Silicon-based infrared diaphragm with sunlight thermal effect inhibiting effect and application thereof

Abstract

The invention discloses a silicon-based infrared diaphragm with a photothermal effect inhibition effect. The silicon-based infrared diaphragm is a photon super-structure film formed by alternately stacking heterogeneous photonic crystal film layers with relatively small infrared band extinction coefficients. Therefore, the reflection bandwidth is widened through mutual coupling of a plurality of functional film sequences, impedance matching and interlayer coupling are adjusted, and the infrared antireflection effect is improved. The silicon-based infrared diaphragm provided by the invention has the characteristic of high reflection of solar spectrum (280-2500 nm), can reject heat absorption in a working environment with high solar radiation in the daytime, and reduces the thermal load of a photoelectric device, so that the device can work in a stable temperature environment. Meanwhile, the high infrared transmittance is kept, the photoelectric property of the silicon wafer in the infrared band (2.5-14 microns) is not affected, and compared with a bare silicon wafer, the performance is improved.

Description

Technical Field

[0001] The present invention relates to the fields of spectral regulation and metasurface thin films, and particularly to a silicon-based infrared window sheet with a photothermal effect suppression function and its application. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and it is not necessarily regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Thermal load seriously affects the working stability of optoelectronic devices and optical systems. Long-term thermal loading cycles will accelerate the aging and failure of equipment. For optoelectronic devices, especially infrared optoelectronic devices, such as the optical windows of aerospace vehicles, detectors, and ground optical stations, etc., when facing daytime solar radiation, the operating temperature of their equipment rises significantly. And in order to ensure good optical performance in the detection window, it is impossible to slow down the photothermal effect by covering a protective film. This results in difficulty in balancing the detection performance of photodetectors and the thermal load effect.

[0004] Silicon-based window sheets are very suitable for large-area optoelectronic devices due to their low price and good infrared transmission performance. However, the reflectivity of silicon wafers in the solar thermal radiation band is relatively low, only about 30%, and it is unable to effectively suppress the photothermal effect in the outdoor exposure environment. Although optical coating can be used as a way to improve optical performance, current technologies mostly focus on infrared antireflection thin films. For functional film systems with both thermal radiation suppression and high infrared transmission, due to the conflict of cross-band requirements of both high reflection and high transmission, it is difficult to achieve this technology.

[0005] In summary, the applicant believes that: to achieve the suppression of the solar thermal radiation effect of optoelectronic devices and at the same time maintain high infrared performance, it is necessary to develop a multi-band compatible film system with strong reflection in the solar spectrum and high transmission in the infrared spectrum, tune the conflict of different spectral bands, reduce the thermal load of optoelectronic devices working outdoors during the day, and effectively improve the working stability and service life of the devices. Summary of the Invention

[0006] In view of this, the present invention proposes a silicon-based infrared window sheet with a photothermal effect suppression function and its application. While having the characteristic of high reflection in the solar spectrum (280 - 2500 nm), it can maintain a high infrared transmittance, so that its optoelectronic performance in the infrared band (2.5 - 14 μm) is not affected, and the performance is improved compared with a bare silicon wafer. Specifically, the present invention discloses the following technical solutions.

[0007] First, the present invention discloses a silicon-based infrared window sheet with a photothermal effect suppression function, which is a photonic metasurface film composed of alternating stacks of heterogeneous photonic crystal film layers with an extinction coefficient not greater than 0.5 in the infrared band. Thus: the reflection bandwidth is broadened by the mutual coupling of multiple functional film sequences, and the impedance matching and interlayer coupling are adjusted to improve the infrared antireflection effect.

[0008] Further, the heterogeneous photonic crystal includes a high refractive index crystal material a and a low refractive index crystal material b, and the refractive indices of the two differ by not less than 1.

[0009] Further, the high refractive index crystal material a includes any one of ZnS, ZnSe, CdSe, CdTe, GaAs, Ge, SrTiO3, Si, etc.

[0010] Further, the low refractive index crystal material b includes any one of YF3, YbF3, CaF2, BaF2, BeO, LiF, MgO, SrF2, ZbLa, Al2O3, KBr, etc.

[0011] Further, the thickness of each film layer follows the quarter-wavelength interference theory, that is, nHtH = nLtL = λ0 / 4. Where: nH represents the refractive index of the high refractive index crystal material a, nL represents the refractive index of the low refractive index crystal material b, tH represents the thickness of the high refractive index crystal material a, tL represents the thickness of the low refractive index crystal material b, and λ0 is the central wavelength.

