Self-focusing infrared detector and method of manufacturing the same

Abstract

The application provides a self-focusing infrared detector and a manufacturing method thereof. The self-focusing infrared detector comprises a superlens and a micro-bridge structure. The superlens is suspended above the micro-bridge structure by a support column and is used for focusing infrared radiation. The superlens has a periodic microstructure which is used for increasing the area and efficiency of the superlens for focusing infrared radiation. The micro-bridge structure comprises a bridge pier, a bridge deck and a readout circuit. The bridge deck is suspended above and connected to the readout circuit by the bridge pier and is used for absorbing the infrared radiation focused by the superlens. The readout circuit outputs a result signal according to the infrared radiation absorbed by the bridge deck to reflect the temperature of a target. The micro-bridge structure size can be reduced while maintaining a larger infrared absorption area, without increasing the thermal capacity of the micro-bridge structure, and the product yield and reliability can be greatly improved.

Description

Technical Field

[0001] This application relates to the field of micro-opto-electro-mechanical technology, and in particular to a self-focusing infrared detector and its manufacturing method. Background Technology

[0002] Infrared detectors are generally micro-electro-mechanical systems (MEMS) microbridge structures integrated on CMOS circuits. They utilize infrared absorption thermistor materials to absorb infrared radiation and convert it into heat, causing a change in the resistance of the thermistor materials, which is then read out by the readout circuit.

[0003] Current development trends in infrared detectors focus on reducing the size of microbridge structures and increasing array size to improve image resolution and expand application range. The size of the microbridge structure has become a major factor limiting product performance. Infrared detector microbridges have shrunk from 100 μm × 100 μm in the early days to 8 μm × 8 μm today. Smaller microbridge structures reduce stress mismatch in the thin film and enhance detector sensitivity and resolution. Furthermore, for the same array size, smaller microbridge structures mean smaller detectors and lenses, thus reducing the weight and size of infrared thermal imagers and increasing their portability.

[0004] However, reducing the size of microbridge structures places higher demands on their infrared absorption performance. Traditional microbridge structures mainly consist of piers and a deck. The size of the infrared-absorbing thermistor layer distributed on the deck determines the infrared absorption performance of the microbridge structure. However, as the size of the microbridge structure decreases, the proportion of piers does not decrease accordingly, resulting in a smaller and smaller infrared absorption area on a single microbridge structure. Although double-layer and multi-layer microbridge structures can be fabricated to increase the infrared absorption area, multi-layer microbridge structures create multiple electrical connections, leading to poorer electrical connectivity and increased heat capacity.

[0005] Therefore, how to maintain a large infrared absorption area while reducing the size of the microbridge structure, without increasing the heat capacity of the microbridge structure, and significantly improving the product yield and reliability has become a technical problem that the industry urgently needs to solve. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide a self-focusing infrared detector and its manufacturing method, which maintains a large infrared absorption area while reducing the size of the microbridge structure, without increasing the heat capacity of the microbridge structure, and significantly improving the product yield and reliability.

[0007] To address the aforementioned problems, this application provides a self-focusing infrared detector, comprising: a superlens and a microbridge structure. The superlens is suspended above the microbridge structure via a support column and is used to focus infrared radiation. The superlens has a periodic microstructure, which is used to increase the area and efficiency of the superlens in focusing infrared radiation. The microbridge structure includes piers, a bridge deck, and a readout circuit. The bridge deck is suspended above the readout circuit via the piers and connected to the readout circuit, and is used to absorb the infrared radiation focused by the superlens. The readout circuit outputs a result signal based on the infrared radiation absorbed by the bridge deck to reflect the temperature of the target.

[0008] In some embodiments, the superlens further includes a substrate, wherein the periodic microstructure is disposed on a surface of the substrate remote from and / or close to the microbridge structure.

[0009] In some embodiments, the superlens further includes an antireflective coating disposed on a surface of the substrate opposite to the surface on which the periodic microstructure is disposed.

[0010] In some embodiments, the shape of the periodic microstructure is one or more of a cylinder, a polygon, and a cone.

