Systems for Photomultiplier Tubes

Abstract

A system for a photomultiplier tube device is provided. In one embodiment, a photomultiplier tube device includes: a microcell including an active area coupled to a quenching resistor; and a signal line coupled to the quenching resistor, the signal line including a first side surface, a second side surface, and a substrate, the first side surface and the second side surface being angled inwardly toward each other.

Description

Technical Field

[0001] Embodiments of the subject matter disclosed herein relate to medical imaging and, more particularly, to photomultiplier tubes for use in medical imaging detectors. Background Art

[0002] A PET detector may have a scintillator component that illuminates upon receipt of radiant energy and a photodiode component that detects the illumination of the scintillator component and provides an electrical signal that varies with the intensity of the illumination. In this configuration, the scintillator may be coupled to a solid-state photomultiplier (SSPM). The SSPM is comprised of multiple Geiger-mode avalanche photodiodes (APDs) or "microcells" that amplify each single photon from the scintillator into a large, rapid pulse of signal current.

[0003] In some examples, the microcells can be arranged in an array. Each microcell output can be connected to a signal line through a respective quenching resistor. These multiple signal lines and resistors across the array represent inactive (e.g., non-photosensitive) regions of the photomultiplier tube, which reduces the photon detection efficiency of the detector. Summary of the invention

[0004] In one embodiment, a photomultiplier tube device includes a microcell including an active area coupled to a quenching resistor and a signal line coupled to the quenching resistor. The signal line includes a first side surface, a second side surface, and a substrate. The first side surface and the second side surface are angled inwardly toward each other. In this way, the side surface of the signal line can be used to reflect incident photons back to the active area.

[0005] It should be understood that the above brief description is provided to introduce in a simplified form a series of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is solely defined by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0007] Figure 1 is a block diagram of a PET imaging system.

[0008] Figure 2 An example detector ring assembly is schematically shown.

[0009] Figure 3 An example detector unit is schematically shown.

[0010] Figure 4 is a cross-sectional view of an embodiment of a microcell array.

[0011] Figure 5 yes Figure 4 A first cross-sectional view of a microcell array.

[0012] Figure 6 yes Figure 4 A second cross-sectional view of a microcell array.

[0013] Figure 7 and 8 are cross-sectional views of additional embodiments of microcell arrays.

[0014] Fig. 9 It is used to manufacture Figure 4 Method for microcell arrays. DETAILED DESCRIPTION

[0015] Various embodiments of photomultiplier tube devices (e.g., solid-state photomultipliers, referred to as SSPMs) for radiation detectors are described below. Specifically, systems and methods are provided for increasing the photon detection efficiency of the detector by redirecting photons that strike an inactive region of the photomultiplier tube device to an active region without increasing the cost or manufacturing complexity of the photomultiplier tube device.

[0016] Silicon photomultiplier (SiPM) devices can include 100-10,000 microcells with dimensions ranging from 25 μm × 25 μm to 100 μm × 100 μm. Each microcell output is connected to the signal acquisition line through a quenching resistor. The quenching resistor and the signal / bias lines are not active (photosensitive) areas. Therefore, even if efforts to improve the quantum efficiency of the microcell active area have been successful, the photon detection efficiency (PDE) of the microcell is still limited by the relatively high area occupied by the inactive area.

[0017] Other attempts to increase PDE by reducing the impact of the ineffective area include adding microlenses, flat reflective coatings on the ineffective area, and shaped reflective areas built on top of the ineffective area to redirect the light / photons in the ineffective area toward the effective area. However, each of these configurations has disadvantages that make it difficult to implement. For example, building a separate structure on top of the ineffective area is a complex process that adds a lot of cost. Simply adding a reflective coating on the (originally flat) ineffective area is also problematic because the light first reflects from the coating back to the scintillation crystal before traveling toward the effective area. These photons travel a longer distance with a certain probability of absorption. Since these photons come later than the initial fast photons, this configuration does not improve the timing resolution. Finally, adding microlenses increases manufacturing cost and complexity, and the optical glue used to attach the microlenses to the SiPM and scintillation crystal has a refractive index similar to that of microlenses made of glass, thus greatly weakening the focusing function.

[0018] Thus, as described in more detail herein, by using lithography techniques capable of 3D patterning, the 3D shapes of the conductive signal lines and the quenching resistors themselves can be used to redirect injected photons toward the active area. Instead of building a separate structure as described above, the reflective surface structures of the SiPM components are formed directly by utilizing lithography techniques capable of forming shaped structures. By doing so, manufacturing costs can be reduced relative to building a separate structure, and focusing or other light effects that may be introduced by coupling a separate structure to the SiPM can be avoided.

[0019] The SiPMs disclosed herein can be integrated into any number of radiation detection devices, including gamma spectrometers / isotope identifiers, neutron detectors, computed tomography systems, and positron emission tomography (PET) systems.

[0020] Figure 1 1 is a block diagram of an exemplary embodiment of a PET system 100 in which various embodiments of the present disclosure may be implemented. The PET system 100 includes a detector ring assembly 20. The PET system 100 also includes a controller 103 to control data acquisition and image reconstruction processes. The controller 103 includes a processor 104 and an operator workstation 105. The processor 104 includes a data acquisition processor 106 and an image reconstruction processor 108 interconnected via a communication link 110. The PET system 100 acquires scan data and sends the data to the data acquisition processor 106. The scanning operation is controlled by the operator workstation 105. The data acquired by the data acquisition processor 106 is reconstructed using the image reconstruction processor 108.

[0021] The detector ring assembly 20 includes a central opening in which the object 109 can be positioned using, for example, a motorized stage that is aligned with the central axis of the detector assembly 20. The motorized stage moves the object 109 into the central opening of the detector ring assembly 20 in response to one or more commands received from the operator workstation 105. A PET scanner controller 116 (also referred to as a gantry controller) is disposed (e.g., mounted) within the PET system 100. The PET scanner controller 116 responds to commands received from the operator workstation 105 via the communication link 110. Thus, the scanning operation is controlled by the operator workstation 105 via the PET scanner controller 116.

