A focused high extinction ratio infrared polarization integrated detector structure and its design method

Abstract

The present invention discloses a focused, high-extinction-ratio infrared polarization integrated detector structure and its design method. The structure comprises a readout circuit layer, an indium pillar interconnect layer, a photosensitive chip absorption layer, an air spacer layer, an integrated indium pillar layer, a metal grating layer, a substrate layer, and a meta-lens focusing layer. By aligning the meta-lens focusing layer and the metal grating layer, the detector simultaneously provides both light convergence and polarization filtering for linearly polarized light. When aligned and integrated with focal plane pixels, the detector achieves a high-extinction-ratio infrared polarization detector.

Description

Technical Field

[0001] The present invention belongs to the field of infrared polarization imaging, and in particular relates to a focused high-extinction ratio infrared polarization integrated detector structure and a design method thereof. Background Art

[0002] Infrared detection technology has demonstrated significant application value in a wide range of fields, including space remote sensing, search and identification, reconnaissance and tracking, missile precision guidance, and medical testing. However, with the rapid development of metamaterial stealth and camouflage technologies, as well as the increasingly complex and variable detection environments, traditional infrared detection technology, which primarily relies on increasing light response intensity, is increasingly unable to meet current detection needs.

[0003] To address this challenge, with the continuous advancement of advanced nanofabrication technologies such as electron beam lithography, holographic exposure, and nanoimprinting, pixel-level (i.e., sub-focal plane) polarization-integrated infrared detectors have emerged. These detectors can largely overcome the inherent shortcomings of system-level and component-level infrared polarization detectors, such as bulk, weight, high energy consumption, and complex image registration. Pixel-level polarization-integrated infrared detectors can achieve simultaneous and co-located polarization imaging of the same dynamic target, eliminating the need for image registration during image information fusion processing, significantly improving detection efficiency and accuracy. Furthermore, their small size, light weight, and low energy consumption further broaden their application range. For example, patent document CN107342343 discloses an infrared polarization focal plane device structure and its fabrication method. These devices can acquire polarization images of scene light waves in real time, avoiding the bulkiness and cost of traditional equipment and offering high practicality and cost-effectiveness. However, due to the limitations of pixel center-to-center distance and operating wavelength, these polarization-integrated detectors are prone to optical crosstalk between adjacent pixels with different polarization orientations, resulting in a low focal plane extinction ratio, which in turn seriously affects image quality.

[0004] Therefore, how to effectively solve the optical crosstalk problem and improve the focal plane extinction ratio has become a key technical issue that needs to be urgently solved in this field. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the present invention proposes a focused high-extinction ratio infrared polarization integrated detector structure and its design method. The structure vertically integrates the meta-lens, metal grating and detector in a pixel-level aligned stack, effectively reducing the signal diffraction crosstalk between adjacent pixels and improving the polarization extinction ratio, which can realize the simultaneous collection and imaging of information in different polarization directions of the target.

[0006] The technical solutions of the present invention are as follows:

[0007] In one aspect, the present invention provides a focused high extinction ratio infrared polarization integrated detector structure, which is characterized by comprising:

[0008] bottom readout circuit layer;

[0009] an indium pillar interconnect layer, disposed on the bottom readout circuit layer;

[0010] A photosensitive chip absorption layer is interconnected with the bottom readout circuit layer through the indium pillar interconnection layer to form a photosensitive infrared detection chip, including a photosensitive element for absorbing infrared light;

[0011] an air spacer layer, disposed on the photosensitive chip absorption layer;

[0012] An integrated indium pillar layer is disposed on the air spacer layer to provide structural support and electrical connection;

[0013] a metal grating layer, disposed on the integrated indium column layer, comprising four linear gratings with different polarization orientations for polarization filtering of infrared light;

[0014] A substrate layer is provided on the metal grating layer to provide support for the metal grating layer;

[0015] The meta-lens focusing layer is disposed on the other side of the substrate layer and aligned with the metal grating layer. It is composed of microstructure arrays of different sizes. Each unit lens corresponds one-to-one with a linear grating of different polarization orientation and a photosensitive element in the absorption layer of the photosensitive chip. The meta-lens is located directly above the corresponding photosensitive element to completely cover it.

