Optical design and roll‐to‐roll fabrication process of microstructure film for wide viewing LCDs

Abstract

-We have developed a new microstructure film for wide viewing liquid crystal displays (LCDs). By attaching it to the surface of a conventional LCD, the viewing angle characteristics of LCD has drastically improved without causing a blur of the frontal image and a decrease in the contrast ratio under bright ambient light conditions. This film can be applied to various LC modes including twisted nematic and multidomain vertical alignment by changing its internal micrometer-size 3D structure. Further, this film can be mass-produced efficiently by self alignment roll-to-roll process.Keywords -optical film, microstructure, liquid crystal display, wide viewing angle, self-alignment, rollto-roll processing.DOI # 10.1002/jsid.249 BackgroundTwisted nematic (TN) mode liquid crystal display (LCD) is still widely used especially in middle-size display, such as small TV, mobile phone, and PC monitor because TN-LCD has many advantages: high transmissivity, fast response speed, wide operating temperature range, high durability, and existing many fabrication lines. One of the disadvantages of TN-LCD is direction dependence of viewing angle characteristics, but previously, it was not a serious issue in the use of middle-size display because middle-size display is viewed from almost a fixed direction. However, new applications of middle-size display such as a tablet computer are recently growing, and with this trend, the improvement of viewing angle characteristics of TN-LCD has been highly expected. Various efforts have ever been investigated to improve the viewing angle characteristics of TN-LCD. They are mainly classified into three approaches. The first approach was to divide a pixel into subpixels or multidomains, 1-5 which required complicated fabrication processes. The second approach was to insert optical compensation films between glasses and polarizers, which still had a grayscale inversion with asymmetric viewing angle characteristics especially at high polar angles.6,7 The third approach was to attach a diffusing film to the surface of LCD, which caused a blur in the frontal image and degraded a contrast ratio under the bright ambient light owing to its backscattering.8-10 Therefore, we have developed a new microstructure film to solve these issues by just attaching it to the surface of TN-LCD. 11-15In addition, the improvement effect of viewing angle characteristics of the microstructure film is not limited to the TN-LCD. We have applied this technology to multidomain vertical alignment (MVA)-LCD. 15In this paper, we mainly report the details of optical design and roll-to-roll fabrication process of our microstructure film. System structure and characteristicsThe structure of our system is shown in Fig. 1. The difference from the conventional system is only a film attached to the surface of the conventional LCD. There were approaches of attaching a diffusing film to the surface of LCD so far, but they usually needed a collimated backlight for preventing the blur of the frontal image. Our system, however, does...

4.1: Distinguished Paper: Cavity Shape Control of the Roll‐to‐Roll Fabricated Novel Microstructure Film for Improving the Viewing‐Angle Characteristics of LCDs

“…To analyze the characteristics of the LCD with the film, the transparent photoresist layer with the cavities has been attached to the surface of commercially available TN-LCD (Figure 1). The optimum cavity shape for TN-LCD has 85 degrees taper angle [12], so the microstructure film for TN-LCD has been fabricated by the simple equipment method, the diffused UV light method (Figure 3 (b)). Figure 6 shows the actual display images of the commercially available TN-LCD (Figure 6 (a)) and the TN-LCD with the microstructure film with the optimum cavity shape (Figure 6 (b)).…”

“…For the improvement of the LCD viewing-angle characteristics, fabricating the truncated cone shape with the optimum taper angle is required [11,12]. To achieve the optimum cavity shape, we have investigated the UV exposure processes in the photolithography of the transparent photoresist, and found that UV dose and UV diffusivity are major factors for the cavity shape control.…”

“…Therefore, we have developed a microstructure film, a kind of scattering film, without the blur in the front image and the backscatter of the ambient light [11][12][13]. The film is composed of many black dots, which are much smaller than LCD pixel size, a transparent photoresist layer, and truncated cone shape cavities with a taper angle located exactly behind each black dot ( Figure 1).…”