[0011] In some embodiments, the self-focusing infrared detector further includes: a base for supporting the bridge pier, the readout circuit being disposed in the base, and a metal reflective layer being disposed on the surface of the base near the bridge deck; wherein, an optical resonant cavity is formed between the metal reflective layer and the bridge deck to reflect infrared radiation transmitted from the bridge deck back to the bridge deck for secondary absorption of the infrared radiation.

[0012] This application also provides a method for manufacturing a self-focusing infrared detector, the method comprising: providing a substrate; forming a microbridge structure on the substrate, the microbridge structure including piers, a bridge deck, and a readout circuit, the bridge deck being suspended above the readout circuit via the piers and connected to the readout circuit for absorbing infrared radiation, the readout circuit outputting a result signal based on the infrared radiation absorbed by the bridge deck to reflect the temperature of a target; forming a superlens with periodic microstructures on the microbridge structure, the superlens being suspended above the microbridge structure via support columns for focusing infrared radiation, the periodic microstructures being used to increase the area and efficiency of the superlens in focusing infrared radiation.

[0013] In some embodiments, the step of forming a microbridge structure on the substrate further includes: forming a readout circuit in the substrate; forming a metal reflective layer on the substrate; forming a first sacrificial layer on the metal reflective layer; etching the first sacrificial layer and filling it with a dielectric material to form a bridge pier and a bridge deck, wherein the bridge deck is suspended above the readout circuit and connected to the readout circuit via the bridge pier.

[0014] In some embodiments, the step of forming a superlens with periodic microstructures on the microbridge structure further includes: forming a second sacrificial layer on the microbridge structure; partially etching the second sacrificial layer and the first sacrificial layer to the substrate to form etch holes located at both ends of the microbridge structure; forming support pillars in the etch holes and forming a substrate on the remaining surface of the second sacrificial layer; forming periodic microstructures on the surface of the substrate away from the microbridge structure; and releasing the remaining first sacrificial layer and the second sacrificial layer to form an optical resonant cavity between the metal reflective layer and the bridge surface and to suspend the substrate above the microbridge structure.

[0015] In some embodiments, prior to the step of releasing the remaining first sacrificial layer and the first sacrificial layer, the method further includes: etching a portion of the second sacrificial layer on the surface of the substrate near the microbridge structure; and forming a periodic microstructure in the etched region.

[0016] In some embodiments, the materials of the first sacrificial layer and the second sacrificial layer are polyimide, and the height of the second sacrificial layer is set to the focal length from the superlens to the bridge surface.

[0017] The above technical solution, by incorporating a superlens with periodic microstructures on the microbridge structure, increases the infrared radiation receiving area of ​​the microbridge structure without increasing its heat capacity. Furthermore, by focusing infrared radiation, a large area of ​​infrared radiation is concentrated into the effective region of the microbridge structure, thereby improving its infrared absorption performance. This approach maintains a large infrared absorption area while reducing the size of the microbridge structure, without increasing its heat capacity, and significantly improves product yield and reliability.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this application. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and apparatus should be considered part of the specification. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the specific implementation of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a cross-sectional view of the self-focusing infrared detector in the first embodiment of this application;

[0021] Figure 2 This is a top view of the bridge deck in the first embodiment of this application;

[0022] Figure 3 This is a cross-sectional view of the self-focusing infrared detector in the second embodiment of this application;

[0023] Figure 4 This is a cross-sectional view of the self-focusing infrared detector in the third embodiment of this application;

[0024] Figure 5 This is a top view of a periodic microstructure in one embodiment of this application;

[0025] Figure 6 This is a top view of a periodic microstructure in another embodiment of this application;

[0026] Figure 7 This is a flowchart of a method for manufacturing a self-focusing infrared detector according to an embodiment of this application;

[0027] Figures 8A-8B This is a schematic diagram of a microbridge structure formed in one embodiment of this application;

[0028] Figures 9A to 9D This is a schematic diagram of a microbridge structure formed in one embodiment of this application. Detailed Implementation

[0029] The technical solutions of the specific embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described specific embodiments are only a part of the specific embodiments of this application, and not all of them. Based on the specific embodiments of this application, all other specific embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] To address the problem in existing technologies where the proportion of bridge piers does not decrease accordingly as the size of microbridge structures shrinks, resulting in a decreasing infrared absorption area on a single microbridge structure, this application provides a self-focusing infrared detector and its manufacturing method.

