Low-crosstalk refrigeration type infrared polarization detector and preparation method thereof

Abstract

The invention discloses a low-crosstalk refrigeration type infrared polarization detector and a preparation method thereof, and the detector sequentially consists of a refrigeration type infrared detector chip group, a polarization modulation array, a micro-support and a light field convergence array from bottom to top. The preparation method comprises the following steps of: realizing on-chip integration of the polarization modulation array by combining processes of film growth, photoetching, etching and the like, and inhibiting diffraction crosstalk; preparing a light field convergence array by combining processes such as nanoimprint lithography and the like based on the discrete substrate; three-dimensional stacking integration is adopted, device damage is avoided, the requirement for the specific vertical distance between the light field convergence array and the detector chipset is met, and high coupling precision is achieved. The metal wire grating array is directly prepared on the surface of the detector chipset, and the light field convergence array is configured in front of the detector chipset, so that a focusing light spot falls at the central position of a corresponding pixel, and the diffraction effect and signal crosstalk caused by photon-generated carrier cross-pixel transport are inhibited. The detector has the advantages of high extinction ratio and high sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of infrared detection, specifically relating to a low-crosstalk cooled infrared polarization detector and its fabrication method. Technical Background

[0002] The light field contains multi-dimensional information such as intensity, polarization, phase, and wavelength. Traditional thermal imagers can only acquire the thermal radiation intensity within a scene, obtaining a temperature distribution image and using temperature differences to distinguish targets from the background. This approach has a single sensing dimension and limited information. In complex and interference-prone environments, the radiation intensity between targets and the background is similar, making effective identification difficult based solely on intensity perception. There is an urgent need to expand the sensing dimensions, obtain richer light field information, highlight the differences between targets and the background, and improve the detection and recognition capabilities of thermal imagers.

[0003] Polarization is one of the fundamental properties of light. Whether an object spontaneously emits or reflects infrared signals, its polarization state is closely related to the object's material, surface shape, roughness, and other intrinsic characteristics. Even at the same temperature, different objects exhibit significant differences in their polarization properties. Infrared polarization detection utilizes this optical quantity—polarization state—which better reflects the intrinsic characteristics of an object, to suppress background interference signals, highlight target outline details, and improve the distinction between targets and backgrounds. It has broad application prospects in important fields related to people's livelihoods, such as optical remote sensing, cloud detection, hydrological monitoring, and oil spill detection.

[0004] Thanks to the rapid development of micro-nano fabrication technology, focal plane array technology is currently receiving the most attention in the field of polarization imaging. Its feature is the device-level integration between the micro-polarizer array and the detector chip, thereby realizing an integrated modulation-sensing infrared polarization detector, which can support the construction of lightweight, miniaturized, and integrated polarization imaging systems. In addition, this technology arranges multiple polarization units with different orientations in a mosaic pattern to form superpixels, which can simultaneously acquire multiple polarization components of the incident light, thereby realizing real-time polarization detection.

[0005] In the current focal plane array technology, crosstalk between adjacent pixels is one of the main sources affecting the extinction ratio of polarization detectors. Due to the diffraction effect, the emitted signals from adjacent polarization units will exhibit off-axis phenomena, leading to overlap. When the signal is transmitted to the detector pixel, photogenerated carriers at the edge of the photosensitive area may diffuse to adjacent pixels. For a pixel with a certain polarization orientation, when its corresponding TE wave is incident, the generated response signal is very weak. If there is a strong crosstalk signal from adjacent pixels, its own signal is easily masked, resulting in the loss of polarization information. For the commonly used metal wire grid polarization modulation array, the most effective way to suppress the above-mentioned optical and electrical crosstalk is to set a large area of ​​blocking region at the pixel edge to reduce the aperture and reduce the overlap between light fields; at the same time, to confine the photogenerated carriers as much as possible to the central region of the pixel to reduce the possibility of their cross-pixel transport. However, this method of maintaining the extinction ratio at the cost of energy loss causes a serious decrease in the photoelectric response performance of the polarization detector, limiting its applicable scenarios and application range. Therefore, there is an urgent need to develop a technical method that can effectively suppress crosstalk without sacrificing energy, while taking into account the extinction ratio and photoelectric response performance requirements of polarization detectors. Summary of the Invention

[0006] In view of the problems existing in the above background technology, the present invention provides a low crosstalk cooled infrared polarization detector and its preparation method.

[0007] The overall concept of this invention includes: an infrared polarization detector directly fabricates a metal wire grid array on the surface of a detector chip, and a light field converging array is configured in front of the detector chip to ensure that the focused light spot falls on the center of the corresponding pixel. On the one hand, this avoids light field overlap caused by diffraction effects and suppresses optical crosstalk; on the other hand, it concentrates most of the energy at the pixel center, ensuring energy utilization while making photoelectric conversion occur at the pixel center, increasing the transport distance of photogenerated carriers across pixels, reducing the possibility of photogenerated carriers transporting across pixels, and suppressing electrical crosstalk. The fabrication method provided by this invention can achieve high-precision integration between the detector chip, polarization modulation array, and light field converging array, ensuring full matching and effective coupling of the photoelectric interfaces between the components, and obtaining a polarization detector with both high extinction ratio and excellent photoelectric response performance, providing a hardware foundation for the new concept of multidimensional imaging.