[0016] Among them, the thickness of the air spacer layer matches the focal length of the meta-lens focusing layer. Through the double-sided pixel alignment design of the meta-lens focusing layer and the metal grating layer, it has the functions of light convergence of corresponding linearly polarized light and filtering in different polarization directions, thereby forming an infrared polarization detector with a high extinction ratio after alignment and integration with the focal plane pixels.

[0017] Preferably, the dielectric column cell structure of the meta-lens focusing layer uses the finite difference time domain method (FDTD) or the finite element method (FEM) to calculate the phase size corresponding to the interaction between the incident light and each dielectric column cell, and obtain the relationship between the phase, transmittance and different dielectric column diameters or duty cycles.

[0018] Preferably, the dielectric column cell parameters of the microstructure of the meta-lens focusing layer mainly include the array period, the duty cycle of the dielectric column, the height of the dielectric column, etc., and their arrangement is controlled according to the Fresnel hyperbola law to achieve the focusing of light and the control of polarized light. The formula is:

[0019] ,

[0020] in x 、 y is the position of the meta-lens cell,λ is the target wavelength, n is the refractive index of the material background, f is the design focal length, is the initial phase constant.

[0021] Preferably, the unit structure of the meta-lens focusing layer is a centrosymmetric structure, and is made of an optical medium material with no absorption in the corresponding wavelength band.

[0022] Preferably, the photosensitive chip absorption layer and the metal grating layer are interconnected via an integrated indium column layer.

[0023] Preferably, the metal grating layer is arranged on the integrated indium column layer, and comprises four linear gratings with different polarization orientations, whose angles are 0°, 45°, 90° and 135° respectively. The material of the metal grating is Au or Al, the grating period is less than 1 μm, the metal line width duty cycle ranges from 0.4 to 0.6, and the grating height ranges from 0.3 to 0.5 μm.

[0024] On the other hand, the present invention also provides a method for designing an infrared high extinction ratio polarization detector structure, which is characterized by comprising:

[0025] Design the readout circuit layer;

[0026] Designing and preparing an indium pillar interconnection layer on the readout circuit layer;

[0027] Designing and preparing a photosensitive chip absorption layer on the indium pillar interconnection layer;

[0028] Designing and preparing an air spacer layer on the photosensitive chip absorption layer, the thickness of which matches the focal length of the subsequent meta-lens focusing layer;

[0029] Designing and preparing a metal grating layer comprising a metal grating array structure with four different polarization orientations above the air spacer layer or above the integrated indium column layer;

[0030] Selecting silicon (Si) or germanium (Ge) as the substrate material, and designing and preparing a meta-lens light-concentrating layer on the other side of the substrate, wherein the meta-lens light-concentrating layer is composed of an array of microstructures of different sizes obtained by etching;

[0031] Ensure that the metal grating layer and meta-lens focusing layer at each angle corresponds to the photosensitive element in the photosensitive chip absorption layer and is located directly above it;

[0032] Through double-sided alignment technology, the metal grating layer and the meta-lens focusing layer are integrated with the photosensitive chip absorption layer to form an infrared high extinction ratio polarization detector with light focusing and polarization filtering functions.

[0033] Furthermore, it also includes the optimization design steps of the materials, sizes and structures of the readout circuit layer, indium pillar interconnection layer, photosensitive chip absorption layer, air spacer layer, metal grating layer and meta-lens focusing layer to ensure the performance of the detector.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. By adopting a meta-lens, effective filtering and focusing of light with different linear polarizations is achieved within the pixel space, significantly reducing the optical crosstalk problem between different polarization angles in the existing technology, improving the polarization extinction ratio of the device, and ensuring the accuracy and reliability of the detection results.

[0036] 2. Fabricating submicron-scale structures such as metalenses and metal gratings on both sides of a single substrate offers the advantages of simple processing technology and avoids damage to the infrared focal plane detector during processing, thereby improving the yield of polarization-integrated detectors. Furthermore, this processing method reduces production costs and improves production efficiency, providing strong support for large-scale production.

[0037] 3. The detector adopts a stacked design, integrating a meta-lens, a metal grating and a photosensitive chip to achieve high extinction ratio polarization detection capability, eliminating the need for independent optical components. It has the advantages of high integration, easy preparation, small size, high stability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a cross-sectional view of the structure of the focused high extinction ratio infrared polarization integrated detector of the present invention;

[0039] Figure 2 is a top view of the metal grating layer of the present invention;

[0040] Figure 3 Schematic diagram of an embodiment of the metalens light-gathering layer of the present invention, including: (a) a cell unit in the metalens structure; (b) the relationship between phase, transmittance, and nanopillar radius; (c) a top view of a 2×2 lens unit in the metalens structure; and (d) the light field convergence effect after passing through the metalens.

