Fabrication of a Tapered Structure by Means of Exposure to Diffracted UV Light

Demands for personal digital assistants (PDA) call for them to be additionally low profile, lightweight, and low power. To fulfil these demands, it is necessary to develop a backlight unit that features low-power consumption, high brightness, and high efficiency. The light source in a backlight unit has a light guide plate, which is a highly important component. The light guide plate has dots to reflect light. It is known that the smaller the dots and the higher the aspect ratio, the brighter the screen. The result of a simulation revealed that it is possible to improve the brightness of light guide plate by forming the shape of a truncated cone with a taper angle of 68 to 78 degrees. However, using the existing machining technology, it is difficult to form the dots into such a shape. Producing a desired shape, like a tapered shape, in the depthwise direction is difficult even with lithography, although using an elaborate mask pattern, this technique can produce a sophisticated shape on a two-dimensional plane. We have produced a tapered microstructure with a high aspect ratio, devising an innovative method of diffracted light exposure based on a lithography technique making use of UV light source. Furthermore, we controlled the taper angle and fabricated a light guide plate through a mold master, Ni-electroforming, and an injection molding by using UV-LIGA process