CT detector structure

Abstract

The invention provides a CT detector structure, which comprises photodiodes, a readout integrated circuit and a flexible thin film, and is characterized in that the photodiodes are arranged in an array mode and 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 both integrated on the flexible thin film, the edge of the flexible thin film is provided with golden fingers arranged in a finger shape, and an electrode structure of the photodiode is connected with the golden fingers and used for communicating the photodiode with a conductive circuit of the flexible thin film. According to the CT detector structure, the sensitivity, the system integration degree, the long-term reliability and the yield are all improved, and the production cost is reduced; based on the mechanical adaptability of the flexible thin film, seamless splicing is realized during four-side butt joint of the CT detector structure, so that the module has certain flexibility during splicing.

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.

[0008] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0009] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a CT detector structure, which is at least used to solve the problems of low yield and high cost caused by complex processes in the prior art.

[0010] To achieve the above-mentioned object and other related objects, the present invention provides a CT detector structure, the CT detector structure comprising:

[0011] Photodiodes, which are arranged in an array and are used to convert optical signals into electrical signals;

[0012] a readout integrated circuit, the readout integrated circuit being used to process the electrical signal output by the photodiode;

[0013] A flexible film, the photodiode and the readout integrated circuit are integrated on the flexible film, the edge of the flexible film is provided with gold fingers arranged in finger shapes, the electrode structure of the photodiode is connected to the gold fingers, and is used to connect the photodiode with the conductive circuit of the flexible film.

[0014] Preferably, the photodiode is a back-illuminated photodiode, the back-illuminated photodiode comprises a PN junction, and the electrode structure is located on the front side of the PN junction.

[0015] Preferably, the photodiode further includes a photosensitive region, the photosensitive region is located on the back side of the PN junction, and the photosensitive region further includes a microlens and a color filter to improve the collection efficiency and imaging quality of the optical signal.

[0016] Preferably, the electrode structure forms pads matching the gold fingers through multi-layer metal wiring, and the pads are spaced apart on both sides of the front side of the PN junction and arranged linearly.

[0017] Preferably, the electrode structure and the gold finger are connected by a thermal compression bonding process.

[0018] Preferably, the thermocompression bonding process is specifically to align the pads of the electrode structure with the gold fingers one by one, and use ACF glue as welding material for welding.

[0019] Preferably, after welding is completed, a protective glue is applied to the welding position for protection, wherein the protective glue includes UV glue.

[0020] Preferably, the readout integrated circuit is soldered onto the flexible film by a flip-chip process.

[0021] Preferably, the flexible film is made of polyimide material.

[0022] 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.

[0023] As described above, the CT detector structure of the present invention has the following beneficial effects:

[0024] The present invention realizes flexible film integration of photodiodes and readout integrated circuits, allows multiple functions to be integrated into a single flexible film, reduces gaps between modules, and improves the fill factor of the detector; based on the mechanical adaptability of the flexible film, the CT detector structure can achieve seamless splicing when the four sides are butted, so that the modules have a certain degree of flexibility when splicing, eliminates the physical dead zone of traditional rigid splicing, and avoids the risk of splicing misalignment.

[0025] The present invention adopts a back-illuminated photodiode, and also integrates a microlens and a color filter, thereby greatly improving the light collection efficiency and improving the sensitivity of the detector structure; the photodiode is rewired into an electrode structure corresponding to the gold finger of the flexible film, and the two are directly interconnected by a hot pressing bonding process, thereby reducing the manufacturing complexity and cost, and also reducing the impedance fluctuation of the signal path. In addition, the hot pressing bonding process is combined with a protective glue to greatly improve the welding yield without the need for complicated post-processing; the flip-chip welding process is used to integrate the readout integrated circuit, which greatly improves the pad yield; the polyimide flexible film is used to reduce the cost of a single module; the CT detector structure in the present invention achieves improvements in sensitivity, system integration, long-term reliability and yield, and reduces production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram showing the structure of the photodiodes arranged in an array in a specific embodiment of the present invention.

[0027] Figure 2Shown is a top view of a photodiode according to an embodiment of the present invention.

[0028] Figure 3 Shown is a bottom view of a CT detector structure according to a specific embodiment of the present invention.

[0029] Figure 4 Shown is a left side view of the CT detector structure in a specific embodiment of the present invention.

[0030] Figure 5 It is a schematic diagram showing the structure of a back-illuminated photodiode in a specific embodiment of the present invention.

[0031] Figure 6 Display as Figure 5 Schematic diagram of the structure of the middle photosensitive area.

