A long-wavelength filter support assembly for cryogenic packaging and its implementation method

Abstract

This invention discloses a long-wavelength filter support assembly and its implementation method for cryogenic packaging. The long-wavelength filter support assembly for cryogenic packaging of this invention consists of a filter, a filter holder, and a light-blocking ring with anti-stray light. The filter has a reserved uncoated area, and the filter holder is made of molybdenum, which is compatible with germanium at low temperatures. A specific structure is set in the filter holder, and then the filter substrate is bonded to the filter holder to prevent adhesive contamination of the film and reduce stress on the film. In addition, a light-blocking ring is set on the lower surface of the filter facing the detector, so that the filter installation forms a "drawer" structure to prevent stray light from the filter edges and the uncoated areas on the top and bottom surfaces from affecting the detector. This invention is applicable to cryogenic packaging of long-wavelength filters integrated with mercury cadmium telluride, quantum wells, and type-2 superlattices, and is also applicable to other cryogenic cold platform integrated long-wavelength filters.

Description

Technical Field

[0001] This invention relates to low-temperature packaging technology for infrared detectors, specifically a method for preparing and screening long-wavelength filter support components for low-temperature packaging. It is applicable to low-temperature packaging of mercury cadmium telluride, quantum wells, and type-2 superlattice integrated long-wavelength filters, and is also applicable to other low-temperature cold platform integrated long-wavelength filters. Background Technology

[0002] In the field of infrared remote sensing, especially in area array or linear array detection, a low-temperature filter is generally required in front of the detector. The filter is an essential component in an optical system, allowing only specific wavelengths of light to pass through. It is a crucial part of infrared detector assemblies, its surface coated with a filter film. The thickness of this film is related to technical specifications such as the filtering band, bandwidth, and waveform coefficient. In the long-wavelength band, the filter film is thicker; for example, a 11.5μm–12.5μm bandpass filter can have a film thickness exceeding 40μm. During detector assembly packaging, the filter is typically mounted on a specific support before being installed in front of the detector. With the engineering applications of long-wavelength or very long-wavelength infrared detectors, operating temperatures have decreased from 80K to around 40K. Correspondingly, the filter temperature has also decreased to around 40K. Therefore, the filter support, the impact of low-temperature stress on spectral performance, and the robustness of the filter film become particularly important.

[0003] Chinese Patent 201410121102.9, "An Elastic Fixing Mounting Device for Rectangular Filters," installs the filter between a filter holder and a cover, securing the filter to the holder via screws and contacts on the cover. Its advantages include the elimination of adhesives and the absence of contamination of the filter film layer by other substances. However, the operating temperature range of the filter is unknown, and its ability to operate at low temperatures (especially 40K-50K) is also unknown. Furthermore, it is unknown whether the impact force exerted on the filter film layer by the contacts on the cover during environmental testing of the cooling assembly will cause damage. Chinese Patent 201310469781.4, "A Filter Mounting Bracket with a Thermal Stress Buffer Structure," uses a 4J29 or 4J42 iron-nickel alloy material for its filter holder. It reduces stress caused by the difference in expansion coefficients between the filter holder and the filter by incorporating inner and outer buffer grooves. Its advantages include a simple structure, ease of implementation, and effective stress reduction when the filter size is relatively small. As filter sizes increase, the stress caused by the coefficient of thermal expansion between the filter and its supporting components becomes insurmountable. The support structure helps buffer the installation and temperature stresses associated with the filter holder and its external structure. When temperatures reach 40K-50K, the coefficients of thermal expansion of the filter holder materials 4J29 and 4J42 differ significantly from those of the germanium substrate for long-wavelength filters. The average coefficient of thermal expansion for 4J29 is 6.256 ppm / K (300K-45K), while that for the Germanium filter substrate is 3.6 ppm / K (300K-45K). The filter holder and filter are typically bonded together with epoxy adhesive. The filter film near the bonding area inevitably comes into contact with the epoxy adhesive, forming the bonding surface. Since the filter body and the holder usually differ in their coefficients of thermal expansion and other properties, the filter film layer inevitably experiences thermal stress after cooling. Experiments show that the stress caused by this thermal mismatch leads to changes in the spectral characteristics of the filter, resulting in spectral distortion, and in severe cases, causing the detector assembly to fail and become unusable. The magnitude of thermal stress is usually related to temperature difference; therefore, the probability of filter failure caused by cryogenic conditions and temperature cycling is greatly increased. With the increasing use of mercury cadmium telluride, quantum well, and type-2 superlattice integrated long-wavelength filters operating at cryogenic temperatures, especially around 40K-50K, it is necessary to explore a new method to solve this problem. Summary of the Invention