[0008] The cooled infrared polarization detector and its fabrication method of the present invention can meet the following technical requirements:

[0009] 1. In terms of device performance, the energy concentration is improved without sacrificing the pixel area; while fully receiving energy, the optical and electrical crosstalk generated by the polarization detector during signal modulation-sensing process is effectively suppressed, maintaining good photoelectric response performance and obtaining a high extinction ratio.

[0010] 2. In terms of fabrication process, it can process micro-nano optical arrays with expected performance and achieve good process compatibility among the light field focusing array, polarization modulation array and detector chip. For components with different materials, structures and working principles, it ensures that they are not damaged during integration, so as to achieve functional synergy and efficient coupling.

[0011] Specifically, the technical solution of the present invention is as follows:

[0012] A low-crosstalk cooled infrared polarization detector, comprising:

[0013] (1) An infrared detector chip set, fixed on a mounting substrate, is used for optical signal sensing and photoelectric conversion. Its components include:

[0014] A cooled infrared focal plane array with a pixel size of M×N;

[0015] The readout circuit has alignment marks in its peripheral non-functional area.

[0016] The electrical interconnection structure between the cooled infrared focal plane detector and the readout circuit;

[0017] (2) A polarization modulation array, used for filtering specific polarization states of infrared incident light, characterized in that:

[0018] It is directly fabricated on the surface of the cooled infrared focal plane array and contains a total of M×N polarization units;

[0019] (3) A light field converging array, used to converge the incident light corresponding to each polarization unit into a light spot not exceeding the size of the unit, characterized in that:

[0020] Suspended above the infrared detector chip group and the polarization modulation array, it contains a total of M×N focusing units;

[0021] In the peripheral area where the focusing unit is not arranged, alignment marks of the same size and shape as the readout circuit are arranged.

[0022] (4) A micro-support, placed on the mounting substrate or the readout circuit of the infrared detector chip group, is mechanically connected to the peripheral area of ​​the light field converging array to support the light field focusing array;

[0023] The pixels of the cooled infrared focal plane array, the polarization units of the polarization modulation array, and the focusing units of the light field converging array are all the same size, have the same center spacing, and are in one-to-one correspondence.

[0024] Preferably, a shielding area is provided at the edge of the polarization unit for transition between units; a polarization filtering area is provided in the middle of the polarization unit, which is composed of rectangular or involute gratings of subwavelength scale, or two-dimensional materials with anisotropic transmission characteristics, and has a specific polarization orientation for transmitting specific polarized light; four polarization units with different polarization orientations form a polarization superpixel in a "2×2" topology, and the polarization superpixel is arranged periodically, covering the entire focal plane;

[0025] Preferably, the focusing unit may be a spherical refractive lens, a diffractive lens with alternating translucent and opaque concentric rings, or a two-dimensional planar meta-lens composed of multiple superatoms;

[0026] Preferably, the superatoms constituting the metalens are nanopillars with a four-fold symmetric structure, a phase modulation range of not less than 2π, and a feature size smaller than the minimum wavelength of the incident infrared light. Their arrangement is as follows:

[0027] To maintain the uniformity of all superatoms, for a focused spot at a specific focal length, based on the corresponding phase gradient distribution, and utilizing the mapping relationship between the superatom planar size and the phase gradient it introduces, superatom nanopillars with corresponding planar sizes are set at different spatial locations.

[0028] Preferably, the microscaffold can be fabricated as a single unit or composed of multiple independent components; the material used is metal or ceramic.

[0029] The present invention also proposes a method for preparing the cooled infrared polarization detector, comprising the following steps:

[0030] (1) The light field converging array is fabricated using micro-nano fabrication technology on a discrete substrate;

[0031] (2) The polarization modulation array is fabricated on the surface of the cooled infrared focal plane array using on-chip integration technology;

[0032] (3) Fix the infrared detector chip assembly with the polarization modulation array on the mounting substrate;

[0033] (4) Apply a first layer of adhesive to the corresponding position on the mounting substrate or readout circuit, and then fix the micro-support thereon;

[0034] (5) At the contact position between the micro-support and the light field converging array, a second layer of adhesive is applied to fix the light field converging array; in particular, the sum of the thickness of the first layer of adhesive, the height of the micro-support and the thickness of the second layer of adhesive should satisfy the following: after the light field converging array is fixed, the vertical distance between the plane where the focusing unit is located and the polarization modulation array is within the focal depth range of the focusing unit.

[0035] (6) Place the mounting substrate with the infrared detector chip set and the micro-support fixed on the stage of the flip soldering equipment, with the focusing unit of the light field converging array facing down, and use the suction head of the flip soldering equipment to adsorb it and suspend it above the infrared detector chip set.

[0036] (7) Using the bidirectional microscope of the device, observe the alignment of the light field converging array and the infrared detector chip group simultaneously, and adjust their positions until the alignment marks of the two are completely superimposed.

[0037] (8) Lower the device suction head to make the light field converging array contact the micro-support, maintain the adsorption state of the light field converging array, and apply a certain pressure to the light field converging array until the adhesive is cured, and then remove the suction head;

[0038] Preferably, the fabrication steps of the light field converging array are as follows:

[0039] (1) Based on the optical properties of the substrate material and the focusing unit material, a matching antireflection film is deposited on the discrete substrate. The coating process can be thermal evaporation, magnetron sputtering or ion milling sputtering.

