Development of advanced backlight unit and frontlight unit using 3D micromachining technologies

Abstract

In this thesis, advanced backlight unit (BLU) and frontlight unit (FLU) using 3D micromachining technologies have been proposed and developed. The 3D micromachining techniques we used were 3D diffuser lithography and backside 3D diffuser lithography, which are simple and unique microfabrication methods to produce various rounded 3D structures like microlens arrays (MLA). The advanced BLU were developed in two ways: one was two MLA-sheets BLU where a MLA-mounted light-guide plate (LGP) concentrated lights inside LGP at ±30 degrees and a conical MLA film like a prism sheet collimated the concentrated light to vertical direction. The MLA which was fabricated 3D diffuser lithography shows superior optical properties owing to high fill-factor and low radius of curvature on top surface. The truncated conical MLA which was fabricated by proximity lithography had a sidewall angle of 54 degrees to adjust the angle of light emitted from the MLA-mounted LGP to direct vertically to viewer. The proposed two MLA-sheets BLU shows the average luminance at zero degree was 2040 nit and the viewing angle of was 108 degrees. The other advanced BLU was single-sheet polydimethylsiloxane (PDMS) BLU with inverse-trapezoidal microstructures. The inverse-trapezoidal micropatterns play a role as a prim sheet, which sidewall angle of 55 degrees of the inverse-trapezoidal microstructures extract light vertically from an LGP. According to the sidewall angle of 55 degrees, the dimension of the microstructure was designed: a bottom diameter of 12.9 μm, a top diameter of 30 μm, and a height of 12 μm. In order to monolithically fabricate the inverse-trapezoidal microstructures on the LGP, backside 3D diffuser lithography and two consecutive PDMS replication processes were used. The optical properties of the proposed single-sheet PDMS BLU resulted in the average luminance of 3009 nit and a uniformity of 84.9% with four 0.85 cd LEDs, which are comparable to the conventional BLU. The advanced FLU ...