Development Of Ultra-thin Infrared Cut Filter For Fingerprint Recognition Under Optical Screen

Infrared cut-off filters are currently widely used in military and medical fields.With the increasing standard of living,consumer electronics such as smartphones and tablet PCs are rapidly entering people’s vision and becoming irreplaceable tools.Optical screen fingerprint identification system as an important component of consumer electronics,visible light high transmission near infrared high cut-off filter plays an important role.According to the literature reviewed,there are more studies on IR cut-off filter films at home and abroad,but there are fewer references available on the simultaneous deposition of this film on both sides of ultrathin,large-diameter substrates using magnetron sputtering.In this paper,the effect of the magnetic field uniformity of the target material,the rotation speed ratio of the metric-self-rotation system and the masking angle of the substrate jig on the thickness uniformity of the film are investigated.In this paper,according to the theory of interference cut-off filter film design and material optical constant fitting theory,Nb/Si is used as the coating target,Nb₂O₅and Si O₂are prepared by reaction sputtering as high and low refractive index materials,and with the help of the film system design software Essential Macleod,the symmetric film system design idea is adopted to achieve the stress balance on the upper and lower surfaces of the substrate.The designed IR cut-off filter film has a mean reflectance of 0.45%in the 450-550 nm passband band,a transmittance of 50%at 570 nm and a mean transmittance of less than 0.03%in the 590-1100 nm cut-off band.In the study of the influence of the magnetic field of the target on the uniformity of film thickness,the basic principle of magnetron sputtering was used as a guide to adjust the magnetic field distribution of the target using a magnetic guide sheet to reduce the degree of uneven etching of the target and improve the uniformity of film thickness;in the study of the influence of the rotational speed ratio of the metric-self rotating system on the uniformity of film thickness,the computer generated the motion trajectory of the test sheet and combined with the film thickness distribution model to find the 5:4 rotational speed ratio that has the greatest influence on the uniformity of film thickness.In the study of the effect of the rotation speed ratio of the TAR on the film thickness uniformity,the 5:4rotation speed ratio was found to have the greatest improvement on the film thickness uniformity,0.47%.Combining the theory of film stress calculation and the theory of finite element analysis of heat transfer process,using COMSOL Multiphysics software,the two physical fields of solid mechanics and shell heat transfer were coupled to simulate the thermal stress of the substrate,the simulated temperature ranged from 25 to 125,according to the simulation results,the maximum thermal stress of the substrate is about 6.32MPa.The thermal stress simulation analysis of single layer film and multilayer film is also made.The vacuum in situ annealing method can effectively improve the influence of thermal stress on the surface of the substrate,and restore to the room temperature of 25,and the peak thermal stress of multilayer film is about 7.47MPa.The results showed that the transmittance was 572.6 nm and 572.5 nm at 50%,97.59%and 98.14%at 450-550 nm,0.042%and 0.048%at 590-1100 nm and the warpage of the filter was 0.085 mm.The film adhesion,high and low temperature and constant temperature and humidity tests did not show any film cracking or delamination,and the spectral and environmental tests all met the requirements of the specifications.