[0040] (2) On the surface of the deposited antireflective film, a dielectric layer is grown as the structural layer of the light field converging array. The growth process can be atomic layer deposition, chemical vapor deposition, electron beam evaporation, magnetron sputtering or ion milling sputtering.

[0041] (3) On the surface of the grown dielectric layer, spin-coat photoresist and use patterning process to obtain the mask pattern of the focusing unit. The patterning process can be optical transfer technology such as contact exposure, step exposure, electron beam exposure, laser direct writing exposure, or mechanical transfer technology such as nanoimprinting. If nanoimprinting is used, the bottom film removal process is required after patterning.

[0042] (4) Based on the structural characteristics of different types of focusing units and the patterning process used, perform pre-etching pretreatment on the photoresist mask pattern;

[0043] (5) The final forming of the focusing unit is achieved by etching process and the photoresist is removed. The etching process can be inductively coupled plasma etching, ion beam etching, or reactive ion etching. The photoresist is removed by immersion in organic solvent or plasma reaction.

[0044] Preferably, the on-chip integration of the polarization modulation array on the surface of the cooled infrared focal plane array is as follows:

[0045] (1) A metal thin film is deposited on the surface of the cooled infrared focal plane array. The deposition process can be electron beam thermal evaporation, magnetron sputtering or ion milling sputtering.

[0046] (2) On the surface of the deposited metal thin film, spin-coat photoresist and use a patterning process to obtain the mask pattern of the polarization modulation array. The patterning process can be optical transfer technology such as electron beam exposure or laser direct writing exposure, or mechanical transfer technology such as nanoimprinting. If nanoimprinting is used, the base film removal process is required after the patterning is completed.

[0047] (3) The final shape of the polarization modulation array is achieved by etching process and the photoresist is removed. The etching process can be inductively coupled plasma etching, ion beam etching, or reactive ion etching. The photoresist is removed by immersion in organic solvent or plasma reaction.

[0048] The beneficial effects of this invention are:

[0049] 1. Converging the light field before polarization modulation can effectively avoid the overlap caused by light field divergence and the cross-pixel transport of charge carriers at the pixel edge. This eliminates the need for a large area of ​​shading at the edge of the polarization unit, thereby effectively alleviating the prominent problem that existing technologies have to lose a considerable amount of energy to maintain the extinction ratio. While achieving a high extinction ratio, it maintains good photoelectric response characteristics and improves the overall performance of the polarization detector component.

[0050] 2. A fabrication method is proposed that achieves high-precision opto-mechanical-electrical coupling between the detector chip and various micro-nano optical components under the premise of no process overlap or conflict. This provides a practical way to realize an infrared polarization detector with both good polarization selectivity and photoelectric response performance. It can be at least partially transplanted to devices of different specifications and operating bands. It also provides some reference for the integration of other micro-nano optical components and detector chips to achieve functional expansion and performance improvement.

[0051] 3. Based on breakthroughs in the performance of core components, key indicators of the infrared polarization imaging system are improved, higher polarization imaging quality is obtained, the applicable scenarios of the infrared polarization imaging system are broadened, and its effective performance is enabled in more application fields. Attached Figure Description

[0052] Figure 1 A schematic diagram of the overall infrared polarization detector provided for this invention;

[0053] Figure 2 The structure of the polarization modulation array and the arrangement of the polarization units provided by the present invention;

[0054] Figure 3The structure of the light field converging array and the arrangement of the microlens units provided by the present invention;

[0055] Figure 4 A schematic diagram of the microscaffold structure and its height relative to the adhesive, provided for the present invention;

[0056] Figure 5 The present invention provides the transmission process of the optical path and the corresponding modulation effect in an infrared polarization detector;

[0057] Figure 6 The present invention provides a schematic diagram of the edge shielding layer of the polarization unit and the illumination of incident light before and after the introduction of the light field converging unit;

[0058] Figure 7 The present invention provides a process flow for fabricating a polarization modulation array on the surface of a detector chipset.

[0059] Figure 8 Cross-sectional views of the various processes involved in fabricating a polarization modulation array on the surface of a detector chipset, provided for this invention;

[0060] Figure 9 The present invention provides a process flow for fabricating optical field converging arrays based on discrete substrates;

[0061] Figure 10 Cross-sectional views of each step of the fabrication process for an optical field converging array based on a discrete substrate, provided for this invention;

[0062] Figure 11 The present invention provides a three-dimensional integration process flow for a detector chip with a polarization modulation array fabricated on its surface and an optical field converging array.

[0063] Figure 12 The present invention provides cross-sectional views of the process steps for the three-dimensional integration of a detector chip with a surface-mounted polarization modulation array and an optical field converging array.

