CT detector structure

Abstract

The invention provides a CT detector structure, which comprises a plurality of photodiodes, at least one readout integrated circuit and at least one flexible film, and is characterized in that the photodiodes are used for converting optical signals into electric signals; the readout integrated circuit is used for processing an electric signal output by the photodiode; the photodiode and the readout integrated circuit are integrated on the flexible film. Flexible film integration of a photodiode and a readout integrated circuit is realized, multiple functions are allowed to be integrated on a single flexible film, gaps between modules are reduced, and filling factors of a detector are provided; based on the mechanical adaptability of the flexible film, seamless splicing of four-side butt joint of the CT detector is realized, so that the module has certain flexibility during splicing, the physical dead zone of traditional rigid splicing is eliminated, and the risk of splicing dislocation is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of medical equipment, and in particular relates to a CT detector structure. Background Art

[0002] As a core innovation direction in the field of medical imaging, the four-sided splicing technology of computed tomography (CT) detectors has a direct impact on the imaging quality, manufacturing cost and reliability of the system due to its structural design. "Four-sided splicing" means that in the detector splicing process, the four sides of the detector module are used for splicing to form a complete detector array. This splicing method can achieve seamless connection, reduce the impact of splicing gaps on imaging quality, and achieve large-area, high-resolution imaging capabilities. The current mainstream four-sided detector solution still faces multiple technical bottlenecks in packaging technology, thermal management and signal integrity, and a breakthrough solution is urgently needed.

[0003] In the existing technology, the packaging solution based on through silicon via (TSV) achieves high-density integration between modules through vertical interconnection, effectively reduces the gap width of the detection array and improves the fill factor, but this technology has significant defects. The TSV process requires the preparation of micro-holes with an aspect ratio greater than 10:1 on the silicon substrate and the completion of metal filling. Its manufacturing yield is limited by the volatility of silicon wafer thinning, through-hole etching and electroplating processes, resulting in high production costs. In addition, although the four-sided docking of the TSV module can reduce the dead zone, the inherent brittleness of the silicon substrate is prone to cause micro-cracks during mechanical splicing, further restricting the feasibility of large-scale production.

[0004] Another typical rigid-flex PCB solution, although it achieves the flexibility of multi-module three-dimensional wiring through a rigid-flexible composite substrate, it exposes two problems in actual application: first, the fluctuation of the dielectric layer thickness of the flexible section will lead to signal transmission impedance mismatch, especially in GHz-level high-speed signal transmission, which will generate reflection noise and seriously affect the imaging signal-to-noise ratio; second, the stress concentration phenomenon at the rigid-flex interface will easily cause fatigue fracture of copper wires under thermal cycling conditions, resulting in long-term reliability degradation. More importantly, this solution needs to be manufactured using a multi-stage HDI process, and its inter-layer alignment accuracy is required to reach ±5μm, which causes the cost of a single board to increase by more than 3 times compared with the traditional FR4 substrate.

[0005] In terms of circuit layout architecture, the traditional design flips the read-out integrated circuit (ROIC) onto the bottom of the printed circuit board (PCB). Although this can reduce the complexity of external routing, the limited wiring space may cause the signal transmission path to be too long or too narrow, increase signal interference and transmission loss, and may affect production efficiency and reliability. In addition, the ROIC will generate a lot of heat during operation, which may cause the chip performance to degrade or even be damaged, and the heat dissipation risk is high.

[0006] In addition, in the CT four-sided detector solution, the use of connectors is crucial to achieving electrical connection and signal transmission between modules. Through its high performance and flexible design, it can ensure stable connection and signal transmission between detector modules. However, in high-channel count systems such as CT detectors, the cost of high-speed connectors accounts for a high proportion.

[0007] Therefore, it is necessary to provide an improved technical solution to address the above-mentioned deficiencies in the prior art. Summary of the invention

[0008] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a CT detector structure for solving the problems of low yield and high cost caused by complex processes in the prior art, as well as the problems of difficult rework and maintenance in the existing design.

[0009] To achieve the above-mentioned object and other related objects, the present invention provides a CT detector structure, the CT detector structure comprising:

[0010] A plurality of photodiodes, wherein the photodiodes are used to convert optical signals into electrical signals;

[0011] at least one readout integrated circuit, the readout integrated circuit being used to process the electrical signal output by the photodiode;

[0012] At least one flexible film, on which the photodiode and the readout integrated circuit are integrated.

[0013] Preferably, the photodiode is a back-illuminated photodiode, which includes a PN junction, a photosensitive region located at the back of the PN junction, and an electrode structure located at the front of the PN junction.