[0022] The detector ring assembly 20 includes a plurality of detector cells arranged in one or more detector rings. Each detector cell includes a set of scintillator crystals arranged in a matrix, which is disposed in front of an array of silicon photomultiplier tube cells (described in more detail below). When a photon collides with a crystal on the detector, it produces a scintillation on the crystal. When a scintillation event occurs, the cells of the silicon photomultiplier tube array produce analog signals on the communication line 119. A set of acquisition circuits 120 are configured to receive these analog signals. The acquisition circuits 120 produce digital signals indicating the gamma ray interaction location and total energy of the event. The acquisition circuits 120 also produce event detection pulses, which indicate the time or instant when the scintillation event occurred. These digital signals are transmitted to the event locator circuit 122 in the data acquisition processor 106 via a communication link (e.g., a cable).

[0023] The data acquisition processor 106 includes an event locator circuit 122, an acquisition CPU 124, and a coincidence detector 126. The data acquisition processor 106 periodically samples the signals generated by the acquisition circuit 120. The acquisition CPU 124 controls the communication on the backplane bus 128 and on the communication link 110. The event locator circuit 122 processes information about each valid event and provides a set of digital numbers or values ​​indicating the detected event. For example, the information indicates the time when the event occurred and the position of the scintillation crystal that detected the event. Event data packets are transmitted to the coincidence detector 126 via the backplane bus 128. The coincidence detector 126 receives the event data packets from the event locator circuit 122 and determines whether any two detected events are coincident. Coincidence is determined by a number of factors. First, the time stamps in each event data packet must be within a predetermined time period of each other, such as 4.5 nanoseconds. Second, the line of response (LOR) formed by the straight line joining the two detectors that detected the coincident event should pass through the field of view in the PET system 100. Events that cannot be paired are discarded. Coincident event pairs are located and recorded as coincident data packets, which are transmitted via a communication link to a classifier 130 in the image reconstruction processor 108 .

[0024] The image reconstruction processor 108 includes a classifier 130, a memory module 132, an image CPU 134, an array processor 136, and a backplane bus 138. The classifier 130 counts all events that occur along each projection ray and organizes the events into 4D data. The 4D data (or sinogram) is organized as a data array 140 in an exemplary embodiment. The data array 140 is stored in the memory module 132. The backplane bus 138 is linked to the communication link 110 through the image CPU 134. The image CPU 134 controls the communication through the backplane bus 138. The array processor 136 is also connected to the backplane bus 138. The array processor 136 receives the data array 140 as input and reconstructs the image in the form of an image array 142. The resulting image array 142 is stored in the memory module 132.

[0025] The images stored in the image array 142 are transmitted by the image CPU 134 to the operator workstation 105. The operator workstation 105 includes a CPU 144, a display device 146, and an input device 148. The CPU 144 is connected to the communication link 110 and receives input (e.g., user commands) from the input device 148. The input device 148 can be, for example, a keyboard, a mouse, or a touch screen panel. Through the input device 148 and associated control panel switches, the operator can control the calibration of the PET system 100 and the positioning of the scan object 109. Similarly, the operator can control the display of the resulting images on the display device 146 and perform image enhancement functions using a program executed by the workstation CPU 144.

[0026] Generally, the data array received by the array processor 136 must be corrected prior to reconstruction. This level of correction includes normalization, scatter correction, and geometric correction.

[0027] Figure 2A PET detector ring assembly 20 is shown that includes a plurality of detector modules 22 arranged in a ring to form the PET detector ring assembly 20. Each detector module 22 is assembled from a plurality of detector units 24. Thus, a plurality of detector units 24 are assembled to form a single detector module 22, and a plurality of detector modules 22 are assembled to form the detector ring assembly 20. In one embodiment, the detector ring assembly 20 includes 28 detector modules 22 that are coupled together such that the detector ring assembly 20 has a ring shape. In some embodiments, each detector module 22 includes 20 detector units 24 arranged in a 4×5 matrix. It should be appreciated that the number of detector modules 22 used to form the detector ring assembly 20 is exemplary, and the detector ring assembly 20 may have more or less than 28 detector modules 22. Furthermore, it should be appreciated that the number of detector units 24 used to form each detector module 22 is exemplary, and the detector module 22 may have more or less than 20 detector units 24.

[0028] Figure 3 It can be formed Figure 2 A perspective view of an exemplary detector unit 24 of a portion of the detector ring module 22 is shown. In various embodiments, the detector unit 24 includes a scintillator block 30 having one or more scintillator crystals 32 arranged along the x-axis and the z-axis. In one embodiment, the scintillator block 30 has 36 crystals 32 arranged in a 4×9 matrix. However, it should be appreciated that the scintillator block 30 can have fewer than or more than 36 crystals 32, and the crystals 32 can be arranged in a matrix of any suitable size. It should also be noted that the scintillator crystals 32 can be formed of any suitable material, such as bismuth germanate (BGO), cerium-doped yttrium lutetium silicate (LYSO), or gadolinium silicate (GSO), etc.

[0029] The detector unit 24 also includes a plurality of light sensors 34, shown as a plurality of photosensors, which can be any suitable photodetector for sensing or detecting light or other electromagnetic energy. In the illustrated embodiment, the light sensors 34 are silicon photomultipliers (SIPMs). The plurality of light sensors 34 are coupled to the end of the scintillator block 30 opposite the detector face 38. The surface of the crystal block 30 not coupled to the light sensors 34 is covered with a reflective layer, such as polytetrafluoroethylene, TiO2 loaded epoxy, or a spectral reflector. It should be noted that in some embodiments, a reflector or reflective material can be placed between some of the crystals in the crystal block 30.