[0064] The attached figures are labeled as follows:

[0065] 1. Polarization modulation array; 11. Polarization unit; 12. Polarization superpixel; 2. Light field converging array; 21. Light field converging array substrate; 22. Light field converging array antireflection film; 23. Light field converging unit; 24. Light field converging array alignment mark; 3. Micro-support; 4. Cooled detector chipset; 41. Cooled focal plane array; 42. Readout circuit; 43. Indium pillar interconnect structure; 44. Detector chipset alignment mark; 5. Mounting substrate; 6. Adhesive; 61. Lower layer adhesive; 62. Lower layer adhesive; 7. Surface metal layer of cooled focal plane array; 8. Photoresist; 9. Nanoimprint stencil; 10. Nanoimprint master plate. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0067] Example 1

[0068] This embodiment illustrates the structure and working principle of an infrared polarization detector. Please refer to the instructions. Figure 1 The infrared polarization detector shown, from bottom to top, consists of a mounting substrate 5, a cooled detector chipset 4, a polarization modulation array 1, a micro-support 3, and a light field focusing array 2. The connections between the components are as follows:

[0069] The mounting substrate 5 is located at the bottom layer and serves as the carrier for all components and supporting structures;

[0070] The cooled detector chipset 4 is fixed on the mounting substrate 5;

[0071] The polarization modulation array 1 is directly fabricated on the surface of the cooled focal plane array 41 in the cooled detector chip group 4, forming an integral whole with the cooled detector chip group 4;

[0072] The bottom end of the micro-support 3 is fixed on the mounting substrate 5, and the top end is connected to the light field converging array 2, so that the light field converging array 2 is suspended above the cooled detector chip group 4, and the vertical gap between the light field converging array 2 and the polarization modulation array 1 is D.

[0073] The light field converging array 2 is located at the top, with the side without microstructure facing upwards and the side with microstructure facing downwards, facing the cooled detector chip 4 and the polarization modulation array 1 on its surface.

[0074] The functions and specific composition of each component are further explained below.

[0075] The cooled detector chipset 4 functions as a signal sensing device, that is, it uses the photoelectric conversion effect to convert the received optical signal into an electrical signal for subsequent signal processing. It includes a cooled focal plane array 41, a readout circuit 42, an indium pillar interconnect structure 43, and a detector chipset alignment mark 44. The cooled focal plane array 41 consists of M×N pixels and uses the photoelectric conversion effect to convert the incident light signal into an electrical signal. The indium pillar interconnect structure 43 transmits the electrical signal to the readout circuit 42, where it is amplified, read, and processed before being output for further imaging processing. The detector chipset alignment mark 44 is fabricated in the peripheral area of ​​the readout circuit 42 for alignment during integration.

[0076] The polarization modulation array 1, comprising M×N polarization units 11, functions to select polarization. Specifically, it utilizes polarization-sensitive micro / nano structures arranged in a specific manner to obtain the intensity components of incident light in different polarization directions, transmitting these components to the cooled detector chipset 4 for photoelectric sensing and subsequent polarization inversion. Please refer to [reference needed]. Figure 2 (a) The polarization modulation array 1 is directly fabricated on the surface of the cooled focal plane array 41, thereby achieving zero-vertical-gap coupling between the polarization modulation array 1 and the cooled detector chip group 4. This design is adopted because, during the transmission of the optical signal emitted from the polarization modulation array 1 to the cooled detector chip group 4, due to diffraction effects, the emitted optical signals corresponding to adjacent polarization units 11 overlap, thus causing crosstalk. The greater the vertical distance between the polarization modulation array 1 and the cooled detector chip group 4, the more pronounced the optical crosstalk effect caused by diffraction becomes, resulting in a lower polarization extinction ratio and poorer polarization imaging quality. This embodiment uses a direct integration method to eliminate the vertical gap between the polarization modulation array 1 and the cooled detector chip group 4, suppressing optical crosstalk to the greatest extent. The size and position of each polarization unit 11 are consistent with the pixels of its cooled focal plane array 41. Please refer to... Figure 2 (b) In this embodiment, the micro / nano structure used to constitute the polarization unit 11 is a subwavelength metal wire grid. Alternatively, a polarization-sensitive two-dimensional material can also be selected. Four polarization units 11 with different polarization orientations are arranged in a "2×2" topology to form a polarization superpixel 12, thereby synchronously obtaining the polarization components of the incident light in four different directions. The four selected polarization orientations are 0°, 45°, 90°, and 135°. The polarization information of the spatial position corresponding to a certain superpixel can be inverted according to the following formula:

[0077] ;

[0078] ;

[0079] Where DOLP is the degree of polarization, AOP is the polarization angle, and I0 and I... 45 I 90 I 135 These are the response signals corresponding to each orientation polarization unit. The aforementioned polarization superpixels 12 are arranged periodically, filling the entire focal plane, enabling the detection of polarization information throughout the entire scene.

[0080] The light field converging array 2 has its converging micro / nano structure facing the polarization modulation array 1. It utilizes light field converging units 23, matched with polarization units 11, to focus the light field at various spatial locations. The focal point is precisely located in the central region of the polarization unit 11, thereby suppressing optical and electrical crosstalk caused by light field divergence and avoiding extinction ratio degradation. Simultaneously, because the energy is concentrated at the pixel center rather than dispersed across different areas of the pixel, energy loss caused by edge transition structures between pixels is avoided. The light field converging array 2 can employ a microlens array.

