Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-08-19
2004-06-08
Ngo, Huyen (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S132000
Reexamination Certificate
active
06747722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device of a thin film transistor (hereinafter referred to as “TFT”) type or the like and a manufacturing method thereof.
2. Description of the Related Art
A liquid crystal display device, in view of its characteristics that the device is thin, light-weighted and exhibits low power consumption, has been popularly used as a display equipment for image information and character information of an information equipment as represented by a personal computer, a portable information terminal, a portable telephone, a digital camera, and a visual equipment such as a camera-built-in type VTR equipment. Recently, along with spreading of large-capacity media or starting of BS digital broadcasting due to the advent of DVD and the rapid progress of large-capacity magnetic drives, the fusion of a personal computer and a video digital media is in progress and the demand for an image display device having high image quality which can cope with such an application is increased. A liquid crystal display adopting an in-plane switching (IPS) mode which applies a lateral electric field to liquid crystal sealed in a gap defined between upper and lower substrates has been recognized as a display method which is capable of satisfying such a demand for high image quality and various improvements have been made aiming at the further enhancement of the image quality.
On the other hand, along with spreading of portable telephones and portable information terminals, the demand for medium-sized or small-sized liquid crystal display devices which exhibit extremely small power consumption has been increased.
In the liquid crystal display device adopting the IPS mode, as disclosed in Japanese Patent Laid Open H07-36058, a method which performs switching of liquid crystal using a lateral electric field which is generated between two-layered metal electrodes sandwiching an insulation film therebetween has been most popularly used. A defect of such a structure lies in that, compared to a display device adopting a usual TN method, it is difficult to increase the numerical aperture of pixels so that the light utilization efficiency is low. Since it is necessary to increase the brightness of a backlight to compensate for this defect, as the whole LCD module, it is difficult to seek for the low power consumption which is demanded with respect to a notebook type personal computer or a portable terminal.
SUMMARY OF INVENTION
In the IPS type liquid crystal display device, there has been a task that the IPS type liquid crystal display device exhibits the smaller numerical aperture compared to the TN type liquid crystal display device and hence, it is necessary to enhance the numerical aperture. The IPS type liquid crystal display device also has a task that the brightness must be increased to cope with the video digital media. Further, the IPS type liquid crystal display device has a task that the low power consumption must be realized.
Further, inventors of the present application also have found a following new task. That is, when portions of the pixel electrodes or the common electrode are constituted of transparent conductors such as indium-tin-oxide (ITO), for example, light passes through a region of a fixed width from an end of the electrode and hence, the numerical aperture (transmissivity) can be substantially increased. However, when liquid crystal material is formed of positive-type material, liquid crystal molecules at an end portion have components which are erected with respect to a surface of a substrate due to applying of the electric field and are arranged obliquely with respect to the transmitting light and hence, a viewing angle becomes narrow and the wide viewing angle which is the characteristics of the IPS type liquid crystal display device is damaged.
Further, the present invention also copes with a task to suppress the increase of a leak current when the TFTs are turned off which is generated due to the increase of a light irradiation amount to semiconductor elements to cope with high brightness.
One of the advantages of the present invention is to improve or solve one or a plurality of these tasks. To describe some of advantages realize in any one of the present invention in detail, they are as follows. The first advantage is enable providing a liquid crystal display device which can arrange the holding capacitance in an increased quantity without deteriorating the numerical aperture (transmissivity) in an IPS type liquid crystal display device using low-temperature polysilicon TFTs as pixel TFTs. The second advantage is enable providing a liquid crystal display device which can enhance the numerical aperture (transmissivity) by dividing each pixel into four or more portions or increases the holding capacitance when the pixel electrodes or the common electrode are arranged on organic resin in an IPS type liquid crystal display device. The third advantage is enable providing a liquid crystal display device which can satisfy both of broad viewing angle characteristics and low voltage driving.
Other advantages and tasks of the present invention will be apparent in the specification of this application described hereinafter. To describe major examples of the present invention, they are as follows.
(1) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first substrate, pixels are formed in respective regions surrounded by the plurality of gate lines and the plurality of drain lines, and each pixel includes a common electrode line, a common electrode, at least one TFT element and a pixel electrode to which a signal from the drain line which is selected in response to a signal from the gate line by the TFT element is electrically supplied, the common electrode is formed over the drain line by way of an insulation film and the pixel electrode has a comb-teeth shape and is formed over the same layer as the common electrode, at least one of comb-teeth shaped portions of the pixel electrode has a multi-layered structure, and a holding capacitance is formed by a pixel electrode which constitutes a lower layer out of the multi-layered pixel electrode and the common electrode line layer.
(2) In (1), the common electrode line is formed substantially parallel to the gate line, and the common electrode and the common electrode line are connected through apertured portions of an insulation film including the insulation film.
(3) In either one of (1) and (2), the pixel electrode which constitutes the lower layer is arranged on the other layer of the pixel electrode by way of an insulation film.
(4) In any one of (1) to (3), the liquid crystal display device includes at least four main light transmitting portions which are formed within one pixel along a transverse line extending between the neighboring drain lines, the pixel further includes a through hole portion through which the common electrode on the drain line and the common electrode line are connected therein, and the pixel electrode which is disposed close to the drain line arranged at a side remote from the through hole portion within the pixel forms the holding capacitance.
(5) In any one of (1) to (4), the TFT element is formed of polysilicon and an insulation film of the holding capacitance is formed of an inorganic insulation film which covers the gate line of the TFT element.
(6) In a lateral electric field liquid crystal display device including a liquid crystal layer sandwiched between a transparent first substrate and a transparent second substrate, wherein a plurality of gate lines and a plurality of drain lines which intersect the plurality of gate lines in a matrix array are formed over the first
Imayama Hirotaka
Ochiai Takahiro
Oke Ryutaro
Ono Kikuo
A. Marquez, Esq. Juan Carlos
Fisher Esq. Stanley P.
Hitachi , Ltd.
Ngo Huyen
Reed Smith LLP
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