[0031] The following is a description of a self-focusing infrared detector provided by a specific embodiment of this application.

[0032] Figure 1 This is a cross-sectional view of the self-focusing infrared detector in the first embodiment of this application. Please refer to the following. Figure 1 The self-focusing infrared detector includes a superlens 1 and a microbridge structure 2. The superlens 1 is suspended above the microbridge structure 2 by a support column 7 and is used to focus infrared radiation. Figure a shows infrared radiation irradiating the upper surface of the superlens 1, and figure b shows infrared radiation focused by the superlens 1. The superlens 1 has a periodic microstructure 3, which increases the area and efficiency of the superlens 1 in focusing infrared radiation. The microbridge structure 2 includes piers 8, a bridge deck 4, and a readout circuit 5. The piers 8 support the bridge deck 4, and the bridge deck 4 is suspended above and connected to the readout circuit 5 via the piers 8, absorbing the infrared radiation focused by the superlens 1. The readout circuit 5 outputs a result signal based on the infrared radiation absorbed by the bridge deck 4 to reflect the temperature of the target.

[0033] In this embodiment, the bridge deck 4 is connected to the bridge pier via a cantilever 11. Figure 2 This is a top view of the bridge deck in the first embodiment of this application. Please refer to the following: Figure 2 The bridge deck 4 is connected to the cantilever 11, and a pier 8 is provided at the bottom of the cantilever 11. The cantilever 11 has a U-shaped structure for easy heat insulation.

[0034] In some embodiments, the pier 8 is a metal column, made of conductive materials such as aluminum, titanium, tungsten, copper, and titanium nitride.

[0035] In some embodiments, the support post 7 is insulated from the readout circuit 5, and the support post 7 is heat-insulating to the readout circuit 5.

[0036] In this embodiment, the superlens 1 further includes a substrate 61, wherein the periodic microstructure 3 is disposed on the surface of the substrate 61 away from the microbridge structure 2 (shown as the upper surface of the substrate 61); the substrate 61 is suspended above the microbridge structure 2 by the support column 7.

[0037] Figure 3 This is a cross-sectional view of a self-focusing infrared detector in the second embodiment of this application. In this embodiment, the periodic microstructure 3 is located on the surface of the substrate 61 near the microbridge structure 2 (shown as the lower surface of the substrate 61). Figure 4This is a cross-sectional view of the self-focusing infrared detector in the third embodiment of this application. In this embodiment, the periodic microstructure 3 is provided on both the surface of the substrate 61 away from the microbridge structure 2 and the surface close to the microbridge structure 2.

[0038] In some embodiments, the orthogonal projection area of ​​the superlens 1 is set to be consistent with the orthogonal projection area of ​​the microbridge structure 2, so as to focus all the infrared radiation of the area of ​​the microbridge structure 2 onto the bridge surface 4, thereby improving the utilization efficiency of infrared radiation without increasing the heat capacity of the microbridge structure 2.

[0039] The substrate 61 can be made of organic materials, such as any one or more of poly(4-methyl-1-pentene) (PMP), polyethylene (PE), and polypropylene (PP); or it can be made of inorganic materials, such as any one of silicon, germanium, chalcogenide glass, calcium fluoride glass, or silicon dioxide.

[0040] In the first and second embodiments of this application, the superlens 1 further includes an antireflective coating (not shown in the figure), which is disposed on the other surface of the substrate 61 opposite to the surface where the periodic microstructure 3 is disposed. Specifically, in the first embodiment of this application, the periodic microstructure 3 is disposed on the upper surface of the substrate 61, and the antireflective coating is disposed on the lower surface of the substrate 61; in the second embodiment of this application, the periodic microstructure 3 is disposed on the lower surface of the substrate 61, and the antireflective coating is disposed on the upper surface of the substrate 61.

