Infrared absorption structure, preparation method thereof and uncooled infrared detector

Abstract

The invention discloses an infrared absorption structure, a preparation method thereof and an uncooled infrared detector. The infrared absorption structure comprises a substrate and a porous light trapping layer, the porous light trapping layer comprises nanostructures and is provided with a hole structure, and the hole structure is defined by a plurality of adjacent nanostructures; the nanostructure is made of pure metal or alloy, and a non-vertical included angle is formed between the extending direction of the growth axis of the nanostructure and the normal direction of the substrate. The novel infrared porous light trapping layer of the porous metal is prepared in a high-vacuum-degree environment by adopting an oblique angle incidence deposition method and utilizing a shadow effect, the infrared porous light trapping layer has excellent light absorption performance, the processing technology is simple, the cost is low, and compared with a traditional technical scheme of preparing a porous metal layer in a low-vacuum N2 environment, the porous film is good in uniformity and good in light absorption performance. And meanwhile, the heat absorption efficiency of the infrared detector can still be improved under the conditions that the film thickness is small and the heat mass is relatively small.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano manufacturing technology, and in particular to an infrared absorption structure, a preparation method thereof and a non-refrigerated infrared detector. Background Art

[0002] Infrared radiation is a type of electromagnetic wave that is invisible to the human eye. Its wavelength range is generally defined as 0.78μm to 1000μm. In the electromagnetic spectrum, the frequency of infrared radiation is between visible light and microwaves. In nature, objects with a temperature above absolute zero (-273.15℃) will radiate infrared energy due to their own molecular motion, so the infrared band contains rich information about objects. This is the basis of infrared detection technology and the reason why people work hard to research and develop infrared radiation detectors.

[0003] In infrared systems, infrared detectors are the key to detecting and identifying targets. Their main function is to convert incident infrared radiation into readable electrical signals. Infrared detection technology has a wide range of applications in medical imaging, environmental monitoring, remote sensing, spectroscopy, communications, fire monitoring, gas detection and other fields.

[0004] Infrared detectors are divided into photon detectors and thermal detectors according to the detection principle. Photon detectors generally need to be cooled before they can detect, while thermal detectors are uncooled infrared detectors, whose basic principle is to use the thermal effect of infrared radiation to achieve infrared detection.

[0005] The principle of thermal detectors is generally that when the incident infrared radiation is absorbed by the device and converted into heat energy, it causes changes in the physical properties of the material, such as resistance, volume or charged polarity, to achieve the detection of infrared radiation. Compared with photon detectors, thermal detectors have the advantages of wide response band, low cost, room temperature operation, good long-term stability, and no need for a cooling system during operation. These advantages make thermal detectors widely used in security, especially in the civilian field.

[0006] It can be seen that uncooled infrared detectors detect by measuring the temperature response of the device's sensitive unit to infrared radiation. In order to improve the infrared thermal detector's absorption effect on external infrared radiation, it is often necessary to coat certain absorption coatings on the surface of the infrared sensitive element.

[0007] At present, the mainstream absorption coating materials include organic black paint, colloidal graphite black, subwavelength resonant structure and porous metal. Traditional graphite coating will damage the absorption layer due to a large amount of heat absorption in a short time. Although organic black paint can achieve good absorption rate in a wide band range, the black paint coating is often applied by researchers manually, which has high requirements for the experience of the operator. It is difficult to achieve uniform coating and the raw materials are harmful to the operator. Subwavelength resonant structure can obtain extremely high absorption rate in a specific wavelength range, but the absorption band range of this structure is small, the processing technology is complex and the cost is high. Porous metal (also known as "metal black", such as black gold, black silver, black platinum and silicon nanostructure) is currently an ideal absorption coating material, mainly because of its porous structure, the incident light is reflected multiple times in the structure, achieving the effect of trapping light, reducing the transmission and reflection of light, and thus enhancing absorption. This coating not only has a high absorption rate for light in a wide spectral range, but also has good electrical properties.