[0030] In various embodiments, the detector unit 24 has 18 light sensors 34 on each end of the scintillator block 30, which are arranged in a 3×6 matrix. However, it should be appreciated that the detector unit 24 can have fewer than or more than 18 light sensors 34, and the light sensors 34 can be arranged in a matrix of any suitable size. For example, some embodiments include 36, 54, or 100 crystals 32, with the crystals 32 having corresponding light sensors 34, and the light sensors 34 are arranged in a 6×6 matrix, a 9×6 matrix, or a 10×10 matrix, respectively. It should be noted that in various embodiments, a one-to-one connection between the light sensors 34 (e.g., photosensors) and the crystals 32 is not provided, so that there is a one-to-many connection between the light sensors 34 and the crystals 32. However, in other embodiments, a one-to-one connection between the light sensors 34 (e.g., photosensors) and the crystals 32 can be provided. In addition, the light sensors 34 can have different sizes or shapes. In some embodiments, the light sensors 34 are larger than 3×3 mm 2 However, in other embodiments, larger or smaller light sensors 34 may be used, such as 4×6 mm 2 The light sensor 34 is provided.

[0031] In one embodiment, light sensor 34 is a parallel connected avalanche photodiode and operates above the breakdown voltage in Geiger mode. For example, in various embodiments, light sensor 34 may be a SIPM, a single photon sensitive device formed by an array of avalanche photodiodes on a silicon substrate.

[0032] In operation, the scintillator crystals 32 convert the energy deposited by the gamma rays that strike the scintillator crystals 32 into visible (or near ultraviolet) light photons. The photons are then converted into electrical analog signals by the light sensors 34. More specifically, when a gamma ray strikes any one of the scintillator crystals 32 in the detector units 24, the scintillator that detects the gamma ray converts the energy of the gamma ray into visible light that is detected by the light sensors 34 in the detector units 24. Thus, in the exemplary embodiment, each detector unit 24 outputs "n" analog signals 40.

[0033] A portion of the detector unit 24 is Figure 4 It is shown in FIG. 1 as being composed of multiple avalanche photodiodes (APDs) or "microcells" that amplify single photon arrivals from the scintillator into a large signal. Figure 4Six microcells 62a-62f are shown. Typically, each detector unit will include between 100 and 2500 APDs per square millimeter, each microcell having a length of 20 to 100 microns. Each microcell operates as a separate Geiger mode APD, a few volts higher than the breakdown voltage, and each microcell is virtually identical to all other microcells. In this mode of operation, when one or more photons are absorbed by a single microcell, the electrons generated by the photon absorption trigger an avalanche breakdown that is confined to that microcell. Independent of the number of photons absorbed in the microcell, a single discrete unit of charge is emitted from the microcell. That is, for each Geiger breakdown, the output signal of the microcell will have the same shape and charge, except for minor variations caused by differences between cells in the PN junction structure introduced during the production process.

[0034] Each microcell of the pixel is positioned on a common N-doped silicon substrate 68, but P-doped substrates are also possible. Each microcell includes an entrance window (also called an active area) made of P-doped silicon. This forms a pn junction (e.g., a p-on-n configuration). During use, a depletion region 66 is formed. A depletion region is an insulating region where mobile carriers have diffused away, or have been separated by an electric field. This can occur when a p-type dopant with an acceptor impurity (excess holes) comes into contact with n-type silicon doped with a donor impurity (excess electrons), and the holes and electrons flow through the junction into a lower potential region on the opposite side of the junction.

[0035] Therefore, microcell 62a includes incident window 64a, microcell 62b includes incident window 64b, microcell 62c includes incident window 64c, microcell 62d includes incident window 64d, microcell 62e includes incident window 64e, and microcell 62f includes incident window 64f. Each incident window may include an antireflection layer composed of, for example, silicon nitride.

[0036] The active areas of the microcells are each surrounded by photon-insensitive inactive areas that electrically isolate the microcells from each other and may also accommodate contact lines for bias and / or signal contacts and, in some cases, other features such as polysilicon or metal quenching resistors, transistors, optical isolation trenches, or protection structures. As shown, each microcell is surrounded by its own silicon dioxide insulator. Microcell 62a is surrounded by insulator 72a, microcell 62b is surrounded by insulator 72b, and microcell 62c is surrounded by insulator 72c. It should be understood that Figure 5 The remaining microcells shown are similarly Figure 5 In addition, for clarity, the insulators are provided with separate reference numerals, but it should be understood that the insulators may include integrated / continuous components and may not be discrete insulators, and that differently labeled insulators may share overlapping components.

[0037] Each microcell is connected to a signal line, such as signal line 74, on the front side of the detector cell. In one embodiment, signal line 74 is made of aluminum, but other similar materials that are conductive and non-magnetic are also contemplated, at least in some examples. The connection between the active area of ​​each microcell and the corresponding signal line is formed by a quenching resistor, which is made of polysilicon in one embodiment and a metal resistor in another embodiment. The resistor is connected to the active area of ​​the microcell through a contact, and the resistor is used to quench the avalanche in the microcell once the battery capacitor is discharged. Therefore, microunit 62a is connected to signal line 74 via contact 70a and resistor 76a, microunit 62b is connected to signal line 74 via contact 70b and resistor 76b, microunit 62c is connected to signal line 74 via contact 70c and resistor 76c, microunit 62d is connected to signal line 74 via contact 70d and resistor 76d, microunit 62e is connected to signal line 74 via contact 70e and resistor 76e, and microunit 62f is connected to signal line 74 via contact 70f and resistor 76f.

[0038] Although in Figure 4 Only six microcells and one signal line are shown in FIG. 1 , but it should be understood that the detector unit may include a plurality of additional microcells (e.g., 3600 microcells of an array of 50×50 micron microcells). There may be a plurality of additional signal lines, such as one signal line per row of microcells or one signal line per two rows of microcells.

