Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-06-29
2004-03-16
Chow-hung, T. (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S113000, C349S162000
Reexamination Certificate
active
06707511
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a reflective and transflective liquid crystal display device, which has a storage capacitor, and its manufacturing method.
2. Description of the Related Art
In general, a liquid crystal display device is classified into two types, i.e., a transmissive liquid crystal display device using a back light as a light source and a reflective liquid crystal display device using not the back light but a natural light as the light source. The transmissive liquid crystal display device embodies luminous picture using the backlight as the light source even in a dark outside environment. However, the transmissive liquid crystal display device cannot use in a bright place and electricity is largely wasted.
On the other hand, the reflective liquid crystal display device, which does not use the backlight, can reduce largely the power consumption and its volume, thereby achieving a super thin type and lightweight type. However, there are limitations that the reflective liquid crystal display device cannot be used when the outside natural light is dim.
To overcome the above limitations, a transflective liquid crystal display device is disclosed. The transflective liquid crystal display device can be used as a reflective type or a transmissive type at need, as having both a reflection part and a transmission part inside unit pixel.
That is, the transflective liquid crystal display device is operated as the reflective liquid crystal display device by reflecting the outside light incident through a first substrate when the outside natural light is bright to an extent that the display function is capable without the back light. Moreover, when the outside light is not bright, the transflective liquid crystal display device is operated as the transmissive liquid crystal display device by irradiating the light of the back light to a liquid crystal layer through an opening part of a reflective electrode by using the back light.
Meanwhile, the liquid crystal display devices connect parallel a storage capacitor and a liquid crystal capacitor to assist the electric charge conservation capacity. The structure of the liquid crystal display devices is called a previous gate structure, as being formed between a gate and a pixel electrode.
The storage capacitor maintains voltage charged into the liquid crystal capacitor in a turn-off area of a corresponding thin film transistor. Therefore, in the turn-off area, the occurrence of leakage current can be prevented by the liquid crystal capacitor and the deterioration of picture due to the occurrence of flicker can be prevented.
Hereinafter, referring to the drawings, conventional reflective and transflective liquid crystal display device and its manufacturing method will be described.
FIG. 1
a
is a plan view of a conventional reflective liquid crystal display device and
FIG. 1
b
is a sectional view of the reflective liquid crystal display device showing a cut surface along the line of I-I′ of
FIG. 1
a.
FIG. 2
a
is a plan view of a conventional transflective liquid crystal display device and
FIG. 2
b
is a sectional view of the transflective liquid crystal display device showing a cut surface along the line of II-II′ of
FIG. 2
a.
In general, the liquid crystal display device includes a lower substrate called an aligning substrate of the thin film transistor, an upper substrate called a color filter substrate, and a liquid crystal layer formed between the two substrates. Hereinafter, the aligning substrate of the thin film transistor, which is the lower substrate, of the liquid crystal display device will be described.
First, as shown in
FIGS. 1
a
and
1
b,
the lower substrate of the reflective liquid crystal display includes a data line
105
and a gate line
102
, which are aligned on a substrate
101
in the form of a matrix to define the unit pixel, a thin film transistor having a gate electrode
102
a
formed at an intersection between the data line
105
and the gate line
102
, a gate insulation film
103
, an semiconductor layer
104
, source/drain electrodes
105
a
and
105
b,
a reflective electrode
107
electrically connected to the drain electrode
105
b
of the thin film transistor and occupying most of unit pixel area, and a storage capacitor having a capacitor lower electrode
102
c
and an capacitor upper electrode
105
c
electrically connected to the reflective electrode
107
.
In detail, the gate line
102
, the gate electrode
102
a
of the thin film transistor and the capacitor lower electrode
102
c
of the storage capacitor are formed by patterning simultaneously after depositing metal of low resistance by a sputtering method.
Furthermore, also the data line
105
, the source/drain electrodes
105
a
and
105
b
of the thin film transistor and the capacitor upper electrode
105
c
of the storage capacitor are formed by patterning simultaneously after depositing conductive material of low resistance by the sputtering method.
At this time, on the entire surface of the substrate including the gate line
102
, the gate electrode
102
a
and the capacitor lower electrode
102
c
is the gate insulation film
103
of silicon nitride (SiN
x
) film to insulate upper and lower layers, and an semiconductor layer
104
of an island form between the gate insulation film
103
and the source/drain electrodes
105
a
and
105
b
. On the entire surface of the substrate including the data line
105
, the source/drain electrodes
105
a
and
105
b
and the capacitor upper electrode
105
c
is a passivation film
106
coated in a prescribed thickness.
The passivation film
106
has a pixel contact hole
108
of a prescribed depth and a capacitor contact hole
109
of a prescribed depth exposing a portion of the drain electrode
105
b
and a portion of the capacitor upper electrode
105
c
respectively. There is a reflective electrode
107
covering the contact holes at the unit pixel area on the passivation film. At this time, the reflective electrode has a depressed part in the contact hole.
The pixel contact hole
108
electrically connects the drain electrode
105
b
and the reflective electrode
107
and the capacitor contact hole
109
connects the reflective electrode
107
and the capacitor upper electrode
105
c.
The reflective electrode
107
is formed to occupy most of the unit pixel area constituted with only a reflection part(I) and made of metal having high reflectance, such as copper(Cu), chrome(Cr), Aluminum(Al), molybdenum(Mo), chrome/molybdenum(Cr/Mo) and chrome/aluminum(Cr/Al). The reflective electrode of the reflective liquid crystal display is important as being closely connected with brightness of picture. The transflective liquid crystal display further includes a transmission part(II) on the reflective liquid crystal display.
That is, as shown in
FIGS. 2
a
and
2
b,
the transflective liquid crystal display includes a data line
205
and a gate line
202
aligned in the form of a matrix on a substrate
201
, a thin film transistor formed on an intersection between the data line
205
and the gate line
202
, a storage capacitor formed at a prescribed portion of the gate line, a first passivation film
206
a
formed on the thin film transistor and the storage capacitor, a reflective electrode
207
a
electrically connected with the thin film transistor and formed on the reflective part(I) of the unit pixel area, a second passivation film
206
b
formed on the entire surface including the reflective electrode
207
a,
and a transmissive electrode
207
b
formed on the transmission part(II) on the second passivation film
206
b.
At this time, the transmissive electrode
207
b
is made of ITO(Indium Tin Oxide), which is a transparent conductive material. The reflective electrode
207
a
is made of metal having a reflectance, such as copper(Cu), chrome(Cr), Aluminum(Al), molybdenum(Mo), chrome/molybdenum(Cr/Mo) and chrome/aluminum(Cr/Al), to reflect the outside light wel
Baek Heume Il
Ha Kyoung Su
Kim Dong Guk
Kim Woong Kwon
Kim Yong Beom
Chow-hung T.
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
Qi Mike
LandOfFree
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