Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-10-12
2004-08-10
Jackson, Jerome (Department: 2815)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S105000, C349S080000, C349S108000, C349S106000
Reexamination Certificate
active
06774963
ABSTRACT:
TECHNICAL FIELD
The present invention relates to color filters and liquid crystal display devices (or display elements, display units). More particularly, the invention relates to color filters and liquid crystal display devices which are used for portable data terminals or the like and further relates to color filters and liquid crystal display devices of types usable for both transmission and reflection.
BACKGROUND OF THE INVENTION
General Background Art
Liquid crystal display devices are roughly divided into transmissive type and reflective type devices.
First, with regard to transmissive type devices, commonly used transmissive type color liquid crystal display devices employ absorption type color filters. The transmissive type color liquid crystal display device has a structure as shown in FIG.
1
. In the figure, the reference numeral
11
denotes a light guide plate provided with a reflection plate (not shown in the figure) on its lower side or the like. The reference numeral
12
denotes a polarizer. The reference numeral
14
denotes a back (lower) side substrate. The reference numeral
15
denotes a front (upper; viewers operate and watch the display screen there) side substrate. The reference numeral
17
denotes a polarizer on the front side. The reference numeral
61
denotes an absorption type color filter for transmitting red light (absorbing light of wavelengths other than red). The reference numeral
62
denotes an absorption type color filter for transmitting green light. The reference numeral
63
denotes an absorption type color filter for transmitting blue light. The reference numeral
21
denotes a light source as a sidelight or a backlight.
Basic function, structure, material and the like of each of these portions are so-called well-known arts; therefore general descriptions thereof are not provided herein.
Actually, in addition to the above, TFT (Thin Film Transistor) for pixels and for driving pixels is formed on either of the upper and lower substrates, and transparent conductive film and alignment film are disposed on the sides on which those substrates face a liquid crystal layer. The TFT, the transparent conductive film and the alignment film also are so-called well-known arts and additionally are not directly related to the scope of the present invention; therefore illustrations and descriptions thereof are not provided herein.
Only contents, functions and the like which are directly related to the scope of the present invention are described below in principle.
The backlight disposed on the back side of a liquid crystal panel is a so-called white light source (which comprises light of any wavelength so as not to make light of particular colors observable).
Each pixel is provided with an absorption type color filter which transmits only predetermined light corresponding to a color of the pixel and absorbs light other than the predetermined light. Thus, each color of red, green and blue is displayed.
The use of the absorption type color filter, however, causes an extremely great loss of light due to the absorption of approximately two-thirds (or more in some cases) of the light. Accordingly, it has been proposed that an interference filter should be substituted for the absorption type color filter (for example, Japanese Unexamined Patent Publications No. 11-38397, No. 10-197859 and Japanese Patent Application No. 9-273042). An interference filter transmits light of particular colors and reflects light other than the light of particular colors, in other words, reflects light of unnecessary colors for the pixel on the side of the light source. This reflected light thereby is reflected again in a display surface by a reflection plate or the like on the lower side of the light guide plate
11
to be reused for display, resulting in the improvement of utilization efficiency of light as well as the decrease of power consumption and the improvement of luminance.
An example such that an interference filter is applied to a reflective type liquid crystal element is disclosed in Japanese Unexamined Patent Publication No. 11-38397, a model such that an interference filter is formed under a color filter is disclosed in Japanese Unexamined Patent Publication No. 10-197859, and an example of a backlight for color separation using an interference filter is disclosed in Japanese Patent Application No. 9-273042.
An interference filter is generally formed with a multilayer film, while a type such that an interference filter is formed by curing cholesteric liquid crystal has been proposed in recent years (for further details, refer to ‘the development of color filters by using cholesteric liquid crystal presented by Tokuhisa MORIYA in DAI NIPPON PRINTING CO., LTD. at the 6th research report meeting of HLC°).
Next, with regard to reflective type devices, commonly used reflective type color liquid crystal display devices also employ absorption type reflection plates. The reflective type color liquid crystal display device has a structure shown in
FIG. 2
such that a reflection plate
71
which reflects only predetermined light and absorbs light other than the predetermined light is formed on a substrate on the back side of a liquid crystal panel. Thus, only pixels for brightly displaying predetermined light reflect the predetermined light; the reflection plate reflects the predetermined light on the display side (the side of viewers);.and only the pixels for brightly displaying predetermined light absorb the predetermined light, while a circular light plate and a liquid crystal layer shut off (absorb) the predetermined light in the case of pixels for not brightly displaying predetermined light. In
FIG. 2
, corresponding numbers are given to members and portions having the same function, structure and the like as in FIG.
1
. Similarly, these numbers apply to liquid crystal display devices according to embodiments of the present invention described after. The reference numeral
71
in
FIG. 2
is a reflection plate as well as an electrode.
It is noted for confirmation that transmitted light in this type passes back and forth through a liquid crystal layer, namely, passes through twice for display (this is related to embodiments described after).
In addition to the above, partially transmissive type liquid crystal display devices are mentioned as an intermediate type between the transmissive type and the reflective type. This type is such that a half mirror is disposed on the upper or lower side of the back side substrate
14
of the liquid crystal display device shown in
FIG. 1
to transmit a certain quantity of light and reflect a certain quantity of light. A liquid crystal display element of this type is used as the transmissive type when an AC power supply can be used and is used as the power-saving reflective type when battery-operated, being widely used particularly for portable data terminals or the like.
Furthermore, a type of device usable as both a transmissive type and a reflective type device was announced in recent years (in a news release by SHARP CORPORATION on Apr. 1, '99). This type of device is an improved conventional partially transmissive type device and is characterized in that a reflection plate is partially formed at every pixel.
Background Art in View of the Problems to be Solved by the Present Invention
Brightness, however, is not sufficiently secured in liquid crystal display elements described above. Since polarized light has, from the start, been utilized in liquid crystal display devices, utilization efficiency of light is reduced to approximately a half in principle even for mere black-and-white display.
In particular, brightness is further reduced in a type of device usable as both a transmissive type and a reflective type device. For example, if, for the sake of simplicity of explanation, transmittance of a half mirror is assumed to be 50%, only 50% of brightness of a backlight is utilized in the case of transmissive type display, while only 50% of reflected light is utilized in the case of reflective type display. Resultingly, ut
Kumagawa Katsuhiko
Nakao Kenji
Uemura Tsuyoshi
Wakita Naohide
Jackson Jerome
Lee Eugene
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
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