[0081] Figure 3 (a) A design scheme for a light field converging array is presented, which consists of a silicon substrate 21, an antireflection coating 22, M×N light field converging units 23, and light field converging array alignment marks 24. The light field converging unit 23 is a refractive lens with a square bottom and a spherical top, and its focal length f is equal to the vertical gap D between the light field converging array 2 and the polarization modulation array 1. The antireflection coating 22 is obtained by multiple cross-growths of at least two dielectric layers with significantly different refractive indices, and is deposited on the lens side and bottom side respectively after the microlens unit is formed. Figure 3 As shown in (b), an alignment mark 24 for the light field converging array is disposed in the peripheral region where the microlens units are not arranged, and its position is consistent with the alignment mark 44 of the detector chip group. It is worth noting that, in addition to refractive lenses, the light field converging unit 23 can also be a metalens formed by arranging nanopillar structures in a specific manner in two-dimensional space, a diffraction lens formed by arranging diffraction layers of different thicknesses according to diffraction relationships, etc.

[0082] The micro-support 3, serving as the mechanical structure to support the light field converging array 2, is coated with adhesive 6 at its connection points with the mounting substrate 5 and the light field converging array 2. Please refer to [reference needed]. Figure 4 Adhesive thickness and the height of the micro-scaffold 3 The sum of these factors determines the vertical distance D between the light field converging array 2 and the polarization modulation array 1. Since the micro-support 3 is connected to the light field converging array 2 at more than one location, and considering non-ideal factors such as the thickness fluctuation of the adhesive 6 and the height difference at different positions of the micro-support 3, the light field converging array 2 may have a certain tilt. However, the vertical distance between each microlens unit and its corresponding polarization unit remains within the depth of focus.

[0083] Based on the above description, the transmission process of incident light between the various components of the infrared polarization detector can be obtained as follows: Figure 5 As shown:

[0084] Infrared light is incident from the back side of the light field converging array 2 and exits from one side of the microlens structure. Since the vertical distance between the microlens unit and its corresponding polarization unit is within the focal depth range of the microlens, the infrared light emitted from each microlens unit is focused at the center position of the corresponding polarization unit, thereby avoiding optical crosstalk caused by the divergence and overlap of the light field;

[0085] The polarization modulation array 1 uses the polarization orientation of different polarization units 11 to filter out the specific polarization state of the focused spot at each unit;

[0086] Since the polarization modulation array 1 is directly fabricated on the cooled focal plane array 41, the outgoing light after polarization screening by each polarization unit directly enters the cooled focal plane array 41, generating photogenerated carriers, which are eventually extracted by the readout circuit 42.

[0087] From the above description, it is easy to see that the polarization detector proposed in this invention has at least the following technological innovations and advancements:

[0088] (1) The working characteristics of different micro-nano optical components and the matching requirements of their corresponding coupling interfaces are cleverly utilized. The polarization modulation array only has the ability to filter specific polarization states but not the ability to focus the light field. Its extinction ratio is easily reduced due to diffraction interference. Therefore, it is very sensitive to the vertical distance between itself and the detector chip group. Integrating it directly on the surface of the detector chip group is beneficial to suppressing optical crosstalk. The light field converging array plays a focusing role and needs to maintain a vertical distance from the detector chip group equal to the focal length so that the focused light spot falls exactly on the focal plane, thereby improving energy utilization and suppressing electrical crosstalk. The clever combination of the two maximizes their respective functional characteristics. Correspondingly, the on-chip integration plus three-dimensional stacked integration architecture design also achieves a balance between performance and process feasibility (for a more detailed explanation, please refer to Example 2).

[0089] (2) Significant performance improvements have been achieved. First, energy efficiency has been greatly improved. Please refer to... Figure 6 (a) Taking a 15 μm × 15 μm polarization unit as an example, in order to avoid the polarization unit spanning two pixels due to alignment errors, a certain width of shielding area (e.g., Figure 6 (a) As shown in the gray area, if the width of the shading area is 2μm, then before the introduction of the light field converging unit, the incident light evenly illuminates the polarization unit, and the energy utilization rate is only... ; however, after introducing the light field converging unit, such as Figure 6 As shown in (b), with existing design and manufacturing capabilities, the spot size can be controlled to within 10 μm in diameter, concentrating over 90% of the incident light energy, thus improving energy utilization by approximately 70% compared to the original. Secondly, the extinction ratio is effectively improved. According to the extinction ratio calculation formula:

[0090] ;

[0091] Among them, T TM and T TE These are the transmittances of TM and TE waves, respectively. Based on current design and processing capabilities, and assuming a TM transmittance of over 90% and a TE transmittance of around 1%, the theoretical extinction ratio of the wire grating is 90. Before the introduction of the light field converging unit, for... Figure 6 In the case of uniform incident light shown in (a), according to literature reports, approximately 4% of photogenerated carriers will be transported across pixels. This, combined with the 1% TE transmittance, results in a measured TE transmittance of 5%, causing the actual extinction ratio to drop to around 18. It is evident that even a small amount of crosstalk superimposed on extremely weak TE signals can cause a severe attenuation of the extinction ratio. However, after introducing a light field converging unit, as... Figure 6 As shown in (b), since the photogenerated carriers are mainly concentrated in the center of the pixel, the number of photogenerated carriers transported across the pixel will be reduced by at least half to 2%. After being superimposed with the 1% TE transmittance, the measured TE transmittance is 3%, and the actual extinction ratio is restored to about 30.

[0092] Example 2

[0093] This embodiment is used to illustrate the fabrication process of the infrared polarization detector 1 described in Embodiment 1.