[0041] In some embodiments, the shape of the periodic microstructure 3 is one or more of a cylinder, a polygon, and a cone. Figure 5 This is a top view of a periodic microstructure in one embodiment of this application, in which the periodic microstructure 3 is a circular cylinder. Figure 6 This is a top view of a periodic microstructure 3 in another embodiment of this application, in which the periodic microstructure 3 is a square prism. In other embodiments, the periodic microstructure 3 can be a rhomboid prism, or one or more of square, circular, and rhomboid prisms. The periodic microstructure 3 allows infrared radiation to pass through and be focused onto the microbridge structure 2, and increases the area of ​​the infrared detector that receives infrared radiation by increasing the surface area of ​​the periodic microstructure 3. In some embodiments, by adjusting the size and period of the periodic microstructure 3, the operating wavelength of the superlens 1 can be adjusted to achieve beam focusing in the infrared band and improve the infrared absorption performance of the microbridge structure. The material of the periodic microstructure 3 can be any one of silicon, germanium, gold, silver, and aluminum.

[0042] Please continue reading below. Figure 1In this embodiment, the microbridge structure 2 further includes a base 62 for supporting the bridge pier 8. The readout circuit 5 is disposed in the base 62; a metal reflective layer 10 is disposed on the surface of the base 62 near the bridge surface 4; wherein, an optical resonant cavity 9 is formed between the metal reflective layer 10 and the bridge surface 4 to reflect the infrared radiation transmitted from the bridge surface 4 back to the bridge surface 4 for secondary absorption of the infrared radiation.

[0043] In some embodiments, the bridge deck 4 includes a thermosensitive layer (not shown in the figure), the thermosensitive layer being mainly made of amorphous silicon or vanadium oxide, used to convert infrared radiation into electrical signals; the electrical signals are transmitted to the readout circuit 5 through the bridge pier 8, so that the readout circuit 5 outputs a result signal based on the electrical signals to reflect the temperature of the target.

[0044] The above technical solution, by setting a superlens 1 with periodic microstructures 3 on the microbridge structure 2, increases the infrared radiation receiving area of ​​the microbridge structure 2 without increasing its heat capacity, and improves its infrared absorption performance by converging a large area of ​​infrared radiation into the effective region of the microbridge structure 2. This technical solution avoids the problem of reduced infrared absorption area caused by the large area occupied by the piers 8 as the size of the microbridge structure 2 decreases. Furthermore, it does not affect the thermal performance of the detector and can be used in applications such as power grid security detection, forest fire detection, and human body temperature detection.

[0045] Corresponding to the above-mentioned self-focusing infrared detector, this application also provides a method for manufacturing a self-focusing infrared detector.

[0046] Figure 7 This is a flowchart of a method for manufacturing a self-focusing infrared detector according to an embodiment of this application. Please refer to the following. Figure 7 The manufacturing method of the self-focusing infrared detector includes: step S601, providing a substrate; step S602, forming a microbridge structure on the substrate, the microbridge structure including piers, a bridge deck, and a readout circuit, the bridge deck being suspended above the readout circuit via the piers and connected to the readout circuit for absorbing infrared radiation, the readout circuit outputting a result signal based on the infrared radiation absorbed by the bridge deck to reflect the temperature of the target; step S603, forming a superlens with periodic microstructures on the microbridge structure, the superlens being suspended above the microbridge structure via support columns for focusing infrared radiation, the periodic microstructures being used to increase the area and efficiency of the superlens in focusing infrared radiation.

[0047] In some embodiments, the bridge deck includes a thermosensitive layer, the material of which is primarily amorphous silicon or vanadium oxide. The thermosensitive layer is used to convert infrared radiation into an electrical signal; the electrical signal is transmitted through the bridge pier to the readout circuit, causing the readout circuit to output a result signal reflecting the temperature of the target based on the electrical signal.