[0008] Traditional porous metal coatings are often prepared by evaporation in a low vacuum N2 atmosphere, but excessive pressure will cause the generated porous metal coating to be unevenly distributed on the sample surface, affecting device performance. Therefore, it is necessary to develop a new porous metal structure absorption coating and its preparation method. Summary of the invention

[0009] In view of the deficiencies in the prior art, an object of the present invention is to provide an infrared absorption structure, a preparation method thereof and a non-cooling infrared detector.

[0010] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: In a first aspect, the present invention provides an infrared absorption structure, which includes a substrate and a porous light-trapping layer disposed on the surface of the substrate, wherein the porous light-trapping layer includes a nanostructure and has a hole structure, and the hole structure is formed by enclosing a plurality of adjacent nanostructures; The material of the nanostructure is pure metal or alloy, and the nanostructure has a growth axis, which points from the bottom end of the nanostructure in contact with the substrate to the top end away from the substrate, and the extension direction of the growth axis forms a non-vertical angle with the normal direction of the substrate.

[0011] In a second aspect, the present invention further provides a method for preparing an infrared absorption structure, which comprises: Pure metal or alloy is deposited on the surface of the substrate by electron beam evaporation to form a nanostructure. The direction of the line connecting the evaporation source and the substrate during the electron beam evaporation forms an angle with the normal direction of the substrate. The angle ranges from 10 to 90 degrees, so that a plurality of adjacent nanostructures are surrounded to form a hole structure. The nanostructure and the hole structure constitute a porous light trapping layer.

[0012] In a third aspect, the present invention further provides a non-cooled infrared detector, which includes a detection structure and the above-mentioned infrared absorption structure, wherein the detection structure is tightly combined with the infrared absorption structure to detect temperature changes of the infrared absorption structure.

[0013] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention at least include: The technical solution provided by the present invention adopts the method of oblique incident deposition and utilizes the shadow effect to prepare a new type of porous metal infrared porous light trapping layer under a high vacuum environment. It has excellent light absorption performance, simple processing technology and low cost. Compared with the traditional technical solution of preparing porous metal layers under a low vacuum N2 environment, the present invention is prepared under a higher vacuum environment, and the porous film has better uniformity. At the same time, when the film thickness is small and the thermal mass is small, the thermal absorption efficiency of the infrared detector can still be improved. It can be used to construct high-performance infrared detectors, which plays an important role in monitoring environmental safety, health care, industrial safety and other fields.

[0014] The above description is only an overview of the technical solution of the present invention. In order to enable those skilled in the art to more clearly understand the technical means of the present application and implement them according to the contents of the specification, the following is a description of the preferred embodiments of the present invention in conjunction with detailed drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a state schematic diagram of a preparation method provided by a typical implementation case of the present invention; Figure 2 It is a schematic diagram of the shadow effect principle in the preparation method provided by a typical implementation case of the present invention; Figure 3a This is an electron microscope photograph of the cross-sectional morphology of an oblique rod-shaped porous light-trapping layer provided in a typical embodiment of the present invention; Figure 3b This is an electron microscope photograph of the surface morphology of an oblique rod-shaped porous light-trapping layer provided in a typical embodiment of the present invention; Figure 4a This is an oblique-angle electron microscope photograph of the spiral porous light-trapping layer provided in another typical embodiment of the present invention; Figure 4b is an electron microscope photograph of the cross-sectional morphology of a spiral porous light-trapping layer provided in another typical embodiment of the present invention; Figure 4c is an electron microscope photograph of the surface morphology of a spiral porous light-trapping layer provided in another typical embodiment of the present invention; Figure 5 These are light absorption curve test diagrams of multiple different porous light-trapping layers provided by some typical implementation cases of the present invention. DETAILED DESCRIPTION

[0016] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0017] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0018] An embodiment of the present invention provides an infrared absorption structure, which includes a substrate and a porous light-trapping layer arranged on the surface of the substrate, the porous light-trapping layer includes a nanostructure and has a hole structure, and the hole structure is formed by enclosing a plurality of adjacent nanostructures; the material of the nanostructure is pure metal or alloy, and the nanostructure has a growth axis, and the growth axis points from the bottom end of the nanostructure in contact with the substrate to the direction away from the top end of the substrate, and the extension direction of the growth axis forms a non-vertical angle with the normal direction of the substrate.

