Research On High Luminance For Mini-LED Backlight Unit

As nowadays mainstream display device,Liquid Crystal Display(LCD)has been widely used in aviation equipment,household appliance,mobile devices,and many other applications,which has been closely related to people's lives.With the continuous development of flat panel display technology,the requirements for liquid crystal display become higher and higher,LCD is required to be more larger,thinner and higher resolution.Backlight module plays an important role on LCD characteristics,including brightness,color gamut,uniformity,angle of view and thickness.As a new type of backlight,Mini-LED backlight unit has great advantages in thickness and uniformity.However,the viewing angle is large that leads to relatively low brightness at normal direction.Therefore,it is of great significance for the design of Mini-LED backlight unit to improve the brightness at normal direction.In this paper,three kinds of brightness enhancement schemes for Mini-LED backlight unit are proposed.The first one is to design pyramid microstructure on a single layer of substrate according to the working principle of double-layer brightness enhancement films.Compared with single layer prism film,it can shrink the angle of view in two directions,and as a result,the brightness at normal direction is increased.The parameters affecting the brightness at normal direction are simulated and optimized to determine the optimal parameters of the pyramid microstructure.The second is using Simultaneous Multiple Surface method for extended source to design double free-form surface microstructure.The method is improved and optimized according to the practical applications.A single microstructure and 3×3microstructure array are modeled and simulated.The simulation results are analyzed and an improve scheme is put forward to solve the problems encountered.Thirdly,a designed method for extended light source is proposed to modulate the light emitted from the Mini-LED die.Based on Snell's law and edge light principle,a set of equations is set up,and the single free-form surface microstructure is obtained by iterative calculation.The feasibility of the method is verified by modeling and simulation of single microstructure and microstructure array.Based on simulations results of three methods,the third method is selected as the final design scheme.The single-layer microstructure optical film is fabricated by maskless lithography device.The process parameters of maskless lithography are optimized and the microstructure optical film that complys with the design is obtained.Themicrostructure pattern is transferred to colorless resin material by UV imprint technology,and the influence of photoresist on the absorption of light is eliminated.Then,the microstructure optical film is put into the Mini-LED backlight unit for testing.The results show that compared with the case of only adding diffusion film,the brightness at normal direction with the two-layer prism films and diffuser increases by 17.8%.The brightness at normal direction with microstructure optical film and diffuser increases by 44.5%,22.7% higher than double-layer prism films.The test result shows that the proposed design can effectively improve the brightness at normal direction of the Mini-LED backlight unit.