[0014] Preferably, the electrode structure of the photodiode is connected to the conductive pad of the flexible film through a silver paste welding process to achieve reliable transmission of electrical signals.

[0015] Preferably, the photosensitive area further includes a microlens and a color filter to improve the collection efficiency and imaging quality of the optical signal.

[0016] Preferably, the readout integrated circuit is soldered onto the flexible film by a flip-chip process.

[0017] Preferably, the flexible film is an integrated flexible film or a split flexible film.

[0018] Preferably, when the flexible film is an integrated flexible film, the photodiode and the readout integrated circuit are both welded on the same piece of the flexible film.

[0019] Preferably, when the flexible film is a split flexible film, the photodiode and the readout integrated circuit are independently welded on two pieces of the flexible film, and the two pieces of the flexible film are connected by a bonding process. Preferably, the flexible film is made of polyimide material.

[0020] Preferably, the CT detector structure further comprises a heat management structure for heat dissipation, wherein the heat management structure comprises a thermal via and a thermally conductive pad for conducting and dissipating heat.

[0021] As described above, the CT detector structure of the present invention has the following beneficial effects:

[0022] The present invention realizes the flexible film integration of photodiodes and readout integrated circuits, allows multiple functions to be integrated into a single flexible film, reduces the gap between modules, and provides a fill factor for the detector; the flexible film includes an integrated flexible film and a split flexible film, the integrated flexible film is to integrate the photodiode and the readout integrated circuit into a single flexible substrate, eliminates the multi-layer interconnection of traditional circuit boards, shortens the signal path, simplifies the packaging process and improves production efficiency; the split flexible film is to place the photodiode and the readout integrated circuit in independent flexible films, and connect them through bonding, thereby avoiding mutual interference in the welding process, and realizing modular assembly and yield control; based on the mechanical adaptability of the flexible film, the seamless splicing of the CT detector on four sides in the present invention is realized, so that the module has a certain flexibility during splicing, eliminates the physical dead zone of traditional rigid splicing, and avoids the risk of splicing misalignment.

[0023] The present invention adopts a back-illuminated photodiode to improve the sensitivity of the detector structure, and also integrates a microlens and a color filter to achieve a significant improvement in light collection efficiency; a silver paste welding process is used to achieve high-reliability connection between the electrode structure of the photodiode and the flexible film pad, and a flip-chip welding process is used to integrate the readout integrated circuit, which greatly improves the pad yield; a polyimide flexible film is used to reduce the cost of a single module; the CT detector structure in the present invention is improved in terms of sensitivity, system integration, manufacturing cost and long-term reliability, and the split flexible film design supports independent replacement of the photodiode and the readout integrated circuit, thereby enhancing maintainability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It shows a schematic structural diagram of the integrated CT detector structure in the specific embodiment 1 of the present invention.

[0025] Figure 2 It shows a schematic structural diagram of a split-type CT detector structure in specific embodiment 2 of the present invention.

[0026] Figure 3It is a schematic diagram showing the structure of a back-illuminated photodiode in a specific embodiment of the present invention.

[0027] Figure 4 Display as Figure 3 Schematic diagram of the structure of the middle photosensitive area.

[0028] Figure 5 It is a schematic diagram showing the bonding process of two flexible films in the split CT detector structure in Example 2 of the present invention.

[0029] Component number description

[0030] 10 Flexible film

[0031] 101 First Flexible Film

[0032] 102 second flexible film

[0033] 1011, 1021 Gold Finger

[0034] 103 ACF rubber

[0035] 20 Photodiode

[0036] 201 PN Junction

[0037] 202 Photosensitive area

[0038] 2021 Microlens

[0039] 2022 Color Filters

[0040] 2023 Absorption Layer

[0041] 203 Electrode structure

[0042] 30 Readout IC DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention. The test methods in the following examples without specifying specific conditions are generally carried out under conventional conditions or under conditions recommended by the manufacturers.

[0045] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0046] See also Figures 1 to 5 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0047] The present invention provides a CT detector structure, which includes a plurality of photodiodes 20, at least one readout integrated circuit 30 and at least one flexible film 10; wherein the photodiode 20 is used to convert an optical signal into an electrical signal; the readout integrated circuit 30 is used to process the electrical signal output by the photodiode 20; and the photodiode 20 and the readout integrated circuit 30 are integrated on the flexible film 10.