[0039] Through resistors and signal lines, the independently operated APD cells are electrically connected, and the individual outputs of all microcells are summed to form a common readout signal. Figure 4 As shown, the common readout signal output from the detector cell is the superposition of the normalized signals of all excited microcells. That is, the output of each detector cell is determined by the sum of the discrete charge units from the excited microcells. Therefore, Figure 4 The output of the detector cell depends on the number of microcells that absorb photons, rather than the number of photons absorbed by each microcell. Under operating conditions where the number of absorbed photons is lower than the number of microcells, the output from each detector cell is in the form of an analog pulse whose charge is proportional to the number of absorbed photons.

[0040] Therefore, silicon photomultiplier (SiPM) devices, e.g. Figure 4The device shown may include 100-10,000 microcells with dimensions ranging from 25μm×25μm to 100μm×100μm. In the case of passive quenching, each microcell output is connected to the signal collection line through a quenching resistor. For active quenching, the digital circuit senses the avalanche and generates a corresponding digital (e.g., CMOS, transistor-transistor logic) output, which is fed to the signal collection line. The quenching resistor, digital circuit, and signal line / bias line are not effective (photosensitive) areas. Since the gap or width of the ineffective area between two microcells is independent of the microcell size, the effective area decreases as the microcell size decreases. Therefore, when the microcell becomes smaller, the relative size of the ineffective area around the microcell increases. As a result, although the quantum efficiency of the effective area can reach 81% and above, the small filling factor of 61.5% reduces the photon detection efficiency (PDE) in the 50μm×50μm microcell SiPM to 81%x61.5%=50%. The PDE of a 25 μm×25 μm microcell with a fill factor of 30% is 81%×30%=24.3%.

[0041] The SiPM operates above the PN junction breakdown voltage. When a charge avalanche occurs with the injection of a single photon, current begins to flow through the quenching resistor and causes a voltage drop across the resistor while passively quenching the SiPM. The voltage drop reduces the microcell voltage to below its breakdown voltage, which stops / quenches the current flow. Then, microcell charging begins, requiring C 微单元 *R 淬灭 The recovery time, which may take 20 nanoseconds to 1 microsecond, depends on the C 微单元 and R 淬灭 To reduce the long recovery time after avalanche, an active quenching circuit can be used, which can include a current sensing circuit, a microcell voltage control circuit (e.g., a quenching circuit), and a recharging circuit. The entire circuit can consist of two to six transistors. In the case of an active quenching circuit, at least one additional power line can be provided for the electronic device, and these additional power lines can be shaped in the manner described herein (e.g., a triangle) to redirect light / photons to the active area.

[0042] In order to increase the PDE which is valuable for timing resolution, light / photons in the invalid region can be redirected to the effective region. According to the embodiments disclosed herein, the 3D shape of the conductive signal line and the quenching resistor can be used to redirect the injected photons toward the effective region. Using photolithography techniques capable of 3D patterning, the signal line and the quenching resistor can have a triangular, trapezoidal or other shape. In doing so, the additional reflective surface area provided by the signal line and the resistor can redirect the photons originally directed to the signal line and the resistor to the nearby effective region. By utilizing the structure of the photomultiplier tube itself, rather than adding an additional separate structure on top of the photomultiplier tube, the cost and complexity of the manufacturing process can be reduced.

[0043] The signal line and the resistor may have a suitable 3D shape suitable for redirecting incident photons to the active area nearby / below. Therefore, the signal line and the resistor may have side surfaces that are tilted / angled inwardly. For example, the signal line may include a substrate that shares contact with an insulator surface, wherein the insulator is positioned on a microcell array on an ineffective area (e.g., an area between two adjacent active areas). The signal line may include a first side surface that extends vertically and intersects the substrate and a second side surface that extends vertically, intersects the substrate and is opposite to the first side surface. The first side surface and the second side surface may be angled inwardly, for example, toward each other. In this way, the signal line may include a first internal angle of less than 90° between the first side surface and the substrate and a second internal angle of less than 90° between the second side surface and the substrate. In some examples, the signal line may include a top surface, resulting in the signal line having a cross-sectional shape of a parallelogram. In other examples, the signal line may not include a flat top surface, resulting in the signal line having a cross-sectional shape of a triangle or a rounded triangle. Similar parameters apply to resistors, as described in more detail below.

[0044] The cross-sectional shapes of the signal line 74 and the representative resistor 76b are respectively Figure 5 and 6 Shown in. Figure 5 is along Figure 4 500 is a cross-sectional view of a portion of the detector unit 24 taken along line A-A' of FIG. 500 . The signal line 74 is positioned on the insulator 72c and the incident windows 64c and 64d. The signal line 74 includes a base 77, a first side surface 73 and a second side surface 75. The signal line 74 has a triangular cross-sectional shape. The triangular cross-sectional shape of the signal line 74 includes a peak 71 vertically located above the microcell array, wherein the peak is located at a height h above the insulator 72c below. The signal line 74 has a width w at its base (e.g., where the signal line is connected to the insulator). The first side surface and the second side surface are angled inwardly so that the inner angle a and the inner angle b are each less than 90°.

[0045] In the example shown, the triangle is an equilateral triangle with three 60° angles (e.g., angles a, b, and c are the same), but other angles are possible. In some examples, each angle of the triangle can be selected to provide a desired reflectivity. In one example, the angles of the triangle can be selected based on the size of the microcell. For example, a larger / steeper angle can be selected for a smaller microcell (e.g., where the area of ​​the entrance window is smaller) relative to a larger microcell in order to direct as many incident photons as possible from the inactive area to the active area. In this way, in Figure 5 In the example shown, where the signal line is connected to the microcell, the angle of the signal line 74 (e.g., angles a and b) can be increased relative to 60° if the microcell is larger (e.g., to 75°), or reduced relative to 60° if the microcell is smaller (e.g., to 45°). Depending on the capabilities of the lithography, the width of the substrate can be between 1 μm and 6 μm. The height of the signal line structure can be equal to the width of the substrate or higher.