[0041] Figure 4 It is the relationship between the polarization extinction ratio and the integration distance between the grating array and the focal plane photosensor. DETAILED DESCRIPTION

[0042] In order to better understand the present invention, the content of the present invention is further explained below with reference to the embodiments and drawings, but the present invention is not limited to the following embodiments.

[0043] See also Figure 1 , Figure 1This is a schematic diagram of an embodiment of the focused high-extinction-ratio infrared polarization integrated detector structure of the present invention. As shown in the figure, the focused high-extinction-ratio infrared polarization integrated detector structure consists of multiple functional layers from bottom to top, each layer working together to achieve polarization detection and light focusing of infrared light. The specific structure is as follows:

[0044] The bottom readout circuit layer 1, serving as the bottom layer of the detector, is used to read and process the electrical signals generated by the photosensitive chip absorption layer 3;

[0045] The indium pillar interconnection layer 2 is used to connect the bottom readout circuit layer 1 and the photosensitive chip absorption layer 3 to achieve the transmission of electrical signals.

[0046] The photosensitive chip absorption layer 3 is used to absorb infrared light and generate corresponding electrical signals, and is prepared through a conventional wafer process.

[0047] The air spacer layer 4 provides a certain space interval for optimizing the optical path and reducing inter-layer interference.

[0048] The integrated indium column layer 5 is used for integration between the photosensitive chip absorption layer 3 and the metal grating layer 6 to ensure electrical connection and optical coupling.

[0049] The metal grating layer 6 is used to perform polarization filtering on the mid-wave infrared light, and selectively transmits light of different polarization directions by designing specific structural parameters. Figure 2 As shown, in this embodiment, the grating material of the metal grating layer 6 is Au or Al, and the grating period is p 0 less than 1μm, grating line width w 0 duty cycle range 0.4~0.6, grating height h The 0 range is 0.3~0.5μm, and there are four linear gratings with different polarization orientations (0°, 45°, 90° and 135°) to achieve polarization filtering in different directions.

[0050] The meta-lens focusing layer 8 focuses the mid-wave infrared light to improve the light collection efficiency. It can be composed of microstructures of different sizes or replaced by a hemispherical micro-lens array. Figure 3 As shown, in the cell structure aligned with the metal grating layer 6, the dielectric column cell period p 1Range is 1~3μm, dielectric column radius r 1 (duty cycle) range is 0.1~0.8, dielectric column height h The range is 1~10μm. By adjusting these parameters, the optical performance of the metalens can be optimized.

[0051] The substrate layer 7 is made of germanium or silicon and is used to support the metal grating layer 6 and the meta-lens focusing layer 8 and ensure alignment between them.

[0052] The metal grating layer 6 and the meta-lens focusing layer 8 are designed and fabricated on both sides of the germanium or silicon substrate layer 7. Each unit lens is aligned with a polarization grating of a different polarization orientation. The thickness of the substrate layer 7 is in the range of 100-400 μm.

[0053] The cell structure of the meta-lens focusing layer 8 and the metal grating layer 6 is aligned as shown in FIG. Figure 3 As shown in (a), the dielectric pillar cell period ranges from 1 to 3 μm, the dielectric pillar duty cycle ranges from 0.1 to 0.8, and the dielectric pillar height ranges from 1 to 10 μm. Under the conditions of selected dielectric pillar cell period and height, the finite-difference time-domain method (FDTD) or the finite element method (FEM) is used to calculate the phase magnitude of the incident light after interacting with each dielectric pillar cell, and the relationship between phase and transmittance and different dielectric pillar diameters or duty cycles is obtained.

[0054] The meta-lens focusing layer 8 is composed of microstructures of different sizes, such as Figure 3 As shown in (c), the arrangement is controlled according to the Fresnel hyperbola law to achieve the light convergence effect. The formula is:

[0055] ,

[0056] in x, y is the position of the meta-lens cell, λ is the target wavelength, n is the refractive index of the material background, f is the design focal length, C( ) is the initial phase constant.

[0057] The meta-lens focusing layer 8 array can also be replaced by a hemispherical micro-lens array to achieve the focusing effect.

