Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-09-22
2004-03-02
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S058000, C349S141000
Reexamination Certificate
active
06700558
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal display device, which is capable of controlling any change in molecular orientation by electric fields having different directions and strengths so as to achieve fast response of an electric field, of liquid crystal display devices in which an electric field alters a molecular orientation of liquid crystal having dielectric anisotropy, and further concerns a displaying method thereof.
BACKGROUND OF THE INVENTION
As shown in
FIGS. 12 and 13
, a liquid crystal display device is formed by bonding a pair of substrates
101
and
102
together such that surfaces having the electrodes
103
and
104
oppose each other.
FIG. 14
shows a sectional view of the device, in which insulating films
107
and
108
and orientation films
109
and
110
are stacked if necessary on electrodes
103
and
104
between a pair of substrates
101
and
102
, and if necessary, an orientating operation such as rubbing is performed on the orientation films. Spacers
111
, each having a desired diameter, are disposed on the substrate so as to bond the substrates together with an even gap. The substrates are fixed with a sealing agent
112
. Finally, liquid crystal
113
is filled from an opening formed on the sealing agent, and the opening is sealed so as to complete the device. An orientating operation performed on the orientation films can achieve even orientation.
Each of the electrodes externally includes an extended part so as to apply an electric field having an arbitrary signal waveform to the liquid crystal. The liquid crystal alters its orientation according to an applied electric field and polarizes and modulates light passing through liquid crystal. A polarizer for visualizing polarization and modulation is provided if necessary so as to obtain a function of a display device. To transmit light through the liquid crystal layer, at least one of the electrodes needs to be a transparent electrode made of material such as ITO (indium tin oxide).
Further, liquid crystal display devices are broadly categorized into two kinds in view of an electrode structure. The following methods are available: a direct matrix method of forming stripe electrodes intersecting with one another, and an active-matrix method (see
FIG. 13
) of forming signal electrodes
105
intersecting on another on one of the substrates and forming switching elements
106
such as a transistor. In many cases, nematic liquid crystal is currently used as a liquid crystal material for any one of the methods.
The direct matrix method is simple in construction and manufacturing; however, a switching element is not provided for each pixel, so that all the pixels are coupled to one another with a capacitance. Thus, so-called crosstalk may appear, in which a switching threshold value becomes less clear in each of the pixel and a displayed image becomes less sharp with increasing number of pixels. Moreover, a transparent electrode such as ITO is a conductive material but is 100 to 1000 times higher than metal, etc. in resistance value. Thus, deformation on a signal waveform becomes more serious due to an electrode resistance of a transparent electrode, in response to the needs for a larger display device and a larger display capacity.
According to Japanese Unexamined Patent Application No. 287671/1995 (Tokukaihei 9-127494), a transparent electrode and a metallic wire are disposed in parallel so as to reduce an electrode resistance; however, a smaller aperture ratio lowers a luminance and reduces simplicity in manufacturing, that has been a characteristic of a direct matrix method.
Meanwhile, in the active-matrix method, a switching element is formed for each pixel, so that the manufacturing is more difficult than the direct matrix method. However, the pixels can be separately driven, so that no crosstalk occurs and a considerably clear image can be displayed. Also, it is possible to form a signal line making no contribution to transmission of light by using a metal such as Ti and Al. An opposing transparent electrode has a flat shape requiring no patterning, so that an electrode resistance hardly causes deformation on a signal waveform. Consequently, it is relatively easy to respond to a larger display device and a larger display capacity.
Therefore, a simple construction of the direct matrix method and a characteristic of a ferroelectric liquid crystal have been used in an attempt to solve crosstalk (N. Itoh et. al, Proceedings of The Fifth International Display Workshops (IDW'98), (1998) p. 205, ‘17” Video-Rate Full Color FLCD'). Ferroelectric liquid crystal is characterized by a property of memory and &mgr;s-digit fast response (N. Clark et. al, “Apply. Phys. Lett., 36” (1980), p.899 “Submicrosecond bistable electro-optic switching in liquid crystals”), so that displayed information can be successively written at a high speed for each scanning line and the written information can be maintained until a rewriting signal is inputted without applying voltage. Thus, it is possible to adopt a line-sequential driving method. With this arrangement, the direct matrix method can display a clear image as the active-matrix method, without causing crosstalk.
However, in the case of the direct matrix method, a problem of an electrode resistance cannot be solved by ferroelectric liquid crystal. An electrode resistance adversely affects a speed of a signal waveform as well as deformation thereof. Particularly in the case of a ferroelectric liquid crystal characterized by fast response, the foregoing technique of disposing a transparent electrode and a metallic wire in parallel is necessary. Consequently, a luminance is reduced by a smaller aperture ratio and a simple manufacturing cannot be achieved. Further, an electrode resistance increases power consumption and causes heat on a panel.
Considering this point, except for some of low-grade display devices, the active-matrix method is more suitable to a liquid crystal display device for displaying a moving picture with high resolution. Particularly, a thin-film transistor (TFT) method using a three-terminal element is superior to other methods such as a metal insulating film metallic layer (MIM) method using two-terminal element.
In order to allow a liquid crystal display device to contend with a CRT, which has been currently used as a main display device, and to replace the CRT as a flat display device in the future, some problems on picture quality need to be solved. The most critical problem of liquid crystal is a slow response to a signal waveform electric field. Here, the following describes the relationship between response speed and picture quality of liquid crystal.
On a currently used TFT-nematic liquid crystal display device (hereinafter, abbreviated as LCD), a moving image may be recognized as a blurred image. The cause is fully discussed in “Kurita, under the sponsorship of a LCD forum, “For LCD Advancement to CRT monitor market, -from the viewpoint of moving image display-”, section 1 “displaying method of a hold type display and picture quality of a moving picture display, Liquid Crystal Society, 1998”.
CRT and LCD differ in time response of displayed light. As shown in
FIGS. 15 and 16
, CRT has a displayed light of impulse type (FIG.
15
), and LCD has a displayed light of hold type (FIG.
16
). This is because liquid crystal only acts as a shutter for transmitting and shielding backlight, not spontaneous light, and because TN liquid crystal, which has been known and widely used, has a response speed of about 15 ms so as to make response by fully using one field of 16.7 ms. Hereinafter, for convenience of explanation, response time is equal to response speed in meaning.
In such a hold-type display, of eyeball movements, when a tracking movement (right and left eyeballs smoothly track a moving object substantially in the same manner), which is the most important for perceiving a moving image, and visual time integral effect are obtained in a substantially complete manner, the observer perceives an average
Alphonse Fritz
Birch & Stewart Kolasch & Birch, LLP
Saras Steven
Sharp Kabushiki Kaisha
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