[0019] The basic concept of the present invention is to use an oblique angle incident deposition method to prepare a new type of porous metal infrared absorption structure to achieve wide-band absorption of infrared radiation. Due to the shadow effect generated during the oblique angle incident deposition process, the prepared film presents a porous structure, and the incident light is reflected multiple times in this porous structure to achieve the effect of trapping light, thereby improving the light absorption capacity of the structure. At the same time, due to the use of a high vacuum and thin thickness growth method, the porous light trapping layer formed has significantly stronger uniformity than the traditional porous metal coating, thereby improving the consistency and quality of the device.

[0020] See also Figure 2 As shown in the figure, the nanostructure formed in oblique incidence deposition is caused by the unique shadow effect, surface migration and adsorption during the deposition process. Simply put, the deposition raw materials are bombarded by electron beams to form a gaseous particle flow, which reaches the substrate at a certain angle and is deposited on the substrate. In the initial stage of film growth, the gaseous particles will gather on the substrate to form a small island structure. At the same time, due to the shielding effect of the initially formed island structure, a shadow area will be formed in the direction of the gaseous particle flow, making it impossible for the particles deposited thereafter to reach this area, so they can only continue to gather on the island, thereby forming a nano-microstructure with a certain spacing.

[0021] The specific practice is usually: when performing deposition, the sample stage is tilted so that the angle between the normal direction of the sample stage and the normal direction of the evaporation source is set between 10-90 degrees to form the above-mentioned shadow effect.

[0022] Some existing technical solutions have proposed technical solutions using inclined silicon columns or oxide columns for light trapping and absorption. However, first of all, the material of its nanostructure is not the same as that of the present invention. The metal or alloy material used in the present invention has better corrosion resistance, heat resistance, and high hardness, which is beneficial to the long-term stability and durability of this micro-nano structure. Secondly, the alloy material has adjustable composition and diversity; and compared with semiconductor materials, alloy or metal materials have lower electrical conductivity, so the skin depth is smaller, and the transmittance of the formed nanocolumns is lower, which is conducive to repeated reflection of light in the structure, thereby achieving the purpose of light trapping and enhanced absorption. In particular, the k value of the NiCr alloy itself preferred by the present invention, that is, the extinction coefficient is relatively high in the infrared band, so it will show a light absorption ability that is significantly better than the traditional light trapping solution.

[0023] Specifically in some embodiments, the pure metal may include any one of Ti, W, Al, Ni, Fe, Au, Ag, and Cu, and the alloy may include any one of NiCr binary or multi-component alloys and NiCu binary or multi-component alloys, and is further preferably NiCr binary or multi-component alloys.

[0024] In some embodiments, the vertical thickness of the porous light trapping layer is 100nm-5μm; the non-vertical angle is 10-80°. It should be noted that in the technical solution of the present invention, the angle generally refers to the size of the acute angle formed by two directions, and the vertical deposition thickness is between 100nm~5μm, which is much smaller than the thickness of the traditional low vacuum deposited gold black film (5~10μm).

[0025] In some embodiments, along the extension direction of the growth axis, the shape of the nanostructure is any one of a straight column, a zigzag line or a spiral. Specifically, the structure is a porous metal structure prepared by oblique angle deposition and selectively cooperating with the rotation of the sample stage, and its surface is porous. Each nanostructure constituting the absorption structure can be a vertical cylinder (rotation to certain angles may form a vertical column), an inclined cylinder, a zigzag shape, a spiral, etc.