[0046] The signal line 74 may be made of aluminum, which has a reflectivity of 90% at 400 nm. Figure 5 The triangular shape of the signal line shown, the reflectivity of aluminum can be used to redirect incident photons to the active area / entrance window. Because the signal line is made of aluminum, no external reflective coating is used, thereby reducing the cost and complexity of the manufacturing process. However, other types of materials, such as copper-containing materials, can be used. In addition, the signal line can be a shape other than a triangle, as described in more detail below.

[0047] Figure 5 An insulator 72c and signal line 74 are shown extending over a portion of the entrance window 64c and the entrance window 64d. It is expected that the PDE at the edge of the active area is lower than the central area, so the insulator and signal line can extend over the edge of the entrance window to ensure that the entire inactive area is covered. As mentioned above, the insulator can be made of silicon dioxide, which is transparent because it is also used to make the anti-reflection layer in the active area.

[0048] In addition, by shaping the signal line into a triangle or other 3D shape, the thickness of the signal line is increased, which reduces the impedance (resistance and inductance) of the aluminum trace. By reducing the impedance, the signal's transit time dispersion between microcells is reduced, thereby improving the timing resolution of time-of-flight (TOF) PET.

[0049] Figure 6 It is along Figure 4600 of a portion of the detector unit 24 taken along line BB' of FIG. 600. The resistor 76b is positioned on the insulator 72b and the entrance windows 64a and 64b. The resistor 76b is comprised of a polysilicon core 84 and a reflective coating 86. The resistor 76b includes a base 87, a first side surface 83, and a second side surface 85. The resistor 76b has a triangular cross-sectional shape. The triangular cross-sectional shape of the resistor 76b includes a peak 81 vertically positioned above the microcell array, wherein the peak is positioned at a height h above the insulator 72b below. The resistor 76b has a width w at its base (e.g., where the resistor is coupled to the insulator). The first side surface and the second side surface are angled inwardly such that the interior angle a and the interior angle b are each less than 90°.

[0050] In the example shown, the triangle is an equilateral triangle with three 60° angles (e.g., angles a, b, and c are the same), but other angles are possible. In some examples, each angle of the triangle can be selected to provide a desired reflectivity. In one example, the angles of the triangle can be selected based on the size of the microcell. For example, a larger / steeper angle can be selected for a smaller microcell (e.g., where the area of ​​the entrance window is smaller) relative to a larger microcell in order to direct as many incident photons as possible from the inactive area to the active area. In this way, in Figure 6 In the example shown, where resistor 76b is coupled to a microcell, the angle of the resistor (e.g., angles a and b) can be increased relative to 60° if the microcell is larger (e.g., to 75°), or reduced relative to 60° if the microcell is smaller (e.g., to 45°). Depending on the capabilities of photolithography, the width of the substrate region can be between 1 μm and 6 μm. The height of the resistor structure can be equal to the width of the substrate or higher.

[0051] Resistor 76b can be made of polysilicon, which has low reflectivity at 400nm. Therefore, the polysilicon core can be coated with a reflective coating to redirect incident photons to the active area / incident window. The reflective coating can be made of silicon nitride. The thickness of the silicon nitride layer can be controlled to generate a reflective layer. In other examples, the reflective layer can be made of aluminum. In such an example, a silicon dioxide insulating layer can be formed on the polysilicon core. Then, an aluminum layer can be deposited on top of the silicon dioxide to make the surface of the resistor reflective. In other examples, the resistor can be made of a metal (e.g., aluminum, tungsten) that has sufficient reflectivity to avoid the need for a reflective coating.

[0052] Figure 6An insulator 72b and a resistor 76b are shown extending over a portion of the entrance window 64a and a portion of the entrance window 64b. As described above, the PDE at the edge of the active area is expected to be lower than the central area, so the insulator and resistor can extend over the edge of the entrance window to ensure that the entire inactive area is covered.

[0053] Figure 7 and 8 Additional exemplary cross-sectional shapes other than triangles that may be used for one or both of the signal line and the resistor are shown. Figure 7 A cross-sectional view 700 of a first signal line 90 positioned on an insulator 92 positioned on a first entrance window 94 , a second entrance window 96 , and a gap region in an N-doped base region 98 is shown. Figure 8 A cross-sectional view 800 of a second signal line 91 positioned on an insulator 93 is shown, the insulator 93 being positioned on the first incident window 95, the second incident window 97, and the gap region in the base region 99. Each of the first signal line 90 and the second signal line 91 is a non-limiting example of a signal line 74. In addition, in addition to or in place of the signal line, Figure 7 and 8 The cross-sectional shape shown may be applied to a resistor.

[0054] As mentioned above, the signal lines (and resistors) can be fabricated using photolithography, which may make fabrication Figure 5 and 6 The sharp corners of the triangular cross-sectional shape shown are challenging. Therefore, instead of using a strict triangular shape, the signal line can have a cross-sectional shape of a parallelogram (as in the case of signal line 91) or a rounded triangle (as in the case of signal line 90), which still allows most of the inactive area to redirect incident light to the active area. In the case of a parallelogram, the signal line includes a flat top surface. In the case of a rounded triangle, the signal line includes a curved top surface. The side surfaces can be similar to those described above with respect to Figure 5 The described side surfaces are, for example, angled inwardly to produce an internal angle of less than 90° at the base of the signal line.

[0055] Return to Figure 4 , signal line 74 can be a continuous line extending uninterruptedly from one side of the microcell array / pixel to the other side. Signal line 74 can be a triangular shape along the entire signal line. Therefore, the peak of the triangle can extend uninterruptedly from one end of the microcell array to the other end. Signal line 74 intersects with multiple resistors. As shown in the figure, signal line 74 intersects with each of resistors 76a-76f. At each intersection, signal line 74 is electrically connected to a corresponding resistor.