[0094] First, based on the cooled detector chipset 4 fabricated using mature technology, the polarization modulation array 1 is integrated on-chip. For detailed process flow, please refer to [link / reference needed]. Figure 7 ,include:

[0095] (A1) A metal layer is grown on the surface of the cooled focal plane array 41. The growth process can be magnetron sputtering, ion beam sputtering or electron beam evaporation.

[0096] (A2) Spin-coating photoresist onto the metal surface;

[0097] (A3) The photoresist is patterned using photolithography to obtain a grid pattern. The photolithography process can be laser direct writing, electron beam exposure or step-out exposure.

[0098] (A4) The metal layer is etched up to the surface of the cooled focal plane array 41 using photoresist as a mask;

[0099] (A5) Remove the residual photoresist to complete the fabrication of polarization modulation array 1.

[0100] Figure 8A schematic diagram of each of the above process steps is provided. It should be noted that during the implementation of the above processes, process conditions (such as baking temperature, etching power, etc.) should be reasonably set according to the optomechanical, electromechanical, and thermal characteristics of the cooled detector chipset 4 to avoid device damage or even failure caused by process incompatibility. The advantage of the above method is that it achieves gapless coupling between the polarization modulation array and the detector chip, allowing the modulated polarized light to be directly sensed by the device before the optical field diverges and causes crosstalk, thereby suppressing optical crosstalk.

[0101] The light field focusing array 2 was fabricated on a discrete substrate. For detailed fabrication process, please refer to [reference needed]. Figure 9 ,include:

[0102] (B1) Spin-coating nanoimprint adhesive 9 onto one side of a discrete substrate;

[0103] (B2) The nanoimprinting master plate 10 is used to pattern the nanoimprinting adhesive. The surface of the master plate is prepared with a pattern complementary to the light field focusing array 2 to be processed. The master plate is pressed onto the nanoimprinting adhesive layer and then desorbed to obtain the expected nanoimprinting adhesive pattern.

[0104] (B3) Remove the residual substrate of the patterned nanoimprint adhesive to expose the substrate;

[0105] (B4) Using nanoimprint etchant as a mask, etch a discrete substrate until the nanoimprint etchant pattern is completely transferred onto the substrate. The etching process can employ techniques such as inductively coupled plasma etching, reactive ion etching, and ion milling etching.

[0106] (B5) Remove residual nanoimprint adhesive;

[0107] (B6) Antireflection films are deposited on both the side and the back of the discrete substrate with microstructures to enhance the overall transmission effect;

[0108] (B7) Using a stripping technique, an alignment mark is prepared on the side where the microstructure is located, at a position corresponding to the alignment mark of the readout circuit.

[0109] Figure 10 A schematic diagram of each of the above processes is provided.

[0110] It is important to emphasize that optical field converging arrays have more complex three-dimensional patterns than polarization modulation arrays. For example, the wire grids in a polarization modulation array can be considered as regular structures in a plane, while the microlenses in an optical field converging array are three-dimensional spherical structures. Fabricating optical field converging arrays on discrete substrates has at least two advantages:

[0111] First, the manufacturing process is significantly simplified. Processing on discrete substrates eliminates concerns about device compatibility. For complex optical field focusing arrays, there is a greater range of process options, allowing for the use of high-fidelity, high-precision mechanical pattern transfer processes requiring high pressure and high temperatures, such as nanoimprinting, with fewer restrictions on parameter settings.

[0112] Secondly, the performance of the fabricated microstructures and the overall integrated device is more guaranteed. In the current integration process of micro / nano structure arrays and detector chips, monolithic integration is mainly for non-focusing structures that are sensitive to the vertical distance between the micro / nano array and the focal plane. However, in this invention, the light field converging array needs to maintain a certain vertical distance from the detector chip group. If a secondary monolithic integration is performed based on the detector chip group with the existing wire grid structure, the presence of the wire grid will cause the thickness fluctuation of the light field converging array to seriously affect the focusing performance. In addition, the vertical distance between the light field converging array and the detector chip group is mostly on the order of tens of micrometers. In monolithic integration technology, film deposition is required as the structural layer of the light field converging array, and the growth of a thick film of tens of micrometers is extremely difficult.

[0113] Another common integration technology adopts a hybrid integration approach. Although this approach is also based on the fabrication of micro-nano structure arrays on discrete substrates, this technology uses adhesives to bond the micro-nano structure arrays to the detector chipset, making the two directly contacted. During the cooling process of the detector chipset, thermal stress can easily cause damage or even failure of the components. In addition, most of the adhesives currently used have low infrared transmittance, which can easily cause energy loss.

[0114] Clearly, the use of discrete substrates for micro-nano fabrication, combined with the three-dimensional stacking integration technology mentioned later, ensures the processing effect and focusing performance of the light field converging array, while also ensuring the performance of the entire polarization detector assembly after its integration with the detector chipset.

[0115] After completing the on-chip fabrication and discrete fabrication of the light field focusing array, a three-dimensional stacking integration technique is used to couple the two. For the specific process flow, please refer to [link / reference needed]. Figure 11 ,include:

[0116] (C1) At the corresponding positions on the mounting substrate 5, a first layer of adhesive 61 is applied to fix the micro-support 3 and the cooled detector chip 4 with the polarization modulation array 1 fabricated on its surface onto the mounting substrate 5. The micro-support 3 is an integrated frame structure, with both ends of the two supports fixed to the left and right end faces, used to support the peripheral non-patterned area of ​​the light field converging array, thus suspending the light field converging array. The height of the micro-support 3 should meet the following requirements:

[0117]

[0118] In the formula, H 微支架H 胶 H 探测器组件 These represent the height of the micro-support, the thickness of the cured adhesive 6, and the total height of the detector chip 4 after the polarization modulation array 1 is integrated on the surface, respectively. D represents the distance between the light field converging array 2 and the polarization modulation array 1, f is the focal length of the light field converging array 2, and DOF represents the depth of focus. This formula means that the height of the micro-support should ensure the vertical distance between the light field converging array 2 and the polarization modulation array 1.