[0012] Further, the photonic metasurface film is obtained by coupling seven groups of photonic crystals distributed from top to bottom, and there is a defect layer among them. The corresponding photonic bandgaps are the first, second to seventh photonic bandgaps from the top layer of the film, and the photonic bandgaps gradually change from short-wave bandgap to long-wave bandgap from top to bottom, and the film system configuration of the photonic bandgaps shows an increasing trend in gradient. On the one hand, it can ensure good coupling of the bandgaps, and on the other hand, it can ensure good impedance matching and avoid strong reflection in the infrared band. The present invention broadens the visible light reflection bandwidth by coupling the respective bandgaps of these photonic crystals. And introducing a resonant cavity using the defect layer helps to reduce the reflection in the infrared band and improve the infrared transmittance.

[0013] Further, the first photonic bandgap is composed of a double-period defect photonic crystal, and the film system configuration is LHL, where L represents the low refractive index crystal material b and H represents the high refractive index crystal material a, and their thicknesses are L = 50 ± 2.5 nm and H = 274 ± 13.7 nm respectively.

[0014] Further, the second photonic bandgap is composed of a three-period photonic crystal, and the film system configuration is (HL) 3Their thicknesses are L = 90 ± 4.5 nm and H = 50 ± 2.5 nm respectively.

[0015] Further, the third photonic bandgap is composed of a four - period symmetric photonic crystal and a defect - coupled interlayer, and its film system configuration is (HL) 2 HL0(HL) 2 , where L0 represents the middle low - refractive - index defect interlayer. Their thicknesses are L = 110 ± 5.5 nm and H = 50 ± 2.5 nm respectively.

[0016] Further, the fourth photonic bandgap is composed of a three - period photonic crystal, and its film system configuration is (HL) 3 , and their thicknesses are L = 150 ± 7.5 nm and H = 70 ± 3.5 nm respectively.

[0017] Further, the fifth photonic bandgap is composed of a four - period photonic crystal, and its film system configuration is (HL) 4 , and their thicknesses are L = 220 ± 11 nm and H = 130 ± 6.5 nm respectively.

[0018] Further, the sixth photonic bandgap is composed of a five - period photonic crystal, and its film system configuration is (HL) 5 , and their thicknesses are L = 170 ± 8.5 nm and H = 130 ± 6.5 nm respectively.

[0019] Further, the seventh photonic bandgap is composed of a four - period photonic crystal, and its film system configuration is (HL) 4 H, and their thicknesses are L = 280 ± 14 nm and H = 200 ± 10 nm respectively.

[0020] Further, the width of each group of the photonic bandgaps is determined by the following formula: . Where: Δλ0 represents the bandgap width, n H represents the refractive index of the high - refractive - index crystal material a, n L represents the refractive index of the low - refractive - index crystal material b, t H represents the thickness of the high - refractive - index crystal material a, t L represents the thickness of the low - refractive - index crystal material b, and λ0 is the central wavelength.

[0021] Further, the photonic metasurface thin film is loaded on a silicon substrate. Optionally, the material of the silicon substrate includes any one of high - resistivity silicon, low - resistivity silicon, single - crystal silicon, doped silicon wafers, etc.

[0022] Furthermore, there is also a layer of the low-refractive-index crystal material b between the silicon substrate and the lower surface of the photonic metamaterial thin film to reduce the reflection on the upper surface of the silicon wafer and ensure that more infrared light can pass through. Optionally, the thickness of the low-refractive-index crystal material b is 705 nm.

[0023] Secondly, the present invention discloses the application of the silicon-based infrared window sheet with the function of suppressing the photothermal effect in the fields of aerospace, optoelectronic detection, national defense and military, etc.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention include: The silicon-based infrared window sheet proposed by the present invention can suppress the thermal load caused by solar radiation during the day and can improve the transmittance in the infrared band to ensure the efficient and stable operation of optoelectronic devices. The reason is as follows: By utilizing the bandgap effect of gradient photonic crystal coupling, the present invention covers the reflection peak to cover the entire visible-near infrared (280 - 2500 nm band, with an average reflectance greater than 72%. Its gradient impedance gradient design ensures good coupling of multiple bandgaps and gradient impedance matching, realizing the compatible effect of high reflection in the solar radiation band and high transmittance in the infrared band, with an average transmittance greater than 61% in the infrared band of 2.5 - 14 um. At the same time, defect interlayers are inserted into the gradient photonic crystal to ensure the local effect of the optical field, which can reduce the impedance mismatch caused by the refractive index change at the interface between photonic crystals and suppress the reflection of the infrared band, thereby improving the infrared transmittance. The silicon-based infrared window sheet proposed by the present invention can provide a low-thermal-load working environment for optoelectronic devices to work stably and efficiently in outdoor and space environments, ensure that there is no obvious temperature fluctuation in optoelectronic devices, and provide a feasible method for extending the working life of optoelectronic devices and ensuring data validity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention and do not constitute an improper limitation to the present invention.