[0032] Component number description

[0033] 10 Flexible film

[0034] 20 Photodiode

[0035] 201 PN Junction

[0036] 202 Photosensitive area

[0037] 2021 Microlens

[0038] 2022 Color Filters

[0039] 2023 Absorption Layer

[0040] 203 Electrode structure

[0041] 30 Readout IC DETAILED DESCRIPTION

[0042] The following embodiments of the present application are described in conjunction with the drawings in the embodiments of the present application. People familiar with this technology can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present application 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 application. For example, when describing the embodiments of the present application in detail, for ease of explanation, the cross-sectional view representing the device structure will not be partially enlarged according to the general proportion, and the schematic diagram is only an example, which should not limit the scope of protection of the present application. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual production.

[0043] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "installation" and "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. It should be understood that when component A is fixedly connected to component C through component B, changes in the relative position relationship caused by the deformation of component A, component B and component C itself are allowed. "Rotational connection" means that they are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that they are connected to each other and can slide relative to each other after the connection. Among them, the two components are obtained by an integrated structure through an integrated molding process, which means that in the process of forming one of the two components, the component is connected to the other component, and there is no need to connect the two components together through reprocessing (such as bonding, welding, snap connection, screw connection).

[0044] The directional terms mentioned in the embodiments of the present application, such as "upper", "lower", "side", "top", "bottom", etc., are only references to the directions of the drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0045] The term "plurality" means at least two. The term "above" includes the number itself. The term "and / or" is a description of an association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", etc. are used only for descriptive purposes and cannot be understood as suggesting or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0046] Please refer to Figures 1 to 5 The present invention provides a CT detector structure, which includes a photodiode 20, a readout integrated circuit 30 and a flexible film 10, wherein the photodiode 20 is arranged in an array and 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; the photodiode 20 and the readout integrated circuit 30 are both integrated on the flexible film 10, and a gold finger arranged in a finger shape is provided at the edge of the flexible film 10, and the electrode structure 203 of the photodiode 20 is connected to the gold finger, which is used to connect the photodiode 20 with the conductive circuit of the flexible film 10.

[0047] Specifically, the present invention is a new type of 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, the photodiode 20 and the 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 high integration. In a specific embodiment of the present invention, the gold finger is a conductive part that connects the flexible film 10 and the external circuit. The gold finger is connected to the electrode structure 203 of the photodiode 20 to achieve conduction between the two, and the flexible film 10 is used to simplify the number of wiring layers, which greatly simplifies the process and reduces the manufacturing complexity and cost; at the same time, based on the mechanical adaptability of the flexible film 10, seamless splicing is achieved when the four sides of the CT detector are butt-jointed.

[0048] As an example, the photodiode 20 is a back-illuminated photodiode 20 , which includes a PN junction 201 , and the electrode structure 203 is located on the front side of the PN junction 201 .

[0049] As an example, the photodiode 20 further includes a photosensitive region 202 , which is located on the back side of the PN junction 201 . The photosensitive region 202 further includes a microlens 2021 and a color filter 2022 to improve the collection efficiency and imaging quality of the optical signal.

[0050] For details, see Figure 5 PN 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] See also Figure 6The 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.

[0052] As an example, the electrode structure 203 forms pads matching the gold fingers through multi-layer metal wiring, and the pads are arranged at intervals on both sides of the front side of the PN junction 201 and are arranged linearly.

[0053] In a specific embodiment of the present invention, refer to Figure 1 and Figure 2 , Figure 1 The photodiode 20 in the embodiment is a 15×7 array. After redesign, the electrodes of the 105 pixel points are rewired through multi-layer metal wiring during the manufacturing process to match the layout of the gold finger. The electrode structure 203 of the photodiode 20 can be connected to the gold finger of the flexible film 10 by welding, so that the electrode structure 203 of the photodiode 20 and the gold finger are reliably electrically connected, and no additional wiring adjustment is required during the manufacturing process. In addition, after the electrode structure 203 is rewired, the photosensitive area 202 and the overall layout remain unchanged, and there is no effect on photon collection.

[0054] See also Figure 2 The electrode structure 203 is rewired into two rows with intervals and arranged linearly, which can increase the spacing between the electrodes, make wiring easier, and avoid interference between signals. The two-row electrode design can avoid the use of a complex bottom circuit board and save costs. The two-row electrode design can directly output signals to the flexible film 10 without the need for a complicated multi-layer circuit board, reducing manufacturing complexity and cost.

[0055] As an example, the electrode structure 203 is connected to the gold finger by a thermal compression bonding process.

