1. Field of Invention
The present invention relates to active-matrix-driven electro-optical devices. More particularly, the invention relates to an electro-optical device in which thin film transistors (hereinafter sometimes referred to as “TFTs”) for switching pixels are provided in a laminated structure on a substrate. The invention also relates to a manufacturing method for such an electro-optical device and to an electronic apparatus provided with the electro-optical device as a light valve. The invention also pertains to electrophoretic devices for, for example, electronic paper, EL (electroluminescent) devices, and devices using electron emission elements (field emission display and surface-conduction electron-emitter display).
2. Description of Related Art
In a TFT-active-matrix-driven electro-optical device, when light is incident on a channel region of a pixel-switching TFT provided for each pixel, a light leakage current is generated due to the optical excitation, which changes the characteristics of the TFT. Particularly in an electro-optical device used as a light valve of a projector, since the intensity of incident light is high, it is important to shield the TFT channel region and the areas therearound from the incident light.
Accordingly, the channel region and the areas therearound are shielded by a light-shielding film, which defines the aperture area of each pixel, provided for an opposing substrate, or by data lines formed of a metal film, such as an Al (aluminum) film, disposed on a TFT array substrate and passing over the TFTs. Additionally, a light-shielding film formed of, for example, a high melting-point metal, is sometimes provided at an opposing position under the TFTs on the TFT array substrate.
By providing a light-shielding film under the TFTs as described above, light reflected by the rear surface of the TFT array substrate, or, if a plurality of electro-optical devices are combined via a prism to form one optical system, returning light of, for example, projection light passing through the prism from another electro-optical device can be prevented from being incident on the TFTs of the electro-optical device.
However, the following problems are presented by the above-described related art light-shielding techniques. According to the technique to form a light-shielding film on the opposing substrate or the TFT array substrate, the spacing between the shielding film and the channel region with, for example, a liquid crystal layer, electrodes, and interlayer insulating film therebetween is three-dimensionally considerably large. Thus, light obliquely applied between the shielding film and the channel region cannot be sufficiently shielded. Particularly in a small electro-optical device used as a light valve of a projector, incident light is a beam of light output from a light source and converged by a lens, and contains obliquely incident light components, which cannot be ignored (for example, 10% components tilted from the direction perpendicular to the substrate by 10 to 15 degrees). Therefore, insufficient shielding for the obliquely incident light presents a problem in a practical sense.
Additionally, light applied to the electro-optical device from an area without the light-shielding film is reflected on the top surface of the substrate, or on the top surface of the light-shielding film formed on the top surface of the substrate, or on the bottom surface of the data lines (namely, the internal surface facing the channel region). Then, such reflected light, or multiple reflection light, if such reflected light is further reflected on the top surface of the substrate or the internal surface of the shielding film or the data lines, sometimes reaches the TFT channel region.
In particular, as the definition of electro-optical devices becomes higher or the pixel pitch becomes smaller in response to recent demands for increasing the quality of display images, the intensity of the incident light is increased in order to display brighter images. Accordingly, it becomes more difficult to provide sufficient light-shielding by the above-described related art light-shielding techniques, and thus, flickering occurs due to a change in the TFT transistor characteristics, thereby reducing the quality of display images.
In order to increase the light-shielding characteristic, it seems that the area in which the light-shielding film is formed can be simply increased. If such an area is increased, however, it is difficult to respond to demands for increasing the aperture ratio of each pixel for enhancing the brightness of display images. As stated above, the internal-surface reflection light or the multiple reflection light resulting from the oblique light is generated by the presence of the light-shielding film, that is, the light-shielding film disposed below the TFTs or the light-shielding film formed of, for example, data lines, disposed above the TFTs. In view of this point, an increased area in which the light-shielding film is formed disadvantageously intensifies the internal-surface reflection light or the multiple reflection light.
USPTO Backgrounds
USPTO Backgrounds