[0048] Figures 8A-8B This is a schematic diagram of a microbridge structure formed in one embodiment of this application. In this embodiment, the step of forming the microbridge structure on the substrate further includes: forming a readout circuit 5 in the substrate 62, such as... Figure 8A As shown; a metal reflective layer 10 is formed on the substrate 62; a first sacrificial layer 101 is formed on the metal reflective layer 10; the first sacrificial layer 101 is etched and filled with a dielectric material to form a bridge pier 8 and a bridge deck 4, wherein the bridge deck 4 is suspended above the readout circuit 5 through the bridge pier 8 and connected to the readout circuit 5. The formation of the first sacrificial layer 101 on the metal reflective layer 10 includes spin-coating polyimide (PI) onto the metal reflective layer 10. The dielectric material is silicon dioxide, silicon nitride, or non-stoichiometric silicon dioxide or silicon nitride, or the above materials doped with impurity elements such as boron, phosphorus, carbon, or fluorine.

[0049] Figures 9A to 9D This is a schematic diagram of a microbridge structure formed in one embodiment of this application. In this embodiment, the step of forming a superlens 1 with periodic microstructures 3 on the microbridge structure further includes: forming a second sacrificial layer 102 on the microbridge structure 2, such as... Figure 9A As shown; the second sacrificial layer 102 and the first sacrificial layer 101 are partially etched to the substrate 62 to form etched holes 71 located at both ends of the microbridge structure 2, as shown. Figure 9B As shown; a support pillar 7 is formed within the etched hole 71, and a substrate 61 is formed on the remaining upper surface of the second sacrificial layer 102, as shown. Figure 9C As shown; periodic microstructures 3 are formed on the surface of the substrate 61 away from the microbridge structure 2, such as... Figure 9D As shown; the remaining first sacrificial layer 101 and second sacrificial layer 102 are released to form an optical resonant cavity 9 between the metal reflective layer 10 and the bridge surface 4, and to suspend the substrate 61 above the microbridge structure 2, as shown. Figure 1As shown. In this embodiment, the material forming the second sacrificial layer 102 is the same as the material of the first sacrificial layer 101, and the height of the second sacrificial layer 102 is set to the focal length from the superlens 1 to the bridge surface 4. Releasing the remaining first sacrificial layer 101 and second sacrificial layer 102 includes releasing the first sacrificial layer 101 and the second sacrificial layer 102 in xenon difluoride gas to form a suspended microbridge structure 2 and superlens 1. In some embodiments, a protective layer may also be applied to the surface of the thermosensitive layer away from the substrate 62, and the protective layer may be made of SiO2 and SiN. X Medium materials are used to protect the thermal layer when the first sacrificial layer 101 and the second sacrificial layer 102 are released.

[0050] In some embodiments, prior to the step of releasing the remaining first and second sacrificial layers, the method further includes: etching a portion of the second sacrificial layer 102 on the surface of the substrate 61 near the microbridge structure 2; forming periodic microstructures 3 in the etched region, such as... Figure 4 As shown, the periodic microstructure 3 is located on the lower surface of the substrate 61.

[0051] In some embodiments, the periodic microstructure 3 is not formed before the step of releasing the remaining first and second sacrificial layers, but is formed on the surface of the substrate 61 near the microbridge structure 2 after the step of releasing the remaining first and second sacrificial layers, such as... Figure 3 As shown.

[0052] The above technical solution, by setting a superlens 1 with periodic microstructures 3 on the microbridge structure 2, increases the infrared radiation receiving area of ​​the microbridge structure 2 without increasing its heat capacity. Furthermore, it concentrates a large area of ​​infrared radiation into the effective region of the microbridge structure 2, thereby improving its infrared absorption performance. This avoids the problem of reduced infrared absorption area caused by the large area occupied by the piers 8 as the size of the microbridge structure 2 decreases. Moreover, it has no impact on the thermal performance of the detector and can be used in applications such as power grid security detection, forest fire detection, and human body temperature detection.

[0053] It should be noted that, in this document, relational terms such as "second" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "also includes a..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0054] The various specific embodiments in this specification are described in a related manner. Similar or identical parts between different specific embodiments can be referred to interchangeably. Each specific embodiment focuses on its differences from other specific embodiments. In particular, for the specific embodiment described above, since it is fundamentally similar to the specific embodiment described above, the description is relatively simple; relevant parts can be found in the description of the specific embodiment described above.