[0004] The purpose of this invention is to provide a long-wavelength filter support assembly and its implementation method for cryogenic packaging. It is applicable to cryogenic packaging of mercury cadmium telluride, quantum well, and type-II superlattice integrated long-wavelength filters, and also applicable to other cryogenic cold platform integrated long-wavelength filters. This invention solves the problems of thermal matching between the long-wavelength filter and its support, the impact on spectral performance, the resilience of the film after temperature shock, and the environmental adaptability of the filter support assembly when the long-wavelength filter, mercury cadmium telluride, quantum well, and type-II superlattice integrated long-wavelength filters operate at deep cryogenic temperatures, especially 40K-50K.

[0005] The long-wavelength filter support assembly for low-temperature packaging of the present invention is shown in the appendix. Figure 1 As shown, it includes a filter 1, a filter holder 2, and a light-blocking ring 3 with anti-stray light. In the coating process, the filter 1 has a non-coated area 101 reserved around the germanium substrate by means of a metal mask or photolithography. The filter holder 2 is provided with an upper field-view aperture 201, a bonding boss 202, a glue reservoir 203, and a lower mounting step 204. The non-coated area (101) on the filter (1) is bonded to the bonding boss (202) of the filter holder (2) by low-temperature adhesive. The light-blocking ring (3) with anti-stray light is bonded to the lower mounting step (204) on the filter holder (2) by low-temperature adhesive. The filter is installed to form a "drawer" structure to prevent stray light from the edge of the filter (1) and the uncoated areas on the top and bottom surfaces from affecting the detector.

[0006] The parameters of the long-wavelength filter support assembly filter 1 for cryogenic packaging are shown in the appendix. Figure 2 The design principles are as follows:

[0007] 1) The method for confirming the parameters of the upper coating area 102 and the lower coating area 103 is as follows:

[0008] The length L102, width W102, and thickness H102 of the coating area, as well as the thickness H1 of filter 1, are determined based on the input of the overall optical system and used as input for subsequent design.

[0009] 2) The method for confirming the parameters of the non-coated area 101 is as follows:

[0010] 1.5mm≥δ≥0.8mm (1);

[0011] 3) The method for confirming the length L1 parameter of filter 1 is as follows:

[0012] L1=L102+2δ (2);

[0013] 4) The method for confirming the width W1 parameter of filter 1 is as follows:

[0014] W1=W102+2δ (3);

[0015] The filter holder 2 is made of high-temperature molybdenum, whose average coefficient of thermal expansion is 3.73 ppm / k (300K~45K). Figure 3 The upper field-view aperture 201, filter bonding boss 202, glue storage tank 203, and lower mounting step 204 are processed as required, and local blackening treatment is applied.

[0016] The parameters of the filter holder 2 of the long-wavelength filter support assembly for cryogenic packaging are shown in the appendix. Figure 3 The design principles are as follows:

[0017] 1) The method for confirming the length L201 of the upper field aperture 201 is as follows:

[0018] L201=L102+(0.2~0.4)mm (4)

[0019] 2) The method for confirming the width W201 of the upper field-of-view aperture stop 201 is as follows:

[0020] W201=W102+(0.2~0.4)mm (5);

[0021] 3) The method for confirming the length L2 of the filter holder 2 is as follows:

[0022] L2 = L1 + 1mm (6), where the single-sided spacing is 0.5mm;

[0023] 4) The method for confirming the width W2 of filter holder 2 is as follows:

[0024] W2 = W1 + 1mm (7), where the single-sided spacing is 0.5mm;

[0025] 5) The method for confirming the depth H2 of filter holder 2 is as follows:

[0026] H2 = H1 + 0.2 mm (8);

[0027] 6) The method for confirming the length L202 and width W202 of the filter bonding boss 202 is as follows:

[0028] L202=W202=1.1mm~1.8mm (9);

[0029] The filter bonding boss 202 is located at half of the side it is on;

[0030] 7) The method for confirming the height H202 of the filter bonding boss 202 is as follows:

[0031] H102+0.02mm≥H202≥H102; (10)

[0032] 8) The method for confirming the diameter D parameter of the glue storage tank 203 is as follows:

[0033] 0.8mm ≥ D ≥ 0.3mm; (11)

[0034] The glue storage tank 203 is located in the center of the filter bonding boss 202;

[0035] 9) The method for confirming the depth H203 of the glue storage tank 203 is as follows:

[0036] 0.1mm ≥ H2O3 ≥ 0.05mm; (12)

[0037] The light-blocking ring 3, which includes anti-stray light, is made of molybdenum and has a blackened surface treatment. Figure 4 Process as required as shown.

