that the electrode of the second X-ray absorbing layer is electrically connected to at least one of the electrical contacts. Method.   The method of claim 3, wherein a gap between the first chip and the second chip is less than 100 microns.   The method of claim 1, wherein the first chip has a smaller area than the substrate.   The method of claim 1, wherein a ratio of a coefficient of thermal expansion of the first chip to a coefficient of thermal expansion of the substrate is 2 or more.   The method of claim 1, wherein the X-ray absorbing layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof.   The method according to claim 1, wherein the X-ray absorbing layer is doped with chromium.   The method of claim 1, wherein the X-ray absorbing layer has a thickness of no more than 200 microns.   The method of claim 1, wherein the first chip comprises a redistribution layer (RDL) on the second surface.   The method of claim 1, wherein the first chip includes a via, the via extending from the first surface to the second surface. The electronic system comprises:
A first voltage comparator configured to compare the voltage of the electrode with a first threshold;
A second voltage comparator configured to compare the voltage with a second threshold;
A counter configured to record a plurality of X-ray photons reaching the X-ray absorption layer;
With a controller and
The controller is configured to start a time delay from the time when the first voltage comparator determines that the absolute value of the voltage is equal to or greater than the absolute value of the first threshold,
The controller is configured to activate the second voltage comparator during the time delay;
The controller is configured to increase the number recorded by the counter by one when the second voltage comparator determines that the absolute value of the voltage is equal to or greater than the absolute value of the second threshold. The method of claim 1, wherein The electronic system further includes a capacitor module electrically connected to the electrode of the first X-ray absorption layer,
The method of claim 12, wherein the capacitor module is configured to collect charge carriers from the electrodes of the first X-ray absorbing layer.   The method of claim 12, wherein the controller is configured to activate the second voltage comparator at the start or end of the time delay. The electronic system further includes a voltmeter,
3. The method of claim 2, wherein the controller is configured to cause the voltmeter to measure the voltage at the end of the time delay.   The method of claim 15, wherein the controller is configured to determine an X-ray photon energy based on the value of the voltage measured at the end of the time delay.   The method of claim 12, wherein the controller is configured to connect the electrode of the first X-ray absorbing layer to electrical ground.   13. The method of claim 12, wherein the rate of change of the voltage is substantially zero at the end of the time delay.   13. The method of claim 12, wherein the rate of change of the voltage is substantially non-zero at the end of the time delay.   The method of claim 1, wherein the X-ray absorbing layer comprises a diode.

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