[0026] In some embodiments, the shape of the nanostructure is preferably a spiral, and the total number of spiral turns in the entire length of the nanostructure is 2-5 turns.

[0027] To obtain the above infrared absorption structure, see Figure 1 The embodiment of the present invention also provides a method for preparing an infrared absorption structure, which comprises the following steps: Pure metal or alloy is deposited on the surface of the substrate by electron beam evaporation to form a nanostructure. The direction of the line connecting the evaporation source and the substrate during the electron beam evaporation forms an angle with the normal direction of the substrate. The angle ranges from 10 to 90 degrees, so that a plurality of adjacent nanostructures are surrounded to form a hole structure. The nanostructure and the hole structure constitute a porous light trapping layer.

[0028] In some embodiments, the atmosphere pressure during the electron beam evaporation is 1×10 -4 ~5×10 -4 Pa.

[0029] In some embodiments, while the electron beam evaporation is being performed, the substrate is rotated along its normal direction as an axis.

[0030] In some embodiments, the deposition rate of the electron beam evaporation is 0.1Å~5Å / S (referring to the vertical growth and thickening speed), and the rotation rate of the substrate is greater than 0 and less than or equal to 5rpm.

[0031] The above preferred scheme forms a spirally deposited nanostructure through the rotation of the substrate. The spiral shape provides a more complex light-trapping structure, which can significantly improve the infrared absorption efficiency. In addition, during the rotation of the substrate, shadow effects are generated in different directions, avoiding the angle unevenness caused by a single direction (when the substrate area is large, different positions, such as the end of the substrate close to the evaporation source and the other end away from the evaporation source, will have obvious angle differences in the direction of the line connecting the evaporation source, and rotation avoids different positions from being at a fixed angle all the time), further improving the uniformity of large-area preparation.

[0032] In addition, the rotation of the substrate can also bring more technical effects, such as: 1. By setting different substrate rotation programs, a variety of different microstructures can be formed. 2. The structure formed by the substrate rotation has a higher degree of symmetry, which can have better angle insensitivity when used in actual light absorption layer applications.

[0033] The rotation mode of the substrate plays a very important role in the preparation of nanocolumn arrays. When the substrate is fixed and non-rotating, the microscopic morphology of the prepared film is inclined nanocolumns or feathers; when the substrate has a certain rotation speed, and the rotation speed of the substrate forms a certain ratio with the deposition rate, the film morphology can be spiral; when the rotation speed of the substrate is very large, the prepared film presents a distinct columnar structure, and can even be a columnar structure completely perpendicular to the substrate. Therefore, in order to form a spiral structure, it is necessary to set the rotation speed to match the growth rate. The ratio of the two is related to the number of turns of the spiral structure. Generally, the substrate rotates the desired number of times during the entire growth cycle. For example, if you want to prepare a spiral structure with 2 turns, you should rotate 2 turns during the growth and thickening process.

[0034] As a typical example of the above technical solution, during the electron beam evaporation process, the sample stage is rotated so that the normal direction of the sample stage is at a certain angle to the normal direction of the evaporation source, and the shadow effect produced by oblique incident deposition is used to prepare an absorption structure with a porous structure. The preparation steps include at least the following steps: (1) sample cleaning; (2) vacuuming; (3) rotating the sample stage; (4) starting or not starting the rotation of the sample stage as required; (5) depositing the material according to the required thickness.

[0035] The specific preparation steps are as follows: Step (1): Sample cleaning: Clean the sample on which the absorption layer is to be deposited, and place the sample and the raw material in a vacuum chamber.

[0036] Step (2): Vacuum the chamber to a vacuum degree of 1×10 -4 Pa~5×10 -4 Pa.

[0037] Step (3): Rotate the sample stage: Rotate the sample stage so that the normal direction of the sample stage forms a certain angle with the normal direction of the evaporation source.

[0038] Step (4): Depending on whether a non-inclined rod-shaped structure needs to be formed, such as a spiral structure, the rotation of the sample stage may be started or not.