[0119] (C2) Apply a second layer of adhesive 62 at the position where the micro-support 3 contacts the light field converging array 2, and before the second layer of adhesive 62 is cured, place the mounting substrate 5 on the stage of the flip-chip interconnect device; with the lens side of the light field converging array 2 facing down, use the vacuum suction head of the flip-chip interconnect device to adsorb the light field converging array 2 and transfer it above the cooled detector chipset 4.

[0120] (C3) Use a bidirectional microscope to observe the cooled detector chip 4 and the light field converging array 2 in real time, and adjust their positions until the detector chip alignment mark 44 and the light field converging array alignment mark 24 are completely aligned.

[0121] (C4) Lower the suction head to bring the light field converging array 2 into contact with the upper surface of the micro-support 3, apply a certain pressure, maintain it for a certain time until the second layer of adhesive 62 is cured, remove the suction head, and the infrared polarization detector is now ready.

[0122] Figure 12 A schematic diagram of each of the above processes is provided.

[0123] The above-described three-dimensional stacking integration process has the following advantages:

[0124] (1) Higher yield. Based on the characteristic that the optical field converging array has a focal length and therefore needs to maintain a specific distance from the detector's focal plane, an additional support structure is introduced. This couples the focusing and polarization selection functions while the optical field converging array is suspended, eliminating the need for on-chip micro / nano fabrication on the detector surface and avoiding process risks. Furthermore, the optical field converging array does not contact the detector chipset, avoiding the risk of thermal stress mismatch. These benefits effectively control costs and improve yield.

[0125] (2) Higher alignment accuracy. The bidirectional microscope built into the flip-chip interconnect device enables visual alignment between the light field converging array and the detector chipset. In contrast, on-chip integration and other processes require the calculation of the x and y axial distances between a specific position of the cooled focal plane array and the alignment mark of the readout circuit, which is prone to errors due to factors such as step height. Therefore, the alignment technology of three-dimensional stacked integration is more intuitive and has higher accuracy.

[0126] (3) Superior performance. The vertical distance between the light field converging array and the detector chip is adjusted by using a micro-support and double-layer adhesive, which is highly flexible and can ensure that the vertical distance is within the depth of focus range. This ensures sufficient crosstalk suppression and energy utilization, improves the extinction ratio and detector sensitivity, and lays a solid hardware foundation for high-quality polarization imaging.

[0127] The above description of the embodiments of the present invention with reference to the figures is intended to explain the overall inventive concept of the present invention, and should not be construed as a limitation of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low cross-talk cryogenic infrared polarimetric detector, characterized in that, The refrigeration type infrared polarization detector comprises a loading substrate (5), a refrigeration type detector chip set (4), a polarization modulation array (1), a micro support (3) and a light field convergence array (2); The loading substrate (5) is located at the lowermost layer as a carrier; The refrigeration type detector chip set (4) is fixed on the loading substrate (5) and used for optical signal sensing and photoelectric conversion; The polarization modulation array (1) is directly prepared on the surface of a refrigeration type infrared focal plane array (41) of the infrared detector chip set (4) and forms an integral whole with the refrigeration type detector chip set (4) and is used for screening specific polarization states of infrared incident light; The bottom end of the micro support (3) is fixed on the loading substrate (5), and the top end is connected with the light field convergence array (2), so that the light field convergence array (2) is suspended above the refrigeration type detector chip set (4) and the polarization modulation array (1); the vertical gap between the light field convergence array (2) and the polarization modulation array (1) is D; The light field convergence array (2) is located at the uppermost end, and the side without microstructure faces upward, and the side with microstructure faces downward.

2. The low cross-talk cryogenic infrared polarization detector of claim 1, wherein, The infrared detector chip set (4) further comprises: A readout circuit (42) provided with an alignment mark in a peripheral non-functional area; The pixel size of the refrigeration type infrared focal plane array (41) is MxN; An electrical interconnection structure between the refrigeration type infrared focal plane detector and the readout circuit (42); The polarization modulation array (1) comprises MxN polarization units (11); The light field convergence array (2) comprises MxN focusing units (21).

3. The low cross-talk cryogenic infrared polarization detector of claim 2, wherein, The focusing unit (21) is used for converging incident light corresponding to the polarization unit (11) into a light spot not exceeding the size of the unit; the peripheral area of the light field convergence array (2) where no focusing unit (21) is arranged is provided with an alignment mark corresponding to the position of the readout circuit (42) and consistent in size and shape.

4. The low cross-talk cryogenic infrared polarization detector of claim 2, wherein, The pixel of the refrigeration type infrared focal plane array (41), the polarization unit (11) and the focusing unit (21) of the light field convergence array (2) are consistent in size, same in center distance and one-to-one corresponding in position.