[0026] Figure 1 It is a configuration schematic diagram of the silicon-based infrared window sheet with the function of suppressing the solar photothermal effect in the following embodiments.

[0027] Figure 2 It is a sample diagram of the silicon-based infrared window sheet with the function of suppressing the solar photothermal effect prepared in the following embodiments.

[0028] Figure 3 It is a comparison diagram of the measured and simulated spectra of the infrared window sheet in the following embodiments.

[0029] Figure 4 It is a visible-infrared spectrum diagram of the ordinary silicon wafer before coating in the following embodiments.

[0030] Figure 5 It is the simulated electric field distribution diagram of the infrared window sheet in the following embodiments. Specific embodiments

[0031] For the convenience of description, if the words "upper", "lower", "left", and "right" appear in the present invention, they only indicate the same as the upper, lower, left, and right directions of the accompanying drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to needs to have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of the present invention. The present invention will be further described below with reference to the accompanying drawings of the specification and specific embodiments.

[0032] Embodiment 1 Reference Figure 1 , an example of a silicon-based infrared window sheet with the function of suppressing solar thermal effect is shown. It has a strong visible light reflection appearance. By using the design of multiple photonic crystal coupled defect intercalations, it is compatible with the spectral selectivity characteristics of high reflection in the solar radiation spectral band (0.28 - 2.5 μm) and high transmission in the mid-infrared band (2.5 - 14 μm). The solar spectral radiation band is divided into seven photonic bandgaps for distributed coupling. According to the gradient impedance gradual change design, in the order of short-wave to long-wave bandgaps from top to bottom, adjacent bandgaps are well coupled, and a high refractive index defect layer is introduced at the interface of the photonic crystal to introduce the photonic localization effect, reduce the impedance mismatch between interfaces and enhance the infrared light trapping effect, reduce the reflection in the mid-infrared band, and ensure that it can both reflect the light in the solar spectral band and transmit the infrared light well. Specifically, the silicon-based infrared window sheet from top to bottom is successively the photonic crystal thin films corresponding to the first to seventh photonic bandgaps. Each photonic bandgap is composed of alternating stacks of a high refractive index crystal material a (ZnS is used in this embodiment) and a low refractive index crystal material b (YF3 is used in this embodiment). Among them: The first photonic bandgap is composed of a double-period defect photonic crystal, and the film system configuration is LHL, where L represents the low refractive index crystal material b, and H represents the high refractive index crystal material a. Their thicknesses are L = 50 nm and H = 274 nm respectively. It mainly plays the role of impedance matching to induce transmission and constructing a pseudo-photonic bandgap with a central wavelength of 300 nm.

[0033] The second photonic bandgap is composed of a three-period photonic crystal, and the film system configuration is (HL) 3 . Their thicknesses are L = 90 nm and H = 50 nm respectively, and a bandgap with a width of 180 nm is constructed with a central wavelength of 450 nm.

[0034] The third photonic bandgap is composed of a four-period symmetric photonic crystal and a defect coupling intercalation, and its film system configuration is (HL) 2 HL0(HL) 2, L0 represents the intermediate low-refractive-index defect interlayer. Their thicknesses are L = 110 nm and H = 50 nm respectively, and a stopband with a width of 200 nm is constructed with a central wavelength of 500 nm The fourth photonic stopband is composed of a three-period photonic crystal, and its film stack configuration is (HL) 3 , and their thicknesses are L = 150 nm and H = 70 nm respectively. A stopband with a width of 260 nm is mainly constructed with a central wavelength of 650 nm. The fifth photonic stopband is composed of a four-period photonic crystal, and its film stack configuration is (HL) 4 , and their thicknesses are L = 220 nm and H = 130 nm respectively. A stopband with a width of 480 nm is mainly constructed with a central wavelength of 1200 nm.