[0048] Specifically, the present invention is a novel CT detector structure designed using COF (chip on film) technology. COF is a packaging technology that directly mounts a chip on a flexible film 10. In the present invention, a photodiode 20 and a readout integrated circuit 30 are specifically integrated on the flexible film 10. The flexible film 10 is used to connect the photodiode 20 and the readout integrated circuit 30 in the detector, which not only provides electrical connection but also plays a role of mechanical support. The COF solution allows multiple functions to be integrated into a single flexible film 10, with a high degree of integration.

[0049] For example, see Figure 3 The photodiode 20 is a back-illuminated photodiode 20 , which includes a PN junction 201 , a photosensitive region 202 located at the back of the PN junction 201 , and an electrode structure 203 located at the front of the PN junction 201 .

[0050] For details, see Figure 3PN junction 201 is a key part to realize photoelectric conversion, and plays an important role in converting optical signals into electrical signals in the CT detector structure. PN junction 201 includes a front and a back side that are arranged relatively, a photosensitive area 202 is located on the back side, and an electrode structure 203 is located on the front side; the back-illuminated photodiode 20 is a photosensitive area 202 of the photodiode 20 placed on the back side of the PN junction 201. When light directly irradiates the photodiode 20, the interference of the metal line is avoided, the reflection and absorption of light inside the PN junction 201 are reduced, the light collection efficiency is significantly improved, and the imaging quality is further improved; at the same time, the back-illuminated layout adopted in the specific embodiment of the present invention can improve the sensitivity and resolution of the CT detector and reduce signal interference.

[0051] As an example, the electrode structure 203 of the photodiode 20 is connected to the conductive pad of the flexible film 10 through a silver paste welding process to achieve reliable transmission of electrical signals.

[0052] Specifically, the photodiode 20 is connected to the flexible film 10 through a silver paste welding process. This process has good conductivity and thermal stability, and can ensure a reliable connection between the photodiode 20 and the flexible film 10. The silver paste welding process specifically includes forming a silver paste layer on the pad of the flexible film 10, aligning the electrode structure 203 with the pad of the flexible film 10, and then connecting the two through hot pressing and curing. Among them, the specific thickness of the silver paste layer, the viscosity of the silver paste, etc. are not excessively restricted here. A certain temperature and pressure must be maintained during hot pressing, and the specific parameters are not restricted here.

[0053] As an example, the photosensitive area 202 further includes a microlens 2021 and a color filter 2022 to improve the collection efficiency and imaging quality of the optical signal.

[0054] For details, see Figure 4 The photosensitive region 202 is the surface portion of the photodiode 20, which is used to receive and absorb light signals. The photosensitive region 202 includes an absorption layer 2023, a microlens 2021 and a color filter 2022. The microlens 2021 can focus light onto the photodiode 20 to improve the light collection efficiency. The color filter 2022 is used to separate light of different wavelengths. The absorption layer 2023 is used to absorb photons and generate electron-hole pairs.

[0055] As an example, the readout integrated circuit 30 is bonded to the flexible film 10 by a flip chip bonding process.

[0056] Specifically, the readout integrated circuit 30 is used to digitally process the electrical signal output by the photodiode 20. In a specific embodiment of the present invention, the readout integrated circuit 30 is also integrated with a preamplifier, which amplifies the weak electrical signal to provide signal strength and quality, so as to reduce interference and loss during signal transmission.

[0057] In flip-chip soldering, the active surface of the readout integrated circuit 30 faces downward and is aligned with the pads on the flexible film 10 for soldering. The active surface of the readout integrated circuit 30 is made with bumps. After the bumps are aligned with the pads on the flexible film 10, they are placed in a reflow soldering furnace. The bumps are melted by heating and form solder joints with the pads of the flexible film 10. The temperature and time during the soldering process are not specifically limited in the specific embodiments of the present invention.

[0058] As an example, the flexible film 10 is an integrated flexible film 10 or a split flexible film 10 .

[0059] For example, see Figure 1 When the flexible film 10 is an integrated flexible film 10 , the photodiode 20 and the readout integrated circuit 30 are both soldered on the same flexible film 10 .

[0060] Specifically, the connection between the photodiode 20 and the readout integrated circuit 30 (ROIC) is integrated on the same flexible film 10. This design can simplify the packaging process, reduce packaging steps, improve production efficiency, and significantly reduce costs.

[0061] For example, see Figure 2 When the flexible film 10 is a split flexible film 10, the photodiode 20 and the readout integrated circuit 30 are independently welded on two flexible films 10, and the two flexible films 10 are connected by a bonding process.

