CN104614077A - Optical window with high terahertz wave transmission rate and low infrared light transmission rate - Google Patents
Optical window with high terahertz wave transmission rate and low infrared light transmission rate Download PDFInfo
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- CN104614077A CN104614077A CN201510061166.9A CN201510061166A CN104614077A CN 104614077 A CN104614077 A CN 104614077A CN 201510061166 A CN201510061166 A CN 201510061166A CN 104614077 A CN104614077 A CN 104614077A
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Abstract
The invention belongs to the technical field of terahertz detection, and provides an optical window with high terahertz wave transmission rate and low infrared light transmission rate and a preparation method of the optical window. The optical window is equipped with four layers from top layer to bottom layer, wherein the first layer is equipped with a metal grid structure, the second layer is equipped with a dielectric film, the third layer is equipped with a window substrate, and the fourth layer is equipped with a sub-wavelength anti-reflecting structure; the metal grid structure is in a shape of a periodically-arranged metal square block graph; the sub-wavelength anti-reflecting structure is a square cylinder relieving structure periodically arranged in a matrix form. According to the optical window, the transmission rate at the terahertz wave band is more than 90%, and the radiation transmission rate of the background infrared wave band is less than 1%; the optical window is widely applied to various terahertz detection imaging devices.
Description
Technical field
The invention belongs to terahertz detection technical field, be specifically related to the optical window of a kind of high THz wave transmitance and low infrared light percent of pass.
Background technology
THz wave refers to the electromagnetic radiation of frequency between 0.1-10THz (wavelength 3mm-30 μm), and its electromagnetic wave spectrum is between microwave and infrared band, and therefore, Terahertz system takes into account the advantage of electronics and optical system.For a long time, owing to lacking the method that effective THz radiation produces and checks, people are very limited for the understanding of this wave band properties of electromagnetic radiation, to such an extent as to this wave band is called as the THz space in electromagnetic wave spectrum.This wave band is also last frequency window having pending comprehensive research in electromagnetic wave spectrum.
Common THz type photodetector mainly contains unit or the multiunit detector such as Ge, Si and InSb bolometer (Bolometer), Golay detector (Golay Cell), pyroelectricity (Pyroelectric), schottky diode, field effect transistor of refrigeration.The pyroelectricity of current comparative maturity and micro-metering bolometer (Micro-Bolometer) all belong to thermal detector, are all to the thermal effect that THz radiation absorption produces, the physical property of corresponding sensitive material changed by absorbing material and detect radiation intensity.Because the thermal effect of infrared radiation is stronger than THz radiation, therefore practical application greatly can be subject to the impact of infrared radiation, adds ground unrest.In THz radiation detection, the absorption of its radiation wavelength and the screening filtering of infrared background noise are treated as solving as an inevitable task.
Terahertz detector optical window requires to have high terahertz emission transmitance.Traditional antireflection method utilizes physics on the surface or the method for chemistry applies one or more layers dielectric film at optical window.But there is the tack of coating and substrate in this traditional antireflection method, the etch resistant properties of film, thermal expansivity do not mate and rete and substrate, diffusion between rete and rete and components permeate problem.
Sub-wavelength anti-reflection structure well solves the shortcoming of traditional anti-reflective film.Sub-wavelength structure refers to that its characteristic dimension is less than the structure of operation wavelength, has higher diffraction efficiency.Because sub-wavelength structure is produced on device surface by the method for etching, anti-reflection structure and substrate, with being integrated, thus can solve the problem of traditional anti-reflective film tack, corrosion stability, thermal expansion mismatch, components permeate and diffusion.
Terahertz detector optical window also requires to have low infrared spectrum percent of pass, because the response of background infrared radiation interference terahertz detection unit.Consider earth silicon material, it only exists infrared band spectral absorption and the antisymmetric stretching vibration of Si-O-Si key and the symmetrical stretching vibration of Si-O key produce absorption peak; This absorption peak is formed for the superposition of some narrow band peak values, can not shield completely whole infrared band.Therefore, need to find a kind of material that effectively can shield infrared band.
