用于车载激光雷达导电滤光膜的研究

Research on Conductive Filter Film for Vehicle-Mounted Lidar

为了使车载激光雷达视窗在大角度下具有高透过率并且具有除霜防雾的功能,研制了近红外导电滤光膜。选择SiH_(x)与SiO_(2)作为高、低折射率材料,调节氢气流量,改变SiH_(x)的折射率及消光系数,使得SiH_(x)可吸收可见光,同时在红外波段的吸收率较低,最终薄膜外观呈黑色。利用软件Macleod与Optilayer设计并优化膜系,使薄膜在(905±30)nm波段增透,同时减低了大角度入射时的光谱偏移量。在滤光膜最外层加镀了一层氧化铟锡(ITO)薄膜,通过调整工艺参数,在不影响光谱性能的前提下降低了方块电阻值。经测试,所制备的导电滤光膜在入射角为0°时的平均透过率为92.58%,入射角为30°时的透过率为91.9%,方块电阻值达到24Ω/square,适用于车载激光雷达视窗。

Objective The vehicle-mounted laser radar acts as the car’s eyes,transmitting radio waves to the target object,and comparing the transmitted signal to the target reflection signal to achieve the detection and ranging function of the target object.The infrared Lidar window,as the vehicle-mounted radar’s outermost layer,also participates in optical imaging.People are increasingly demanding that filters filter light at a wide-angle.And because the optical window is prone to frost and fog in cold and humid weather,which affects the transmittance,the filter must also have heating and conducting functions.According to information,domestic research on Lidar window components has begun in recent years.However,current research typically cannot simultaneously increase the transmittance,increase the working angle,and reduce the square resistance of the film.Therefore,the primary research focus of the near-infrared conductive filter is the improvement of multiple indicators.In this paper,SiHx and SiO_(2) are selected as high and low refractive index materials.Adjusting the amount of hydrogen changes the optical constants of SiHx.A 905 nm filter is designed and prepared,and the outermost layer is plated with a single layer of indium tin oxide(ITO).The square resistance of the film is reduced under the premise of spectral performance.Methods According to the index requirements,the filter cannot produce a large shift in the spectrum at a large angle of incidence.SiHx,which has a large absorptivity in the visible wavelength band and a small absorptivity in the near-infrared band,is selected as the high-refraction filter material and the low-refraction material SiO_(2) is superimposed on each other to prepare a filter.The filter is made using radio frequency magnetron sputtering technology.First,the optical constant of SiHx is investigated,and the gradient test on the inductively coupled plasma(ICP)hydrogen charge is performed to validate the theoretical experimental calculation results(Figs.1 and 2).Then,using the material’s optical constants,a filter that meets the requirements is designed(Fig.3),and the error analysis of the designed film is performed(Fig.4).Select the best sputtering process to match the refractive index of SiHx with that of SiO_(2)(Table 1),and test the spectral curve with spectrophotometers(Fig.5).A layer of ITO transparent conductive film is plated on the filter to achieve the function of defrosting and anti-fogging in a low-temperature environment.First,perform square resistance tests on ITO single-layer films with different thicknesses(Fig.6),and then use ITO with a thickness of 250 nm to perform gradient tests on the oxygen charge of the plasma source and the argon charge of the target material(Tables 2 and 3).Determine the best process for ITO(Table 4).First,prepare the filter as described above,then add a layer of ITO to the outermost layer after the standby device has been cooled,measure the spectrum(Fig.8),and use a low impedance analyzer to measure the square resistance.Results and Discussions After testing,when the incident angle of the filter is 0°,the average transmittance in the 400-700 nm band is 0.09%,the average reflectance is 6.17%,and the average transmittance at(905±30)nm is 93.53%.When the incident angle is 30°,the average transmittance in the 400-700 nm band is 0.09%,the average reflectance is 6.77%,and the average transmittance at(905±30)nm is 92.43%.After adding 250 nm thick ITO to the outermost layer,the average transmittance under the incident angle of 0°at(905±30)nm is 92.58%,and the average transmittance at the incident angle of 30°is 91.9%;the average transmittances at the incident angles of 0°and 30°in the visible light band are both 0.1%,which meets the design requirements,and the final square resistance of the prepared near-infrared conductive filter is 24Ω/square.While the ITO film has no effect on the filter’s transmittance,the square resistance of the film is significantly reduced by adjusting the process.The film is subjected to high and low-temperature cycle tests,stretched films tests,and hundred-grid tests,and there is no film peeling,cracking,etc.Conclusions Using SiHx and SiO_(2) as the high and low refractive index materials,a large-angle near-infrared filter for automotive ranging lidar is developed,and a low square resistance ITO film is coated on the outermost layer of the film to facilitate shield electromagnetic interference and energize heating to achieve the function of defrosting and anti-fogging.The film has a very good anti-reflection effect in the(905±30)nm band.To reduce the reflectivity of the film,the Macleod and Optilayer softwares are used for design and calculation.SiHx is used as the high refractive index material to absorb the visible light wave to achieve the effect of black film.The developed(905±30)nm conductive filter has an average transmittance of 92.58%at the incident angles of 0°,91.9%at the incident angles of 30°,and a square resistance of 24Ω/square.It is suitable as the window of vehicle radar and has important reference significance for the black film required by augmented reality/virtual reality,face recognition,etc.