[0056] Specifically, thermocompression bonding is a process of connecting the electrode structure 203 of the photodiode 20 to the gold fingers on the flexible film 10 by applying pressure and heat. This process requires high-precision alignment and high-reliability electrical connection. The thermocompression bonding process can achieve sub-micron level alignment accuracy, ensuring high-precision connection between the electrode structure 203 and the gold fingers.

[0057] As an example, the thermal compression bonding process specifically includes aligning the pads of the electrode structure 203 with the gold fingers one by one, and using ACF glue as the welding material for welding.

[0058] Specifically, first, align the pads of the electrode structure 203 with the gold fingers one by one, place the ACF glue (anisotropic conductive film) in the connection area, and align the position of the pads; then, pre-press the ACF glue with appropriate temperature, time and pressure, but no actual electrical connection is formed at this time; then, apply higher temperature and pressure through hot pressing welding equipment. During this process, the conductive particles of the ACF glue will form a conductive path to achieve electrical connection between the electrode structure 203 and the gold fingers; after hot pressing, cool and solidify.

[0059] As an example, after welding is completed, a protective glue needs to be applied to the welding position for protection, wherein the protective glue includes UV glue.

[0060] Specifically, UV glue is cured by ultraviolet rays to form a protective film.

[0061] As an example, the readout integrated circuit 30 is bonded to the flexible film 10 by a flip chip bonding process.

[0062] 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.

[0063] 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.

[0064] As an example, the flexible film 10 is made of polyimide material.

[0065] Specifically, the flexible film 10 made of polyimide has good mechanical flexibility and electrical insulation performance.

[0066] 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.

[0067] In summary, the present invention realizes the flexible film integration of the photodiode and the readout integrated circuit, allows multiple functions to be integrated into a single flexible film, reduces the gap between modules, and increases the fill factor of the detector; based on the mechanical adaptability of the flexible film, the CT detector structure can achieve seamless splicing when the four sides are butted, so that the modules have a certain flexibility when splicing, eliminates the physical dead zone of traditional rigid splicing, and avoids the risk of splicing misalignment. The present invention adopts a back-illuminated photodiode, and also integrates a microlens and a color filter, so as to achieve a significant improvement in light collection efficiency and improve the sensitivity of the detector structure; the photodiode is rewired into an electrode structure corresponding to the gold finger of the flexible film, and the two are directly interconnected by a hot pressing bonding process, so as to reduce manufacturing complexity and cost, and also reduce signal path impedance fluctuations. In addition, the hot pressing bonding process is combined with a protective glue to greatly improve the welding yield without complicated post-processing; the flip-chip welding process is used to integrate the readout integrated circuit, which greatly improves the pad yield; the polyimide flexible film is used to reduce the cost of a single module; the CT detector structure in the present invention is improved in sensitivity, system integration, long-term reliability and yield, and reduces production costs. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has a high industrial utilization value.

[0068] The above description is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present application, which should be included in the protection scope of the present application; in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. The structural member materials, sizes, shapes, etc. mentioned in the embodiments of the present application are all schematic descriptions and do not constitute strict or absolute limitations. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A CT detector structure, characterized in that: The CT detector structure comprises: Photodiodes, which are arranged in an array and are used to convert optical signals into electrical signals; a readout integrated circuit, the readout integrated circuit being used to process the electrical signal output by the photodiode; A flexible film, the photodiode and the readout integrated circuit are integrated on the flexible film, the edge of the flexible film is provided with gold fingers arranged in finger shapes, the electrode structure of the photodiode is connected to the gold fingers, and is used to connect the photodiode with the conductive circuit of the flexible film.

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

3. The CT detector structure according to claim 2, characterized in that: The photodiode further includes a photosensitive region, which is located on the back side of the PN junction. The photosensitive region further includes a microlens and a color filter to improve the collection efficiency and imaging quality of the optical signal.

4. The CT detector structure according to claim 2, characterized in that: The electrode structure forms pads matching the gold fingers through multi-layer metal wiring, and the pads are arranged at intervals on both sides of the front side of the PN junction and are arranged linearly.

5. The CT detector structure according to claim 4, characterized in that: The electrode structure is connected to the gold finger through a thermal compression bonding process.

6. The CT detector structure according to claim 5, characterized in that: The thermocompression bonding process specifically includes aligning the pads of the electrode structure with the gold fingers one by one, and using ACF glue as welding material for welding.

7. The CT detector structure according to claim 6, characterized in that: After welding is completed, protective glue needs to be applied to the welding position for protection, wherein the protective glue includes UV glue.

8. 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.

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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