[0039] Step (5): Deposition of porous structure film: The porous metal structure is gradually formed through the shadow effect generated during the oblique angle incident deposition process. The deposition is performed for a certain period of time and the preparation is completed when the required thickness is reached.

[0040] In addition, as a further application of the above technical solution, an embodiment of the present invention also provides a non-cooled infrared detector, which includes a detection structure and an infrared absorption structure provided by any of the above embodiments, and the detection structure is tightly combined with the infrared absorption structure to detect the temperature change of the infrared absorption structure.

[0041] Specifically, the detection structure, such as a thermistor or other component that can sense heat changes, is mounted on the surface of the substrate and can even directly serve as a substrate for the infrared absorption structure. Various implementations can achieve corresponding purposes and are not specifically limited here.

[0042] The technical solution of the present invention is further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only used to illustrate the present invention, and do not limit the scope of the present invention.

[0043] Example 1 In this embodiment, NiCr alloy is selected as the deposition material, the angle between the normal direction of the sample stage and the normal direction of the evaporation source is 83°, and the deposition thickness in the direction perpendicular to the substrate is 300 nm.

[0044] Step 1: Sample cleaning: Place the sapphire substrate in a solution of concentrated H2SO4:H2O2=3:1, heat to 100℃ for 1h, and place the sample and raw materials in a vacuum chamber.

[0045] Step 2: Vacuum: The vacuum degree in the vacuum chamber is reduced to 1×10 -4 Pa~5×10 -4 Between Pa.

[0046] Step 3: Rotate the sample stage: Rotate the sample stage so that the angle between the normal direction of the sample stage and the normal direction of the evaporation source is 83°.

[0047] Step 4: Sample stage rotation: The sample stage rotation speed is 0 rpm.

[0048] Step 5: Deposition of porous structure film: The deposition thickness is 300 nm in the direction perpendicular to the substrate, and the deposition rate is controlled to 3 Å / s by adjusting the current of the electron beam.

[0049] The cross-sectional morphology of the final infrared absorption structure is as follows: Figure 3a As shown, the surface morphology is Figure 3b As shown, the inclined growing nanocolumnar structure can be clearly observed, with the angle between the axial direction and the substrate normal being 56°. Multiple nanocolumnar structures enclose multiple hole structures to form an excellent light trapping layer.

[0050] Example 2 In this embodiment, NiCr alloy is selected as the deposition material, the angle between the normal direction of the sample stage and the normal direction of the evaporation source is 83°, and the deposition thickness in the direction perpendicular to the substrate is 100 nm.

[0051] Step 1: Sample cleaning: Place the sapphire substrate in a solution of concentrated H2SO4:H2O2=3:1, heat to 100℃ for 1h, and place the sample and raw materials in a vacuum chamber.

[0052] Step 2: Vacuum: The vacuum degree in the vacuum chamber is reduced to 1×10 -4 Pa~5×10 -4 Between Pa.

[0053] Step 3: Rotate the sample stage: Rotate the sample stage so that the angle between the normal direction of the sample stage and the normal direction of the evaporation source is 83°.

[0054] Step 4: Sample stage rotation: The sample stage rotation speed is 0 rpm.

[0055] Step 5: Deposition of porous structure film: The deposition thickness is 100 nm in the direction perpendicular to the substrate, and the deposition rate is controlled to 2 Å / s by adjusting the current of the electron beam.

[0056] The infrared absorption structure obtained in this embodiment has the inclined porous structure, uniformity and infrared absorption performance similar to those in Embodiment 1.

[0057] Example 3 This embodiment is substantially the same as Embodiment 1, and the main difference is that: During the evaporation, the sample stage was started to rotate, and the sample stage speed was adjusted to 0.03 rpm.

[0058] The final infrared absorption structure has a spiral nanostructure, and its morphology is as follows: Figure 4a-4c As shown, the spiral structure can be clearly observed, and multiple spiral structures are arranged in an array.