[0058] The substrate layer 7 is made of germanium or silicon, with a thickness ranging from 100 to 400 μm, and is used to support the metal grating layer 6 and the meta-lens focusing layer 8 and ensure alignment between them.

[0059] The photosensitive chip absorption layer 3 and the metal grating layer 6 are integrated by using an integrated indium column layer 5 to ensure optical coupling between the photosensitive chip absorption layer 3 and the metal grating layer 6 .

[0060] Example:

[0061] The following steps are involved in determining the structural parameters of the polarization filter and light-converging stack for 3-5μm mid-wave infrared light and designing the overall structure:

[0062] Structural parameter design of photosensitive chip absorption layer 3: The photosensitive element size is 30μm×30μm, which is used to absorb and convert medium-wave infrared light signals.

[0063] Metal grating layer 6: Located on one side of the Si substrate, each polarization direction covers an area of ​​30μm×30μm, aligned with the meta-lens focusing layer 8, the material is Al, the polarization directions are 0°, 45°, 90°, 135°, as shown in the figure. Figure 2 As shown. The structural parameters of a single polarization angle are all grating periods. p 0 = 400nm, grating line width w 0 = 200nm (duty cycle is 0.5), grating height h 0=300nm, ensuring the extinction ratio of a single polarization angle is greater than 500:1.

[0064] The meta-lens focusing layer 8 is located on the other side of the Si substrate and is aligned with the metal grating layer. The Si substrate thickness is 200 μm. The nano-unit structure is as follows: Figure 3 As shown in (a), the design method is as follows:

[0065] Determine the period of the nanounit p 1. Nanopillar radius r 1 (duty cycle), column height h 1 and phase phase and transmittance T The dispersion relation of Figure 3 As shown in (b). The nanometer unit parameters of this embodiment are p 1 = 1 μm, 150 nm ≤ r 1≤400nm, h 1= 1μm.

[0066] By formula Determine the phase distribution requirements at different spatial positions (x, y), determine the combination of nanopillars with different radii, and obtain the basic parameters of the metalens, such as Figure 3 As shown in (c).

[0067] The effect of focusing light with a central wavelength of 4 μm is as follows: Figure 3 As shown in (d), the focal length is 217 μm, which is close to the designed value of 220 μm.

[0068] The stacked structure integration uses a 200μm thick Si substrate to design a double-sided aligned meta-lens and metal grating array. After the meta-lens-metal grating array structure is aligned and integrated with the focal plane pixel, Figure 1 As shown in the figure, after integration, the relationship between the polarization extinction ratio and the integration distance between the grating surface and the photosensitive element is as follows: Figure 4 The results show that when the integration distance is 20μm, the polarization extinction ratio of the focal plane integrated with the meta-lens focusing structure is 35:1, which is about 100% higher than that without the meta-lens focusing structure.

[0069] This embodiment, through the collaborative design of a metalens and a metal grating, significantly reduces optical crosstalk between different polarization angles, increasing the polarization extinction ratio to 35:1 (at an integration distance of 20μm), approximately double that of conventional structures. The metalens' light-concentrating layer achieves precise focusing of light through a microstructure array, improving light collection efficiency and enhancing detection sensitivity. It also achieves polarization filtering and light focusing for mid-wave infrared light. The metalens and metal grating are independently fabricated on opposite sides of the substrate, avoiding damage to the infrared focal plane detector (FPD), improving yield, and reducing production costs, making them suitable for large-scale production. Optimizing the structural parameters of the metalens and metal grating using the finite-difference time-domain (FDTD) method or the finite element method (FEM) allows performance to be tailored to the requirements of different wavelength bands, providing wide adaptability. In summary, this invention, through multi-layer integration and double-sided alignment, achieves infrared polarization detection with a high extinction ratio and efficient light focusing, addressing the issues of severe optical crosstalk and bulkiness associated with conventional detectors, and providing a new technical approach for infrared polarization detection.