[0055] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A self-focusing infrared detector, characterized by The self-focusing infrared detector comprises: a superlens and a micro-bridge structure, the superlens is suspended above the micro-bridge structure by support columns for focusing infrared radiation, the superlens has a substrate, a periodic microstructure and an anti-reflection film, the periodic microstructure is arranged on a surface of the substrate away from the micro-bridge structure and / or a surface of the substrate close to the micro-bridge structure, the periodic microstructure has one or more of a cylindrical shape, a polyhedral shape and a pyramidal shape, the anti-reflection film is arranged on another surface of the substrate opposite to the surface on which the periodic microstructure is arranged, and the periodic microstructure is used to increase the area and efficiency of the superlens for focusing infrared radiation; the micro-bridge structure comprises a pier, a bridge deck and a readout circuit, the bridge deck is suspended above and connected to the readout circuit by the pier, and is used to absorb infrared radiation focused by the superlens, and the readout circuit outputs a result signal according to the infrared radiation absorbed by the bridge deck to reflect the temperature of a target. The self-focusing infrared detector further comprises a substrate for bearing the pier, the readout circuit is arranged in the substrate, and a metal reflection layer is arranged on a surface of the substrate close to the bridge deck; wherein an optical resonant cavity is formed between the metal reflection layer and the bridge deck to reflect infrared radiation transmitted from the bridge deck back to the bridge deck for secondary absorption of the infrared radiation.

2. The self-focusing infrared detector according to claim 1, characterized in that The method comprises: providing a substrate; forming a micro-bridge structure on the substrate, the micro-bridge structure comprising a pier, a bridge deck and a readout circuit, the bridge deck being suspended above and connected to the readout circuit by the pier, and being used to absorb infrared radiation, and the readout circuit outputting a result signal according to the infrared radiation absorbed by the bridge deck to reflect the temperature of a target; and forming a superlens with a substrate, a periodic microstructure and an anti-reflection film on the micro-bridge structure, the superlens being suspended above the micro-bridge structure by support columns for focusing infrared radiation, the periodic microstructure being arranged on a surface of the substrate away from the micro-bridge structure and / or a surface of the substrate close to the micro-bridge structure, the periodic microstructure having one or more of a cylindrical shape, a polyhedral shape and a pyramidal shape, the anti-reflection film being arranged on another surface of the substrate opposite to the surface on which the periodic microstructure is arranged, and the periodic microstructure being used to increase the area and efficiency of the superlens for focusing infrared radiation.

3. A method of fabricating a self-focusing infrared detector, comprising: The step of forming the micro-bridge structure on the substrate further comprises: forming a readout circuit in the substrate; forming a metal reflection layer on the substrate; forming a first sacrificial layer on the metal reflection layer; 4. The method of claim 3, wherein, etching the first sacrificial layer and filling a dielectric material to form a pier and a bridge deck, wherein the bridge deck is suspended above and connected to the readout circuit by the pier. ​ 5. The method of claim 4, wherein, The step of forming the superlens with a periodic microstructure on the micro-bridge structure further comprises: forming a second sacrificial layer on the micro-bridge structure; partially etching the second sacrificial layer and the first sacrificial layer to the substrate to form etching holes at both ends of the micro-bridge structure; forming support columns in the etching holes and forming the substrate on the surface of the remaining second sacrificial layer; forming a periodic microstructure on the surface of the substrate away from the micro-bridge structure; releasing the remaining first sacrificial layer and the second sacrificial layer to form an optical resonant cavity between the metal reflective layer and the bridge surface and to suspend the substrate above the micro-bridge structure.

6. The method of claim 5, wherein, The step of releasing the remaining first sacrificial layer and the second sacrificial layer further comprises: etching part of the second sacrificial layer on the surface of the substrate close to the micro-bridge structure; forming a periodic microstructure in the etching area.

7. The method of claim 5, wherein, The materials of the first sacrificial layer and the second sacrificial layer are polyimide, and the height of the second sacrificial layer is set to the focal length of the superlens to the bridge surface.

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