[0056] Referring to resistor 76a as an example, resistor 76a is coupled to signal line 74. Similarly, resistors 76b-76f may each be coupled to signal line 74 (although in Figure 4 76a and 76f are not directly connected to each other). At the intersection with the signal line 74, the resistor 76a can be substantially flat, rather than triangular. The signal line 74 can extend above the flat surface of the resistor 76a. In this way, the signal line 74 can remain triangular, even above the area where the signal line intersects with the resistor. The resistor can be made flat in the area where it intersects with the signal line, but can be triangular in the remaining area of ​​the resistor. However, other configurations are also possible, such as the resistors are triangular along their entirety, and the signal line is made flat in the area where the signal line intersects with the resistor. In the example where the resistor is a triangle, in addition to the area where the resistor intersects with the signal line, in the area where the triangular shape of the resistor transitions to a flat shape, the resistor can be shaped to match the contour of the signal line surface so that there is no gap between the signal line and the resistor. However, in other examples, the resistor can have a transition to a flat area with a flat (non-wavy) edge of a triangular area, so that a small gap can be at least partially present between the resistor and the signal line.

[0057] exist Figure 4 , contacts 70a-70f are shown as having substantially flat surfaces. Because the contacts represent a small portion of the inactive area, suitable photon redirection can be obtained without reshaping the contacts. In other examples, the contacts can have a desired 3D shape to further increase photon redirection to the active area, such as contacts having a shape similar to a signal line. In addition, the resistor can have a substantially flat shape in the area where the contact intersects the resistor (e.g., Figure 4 ), or the contacts may be shaped to match the triangular shape of the resistor. In addition, the borders of the microcell array, which may not have resistors and contacts in at least some examples, may also be triangular or other shapes to redirect incident photons. In general, any area of ​​the inactive area may be shaped to increase the redirection of photons to the active area.

[0058] Now go to Fig. 9 , shows the use of the Figure 4 Method 900 of a microcell array of a microcell array. At 902, method 900 includes generating a microcell array, such as described above with respect to Figure 4Silicon photomultiplier (SiPM) microcells described. An array of SiPM microcells can be formed in a suitable manner. In one example, an array can be formed by forming a P-doped well in an N-doped ordinary silicon body (e.g., a wafer) using photolithography. For example, an N-doped silicon wafer can be coated with silicon dioxide by a thermal growth process. Then, a photoresist mask is spin-coated on the silicon dioxide. The photoresist is exposed to ultraviolet light through a mask (e.g., a P-well mask) to generate a desired pattern. The exposed photoresist can then be removed with chemicals. The now exposed silicon dioxide can be removed with hydrofluoric acid or other suitable processes. The remaining photoresist is then removed using a suitable acid mixture. The P-doped active region (also referred to as an incident window or P-well) can be formed by diffusion or ion implantation. Only areas without a silicon dioxide layer will form a P-well; the area below the silicon dioxide will remain n-type. In addition, the P-doped active region can be grown on top of the N-doped base region using an epitaxial process.

[0059] At 904, method 900 includes forming a quenching resistor along each column of the array. The resistors can be formed by chemical vapor deposition (CVD) followed by photolithography. For example, a silicon dioxide layer can be deposited on the array followed by CVD of silicon. The silicon can be deposited in a relatively thick layer to allow for a triangular or trapezoidal cross-sectional shape of the resistor to be ultimately formed. The array can then be placed in a furnace with silane gas to form a polysilicon layer.

[0060] The polysilicon layer can be patterned in a manner similar to the formation of a p-well. Thus, a silicon dioxide layer can be deposited on the polysilicon, followed by a photoresist layer. The photoresist can be exposed to ultraviolet light via a resistor mask, and the exposed photoresist and underlying silicon dioxide removed as described above. The exposed polysilicon is then removed using wet etching or other suitable techniques.

[0061] As indicated at 906, the above-mentioned Figure 6 The photolithography process may be patterned to remove the exposed polysilicon in a manner that produces a resistor of a suitable shape (e.g., a triangle, a parallelogram form, etc.) as described. In one example, a series of photolithography steps may be performed using different masks and different amounts of time in the chemical etch. Additionally, as indicated at 908, the photolithography process may be patterned so that the area of ​​the resistor that will be positioned to contact / under the signal line is flat, rather than a triangle, or in the form of a parallelogram with different masks and different amounts of time in the chemical etch.

[0062] Forming the resistor may further include forming a reflective layer, as indicated at 910. As described above, the reflective layer may be formed from silicon nitride or aluminum on top of the resistor by chemical vapor deposition, with the reflectivity of the reflective layer being controlled by the thickness of the layer.

[0063] At 912, method 900 includes forming a signal line along each row (or every other row) of the array. As indicated at 914, forming a signal line along each row (or every other row) of the array may include forming contacts and signal lines. The signal line may be formed of aluminum. Aluminum may be sputtered over the microcell in a relatively thick layer to allow the final formation of a triangular (or parallelogram) shaped signal line. The contacts may be formed of aluminum and may be formed while forming the signal line. As indicated at 916, the shape of the signal line may be generated by a photolithography process similar to that discussed above regarding the formation of a resistor. For example, a series of masks may be used for multiple photolithography steps to form the triangular shape of the signal line.

[0064] Forming the signal line may also include applying a reflective coating, as indicated at 918. Aluminum itself has a reflectivity of over 90%, but the passivation layer on top of the signal line may be a reflective layer. As performed for the resistor at 910, SiO2 or SiN may be vapor deposited as a reflective layer with an appropriate thickness. Method 900 then returns.

[0065] In this way, a silicon photomultiplier tube can be formed. The silicon photomultiplier tube may include a plurality of microcells, wherein each microcell includes an active region electrically connected to a quenching resistor (e.g., a P-doped silicon region formed in an N-doped silicon substrate). A plurality of microcells may be arranged in an array, with each subset of the array being connected to a corresponding signal line. For example, each row of the microcell array may be connected to a corresponding signal line, or two rows of microcells may be connected to a given signal line, or other suitable arrangements. Each microcell may be connected to an associated signal line via its quenching resistor. The quenching resistor may be made of polysilicon or metal, and the signal line may be made of aluminum.