[0038] The parameters of the long-wavelength filter support assembly for cryogenic packaging with a light-blocking ring 3 to prevent stray light are shown in the appendix. Figure 4 The design principles are as follows:

[0039] 1) The method for confirming the length L3 of the light-blocking ring 3 with anti-stray light is as follows:

[0040] L3 = L201 (14)

[0041] 2) The method for confirming the width W3 of the light-blocking ring 3 with anti-stray light is as follows:

[0042] W3 = W201 (15)

[0043] 3) The method for confirming the thickness H3 of the light-blocking ring 3 with anti-stray light is as follows:

[0044] H3 = 0.1mm~0.5mm (16)

[0045] The method for fabricating and screening long-wavelength filter support components for low-temperature packaging according to the present invention is as follows:

[0046] 1) Prepare the low-temperature adhesive required for bonding. Place the mixed adhesive in a 45℃ oven and bake for 30 minutes before use.

[0047] 2) Apply the adhesive prepared in step 1) to the adhesive reservoir 203 on the L2 side of the filter holder 2. The amount of adhesive applied should be enough to fill the adhesive reservoir 203.

[0048] 3) Place the filter holder 2 upside down on the dedicated equipment platform, and use a special tool to adsorb and place the filter 1 onto the filter bonding boss 202 of the filter holder 2. Let it cure for more than 72 hours.

[0049] 4) Prepare the low-temperature adhesive, then stir it evenly, and bake the mixed adhesive in a 60℃ oven for 3 hours;

[0050] 5) Gently apply the prepared low-temperature adhesive from step 4) to the connection between the side of filter 1 and the filter holder 2, i.e., the three-point bonding. Figure 5 The shaded area shown was cured at room temperature for 24 hours, then cured at 45°C for 24 hours.

[0051] 6) Apply the low-temperature adhesive prepared in step 1) to the edge of the step of the filter holder 2. Install the light-blocking ring 3 with anti-stray light on the designated position of the step 204 of the filter holder 2. After curing at room temperature for 24 hours, cure at 45°C for 24 hours.

[0052] The above demonstrates the fabrication of a low-temperature packaged long-wavelength filter support assembly.

[0053] The advantages of this invention are:

[0054] (1) The present invention has a simple structure, is easy to operate, and has low cost;

[0055] (2) This invention solves the problems of thermal matching between long-wavelength filters and their supports, the spectral performance, the film strength after temperature shock, and the environmental adaptability of filter support components when long-wavelength filters, such as mercury cadmium telluride, quantum traps, and type II superlattice integrated long-wavelength filters are used in deep low temperature operation, especially 40K-50K.

[0056] (3) It has good compatibility. It is suitable for cryogenic packaging of mercury cadmium telluride, quantum trap, and type II superlattice integrated long-wavelength filters, as well as for other cryogenic cold platform integrated long-wavelength filters.

[0057] (4) The present invention has a good anti-stray light effect. The filter locking plate can effectively prevent stray light formed by reflection between the detector and the uncoated area of ​​the filter. Attached Figure Description

[0058] Figure 1 General layout of a long-wavelength filter support assembly for cryogenic packaging;

[0059] In the diagram: 1—Filter;

[0060] 2—Filter holder;

[0061] 3—A light-blocking ring with anti-stray light;

[0062] Figure 2 The image shows a filter diagram of a long-wavelength filter support assembly for low-temperature packaging, where (1) is a front view of the filter and (2) is a top view of the filter.

[0063] In the diagram: 1—Filter;

[0064] 101—Non-coated area;

[0065] 102—Upper coating area;

[0066] 103—Lower coating area;

[0067] Figure 3 The diagram shows a filter support for a long-wavelength filter support assembly used for low-temperature packaging, where (1) is a top view of the filter support, (2) is a front sectional view of the filter support, and (3) is a partial enlarged view of the filter bonding boss.

