1. Field of the Invention
The present invention relates to a reflection type liquid crystal display device which forms an image by modulating light reflected from a reflection type matrix substrate with liquid crystals.
2. Related Background Art
Liquid crystal display devices are presently used as thin display devices for various industrial and commercial apparatuses. Projection type display devices for projecting and magnifying light modulated with liquid crystals are widely used for large screen display devices. A reflection type liquid crystal display device which has a high efficiency of light utilization is expected as a device capable of displaying an image of high precision and brightness.
FIG. 14A is a cross sectional view showing a typical example of a conventional reflection type liquid crystal color display device. The display device has a pair of a transparent substrate 1 and an active matrix substrate 2 between which liquid crystals 3 are sandwiched. Incident light indicated by an arrow to modulated at each pixel with liquid crystals driven on the active matrix substrate, reflected by a reflection electrode 10, projected and magnified to obtain a desired image.
The transparent substrate 1 has a glass substrate 4 on which a color filter array 5 of R (red), G (green), and B (blue) is formed. At the interface with liquid crystals, there are a transparent electrode 8 for applying a voltage and an orientation film 9 laminated with the transparent electrode 8. A microlens array 7 is formed on the color filter array 5 in order to improve the efficiency of light utilization. Each lens has a radius of curvature which makes incident parallel light focus generally upon the reflection electrode 10. In order to cut stray light between pixels, a black matrix 6 is formed to fill the space between adjacent color filters of the color filter array 5.
The above-described conventional display device is, however, associated with the problem that light components not focussed upon the reflection electrode 10 because of aberration of the microlens array 7 and stray light components incident upon the microlens array 7 are mixed with light reflected from the reflection electrode 10 and this mixed light lowers the quality of a projected image.
FIG. 14B shows the details of optical paths of one pixel. Light 20 generally vertically incident upon the substrate 1 is refracted by a microlens 7, focussed upon an approximately central area 26 of the reflection electrode 10, reflected by the reflection electrode 10, again becomes incident upon the microlens 7, and is output as vertical light 21. If the microlens provides incident light of different wavelengths with the same refraction and has a perfect parabolic shape, light of different wavelengths can be focussed upon one focal point 26. However, in practice, the parabolic shape is imperfect and the focal length changes with wavelength (aberration). Therefore, for example, some light propagates along a path 22 and is reflected at a position shifted from the focal point so that it is output along a direction 22 shifted from the vertical direction. Further, light incident along a direction 24 is reflected at a position 28 and output along a is direction 25. Such phenomena are superposed upon at a number of pixels. In addition, there is a variation of shapes of microlenses of respective pixels. Output unnecessary light components are mixed with a normal image so that the contrast and image quality may be lowered by these noise components.
If the size of the reflection electrode is made small in order to solve the above problem, a space between adjacent pixels becomes large so that an electric field in this space does not become vertical to the substrate plane and orientation of liquid crystals may be disturbed. From this reason, the contrast is lowered and defects in an image increase.