[0066] In order to redirect incident photons that may strike the signal line and / or resistor to the active area, only the signal line (e.g., but not the quenching resistor) or both the signal line and the resistor can be shaped to redirect incident photons to the active area by having the side surfaces extend vertically away from the microcell and angled inward toward each other, such as into a triangle, parallelogram, rounded triangle, trapezoid, or other suitable shape configured to reflect photons to a nearby active area. In this way, the signal line and resistor can extend an appropriate height above the surface of the active area, and the triangle or parallelogram shape can have a suitable steepness to provide a desired amount of photon redirection. During the manufacture of silicon photomultiplier tubes using a subtractive lithography process, the signal line and resistor can be formed into a triangle or parallelogram shape.

[0067] Although the photomultiplier tubes described herein are p-on-n semiconductor configurations made of silicon, other types of photomultiplier tubes are possible, such as germanium, indium gallium arsenide, etc. In addition, the photomultiplier tubes may be made of n-on-p, pn junctions, pin diodes, or other suitable configurations instead of a p-on-n configuration.

[0068] The technical effect of configuring the photomultiplier tube signal lines and resistors to have three-dimensional shapes suitable for reflecting photons is to increase the photon detection efficiency of the photomultiplier tube without significantly increasing manufacturing cost or complexity.

[0069] One example provides a photomultiplier tube device, the device comprising: a microcell including an active area coupled to a quenching resistor; and a signal line coupled to the quenching resistor, the signal line including a first side surface, a second side surface and a substrate, the first side surface and the second side surface being angled inwardly toward each other. In a first example, the signal line is made of aluminum without any additional layers. In a second example that optionally includes the first example, the first side surface and the second side surface are joined to form a peak. In a third example that optionally includes one or more or both of the first and second examples, the signal line includes a top surface positioned above the substrate and joining the first side surface and the second side surface. In a fourth example that optionally includes one or more or each of the first to third examples, the signal line includes a first internal angle of less than 90° between the first side surface and the substrate, and wherein the signal line includes a second internal angle of less than 90° between the second side surface and the substrate. In a fifth example that optionally includes one or more or each of the first to fourth examples, the first internal angle and the second internal angle are both greater than 45°. In a sixth example that optionally includes one or more or each of the first to fifth examples, the quenching resistor includes an active quenching circuit. In a seventh example, which optionally includes one or more or each of the first to sixth examples, the quenching resistor includes a first resistor side surface, a second resistor side surface, and a resistor substrate, and the first resistor side surface and the second resistor side surface are angled inward toward each other. In an eighth example, which optionally includes one or more or each of the first to seventh examples, the quenching resistor includes a polysilicon core and a reflective layer. In a ninth example, which optionally includes one or more or each of the first to eighth examples, the quenching resistor includes a metal resistor. In a tenth example, which optionally includes one or more or each of the first to ninth examples, the active area includes a P-doped silicon incident window positioned in an N-doped silicon substrate. In an eleventh example, which optionally includes one or more or each of the first to tenth examples, the device also includes an insulator positioned below the substrate of the signal line.

[0070] One example provides a photomultiplier tube device, the device comprising: a plurality of microcells, each microcell comprising an active area; a plurality of quenching resistors, each corresponding quenching resistor coupled to a corresponding active area, each quenching resistor having a triangular cross-section; and a signal line coupled to each quenching resistor, the signal line having a triangular cross-section. In a first example, the signal line comprises aluminum. In a second example that optionally includes the first example, each quenching resistor comprises polysilicon and a reflective coating, the reflective coating comprising aluminum, silicon nitride, or silicon dioxide.

[0071] One example provides a medical imaging detector module, the module including: a scintillator that absorbs ionizing radiation and converts the ionizing radiation into photons; and a photomultiplier tube that is coupled to the scintillator, the photomultiplier tube receiving the photons and converting the photons into corresponding electrical signals, the photomultiplier tube including: a plurality of photon-sensitive active regions, each photon-sensitive active region surrounded by a photon-insensitive inactive region; a plurality of quenching resistors, each corresponding quenching resistor coupled to a corresponding active region and positioned above a portion of the corresponding inactive region; and a signal line coupled to each quenching resistor and positioned above another portion of the corresponding inactive region, the signal line including a first side surface, a second side surface and a substrate, a first internal angle less than 90° formed between the first side surface and the substrate, and a second internal angle less than 90° formed between the second side surface and the substrate. In the first example, the signal line is coupled to a data acquisition system that reconstructs one or more images based on the electrical signals. In a second example that optionally includes the first example, each quenching resistor includes a first resistor side surface, a second resistor side surface and a resistor substrate, a third internal angle less than 90° formed between the first resistor side surface and the resistor substrate, and a fourth internal angle less than 90° formed between the second resistor side surface and the resistor substrate. In a third example that optionally includes one or more or each of the first and second examples, the signal line includes aluminum, and wherein each quenching resistor includes polysilicon and a reflective coating. In a fourth example that optionally includes one or more or each of the first to third examples, the first internal angle and the second internal angle are both greater than 45°.

[0072] In another representation, a photomultiplier tube device includes: a plurality of microcells, each microcell including an active area; a plurality of active quenching circuits, each corresponding active quenching circuit coupled to a corresponding active area; and a signal line coupled to each corresponding active quenching circuit, the signal line having a triangular cross-section.

[0073] In another representation, a method of manufacturing a photomultiplier tube device includes: generating an array of photomultiplier tube cells; forming one or more resistors along each column of the array; and forming a signal line along each row or every other row of the array, wherein forming the signal line includes forming each signal line into a three-dimensional shape using photolithography. The three-dimensional shape may include a triangular cross-sectional shape, a trapezoidal cross-sectional shape, or a parallelogram-form cross-sectional shape.