Meta Materials (Metamaterial), from frequency-selective surfaces FSS (Frequency Selective Surface) structural development, is a kind of special type composite material with extraordinary physical property not available for traditional material.By the structurally ordered design on material key physical yardstick, break through the restriction of some apparent natural law, obtain the meta-materials function exceeding the intrinsic common character of nature, thus realize the demand customizing function solenoid.
From LC resonance, (L is inductance to Meta Materials, C is electric capacity) and electric dipole resonance principle set out, devise the meta-material absorber that can absorb wave electromagnetic radiation near fixed frequency, its negative index effect produce phase place change 1/4th slide structures and to the mudulation effect of certain wavelength and switching effect etc.Metal mesh structure utilizes to the resonance of electromagnetic field modulation function and cut-off effect in metamaterial structure, can adapt to low-frequency band carry out through and modulation, to high frequency band shielding and cut-off filter, be the preferably selection to THz radiation transmission and infrared shielding.
Summary of the invention
The object of this invention is to provide the optical window of a kind of high THz wave transmitance and low infrared light percent of pass, this window can in the transmitance of hertz wave band higher than 90%, and the percent of pass of background infrared band radiation is lower than 1%, be widely used in the optical window of various terahertz detection image device.
Technical scheme of the present invention is:
The optical window of a kind of high THz wave transmitance and low infrared light percent of pass, described optical window comprises four-layer structure by top layer down to bottom, ground floor is metal mesh structure, the second layer is dielectric film, third layer is window substrate, 4th layer is sub-wavelength anti-reflection structure, and described metal mesh structure is the metal squares figure of periodic arrangement, and described sub-wavelength anti-reflection structure is the cubic cylinder embossment structure of the arrangement in period matrix.
Further, the metal squares figure length of side of described metal mesh structure is 4 ~ 6 μm, and the arrangement cycle is 6-8 μm, and metal thickness is 50-200nm; Described metal material is gold, copper, iron, aluminium, nickel, chromium or its alloy.
Described dielectric film is the dielectric material such as silicon nitride, monox, has good absorption to infrared band, and absorb faint to THz wave, its thickness is 50 ~ 500nm.
Described window substrate is the window materials such as silicon, germanium, High Resistivity Si, quartz crystal, methylpent ethene polymers or tygon, and substrate thickness is 0.5 ~ 3mm.
Described sub-wavelength anti-reflection structure is the cubic cylinder embossment structure of the arrangement in period matrix, and for improving window substrate THz wave transmitance, its embossment size design is determined according to transmission Terahertz frequency, and periodic dimensions is 5 ~ 50 μm.
In addition, optical window modes of emplacement of the present invention is that top layer incidence, bottom outgoing or bottom are incident, top layer outgoing.
The preparation method of the optical window of high THz wave transmitance of the present invention and low infrared light percent of pass, comprises the following steps:
Step 1. window substrate processing, carries out cleaning post-drying to window substrate for subsequent use;
Step 2. etches sub-wavelength anti-reflection structure, adopts ion reaction etching method at the cubic cylinder embossment structure of window substrate lower surface etching arrangement in period matrix;
Step 3. deposition medium film, adopts PECVD method at window substrate top surface deposition medium film;
Step 4. splash-proofing sputtering metal network, adopts magnetron sputtering technique to prepare metal mesh structure on dielectric film surface, is namely prepared into optical window.
The present invention compared with prior art tool has the following advantages:
The optical window of high THz wave transmitance provided by the invention and low infrared light percent of pass can reach 99.05% in the transmitance of 2.52THz Terahertz frequency, and filters the mid and far infrared wave band radiation of more than 99%; In addition, this optical window preparation technology is simple, and structure multiplicity is high, is applicable to large-scale production.
Accompanying drawing explanation
Fig. 1 is optical window structure schematic diagram of the present invention, and wherein, 1 is metal mesh structure, and 2 is dielectric film, and 3 is window substrate, and 4 is sub-wavelength anti-reflection structure.
