Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2001-06-11
2003-09-30
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S156000, C349S042000, C349S043000, C349S155000
Reexamination Certificate
active
06628367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to the technical field of an electrooptic device such as a liquid-crystal device, and more particularly, to a thin-film transistor (hereinafter referred as TFT) and an active-matrix liquid-crystal display device, which adopts an alternating drive method in which the polarities of the voltages applied to adjacent pixels are periodically alternated in every pixel row or every pixel column so that the voltages applied to adjacent pixels in a row direction or in a column direction are inverted in polarity.
2. Description of Related Art
The electrooptic device of this sort typically adopts an alternating drive method in which the polarity of a voltage applied to the pixel electrodes is alternated at a predetermined pattern to prevent degradation of the electrooptic material, as a result of the application of a direct current, and to control a cross-talk and flickering of a display screen image. A 1H alternating drive method is relatively easy to control and presents a high-quality image display, wherein during the presentation of a video signal of one frame or one field, the pixel electrodes arranged on an odd row are driven by a voltage that is positive relative to the potential of a counter electrode, while the pixel electrodes arranged on an even row are driven by a voltage that is negative relative to the potential of the counter electrode, and during the presentation of a video signal of a next frame or a next field, conversely, the pixel electrodes arranged on the even row are driven by a positive voltage while the pixel electrodes arranged on the odd row are driven by a negative voltage (in other words, the pixel electrodes on the same row are driven by the same polarity voltage and the voltage polarity is alternated every row with the period of frame or field).
A 1S alternating drive method is also easy to control and presents a high-quality image display, wherein the pixel electrodes on the same column are driven by the same polarity voltage, while the voltage polarity is alternated every column with the period of frame or field.
Further, a dot alternating drive method has been developed which periodically reverses the polarity of the voltage applied to each pixel electrode from pixel electrode to pixel electrode in the direction of columns or in the direction of rows.
SUMMARY OF THE INVENTION
When the voltages of the adjacent pixel electrodes in a TFT array substrate (i.e., the voltages applied to the pixel electrodes adjacent in the column direction in the 1H alternating drive method, the voltages applied to the pixel electrodes adjacent in the row direction in the 1S alternating drive method, and the voltages applied to the pixel electrodes adjacent in the row direction and the column direction in the dot alternating drive method) are opposite in polarity as in the above-referenced 1H alternating drive method, the 1S alternating drive method, and the dot alternating drive method, a transverse electric field (specifically, an electric field in parallel with the surface of the substrate or an slant electric field having a component in parallel with the surface of the substrate) takes place between the adjacent pixel electrodes. If such a transverse electric field is applied to the electrooptic material, which is expected to work under a longitudinal electric field present between the pixel electrodes and the counter electrode (i.e., an electric field perpendicular to the surface of the substrate), an orientation defect takes place in the electrooptic material, an unlit defect occurs there, and the contrast ratio drops. Although the area of the transverse electric field can be covered with the light shield layer, the aperture of the pixel is reduced with the size of the area of the transverse electric field. As the distance between the adjacent pixel electrodes is reduced with a fine pixel pitch, the transverse electric field intensifies, and these become more problematic as high-definition design increases in the electrooptic device.
The present invention has been developed in view of the above problems, and it is an object of the present invention to provide a method for manufacturing an electrooptical device and the electrooptical device which reduces a malfunction due to the transverse electric field in the electrooptical material, such as a liquid crystal, while presenting a high-contrast, bright and high-quality image.
To achieve the above object, in accordance with the invention, a method for manufacturing an electrooptical device, which includes a first substrate, a second substrate, and an electrooptical material interposed between the first and second substrates, the first substrate including a plurality of two-dimensionally arranged pixel electrodes, including pixel electrodes in a first group driven in a periodic polarity reversal manner with a first period and pixel electrodes in a second group driven in a periodic polarity reversal manner with a second period which is complementary to the first period, and the second substrate including a counter electrode arranged to face the plurality of pixel electrodes, includes a step of forming a pattern including a wiring that drives the pixel electrodes, and elements on the first substrate, a step of planarizing the top surface of the laminate on the first substrate including the pattern, a step of forming a protrusion in an area in a spacing between pixel electrodes adjacent in a plan view, by subjecting the planarized surface to photolithographic and etching processes, and a step of fabricating the plurality of pixel electrodes.
The electrooptical device manufactured in accordance with the manufacturing method of the present invention includes, on the first substrate, the plurality of two-dimensionally arranged pixel electrodes, including the first group pixel electrodes driven in the periodic polarity reversal manner with the first period and the second group pixel electrodes driven in the periodic polarity reversal manner with the second period which is complementary to the first period, and the second substrate includes a counter electrode arranged to face the plurality of pixel electrodes. Therefore, the first substrate includes (i) adjacent pixel electrodes that are respectively driven by mutually opposite polarity voltages during the periodic polarity reversal driving, and (ii) adjacent pixel electrodes that are respectively driven by the same polarity voltages during the periodic polarity reversal driving. The two types of pixel electrodes are present in the electrooptic device, such as a matrix-type liquid-crystal display device, as long as it is driven in the above-referenced 1H alternating drive method or 1S alternating drive method. The transverse electric field takes place between the adjacent pixel electrodes belonging to the different pixel electrode groups (i.e., the adjacent pixel electrodes supplied with the opposite polarity voltages).
In accordance with the present invention, the planarizing step planarizes the top surface of the laminate on the first substrate (i.e., the top surface of an insulator to be planarized formed on top of an irregular surface having a wiring on an interlayer insulator) including the pattern of the wiring for driving the pixel electrodes (such as data lines, scanning lines, and capacitive lines) and elements (such as pixel switching TFTs). The step of forming the protrusion in the area in the spacing between the pixel electrodes adjacent in a plan view is accomplished by subjecting the planarized surface to photolithographic and etching processes in succession. The pixel electrodes are then formed.
Regardless of the wiring and the elements formed below, the surface underlying the pixel electrodes includes the positively planarized area having no protrusion, and the area having the protrusion which is positively elevated to a predetermined height in a predetermined configuration. As a result, the central portion of each pixel electrode centered in the aperture of each pixel is formed on the p
Hirabayashi Yukiya
Yamazaki Yasushi
LandOfFree
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