5. The low cross-talk refrigeration type infrared polarization detector according to claim 1, wherein: A shielding area is arranged at the edge of the polarization unit (11) and used for transition between units; The middle part of the polarization unit (11) is arranged as a polarization screening area and is composed of a subwavelength scale rectangular or involute-shaped grating or a two-dimensional material with anisotropic transmission characteristics, has a specific polarization orientation and is used for transmitting specific polarized light; Four polarization units with different polarization orientations form a polarization superpixel in a "2x2" topological structure, the polarization superpixel (12) is periodically arranged and covers the entire focal plane.

6. The low cross-talk refrigeration type infrared polarization detector according to claim 2, wherein: The focal length of the focusing unit is f, the focal depth is DOF, a spherical refractive lens, a diffractive lens with light-transmitting and non-light-transmitting concentric rings alternating or a two-dimensional planar superlens composed of multiple superatoms is adopted.

7. The low cross-talk cryogenic infrared polarization detector of claim 6, wherein: The superatoms constituting the superlens are nanocolumns with a four-fold symmetric structure, the phase control range is not less than 2π, and the characteristic size is less than the minimum wavelength of the incident infrared light, and the arrangement mode is as follows: The heights of all superatoms are kept consistent, for a focused spot with a specific focal length, according to the corresponding phase gradient distribution, the mapping relationship between the plane size of the superatom and the phase gradient introduced by the superatom is used to set the superatom nanocolumns with the corresponding plane size at different spatial positions.

8. A method of producing a low cross-talk cryogenic infrared polarimetric detector according to any one of claims 1-7, characterized in that, The method comprises the following steps: (1) The light field converging array is prepared on a discrete substrate by using micro-nano processing technology; (2) The polarization modulation array is prepared on the surface of the cryogenic infrared focal plane array by using on-chip integration technology; (3) The infrared detector chip group provided with the polarization modulation array is fixed on the loading substrate; (4) A first layer of adhesive is coated on the corresponding position on the loading substrate or the readout circuit, and then the micro support is fixed thereon; (5) A second layer of adhesive is coated at the contact position of the micro support and the light field converging array, and is used for fixing the light field converging array; in particular, the sum of the thickness of the first layer of adhesive, the height of the micro support and the thickness of the second layer of adhesive should satisfy that after the fixing of the light field converging array is completed, the vertical distance D between the light field converging array and the polarization modulation array is within the range of f - 0.5·DOF to f + 0.5·DOF; (6) The loading substrate provided with the infrared detector chip group and the micro support is placed on the stage of a flip-chip device, the surface where the focusing units of the light field converging array are located faces downward, the focusing units are adsorbed by the suction head of the flip-chip device and are suspended above the infrared detector chip group; (7) The alignment of the light field converging array and the infrared detector chip group is observed synchronously by using the bidirectional microscope of the device, the positions of the two are adjusted until the alignment marks of the two are completely overlapped; (8) The suction head of the device is lowered, the light field converging array is brought into contact with the micro support, the adsorption state of the light field converging array is maintained, and a certain pressure is applied to the light field converging array until the adhesive is cured, and then the suction head is removed.

9. The preparation method according to claim 8, characterized in that, The processing steps of the light field converging array are as follows: (1) According to the optical properties of the substrate material and the focusing unit material, a matching antireflection film is plated on the discrete substrate, and the plating process can adopt thermal evaporation, magnetron sputtering or ion milling sputtering; (2) A medium layer is grown on the surface of the plated antireflection film as a structure layer of the light field converging array, and the growth process can adopt atomic layer deposition, chemical vapor deposition, electron beam evaporation, magnetron sputtering or ion milling sputtering; (3) After the medium layer is grown, photoresist is spin-coated on the surface of the medium layer, and a mask pattern of the focusing unit is obtained by using a patterning process, and the patterning process can be contact exposure, step exposure, electron beam exposure, laser direct writing exposure and other optical transfer technologies, or nanoimprinting, a mechanical transfer technology; if nanoimprinting is adopted, bottom film removal treatment is further required after the patterning is completed. (4) According to the structural characteristics of different types of focusing units and the used patterning process, the photoresist mask pattern is pretreated before etching; (5) The final forming of the focusing unit is realized by using etching process, and the photoresist is removed, and the used etching process can be inductively coupled plasma etching, ion beam etching, and reactive ion etching, and the method for removing the photoresist is organic solvent soaking or plasma reaction.

10. The preparation method according to claim 8, characterized in that, The on-chip integration of the polarization modulation array on the surface of the refrigeration type infrared focal plane array is as follows: (1) Depositing a metal film on the surface of the refrigeration type infrared focal plane array, and the deposition process can adopt electron beam thermal evaporation, magnetron sputtering or ion milling sputtering; (2) Spinning photoresist on the surface of the deposited metal film, and using patterning process to obtain the mask pattern of the polarization modulation array, and the used patterning process can be optical transfer technology such as electron beam exposure and laser direct writing exposure, or mechanical transfer technology such as nano-imprinting; if nano-imprinting is used, bottom film removal treatment is also needed after patterning is completed; (3) The final forming of the polarization modulation array is realized by using etching process, and the photoresist is removed, and the used etching process can be inductively coupled plasma etching, ion beam etching, and reactive ion etching, and the method for removing the photoresist is organic solvent soaking or plasma reaction.

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