Fig. 2 is optical window metal mesh structure schematic diagram of the present invention.
Fig. 3 is the cubic cylinder embossment structure structure vertical view of window lower surface.
Fig. 4 is that in the embodiment of the present invention, terahertz optics window, in the transmitance of terahertz wave band, reaches 99.05% in the transmitance of 2.52THz Terahertz frequency.
Fig. 5 is that in the embodiment of the present invention, terahertz optics window is in the transmitance at infrared band, and the transmitance near 10 μm is lower than 1%.
Embodiment
Below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation.
The invention provides the optical window of a kind of high THz wave transmitance and low infrared light percent of pass, its structure as shown in Figure 1, described optical window comprises four-layer structure by top layer down to bottom, ground floor is metal mesh structure 1, the second layer is dielectric film 2, and third layer is window substrate the 3, four layer is sub-wavelength anti-reflection structure 4, described metal mesh structure 1 is the metal squares figure of periodic arrangement, and described sub-wavelength anti-reflection structure 4 is the cubic cylinder embossment structure of the arrangement in period matrix.
Described optical window substrate is high resistant silicon chip, and dielectric film is silicon nitride film, and the metal mesh structure that dielectric film plates above is square, and material is aluminium, and as shown in Figure 2, periodic arrangement projected square part is metal to its structure vertical view, is around dielectric layer.
The sub-wavelength anti-reflection structure of described terahertz optics window bottom is the cubic cylinder embossment structure of the arrangement in period matrix, and as shown in Figure 3, little square frame is the embossment cylinder of projection to its structure vertical view, is around window substrate.
Further, described silicon nitride thickness is 200nm; Described square-shaped metal aluminium network thickness is 100nm, and the length of side is 5.5 μm, and the arrangement cycle is 6.5 μm; Described optical window substrate thickness is 500 μm; The height of the cubic cylinder embossment structure of the described arrangement in period matrix is 13 μm, and the cycle is 27 μm, takes up space than being 0.75.
The preparation method of the optical window of above-mentioned high THz wave transmitance and low infrared light percent of pass, comprises the following steps:
The process of step 1. silicon chip, uses acetone to carry out Ultrasonic Cleaning to the silicon chip of twin polishing, then uses alcohol immersion, clean with deionized water rinsing afterwards, then use hydrofluoric acid clean silicon chip, then use a large amount of deionized water rinsing, nitrogen dries up, and puts into baking oven and dries, be then cooled to room temperature;
Step 2. etches sub-wavelength anti-reflection structure, and adopt the method for ion reaction etching on high resistant silicon chip, etch the cubic cylinder embossment structure arranged in period matrix, be highly 13 μm, the cycle is 27 μm, takes up space than being 0.75;
Step 3. vapour deposition silicon nitride, adopt the surface deposition silicon nitride layer that the method for PECVD is selected at high resistant silicon chip, the thickness of silicon nitride layer is at about 200nm;
Step 4. adopts spin-coating method effects on surface to apply AZ5214 type reversion glue, and spin coating rotating speed is 1000r/min, 5s, then 3000r/min, 40s, rubberization thickness about 1300nm;
Step 5. front baking, toasts the silicon chip after gluing, and baking temperature is set as 100 DEG C, and baking time is set as 70s;
Step 6. first time exposure, adopts the method for contactless exposure to expose photoresist layer, makes Graphic transitions on mask plate on photoresist, and the time shutter of exposure first time is 2.9s;
Dry after step 7., toast the silicon chip after first time exposure, baking temperature is set as 120 DEG C, and baking time is 90s;
The exposure of step 8. second time, adopt the method for contactless exposure to carry out general exposure to photoresist layer, the figure on photoresist is reversed, and secondary time shutter is 40s;
Step 9. is developed, and adopt RZX-308 developing rubber to develop to the silicon chip exposed, development temperature is 25 DEG C, and development time is 40s, uses a large amount of deionized water repeatedly to rinse after development;
Step 10. adopts sputter coating machine, and base vacuum is 4 × 10
-4pa, sputtering vacuum is 2.4 × 10
-1pa, silicon substrate temperature is 120 DEG C, and sputtering power is 76W, and sputtering time is 6min, then cools silicon chip to room temperature;
The silicon chip that step 11. has sputtered uses the ultrasonic stripping of acetone, uses alcohol immersion, then uses a large amount of deionized water rinsing totally in drying in oven, prepared required terahertz optics window after getting rid of residual photoresist and surface metal.
