Liquid crystal display devices have been applied to various fields, for example, monitors of notebook or desktop personal computers, car navigation systems, scientific electronic calculators, small to medium television sets, and domestic electric appliances. Among others, reflection liquid crystal display devices do not require the use of any backlight. Therefore, the application of the reflection liquid crystal display devices to displays for portable equipment, such as mobile PCs, has been made utilizing features of the reflection liquid crystal display devices, i.e., low power consumption and small thickness/lightweight. In conventional reflection liquid crystal display devices, however, since external light is utilized for display, the display screen is dark when the environment, where the display device is used, is dark. In particular, in a dark place, the display screen is not viewable at all, and, thus, the display device cannot be used.
In order to overcome the above problem, a semi-transmission liquid crystal display device, for example, using as a reflecting plate a semi-transmission reflecting plate such as a half mirror, has been developed so that, in a dark environment, the display can be used as a transmission liquid crystal display device. Methods for half mirror formation are shown in FIGS. 1 and 2. In the method shown in FIG. 1, light semi-transmission metallic thin film formed by vacuum deposition or the like is disposed on the whole reflecting surface (hereinafter referred to as “metallic thin film method”). In the method shown in FIG. 2, a total reflection metallic plate part, which is a total reflection part provided as a reflecting electrode and formed of a metal such as aluminum, and a transparent part disposed as a transparent electrode are alternately provided, and the ratio of quantity of light between reflected light and transmitted light is regulated by varying the area ratio between the total reflection part and the transparent part (hereinafter referred to as “area division method”). Display devices utilizing a semi-transmission film formed by the metallic thin film method have been put to practical use in inexpensive game machines and the like. On the other hand, semi-transmission films formed by the area division method have been put to practical use in display devices, which are in many cases used outdoors, such as digital cameras and portable telephones (cellular phones).
Further, in these liquid crystal display devices, the provision of a color filter can realize color display. Display devices using a semi-transmission film formed by the metallic thin film method, however, suffer from a problem that the light utilization efficiency is less than 50% and the brightness of the display screen is much inferior to that of the transmission display device or the reflection display device.
Further, the use of the total reflection film formed of a metal formed by the area division method causes the so-called coloring phenomenon and thus disadvantageously deteriorates color tone quality of reflected light.
Furthermore, since the metallic thin film and the metallic plate are electrically conductive, the provision of an electric circuit in direct contact with the metallic thin film and the metallic plate is impossible. This imposes restriction on the design of the display device.
Furthermore, the conventional semi-transmission color liquid crystal display device as shown in FIG. 2 suffers from a problem of a difference in brightness of display between transmission display and reflection display due to a difference in length of path of light, which passes through the color filter, between transmission display and reflection display.
USPTO Backgrounds
USPTO Backgrounds