[0062] Specifically, the connection between the photodiode 20 and the readout integrated circuit 30 is designed on two different flexible films 10, and then the two flexible films 10 are connected together through an additional bonding process. Although this design adds the bonding process of the two flexible films 10, it can ensure that the yield of the photodiode 20 welding and the readout integrated circuit 30 welding do not affect each other, thereby improving the overall reliability. At the same time, the design of the split flexible film 10 allows a certain degree of flexibility in splicing between the modules, adapting to complex mechanical structures.

[0063] In a specific embodiment of the present invention, the bonding process includes thermal compression bonding, see Figure 2 The flexible film 10 is provided with gold-plated contact points for electrical connection, and the contact points are arranged in finger shapes and are called "gold fingers 1011, 1021".

[0064] See also Figure 5 As shown in the structural schematic diagram in FIG, the hot pressing bonding process between the two flexible films 10 is specifically as follows: first, the gold finger 1011 of the first flexible film 101 is aligned with the gold finger 1021 of the second flexible film 102, and ACF glue 103 (anisotropic conductive film) is used for preliminary bonding; then, the ACF glue 103 is heated and pressurized by a hot pressing device to form a bond under high temperature and high pressure.

[0065] Among them, the conduction principle of ACF is that during the hot pressing process, the conductive particles in the ACF are captured and squeezed by the electrodes of the upper and lower substrates to form a conductive path, and the conductive particles that are not squeezed remain in the resin to maintain horizontal insulation. This design ensures conductivity in the Z-axis direction while avoiding short circuits in the XY plane direction.

[0066] As an example, the flexible film 10 is made of polyimide material.

[0067] Specifically, the flexible film 10 made of polyimide has good mechanical flexibility and electrical insulation performance.

[0068] As an example, the CT detector structure further includes a thermal management structure (not shown in the figure) for heat dissipation, and the thermal management structure includes a thermal via (not shown in the figure) and a thermal pad (not shown in the figure) for conducting and dissipating heat.

[0069] In order to better understand the CT detector structure in the present invention, the CT detector structure in the present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0070] Example 1

[0071] See also Figure 1 , this embodiment provides an integrated CT detector structure, including a plurality of photodiodes 20, at least one readout integrated circuit 30, at least one flexible film 10, and also includes a thermal management structure for heat dissipation (not shown in the figure);

[0072] The photodiode 20 is used to convert the optical signal into an electrical signal. The photodiode 20 is a back-illuminated photodiode 20. The back-illuminated photodiode 20 includes a PN junction 201, a photosensitive region 202 located on the back of the PN junction 201, and an electrode structure 203 located on the front of the PN junction 201. The photosensitive region 202 also includes a microlens 2021 and a color filter 2022 to improve the collection efficiency and imaging quality of the optical signal.

[0073] The readout integrated circuit 30 is used to process the electrical signal output by the photodiode 20;

[0074] The flexible film 10 is an integrated flexible film 10, the photodiode 20 and the readout integrated circuit 30 are both welded on the same flexible film 10, the electrode structure 203 of the photodiode 20 is connected to the conductive pad of the flexible film 10 through a silver paste welding process to achieve reliable transmission of electrical signals; the readout integrated circuit 30 is welded on the flexible film 10 through a flip-chip welding process; wherein the flexible film 10 is made of polyimide material.

[0075] The preparation process of the integrated CT detector structure in the present embodiment includes: firstly, welding the readout integrated circuit 30 to the flexible film 10 by a flip-chip welding process, and then connecting the electrode structure 203 of the photodiode 20 and the conductive pad of the flexible film 10 by a silver paste welding process, thereby forming the integrated CT detector structure in the present embodiment. The integrated design simplifies the process flow, reduces the production steps, improves production efficiency and significantly reduces costs.

[0076] Example 2

[0077] See also Figure 2 This embodiment provides a split-type CT detector structure, including a plurality of photodiodes 20, at least one readout integrated circuit 30, two flexible films 10, the two flexible films 10 are respectively a first flexible film 101 and a second flexible film 102, and also includes a thermal management structure for heat dissipation (not shown in the figure);

[0078] The photodiode 20 is used to convert the optical signal into an electrical signal. The photodiode 20 is a back-illuminated photodiode 20. The back-illuminated photodiode 20 includes a PN junction 201, a photosensitive region 202 located on the back of the PN junction 201, and an electrode structure 203 located on the front of the PN junction 201. The photosensitive region 202 also includes a microlens 2021 and a color filter 2022 to improve the collection efficiency and imaging quality of the optical signal.