High THz wave transmitance in the present embodiment and the optical window of low infrared light percent of pass, through test, as shown in Figure 4, this optical window, in the transmitance of terahertz wave band, reaches 99.05% in the transmitance of 2.52THz Terahertz frequency.As shown in Figure 5, this optical window is in the transmitance at infrared band, and the transmitance near 10 μm is lower than 1%.Further, this structure preparation technology is simple, and structure multiplicity is high, is applicable to large-scale production.
Claims (7)
1. the optical window of one kind high THz wave transmitance and low infrared light percent of pass, described optical window comprises four-layer structure by top layer down to bottom, ground floor is metal mesh structure, the second layer is dielectric film, third layer is window substrate, 4th layer is sub-wavelength anti-reflection structure, and described metal mesh structure is the metal squares figure of periodic arrangement, and described sub-wavelength anti-reflection structure is the cubic cylinder embossment structure of the arrangement in period matrix.
2., by optical window described in claim 1, it is characterized in that, in described metal mesh structure, the metal squares figure length of side of periodic arrangement is 4 ~ 6 μm, and the arrangement cycle is 6-8 μm, and metal thickness is 50-200nm; Metal material is gold, copper, iron, aluminium, nickel, chromium or its alloy.
3., by optical window described in claim 1, it is characterized in that, described dielectric film is silicon nitride, silicon oxide film, and thickness is 50 ~ 500nm.
4., by optical window described in claim 1, it is characterized in that, described window backing material is silicon, germanium, High Resistivity Si, quartz crystal, methylpent ethene polymers or tygon, and substrate thickness is 0.5 ~ 3mm.
5. by optical window described in claim 1, it is characterized in that, described sub-wavelength anti-reflection structure is the cubic cylinder embossment structure of the arrangement in period matrix, and its embossment periodic dimensions is designed to 5 ~ 50 μm.
6. by optical window described in claim 1, it is characterized in that, described optical window modes of emplacement is that top layer incidence, bottom outgoing or bottom are incident, top layer outgoing.
7., by the preparation method of optical window described in claim 1, comprise the following steps:
Step 1. window substrate processing, carries out cleaning post-drying to window substrate for subsequent use;
Step 2. etches sub-wavelength anti-reflection structure, adopts ion reaction etching method at the cubic cylinder embossment structure of window substrate lower surface etching arrangement in period matrix;
Step 3. deposition medium film, adopts PECVD method at window substrate top surface deposition medium film;
Step 4. splash-proofing sputtering metal network, adopts magnetron sputtering technique to prepare metal mesh structure on dielectric film surface, is namely prepared into optical window.
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Cited By (3)
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| CN106206867B (en) * | 2016-07-21 | 2018-10-19 | 中北大学 | The infra red radiation light source and production method of Sandwich-shaped superstructure |
| CN113237846A (en) * | 2021-05-06 | 2021-08-10 | 南京大学 | Preparation of pixilated terahertz spectrum sensing chip and preparation method thereof |
| WO2023013121A1 (en) * | 2021-08-05 | 2023-02-09 | ソニーセミコンダクタソリューションズ株式会社 | THz DETECTION DEVICE |
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Cited By (3)
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| CN113237846A (en) * | 2021-05-06 | 2021-08-10 | 南京大学 | Preparation of pixilated terahertz spectrum sensing chip and preparation method thereof |
| WO2023013121A1 (en) * | 2021-08-05 | 2023-02-09 | ソニーセミコンダクタソリューションズ株式会社 | THz DETECTION DEVICE |
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Application publication date: 20150513 |