[0068] In the diagram: 2—Filter holder;

[0069] 201—Upper field aperture;

[0070] 202—Filter bonding boss;

[0071] 203—Glue storage tank;

[0072] 204 - Install steps and treads below;

[0073] Figure 4 The diagram shows a light-blocking ring with anti-stray light for a long-wavelength filter support assembly used in low-temperature packaging, wherein (1) is a front view of the anti-stray light-blocking ring and (2) is a top view of the anti-stray light-blocking ring.

[0074] Figure 5 A diagram showing the bonding of the filter and filter holder in a long-wavelength filter support assembly for cryogenic packaging. Detailed Implementation

[0075] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings:

[0076] An example is the Dewar component structure of a long-wavelength 640×512 infrared detector used in a hyperspectral project. The assembly structure is as follows: The detector filter support assembly consists of a filter 1, a filter holder 2, and a light-blocking ring 3 with anti-stray light. During the coating process, the filter 1 has a non-coated area 101 reserved around the germanium substrate using a metal mask or photolithography. The filter holder 2 is equipped with an upper field-of-view aperture 201, a bonding boss 202, a glue reservoir 203, and a lower mounting step 204. The non-coated area 101 on the filter 1 rests on the bonding boss 202 of the filter holder 2. Glue is injected into the glue reservoir 203 on the filter holder 2. After baking and curing, the light-blocking ring 3 with anti-stray light is installed on the lower mounting step 204 of the filter holder 2 and fixed with glue. This creates a "drawer" structure for the filter installation, preventing stray light from the edges and the uncoated areas on the top and bottom surfaces of the filter 1 from affecting the detector.

[0077] 1. The method for preparing each component in this invention:

[0078] (a) Filter 1 is made of Ge. It is cold-processed into a rectangular substrate L1×W1 (18mm×22mm) as required. Then, non-coated areas 101 are reserved around the Germanium substrate using a metal mask or photolithography. Anti-reflection is performed on the upper and lower surfaces of the filter, which are respectively the upper coating area 102 and the lower coating area 103. The size of the coating area is L102×W102 (15mm×19mm), and its film thickness H102 is 0.04mm. The thickness H1 of the filter 1 is 1.2mm, and the distance δ from the edge of the coating area to the edge of the filter 1 is 1.5mm.

[0079] (b) The filter holder 2 is made of molybdenum, with an average coefficient of thermal expansion of 3.73 ppm / k (300K~45K). The upper field-view aperture 201, filter bonding boss 202, adhesive reservoir 203, and lower mounting step 204 are machined as required. The opening of the upper field-view aperture 201 is L201×W201 (15.4mm×19.4mm). The interface of the filter 1 in the filter holder 2 is L2×W2×H2 (19mm×23mm×1.22mm). The L202 and W202 of the filter bonding boss 202 are both 1.8mm×1.8mm, and the height H202 of the filter bonding boss 202 is 0.04mm. The adhesive storage tank 203 has a diameter (D) of φ0.8mm. The adhesive storage tank 203 is located in the center of the filter bonding boss 202, and the depth (H203) of the adhesive storage tank 203 is 0.05mm.

[0080] (c) The light-blocking ring 3 with anti-stray light is made of high-temperature molybdenum with a blackened surface. The parameters of the light-blocking ring 3 with anti-stray light are L3×W3, which are 15.4mm×19.4mm, and its thickness H3 is 0.25mm.

[0081] 2. Assembly and connection steps:

[0082] 1) Prepare the low-temperature adhesive LTG-3 required for bonding. Place the mixed adhesive in a 45℃ oven and bake for 30 minutes before use.

[0083] 2) Apply the adhesive prepared in step 1) to the adhesive reservoir 203 on the L2 side of the filter holder 2. The amount of adhesive applied should be enough to fill the adhesive reservoir 203.

[0084] 3) Place the filter holder 2 upside down on the platform of the special equipment, use a special tool to adsorb the filter 1 and place it on the filter bonding boss 202 of the filter holder 2, and cure for more than 72 hours;

[0085] 4) Prepare the low-temperature adhesive LTG-3, then stir it evenly and bake it in a 60℃ oven for 3 hours.

[0086] 5) Gently apply the prepared low-temperature adhesive LTG-3 from step 4) to the side of filter 1 and the connection point between filter 1 and filter holder 2, as shown. Figure 5 The shaded area shown was cured at room temperature for 24 hours, then cured at 45°C for 24 hours.