[0079] The readout integrated circuit 30 is used to process the electrical signal output by the photodiode 20;

[0080] The flexible film 10 is a split flexible film 10, the electrode structure 203 of the photodiode 20 is independently welded on the first flexible film 101 through a silver paste welding process, the readout integrated circuit 30 is independently welded on the second flexible film 102 through a flip-chip welding process, and the first flexible film 101 and the second flexible film 102 are connected through a hot pressing bonding process; wherein the flexible film 10 is made of polyimide material.

[0081] The preparation process of the split CT detector structure in this embodiment includes: first, flip-chip welding the readout integrated circuit 30 on the second flexible film 10, then connecting the first flexible film 101 and the second flexible film 102 through a thermocompression bonding process, and finally welding the electrode structure 203 of the photodiode 20 on the first flexible film 101 using a silver paste welding process, thereby forming a split CT detector structure. Although the split CT detector structure has one more thermocompression bonding process than the integrated CT detector structure, the split flexible film 10 can ensure that the yields of the photodiode 20 welding and the readout integrated circuit 30 welding do not affect each other, and are easy to replace independently according to needs, have strong maintainability, and have flexibility in splicing.

[0082] In summary, the present invention realizes the flexible film integration of photodiodes and readout integrated circuits, allows multiple functions to be integrated into a single flexible film, reduces the gap between modules, and provides a fill factor for the detector; the flexible film includes an integrated flexible film and a split flexible film, the integrated flexible film is to integrate the photodiode and the readout integrated circuit into a single flexible substrate, eliminates the multi-layer interconnection of traditional circuit boards, shortens the signal path, simplifies the packaging process and improves production efficiency; the split flexible film is to place the photodiode and the readout integrated circuit in independent flexible films, and connect them through bonding, avoiding mutual interference of the welding process, and realizing modular assembly and yield control; based on the mechanical adaptability of the flexible film, the seamless splicing of the four-sided butt joint of the CT detector in the present invention is realized, so that the module The blocks have a certain flexibility when splicing, eliminating the physical dead zone of traditional rigid splicing and avoiding the risk of splicing misalignment; the photodiode with back-illuminated layout is adopted in the present invention, which improves the sensitivity of the detector structure, and also integrates microlenses and color filters to achieve a significant improvement in light collection efficiency; the silver paste welding process is adopted to achieve high-reliability connection between the electrode structure of the photodiode and the flexible film pad, and the flip-chip welding process is adopted to integrate the readout integrated circuit, which greatly improves the pad yield; the polyimide flexible film is adopted to reduce the cost of a single module; the CT detector structure in the present invention is improved in sensitivity, system integration, manufacturing cost and long-term reliability, and the split flexible film design supports the independent replacement of the photodiode and the readout integrated circuit, and the maintainability is enhanced. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A CT detector structure, characterized in that: The CT detector structure comprises: A plurality of photodiodes, wherein the photodiodes are used to convert optical signals into electrical signals; at least one readout integrated circuit, the readout integrated circuit being used to process the electrical signal output by the photodiode; At least one flexible film, on which the photodiode and the readout integrated circuit are integrated.

2. The CT detector structure according to claim 1, characterized in that: The photodiode is a back-illuminated photodiode, which includes a PN junction, a photosensitive region located at the back of the PN junction, and an electrode structure located at the front of the PN junction.

3. The CT detector structure according to claim 2, characterized in that: The electrode structure of the photodiode is connected to the conductive pad of the flexible film through a silver paste welding process to achieve reliable transmission of electrical signals.

4. The CT detector structure according to claim 2, characterized in that: The photosensitive area also includes a microlens and a color filter to improve the collection efficiency and imaging quality of the light signal.

5. The CT detector structure according to claim 1, characterized in that: The readout integrated circuit is welded on the flexible film through a flip-chip welding process.

6. The CT detector structure according to claim 1, characterized in that: The flexible film is an integrated flexible film or a split flexible film.

7. The CT detector structure according to claim 6, characterized in that: When the flexible film is an integrated flexible film, the photodiode and the readout integrated circuit are both welded on the same piece of the flexible film.

8. The CT detector structure according to claim 6, characterized in that: When the flexible film is a split flexible film, the photodiode and the readout integrated circuit are independently welded on two pieces of the flexible films, and the two pieces of the flexible films are connected by a bonding process.

9. The CT detector structure according to claim 1, characterized in that: The flexible film is made of polyimide material.

10. The CT detector structure according to claim 1, characterized in that: The CT detector structure further includes a heat management structure for heat dissipation, wherein the heat management structure includes a thermal via and a thermally conductive pad for conducting and dissipating heat.

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