[0035] The sixth photonic stopband is composed of a five-period photonic crystal, and its film stack configuration is (HL) 5 , and their thicknesses are L = 170 nm and H = 130 nm respectively. A stopband with a width of 500 nm is mainly constructed with a central wavelength of 1500 nm The seventh photonic stopband is composed of a four-period photonic crystal, and its film stack configuration is (HL) 4 H, and their thicknesses are L = 280 nm and H = 200 nm respectively. A stopband with a width of 760 nm is mainly constructed with a central wavelength of 1900 nm.

[0036] The physical sample of the silicon-based infrared window chip prepared in this embodiment is as Figure 2 shown. The comparison diagram of the measured and simulated spectra of this silicon-based infrared window chip is as Figure 3 shown. It can be seen that: the simulated spectrum of the metasurface photonic thin film is in good agreement with the measurement, which proves the good adhesion between the film layers and the deposition thickness. Among them, the average reflectivity in the range of 0.4 - 1.2 μm is 78.4%, the average reflectivity in the range of 0.4 - 0.8 μm is 61%, the average reflectivity in the entire solar spectral radiation band (0.28 - 2.5 μm) is greater than 72%, and the average transmittance in the mid-infrared band of 2.5 - 14 μm is greater than 61%. It is confirmed that the photonic stopbands covering the entire solar spectral radiation band are successfully coupled, and their stopband ranges do not affect the reflectivity in the mid-infrared band. Thanks to the gradient impedance-graded photonic structure design, the impedance matching characteristics in the infrared band will not deteriorate, enabling the suppression of daytime thermal radiation with high reflectivity in the solar spectrum while being compatible with high transmittance in the infrared.

[0037] Figure 4is the reflectivity of the bare silicon wafer in the solar spectral band and the infrared band. It can be seen that without the photonic metamaterial thin film, its solar spectral reflectivity is only about less than 40%, making it difficult to effectively reduce the thermal load and the daytime thermal radiation effect. And the transmittance in the mid-infrared band is about 55%. After increasing the transmittance through the photonic metamaterial thin film, the infrared transmittance can be increased by 6%, ensuring the more efficient and accurate operation of optoelectronic devices.

[0038] Figure 5 is the simulation diagram of the electric field distribution of the silicon-based infrared window chip prepared in this embodiment. Among several selected typical bands, at 500 nm in the solar spectral radiation band, the electric field is localized in the top-layer photonic crystal part, which is also the position of the photonic crystal corresponding to the designed bandgap. It is difficult for the electric field to enter the interior of the thin film, so a strong reflection effect is exhibited in the spectral characteristics. From the electric field distribution diagrams at 3000 nm, 7500 nm, 10000 nm, and 14000 nm, it can be seen that the electric field distribution shows an obvious periodic distribution trend, which also corresponds to the optical field localization effect caused by impedance matching gradient, increasing the mid-infrared transmittance. And the electromagnetic wave can successfully enter the interior of the thin film, verifying the spectral selectivity effect, enabling the electromagnetic wave to enter the photonic thin film in the form of transmission rather than reflection.

[0039] Example 2 Reference Figure 1 , another silicon-based infrared window chip with the effect of suppressing the solar photothermal effect is exemplified. The difference between it and the above Example 1 is that in this embodiment, the high-refractive-index crystal material a is GaAs, and the low-refractive-index crystal material b is YbF3.

[0040] Example 3 Reference Figure 1 , another silicon-based infrared window chip with the effect of suppressing the solar photothermal effect is exemplified. The difference between it and the above Example 1 is that in this embodiment, the high-refractive-index crystal material a is CdSe, and the low-refractive-index crystal material b is SrF2.

[0041] Example 4 Reference Figure 1 , another silicon-based infrared window chip with the effect of suppressing the solar photothermal effect is exemplified. The difference between it and the above Example 1 is that in this embodiment, the high-refractive-index crystal material a is SrTiO3, and the low-refractive-index crystal material b is CaF2.

[0042] Example 5 Reference Figure 1 , another silicon-based infrared window chip with the effect of suppressing the solar photothermal effect is exemplified. The difference between it and the above Example 1 is that in this embodiment, the high-refractive-index crystal material a is CdTe, and the low-refractive-index crystal material b is ZbLa.

[0043] Example 6 Reference Figure 1 , another silicon-based infrared window sheet with the function of suppressing solar heat effect is exemplified. The difference between this example and Example 1 above is that: in this example, the high refractive index crystal material a is ZnSe, and the low refractive index crystal material b is BeO.

[0044] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A silicon-based infrared window sheet with the function of suppressing photothermal effect, characterized in that, The window piece is a photonic metamaterial thin film composed of alternating stacks of heterogeneous photonic crystal films with a small extinction coefficient in the infrared band.

2. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to claim 1, wherein The heterogeneous photonic crystal includes a high refractive index crystal material a and a low refractive index crystal material b, and the refractive index difference between the two is not less than 1; Optionally, the high refractive index crystal material a includes any one of ZnS, ZnSe, CdSe, CdTe, GaAs, Ge, SrTiO3, Si; Optionally, the low refractive index crystal material b includes any one of YF3, YbF3, CaF2, BaF2, BeO, LiF, MgO, SrF2, ZbLa, Al2O3, KBr.

3. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to claim 2, wherein, The thickness of each film layer follows the quarter-wavelength interference theory, that is, nHtH = nLtL = λ0 / 4; where: nH represents the refractive index of the high refractive index crystal material a, nL represents the refractive index of the low refractive index crystal material b, tH represents the thickness of the high refractive index crystal material a, tL represents the thickness of the low refractive index crystal material b, and λ0 is the central wavelength.

4. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to any one of claims 1-3, characterized in that The photonic metamaterial thin film is obtained by coupling six groups of photonic crystals distributed from top to bottom, and has a defect layer therein; the corresponding photonic band gaps are the first, second to sixth photonic band gaps from the top layer of the thin film, and the photonic band gaps gradually change from short-wave band gap to long-wave band gap from top to bottom, and the film system configuration of the photonic band gap follows the trend of increasing gradient.

5. The silicon-based infrared window sheet with the function of suppressing the photothermal effect according to claim 4, wherein The first photonic band gap is composed of a double-period defect photonic crystal, and the film system configuration is LHL, where L represents the low refractive index crystal material b and H represents the high refractive index crystal material a, and their thicknesses are L = 50 ± 2.5 nm and H = 274 ± 13.7 nm respectively; Optionally, the second photonic bandgap is composed of a three - period photonic crystal, and the film system configuration is (HL) 3 ; their thicknesses are L = 90 ± 4.5 nm and H = 50 ± 2.5 nm respectively.

6. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to claim 4, characterized in that, The third photonic bandgap is composed of a four - period symmetric photonic crystal and a defect - coupled interlayer, and its film configuration is (HL) 2 HL0(HL) 2 , where L0 represents the middle low - refractive - index defect interlayer; their thicknesses are L = 110 ± 5.5 nm and H = 50 ± 2.5 nm respectively; Optionally, the fourth photonic bandgap is composed of a three - period photonic crystal, and its film system configuration is (HL) 3 , with thicknesses of L = 150 ± 7.5 nm and H = 70 ± 3.5 nm respectively.

7. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to claim 4, wherein The fifth photonic bandgap is composed of a four - period photonic crystal, and its film system configuration is (HL) 4 , and their thicknesses are L = 220 ± 11 nm and H = 130 ± 6.5 nm respectively; Optionally, the sixth photonic bandgap is composed of a five - period photonic crystal, and its film system configuration is (HL) 5 , and their thicknesses are L = 170 ± 8.5 nm and H = 130 ± 6.5 nm respectively; Optionally, the seventh photonic bandgap is composed of a four - period photonic crystal, and its film system configuration is (HL) 4 H, with thicknesses of L = 280 ± 14 nm and H = 200 ± 10 nm respectively.

8. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to any one of claims 2-7, characterized in that The photonic bandgap width of the metasurface thin film is determined by the following formula: ; where: Δλ0 represents the bandgap width, nH represents the refractive index of the high refractive index crystal material a, nL represents the refractive index of the low refractive index crystal material b, tH represents the thickness of the high refractive index crystal material a, tL represents the thickness of the low refractive index crystal material b, and λ0 is the central wavelength.

9. The silicon-based infrared window sheet with the function of suppressing photothermal effect according to any one of claims 1-3, characterized in that The photonic metamaterial thin film is loaded on a silicon substrate; Preferably, there is also a layer of the low refractive index crystal material b between the silicon substrate and the lower surface of the photonic metamaterial thin film to reduce the reflection on the upper surface of the silicon wafer and ensure that more infrared light passes through; optionally, the thickness of the low refractive index crystal material b is 705 nm; Optionally, the material of the silicon substrate includes any one of high-resistance silicon, low-resistance silicon, single-crystalline silicon, and doped silicon wafers.

10. Application of the silicon-based infrared window piece with the function of suppressing photothermal effect according to any one of claims 1-9 in the fields of aerospace, optoelectronic detection, or national defense and military.

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