[0074] In one example, forming the signal line may include forming the signal line by sputtering aluminum on the array and then photolithography. Forming the signal line using photolithography may include performing a series of photolithography steps using different masks and / or different chemical etching time amounts to form a cross-sectional shape in the form of a triangular cross-section, a trapezoidal cross-sectional shape, or a parallelogram. In one example, forming one or more quenching resistors may include forming one or more quenching resistors by a chemical vapor deposition process followed by photolithography. Forming one or more quenching resistors by CVD followed by photolithography may include patterning in a photolithography process to generate one or more quenching resistors having a triangular (or other shape) cross-sectional shape. Patterning may include a series of photolithography steps using different masks and different chemical etching time amounts. An array of photomultiplier tube units may be generated by a photolithography process to form a P-doped well in an N-doped ordinary silicon body (e.g., a wafer). In one example, a photomultiplier tube cell can be created by the following steps: coating an N-doped silicon wafer with silicon dioxide; spin coating a photoresist mask on the silicon dioxide; exposing the mask to ultraviolet light; removing the photoresist mask; removing the exposed silicon dioxide; and then removing the mask. A p-well can then be formed by diffusion or grown by epitaxy.

[0075] As used herein, the elements or steps described in singular form and followed by the word "one" or "an" should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly stated. In addition, the reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that also combine the stated features. In addition, unless explicitly stated to the contrary, "comprising", "including" or "having" an embodiment of an element or multiple elements with a specific property may include additional such elements without that property. The terms "including" and "wherein" are used as the common language equivalents of the corresponding terms "including" and "wherein". In addition, the terms "first", "second" and "third" etc. are only used as labels, rather than intending to impose numerical requirements or specific positional order on their objects.

[0076] This written description uses examples to disclose the invention, including the best mode, and also to enable a person of ordinary skill in the art to practice the invention, including making and using any device or system and performing any included method. The patentable scope of the invention is defined by the claims, and may include other examples that occur to a person of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that are insubstantially different from the literal language of the claims.

Claims

1. A photomultiplier tube device, comprising: a microcell comprising an active region coupled to a quenching resistor, wherein the quenching resistor is located over an inactive region of the microcell and comprises a first resistor side surface, a second resistor side surface, and a resistor base, the first resistor side surface and the second resistor side surface being angled inwardly toward each other; as well as A signal line is coupled to the quenching resistor, the signal line including a first side surface, a second side surface, and a base, the first side surface and the second side surface being angled inwardly toward each other.

2. The photomultiplier tube device according to claim 1, wherein: The signal line is made of aluminum without any additional layers.

3. The photomultiplier tube device according to claim 1, wherein: The first side surface and the second side surface join to form a peak.

4. The photomultiplier tube device according to claim 1, wherein: The signal line includes a top surface positioned over the substrate and joining the first side surface and the second side surface.

5. The photomultiplier tube device according to claim 1, wherein: The signal line includes a first internal angle between the first side surface and the substrate that is less than 90°, and wherein the signal line includes a second internal angle between the second side surface and the substrate that is less than 90°.

6. The photomultiplier tube device according to claim 5, wherein: The first inner angle and the second inner angle are both greater than 45°.

7. The photomultiplier tube device according to claim 1, wherein: The quenching resistor comprises an active quenching circuit.

8. The photomultiplier tube device according to claim 1, wherein: The quenching resistor includes a polysilicon core and a reflective layer.

9. The photomultiplier tube device according to claim 1, wherein: The quenching resistor includes a metal resistor.

10. The photomultiplier tube device according to claim 1, wherein: The active region includes a P-doped silicon entrance window positioned in an N-doped silicon substrate. 11 . The photomultiplier tube device according to claim 1 , further comprising an insulator positioned below the base of the signal line.

12. A photomultiplier tube device, comprising: a plurality of microcells, each microcell comprising an effective area; a plurality of quenching resistors, each respective quenching resistor coupled to a respective active region and positioned over a respective inactive region, each quenching resistor having a triangular cross-section; as well as A signal line is coupled to each quenching resistor, the signal line having a triangular cross-section.

13. The photomultiplier tube device according to claim 12, wherein: The signal line includes aluminum.

14. The photomultiplier tube device according to claim 12, wherein: Each quenching resistor includes polysilicon and a reflective coating including aluminum, silicon nitride, or silicon dioxide.

15. A medical imaging detector module, comprising: a scintillator that absorbs ionizing radiation and converts the ionizing radiation into photons; as well as A photomultiplier tube, connected to the scintillator, receiving the photons and converting the photons into corresponding electrical signals, the photomultiplier tube comprising: a plurality of photon-sensitive effective regions, each of the plurality of photon-sensitive effective regions being surrounded by a photon-insensitive ineffective region; a plurality of quenching resistors, each respective quenching resistor coupled to a respective active region and positioned over a portion of a respective inactive region; and A signal line coupled to each quenching resistor and positioned over another portion of the corresponding inactive area, the signal line comprising a first side surface, a second side surface and a substrate, a first inner angle less than 90° formed between the first side surface and the substrate, and a second inner angle less than 90° formed between the second side surface and the substrate.

16. The detector module according to claim 15, wherein: The signal line is coupled to a data acquisition system that reconstructs one or more images based on the electrical signal.

17. The detector module according to claim 15, wherein: Each quenching resistor includes a first resistor side surface, a second resistor side surface and a resistor substrate, a third internal angle less than 90° formed between the first resistor side surface and the resistor substrate, and a fourth internal angle less than 90° formed between the second resistor side surface and the resistor substrate.

18. The detector module according to claim 15, wherein: The signal line comprises aluminum, and wherein each quenching resistor comprises polysilicon and a reflective coating.

19. The detector module according to claim 15, wherein: The first inner angle and the second inner angle are both greater than 45°.

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