[0059] The sample prepared in this embodiment firstly shows better uniformity than the sample prepared in Example 1. The rotation compensates for the influence of different geometric angles between different positions of the substrate and the evaporation source, so that different positions of the substrate have almost the same light absorption performance.

[0060] In addition, see Figure 5 As shown, the infrared absorption spectra of the absorption structures of oblique rod and spiral structures of different thicknesses prepared in the above embodiments were tested, and it can be found that the oblique rod structure exhibits relatively excellent light absorption ability; in addition, the light absorption performance of the spiral structure is better when the thickness is lower than that of the oblique rod structure, indicating that the light absorption performance of this absorption structure itself is better than that of the oblique rod.

[0061] Based on the above embodiments and comparative examples, it can be clearly seen that the technical solution provided in the embodiments of the present invention adopts the method of oblique incident deposition to prepare a new type of porous metal infrared porous light trapping layer under a high vacuum environment, which has excellent light absorption performance, simple processing technology and low cost. Compared with the traditional technical solution of preparing porous metal layers under a low vacuum N2 environment, the present invention is prepared under a higher vacuum environment, and the porous film has better uniformity. At the same time, when the film thickness is small and the thermal mass is small, the thermal absorption efficiency of the infrared detector can still be improved, and it can be used to construct high-performance infrared detectors, which play an important role in monitoring environmental safety, health care, industrial safety and other fields.

[0062] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An infrared absorbing structure, characterized in that: It comprises a substrate and a porous light-trapping layer arranged on the surface of the substrate, wherein the porous light-trapping layer comprises a nanostructure and has a hole structure, and the hole structure is formed by enclosing a plurality of adjacent nanostructures; The nanostructure is made of pure metal or alloy and has a growth axis, which points from the bottom of the nanostructure in contact with the substrate to the top away from the substrate, and the extension direction of the growth axis forms a non-vertical angle with the normal direction of the substrate.

2. The infrared absorption structure according to claim 1, characterized in that: The pure metal includes any one of Ti, W, Al, Ni, Fe, Au, Ag, and Cu, and the alloy includes any one of NiCr binary or multi-element alloy and NiCu binary or multi-element alloy.

3. The infrared absorption structure according to claim 1, characterized in that: The vertical thickness of the porous light trapping layer is 100nm-5μm; The non-vertical angle is 10-80°.

4. The infrared absorption structure according to claim 1, characterized in that: Along the extension direction of the growth axis, the shape of the nanostructure is any one of a straight column shape, a broken line shape or a spiral shape.

5. The infrared absorption structure according to claim 4, characterized in that: The nanostructure is in a spiral shape, and the total number of spiral turns in the entire length of the nanostructure is 2-5 turns.

6. A method for preparing an infrared absorption structure, characterized in that: include: Pure metal or alloy is deposited on the surface of the substrate by electron beam evaporation to form a nanostructure. The direction of the line connecting the evaporation source and the substrate during the electron beam evaporation forms an angle with the normal direction of the substrate. The angle ranges from 10 to 90 degrees, so that a plurality of adjacent nanostructures are surrounded to form a hole structure. The nanostructure and the hole structure constitute a porous light trapping layer.

7. The preparation method according to claim 6, characterized in that: The atmosphere pressure during electron beam evaporation was controlled at 1×10 -4 ~5×10 -4 Pa.

8. The preparation method according to claim 6, characterized in that: While the electron beam evaporation is being performed, the substrate is rotated along its normal direction as an axis.

9. The preparation method according to claim 8, characterized in that: The deposition rate of the electron beam evaporation is 0.1Å~5Å / S, and the rotation rate of the substrate is greater than 0 and less than or equal to 5rpm.

10. An uncooled infrared detector, characterized in that: It comprises a detection structure and the infrared absorption structure according to any one of claims 1 to 5, wherein the detection structure is tightly combined with the infrared absorption structure and is used to detect the temperature change of the infrared absorption structure.

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