[0087] 6) Apply the low-temperature adhesive prepared in step 1) to the edge of the step of the filter holder 2. Install the light-blocking ring 3 with anti-stray light onto the designated position of the step 204 of the filter holder 2. After curing at room temperature for 24 hours, cure at 45°C for 24 hours.

[0088] The above describes the low-temperature encapsulation of long-wavelength filter support components and their fabrication.

Claims

1. A long-wavelength filter support assembly for low-temperature packaging, comprising a filter (1), a filter holder (2), and a light-blocking ring (3) for preventing stray light, characterized in that: The filter holder (2) is made of molybdenum; the structure of the long-wavelength filter support assembly is as follows: during the coating process, the filter (1) has a non-coated area (101) reserved around the germanium substrate by means of a metal mask or photolithography. The filter holder (2) is provided with an upper field-view aperture (201), a bonding boss (202), a glue storage tank (203), and a lower mounting step (204). The non-coated area (101) on the filter (1) is bonded to the bonding boss (202) of the filter holder (2) by low-temperature glue. The light-blocking ring (3) for preventing stray light is bonded to the lower mounting step (204) on the filter holder (2) by low-temperature glue. The filter is installed to form a drawer structure to prevent stray light from the edge of the filter (1) and the uncoated areas on the top and bottom surfaces from affecting the detector.

2. The long-wavelength filter support assembly for low-temperature packaging according to claim 1, characterized in that: The filter (1) is made by cold processing a germanium substrate into a substrate of the required shape, which is rectangular or circular. A non-coated area (101) is reserved around the germanium substrate by means of a metal mask or photolithography. The width δ parameter of the non-coated area (101) is determined by the following formula: 1.5mm ≥ δ ≥ 0.8mm.

3. The long-wavelength filter support assembly for low-temperature packaging according to claim 1, characterized in that: Process the upper field-view aperture (201), filter bonding boss (202), glue storage tank (203), and lower installation step (204) as required; and perform local blackening treatment on the filter bracket (2). The length L202 and width W202 of the filter bonding boss (202) are determined by the following formula: L202=W202=1.1mm~1.8mm, Among them, the filter bonding boss (202) is located at half of the side; The height H202 of the filter bonding boss (202) is determined by the following formula: H102 + 0.02mm ≥ H202 ≥ H102, Where H1O2 is the thickness of the coating on filter (1); The diameter D of the glue storage tank (203) is determined by the following formula: 0.8mm ≥ D ≥ 0.3mm; Among them, the glue storage tank (203) is located in the center of the filter bonding boss (202); The depth H203 parameter of the glue storage tank (203) is determined by the following formula: 0.1mm≥H2O3≥0.05mm.

4. The long-wavelength filter support assembly for cryogenic packaging as described in claim 1, characterized in that: The light-blocking ring with anti-stray light (3) is made of molybdenum and has a blackened surface treatment; The length L3 of the light-blocking ring (3) with anti-stray light is determined by the following formula: L3 = L201, Where L201 is the length of the upper field aperture (201); The width W3 of the light-blocking ring (3) with anti-stray light is determined by the following formula: W3 = W201, Where W201 is the width of the upper field-of-view aperture (201); The thickness H3 of the light-blocking ring (3) with anti-stray light is determined by the following formula: H3 = 0.1mm~0.5mm.

5. A method for implementing a long-wavelength filter support assembly for low-temperature packaging as described in claim 1, characterized in that... The steps are as follows: 1) Prepare the low-temperature adhesive required for bonding and bake it in a 45℃ oven for 30 minutes; 2) Apply the prepared adhesive to the adhesive reservoir 203 on the L2 side of the filter holder (2), and apply enough adhesive to fill the entire adhesive reservoir (203); 3) Place the filter holder (2) upside down on the platform of the centering instrument, use a special tool to adsorb the filter (1) and place it on the filter bonding boss (202) of the filter holder (2), and cure for more than 72 hours; 4) Prepare the low-temperature adhesive required for bonding and bake it in a 60℃ oven for 3 hours; 5) Use the adhesive prepared in step 4 to bond: the bonding position is the side of the filter (1) above the filter bonding boss (202) and the connection point of the filter support (2), that is, three bonding points. After curing at room temperature for 24 hours, cure at 45°C for 24 hours. 6) Prepare the low-temperature adhesive required for bonding and bake it in a 45℃ oven for 30 minutes; 7) Install the light-blocking ring (3) with anti-stray light in the appropriate position of the step (204), cure at room temperature for 24 hours, and then cure at 45°C for 24 hours.

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