Claims

1. A focused high extinction ratio infrared polarization integrated detector structure, characterized in that: Including the following settings from bottom to top: A bottom readout circuit layer (1) for signal reading and processing; An indium pillar interconnection layer (2) is bonded to the bottom readout circuit layer (1) through a flip-chip bonding process; A photosensitive chip absorption layer (3) is electrically interconnected with the bottom readout circuit layer (1) through the indium pillar interconnection layer (2), and comprises a plurality of photosensitive elements arranged in an array for absorbing infrared light; An air spacer layer (4) is provided on the surface of the photosensitive chip absorption layer (3); An integrated indium column layer (5) is disposed on the surface of the air spacer layer (4) and is used to provide structural support and electrical connection; A metal grating layer (6) is provided on the integrated indium column layer (5), comprising a plurality of linear gratings arranged in an array, each linear grating having four different polarization orientations of 0°, 45°, 90° and 135°, and each linear grating is aligned with the photosensitive element below, for polarization filtering of infrared light; A substrate layer (7) is disposed on the metal grating layer (6) to provide support for the metal grating layer (6); A meta-lens light-concentrating layer (8) is provided on the other side of the substrate layer (7), and comprises a plurality of lens units arranged in an array, wherein the phase distribution of the lens units satisfies the Fresnel hyperbola regulation law to achieve phase regulation and convergence of light; Each lens unit of the meta-lens focusing layer (8) forms a vertical optical path with the corresponding linear grating of the metal grating layer (6) and the photosensitive element of the photosensitive chip layer (3); the thickness of the air spacer layer (4) matches the focal length of the meta-lens focusing layer (8); by controlling the thickness of the air spacer layer (4), the incident light is focused by the meta-lens focusing layer (8) and converged into the effective area of ​​the corresponding photosensitive element, thereby suppressing optical crosstalk between adjacent pixels and achieving a polarization extinction ratio; The lens unit of the meta-lens focusing layer (8) comprises n cellular structures, the cellular structure having a dielectric column as a core, the arrangement period of the dielectric column in the horizontal direction is p1, and the period in two orthogonal directions is the same; The dielectric column period ranges from 1 to 3 μm, the dielectric column duty cycle ranges from 0.1 to 0.8, and the dielectric column height ranges from 1 to 10 μm. The dielectric column is designed using the finite difference time domain method or the finite element method. The corresponding phase distribution follows the Fresnel hyperbola law: Where x and y are the positions of the metalens cell, λ is the target wavelength, n is the refractive index of the material background, f is the designed focal length, and C(λ) is the initial phase constant.

2. The polarization integrated detector structure according to claim 1, characterized in that: The unit structure of the meta-lens light-gathering layer (8) is a centrosymmetric structure, and is made of an optical medium material with no absorption in the corresponding wavelength band.

3. The focused high extinction ratio infrared polarization integrated detector structure according to claim 1, characterized in that: The material of the metal grating is Au or Al, the grating period is less than 1 μm, the metal grating line width duty ratio range is 0.4-0.6, and the grating height range is 0.1-0.5 μm.

4. A method for designing a focused high extinction ratio infrared polarization integrated detector structure according to any one of claims 1 to 3, characterized in that: include: Design the bottom readout circuit layer (1); Designing and preparing an indium pillar interconnection layer (2) on the bottom readout circuit layer (1); Designing and preparing a photosensitive chip absorption layer (3) on the indium pillar interconnection layer (2); Designing and preparing an air spacer layer (4) on the photosensitive chip absorption layer (3), wherein the thickness of the air spacer layer (4) matches the focal length of the subsequent meta-lens focusing layer (8); Designing and preparing a metal grating layer (6) comprising a metal grating array structure with four different polarization orientations by integrating an indium column layer (5) above the air spacer layer (4); Selecting silicon or germanium as a substrate material, and designing and preparing a meta-lens light-concentrating layer (8) on the other side of the substrate, wherein the meta-lens light-concentrating layer (8) is composed of microstructure arrays of different sizes obtained by etching; Ensure that the metal grating layer (6) and the meta-lens focusing layer (8) of each angle orientation correspond one-to-one with the photosensitive element in the photosensitive chip layer (3) and are located directly above it; By using a double-sided alignment technology, a metal grating layer (6) and a meta-lens focusing layer (8) are integrated with a photosensitive chip layer (3) to form an infrared high extinction ratio polarization detector having both light focusing and polarization filtering functions.

5. The design method of the focused high extinction ratio infrared polarization integrated detector structure according to claim 4 is characterized in that: The method also includes optimizing design steps for the materials, dimensions and structures of the readout circuit layer (1), the indium pillar interconnection layer (2), the photosensitive chip layer (3), the air spacer layer (4), the metal grating layer (6) and the meta-lens focusing layer (8) to ensure the performance of the detector.

Images